Competitive Effect of Magnesium on the Calcium-Dependent Acrosome Reaction in Guinea Pig Spermatozoa

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Abstract
The occurrence of the acrosome reaction was monitored in guinea pig spermatozoa which were incubated in media with varying levels of magnesium and calcium. When the calcium concentration was held constant at 1.71 mM and the magnesium concentration was varied up to 10 mM the acrosome reaction was inhibited with the increase in magnesium concentration. At 10 mM magnesium the acrosome reaction was completely suppressed over the 4 h incubation period. The inhibitory effect was shown to be competitive by holding the magnesium concentration constant at 1 mM and varying the calcium from 0[unknown] to 5 mM. A calcium concentration of 3 or 5 mM in the presence of 1 mM magnesium was shown to overcome the inhibitory effect of magnesium on the acrosome reaction. The magnesium/calcium ratio in the medium influences the occurrence of the acrosome reaction in guinea pig spermatozoa in vitro. The possibility that the magnesium/calcium ratio in vivo is involved in regulating the occurrence of the acrosome reaction is suggested.