Abstract

cDNAs encoding three splice variants of the P2X₂ receptor were isolated from rat cerebellum. The first variant has a serine/proline-rich segment deleted from the intracellularly located carboxyl-terminal domain of the P2X₂ subunit. The second and third variants have the splice site in the second half of the predicted first transmembrane domain. Either a 12-amino acid insertion or a six-amino acid deletion occurs at this position. cRNAs for these isoforms of the P2X₂ subunit were injected intoXenopus laevis oocytes and tested for function. ATP evoked inward currents only with the splice variant [designated P2X_2(b)] having the 69-amino acid deletion. The potencies of various agonists at the homomeric P2X_2(b) receptor were not significantly different from those at the P2X_2(a)homomeric channel. However, the P2X_2(b) receptor showed significantly lower antagonist sensitivity. In contrast to the nondesensitizing P2X_2(a) receptor, prolonged application of ATP produced a more rapid desensitization of the P2X_2(b)receptor. When the P2X_2(a) and P2X_2(b) receptor responses were recorded in transfected mammalian cells, this difference was again found. The change in desensitization may be determined by proline/serine-rich segments and/or phosphorylation motifs that are removed from the tail region in formation of the P2X_2(b)subunit. In situ hybridization of the three newly isolated isoforms of the P2X₂ subunit was performed at the macroscopic and cellular levels; transcripts for two of them [P2X_2(b) and p2x_2(c)] but not the third [p2x_2(d)], which carries the 12-amino acid addition, were present in many structures in the neonatal rat brain and on sensory and sympathetic ganglia. mRNA for the p2x_2(d) splice variant was present only in the nodose ganglion, at a low level.