Increase in Functional Ca 2+ Channels in Cerebral Smooth Muscle With Renal Hypertension

Abstract

Abstract —The hypothesis that availability of functional Ca 2+ 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 1/2 , 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 1/2 , 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<BP sys <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 Ca 2+ channels increases with BP sys with no change in channel properties and that measurable BP sys elevation occurs before the increase in functional channels.