Altering the speract-induced ion permeability changes that generate flagellar Ca 2+ spikes regulates their kinetics and sea urchin sperm motility

Abstract

Speract, an egg-derived sperm-activating peptide, induces changes in intracellular Ca 2+, Na +, pH, cAMP, cGMP, and membrane potential in sperm of the sea urchin Strongylocentrotus purpuratus. Ca 2+ is a key regulator of motility in all sperm and, in many marine species, is required for generating turns interspersed with straighter swimming paths that are essential for chemotaxis towards the egg. We show that speract triggers a train of increases in flagellar Ca 2+, and that each individual Ca 2+ fluctuation induces a transient increase in flagellar asymmetry that leads to a turn. We also find that modifying the amplitude, duration and interval between individual Ca 2+ fluctuations by treating sperm with niflumic acid, an inhibitor of Ca 2+-activated Cl − channels, correspondingly alters the properties of the sperm turns. We conclude that Ca 2+ entry through a fast flagellar pathway not only induces sperm turns, but the kinetics of Ca 2+ entry may shape the nature of these turns, and that these kinetics are tuned by other channels, possibly including Cl − channels. In addition, the speract-induced changes in sperm motility closely resemble those seen during chemotaxis in other marine organisms, yet speract is not a chemoattractant. This implies the Ca 2+-induced motility changes are necessary but not sufficient for chemotaxis.