Increase in Functional Ca2+Channels in Cerebral Smooth Muscle With Renal Hypertension

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 (BPsys) 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. BPsys 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 (gmax), steepness and midpoint potential for the voltage dependence of activation (k and E1/2, respectively), and extrapolated reversal potential for the chord conductance (Erev). Linear regression of normalized conductance (ng(max)=g(max)/cell capacitance) versus BPsys for 103 cells indicated a strong relationship, with a slope of 0.0019 nS x pF(-1) x 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 x pF(-1) x mm Hg(-1) (P=0.001). Voltage-dependent parameters, k, E1/2, and Erev, were not significantly related to BPsys. Single-channel measurements in cell-attached patches revealed that the number of channels in 32 patches was significantly related to BPsys (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<BPsys<200 mm Hg) for approximately 1/2 to 6 weeks, we found that elevation of ngmax depended on duration of hypertension (P=0.003), with no elevation at approximately 1/2 week. We conclude that in the 2K1C model, availability of functional Ca2+ channels increases with BPsys with no change in channel properties and that measurable BPsys elevation occurs before the increase in functional channels.