Alteration of Contractile Response of Artery Strips by a Potassium-Free Solution, Cardiac Glycosides and Changes in Stimulation Frequency

Electrical stimulation of helically cut strips of rabbit carotid artery, mounted so as to allow development of tension isometrically, causes a contraction-relaxation cycle which remains reproducible for many hours, after an initial period of rising contractile response. If the strip is equilibrated in a potassium-free Krebs solution, or if a cardiac glycoside is added, the tension developed on electrical stimulation increases, the time required for relaxation is prolonged and contracture may also be observed. Desoxycorticosterone or progesterone decrease the contractile response of the strip. The arterial smooth muscle strip also exhibits the staircase phenomenon, a stepwise increase in tension on repeated stimulation after a period of rest. It is suggested that the changes in contractile response induced by a potassium-free medium, addition of glycosides, or repetitive stimulation are related to a loss of muscle fiber potassium. The action of the glycosides on the artery strip is discussed from the viewpoint of a model mechanism for altering vascular smooth muscle activity by affecting intracellular electrolytes.