The long term objectives of this proposal is to elucidate the mechanisms by which the mammalian urinary bladder maintains the urine composition near constant without compromising its own viability nor the viability of the underlying musculature and nervous tissue. It is postulated that a breakdown of this function might be a component of interstitial cystitis. The mammalian urinary bladder epithelium has adopted at least three strategies to perform this function. First, the epithelium is relatively impermeable to electrolytes and non-electrolytes. Second, it maintains a minimum ratio of cell surface area to urine volume ratio by the insertion and removal of cytoplasmic vesicles into and out of the apical membrane. Third, it has a hormone (aldosterone) sensitive, active sodium transport system. The major aims of this proposal are three fold. First, is to determine the effects of cell volume perturbations (by ion replacement or solution osmolarity) on the membrane ion conductances of the apical and basolateral membranes and tight junctions of the urinary bladder. Preliminary results have demonstrated that the urinary bladder, once shrunken, seems to activate neutral ion exchangers which might return cell volume towards control values. Second, is to determine the rate of tissue repair using a tissue culture system. Third, is to determine whether the glycosaminoglycan layer (a polysaccharide coat over the apical surface) acts as a significant barrier to transepithelial electrolyte and non-electrolyte permeability. These three goals will be studied using a combination of electrophysiological techniques, optic techniques and tissue culture methods. The electrophysiological methods include monitoring of epithelial resistance and the rate of sodium transport, current fluctuation analysis to determine sodium channel density, microelectrodes to measure the individual membrane ionic permeabilities, ion specific micro-electrodes to measure the alterations in cell ion activities during cell volume regulation and impedance analysis to determine if cell volume changes are correlated with membrane area changes. The optical technique will be used to measure both short and long term alterations in cell volume and correlate the volume changes with the alterations in membrane permeabilities and cell ion activities. Last, tissue culture will be used to determine possible long term strategies that bladder epithelial cells adopt when challenged with increased interstitial osmolarity. In summary, these investigations will advance our understanding of the mechanisms invoked by the bladder to adapt to variations in urine composition and to recover from breakdown of the epithelial barrier. In addition, these studies will elucidate the physiological function of the mammalian urinary bladder and its role in the maintenance of extracellular fluid homeostasis.
