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Involvement of ion fluxes and cAMP pathways in sperm capacitation
After epididymal maturation, sperm capacitation, which encompasses a complex series of molecular events, endows the sperm with the ability to fertilize an egg. It is well established that capacitation requires Na+, HCO3-, Ca2+ and a cholesterol acceptor; however, little is known about the function of Cl- during this important process. In this study, it is shown that Cl- is essential for capacitation and that Cl- act upstream of the cAMP/PKA signaling pathway. To investigate the Cl- transporters involved, sperm incubated in complete capacitation medium were exposed to a battery of anion transport inhibitors. Among them, bumetanide and furosemide, two blockers of Na+, K+, Clcotransporters (NKCC), inhibited all capacitation-associated events suggesting that these transporters may mediate Cl- movements in sperm. Consistent with these results, western blots using anti NKCC1 antibodies showed the presence of this cotransporter in mature sperm.^ Other key issue in sperm capacitation that remains unsolved despite many years of research is the possibility that transmembrane adenylyl cyclases (tmACs) have a role in sperm physiology. If tmACs were involved in the increase of cAMP in sperm, a role of G proteins in these responses would be plausible. Uncertainties exist about the activation of sperm adenylyl cyclase(s) by heterotrimeric G proteins. In this regard, there is some debate as to whether Gα s is present in spermatozoa. In this work, Gαs was detected on membranes purified from mouse sperm by [32 P] ADP-ribosylation with cholera toxin followed by immunoprecipitation with a specific antibody. In addition, immunofluorescence studies identified a specific signal in the sperm acrosomal region. Moreover, forskolin was able to induce acrosome reaction after incubating sperm in capacitating conditions and a higher accumulation of cAMP was observed after incubating sperm with forskolin. In this context, the clarification of the role of the ACs and G proteins will constitute a pivotal step for further investigation on sperm capacitation. Forskolin induces acrosome reaction only on capacitated sperm. These data suggest that a tmAC might be involved in the acrosome reaction and that capacitation is needed to couple this signal to other pathways related to the exocytic process.^
Biology, Cell|Chemistry, Biochemistry|Biology, Veterinary Science
"Involvement of ion fluxes and cAMP pathways in sperm capacitation"
(January 1, 2010).
Electronic Doctoral Dissertations for UMass Amherst.