Ca 2+ Influx is Increased in 2-Kidney, 1-Clip Hypertensive Rat Aorta

Abstract

Abstract — — Arteries from hypertensive rats show a greater contraction in response to Ca 2+ channel activator and an increased sensitivity to Ca 2+ entry blockers compared with those of normotensive rats. These facts suggest an altered Ca 2+ influx through membrane channels. In this study, this hypothesis was tested by direct activation of voltage-gated Ca 2+ channels using Bay K 8644, a dihydropyridine sensitive large conductance (L-type) Ca 2+ channel opener in aortas from 2-kidney, 1-clip (2K1C) hypertensive rats. Because the membrane potential of smooth muscle cells is an important regulator of the conformational state of L-type Ca 2+ channels and, consequently, dihydropyridine affinity, the effect of 10 mmol/L KCl on the responses to Bay K 8644 was also studied. Maximal contraction (ME) and sensitivity to Bay K 8644 were greater 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 KCl concentration was increased from 4.7 to 10 mmol/L in the bathing medium, no differences were observed in the contractile effect of Bay 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 of 2K1C aorta vascular smooth muscle cells were less negative than in 2K (−35.19±4.91 versus −48.32±1.88 mV). Basal intracellular Ca 2+ concentration ([Ca 2+ ] i ) was greater in cultured vascular smooth muscle cells from 2K1C than from 2K (293.4±25.83 versus 205.40±12.83 nmol/L). In 2K1C, Bay K 8644 induced a larger increase in [Ca 2+ ] i than in 2K (190.60±45.65 versus 92.57±14.67 nmol/L), and in 10 mmol/L KCl, 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 to Bay K 8644 in 2K1C aortas is due to an increased Ca 2+ influx through voltage-gated Ca 2+ channels.