Genetic hypertension results from numerous phenotypic expressions. We
hypothesized that increased calcium current in vascular smooth muscle
of genetically hypertensive animals is partly responsible for observed
increases in agonist sensitivity, contractility, and calcium influx.
Using adult, spontaneously hypertensive stroke-prone rats (SHRSP) and
normotensive Wistar-Kyoto (WKY) controls from an inbred colony, we cha
racterized calcium current in smooth muscle cells isolated from cerebr
al arteries. Calcium current in WKY cells reached a maximum of -27.7+/
-2.7 pA (n=32) at +20 mV. Peak inward current at +20 mV in SHRSP cells
had a mean amplitude of -44.4+/-3.0 pA (n=72, P<.05). SHRSP cells exh
ibited a higher calcium current density. Maximal inward current normal
ized to cell capacitance yielded mean values of 2.07+/-0.11 pA/pF for
WKY (n=32) and 2.80+/-0.12 pA/pF (n=79) for SHRSP (P<.05) cells. Trans
ient-type Ca2+ channel current had the same magnitude and current-volt
age relation in both cell types, giving an L-type/T-type ratio of 3.85
for WKY and 6.25 for SHRSP cells. The voltage-dependent inactivation
curve for SHRSP calcium current was shifted to the right only over the
range of -50 to -30 mV, but the half-maximal inactivation voltages an
d Boltzmann coefficients were not significantly different between cell
types. Increased calcium inward current in this model of genetic hype
rtension could account in part for altered calcium homeostasis and inc
reased vascular reactivity, contributing to hypertension and vasospasm
.