The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 microV/K at room temperature.

Leaf nitrogen and phosphorus stoichiometry of Chinese terrestrial plants was studied based on a national data set including 753 species across the country. Geometric means were calculated for functional groups based on life form, phylogeny and photosynthetic pathway, as well as for all 753 species. The relationships between leaf N and P stoichiometric traits and latitude (and temperature) were analysed. The geometric means of leaf N, P, and N : P ratio for the 753 species were 18.6 and 1.21 mg g(-1) and 14.4, respectively. With increasing latitude (decreasing mean annual temperature, MAT), leaf N and P increased, but the N : P ratio did not show significant changes. Although patterns of leaf N, P and N : P ratios across the functional groups were generally consistent with those reported previously, the overall N : P ratio of China's flora was considerably higher than the global averages, probably caused by a greater shortage of soil P in China than elsewhere. The relationships between leaf N, P and N : P ratio and latitude (and MAT) also suggested the existence of broad biogeographical patterns of these leaf traits in Chinese flora.

Invasion of cancer cells into the extracellular matrix (ECM) is a key step in tumor infiltration and metastasis. While the strong influence of ECM stiffness in governing tumor cell migration has been well established in two-dimensional culture paradigms, investigation of this parameter in three-dimensional (3D) ECMs has proven considerably more challenging, in part because perturbations that change 3D ECM stiffness often concurrently change microscale matrix parameters that critically regulate cell migration, such as pore size, fiber architecture, and local material deformability. Here we review the potential importance of these parameters in the context of tumor cell migration in 3D ECMs. We begin by discussing biophysical mechanisms of cell motility in 3D ECMs, with an emphasis on the cell-matrix mechanical interactions that underlie this process and key signatures of mesenchymal and amoeboid modes of motility. We then consider microscale matrix physical properties that are particularly relevant to 3D culture and would be expected to regulate motility, including matrix microstructure and nonlinear elasticity. We also discuss how changes in 3D matrix properties might be expected to trigger transitions in subcellular mechanisms, which in turn contribute to mesenchymal-amoeboid transition (MAT) by imposing restrictions on 3D motility. We expect that the field will gain valuable insight into invasion and metastasis by deepening its understanding of microscale, biophysical interactions between tumor cells and matrix elements and by creating new 3D scaffolds that permit orthogonal manipulation of specific matrix parameters.

The microbial communities of high-latitude ecosystems are expected to experience rapid changes over the next century due to climate warming and increased deposition of reactive nitrogen, changes that will likely affect microbial community structure and function. In moist acidic tundra (MAT) soils on the North Slope of the Brooks Range, Alaska, substantial losses of C and N were previously observed after long-term nutrient additions. To analyse the role of microbial communities in these losses, we utilized 16S rRNA gene tag pyrosequencing coupled with community-level physiological profiling to describe changes in MAT bacterial communities after short- and long-term nutrient fertilization in four sets of paired control and fertilized MAT soil samples. Bacterial diversity was lower in long-term fertilized plots. The Acidobacteria were one of the most abundant phyla in all soils and distinct differences were noted in the distributions of Acidobacteria subgroups between mineral and organic soil layers that were also affected by fertilization. In addition, Alpha- and Gammaproteobacteria were more abundant in long-term fertilized samples compared with control soils. The dramatic increase in sequences within the Gammaproteobacteria identified as Dyella spp. (order Xanthomonadales) in the long-term fertilized samples was confirmed by quantitative PCR (qPCR) in several samples. Long-term fertilization was also correlated with shifts in the utilization of specific substrates by microbes present in the soils. The combined data indicate that long-term fertilization resulted in a significant change in microbial community structure and function linked to changes in carbon and nitrogen availability and shifts in above-ground plant communities.

In microbial mat communities of Yellowstone hot springs, ribosomal RNA (rRNA) sequence diversity patterns indicate the presence of closely related bacterial populations along environmental gradients of temperature and light. To identify the functional bases for adaptation, we sequenced the genomes of two cyanobacterial (Synechococcus OS-A and OS-B') isolates representing ecologically distinct populations that dominate at different temperatures and are major primary producers in the mat. There was a marked lack of conserved large-scale gene order between the two Synechococcus genomes, indicative of extensive genomic rearrangements. Comparative genomic analyses showed that the isolates shared a large fraction of their gene content at high identity, yet, differences in phosphate and nitrogen utilization pathways indicated that they have adapted differentially to nutrient fluxes, possibly by the acquisition of genes by lateral gene transfer or their loss in certain populations. Comparisons of the Synechococcus genomes to metagenomic sequences derived from mats where these Synechococcus stains were originally isolated, revealed new facets of microbial diversity. First, Synechococcus populations at the lower temperature regions of the mat showed greater sequence diversity than those at high temperatures, consistent with a greater number of ecologically distinct populations at the lower temperature. Second, we found evidence of a specialized population that is apparently very closely related to Synechococcus OS-B', but contains genes that function in the uptake of reduced ferrous iron. In situ expression studies demonstrated that these genes are differentially expressed over the diel cycle, with highest expression when the mats are anoxic and iron may be in the reduced state. Genomic information from these mat-specific isolates and metagenomic information can be coupled to detect naturally occurring populations that are associated with different functionalities, not always represented by isolates, but which may nevertheless be important for niche partitioning and the establishment of microbial community structure.

The yeast deletion collections comprise >21,000 mutant strains that carry precise start-to-stop deletions of ∼6000 open reading frames. This collection includes heterozygous and homozygous diploids, and haploids of both MAT A: and MATα mating types. The yeast deletion collection, or yeast knockout (YKO) set, represents the first and only complete, systematically constructed deletion collection available for any organism. Conceived during the Saccharomyces cerevisiae sequencing project, work on the project began in 1998 and was completed in 2002. The YKO strains have been used in numerous laboratories in >1000 genome-wide screens. This landmark genome project has inspired development of numerous genome-wide technologies in organisms from yeast to man. Notable spinoff technologies include synthetic genetic array and HIPHOP chemogenomics. In this retrospective, we briefly describe the yeast deletion project and some of its most noteworthy biological contributions and the impact that these collections have had on the yeast research community and on genomics in general.

The STE4 gene of Saccharomyces cerevisiae encodes the beta subunit of the yeast pheromone receptor-coupled G protein. Overexpression of the STE4 protein led to cell cycle arrest of haploid cells. This arrest was like the arrest mediated by mating pheromones in that it led to similar morphological changes in the arrested cells. The arrest occurred in haploid cells of either mating type but not in MATa/MAT alpha diploids, and it was suppressed by defects in genes such as STE12 that are needed for pheromone response. Overexpression of the STE4 gene product also suppressed the sterility of cells defective in the mating pheromone receptors encoded by the STE2 and STE3 genes. Cell cycle arrest mediated by STE4 overexpression was prevented in cells that either were overexpressing the SCG1 gene product (the alpha subunit of the G protein) or lacked the STE18 gene product (the gamma subunit of the G protein). This finding suggests that in yeast cells, the beta subunit is the limiting component of the active beta gamma element and that a proper balance in the levels of the G-protein subunits is critical to a normal mating pheromone response.

Chitosan-based nanofibers with an average fiber diameter controllable from a few microns down to approximately 40 nm and a narrow size distribution were fabricated by electrospinning solutions containing chitosan, polyethylene oxide (PEO), and Triton X-100. Rheological study showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on chitosan-to-PEO ratio. The nanofibers can be deposited either as a nonwoven mat or as a highly aligned bundle of controllable size. Potential use of this nanofibrous matrix for tissue engineering was studied by examining its integrity in water and cellular compatibility. It was found that the matrix with a chitosan/PEO ratio of 90/10 retained excellent integrity of the fibrous structure in water. Experimental results from cell stain assay and SEM imaging showed that the nanofibrous structure promoted the attachment of human osteoblasts and chondrocytes and maintained characteristic cell morphology and viability throughout the period of study. This nanofibrous matrix is of particular interest in tissue engineering for controlled drug release and tissue remodeling.

OBJECTIVE

We estimated national and state trends in opioid agonist medication-assisted treatment (OA-MAT) need and capacity to identify gaps and inform policy decisions.

METHODS

We generated national and state rates of past-year opioid abuse or dependence, maximum potential buprenorphine treatment capacity, number of patients receiving methadone from opioid treatment programs (OTPs), and the percentage of OTPs operating at 80% capacity or more using Substance Abuse and Mental Health Services Administration data.

RESULTS

Nationally, in 2012, the rate of opioid abuse or dependence was 891.8 per 100 000 people aged 12 years or older compared with national rates of maximum potential buprenorphine treatment capacity and patients receiving methadone in OTPs of, respectively, 420.3 and 119.9. Among states and the District of Columbia, 96% had opioid abuse or dependence rates higher than their buprenorphine treatment capacity rates; 37% had a gap of at least 5 per 1000 people. Thirty-eight states (77.6%) reported at least 75% of their OTPs were operating at 80% capacity or more.

CONCLUSIONS

Significant gaps between treatment need and capacity exist at the state and national levels. Strategies to increase the number of OA-MAT providers are needed.

Measurements of bacterial sulfate reduction and dissolved oxygen (O2) in hypersaline bacterial mats from Baja California, Mexico, revealed that sulfate reduction occurred consistently within the well-oxygenated photosynthetic zone of the mats. This evidence that dissimilatory sulfate reduction can occur in the presence of O2 challenges the conventional view that sulfate reduction is a strictly anaerobic process. At constant temperature, the rates of sulfate reduction in oxygenated mats during daytime were similar to rates in anoxic mats at night: thus, during a 24-hour cycle, variations in light and O2 have little effect on rates of sulfate reduction in these mats.

The replication of putative replication origins (ARS elements) was examined for 200 kilobases of chromosome III of Saccharomyces cerevisiae. By using synchronous cultures and transfers from dense to light isotope medium, the temporal pattern of mitotic DNA replication of eight fragments that contain ARSs was determined. ARS elements near the telomeres replicated late in S phase, while internal ARS elements replicated in the first half of S phase. The results suggest that some ARS elements in the chromosome may be inactive as replication origins. The actively expressed mating type locus, MAT, replicated early in S phase, while the silent cassettes, HML and HMR, replicated late. Unexpectedly, chromosome III sequences were found to replicate late in G1 at the arrest induced by the temperature-sensitive cdc7 allele.

We describe genetic and physical characterization of rearrangements of chromosome III which result in changes of cell type in S. cerevisiae. Two types of rearrangements were obtained as rare events which caused a change at the locus controlling cell type, MAT, associated with a recessive lethal mutation, in one case from MATalpha to MATa-lethal, and in the other case from MATa to MATalpha-lethal. The MATa-lethal mutation is a deletion on the right arm of chromosome III, which we demonstrate extends to (or near) HMalpha. We suggest this deletion removes MATalpha and activates cryptic MATa information stored in HMalpha as proposed in the cassette model of mating type interconversion. The MATalpha-lethal mutation is the result of the formation of a circular chromosome III, which we interpret to remove MATa and activate the cryptic MATalpha information stored at HMa. Strains carrying the MATalpha-lethal chromosome contain a circular chromosome of length 62.6 plus or minus 5.7 mum, which is absent in related strains. This chromosome was confirmed to be chromosome III by hybridization of specific yeast DNA fragments to supercoiled DNA obtained from MATalpha-lethal strains. The isolation of a large circular derivative of chromosome III allows correlation of genetic and physical distance based on large distances-1 centimorgan corresponds to approximately 2700 base pairs.

When PCR was used to recover small-subunit (SSU) rRNA genes from a hot spring cyanobacterial mat community, chimeric SSU rRNA sequences which exhibited little or no secondary structural abnormality were recovered. They were revealed as chimeras of SSU rRNA genes of uncultivated species through separate phylogenetic analysis of short sequence domains.

Mutations in the yeast gene ARD1 lead to inability to respond to alpha-factor, inability to enter stationary phase, and inability to sporulate, suggesting an important role for the ARD1 gene product in controlling the switch between the mitotic cell cycle and alternative cell fates. MATa, ard1 cells seem to be defective in the expression of all a-specific functions, whereas MAT alpha, ard1 cells respond normally to a-factor. We propose that ARD1 is required for the expression of genes involved in a-mating functions, stationary phase, and sporulation. The ARD1 gene has been cloned and sequenced; there is weak homology between the C terminus of the ARD1 protein, the C-terminal region of MAT alpha 2, and the homeo box.

BACKGROUND

Leptospirosis is an emerging infectious disease. The differential diagnosis of leptospirosis is difficult due to the varied and often "flu like" symptoms which may result in a missed or delayed diagnosis. There are over 230 known serovars in the genus Leptospira. Confirmatory serological diagnosis of leptospirosis is usually made using the microscopic agglutination test (MAT) which relies on the use of live cultures as the source of antigen, often performed using a panel of antigens representative of local serovars. Other techniques, such as the enzyme linked immunosorbent assay (ELISA) and slide agglutination test (SAT), can detect different classes of antibody but may be subject to false positive reactions and require confirmation of these results by the MAT.

METHODS

The polymerase chain reaction (PCR) has been used to detect a large number of microorganisms, including those of clinical significance. The sensitivity of PCR often precludes the need for isolation and culture, thus making it ideal for the rapid detection of organisms involved in acute infections. We employed real-time (quantitative) PCR using TaqMan chemistry to detect leptospires in clinical and environmental samples.

CONCLUSIONS

The PCR assay can be applied to either blood or urine samples and does not rely on the isolation and culture of the organism. Capability exists for automation and high throughput testing in a clinical laboratory. It is specific for Leptospira and may discriminate pathogenic and non-pathogenic species. The limit of detection is as low as two cells.

Throughout the first 90 years after their discovery, sulfate-reducing bacteria were thought to be strict anaerobes. During the last 15 years, however, it has turned out that they have manifold properties that enable them to cope with oxygen. Sulfate-reducing bacteria not only survive oxygen exposure for at least days, but many of them even reduce oxygen to water. This process can be a true respiration process when it is coupled to energy conservation. Various oxygen-reducing systems are present in Desulfovibrio species. In Desulfovibrio vulgaris and Desulfovibrio desulfuricans, oxygen reduction was coupled to proton translocation and ATP conservation. In these species, the periplasmic fraction, which contains hydrogenase and cytochrome c3, was found to catalyze oxygen reduction with high rates. In Desulfovibrio gigas, a cytoplasmic rubredoxin oxidase was identified as an oxygen-reducing terminal oxidase. Generally, the same substrates as with sulfate are oxidized with oxygen. As additional electron donors, reduced sulfur compounds can be oxidized to sulfate. Sulfate-reducing bacteria are thus able to catalyze all reactions of a complete sulfur cycle. Despite a high respiration rate and energy coupling, aerobic growth of pure cultures is poor or absent. Instead, the respiration capacity appears to have a protective function. High numbers of sulfate-reducing bacteria are present in the oxic zones and near the oxic-anoxic boundaries of sediments and in stratified water bodies, microbial <em>mats</em> and termite guts. Community structure analyses and microbiological studies have shown that the populations in those zones are especially adapted to oxygen. How dissimilatory sulfate reduction can occur in the presence of oxygen is still enigmatic, because in pure culture oxygen blocks sulfate reduction. Behavioral responses to oxygen include aggregation, migration to anoxic zones, and aerotaxis. The latter leads to band formation in oxygen-containing zones at concentrations of </=20% air saturation.

The mating type locus (MAT) determines the three yeast cell types, a, alpha, and a/alpha. It has been proposed that alleles of this locus, MATa and MAT alpha, encode regulators that control expression of unlinked genes necessary for mating and sporulation. Specifically, the alpha 1 product of MAT alpha is proposed to be a positive regulator of alpha-specific genes. To test this view, we have assayed RNA production from the alpha-specific STE3 gene in the three cell types and in mutants defective in MAT alpha. The STE3 gene was cloned by screening a yeast genomic clone bank for plasmids that complement the mating defect of ste3 mutants. Using the cloned STE3 gene as a probe, we find that alpha cells produce STE3 RNA, whereas a and a/alpha cells do not. Furthermore, mat alpha 1 mutants do not produce STE3 RNA, whereas mat alpha 2 mutants do. These results show that the STE3 gene, required for mating only by alpha cells, is expressed only in alpha cells. They show also that production of RNA from the STE3 gene requires that alpha 1 product of MAT alpha. Thus alpha 1 positively regulates at least one alpha-specific gene by increasing the level of that gene's RNA product.

Examination of the control of cell type in yeast at the molecular level and understanding of the biochemical basis of the cell-cell interactions involved in the mating process are clearly entering an extremely productive and exciting period. The tools and opportunities are now available to answer fundamental questions with regard to the mechanism of differential gene expression in eukaryotic cells by using cloned a-specific, alpha-specific, and haploid-specific genes as the probes. Basic questions concerning eukaryotic chromosome structure and organization can be addressed by elucidating the properties of the SIR/MAR regulators and their mode of action. Furthermore, the availability both of cloned MAT, HML, and HMR regions and of the HO gene will provide the material for unravelling the enzymology of the DNA transposition that occurs during mating type interconversion. The isolation of the structural genes for the pheromones and mutations that block pheromone production will provide useful information on how extracellular hormones are synthesized, processed, and secreted by eukaryotic cells. Moreover, the apparent mode of action of the phermonones through cyclic AMP as an intracellular "second messenger," and the genetic and biochemical tractability of yeast cells, may allow tracing of the entire pathway of hormonal regulation of a eukaryotic cell division cycle. These and other studies of the developmental biology of yeast cells will provide more important insights into fundamental aspects of the genetic control of developmental processes in eukaryotic cells.

DNA was isolated from a circular derivative of chromosome III to prepare a library of recombinant plasmids enriched in chromosome III sequences. An ordered set of recombinant plasmids and bacteriophages carrying the contiguous 210-kilobase region of chromosome III between the HML and MAT loci was identified, and a complete restriction map was prepared with BamHI and EcoRI. Using the high frequency transformation assay and extensive subcloning, 13 ARS elements were mapped in the cloned region. Comparison of the physical maps of chromosome III from three strains revealed that the chromosomes differ in the number and positions of Ty elements and also show restriction site polymorphisms. A comparison of the physical map with the genetic map shows that meiotic recombination rates vary at least tenfold along the length of the chromosome.

In homothallic cells of Saccharomyces cerevisiae, a or alpha mating type information at the mating type locus (MAT) is replaced by the transposition of the opposite mating type allele from HML alpha or HMRa. The rad52-1 mutation, which reduces mitotic and abolishes meiotic recombination, also affects homothallic switching (Malone and Esposito, Proc. Natl. Acad. Sci. U.S.A. 77:503-507, 1980). We have found that both HO rad52 MATa and HO rad52 MAT alpha cells die. This lethality is suppressed by mutations that substantially reduce but do not eliminate homothallic conversions. These mutations map at or near the MAT locus (MAT alpha inc, MATa-inc, MATa stk1) or are unlinked to MAT (HO-1 and swi1). These results suggest that the switching event itself is involved in the lethality. With the exception of swi1, HO rad52 strains carrying one of the above mutations cannot convert mating type at all. MAT alpha rad52 HO swi1 strains apparently can switch MAT alpha to MATa. However, when we analyzed these a maters, we found that few, if any, of them were bona fide MATa cells. These a-like cells were instead either deleted for part of chromosome III distal to and including MAT or had lost the entire third chromosome. Approximately 30% of the time, an a-like cell could be repaired to a normal MATa genotype if the cell was mated to a RAD52 MAT alpha-inc strain. The effects of rad52 were also studied in mata/MAT alpha-inc rad52/rad52 ho/HO diploids. When this diploid attempted to switch mata to MATa, an unstable broken chromosome was generated in nearly every cell. These studies suggest that homothallic switching involves the formation of a double-stranded deoxyribonucleic acid break or a structure which is labile in rad52 cells and results in a broken chromosome. We propose that the production of a double-stranded deoxyribonucleic acid break is the lethal event in rad52 HO cells.

The mating-type locus (MAT) of Saccharomyces cerevisiae is a complex locus that codes for the regulators of cell type. Two unique messages are transcribed from each MAT allele. Using the in vitro mutagenesis technique whereby synthetic oligonucleotides containing restriction sites (linkers) were inserted into plasmids, we have constructed a series of mutations in cloned DNA containing either the MATa or MAT alpha locus. The new restriction site associated with each "linker" mutation has allowed the mutation to be mapped and sequenced. We have complemented genetically defined mutations (mata1, mat alpha 1 and mat alpha 2) with plasmids containing these in vitro mutations by yeast transformation, thereby mapping the genes onto the DNA sequence. MATa1 has been localized to the MATa unique region (Ya) from which the a1 message is transcribed. We find no function for the other MATa message by using our complementation assay. MAT alpha 1 maps to the MAT alpha unique (Y alpha) and adjacent (Z) region from which the alpha 1 message is transcribed. MAT alpha 2 maps to the other major message found in the common (X) region of the MAT alpha loci. Although most linker mutations that have a mutant phenotype appear to disrupt the translated portion of each gene, two mutations may disrupt transcription.

Marine sediments are frequently covered by mats of the filamentous Beggiatoa and other large nitrate-storing bacteria that oxidize hydrogen sulfide using either oxygen or nitrate, which they store in intracellular vacuoles. Despite their conspicuous metabolic properties and their biogeochemical importance, little is known about their genetic repertoire because of the lack of pure cultures. Here, we present a unique approach to access the genome of single filaments of Beggiatoa by combining whole genome amplification, pyrosequencing, and optical genome mapping. Sequence assemblies were incomplete and yielded average contig sizes of approximately 1 kb. Pathways for sulfur oxidation, nitrate and oxygen respiration, and CO2 fixation confirm the chemolithoautotrophic physiology of Beggiatoa. In addition, Beggiatoa potentially utilize inorganic sulfur compounds and dimethyl sulfoxide as electron acceptors. We propose a mechanism of vacuolar nitrate accumulation that is linked to proton translocation by vacuolar-type ATPases. Comparative genomics indicates substantial horizontal gene transfer of storage, metabolic, and gliding capabilities between Beggiatoa and cyanobacteria. These capabilities enable Beggiatoa to overcome non-overlapping availabilities of electron donors and acceptors while gliding between oxic and sulfidic zones. The first look into the genome of these filamentous sulfur-oxidizing bacteria substantially deepens the understanding of their evolution and their contribution to sulfur and nitrogen cycling in marine sediments.

Submarine mud volcanoes are formed by expulsions of mud, fluids, and gases from deeply buried subsurface sources. They are highly reduced benthic habitats and often associated with intensive methane seepage. In this study, the microbial diversity and community structure in methane-rich sediments of the Haakon Mosby Mud Volcano (HMMV) were investigated by comparative sequence analysis of 16S rRNA genes and fluorescence in situ hybridization. In the active volcano center, which has a diameter of about 500 m, the main methane-consuming process was bacterial aerobic oxidation. In this zone, aerobic methanotrophs belonging to three bacterial clades closely affiliated with Methylobacter and Methylophaga species accounted for 56%+/-8% of total cells. In sediments below Beggiatoa mats encircling the center of the HMMV, methanotrophic archaea of the ANME-3 clade dominated the zone of anaerobic methane oxidation. ANME-3 archaea form cell aggregates mostly associated with sulfate-reducing bacteria of the Desulfobulbus (DBB) branch. These ANME-3/DBB aggregates were highly abundant and accounted for up to 94%+/-2% of total microbial biomass at 2 to 3 cm below the surface. ANME-3/DBB aggregates could be further enriched by flow cytometry to identify their phylogenetic relationships. At the outer rim of the mud volcano, the seafloor was colonized by tubeworms (Siboglinidae, formerly known as Pogonophora). Here, both aerobic and anaerobic methane oxidizers were found, however, in lower abundances. The level of microbial diversity at this site was higher than that at the central and Beggiatoa species-covered part of the HMMV. Analysis of methyl-coenzyme M-reductase alpha subunit (mcrA) genes showed a strong dominance of a novel lineage, mcrA group f, which could be assigned to ANME-3 archaea. Our results further support the hypothesis of Niemann et al. (54), that high methane availability and different fluid flow regimens at the HMMV provide distinct niches for aerobic and anaerobic methanotrophs.

A two-part hypothesis has been tested, which proposes that (1) prostate cancer cells are galvanotactic (i.e. respond to an electric field by moving directionally) and (2) voltage-gated Na+ channel activity, which was shown previously to be expressed specifically by strongly metastatic cells, controls galvanotaxis. Two well-defined rat ('Dunning') cell lines, originally derived from the same prostate tumour but differing markedly in their metastatic ability, were used. Cells were exposed to exogenous direct-current electric fields of physiological strength (0.1-4.0 V cm(-1)), their reactions were recorded by light microscopy and analysed by a quantitative tracking method. Voltage-gated Na+ channel activity was modulated pharmacologically using a range of concentrations of a specific channel blocker (tetrodotoxin) or an opener (veratridine). The results showed that the highly metastatic MAT-LyLu cells responded to the application of the electric field strongly by migrating towards the cathode. By contrast, the weakly metastatic AT-2 cells gave no such response. Tetrodotoxin suppressed the galvanotactic response of the MAT-LyLu cells whereas veratridine enhanced it. Both compounds had little effect on the AT-2 cells. These results are consistent with functional voltage-gated Na+ channel expression occurring specifically in highly metastatic cells. This is also the first demonstration of control of galvanotaxis, in any cell type, by voltage-gated Na+ channel activity. The possible underlying mechanisms and the in vivo relevance of these findings are discussed.