Cell membranes and paracellular resistances in isolated renal proximal tubules from rabbit and Ambystoma.

Transepithelial specific resistance (Re) was measured in isolated and perfused rabbit proximal convoluted tubules by cable analysis and intracellular micro-electrode techniques were used to calculate the electrical resistances of the cell membranes and of the paracellular pathway. Re was 16 +/- 2 omega cm2 and the space constant was 130 +/- 14 micron, n = 29. Re was significantly increased by a decrease in temperature from 37 to 10 degrees C, and was practically abolished by nominal removal of Ca2+ from the bathing solution (to 2.0 +/- 0.3 omega cm2, P less than 0.001, n = 6). The apparent ratio of cell membrane resistances (luminal to basolateral) was 3.1 +/- 0.3. The control values of apical and basolateral membrane resistances (Ra and Rb) were calculated from the values of (1) Re, (2) the apparent ratio of cell membrane resistances, and (3) the effects of addition of either Ba2+ (1 mM) to the bath solution or glucose (8 mM) to the perfusate on basolateral and apical membrane voltages (assuming that the initial effects of Ba2+ and glucose are restricted to the ipsilateral membrane). Control values of Ra (omega cm2 of epithelium) were 249 +/- 68 (Ba2+ method) and 227 +/- 42 (glucose method). Values of Rb were 70 +/- 11; and 66 +/- 12 respectively. The low paracellular resistance values obtained with the Ba2+ and glucose methods, respectively, 17 +/- 5 and 15 +/- 1 omega cm2, explain the low transepithelial resistance. The use of the Ba2+ and glucose methods provides alternatives to cell cable determinations for the calculation of cell membrane resistances. Cell membrane and shunt resistances measured by the same methods in isolated perfused Ambystoma tigrinum proximal tubules (in omega cm2 of epithelium) were: Ra, 2650 +/- 180 (glucose method) and 2368 +/- 350 (Ba2+ method). Values of Rb were 665 +/- 99 (glucose method) and 701 +/- 124 (Ba2+ method). The paracellular resistance values were 58 +/- 11 (glucose method) and 84 +/- 12 (Ba2+ method). These results are in good agreement with previously reported values obtained by intracellular cable analysis (Maunsbach & Boulpaep, 1984).