Metabolic studies on rabbit bladder smooth muscle and mucosa

Recent studies indicate that the mucosa of the urinary bladder may play a major role in the maintenance of normal bladder function. The mucosal surface of the urinary bladder serves as a protective layer against the irritative solutes found in the urine. The integrity of this barrier can be broken by overdistension, anoxia, detergents, alcohols, bacterial infection and by contact with agents to which the mucosa has been sensitized.In view that both anoxia and ischemia can mediate a breakdown in the role of the mucosal layer as a permeability barrier, it is reasonable to assume that this function is dependent on cellular metabolism. As an initial investigation we have compared a variety of biochemical and metabolic parameters between the mucosal layer (consisting of the lamina propria, urothelium, and any connective tissue and vascular tissue within this layer); and the muscularis layer.The results of these studies demonstrated that the rate of glucose metabolism to lactic acid (LA) of the mucosa was more than three-fold greater than that of the smooth muscle. The rate of CO₂ production of the mucosa was 60% greater than that of the unstimulated smooth muscle. The maximal activity of the mitochondrial enzyme citrate synthase was significantly greater in the mucosa than in the smooth muscle, however, the activity of malate dehydrogenase was similar for both tissues. The maximal activity of the cytosolic enzyme creatine kinase was more than two-fold greater in the bladder smooth muscle than in the mucosa; although the affinities of the creatine kinase isoforms of the mucosa were sigificantly greater than those of the muscle.Although the concentrations of ATP and ADP were similar in both muscle and mucosa, the level of creatine phosphate (CP) was over four-fold greater in the bladder muscle while the level of AMP in the muscle was only 58% of that in the mucosal epithelium.In summary, the rate of glucose metabolism was greater in the mucosa than in the smooth muscle although the concentrations of high energy phosphates (ATP+CP) was significantly greater in the smooth muscle. Future studies will be directed at identifying the specific cellular processes within the mucosal layer that relate to the function of the urothelium as a permeability barrier.