Effect of Potassium on the Resting Length of Vascular Smooth Muscle of the Rabbit Aorta and its Response to I-Norepinephrine

Abstract

Change in resting length, response to l -nor-epinephrine and tissue concentration of potassium of helical rabbit aorta strips have been investigated, following changes in concentration of extracellular potassium. Increase in potassium decreases resting length, increases sensitivity and slope of log dose - probit response curve: potassium decrease has opposite effects. Alterations in external potassium concentration have no effect on the maximum response to l -norepinephrine. A potassium range between 50% and 300% of normal was investigated. Results show that when the muscle shortened, following an increase in potassium in the presence of l -norepinephrine, the change in resting length due to a direct action of this ion was more important than changes in sensitivity to l -norepinephrine. It is suggested that sensitivity of muscle to l -norepinephrine may be related to the intra-cellular concentration of potassium.