Effect of external K on the block of the inward rectifier during hyperpolarization in guinea-pig ventricular myocytes by external Na

The effect of changes of the external K concentration on the block of the inward-rectifying K current during hyperpolarization in guinea-pig ventricular myocytes by external Na was investigated. The voltage-dependent block of iK1 by external Na ions is decreased when the external K concentration is lowered between 5.4 and 0.54 mM, but is not influenced when Ko is increased from 5.4 to 27 mM. The effect of lowering Ko can be described as a decrease of the rate of entry of blocking Na ions at lower external K.