Calcium and Cyclic AMP Mediate Sperm Activation, but Ca2+Alone Contributes Sperm Chemotaxis in the Ascidian, Ciona savignyi

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Abstract
Sperm-activating and -attracting factor (SAAF) released from the ascidian, Ciona savignyi, was partially purified from egg seawater with ethanol extraction and separation with the two-phase system of chloroform and water. SAAF did not activate sperm motility and cAMP synthesis in calcium-free seawater (CaFSW), but activated the both in the presence of Ca2+ . Sperm activation by SAAF in Ca2+ -containing medium was inhibited by flunarizine, a T-type Ca2+ channel antagonist, but L-type Ca2+ channel specific antagonists had no effect. Theophylline, a phosphodiesterase inhibitor, induced the increase of cAMP level and sperm activation in CaFSW without SAAF. On the other hand, the theophylline-activated sperm in CaFSW did not exhibit chemotaxis toward the tip of glass capillary containing SAAF, but upon the addition of Ca2+ they were attracted toward SAAF in the same manner as chemotaxis in normal artificial seawater. These results suggest that sperm activation is induced by the increased cAMP level caused by Ca2+ influx through T-type Ca2+ channel, and that Ca2+ alone mediates the sperm chemotaxis in Ciona.