Guanosine 5'-thiotriphosphate may stimulate phosphoinositide messenger production in sea urchin eggs by a different route than the fertilizing sperm.
We show that microinjecting guanosine-5'-thiotriphosphate (GTP gamma S) into unfertilized sea urchin eggs generates an intracellular free calcium concentration [( Ca]i) transient apparently identical in magnitude and duration to the calcium transient that activates the egg at fertilization. The GTP gamma S-induced transient is blocked by prior microinjection of the inositol trisphosphate (InsP3) antagonist heparin. GTP gamma S injection also causes stimulation of the egg's Na+/H+ antiporter via protein kinase C, even in the absence of a [Ca]i increase. These data suggest that GTP gamma S acts by stimulating the calcium-independent production of the phosphoinositide messengers InsP3 and diacylglycerol (DAG). However, the fertilization [Ca]i transient is not affected by heparin, nor can the sperm cause calcium-independent stimulation of protein kinase C. It seems that the bulk of InsP3 and DAG production at fertilization is triggered by the [Ca]i transient, not by the sperm itself. GDP beta S, a G-protein antagonist, does not affect the fertilization [Ca]i transient. Our findings do not support the idea that signal transduction at fertilization operates via a G-protein linked directly to a plasma membrane sperm receptor.
Crossley
I
I
Department of Physiology, University College London, United Kingdom.
Whalley
T
T
Whitaker
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D004075:Diglycerides / Q000096:biosynthesis; D005260:Female; D005306:Fertilization / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D006493:Heparin / Q000494:pharmacology; D008297:Male; D010063:Ovum / Q000187:drug effects* / Q000378:metabolism; D010716:Phosphatidylinositols / Q000494:pharmacology*; D012617:Sea Urchins; D015398:Signal Transduction / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D004075:Diglycerides; D010716:Phosphatidylinositols; D017923:Sodium-Hydrogen Exchangers; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006493:Heparin; D019204:GTP-Binding Proteins; D002118:Calcium