Histamine-induced rhythmic contraction of hog carotid artery smooth muscle

Smooth muscle strips isolated from the hog common carotid artery can contract rhythmically, exhibiting low frequency, large amplitude oscillations in tension when stimulated with 10 microM histamine. Strips required at least 1.45 mM calcium and 2.5 mM potassium to exhibit this rhythmic activity. Rhythmic contractions could be converted to tonic contractions by removal of potassium or ouabain treatment. Relaxation by 2 mM lanthanum, 1 mM manganese, or 1 microM verapamil implies that the external medium is the source of calcium mediating the contractions. The involvement of adrenergic nerve terminals in this response was ruled out, since propranolol, phentolamine, tetrodotoxin, bretylium, or 6-hydroxydopamine treatment did not alter the oscillations. Blockade of H1 receptors with 0.1 microM diphenhydramine relaxed the muscle strips. The H2 receptor antagonist cimetidine (5 microM) had no effects. Attempts to obtain rhythmic contractions by stimulating with other vasoactive agents (norepinephrine, acetylcholine, 5-hydroxytryptamine, angiotensin II, and elevated potassium concentrations) were unsuccessful, suggesting that this is a specific histamine response mediated solely by H1 receptors. These results show that this large artery, commonly considered a multi-unit smooth muscle, can sometimes exhibit single-unit behavior.