Differentiation of calcium activation mechanisms in vascular smooth muscle by selective suppression with verapamil and D 600-1.

Mechanical activity of the isolated portal vein and thoracic aorta of the guinea-pig was recorded and the effects of verapamil and D 600 (methoxy-verapamil) on the dose-response curves to noradrenaline were measured. Extracellular electrical activity in portal vein was also sometimes recorded. Two calcium activation mechanisms could be differentiated: a "spike activation mechanism" (SAM) inhibited by verapamil and D 600, and a "spike-free activation mechanism" (SFAM) resistant to these antagonists in their specific concentration range (up to 10-minus 5 mol/1).