Chloride channels are necessary for full platelet phosphatidylserine exposure and procoagulant activity

Abstract

Platelets enhance thrombin generation at sites of vascular injury by exposing phosphatidylserine during necrosis-like cell death. Anoctamin 6 (Ano6) is required for Ca2+-dependent phosphatidylserine exposure and is defective in patients with Scott syndrome, a rare bleeding disorder. Ano6 may also form Cl- channels, though the role of Cl- fluxes in platelet procoagulant activity has not been explored. We found that Cl - channel blockers or removal of extracellular Cl- inhibited agonist-induced phosphatidylserine exposure. However, this was not due to direct inhibition of Ca2+-dependent scrambling since Ca 2+ ionophore-induced phosphatidylserine exposure was normal. This implies that the role of Ano6 in Ca2+ -dependent PS exposure is likely to differ from any putative function of Ano6 as a Cl- channel. Instead, Cl- channel blockade inhibited agonistinduced Ca 2+ entry. Importantly, Cl- channel blockers also prevented agonist-induced membrane hyperpolarization, resulting in depolarization. We propose that Cl- entry through Cl- channels is required for this hyperpolarization, maintaining the driving force for Ca2+ entry and triggering full phosphatidylserine exposure. This demonstrates a novel role for Cl- channels in controlling platelet death and procoagulant activity. © 2013 Macmillan Publishers Limited All rights reserved.