Asterosap, an Egg Jelly Peptide, Elevate Intracellular Ca²⁺ and Activate the Motility of Spermatozoa

Abstract

Components from the outer envelopes of the egg that influence the flagellar beating and acrosome reaction of spermatozoa are regulated by ion flux across the plasma membrane. Asterosap, a sperm-activating peptide from the starfish egg jelly layer, causes a transient increase in intracellular cyclic GMP (cGMP) through the activation of the asterosap receptor, a guanylyl cyclase (GC), and causes an increase in intracellular Ca²⁺. Here we describe the pathway of asterosap-induced Ca²⁺ elevation using different Ca²⁺ channel antagonists. Fluo-4 AM, a cell permeable Ca²⁺ sensitive dye was used to determine the channel caused by the asterosap-induced Ca²⁺ elevation in spermatozoa. Different L-type Ca²⁺ channel antagonists, a non specific Ca²⁺ channel antagonist (nickel chloride), and a store-operated Ca²⁺ channel (SOC) antagonist do not show any significant response on asterosap-induced Ca²⁺ elevation, whereas KB-R7943, a selective inhibitor against Na⁺/Ca²⁺ exchanger (NCX) inhibited effectively. We also analyzed the flagellar movement of spermatozoa in artificial seawater (ASW) containing the asterosap at 100 nM ml^?1. We found that spermatozoa swam vigorously with more symmetrical flagellar movement in asterosap than in ASW and KB-R7943 significantly inhibited the flagellar movement.

DOI: http://dx.doi.org/10.3329/pa.v19i1.17358

Progress. Agric. 19(1): 79 - 88, 2008