Na⁺K⁺-Atpase Activity and Responsiveness of Vascular Smooth Muscle to Norepinephrine, Angiotensin II and Calcium Ionophore A23187 in Guinea Pig Aortic Strips

Abstract

The functional significance of the Na⁺K⁺-ATPase activity in defining the sensitivity of vascular smooth muscle response to pressor stimuli was studied in guinea pig aortic strips. Subthreshold doses of ouabain (10^-8, 10^-7, 10^-6M), potentiated the norepinephrine- and angiotensin II-induced contractile responses, dose-dependently. Furthermore, in the presence of subthreshold dose of ouabain (10^-6M), tension developments were observed with subthreshold doses of norepinephrine and angiotensin II. The mechanism by which subthreshold dose of ouabain potentiated the norepinephrine-induced contractile response was revealed to involve the enhancement both of sensitivity and contractile activity. Ouabain (10^-6M) potentiated the norepinephrine- and A23187-induced contractile responses, even in the presence of verapamil. These facts indicate that suppression of the vascular Na⁺K⁺-ATPase activity could favor the development of hypertension through potentiating contractile responses to various stimuli and that the potentiation could be a reflection, at least partly, of the decrease in Ca²⁺-efflux

Key Words:

• Na⁺K⁺-ATPase
• Vascular smooth muscle
• Norepinephrine
• Angiotensin II
• A23187