Sodium requirement for capacitation and membrane fusion during the guinea-pig sperm acrosome reaction

Abstract

Guinea-pig spermatozoa, incubated in a minimal culture medium (MCM-PL) containing 150 mM-Na+ and no added K+, capacitate within 2 h and respond to added Ca2+ with maximal percentage of acrosome reactions. When spermatozoa, initially capacitated in Medium MCM-PL, were washed and resuspended in saline-based media, the motile spermatozoa showed acrosome reactions only in response to added Ca2+ at an extracellular pH greater than 7.4. In contrast, resuspension of capacitated spermatozoa into isotonic sucrose or choline-based media containing no added Na+ and K+ (pH 7.8) did not support acrosome reactions in response to the addition of Ca2+. Examination under the electron microscope showed that these spermatozoa responded to added Ca2+ with swelling or cavitation of the acrosomal matrix but fusion of the plasma membrane and acrosomal membrane did not occur. Treatment of spermatozoa with monensin, a monovalent cationic ionophore, induced rapid acrosome reactions in the presence of extracellular Ca2+ and Na+. In contrast, spermatozoa incubated for 3 h in a sucrose-based Na+-deficient medium or Medium MCM-PL containing 10 mM-KCl failed to give a significant percentage of acrosome reactions in response to the addition of Ca2+, but the addition of ouabain (0.1 mM) prevented the K+ inhibition. Amiloride, a sodium channel blocker in various other tissues, retarded the development of acrosome reactions of spermatozoa incubated in Medium MCM-PL. Based on these data, it appears that an increase in intracellular Na+ has a functional role in acquisition of guinea-pig sperm fertilizing ability.

Is a Ca2+ -ATPase involved in Ca2+ regulation during capacitation and the acrosome reaction of guinea-pig spermatozoa?

“…Ionic exchanges in mammalian spermatozoa are probably not regulated by changes in membrane potential (Rink, 1977) and voltage-gated channels do not appear to participate in Ca2+ influx ). Instead, a Na + /Ca2+ antiport (Hyne et al, 1984;Bhattacharyya et al, 1986) and ion ATPases (Mrsny & Meizel, 1981;Ashraf et al, 1982;Breitbart etal, 1983Breitbart etal, , 1984; Usui & Yanagimachi, 1986), working alone or in conjunction, may be responsible for the regulation ofthe intracellular concentration of Ca2+ ([Ca2+]…”

Influence of 2-deoxy-D-glucose and energy substrates on guinea-pig sperm capacitation and acrosome reaction

“…However, organic factors such as serum albumin and other 'serum factors' are essential additives to chemically defined media that permit spermatozoa to undergo capacitation and fertilization in vitro (mouse : Hoppe & Whitten, 1974;rat: Niwa & Chang, 1975;Davis, 1976; guinea-pig: Yanagimachi, 1972; Hyne & Garbers, 1981; golden hamster: Lui, Cornett & Meizel, 1977; Mrsny, Waxman & Meizel, 1979; Bavister, 1981 ; rabbit : Oliphant, 1976; dog: Mahi& Yanagimachi, ,1978;man: Yanagimachi, Yanagimachi & Rogers, 1976;Lopata, McMaster, McBain & Johnston, 1978). It has long been proposed that capacitation involves endogenous cellular changes that stem primarily from modifications of the plasmalemma of the spermatozoon (Barros, 1974;0'Rand, 1979;Oliphant &Singhas, 1979;Bearer & Friend, 1982), the state of which in turn may regulate a series of biochemical events associated with Ca2 + influx (Hyne & Garbers, 1979a, b; Hyne, Higginson, Kohlman & Lopata, 1984).…”

In Vitro Behavior of Human Nonfertile Semen in Isoosmotic and Hyperosmotic Media

“…Moreover, Hyne et al [6] demonstrated that in guinea-pig sperm, relatively high extracellular concentration of Na' ions ( > 125 mM) are required for the fusion of the plasma membrane with the outer acrosomal membrane. The H-BWW used in this study (163 mM of Na' ions) probably favors membrane fusion events making more acrosome-reacted spermatozoa available for penetration in the hamster egg.…”