INTERACTION OF HUMAN SPERMATOZOA WITH THE ZONA PELLUCIDA OF OOCYTE: DEVELOPMENT OF THE ACROSOME REACTION

Patricio Morales1 and Miguel Llanos2

1 P. Catholic University of Chile, Faculty of Biological Sciences. P. O. Box 114-D. Santiago, Chile.

2INTA, University of Chile, P. O. Box 138-11. Santiago, Chile.

8. INTRACELLULAR PROTEASES AND THE ZONA PELLUCIDA-INDUCED ACROSOME REACTION

Several investigators have proposed a role for an endogenous trypsin-like activity in the mechanism of the mammalian sperm AR (100). This trypsin-like activity may be involved in the dispersal of the acrosomal matrix, the membrane events of the AR or both (101, 102). In human, the AR induced by the human ZP and FF is inhibited by several trypsin inhibitors (103). These results suggest that hFF and human ZP induce the human sperm AR through a common mechanism mediated by a trypsin-like protease activity. A chymotrypsin-like activity is also involved in the human ZP- and hFF-induced sperm AR (100). The precise role of this chymotrypsin-like activity, however, remains to be elucidated. In sea urchin spermatozoa, a chymotrypsin-like enzyme is involved in the activation of Ca2+ channels and leads to an increase in the level of intracellular Ca2+, a crucial requisite for the AR (104). The hFF-induced AR also induces a rapid and transient increase in the level of intracellular Ca2+ due to Ca2+ influx (54, 55). This event can be inhibited by trypsin and chymotrypsin inhibitors (105, 106), suggesting a role for both types of protease activity in the elevation of intracellular Ca2+ level. In the mouse and bovine spermatozoa, the ZP-induced AR is associated with a Ca2+ influx (71, 74). Therefore, it could be speculated that the effect of trypsin and chymotrypsin inhibitors on the human ZP-induced AR (100, 103) may be due to an inhibition of the ZP-stimulated Ca2+ influx before the induction of the AR. Further research is required to clarify the identity and possible role of these trypsin and chymotrypsin-like activities in the human sperm AR.

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