The ascidian sperm reaction: Ca2+ uptake in relation to H+ efflux |
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Authors: | Charles C Lambert Gretchen Lambert |
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Institution: | Department of Biological Science, California State University, Fullerton, California 92634 USA |
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Abstract: | During the ascidian sperm reaction the single large cylindrical mitochondrion which lies next to the nucleus in the head swells, becomes spherical, and migrates along the tail to be lost when it reaches the end. This sequence is initiated by eggs, egg water, high pH, low Na+, or the ionophore X537A. Accompanying the sperm reaction induced by low Na+ are H+ efflux and Ca2+ influx in a ratio of near 100:1 as determined by 45Ca2+ and atomic absorption analysis. Simultaneous pH and Ca2+ electrode measurements suggest that the movement of H+ begins 10–13 sec before the movement of Ca2+. Ca2+ uptake can be inhibited by verapamil without affecting H+ efflux or the sperm reaction. Acid release and Ca2+ uptake are proportional to the initial pH of the medium when the reaction is triggered by high pH. Acid release initiated by low Na+ is proportional to Ca2+ concentrations above 2 mM. H+ and Ca2+ movements differ in magnitude, kinetics, and inhibition by verapamil, thus suggesting that H+ is probably not exchanged for Ca2+. Instead we propose that loss of H+ triggers the uptake of Ca2+, which initiates the sperm reaction. |
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