Abstract
There are several physiological and pharmacological evidences indicating that opening of voltage dependent Ca 2+ channels play a critical role in induction of acrosome reaction in mammalian sperm. We determined the intracellular free Ca 2+ concentration in ejaculated goat sperm using a fluorescent, Ca 2+ -specific probe, Fura2/AM, after the suspension of sperm in KRB medium, capable of sustaining capacitation and the acrosome reaction. We used nifedipine, D-600 and diltiazem, the Ca 2+ channel antagonists belonging to the classes of dihydropyridines, phenylalkylamines and benzothiazepines, to investigate the possibility that L-type voltage gated Ca 2+ channels play a role in the progesterone-stimulated exocytotic response. Progesterone promoted a rise in intracellular Ca 2+ in goat sperm and addition of nifedipine (100 nM) just prior to progesterone induction, significantly inhibited both intracellular Ca 2+ rise and exocytosis suggesting that Ca 2+ channels are involved in the process. However, the intracellular Ca 2+ increase during the process of capacitation was not affected with the addition of nifedipine suggesting a role of focal channel for Ca 2+ during capacitation. Studies using monensin and nigericin, two monovalent cation ionophores showed that an influx of Na + also may play a role in the opening of Ca 2+ channels. These results strongly suggests that the entry of Ca 2+ channels with characteristics similar to those of L-type, voltage-sensitive Ca 2+ channels found in cardiac and skeletal muscle, is a crucial step in the sequence of events leading to progesterone induced acrosome reaction in goat sperm. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 7 : 949-956)
Highlights
It has long been known that, upon release from the male reproductive tract, mammalian spermatozoa are incapable of fertilizing oocytes, but acquire functional ability during a species-dependent period of residence in the female reproductive tract (Austin, 1951; Chang, 1951)
Studies using monensin and nigericin, two monovalent cation ionophores showed that an influx of Na+ may play a role in the opening of Ca2+ channels. These results strongly suggests that the entry of Ca2+ channels with characteristics similar to those of
At the time of fertilization, capacitated mammalian spermatozoa undergo exocytosis of acrosomal granule in response to oocyte associated agonists. This essential process calledacrosome reaction' (AR) results in a release of enzymes necessary for the penetration of the egg vestments, and allows the spermatozoa to fuse with the oocyte plasma membrane after it penetrates the zona pellucida (ZP)
Summary
It has long been known that, upon release from the male reproductive tract, mammalian spermatozoa are incapable of fertilizing oocytes, but acquire functional ability during a species-dependent period of residence in the female reproductive tract (Austin, 1951; Chang, 1951). At the time of fertilization, capacitated mammalian spermatozoa undergo exocytosis of acrosomal granule in response to oocyte associated agonists. This essential process calledacrosome reaction' (AR) results in a release of enzymes necessary for the penetration of the egg vestments, and allows the spermatozoa to fuse with the oocyte plasma membrane after it penetrates the zona pellucida (ZP). Two major inducers of AR have been identified in the oocyte vestments, progesterone (Meizel et al, 1990) which is trapped in the matrix of the cumulus oophorus and appears to be produced by the cumulus cells (Schuetz and Dubin, 1981) and ZP3 glycoprotein (Bleil and Wassarman, 1983).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
