IN VITRO CALCIUM DEPENDENCE OF ARTERIAL SMOOTH MUSCLE IN HUMAN HYPERTENSION

SUMMARY 1. Digital arteries, removed at autopsy from 12 hypertensives and 11 normotensives, have been compared in vitro for the calcium dependence of contractures produced by potassium chloride and noradrenaline, and the potency of verapamil to antagonize contractures to noradrenaline. 2. No significant differences were found between the vessels from the hypertensives and normotensives for the pD 2 values or the maximum response to either potassium chloride or noradrenaline in bathing solutions containing 2.5, 1.0, 0.5 or 0 mmol/l calcium chloride. 3. There were also no significant differences between the vessels, from the hypertensive or normotensives, in the pD 2 values for the addition of calcium chloride to arteries exposed to potassium chloride or noradrenaline in a calcium free bathing medium, in the ability of verapamil to shift the pD 2 values for noradrenaline, nor in the ability of verapamil to reduce the maximum responses to noradrenaline (except at the two highest concentrations of verapamil tested). 4. It is concluded that it is unlikely to be a primary abnormality of the mechanisms regulating calcium ion entry and release in vascular smooth muscle in human hypertension.