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Am J Physiol Cell Physiol 275: C1342-C1348, 1998;
0363-6143/98 $5.00
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Vol. 275, Issue 5, C1342-C1348, November 1998

Analysis of a Ca2+-activated K+ channel that mediates hyperpolarization via the thrombin receptor pathway

Richard Sullivan, Suneil K. Koliwad, and Diana L. Kunze

Research Service, Houston Veterans Affairs Medical Center, and Departments of Medicine and of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030

Dami human leukemia cells express G protein-coupled thrombin receptors that operate through the phospholipase C pathway. When these receptors are activated by alpha -thrombin or by thrombin receptor-activating peptide, an elevation in cytosolic Ca2+ concentration develops that is accompanied by hyperpolarization of the plasma membrane. This transitory phase of hyperpolarization is primarily mediated by inwardly rectifying, Ca2+-activated K+ channels that have an inward conductance of ~24 pS. In cell-attached patches the channels open within seconds after superfusion of the cell with thrombin receptor-activating peptide. In inside-out patches, perfusion of submicromolar Ca2+ onto the cytosolic surface of the membrane is sufficient to activate the channels. In outside-out patches, channel opening can be blocked by nanomolar concentrations of charybdotoxin. The function of these intermediate-sized inwardly rectifying, Ca2+-activated K+ channels has not been established; however, by analogy with other cell systems, they may serve to regulate cell volume during cellular activation or to increase the electromotive drive that sustains Na+ and/or Ca2+ influx through ligand-gated cation channels.

platelet; megakaryocyte; hematopoietic cell; blood cell


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