Table 1.

Effect of K⁺_o on the ZP-dependent acrosome reaction

	Percent of acrosome-reacted sperm
	30 mM K+o	3 mM K+o
+Buffer	15 (10/68)	12 (5/43)
+Ionomycin	71 (76/107)	84 (70/83)
+ZP	20 (17/83)	57 (43/75)

Sperm were incubated in medium HBCM for 120 min; medium K⁺_o was adjusted to the indicated values; sperm were treated with equal volumes of buffer, of ionomycin (5 μM final concentration), or of ZP (40 μg/ml final protein concentration); and the fraction of acrosome reacted cells was determined after an additional 30-min incubation. Data represent the percent of acrosome-reacted cells as well as the number of acrosome reacted and total sperm examined.