Calcium ion requirement for rabbit spermatozoal capacitation and enhancement of fertilizing ability by ionophore A23187 and cyclic adenosine 3':5'-monophosphate.

The presence of extracellular calcium is required for the in vitro occurrence of rabbit spermatozoal capacitation. However, calcium itself was found to be an inefficient agent for capacitating rabbit spermatozoa (following insemination with spermatozoa incubated for 10 hours in the presence of 2.5 X 10(-3) M calcium, only 9% of the ova cleaved). The addition of the divalent ionophore A23187 induced the early occurrence of capacitation and increased the percentage of full capacitated spermatozoa in a concentration-dependent manner (i.e, following insemination with spermatozoa incubated for 4 hours in the presence of 2.5 X 10(-3) M calcium and 2 X 10(-5) M A23187, 44% of the ova cleaved). Physiologic levels of capacitation were attained as estimated by the high proportion of ova that cleaved following in vitro insemination, when dibutyryl cyclic adenosine 3':5'-monophosphate (10(-6) m) was added in the presence of calcium (2.5 X 10(-3) M) and A23187 (2 X 10(-5) M) for treatment of spermatozoa.