TROUT SPERM SWIMMING PATTERNS AND ROLE OF INTRACELLULAR CA++

We investigated the swimming patterns of trout sperm using computer-assisted analyses of video microscopy. Under full activation conditions, in which 80-100% of sperm activate their motility, sperm swim in circular paths for 2-5 sec, followed by 30-60 sec of a more linear swimming, and, finally, cessation of movement, with a straightening of the flagella. Threshold activation, in which 50% of the sperm activate, is characterized by circular patterns of swimming for less than 20 sec, with straightened flagella upon cessation. Full activation and threshold activation are observed in low-K+ solution or in an Mg++-supplemented K+ solution. Similarities in swimming patterns in low-K+ solution and in a Mg++-supplemented K+ solution suggest a common underlying mechanism of activation. Initiation of movement in solutions with high Ca++ to K+ ratio is similar to activation in K+-free solution. However, sperm in Ca++-supplemented media resume circular swimming within 20-25 sec after activation, and, upon cessation of movement, the flagella are frequently cane shaped or bent. Differences in swimming patterns upon activation by high Ca++ concentration suggest additional effects of Ca++ on regulating swimming patterns. We used the fluorescent Ca++ indicator Fluo-3 to measure changes in intracellular Ca++ concentration upon activation. Intracellular Ca++ concentration transiently increases upon activation, with peak Ca++ concentration coinciding with the period of circular swimming. This transient increase in Ca++ concentration is seen in the absence of external Ca++, providing strong evidence for the released of Ca++ from intracellular stores upon activation.