Concerted action between Ca2+ and hyperosmolality initiates sperm motility in amphioxus Branchiostoma belcheri tsingtauense

This study investigated the effects of different environmental conditions on the initiation and maintenance of sperm motility in amphioxus Branchiostoma belcheri tsingtauense. The findings were that: (1) hyperosmolality in the absence of Ca2+ ions did not initiate amphioxus sperm motility; (2) addition of Ca2+ into EGTA-containing Ca2+-free artificial sea water (ASW), in which no sperm were motile, restored sperm motility; (3) Ca2+ failed to induce sperm motility under conditions of hypoosmolality; (4) K+ channel blockers quinine and 4-aminopiridine did not suppress the initiation of sperm motility; and (5) changes in pH did not cause sperm motility in a solution isotonic to seawater without Ca2+. In conclusion, we inferred that a concerted action between Ca2+ and hyperosmolality was essential to initiate motility of amphioxus sperm, whereas K+ and pH were indispensable to maintain motility.