Intracellular potentials in rabbit proximal tubules perfused in vitro

Conventional microelectrodes were used to measure the basolateral membrane potential (VBL) in isolated perfused superficial proximal convoluted (sPCT) and superficial proximal straight (sPST) tubules of the rabbit kidney. Stable recordings for periods up to 2 h can be obtained. The mean +/- SE (n = number of cells) values of VBL were sPCT = -51.0 +/- 1.63 (24) and sPST = -47.0 +/- 0.97 (94) mV. Inhibitors of active transport, ouabain (10(-5) M) and low bath potassium (0.1 mM), caused a significant depolarization of VBL in sPST. In contrast, short-duration bath cooling (10 degrees C) had no significant effect. Removal of luminal glucose caused a larger hyperpolarization in sPCT (-13.9 +/- 1.77 (9) mV) than in sPST (-3.8 +/- 1.02 (5) mV). Removal of luminal glucose and alanine resulted in an even larger hyperpolarization of VBL in sPCT (-19.0 +/- 0.44 (6) mV). Perfusion of the lumen with a solution resembling late proximal tubular fluid in sPST resulted in hyperpolarization of VBL (-4.3 +/- 0.85 (4) mV). Reducing bath pH to 6.7 depolarized VBL (39.9 +/- 1.77 (13) mV). This effect can be associated with a decrease in the relative potassium permeability of the basolateral membrane. These results demonstrate the feasibility of using intracellular electrical measurements to determine both luminal and basolateral membrane characteristics in isolated proximal tubular segments.