Inhibition of flagellar motility of fowl spermatozoa by L-carnitine: its relationship with respiration and phosphorylation of axonemal proteins.

The action of carnitine in regulating fowl sperm motility was investigated. As the concentration of L-carnitine was increased (0-20 mM), the motility of intact and demembranated fowl spermatozoa was reduced at 30 degrees C. Even the presence of 1 mM CaCl2 before the addition of 10 mM carnitine could not prevent the inhibition of motility at 30 degrees C and 40 degrees C. However, motility was restored by reducing the concentrations of carnitine. Carnitine also inhibited the oxygen consumption and ATP concentrations of intact spermatozoa, and caused a reduction in intracellular free Ca2+ concentrations. Phosphorylation of a 50 kDa protein and dephosphorylation of 24 kDa and 30 kDa proteins of demembranated spermatozoa were observed after the addition of carnitine. In contrast, the flagellar ATPase activity of crude dynein extract was not affected by the addition of carnitine. These results suggest that inhibitory effect of carnitine for motility may be directly on the axonemal phosphoproteins, but not directly on the dynein ATPase activity. The physiological role of carnitine for fowl spermatozoa in the ductus deferens is discussed.