Activation of Ca2+ Transport System of Sea Urchin Sperm by High External pH: 220 kD Membrane Glycoprotein is Involved in the Regulation of the Ca2+ Entry |
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Authors: | Yutaka Sendai Kenji Aketa |
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Institution: | Akkeshi Marine Biological Station, Faculty of Science, Hokkaido University, Akkeshi, Hokkaido 088–11, Japan |
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Abstract: | When sperm of the sea urchin, Hemicentrotus pulcherrimus , were exposed to high pH (9.0) sea water, they showed large increases in intracellular Ca2+ (Ca2+]i) and pH (pHi) and underwent the acrosome reaction (AR) without the aid of the egg jelly. Not only Ca2+]i increase but also pHi rise did not occur under Ca2+-free conditions. Both the increases in Ca2+]i and pHi and the AR by high pH were inhibited by a Ca2+ channel blockers, verapamil and nisoldipine, and by a lectin, wheat germ agglutinin (WGA) which interacts with a 220 kD membrane glycoprotein of sperm. These reagents inhibited also the AR by the egg jelly. The inhibitory effects of WGA were immediately canceled by the addition of N-acetyl-D-glucosamine, a sugar which is known to remove WGA from its binding site. These results suggest that 1) the same Ca2+ transport system is activated by high external pH and the egg jelly, 2) increase in Ca2+]i is prerequisite for the stimulation of the H+-efflux system(s) and 3) the 220 kD WGA-binding membrane protein functions as a regulator protein of Ca2+ transport system. |
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