Effects of hypoxia on energy state and pH in resting pulmonary and femoral arterial smooth muscles

To determine the effects of hypoxia on energy state and intracellular pH (pH(i)) in resting pulmonary and systemic arterial smooth muscles, we used ³¹P nuclear magnetic resonance spectroscopy and colorimetric and enzymatic assays to measure pH(i); intracellular concentrations of ATP, phosphocreatine, creatine, and P(i); and phosphorylation potential in superfused tissue segments from porcine proximal intrapulmonary and superficial femoral arteries. Under baseline conditions (Po₂ 467 ± 12.1 mmHg), energy state and total creatine (phosphocreatine + creatine) concentration were lower and phi was higher in pulmonary arteries. During hypoxia (Po₂ 23 ± 2.4 mmHg), energy state deteriorated more in femoral arteries than in pulmonary arteries. pH(i) fell in both tissues but was always more alkaline in pulmonary arteries. Reoxygenation reversed the changes induced by hypoxia. These results suggest that production and/or elimination of ATP and H⁺ was different in resting pulmonary and systemic arterial smooth muscles under baseline and hypoxic conditions. Because energy state and phi affect a wide variety of cellular processes, including signal transduction, contractile protein interaction, and activities of ion pumps and channels, further investigation is indicated to determine whether these differences have functional significance.