Studies of impedance in cardiac tissue using sucrose gap and computer techniques. I. The influence of sucrose and oil as insulating media.

Impedances of cardiac cells of an insect were determined as a function of time to test the effects of sucrose and oil as insulating media in a gap arrangement. Impedance values are shown to increase markedly with time when sucrose is used as the insulating agent. Although impedance values are steady when oil is used, it is suggested that a layer of trapped electrolyte provides a shunt pathway and seriously impairs the validity of the measurements. A quick wash with sucrose followed by oil does not alleviate the situation but leaves a layer of sucrose trapped at the tissue-medium interface into which ions diffuse. The hypotheses (a) that the diffusion of intracellular K(+) into the sucrose would result in an increase in tissue impedance and (b) that a layer of trapped electrolyte under the oil film provides a shunt pathway are examined by computer analyses of a simple model.