Intracellular calcium regulation in sperm capacitation and acrosomal reaction.
Binding to the egg's zona pellucida stimulates the spermatozoon to undergo acrosome reaction, a process which enables the sperm to penetrate the egg. Prior to this binding, the spermatozoa undergo in the female reproductive tract a series of biochemical transformations, collectively called capacitation. The first event in capacitation is the elevation of intracellular calcium and bicarbonate to activate adenylyl cyclase (AC) to produce cyclic-AMP, which activates protein kinase A (PKA) to phosphorylate certain proteins. During capacitation, there is also an increase in actin polymerization and in the membrane-bound phospholipase C (PLC). Sperm binding to zona-pellucida causes further activation of cAMP/PKA and protein kinase C (PKC), respectively. PKC opens a calcium channel in the plasma membrane. PKA together with inositol-trisphosphate activate calcium channels in the outer acrosomal membrane, which leads to an increase in cytosolic calcium. The depletion of calcium in the acrosome will activate a store-operated calcium entry mechanism in the plasma membrane, leading to a higher increase in cytosolic calcium, resulting in membrane fusion and acrosome reaction.
Breitbart
Haim
H
Faculty of Life Sciences, Bar-Ilan University, 52900, Ramat Gan, Israel. breith@mail.biu.ac.il
D020101:Acrosome Reaction; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008322:Mammals; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D013075:Sperm Capacitation; D013084:Sperm-Ovum Interactions
D011505:Protein-Tyrosine Kinases; D002118:Calcium