The objective of our lab is to identify biomarker which predict fertilization outcome in IVF. Conventional markers such as motility, viability or morphology failed to correlate with fertility potential. Our recent prospective study on infertile couples undergoing their first cycle of IVF demonstrated that >40% of these males exhibited high levels of lead (Pb2+) in their seminal plasma. These high levels of Pb2+ inversely affected sperm function (i.e. increased spontaneous acrosome loss and decreased ability to undergo an acrosome reaction induced by exposure to progesterone (PSAR) or zona ligands (i.e. mannose). The PSAR was the parameter mostly affected by Pb2+. Our preliminary studies on potassium (K+) channel inhibitors suggested that the effects of progesterone on the human sperm acrosome reaction are mediated by a K+ channel. Thus, we hypothesized that sensitivity to Pb2+ exposure alters human sperm acrosome reaction by the interaction with a K+ channel. To test this hypothesis, we characterized the human sperm K+ channel. We examined the ability of human sperm to undergo PSAR in the presence of specific K+ channel inhibitors. Our data clearly showed that sperm from men who respond to progesterone exhibited an average of 30-40% inhibition of the PSAR in the presence of K+ channel inhibitors. These inhibitors similarly affected spontaneous acrosome reaction SAR. Interestingly, Pb2+ induced SAR was inhibited by these channel blockers. We localized human sperm surface K+ channel binding sites using biotin coupled CBTX, a specific K+ channel blocker. Independent to our observation, other members in the lab showed that Pb2+ entry co-localized with K+ channel binding sites on human sperm. Thus, biochemical analyses confirmed our prior preliminary findings that a K+ channel mediated the effects of progesterone on the human sperm acrosome reaction. Thus, Pb2+ associated alternations in human sperm function could be in part mediated by a K+ channel. We examined by RT-PCR the expression of KCNA3 in human sperm. For these analyses, we have designed primers from the S4 and S6 region of KCNA3 that contains the ion conduction pore of the channel and binding sites for all K+ channel inhibitors used in the biochemical analyses described above. RT-PCR analysis on human sperm using these primers generated specific PCR products generated specific PCR products that were 98% homologous to KCNA3. Our data suggest that the presence of these K+ channel mRNA positively correlated with the ability of human sperm to mount a PSAR. We now identified two individuals whose sperm fail to express the K+ channel transcript and do not undergo PSAR. Last, we examined by RT-in situ PCR analyses, the expression pattern of these K+ channel transcripts in human sperm. These channel transcripts were expressed over the entire human sperm head in 20-30% of sperm. Thus, these data provide strong evidence for the presence of either KCNA3 or KCNA3 related K+ channels in human sperm. Our prior studies on that testis K+ channel suggest that more than one isoform of K+ channel is expressed in rat testis. Our preliminary analyses on human sperm also suggest the presence of different isoforms of K+ channels.