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

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.