Effects of hypoxia and glucose-removal condition on muscle contraction of the smooth muscles of porcine urinary bladder

Abstract

To elucidate the dependence of aerobic energy metabolism and utilization of glucose in contraction of urinary bladder smooth muscle, we investigated the changes in the reduced pyridine nucleotide (PNred) fluorescence, representing glycolysis activity, and determined the phosphocreatine (PCr) and ATP contents of the porcine urinary bladder during contractions induced by high K⁺ or carbachol (CCh) and with and without hypoxic (achieved by bubbling N₂ instead of O₂) or in a glucose-free conditions. Hyperosmotic addition of 65 mM KCl (H-65K⁺) and 1 µM CCh induced a phasic contraction followed by a tonic contraction. A glucose-free physiological salt solution (PSS) did not change the subsequent contractile responses to H-65 K⁺ and CCh. However, hypoxia significantly attenuated H-65 K⁺- and CCh-induced contraction. H-65 K⁺ and CCh induced a sustained increase in PNred fluorescence, representing glycolysis activity. Hypoxia enhanced H-65 K⁺- and CCh-induced increases in PNred fluorescence, whereas glucose-free PSS decreased these increases, significantly. In the presence of H-65 K⁺, hypoxia decreased the PCr and ATP contents; however, the glucose-free PSS did not change the PCr contents. In conclusion, we demonstrated that high K⁺- and CCh-induced contractions depend on aerobic metabolism and that an endogenous substrate may be utilized to maintain muscle contraction in a glucose-free PSS in the porcine urinary bladder.