INSULIN ACTIVATES SINGLE AMILORIDE-BLOCKABLE NA CHANNELS IN A DISTAL NEPHRON CELL-LINE (A6)

Using the patch-clamp technique, we studied the effect of insulin on an amiloride-blockable Na channel in the apical membrane of a distal nephron cell line (A6) cultured on permeable collagen films for 10-14 days. NPO (N, number of channels per patch membrane; P(O), average value of open probability of individual channels in the patch) under baseline conditions was 0.88 +/- 0.12 (SE) (n = 17). After making cell-attached patches on the apical membrane which contained Na channels, insulin (1 mU/ml) was applied to the serosal bath. While maintaining the cell-attached patch, NPO significantly increased to 1.48 +/-0.19 (n = 17; P < 0.001) after 5-10 min of insulin application. The open probability of Na channels was 0.39 +/- 0.01 (n = 38) under baseline condition, and increased to 0.66 +/- 0.03 (n = 38, P < 0.001) after addition of insulin. The baseline single-channel conductance was 4 pS, and neither the single-channel conductance nor the current-voltage relationship was significantly changed by insulin. These results indicate that insulin increases Na absorption in the distal nephron by increasing the open probability of the amiloride-blockable Na channel.