Calcium uptake, respiration, and ultrastructure of sperm exposed to ionophore A23187

Calcium accumulation by ram sperm in the presence of 3.0 microM ionophore A23187 increased greatly when the pH of the medium was raised from 7.5 to 8.5. The increase in calcium uptake was remarkable between pH 7.5 and 8.0 and was paralleled by increased oxygen consumption. There was extensive vesiculation of the plasma membrane and membranes of the acrosome and postnuclear cap of ram sperm incubated with the ionophore and calcium at pH 8.0. The mitochondria of the midpiece contained pale and expanded cristae similar to ATP-deprived mitochondria in the "condensed" configuration. Such changes were not observed in ram sperm incubated under similar conditions at pH 7.0. The ionophore-induced calcium and oxygen uptake of cauda and caput epididymal boar sperm also increased with increased pH, but the effect commenced at a lower pH. Control cauda epididymal boar sperm (i.e., without ionophore) had higher oxygen uptake, glucose breakdown, and lactic acid production than caput sperm. The influence of pH on the operation of the membrane calcium pumps between ram boar sperm indicates species differences.