Transepithelial and cell membrane electrical resistances of the rabbit proximal convoluted tubule

A technique using double-barreled perfusion pipettes and intracellular microelectrodes was developed to measure transepithelial, apical, and basolateral membrane electrical resistances in isolated rabbit proximal convoluted tubules (PCT). This technique has been tested successfully with respect to cable analysis: the transepithelial resistance (RT) did not change with tubule length and the measured core resistance of the lumen (RC) varied according to prediction with lumen diameter and perfusate resistivity. In control solutions, a linear I-V relationship was observed at the entry of the tubule for current varying from -300 to +300 nA. The mean RT was 1,050 +/- 70 omega X cm (n = 33) (a specific resistance of 8.2 omega X cm2). Bath proteins and large variations in transtubular hydrostatic pressure had no significant effect on RT, whereas RT was not systematically related to transepithelial PD or to the sodium-to-chloride permeability ratio (n = 22). Perfusate substitution of 50 mM NaCl by mannitol increased RT by 21% (n = 7) but the same maneuver in the peritubular solution had no significant effect after a 5-min equilibration period. The ratio of apical to basolateral cell membrane resistance (RA/RBL) determined with intracellular microelectrodes was 3.1 +/- 0.3 (n = 27) in control solutions and increased within 1 min by 36% (n = 8) when glucose and alanine were replaced by mannitol in the perfusate solution. Using simultaneous initial changes in transepithelial and basolateral potential differences when glucose and alanine were removed, the individual values of RA and RBL were determined. Mean RBL was 4,900 +/- 990 omega X cm (39 +/- 1.3 omega X cm2) and mean RA was 15,000 +/- 4,300 omega X cm (118 +/- 33 omega X cm2).