Sperm increase inositol 1,4,5-trisphosphate mass in Xenopus laevis eggs preinjected with calcium buffers or heparin.
Although it is known that all fertilization events are due to elevated intracellular calcium ([Ca2+]i), it is not known how sperm induce an increase in zygote [Ca2+]i. We report that sperm can increase inositol 1,4,5-trisphosphate in Xenopus laevis eggs that have been preinjected with calcium buffers to prevent the increase in [Ca2+]i (both the initial increase and the subsequent wave) after fertilization. After buffering [Ca2+]i to levels well below basal, IP3 production was not blocked, whereas IP3 metabolism may be inhibited. Also, heparin (an inhibitor of inositol 1,4,5-trisphosphate action and the fertilization response) does not prevent a normal increase in IP3 after fertilization. Conditions that produce various levels of polyspermy are associated with IP3 increases similar to those noted after monospermic fertilization. These data suggest a specific order of fertilization events: sperm utilize an initial production of inositol 1,4,5-trisphosphate to produce the [Ca2+]i increase at fertilization.
Stith
B J
BJ
Biology Department, University of Colorado at Denver 80217-3364.
Espinoza
R
R
Roberts
D
D
Smart
T
T
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005306:Fertilization; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008297:Male; D010063:Ovum / Q000187:drug effects / Q000378:metabolism*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000502:physiology*; D014982:Xenopus laevis
D002021:Buffers; D002614:Chelating Agents; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium