Role of cytosolic Ca2+ in inhibition of InsP3-evoked Ca2+ release in Xenopus oocytes.
1. Calcium liberation induced in Xenopus oocytes by flash photorelease of inositol 1,4,5-trisphosphate (InsP3) from a caged precursor was monitored by confocal microfluorimetry. The object was to determine whether inhibition of Ca2+ release seen with paired flashes arose as a direct consequence of elevated cytosolic free [Ca2+]. 2. Responses evoked by just-suprathreshold test flashes were not inhibited by subthreshold conditioning flashes, but were strongly suppressed when conditioning flashes were raised above threshold. 3. Inhibition at first increased progressively as the inter-flash interval was lengthened to about 2 s and thereafter declined, with a half-recovery at about 4 s. 4. Intracellular injections of Ca2+ caused relatively slight inhibition of InsP3-evoked signals, even when cytosolic free [Ca2+] was elevated to levels similar to those at which strong inhibition was seen in paired-flash experiments. 5. Recovery from inhibition was not appreciably slowed when Ca2+ was injected to raise the free Ca2+ level between paired flashes. 6. We conclude that inhibition of InsP3-evoked Ca2+ liberation is not directly proportional to cytosolic free Ca2+ level and that recovery from inhibition in paired-pulse experiments involves factors other than the decline of cytosolic [Ca2+] following a conditioning response.
Ilyin
V
V
Department of Psychobiology, University of California, Irvine 92717.
Parker
I
I
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D009865:Oocytes / Q000378:metabolism*; D010775:Photic Stimulation; D013997:Time Factors; D014982:Xenopus laevis
D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium