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 lactate production (J(Lac)), force and [Ca2+](i) in longitudinal smooth muscle from urinary bladders of control and diabetic rats. Materials and Methods: Strips of longitudinal smooth muscle were isolated from urinary bladders of diabetic rats and their age-matched controls. Force and [Ca2+](i) were measured simultaneously in muscle strips loaded with the 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 by 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 muscles under both normoxic and anoxic conditions. During stimulation under anoxic conditions, the diabetic muscles were less able to maintain force than the controls. Despite a marked decline in force in both diabetic and control muscles under anoxic conditions, [Ca2+](i) remained elevated to levels that were in fact higher than those observed during stimulation under normoxic conditions. Increasing the glucose concentration had no significant effect during normoxia, however, under anoxic conditions, the higher concentration improved force maintenance in both control and diabetic muscles. There were no apparent effects of the glucose concentration on [Ca2+](i) in either diabetic or control muscles. Conclusion: The results reveal that urinary bladder smooth muscle from diabetic rats has a reduced ability to maintain contraction under anoxic conditions. This most likely reflects a greater energy limitation as evidenced by the reduced J(Lac) in diabetic muscles. In both diabetic and control muscles there was a marked dissociation between force and [Ca2+](i) when oxidative metabolism was inhibited. This may indicate preferential use of glycolytically produced ATP for maintenance of [Ca2+](i) homeostasis under these conditions.