Contributions of the C-terminal domain to the control of P2X receptor desensitization

The P2X purinergic receptor channels (P2XRs) differ among themselves with r espect to the rates of desensitization during prolonged agonist stimulation . Here we studied the desensitization of recombinant channels by monitoring the changes in intracellular free Ca2+ concentration in cells stimulated w ith ATP, the native and common agonist for all P2XRs. The focus in our inve stigations was on the relevance of the P2XR C terminus in controlling recep tor desensitization. When expressed in GT1 cells, the P2XRs desensitized wi th rates characteristic to each receptor subtype: P2X(1)R = P2X(3)R > P2X(2 b)R > P2X(4)R > P2X(2a)R > P2X(7)R. A slow desensitizing pattern of P2X(2a) R was mimicked partially by P2X(3)R and fully by P2X(4)R when the six-amino acid sequences of these channels located in the cytoplasmic C terminus wer e substituted with the corresponding arginine 371 to proline 376 sequence o f P2X(2a)R. Changing the total net charge in the six amino acids of P2X(4)R to a more positive direction also slowed the receptor desensitization. On the other hand, substitution of arginine 371-proline 376 sequence of P2X(2a )R with the corresponding sequences of P2X(1)R, P2X(3)R, and P2X(4)R increa sed the rate of receptor desensitization. Furthermore, heterologous polymer ization of wild-type P2X(2a)R and mutant P2X(3)R having the C-terminal six amino acids of P2X(2a)R at its analogous position resulted in a functional channel whose desensitization was significantly delayed. These results sugg est that composition of the C-terminal six-amino acid sequence and its elec trostatic force influence the rate of receptor desensitization.