The effect of external potassium on the blockade of the inward-going rectification by cesium ions in the frog atrial trabeculae.

The effect of Cs ions on the inward-going rectification of the frog atrial trabeculae was investigated in various external K concentrations using the double sucrose gap technique. In the presence of 10 mM Cs the inward-going rectification disappeared and the steady-state background current was related linearly to the membrane potential. The Cs-sensitive current was obtained by the difference between control and membrane currents measured in the presence of Cs ions. The current rectified in the inward direction and its reversal potential was very close to the K equilibrium potential. At potentials positive to the resting value the effect of Cs was progressively reduced, leaving the outward rectifier component of the background current unaffected. The analysis of the conductances calculated from the current-voltage relationships showed that the Cs effect was insensitive to moderate changes in the external K concentration, indicating that Cs ions strongly reduced K conductance. In the presence of high K concentrations the blocking effect of Cs appeared to be diminished. The lack of Cs action on the outward rectifier component and the results obtained in high K solutions were discussed.