title: 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 Ca(2+)-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 Ca(2+)-dependent scrambling since Ca(2+) ionophore-induced phosphatidylserine exposure was normal. This implies that the role of Ano6 in Ca(2+-)dependent PS exposure is likely to differ from any putative function of Ano6 as a Cl(-) channel. Instead, Cl(-) channel blockade inhibited agonist-induced 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 Ca(2+) entry and triggering full phosphatidylserine exposure. This demonstrates a novel role for Cl(-) channels in controlling platelet death and procoagulant activity.
authors.affiliation: School of Physiology and Pharmacology, Bristol Heart Institute, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: M T
authors.initials: MT
authors.lastname: Harper
authors.affiliation: School of Physiology and Pharmacology, Bristol Heart Institute, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: A W
authors.initials: AW
authors.lastname: Poole
mesh_terms: D000075368:Anoctamins; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000494:pharmacology; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D009336:Necrosis / Q000139:chemically induced / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D010718:Phosphatidylserines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D013917:Thrombin / Q000494:pharmacology; D013927:Thrombosis / Q000378:metabolism*
chemical_list: C555078:ANO6 protein, human; D000075368:Anoctamins; D002352:Carrier Proteins; D018118:Chloride Channels; D010455:Peptides; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; C435908:collagen-related peptide; D013917:Thrombin; D002118:Calcium