Ins(1,4,5)P3 formation and fluctuating chloride current response induced by external ATP in Xenopus oocytes injected with embryonic guinea pig brain mRNA

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Abstract
In voltage‐clamped Xenopus oocytes injected with embryonic guinea pig mRNA, effective concentrations of extracellular ATP elicited an inward fluctuating current. This current, carried by Cl‐ions, was mainly dependent upon liberation of Ca2+ ions from stores as demonstrated by experiments using intracellular EGTA loading and TMB‐8 superfusion. Neomycin inhibited these fluctuating currents indicating that the transplanted purinoceptor is linked to phospholipase C activity and triggers Ins(1,4,5)P3 formation. Ins(1,4,5)P3 production evoked by external ATP was clearly demonstrated by directly measuring the water‐soluble Ins(1,4,5)P3 level in injected oocytes. Finally, it is suggested that the ATP effect was mediated by a Ca2+ release from Ins(1,4,5)P3 sensitive pools since heparin blocked the ATP responsiveness. The acquired purinoceptor may be made apparent to a P2 subtype since ATP and ADP were equipotent in eliciting Cl− current while AMP and Adenosine were ineffective in injected oocytes.