Decrease in order of human sperm lipids during capacitation.
Ejaculated mammalian sperm must undergo a final maturation (capacitation) before they can acrosome-react and fertilize eggs. Loss of the sperm sterols, cholesterol and desmosterol, is an obligatory step in the capacitation of human sperm. Because sterols can increase the order of membrane phospholipids, it has been suggested that the importance of sterol loss is that it decreases membrane lipid order. The present study tested the hypotheses that sterol loss decreases sperm membrane lipid order during capacitation and that lipid disorder is a sufficient stimulus for capacitation. Steady-state fluorescence anisotropy of the membrane probe, 1,6-diphenyl-1,3,5-hexatriene, decreased during capacitation, indicating a decrease in lipid order. The decrease was dependent on the loss of sperm sterols, suggesting that it reflected diminished sterol-mediated phospholipid ordering. However, the lipid-fluidizing agents, benzyl alcohol and 2-(2-methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl) octanoate, did not cause sperm capacitation or overcome inhibition by cholesterol. In summary, loss of sperm sterols caused a significant decline in lipid order during capacitation; however, decreased bulk lipid order was not sufficient to trigger the subsequent events that complete capacitation.
Cross
Nicholas L
NL
Department of Physiological Sciences, Oklahoma State University, Stillwater, Oklahoma 74078, USA. ncross@okstate.edu
D020101:Acrosome Reaction / Q000502:physiology; D000465:Algorithms; D016880:Anisotropy; D019905:Benzyl Alcohol / Q000494:pharmacology; D002784:Cholesterol / Q000494:pharmacology; D005456:Fluorescent Dyes; D006801:Humans; D066298:In Vitro Techniques; D050356:Lipid Metabolism; D008055:Lipids / Q000502:physiology*; D008297:Male; D013075:Sperm Capacitation / Q000502:physiology*; D013079:Sperm Maturation / Q000502:physiology; D013094:Spermatozoa / Q000378:metabolism* / Q000502:physiology*; D013261:Sterols / Q000378:metabolism
D005456:Fluorescent Dyes; D008055:Lipids; D013261:Sterols; D002784:Cholesterol; D019905:Benzyl Alcohol