Practice question

Uncapacitated sea urchin sperm stored within gonads maintains quiescent low-motility state due to relatively acidic intracellular pH around 7.2 and suppressed metabolism. Upon spawning into normal seawater pH approximately 8.0, Na+/H+ exchanger sNHE encoded by SLC9C1 extrudes protons raising internal pH to about 7.6, directly stimulating dynein ATPase activity, adenylate cyclase and flagellar beating. Intracellular pH elevation, potentiated further by resact-induced transient K+ efflux and hyperpolarization that activates sNHE, unlocks flagellar wave propagation. Artificially holding internal pH acidic even with abundant ATP prevents motility. Therefore increased internal pH initiates sperm motility and primes chemotaxis.