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要旨

Necturus urinary bladders were mounted between half chambers filled with Ringer's solution and the electrical potential difference was measured across the luminal and basal membrane of the epithelial cells under open circuit conditions. The measurements were complicated by leak artifacts, which developed at the puncture site during impalements from the mucosal surface, but not during impalements from the serosal surface, probably because the resistance of the mucosal cell membrane was on the average 13 times higher than that of the serosal membrane. In contrast to previous reports on potential profiles in amphibian urinary bladders, in which the possible influence of leak artifacts was neglected, it was observed that the serosal membrane potential was constant at ∼ −90 mV in all bladders, irrespective of the spontaneous transepithelial potential difference. In low potential bladders (bladders with low transepithelial Na⁺ transport, mainly from female animals) the potential profile was trough-like with −30 mV in the mucosal bath, and −90 mV inside the cells, the serosal bath being taken as zero. In high potential bladders (bladders with high rates of Na⁺ transport from male animals) it was stairstep-like from −150 mV in the mucosal bath to −90 mV inside the cells and to zero in the serosal bath. Luminal application of amiloride produced similar changes of the potential profile as caused the transition from high to low potential bladders. In agreement with resistance data reported in the subsequent paper, we conclude that the polarity change of the luminal membrane potential with increasing transepithelial Na⁺ transport reflects an increase of the luminal Na⁺ conductance following the incorporation of Na⁺-selective, amiloride sensitive passive transport channels into the luminal cell membrane in response to hormonal stimuli from androgens and aldosterone.