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

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, Kd = 2.2 nM). At high concentrations, mibefradil (10 microM) and Ni+ (1 mM) blocked I(Na). I(Na) was insensitive to nifedipine (10 microM). 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 approximately 1 ms. Repolarization to membrane potentials between -90 and -120 mV induced recovery from inactivation with a time constant of approximately 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 microM), 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.