Acid Stress Reduces the Function of Na+-K+-ATPase in Superior Mesenteric Artery of Capra hircus

Context: Extracellular hydrogen ion concentration (pH(o)) is an important physiological regulator of vascular tone, maintained within 7.35-7.45 and any change in it leads to complex health problem including maintenance of normal blood pressure. Aims: This study aims to examine the altered function of Na+-K+ pump and inward rectifier potassium channels (K-ir) channels in extracellular acidosis in goat superior mesenteric artery (GSMA). Subjects and Methods: Isolated GSMA rings were mounted in an automatic organ bath containing 20-ml modified Krebs-Henseleit solution at pH 7.4/6.8/6.0 and KCl-induced contraction was elicited either in the absence or presence of ouabain, barium (Ba2+), and combination of ouabain and Ba2+. Rings were dilated with potassium chloride either in the absence or presence of ouabain, Ba2+ and combination of ouabain and Ba2+ while maintaining at acidic pH. The responses were recorded isometrically by highly sensitive isometric force transducer connected to Powerlab and analyzed using LabChart 7.1.3 software. Statistical Analysis Used: Data were analyzed in GraphPad Prism 5 software. Results: K+ vasorelaxation response in K+-free solution precontracted rings the percent maximal response (93.57 +/- 2.57%, 62.60 +/- 3.56%, and 53.38 +/- 5.41%) was decreased with decrease pH(o) (7.4, 6.8 and 6.0). Ouabain, Ba2+, and ouabain and Ba2+ inhibited the maximal vasorelaxation of potassium chloride (26.20 +/- 3.48%, 17.39 +/- 0.54%, 31.92 +/- 1.10%) at pH(o) 7.4, (42.74 +/- 2.48%, 16.12 +/- 3.49%, 22.32 +/- 1.63%) at pH(o) 6.8, and (53.87 +/- 2.18%, 25.24 +/- 2.90%, 39.71 +/- 0.14%) at pH(o) 6.0, respectively. Conclusions: Attenuated vasodilation in acidosis is due to reduced function or expression of ouabain-sensitive sodium-potassium ATPase (Na+-K+-ATPase) and K-ir channels. In clinical acidosis, agents augmenting the activity of Na+-K+-ATPase and K+-Channel could improve hypertensive crisis.