Single Sodium Channels in the Apical Membrane of Proximal Tubule Cells in Culture

Abstract

Isolated proximal tubule cells of Ambystoma kidney were grown in primary cultures to confluence. Using the patch clamp technique single Na+ channels were found in the apical membrane of the proximal tubule cells. In control conditions in the cell attached configuration these Na+ channels showed a single channel conductance of 3 to 4 pS (referred to symmetrical 100 mM Na) and were highly selective. In the presence of 10 µM amiloride added to the pipette solution there was an increased number of transitions without complete block, and the single channel conductance, referred to symmetrical 100 mM Na, increased to 10–13 pS. In control conditions the probability of opening increased with hyperpolarization of the membrane patch. In the presence of amiloride open probability decreased with hyper-polarization. Analysis of open and closed time constants revealed a single open and closed time constant in control conditions, but multiple time constants after the addition of amiloride. It is concluded that the apical membrane of the amphibian proximal tubule has a subtype of Na+ channels whose properties differ, qualitatively and quantitatively, from other epithelial sodium channels.