Arteries from hypertensive rats show a greater contraction in response to C
a2+ channel activator and an increased sensitivity to Ca2+ entry blockers c
ompared with those of normotensive rats. These facts suggest an altered Ca2
+ influx through membrane channels. In this study, this hypothesis was test
ed by direct activation of voltage-gated Ca2+ channels using Bay K 8644, a
dihydropyridine sensitive large conductance (L-type) Ca2+ channel opener in
aortas from 2-kidney, 1-clip (2K1C) hypertensive rats. Because the membran
e potential or smooth muscle cells is an important regulator of the conform
ational state of L-type Ca2+ channels and, consequently, dihydropyridine af
finity, the effect of 10 mmol/L KC1 on the responses to Bay K 8644 was also
studied. Maximal contraction (ME) and sensitivity to Bay K 8644 were great
er in 2K1C rats than in 2K normotensive rats (ME, 1.77 +/-0.15 versus 1.25
+/-0.19 g; negative log molar value [pD(2)], 8.27 +/-0.07 versus 7.92 +/-0.
08). When the KC1 concentration was increased from 4.7 to 10 mmol/L in the
bathing medium, no differences were observed in the contractile effect of B
ay K 8644 between 2K1C and 2K (ME, 1.28 +/-0.13 versus 1.14 +/-0.21 g; pD(2
), 8.56 +/-0.08 versus 8.38 +/-0.07). The cell resting membrane potential o
f 2K1C aorta vascular smooth muscle cells were less negative than in 2K (-3
5.19 +/-4.91 versus -48.32 +/-1.88 mV). Basal intracellular Ca2+ concentrat
ion ([Ca2+](i)) Was greater in cultured vascular smooth muscle cells from 2
K1C than from 2K (293.4 +/- 25.83 versus 205.40 +/- 12.83 nmol/L). In 2K1C,
Bay K 8644 induced a larger increase in [Ca2+](1), than in 2K (190.60 +/-
45.65 versus 92.57 +/- 14.67 nmol/L), and in 10 mmol/L KC1, this difference
was abolished (134.90 +/- 45.12 versus 125.20 +/- 32.17 nmol/L). The main
conclusion of the present work is that the increased contractile response t
o Bay K 8644 in 2K1C aortas is due to an increased Ca2+ influx through volt
age-gated Ca2+ channels.