Sodium Conductance in Cultured Proximal Tubule Cells (OK) Is Inhibited by Extracellular Cationic Amino Acids

Abstract

The Na⁺ membrane conductance in confluent monolayers of cultured opossum kidney cells has been investigated by the whole-cell patch clamp technique. In symmetrical sodium gluconate solutions Na⁺ conductance rises 10-fold during cytosolic ion equilibration. The steady-state conductance is voltage-dependent, being smallest between -60 and -20 mV intracellular clamp potential (4.4 ± 0.7 nS). This sodium conductance is insensitive to amiloride (10^–3 mol/l) and veratridine (5^.10^-5 mol/l). Exposure of the extracellular cell surface to the cationic (‘basic’) amino acids arginine and lysine (3 mmol/l each) reversibly reduces the sodium conductance at negative intracellular potentials by 20-40%. This reduction is significant even at physiological intratubular concentrations of L-arginine (0.3 mmol/l; p < 0.05). The effect is not stereo-specific, as L- and D-arginine cause the same reduction of sodium conductance. In contrast, 3 mmol/l L-arginine produce a net current at negative and positive clamp potentials when the cytosol is equilibrated with a high-potassium pipette solution as the result of electrogenic amino acid transport. It is concluded that cationic amino acids inhibit the Na⁺ conductance of OK cells that is due to an amiloride insensitive sodium conductive channel.