The influence of non-uniformity on the analysis of potassium currents in heart muscle.

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Abstract
A method is described for determining the space constant .lambda. of heart muscle strips using a sucrose gap technique. The average value of .lambda. for frog atrial trabeculae was nearly 700 .mu.m. This value was nearly twice the length of the test gap (400 .mu.m). Near the resting potential, the voltage non-uniformity should be about 10%. This was confirmed experimentally by comparing the membrane voltages recorded across the current-passing and voltage-recording sucrose gaps. The non-uniformity during large depolarizations was calculated using a computer model. This model includes the inward-going rectification displayed by iK1 and the delayed rectification that occurs following depolarizations beyond -40 mV. A single component of delayed rectification was included. Even very large non-uniformities had relatively small effects on the shape of the activation curve and on the time course of onset or decay of current. The fast component of current decay described in a previous paper is probably not attributable to a non-uniformity artifact.