Sodium influx induced by external calcium chelation decreases human sperm motility.

Background: Calcium removal from the medium promptly reduces human sperm motility and induces a Na(+)-dependent depolarization that is accompanied by an increase in intracellular sodium concentration ([Na(+)](i)) and a decrease in intracellular calcium concentration ([Ca(2+)](i)). Sodium loading activates a Na(+)/K(+)-ATPase.

Methods: Membrane potential (Vm) and [Ca(2+)](i) were simultaneously detected in human sperm populations with the fluorescent probes diSC(3)(5) and fura 2.

Activation of protein kinase A stimulates the progesterone-induced calcium influx in human sperm exposed to the phosphodiesterase inhibitor papaverine.

Progesterone induces a fast transient calcium influx in human sperm though the activation of nongenomic receptors. During sperm capacitation, a complex process required for sperm to be able to fertilize the egg, the calcium influx induced by progesterone is enhanced. Sperm capacitation is mediated by an increase in cAMP content and subsequent protein kinase A (PKA) activation.