Some electrical properties of distal tubular epithelium in the rat.

MALNIC, GERHARD, AND GERHARD GIEBISCH. Some electrical properties of distal tubular epithehm in the tat. Am. J. Physiol. 223(4) : 797-808. 1972.-Transtubular electrical potential differences and effective electrical resistances across the distal tubular wall were measured by microelectrode techniques. Specific membrane resistances we& calculated according to cable analysis. A value in the order of 350 ohm cm2 was obtained in control rats. Transepithelial resistance values across distal tubules were lower in animals given 5% NaHC03 or 0.15 M KC1 while rats breathing 15 y0 CO2 had similar values to controls. Perfusion of distal tubules with solutions containing only K, Na, or Cl as the main permeant ion species indicates a progression of relative conductances in the order K > Na >> Cl near neutral pH. Changes in pH ranging from 5.5 to 8.0 did not change the specific potassium conductance. From specific conductances and the electrochemical potential difference of potassium and chloride ions it was possible to evaluate whether the transepithelial electrical driving force is adequate to effect transtubular potassium and chloride movement passively. The transepithelial potassium conductance is high enough to allow passive entry into the lumen by the electrical potential difference, a finding which does not exclude participation of an active transport component. The transepithelial chloride conductance is too small to allow passive reabsorption at the observed transepithelial potential difference. This implies that distal chloride reabsorption may be partly active in nature.