Different triggers for calcium oscillations in mouse eggs involve a ryanodine-sensitive calcium store.
Relative intracellular free Ca2+ concentrations ([Ca2+]i) were monitored in mature unfertilized mouse eggs by measuring fluorescence of intracellular fluo3. A number of different agents were found to cause sustained repetitive transient [Ca2+]i oscillations. These were microinjection of a cytosolic sperm factor, sustained injection of Ins-(1,4,5)P1, or extracellular addition of the thiol reagent thimerosal. Stimulating G-protein activity by injection of guanosine 5'-[gamma-thio]triphosphate plus application of carbachol also caused [Ca2+]i oscillations, but less reliably than other stimuli. A role for Ca(2+)-induced Ca2+ release and a ryanodine-sensitive Ca2+ channel in mouse eggs was suggested by the finding that microinjection, or external addition, of ryanodine also caused [Ca2+]i increases. Furthermore, ryanodine, along with thimerosal, increased the sensitivity of eggs to Ca(2+)-induced [Ca2+]i oscillations. When ryanodine was added to eggs oscillating in response to the sperm factor, InsP3 or thimerosal, it caused a decrease in amplitude of oscillations and eventually a block of [Ca2+]i oscillations associated with a sustained elevation of [Ca2+]i. These data suggest that a ryanodine-sensitive Ca(2+)-release mechanism exists in mouse eggs and that a ryanodine-sensitive Ca2+ store plays a role in generating intracellular [Ca2+]i oscillations.
Swann
K
K
M.R.C. Experimental Embryology and Teratology Unit, St. George's Hospital Medical School, London, U.K.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008297:Male; D051379:Mice; D010063:Ovum / Q000502:physiology*; D010507:Periodicity; D012433:Ryanodine / Q000494:pharmacology; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000502:physiology*; D013849:Thimerosal / Q000494:pharmacology
D012433:Ryanodine; D013849:Thimerosal; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium