Quinidine blockage of K+ channels in the basolateral membrane of larval bullfrog skin.

The skin of frog larvae (Rana catesbeiana) was used to study the characteristics of basolateral K+ channels with fluctuation analysis. K2SO4 and Na2SO4 Ringer's were used as mucosal and serosal solution, respectively. After addition of Nystatin (138 U/ml) the transepithelial conductance and short-circuit current (Isc) increased considerably. Most of Isc was carried by K+, moving from the mucosal to the serosal side. This current could be depressed by quinidine, added to both compartments or to mucosal side only. Fluctuation analysis showed that quinidine induced a Lorentzian component in the power density spectrum. Assuming pseudo-first order kinetics for the channel occlusion by quinidine the current through the open K+ channel and channel density were calculated: iK = 0.22 pA, M = 7.7 channels/microns2.