The effect of theophylline and dibutyryl cyclic AMP on the uptake of radioactive calcium and phosphate ions by boar and human spermatozoa.

Radioactive calcium uptake by suspensions of washed boar and human spermatozoa was inhibited by the mitochondrial uncoupling agent carbonylcyanide-p-trifluoromethoxy-phenylhydrazone (FCCP). Theophylline + dibutyryl cyclic AMP also inhibited calcium uptake in the presence or absence of FCCP. Uptake of low concentrations of calcium (0 . 1 mM) was inhibited by the calcium ionophore A23187, but at high calcium concentrations the ionophore stimulated calcium uptake. These observations are explained in terms of a mechanism for the regulation of calcium uptake in spermatozoa based on competing mitochondrial and plasma membrane pumps. Uptake of 32P was also inhibited. These effects provide evidence that cyclic AMP plays a role in the transport of ions across the plasma membrane of spermatozoa.