The Role of External Potassium Ion in Activation of Sea Urchin Spermatozoa. (sea urchin sperm/respiration/acid release/motility)

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Abstract
When sperm of the sea urchin, H. pulcherrimus, are diluted into K+-free seawater, the pH of the suspension gradually decreases, whereas a rapid decline in pH is observed following dilution into regular seawater. Sperm motility and respiration are also activated after dilution into K+-free seawater, but levels of activity are less that those observed following dilution into regular seawater. Upon addition of 10 mM K+ to K+-free seawater, rapid acid release occurs and motility and respiratory rate in sperm are reactivated. The effect of K+ on respiration was competitive with respect to the external Na+ concentrations. Harmaline, a potent inhibitor of Na+/K+-ATPase, causes a decrease in movement and respiration of the sperm. Harmaline does not inhibit the rapid decline in pH, although it depresses the release of acid from mitochondria. External K+ plays an important role in intracellular alkalinization of sea urchin sperm.