Regulation of human sperm motility and hyperactivation components by calcium, calmodulin, and protein phosphatases

The role of Ca2+, calmodulin, and protein phosphatases on motility and hyperactivation of noncapacitated, capacitating, and detergent-permeabilized reactivated human sperm was examined. In noncapacitated sperm, W7 inhibited percent motility (%MOT), curvilinear velocity (VCL), amplitude of lateral head displacement (ALH), and percent hyperactivation (%HYP) in an extracellular Ca2+ concentration-dependent manner (p < .05). However, in capacitating sperm, inhibition of motility by W7 was independent of external Ca2+. Treatment of reactivated sperm with a synthetic calmodulin inhibitor peptide decreased VCL and ALH in a Ca(2+)-dependent manner (p < .05). Ca2+ exhibited a dramatic influence on motility within a narrow concentration range (0.7 to 1.0 microM) in reactivated sperm. A calmodulin-dependent protein phosphatase (PP2B) was identified by activity assay, immunoblotting, and dephosphorylation of endogenous phosphoproteins. The sperm enzyme, unlike bovine brain PP2B, was inhibited by 1 microM okadaic acid (OA) in the presence of Mn2+, suggesting that the sperm enzyme is unique. In reactivated sperm, inhibition of endogenous PP2B-like activity with anti-PP2B antibodies altered ALH, whereas OA altered both VCL and ALH and also inhibited a subset of Ca(2+)-dependent dephosphorylations of cAMP-dependent phosphoproteins in capacitating sperm. These results suggest (1) an important role for calmodulin and PP2B in Ca(2+)-regulated motility parameters, particularly ALH, and (2) that modulation of human sperm motility, including hyperactivation by cAMP-dependent phosphorylation, requires calmodulin-dependent as well as other protein dephosphorylations.