Store-operated calcium channel regulates the chemotactic behavior of ascidian sperm

The sperm-activating and -attracting factor released from the eggs of the ascidians Ciona intestinalis and Ciona savignyi requires extracellular Ca2+ for activating sperm motility and eliciting chemotactic behavior of the activated sperm toward the egg. Here, we show that modulators of the store-operated Ca2+ channel, SK&F96365, Ni2+, 2-aminoethoxydiphenylborane, and thapsigargin inhibit the chemotactic behavior of the ascidian sperm; on the other hand, blockers of voltage-dependent Ca2+ channels did not inhibit the chemotaxis, even though they inhibited the sperm activation operated by voltage-dependent Ca2+ channels. The blockers of store-operated Ca2+ channels also inhibited the asymmetrical flagellar beating and turning movements of the ascidian sperm, which are typical signs of sperm chemotaxis. Depletion of internal Ca2+ stores by thapsigargin induced capacitative Ca2+ entry into the sperm, which was blocked by SK&F96365. These results suggest that the intracellular Ca2+ concentration increase through the store-operated Ca2+ channels induces asymmetrical flagellar movements to establish the chernotactic behavior of the sperm.