Effects of calpain and Rho-kinase inhibitors on the acrosome reaction and motility of fowl spermatozoa in vitro.

Abstract

At the avian body temperature of 40 degrees C, intact fowl spermatozoa require Ca(2+) for the initiation of motility and a combination of both Ca(2+) and homogenized inner perivitelline layer (IPVL) together to induce the acrosome reaction. Within the range of 1-100 micromol/l, neither PD 150606 (a Ca(2+)-dependent calpain inhibitor) nor Y-27632 (an inhibitor of Ca(2+)-dependent Rho-kinase) were able to inhibit the acrosome reaction induced by the presence of Ca(2+) and IPVL. However, PD 150606, although not Y-27632, was able to inhibit sperm motility initiated by Ca(2+), as well as motility initiated by calyculin A -- a specific inhibitor of protein phosphatases, which also initiates sperm motility at 40 degrees C. The addition of PD 150606 did not reduce the ATP concentrations of intact spermatozoa, nor the motility of demembranated spermatozoa. Immunoblot analysis of sperm extract using a polyclonal antibody against calpain 12 revealed a cross-reacting protein of approximately 80 kDa. These results suggest that Rho-kinase is not involved in the regulation of the acrosome reaction or of motility in fowl spermatozoa. In contrast, calpain appears to be involved in the regulation of flagellar movement, but not izn that of the acrosome reaction. Furthermore, it seems that endogenous calpain is present in the cytoplasmic matrix and/or the plasma membrane, but not retained in the axoneme and/or accessory cytoskeletal components.