Descending vasa recta pericytes express voltage operated Na⁺ conductance in the rat

Abstract

We studied the properties of a voltage-operated Na⁺ conductance in descending vasa recta (DVR) pericytes isolated from the renal outer medulla. Whole-cell patch-clamp recordings revealed a depolarization-induced, rapidly activating and rapidly inactivating inward current that was abolished by removal of Na⁺ but not Ca⁺ from the extracellular buffer. The Na⁺ current (I_Na) is highly sensitive to tetrodotoxin (TTX, K_d= 2.2 nm). At high concentrations, mibefradil (10 μm) and Ni⁺ (1 mm) blocked I_Na. I_Na was insensitive to nifedipine (10 μm). The L-type Ca⁺ channel activator FPL-64176 induced a slowly activating/inactivating inward current that was abolished by nifedipine. Depolarization to membrane potentials between 0 and 30 mV induced inactivation with a time constant of ∼1 ms. Repolarization to membrane potentials between −90 and −120 mV induced recovery from inactivation with a time constant of ∼11 ms. Half-maximal activation and inactivation occurred at −23.9 and −66.1 mV, respectively, with slope factors of 4.8 and 9.5 mV, respectively. The Na⁺ channel activator, veratridine (100 μm), reduced peak inward I_Na and prevented inactivation. We conclude that a TTX-sensitive voltage-operated Na⁺ conductance, with properties similar to that in other smooth muscle cells, is expressed by DVR pericytes.