METABOLIC STUDIES ON RABBIT BLADDER SMOOTH-MUSCLE AND MUCOSA

Recent studies indicate that the mucosa of the urinary bladder may pla y a major role in the maintenance of normal bladder function. The muco sal surface of the urinary bladder serves as a protective layer agains t the irritative solutes found in the urine. The integrity of this bar rier can be broken by overdistension, anoxia, detergents, alcohols, ba cterial infection and by contact with agents to which the mucosa has b een sensitized. In view that both anoxia and ischemia can mediate a br eakdown in the role of the mucosal layer as a permeability barrier, it is reasonable to assume that this function is dependent on cellular m etabolism. As an initial investigation we have compared a variety of b iochemical and metabolic parameters between the mucosal layer (consist ing of the lamina propria, urothelium, and any connective tissue and v ascular tissue within this layer); and the muscularis layer. The resul ts of these studies demonstrated that the rate of glucose metabolism t o 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 w as 60% greater than that of the unstimulated smooth muscle. The maxima l activity of the mitochondrial enzyme citrate synthase was significan tly greater in the mucosa than in the smooth muscle, however, the acti vity of malate dehydrogenase was similar for both tissues. The maximal activity of the cytosolic enzyme creatine kinase was more than two-fo ld greater in the bladder smooth muscle than in the mucosa; although t he affinities of the creatine kinase isoforms of the mucosa were signi ficantly greater than those of the muscle. Although the concentrations of ATP and ADP were similar in both muscle and mucosa, the level of c reatine phosphate (CP) was over four-fold greater in the bladder muscl e while the level of AMP in the muscle was only 58% of that in the muc osal epithelium. In summary, the rate of glucose metabolism was greate r 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 spec ific cellular processes within the mucosal layer that relate to the fu nction of the urothelium as a permeability barrier.