Motility activation and second messenger signalling in spermatozoa from rat cauda epididymidis

This study examined molecular mechanisms involved in the activation of motility in spermatozoa from the cauda epididymidis of rats. A 1.05-fold dilution of semen from the cauda epididymidis with 300 mmol sucrose l(-1) did not activate motility in spermatozoa. Addition of dibutyryl cAMP, pentoxifylline or Ca(2+) to the sucrose activated motility in the short term (<3060 min). A fivefold dilution of semen from the cauda epididymidis with a modified Tyrodeʹs medium (BWW) activated and sustained vigorous motility that could not be attenuated with kinase inhibitors. This motility was associated with a transient increase in intracellular cAMP during the first 60 s of activation. Lower motility was activated in Ca(2+)-deficient media but this was not associated with an increase in cAMP. A fivefold dilution with plasma from the cauda epididymidis did not activate motility. The addition of Ca(2+) to the sucrose induced an increase in cAMP of similar duration but lower magnitude to that associated with dilution in BWW. The results from this study indicate that the cAMP and Ca(2+) signal transduction pathways are involved in activation of sperm motility, and that the increase in intracellular cAMP in rat spermatozoa from the cauda epididymidis undergoing motility activation is Ca(2+)-dependent. This is the first study to report a Ca(2+)-dependent increase in cAMP associated with motility activation in immotile mammalian spermatozoa. In light of these data, a model is proposed whereby cAMP and Ca(2+) act as synarchic messengers, initiating a signal transduction cascade, which is independent of protein kinase A-mediated phosphorylation of flagella proteins in immotile spermatozoa from the cauda epididymidis.