Electrical properties of amphibian urinary bladder epithelia. I. Inverse relationship between potential difference and resistance in tightly mounted preparations.

In an attempt to find a high-resistance epithelium suitable for microelectrode work, we have studied the electrical properties of Necturus and Amphiuma urinary bladders in comparison to toad bladder. Improved mounting techniques were developed, which yield better reproducible degrees of distension and prevent electrical leaks around the edge of the preparation in the Ussing chamber. Transepithelial potential difference and resistance was measured with NaCl Ringer's on either surface of the epithelium, as well as under conditions of ion substitutions and in the presence of amiloride. Compared to data from conventionally mounted toad bladders reported in the literature, our experiments yielded higher potential differences and resistances in all three species. In Necturus values of up to 175 mV and 75 komega cm2 were recorded. Furthermore an inverse relationship was observed between potential difference and resistance, which was not noticed previously with the conventional mounting technique. The relationship is discussed quantitatively in terms of the two-membrane model of active Na+ transport, for which it provides further supportive evidence.