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

To elucidate the dependence of aerobic energy metabolism and utilization of glucose incontraction of urinary bladder smooth muscle, we investigated the changes in the reducedpyridine nucleotide (PNred) fluorescence, representing glycolysis activity, and determinedthe phosphocreatine (PCr) and ATP contents of the porcine urinary bladder duringcontractions induced by high K⁺ or carbachol (CCh) and with and without hypoxia(achieved by bubbling N₂ instead of O₂) or in a glucose-freecondition. Hyperosmotic addition of 65 mM KCl (H-65K⁺) and 1µM CCh induced a phasic contraction followed by a tonic contraction. Aglucose-free physiological salt solution (PSS) did not change the subsequent contractileresponses to H-65K⁺ and CCh. However, hypoxia significantly attenuatedH-65K⁺- and CCh-induced contraction. H-65K⁺ and CCh induced asustained increase in PNred fluorescence, representing glycolysis activity. Hypoxiaenhanced H-65K⁺- and CCh-induced increases in PNred fluorescence, whereasglucose-free PSS decreased these increases, significantly. In the presence ofH-65K⁺, hypoxia decreased the PCr and ATP contents; however, the glucose-freePSS did not change the PCr contents. In conclusion, we demonstrated that highK⁺- and CCh-induced contractions depend on aerobic metabolism and that anendogenous substrate may be utilized to maintain muscle contraction in a glucose-free PSSin the porcine urinary bladder.