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Descending vasa recta endothelia express inward rectifier potassium channels

¹Division of Nephrology, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland; and ²Department of Chemical and Biological Engineering, Tufts University, Medford, Massachusetts

Submitted 18 June 2007 ; accepted in final form 25 July 2007

Descending vasa recta (DVR) are capillary-sized microvessels that supply blood flow to the renal medulla. They are composed of contractile pericytes and endothelial cells. In this study, we used the whole cell patch-clamp method to determine whether inward rectifier potassium channels (K_IR) exist in the endothelia, affect membrane potential, and modulate intracellular Ca²⁺ concentration ([Ca²⁺]_cyt). The endothelium was accessed for electrophysiology by removing abluminal pericytes from collagenase-digested vessels. K_IR currents were recorded using symmetrical 140 mM K⁺ solutions that served to maximize currents and eliminate cell-to-cell coupling by closing gap junctions. Large, inwardly rectifying currents were observed at membrane potentials below the equilibrium potential for K⁺. Ba²⁺ potently inhibited those currents in a voltage-dependent manner, with affinity k = 0.18, 0.33, 0.60, and 1.20 µM at –160, –120, –80, and –40 mV, respectively. Cs⁺ also blocked those currents with k = 20, 48, 253, and 1,856 µM at –160, –120, –80, and –40 mV, respectively. In the presence of 1 mM ouabain, increasing extracellular K⁺ concentration from 5 to 10 mM hyperpolarized endothelial membrane potential by 15 mV and raised endothelial [Ca²⁺]_cyt. Both the K⁺-induced membrane hyperpolarization and the [Ca²⁺]_cyt elevation were reversed by Ba²⁺. Immunochemical staining verified that both pericytes and endothelial cells of DVR express K_IR2.1, K_IR2.2, and K_IR2.3 subunits. We conclude that strong, inwardly rectifying K_IR2.x isoforms are expressed in DVR and mediate K⁺-induced hyperpolarization of the endothelium.

kidney; medulla; microcirculation; electrophysiology; potassium channel; endothelium

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