ABSTRACT
Potential mechanisms of the reversible temperature-dependent immobilization of fowl sperm were investigated. At 30 °C, motility of demembranated fowl sperm was inhibited by adding 2 mM ethylene glycol-bis (2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA), but restored immediately after the subsequent addition of 2 mM CaCl(2), whereas at 40 °C, such additions did not appreciably affect motility (which remained almost negligible). With intact sperm, 10(-9) to 10(-3) M Ca(2+) had no effect on motility at 30 °C, which remained high. In contrast, intact sperm at 40 °C were almost immotile below 10(-5) M Ca(2+), and then gradually recovered motility at higher Ca(2+) concentrations. The negligible motility of demembranated sperm at 40 °C, and at 30 °C in the presence of EGTA, was stimulated by addition of 100 nM of the protein phosphatase inhibitor calyculin A. Dynein-ATPase activities of sperm at 40 °C in the presence of 2 mM EGTA, 2 µM CaCl(2), 2 mM CaCl(2,) or 100 nM calyculin A were higher than those at 30 °C. Therefore, stimulation of fowl sperm motility by temperature, Ca(2+), and phosphatase inhibition was not simply associated with an increase of flagellar dynein-ATPase activity. Furthermore, Ca(2+) was essential, at the axonemal level, for initiation of the 'intrinsic' motility of fowl sperm at 30 °C, but this Ca(2+)-dependent mechanism might be different from that involved in restoration of motility of intact sperm at 40 °C. In addition, perhaps inhibition of protein phosphatase activity was involved in initiation of sperm motility, but acting at a location different from Ca(2+) on the axoneme.