Descending vasa recta endothelia express inward rectifier potassium channels

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 (Kin) exist in the endothelia, affect membrane potential, and modulate intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.cyt]). The endothelium was accessed for electrophysiology by removing abluminal pericytes from collagenase-digested vessels. [K.sub.IR] currents were recorded using symmetrical 140 mM [K.sup.+] 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.sup.+]. [Ba.sup.2+] potently inhibited those currents in a voltage- dependent manner, with affinity k = 0.18, 0.33, 0.60, and 1.20 [micro]M at -160, -120, -80, and -40 mV, respectively. [Cs.sup.+] also blocked those currents with k = 20, 48, 253, and 1,856 [micro]M at -160, -120, -80, and -40 mV, respectively. In the presence of 1 mM ouabain, increasing extracellular [K.sup.+] concentration from 5 to 10 mM hyperpolarized endothelial membrane potential by 15 mV and raised endothelial [[[Ca.sup.2+]].sub.cyt]. Both the [K.sup.+]-induced membrane hyperpolarization and the [[[Ca.sup.2+]].sub.cyt] elevation were reversed by [Ba.sup.2+]. Immunochemical staining verified that both pericytes and endothelial cells of DVR express [K.sub.IR]2.1, [K.sub.IR]2.2, and [K.sub.IR]2.3 subunits. We conclude that strong, inwardly rectifying [K.sub.IR]2.x isoforms are expressed in DVR and mediate [K.sup.+]-induced hyperpolarization of the endothelium. kidney; medulla; microcirculation; electrophysiology; potassium channel; endothelium