Alteration of intracellular [Ca2+] in sea urchin sperm by the egg peptide speract. Evidence that increased intracellular Ca2+ is coupled to Na+ entry and increased intracellular pH.
The egg peptide speract increases intracellular pH (pHi) and cyclic nucleotides in sperm of the sea urchin Strongylocentrotus purpuratus by a mechanism dependent on seawater Na+ but not Ca2+ (Hansbrough, J. R., and Garbers, D. L. (1981) J. Biol. Chem. 256, 2235-2241; Repaske, D. R., and Garbers, D. L. (1983) J. Biol. Chem. 258, 6025-6029). Using the Ca2+ indicators quin2 and indo-1, we show that speract stimulates a transient rise in intracellular [Ca2+] ([a2+]i) when millimolar Ca2+ is present in seawater. The rise is increased and extended by the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), which also enhances 22Na+ uptake with or without Ca2+. Without MIX, speract initiates a rise in [Ca2+]i that peaks within approximately 5 s and decreases with a t1/2 of approximately 9 s. Activation of Na+:H+ exchange without speract by either Na+ addition to sperm in Na+-free seawater (NaFASW) or by monensin also increases [Ca2+]i, but neither change is transient. Inhibition of Na+:H+ exchange by increased seawater [K+] prevents the rise in [Ca2+]i initiated by either speract or Na+ addition to sperm in NaFASW. Increasing pHi by adding 10 mM NH4+ or by addition of Li+ to sperm in NaFASW does not increase [Ca2+]i. The data suggest that speract binding leads to rapid activation of Na+:H+ exchange; and, as a consequence, [Ca2+] entry increases transiently through either Na+:Ca2+ exchange or else through a verapamil-insensitive Ca2+ channel. MIX prevents the inactivation of this entry mechanism.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009550:Nigericin / Q000494:pharmacology; D009842:Oligopeptides / Q000502:physiology*; D010063:Ovum / Q000502:physiology*; D012617:Sea Urchins; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*
D002352:Carrier Proteins; D009842:Oligopeptides; D017923:Sodium-Hydrogen Exchangers; C028364:speract; D012964:Sodium; D009550:Nigericin; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine