ACROSOME REACTION INDUCERS IMPOSE ALTERATIONS IN REPULSIVE STRAIN ANDHYDRATION BARRIER IN HUMAN SPERM MEMBRANES

Spin labeling studies of the lipophilic domains of human spermatozoa d uring capacitation and during acrosome reaction (AR) under the influen ce of selected AR-inducers were performed. Significantly enhanced rota tional function of molecules was obvious during capacitation, with no significant changes in membrane packaging or the lateral diffusion of molecules. The AR inducers appeared to restrict the rotational freedom of molecules, dramatically enhancing the lateral diffusion and orderi ng coefficients. A significant decrease in superoxide anion generation was observed in the acrosome reacted groups when compared to the non- acrosome reacted groups. A high level of superoxide anion radical (O-2 (-)) level maintained in capacitated spermatozoa would add to the Van der Waal's repulsive forces at the polar head of phospholipids, holdin g the membrane in strain where the molecular enjoy little freedom for lateral motion. A sudden drop in the levels of O-2(-) in spermatozoa u pon addition of AR inducers could abruptly release the local hydrophob ic repulsive strain within the membrane. This loss of hydration barrie r explains the observed enhancement in lateral diffusion profiles of l ipids and the packaging of molecules. It is reasonable to assume that these phenomena could be amplified further by interplay of Ca2+ by mod ifying the local charge aggregation. Thus, we would conclude that AR i nducers release the oxyradical load in capacitated spermatozoa, which would modify the repulsive strain and hydration barrier forces in the lipophilic domains permitting vesiculation of the membranes. It appear s that various acrosome reaction inducers act as effecters of grossly similar physical alterations in sperm membranes and that the resulting signal cascades proceed through intercalating biochemical sequences.