Involvement of sodium in early phosphatidylserine exposure and phospholipid scrambling induced by P2X7 purinoceptor activation in thymocytes

Abstract

Extracellular ATP (ATPec), a possible effector in thymocyte selection, induces thymocyte death via purinoceptor activation. We show that ATPec induced cell death by apoptosis, rather than lysis, and early phosphatidylserine (PS) exposure and phospholipid scrambling in a limited thymocyte population (35-40%). PS externalization resulted from the activation of the cationic channel P2X7 (formerly P2Z) receptor and was triggered in all thymocyte subsets although to different proportions in each one. Phospholipid movement was dependent on ATPec-induced Ca2+ and/or Na+ influx. At physiological external Na+ concentration, without external Ca2+, PS was exposed in all ATP ec-responsive cells. In contrast, without external Na+, physiological external Ca2+ concentration promoted a submaximal response. Altogether these data show that Na+ influx plays a major role in the rapid PS exposure induced by P2X7 receptor activation in thymocytes.