Influence of cellular energy metabolism on contractions of porcine carotidartery smooth muscle

A number of cellular metabolites, including inorganic phosphate and ADP, ha ve been proposed to regulate the contractions of smooth muscle. Hypothesizi ng that one of these would have a greater influence than the others, parall el experiments using tissue mechanics and P-31-NMR allowed comparison of se veral metabolic components with the generation of force in porcine carotid artery smooth muscle during long-term contractions. P-i, ADP, ATP, PCr, fre e energy, pH, and free Mg2+ were determined from phosphate spectra during a control-hypoxia-postcontrol sequence generated during K+ stimulation by re placement of oxygen with nitrogen using either pyruvate or glucose as subst rate. Both pH and free Mg2+ were significantly lower in control pyruvate-su pplied tissues than in glucose-supplied tissues. Mechanical experiments fol lowing the same protocol produced variations in force. The pyruvate series produced the greater range of mechanical and metabolic changes. Linear and logarithmic regression analysis found the order of correlation with force t o be highest for P-i, followed by pH, free energy, PCr, ATP, ADP, and free Mg2+ The results are consistent with models for the regulation of myosin AT Pase by free phosphate inhibition. The results are inconsistent with models of ADP as a regulator of smooth muscle force. Perturbations which alter in tracellular phosphate, such as creatine loading, may produce side effects o n the contractions of vascular smooth muscle. Copyright (C) 2000 S. Karger AG, Basel.