Key Role of Glycogen Storage in High K⁺-Induced Contraction of the Smooth Muscles of the Bovine Trachea

Abstract

To elucidate the role of glycogen in the contraction of tracheal smooth muscle, we investigated the changes in the glycogen contents of the bovine trachea during contractions induced by high K⁺ and hypoxia (achieved by bubbling N₂ instead of O₂), either in a glucose-free condition or in the presence of iodoacetic acid (IAA), an inhibitor of glycolysis. Hyperosmotic addition of 65 mM KCl (H-65 K⁺) induced a sustained contraction. A glucose-free condition did not affect H-65 K⁺-induced contraction. However, hypoxia slightly inhibited the contraction, and glucose-free PSS with hypoxia or IAA remarkably inhibited the H-65 K⁺-induced contraction. H-65 K⁺ induced a sustained increase in reduced pyridine nucleotide (PNred) fluorescence, representing glycolysis activity. Hypoxia alone slightly enhanced PNred fluorescence, and when combined with a glucose-free condition, it remarkably enhanced the H-65 K⁺-induced PNred fluorescence. IAA inhibited PNred fluorescence. In the presence of H-65 K⁺, a glucose-free condition, hypoxia and the combination of glucose-free PSS and hypoxia decreased the glycogen contents. However, IAA had no effect on glycogen contents. Although hypoxia or glucose-free PSS did not affect PCr and ATP contents, the combination of hypoxia and glucose-free PSS or IAA induced a gradual decrease of PCr content. In conclusion, we suggest that endogenous glycogen was utilized to increase the activity of glycolysis for maintaining high K⁺-induced contraction of the bovine trachea in the glucose -free and/or hypoxic condition.