Effects of anoxia on force, intracellular calcium and lactate production of urinary bladder smooth muscle from control and diabetic rats

Purpose: To examine the effects of inhibiting oxidative metabolism on lacta te production (J(Lac)), force and [Ca2+](i) in longitudinal smooth muscle f rom urinary bladders of control and diabetic rats. Materials and Methods: Strips of longitudinal smooth muscle were isolated f rom urinary bladders of diabetic rats and their age-matched controls. Force and [Ca2+](i) were measured simultaneously in muscle strips loaded with th e calcium indicator, fura-2. Separate muscle strips were used to determine J(Lac) by standard enzymatic assay. The muscles were stimulated to contract with 65 mM K+ or 1 mu M carbachol (CCh) in the presence of 2.5 mM Ca2+ and either 5, 10 or 25 mM glucose. Oxidative metabolism was inhibited either b y replacing O-2 in solution with N-2, or by addition of 2 mM NaCN. Results: J(Lac) was significantly less in diabetic muscles than control mus cles under both normoxic and anoxic conditions. During stimulation under an oxic conditions, the diabetic muscles were less able to maintain force than the controls. Despite a marked decline in force in both diabetic and contr ol muscles under anoxic conditions, [Ca2+](i) remained elevated to levels t hat were in fact higher than those observed during stimulation under normox ic conditions. Increasing the glucose concentration had no significant effe ct during normoxia, however, under anoxic conditions, the higher concentrat ion improved force maintenance in both control and diabetic muscles. There were no apparent effects of the glucose concentration on [Ca2+](i) in eithe r diabetic or control muscles. Conclusion: The results reveal that urinary bladder smooth muscle from diab etic rats has a reduced ability to maintain contraction under anoxic condit ions. This most likely reflects a greater energy limitation as evidenced by the reduced J(Lac) in diabetic muscles. In both diabetic and control muscl es there was a marked dissociation between force and [Ca2+](i) when oxidati ve metabolism was inhibited. This may indicate preferential use of glycolyt ically produced ATP for maintenance of [Ca2+](i) homeostasis under these co nditions.