Flagellar movement of the sea urchin sperm is regulated by intracellular Ca2+. Flagellasialin, a polysialic acid-containing glycoprotein, as well as other membrane proteins seems responsible for the Ca2+ control. To elucidate the mechanism of Ca2+ dynamics underlying flagellar movement, we analysed the sperm’s mechanosensory behavioural responses by using microtechniques. In sea water containing 10 mM Ca2+, the sperm swim in circular paths. When a mechanical stimulus was applied to the sperm head with a glass microstylus, the sperm showed a series of flagellar responses, consisting of a stoppage of beating (quiescence) and a recovery of swimming in a straight path, followed by swimming in a circular path again; as the result the sperm avoided the obstacle. Ca2+-imaging with Fluo-4 showed that the intracellular Ca2+ was high in the quiescence and gradually decreased after that. The effects of blockers and antibodies against candidate components revealed that the Ca2+ influx was induced by Ca2+ channels and the Ca2+ efflux was induced by a flagellasialin-related Ca2+-efflux system, plasma membrane Ca2+-ATPases and the K+-dependent Na+/Ca2+ exchanger. The results show that the Ca2+-dependent mechanosensory behaviour of the sea urchin sperm is regulated by organized functioning of the membrane environment including the plasma membrane proteins and flagellasialin.
2011 by Japan Society for Cell Biology