Calcium antagonists inhibit elevated potassium efflux from aorta of aldosterone-salt hypertensive rats.

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Abstract
The purpose of this study was to evaluate the effect of calcium antagonists on basal tension and the elevated 42K efflux in aorta from aldosterone-salt hypertensive rats. Diltiazem decreased the basal tension (2.0 +/- 0.4 g) as well as the phasic contractile activity and returned the elevated 42K efflux (0.018 +/- 0.002/min) toward control values (0.010 +/- 0.001/min, p less than 0.001). The diltiazem median inhibitory concentration (IC50) for basal tension (0.04 +/- 0.02 microM), however, was sevenfold less than the IC50 for basal 42K efflux (0.22 +/- 0.08 microM, p less than 0.01). The basal 45Ca influx in aorta from aldosterone-salt hypertensive rats (120 +/- 4 microM/l cell H2O/min) was also decreased by diltiazem in a concentration-dependent manner, whereas the 45Ca influx in aorta from control-salt rats (135 +/- 3 microM/l cell H2O/min) was not altered. Similarly, the dihydropyridine nisoldipine eliminated the basal tension (2.7 +/- 0.5 g) and returned the elevated basal 42K efflux from the hypertensive aorta toward control levels (0.010 +/- 0.0003/min, p less than 0.001). The nisoldipine IC50 for basal tension (0.016 +/- 0.01 nM) was 160-fold less than the IC50 for basal 42K efflux (1.8 +/- 1.2 nm, p less than 0.001). Neither diltiazem nor nisoldipine nisoldipine altered the basal 42K efflux or contractile activity of aorta from control-salt rats. These results suggest that the basal tension and elevated 42K efflux in aorta from aldosterone-salt hypertensive rats are supported by the entry of extracellular calcium into the tissue through potential-operated calcium channels.