Increase in functional Ca2+ channels in cerebral smooth muscle with renal hypertension

Abstract

The hypothesis that availability of functional Ca2+ channels in vascular smooth muscle is augmented in hypertension was tested in basilar artery cells from Wistar rats exhibiting stable systolic blood pressure (BP(sys)) for 2 to 11 weeks after partial renal artery ligation (Goldblatt 2- kidney 1-clip [2K1C] model). Cells were freshly isolated and patch-clamped using a nystatin-perforated patch method. BP(sys) ranged from 110 to 280 mm Hg and correlated with normalized kidney mass. Macroscopic current-voltage curves were fit to a Boltzmann function to obtain maximum conductance (g(max)), steepness and midpoint potential for the voltage dependence of activation (k and E( 1/4 ), respectively), and extrapolated reversal potential for the chord conductance (E(rev)). Linear regression of normalized conductance (ng(max)=g(max)/cell capacitance) versus BP(sys) for 103 cells indicated a strong relationship, with a slope of 0.0019 nS · pF-1 · mm Hg-1 (P<0.0001). Similar analysis of data from 35 other cells exposed to 500 nmol/L Bay K 8644 gave a slope of 0.0041 nS · pF-1 · mm Hg-1 (P=0.001). Voltage-dependent parameters, k, E( 1/4 ), and E(rev), were not significantly related to BP(sys). Single-channel measurements in cell- attached patches revealed that the number of channels in 32 patches was significantly related to BP(sys) (P=0.0024) but that slope conductance, open dwell times at 0 mV, and distribution between 2 open states were not. Finally, in a subgroup of 61 cells from animals made hypertensive (180 mm Hg <200 mm Hg) for ≃1/2 to 6 weeks, we found that elevation of ng(max) depended on duration of hypertension (P=0.003), with no elevation at ≃1/2 week. We conclude that in the 2K1C model, availability of functional Ca2+ channels increases with BP(sys) with no change in channel properties and that measurable BP(sys) elevation occurs before the increase in functional channels.