Identification of a site that modifies desensitization of P2X2 receptors

The time course of desensitization of P2X(2) receptors expressed in Xenopus oocytes and HEK 293 cells was examined. We found that there was virtually no desensitization in response to 5 mu M ATP, but that responses to 50 mu M ATP desensitized with a highly variable time course. The time constant of desensitization varied 250fold among oocytes (from 4 to over 1000 seconds) and 10 fold among HEK cells (from 4 to 40 seconds). Mutation of D349, which lies at the cytoplasmic end of the second transmembrane domain (to either A, N, or R), resulted in a dramatic acceleration of the median rate of desensitization, and eliminated variation in the rate of desensitization. In contrast, mutation of four other charged residues in putative transmembrane domains had no effect on desensitization. These results suggest that P2X(2) receptor desensitization is strongly modulated by the intracellular environment, and that D349 is essential for this modulation. (C) 1998 Academic Press.