Changes in the fluidity of the goat sperm plasma membrane in transit from caput to cauda epididymis

Highly purified maturing plasma membranes of goat caput-, corpus- and cauda-epididymal spermatozoa, were isolated by an aqueous two-phase polymer method and their fluidity was determined using pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH) as the membrane lipid probes. Pyrene following partitioning into the lipid phase of the membrane formed excimers at 480 nm and the amount of excimers formed was markedly higher with the immature caput- than the mature cauda-sperm membrane. The fluorescence polarization values obtained with DPH as the lipophilic probe, were lowest in the immature sperm membrane and highest in that of the mature sperm. The data with both the probes are consistent with the view that the lipid phase fluidity of the sperm plasma membrane undergoes significant decrease during the epididymal maturation of the male gametes.