Voltage-gated divalent currents in descending vasa recta pericytes

Abstract

Multiple voltage-gated Ca2+channel (CaV) subtypes have been reported to participate in control of the juxtamedullary glomerular arterioles of the kidney. Using the patch-clamp technique, we examined whole cell CaVcurrents of pericytes that contract descending vasa recta (DVR). The dihydropyridine CaVagonist FPL64176 (FPL) stimulated inward Ca2+and Ba2+currents that activated with threshold depolarizations to −40 mV and maximized between −20 and −10 mV. These currents were blocked by nifedipine (1 μM) and Ni2+(100 and 1,000 μM), exhibited slow inactivation, and conducted Ba2+> Ca2+at a ratio of 2.3:1, consistent with “long-lasting” L-type CaV. In FPL, with 1 mM Ca2+as charge carrier, Boltzmann fits yielded half-maximal activation potential ( V1/2) and slope factors of −57.9 mV and 11.0 for inactivation and −33.3 mV and 4.4 for activation. In the absence of FPL stimulation, higher concentrations of divalent charge carriers were needed to measure basal currents. In 10 mM Ba2+, pericyte CaVcurrents activated with threshold depolarizations to −30 mV, were blocked by nifedipine, exhibited voltage-dependent block by diltiazem (10 μM), and conducted Ba2+> Ca2+at a ratio of ∼2:1. In Ca2+, Boltzmann fits to the data yielded V1/2and slope factors of −39.6 mV and 10.0 for inactivation and 2.8 mV and 7.7 for activation. In Ba2+, V1/2and slope factors were −29.2 mV and 9.2 for inactivation and −5.6 mV and 6.1 for activation. Neither calciseptine (10 nM), mibefradil (1 μM), nor ω-agatoxin IVA (20 and 100 nM) blocked basal Ba2+currents. Calciseptine (10 nM) and mibefradil (1 μM) also failed to reverse ANG II-induced DVR vasoconstriction, although raising mibefradil concentration to 10 μM was partially effective. We conclude that DVR pericytes predominantly express voltage-gated divalent currents that are carried by L-type channels.