Electrophysiological characterization of rabbit distal convoluted tubule cell

The distal convoluted tubule (DCT) from rabbit kidney were perfused in vitro to study the conductive properties of the cell membranes by using electrophysiological methods. When the lumen and the bath were perfused with a bicarbonate free solution buffered with HEPES, the transepithelial voltage (VT) averaged -2.8 +/- 0.6 mV (n = 20), lumen negative. The basolateral membrane voltage (VB) averaged -77.8 +/- 1.1 mV (n = 33) obtained by intracellular impalement of microelectrodes. Cable analysis performed by injecting a current from perfusion pipette revealed that the transepithelial resistance was 21.8 +/- 1.7 omega.cm2 and the fractional resistance of the luminal membrane was 0.78 +/- 0.03 (n = 8), indicating the existence of ionic conductances in the luminal membrane. Addition of amiloride (10(-5) mol/l) to the luminal perfusate or Na+ removal from the lumen abolished the lumen negative VT and hyperpolarized the apical membrane. An increase in luminal K+ concentration from 5 to 50 mmol/l reduced the apical membrane potential (VA) by 37.5 +/- 2.6 mV (n = 7), whereas a reduction of Cl- in the luminal perfusate did not change VA significantly (0.5 +/- 0.5 mV, n = 4). Addition of Ba2+ to the lumen reduced VA by 42.6 +/- 1.0 mV (n = 4). When the bathing fluid was perfused with 50 mmol/l K+ solution, the basolateral membrane voltage (VB) fell from -76.8 +/- 1.5 to -31.0 +/- 1.3 mV (n = 18), and addition of Ba2+ to the bath reduced VB by 18.3 +/- 4.8 mV (n = 7).