Figure 3. Determination of the acrosomal reaction of human sperm under different experimental conditions. (A) Effect of membrane potential (Vm) depolarization from -71 to -15 mV on the percentage of sperm undergoing an acrosomal reaction in noncapacitated human sperm. Valinomycin (1 µM) was added 1 minute before 60 mM KCl, and the acrosomal reaction was determined as described in "Methods." The effects of 1 µM valinomycin and 10 µM A23187 are included. In control experiments, 5 µL dimethylsulfoxide (DMSO) was added. (B) Effect of valinomycin on the percentage of sperm undergoing an acrosomal reaction induced by progesterone in capacitated sperm. Valinomycin (1 µM) was added 1 minute before either 10 µM A23187 or 4 µM progesterone. The effects of progesterone and A231787 and 5 µL DMSO (control), without valinomycin, are included. Experimental procedures were performed as described in "Methods." The values are means plus or minus standard errors, n = 5. ^*P < .05 compared to the control group.