CHANGES IN LIPID DIFFUSIBILITY IN THE HAMSTER SPERM HEAD PLASMA-MEMBRANE DURING CAPACITATION IN-VIVO AND IN-VITRO

The technique of fluorescence recovery after photobleaching (FRAP) was employed on spermatozoa labeled with the fluorescent lipid analogue C (14)dil to provide two measures of lateral diffusion in the plane of t he sperm plasma membrane during capacitation in vivo and in vitro: the diffusion coefficient (D) for C14dil and the fraction of C14dil that is free to diffuse (%R) within the domain. To evaluate changes in lipi d diffusibility during capacitation in vivo, spermatozoa were recovere d from the uterus within 30 min after ejaculation or from the oviduct at 2, 4, 6 and 8 hr after mating. To compare the changes which occur i n vivo with those which occur during capacitation in vitro, caudal epi didymal spermatozoa were incubated under capacitating or non-capacitat ing (control) conditions for 4 hr. Although transient changes in D occ urred during the course of capacitation, there was no net change in D for either anterior (AH) or posterior head (PH) domains following capa citation in vitro or in vivo, Significant differences in the lipid dif fusion coefficient between the two head domains were observed during t he course of capacitation. A transient decrease in %R was observed for the AH domain during capacitation in vitro and incubation under centr al conditions, but, no significant change in %R was observed in the AH domain during capacitation in vivo. A significant decline in %R of th e PH domain was observed far spermatozoa during capacitation in vivo, in vitro and following incubation under non-capacitating conditions. T hese data indicate that the changes in the lipid diffusibility of the AH and PH domains which occur during capacitation in vivo exhibit both similarities and differences to those which occur during capacitation in vitro. (C) 1998 Wiiey-Liss, Inc.