Further studies on the involvement of protein kinase C in human sperm flagellar motility

Addition of the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) or the membrane-permeable diacylglycerol analog, l-oleoyl-2-acetylglycerol to human sperm resulted in increased motility. The biologically inactive 4α-phorbol 12, 13 didecanoate had no effect on flagellar motility. Basal motility was markedly reduced in the absence of Ca²⁺in the incubation medium, but TPA-induced sperm motility persisted even in the absence of Ca²⁺. Sperm motility was also enhanced by the Ca²⁺ionophore ionomycin in a Ca²⁺-dependent, protein kinase c (PKC)-independent fashion. Although all stimulants examined here reached maximal response at about 15 min of incubation, nevertheless whereas the effect of TPA and l-oleoyl- 2-acetylglycerol declined at 60 min of incubation, that of ionomycin still persisted. Human sperm PKC activity is extremely low and represents only about 20% and 25% of the specific activity recovered from PC-12 and rat pituitary cells, respectively. Immunohistochemical analysis using various type-specific PKC antibodies revealed staining only in the equatorial segment and the principal piece of the tail. Thus, PKC is present in human ejaculated sperm and is involved in flagellar motility.