Acute changes in channel density of amphibian diluting segment.

Intracellular pH is a well-established modulator of the apical membrane potassium conductance of the amphibian diluting segment (early distal tubule). We investigated the modulation of this apical potassium conductance at the single-channel level in everted early distal tubules of the frog. Alkalinization of the bath fluid increased mean channel open probability (NPo) both in the presence and absence of the potassium-hydrogen ionophore nigericin. Reciprocal changes were seen with acidification. Because these effects were observed in cell-attached patches, where the composition of the fluid in the pipette is assumed to remain constant, the observed changes in channel activity were attributed to changes in intracellular pH. Further analysis of the data revealed that the changes in channel activity were produced exclusively by changes in the functional number of channels within the patch (N). We were unable to detect any significant changes in the single-channel open probability (Po). This suggests that the density of channels within a membrane may be far more dynamic than previously assumed.