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Abstract

Necturus urinary bladders were mounted in a two-compartment chamber filled with Ringer's solution and individual cells were punctured with microelectrodes from the serosal surface. By measuring the changes of transepithelial resistance and potential in response to luminal application of amiloride, and measuring the effects of amiloride on the voltage divider ratio and on the serosal cell membrane potential, two independent methods were obtained to calculate the cell membrane resistances and the resistance of the shunt path. The results from both methods agreed favourably. Th mucosal and serosal membrane resistances were found to vary respectively from 9–65 kΩ cm² and from 1–7 kΩ cm² under control conditions. Significant correlations were observed between the luminal membrane resistance as well as the luminal membrane zero current potential and the short circuit current, which indicate that the luminal membrane conductance consists predominantly of Na⁺-selective elements, whose density varies from bladder to bladder and determines the rate of transpithelial Na⁺ transport. Amiloride which blocks these elements increased the luminal resistance to 220 kΩ cm². Increasing short circuit current was also correlated with increasing conductance of the serosal membrane (at fairly constant zero current potential) which points to an electrogenic mechanism of active Na⁺ transport across the serosal cell surface. The paracellular shunt path across the terminal bars plays a minor role in urinary bladder epithelium. Its resistance was estimated to be in the range of 50–125 kΩ cm² or greater.