Alteration of sperm thiol‐disulfide status and capacitation in the guinea pig

Abstract

AbstractEpididymal spermatozoa of the guinea pig were incubated under conditions known to promote a rapid synchronous capacitation in a large proportion of the spermatozoa (Ca2+‐free medium with lysophosphatidylcholine, LC) or in Ca 2+‐free medium without LC. To study the effects of altered thiol‐disulfide status and content, incubations were conducted with reagents that maintain and increase thiol groups (DTT, GSH), maintain and increase disulfide groups (diamide, GSSG), or which irreversibly block thiol groups by alkylation (NEM). The permeable DTT inhibited LC‐induced capacitation and at high concentrations diminished the percentage of acrosome reactions in capacitated spermatozoa. The permeable diamide exhibited a stimulatory effect upon capacitation. The largely impermeable GSH and GSSG exhibited effects similar to their respective permeable counterparts but their effects were moderate and required extremely high concentrations. The DTT inhibition of LC‐induced capacitation was reversible by washing and a further 1 hr incubation. In this final incubation after removal of DTT by washing, LC was absent too so its stimulatory effect must have been accomplished prior to washing and in the presence of DTT. NEM‐alkylation of the existing thiol population did not affect LC‐induced capacitation but alkylation of the increased thiol population after prior DTT treatment was inhibitory of capacitation. These results suggest that the maintenance and/or formation of disulfide groups on enzymes or structural proteins may be a component of the capacitation process. In contrast, the formation and maintenance by alkylation of increased thiol groups but not the maintenance of existing thiol groups, is inhibitory of capacitation. The relevance of these findings to a role for a thiol‐sensitive proteinase in capacitation is discussed.