Capacitation of Bovine Sperm by Heparin: Inhibitory Effect of Glucose and Role of Intracellular pH1

Abstract

Bovine sperm incubated with heparin for 7.5-8.5 h underwent an acrosome reaction in the absence but not the presence of glucose (5mM). When sperm were incubated under capacitating conditions with heparin for 4 h, glucose inhibited sperm penetration of oocytes (p0.05), but capacitation was inhibited by the glycolyzable substrates glucose, mannose, and fructose (p<0.05). The glycolytic inhibitor, fluoride, reversed glucose inhibition of capacitation in a dose-dependent manner similar to its effect on glucose uptake by sperm. Extracellular pH declined from 7.4 to 7.2 during a 4-h incubation of sperm with herapin and glucose. The decline of extracellular pH during sperm incubation with glucose did not affect capacitation, since only an extracellular pH below 7.02 inhibited capacitation. The intracellular pH (pHi) of sperm increased 0.40 units over a 5-h incubation under capacitating conditions. The change in pHi was inhibited by glucose. Incubation of sperm with heparin and glucose for 12 h resulted in capacitated sperm as judged by both LC sensitivity and fertilizing ability. These studies demonstrate that glycolyzable substrates delay capacitation of bovine sperm and suggest the effect is in delaying an alkalinization of pHi.