OUABAIN-INDUGED CHANGES IN THE CONTRACTILE AND ELECTRICAL ACTIVITY, POTASSIUM CONTENT, AND RESPONSE TO DRUGS, OF SMOOTH MUSCLE CELLS

Abstract

Contractile activity, electrical activity, and tissue potassium content were studied in vitro in the guinea pig taenia coli and rabbit anterior mesenteric vein, before, during, and after exposure to ouabain 10⁻⁵M. Ouabain produced a contraction, followed by relaxation, in both preparations; later there was a larger, more prolonged contraction of the vein. Action potential frequency was first increased, then decreased, and finally abolished by ouabain in both preparations. Tissue potassium content was also decreased and membrane potentials were progressively reduced. Ouabain blocked the contractile effect of excitant drugs in the taenia but not in the vein. Yet in both preparations drug-induced electrical changes were completely abolished by ouabain. These results support the conclusion that stimulant drugs are able to contract the anterior mesenteric vein both via action potentials and by a mechanism relatively independent of the electrical events at the cell membrane. They also suggest that smooth muscles vary in regard to the necessity of action potentials as a link in drug-induced contraction.