Inositol trisphosphate may access calcium from stores not coupled to muscarinic receptors in Xenopus oocytes

Gabriella Goldberg, Hagit Shapira, Yoram Oron*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Oocytes of a large fraction of Xenopus females exhibit a complex response to acetylcholine (ACh) consisting of rapid, transient and prolonged, slow chloride currents. Frequent consecutive challenges or a single prolonged challenge with ACh result in a marked decrease in response amplitudes, i. e. refractoriness. In ACh-refractory oocytes, the response to injected inositol 1,4,5,-trisphosphate (Ins P3,), the intracellular mediator of the ACh response, is not affected. Similarly, Ins P3-evoked responses were obtained in oocytes that lacked muscarinic response or that lost their responsiveness as a result of progesterone-induced maturation. To investigate the mechanism of this phenomenon, we have depleted intracellular calcium stores by repeated challenges with ACh in calcium-free medium. Disappearance of the ACh response through depletion of the ACh-coupled calcium store did not prevent a subsequent response to Ins P3. These results imply that Ins P3 can mobilize calcium from other stores, not depleted by previous exposure to ACh. This finding is further reinforced by our results that demonstrate that ACh causes 45Ca efflux in responsive oocytes, while Ins P3 in supramaximal concentrations does not induce 45Ca efflux. Indeed, Ins P3 can induce 45Ca efflux only when more than 2 pmol/oocyte is injected. This is also the concentration of Ins P3 that desensitizes the Ins P3 response. These data suggest that Ins P3 also releases cellular calcium from stores different from those mobilized by ACh.

Original languageEnglish
Pages (from-to)313-318
Number of pages6
JournalPflugers Archiv European Journal of Physiology
Issue number3-4
StatePublished - Mar 1992


  • Calcium stores
  • Inositol 1,4,5-trisphosphate
  • Muscarinic responses
  • Xenopus oocytes


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