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1 Division of Nephrology, Department of Medicine
2 Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201-1595, USA
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 (INa) is highly sensitive to tetrodotoxin (TTX, Kd= 2.2 nM). At high concentrations, mibefradil (10 µM) and Ni+ (1 mM) blocked INa. INa 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 INa 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.
(Received 26 May 2005;
accepted after revision 16 June 2005;
first published online 23 June 2005)
Corresponding author T. L. Pallone: Division of Nephrology, N3W143, 22 S. Greene St, University of Maryland School of Medicine, Baltimore, MD 21201, USA. Email: tpallone{at}medicine.umaryland.edu
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