Effect on sperm-induced activation current and increase of cytosolic Ca2+ by agents that modify the mobilization of [Ca2+]i. I. Heparin and pentosan polysulfate.
The mechanism of the elevation of intracellular free Ca2+ ([Ca2+]i) induced by a single sperm in eggs of the sea urchin Lytechinus variegatus was investigated. Simultaneous measurements of [Ca2+]i, and of the activation current, were carried out on eggs microinjected with Ca Green-1 or Ca Green dextran, and voltage clamped at -20 mV. The microinjection of 0.5 to 1.0 mg/ml heparin (MW 6000) or pentosan polysulfate (MW 3000), final intracellular concentration, causes a concentration-dependent inhibition in all parameters of the sperm-induced elevation of [Ca2+]i and the phase 2 calcium-activated cation current (Ip). For each: (1) the onset is delayed; (2) the rate of change is slowed; and (3) the peak amplitude attained is diminished. In some experiments at the higher concentrations, the microinjected polysulfates cause the complete suppression of the sperm-induced elevation of [Ca2+]i and Ip. The entry of multiple sperm overcomes the inhibitory effects of the polysulfates. Our data suggest that inositol 1,4,5-trisphosphate is the primary mechanism responsible for the sperm-induced release of Ca2+ from intracellular stores.
Mohri
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Department of Physiology and Biophysics, University of Miami School of Medicine, Florida 33101, USA.
Ivonnet
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PI
Chambers
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005260:Female; D005456:Fluorescent Dyes; D006493:Heparin / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D008839:Microelectrodes; D010063:Ovum / Q000187:drug effects / Q000502:physiology*; D010426:Pentosan Sulfuric Polyester / Q000494:pharmacology*; D012617:Sea Urchins; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000502:physiology*
D002614:Chelating Agents; D005456:Fluorescent Dyes; D010426:Pentosan Sulfuric Polyester; D004533:Egtazic Acid; D006493:Heparin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium