Variations in Responses of Vascular Smooth Muscles to Na-K Pump Inhibition

Abstract

There is a paucity of information concerning the variability of Na⁺-K⁺-ATPase activity in various vascular preparations. In this study, we have investigated, comparatively, K⁺-induced relaxation in different vascular tissues, to establish the heterogeneity of the activity of this enzyme. Isometric contractions of ring preparations of porcine tail artery and rat aorta as well as longitudinal strips of rat portal vein, mounted in 20ml organ baths were studied, under an initial load of 1g, at 37^oCand pH of 7.4. The protocols examined were: Contractile responses to phenylephrine, 80mM K⁺ and K⁺-free exposure as well as relaxation responses to K⁺ following exposure to K⁺-free PSS. Phenylephrine, 80mM K⁺ and K⁺-free exposure elicited contractile responses in all tissue preparations. Following 30 minutes exposure to K⁺-free PSS and pre-contraction induced by EC₇₀ (M) concentration of phenylephrine, addition of 5mM K⁺ elicited relaxation responses only in rat aortic rings and rat portal vein strips. Rings from Porcine tail artery failed to relax to K⁺ in all experiments. The magnitude of K⁺-induced relaxation was in the order: Rat Portal Vein > Rat Aorta. The times-to-peak of K⁺-free-induced contractile responses were 2.0 ± 0.0, 3.5 ± 0.5 and 6.25 ± 3.13 minutes for rat portal vein (n=6), rat aorta (n=6) and porcine tail artery (n=6), respectively. The magnitudes of relaxation in response to 5mM K⁺ for rat portal vein and rat aorta were 86.5 ± 16.75 and 60.00 ± 10.0%, respectively while the respective durations of K⁺-induced relaxation were: 30 ± 0 and 180 ± 22 seconds (n=6). The results suggest considerable heterogeneity in the activity of Na⁺-K⁺-ATPase enzyme in vascular smooth muscles from the rat portal vein, rat aorta and porcine tail artery.

Keywords: Na⁺-K⁺-ATPase; Vascular Smooth Muscle; Rat aorta; Rat Portal Vein; Porcine Tail Artery