1. ¹Department of Physiology, University of Tübingen, Germany
2. ²Institute of Pharmacy, University of Tübingen, Germany

Correspondence: F Lang, Physiologisches Institut der Universität Tübingen, Gmelinstr. 5, D-72076 Tübingen, Germany. Tel: +49 7071 29 72194; Fax: +49 7071 29 5618; E-mail: florian.lang@uni-tuebingen.de

Received 5 April 2004; Revised 15 November 2004; Accepted 23 November 2004; Published online 4 March 2005.

Abstract

Hyperosmotic shock, energy depletion, or removal of extracellular Cl^- activates Ca²⁺-permeable cation channels in erythrocyte membranes. Subsequent Ca²⁺ entry induces erythrocyte shrinkage and exposure of phosphatidylserine (PS) at the erythrocyte surface. PS-exposing cells are engulfed by macrophages. The present study explored the signalling involved. Hyperosmotic shock and Cl^- removal triggered the release of prostaglandin E₂ (PGE₂). In whole-cell recording, activation of the cation channels by Cl^- removal was abolished by the cyclooxygenase inhibitor diclophenac. In FACS analysis, phospholipase-A₂ inhibitors quinacrine and palmitoyltrifluoromethyl-ketone, and cyclooxygenase inhibitors acetylsalicylic acid and diclophenac, blunted the increase of PS exposure following Cl^- removal. PGE₂ (but not thromboxane) induced cation channel activation, increase in cytosolic Ca²⁺ concentration, cell shrinkage, PS exposure, calpain activation, and ankyrin-R degradation. The latter was attenuated by calpain inhibitors-I/II, while PGE₂-induced PS exposure was not. In conclusion, hyperosmotic shock or Cl^- removal stimulates erythrocyte PS exposure through PGE₂ formation and subsequent activation of Ca²⁺-permeable cation channels.