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.
Simard
J M
JM
Department of Neurosurgery, University of Maryland School of Medicine, Baltimore 21201, USA. msimard@surgery1.ab.umd.edu
Li
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Tewari
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D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001488:Basilar Artery / Q000187:drug effects / Q000503:physiopathology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D006978:Hypertension, Renovascular / Q000503:physiopathology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000503:physiopathology*; D051381:Rats
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester