ATP-evoked Ca2+ transients and currents in murine thymocytes:: possible role for P2X receptors in death by neglect

The P2X family of ATP receptors (P2XR) have been implicated in thymocyte death in vitro and in vivo. We characterized ATP-evoked Ca2+ transients and membrane currents in thymocytes to better understand the role of P2XR during thymocyte development. ATP(4-), but not UTP or GTP, activated a sustained non-selective cation current in voltage-clamped CD4(-) CD8(-) and CD4(+)CD8(+) thymocytes that was reversed by apyrase, which hydrolyzes ATP, and by the P2XR antagonists suramin and pyridoxalphosphate-6-amophsnyl-2',4'-disulfonic acid (PPADS). The more selective P2XR agonist alpha beta-methylene ATP activated a smaller rapidly decaying current in both thymocyte populations. Reverse transcription-PCR results indicate that P2X1, P2X2, P2X6, and/or P2X7 are expressed in thymocytes. Finally, we used PPADS to examine the role of P2XR during thymocyte development in situ. PPADS-treated thymi yielded significantly more thymocytes (38 %), due to a selective increase in CD4(+)CD8(+) cells. Together these data suggest that one or more PPADS-sensitive P2XR (P2X1, P2X2, P2X7) are involved in thymocyte apoptosis, and we propose more specifically a role associated with death by neglect.