Contraction and membrane activation in several mammalian vascular muscles

Abstract

Intracellular microelectrode recording from helically cut strips of mammalian vascular muscle cells from several blood vessels showed graded membrane activation in response to norepinephrine or electrical stimulation (gradedly responsive), while that from other vessels showed spontaneous, all-or-none activation (regeneratively responsive). Vascular muscle from nine mesenteric arteries, one intercostal artery, one sublingual artery, one aorta, one ophthalmic artery, and one sphenopalatine vein was observed to have gradedly responsive membrane properties. The gradedly responsive character of carotid and pulmonary arteries and the regeneratively responsive character of portal-mesenteric venous vascular muscle was supported. Regeneratively responsive vascular muscle showed pacemaker potentials and was activated either by single spikes or by summation of several spikes. Action potential duration at half-amplitude was about 50 msec. Summed contractions of regeneratively responsive muscle could be reduced to single contractions by alpha adrenergic blocking agents, but not by beta adrenergic, cholinergic, or ganglionic blocking agents; single contractions were not blocked by any blocking agent. Conduction in regeneratively responsive vascular muscle seemed poor as determined by observation of several small, independently contracting areas in a small strip of tissue.