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 Caz+ 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(l,4,5)P, formation. Ins(l,4,5)P, production evoked by external ATP was clearly demonstrated by directly measuring the water-soluble Ins(l,4,5)P, level in injected oocytes. Finally, it is suggested that the ATP effect was mediated by a Ca*+ release from Ins(l,4,5)P, 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.

Characterization of a P2Y Purinoceptor in the Brain

“…While the function and pharmacology of the PZx type of the purinoceptors are well documented at some sites in the central and peripheral nervous systems (Edwards & Gibb 1993), there is only indirect evidence for the presence of Pz purinoceptors of the G-protein coupled receptor type in the central nervous system, from responses after brain total mRNA is injected in the oocyte or from the pharmacology of astrocytes (Fournier et al 1990;Bruner & Murphy 1990). The subtypes, amount and distribution of brain P2 purinoceptors are unknown.…”

Characterization of [35S]‐ATPαS and [3H]‐α,β‐MeATP binding sites in rat brain cortical synaptosomes: regulation of ligand binding by divalent cations

“…Evidence for the occurrence of G protein‐coupled P 2 ‐purinoceptors in brain has been obtained from expression experiments by injection of total brain mRNA into Xenopus oocytes or from the pharmacological studies of nucleotide effects in astrocytes (Fournier et al , 1990; Bruner & Murphy, 1990). In addition, P 2 ‐purinoceptors induce nitric oxide‐dependent cyclic GMP production in the neuronal cell line NG 108–15 (Reiser, 1995) or evoke Ca 2+ ‐oscillations associated with Ca 2+ ‐influx in rat glioma cells (Czubayko & Reiser, 1996a,b).…”