Calcium permeability and block at homomeric and heteromeric P2X2 and P2X3 receptors, and P2X receptors in rat nodose neurones.
1. Whole-cell recordings were made from HEK 293 (human embryonic kidney) cells stably transfected with cDNAs encoding P2X2, P2X3 or both receptors (P2X2/3) and from cultured rat nodose neurones. Nodose neurones all showed immunoreactivity for both P2X2 and P2X3, but not P2X1, receptors. 2. Reversal potentials were measured in extracellular sodium, N-methyl-D-glucamine (NMDG) and NMDG containing 5 mM Ca2+; the values were used to compute relative permeabilities (PNMDG/PNa and PCa/PNa). PNMDG/PNa was not different for P2X2, P2X2/3 and nodose neurones (0.03) but was significantly higher (0.07) for P2X3 receptors. PCa/PNa was not different among P2X3, P2X2/3 and nodose neurones (1.2-1.5) but was significantly higher (2.5) for P2X2 receptors. 3. External Ca2+ inhibited purinoceptor currents with half-maximal concentrations of 5 mM at the P2X2 receptor, 89 mM at the P2X3 receptor and 15 mM at both the P2X2/3 heteromeric receptor and nodose neurones. In each case, the inhibition was voltage independent and was overcome by increasing concentrations of agonist. 4. These results may indicate that Ca2+ permeability of the heteromeric (P2X2/3) channel is dominated by that of the P2X3 subunit, while Ca2+ block of the receptor involves both P2X2 and P2X3 subunits. The correspondence in properties between P2X2/3 receptors and nodose ganglion neurones further supports the conclusion that the native alpha,beta-methylene ATP-sensitive receptor is a P2X2/3 heteromultimer.
Virginio
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Geneva Biomedical Research Institute, Glaxo Wellcome Research and Development, 14 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland. cv49987@ggr.co.uk
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D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D004553:Electric Conductivity; D006801:Humans; D009474:Neurons / Q000378:metabolism*; D009620:Nodose Ganglion / Q000166:cytology / Q000378:metabolism*; D010539:Permeability; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism* / Q000502:physiology
D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D002118:Calcium