Expression of Inwardly Rectifying Potassium Channels in Descending Vasa Recta Endothelial Cells

Abstract

Descending vasa recta (DVR) are 12–15-μm vessels that supply blood flow to the renal medulla. The whole cell patch-clamp method was used to investigate inward rectifier potassium channel (KIR) activity in DVR endothelia. The endothelial monolayer was accessed by removing abluminal pericytes from collagenase digested vessels. KIR currents were recorded in symmetrical 140 mM external K+ solution that served to both maximize KIR currents and eliminate prolonged capacitance transients by closing gap junctions. Large, Ba2+ sensitive, inwardly rectifying currents were observed at membrane potentials less than the K+equilibrium potential. Ba2+ potently inhibited KIR currents in a voltage dependent manner, with affinity, Kd = 0.18, 0.33, 0.60, 1.20 μmol/L at −160, −120, −80 and −40mV, respectively. Extracellular Cs+ also blocked the KIR currents with Kd = 15, 33, 246 and 2266 μmol/L at −160, −120, −80 and −40mV, respectively. In the presence of 1 mM ouabain, elevation of extracellular K+ from 5 to 10 mmol/L hyperpolarized membrane potential by 15 mV, which was reversed by Ba2+ (30 μmol/L). Immunochemical staining verified that DVR expressKIR2.1, KIR2.2 and KIR2.3 isoforms in both the pericytes and endothelium. We conclude that KIR are expressed in DVR endothelial cells and that extracellular K+ can mediate hyperpolarization through their activity. This work was supported by American Heart Association Grant # 0625404U.