Desensitization of P2X2 receptor/channel pore mutants

Properties of five mutants of P2X2 receptor/channel having amino acid residue-substitution at the pore region were examined by expressing the channels in Xenopus oocytes. When the concentration-response relationship for ATP-evoked current was obtained, the current amplitude was increased along with the concentrations of ATP for the wild type channel whereas the amplitude was rather decreased with highest concentrations for four of the five mutants as if an "inactivation-like" mechanism occurs to these mutants. Upon a long exposure (30 s) to ATP, time-dependent decay in the ATP-evoked current was observed for three of the five mutants, suggesting that desensitization occurs to these mutants. The time course of the desensitization was well fitted with a single exponential time whereas that of the recovery from the desensitization could be better fitted with multiple exponentials than with a single exponential. The relationship between the desensitization and the "inactivation-like" mechanism was discussed.