EFFECTS OF OUABAIN ON ELECTRICAL COUPLING OF RABBIT ATRIAL MUSCLE FIBERS

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The effects of ouabain on passive electrical properties of isolated rabbit atrial muscle fibers (crista-terminalis) were investigated. The space constant as well as the time constant of the crista-terminalis was determined using the partition method of Kamiyama and Matsuda based on the cable equation pro-posed by Hodgkin and Rushton. Ouabain treatment for 30 minutes at a lower concentration (2 × 10^-7M), caused no significant change in the space constant and time constant of the crista-terminalis. After ouabain treatment for 30 minutes at a higher concentration (1 × 10<-6>M), the space constant of the crista-terminalis was reduced significantly, whereas the time constant was not affected. An apparent reduction in the resting membrane potential and in the amplitude of action potential was also observed at the higher concentration of ouabain. These effects of ouabain on passive electrical properties of the crista-terminalis are most likely explained by the increase of its axial resistance (electrical uncoupling) due to intracellular calcium accumulation resulting from inhibition of the membrane sodium pump. This suggests that such an electrical uncoupling may play an important role in the intra-atrial conduction disturbance by cardiac glycosides.