Effect of acetylcholine on the passive electrical properties and intercellular electrical link in the sino-atrial node of the rabbit heart

Using the microelectrode technique in an isolated preparation of the sino-atrial (s.a.) region of the rabbit heart the authors have studied the effect of acetylcholine (ACh) an the passive electrical properties and intercellular electrical link with measurement of the the length constant of the decay in electrotonus (λ_e) and input resistance (R_in). It was established that ACh reduces λ_e and increases R_in. From analysis of the experimental data using the model of a thin-layer three-dimensional syncytium it is shown that ACh in concentrations of 10^-7, 10^-6 and 10^-5, m raises the resistance of the intracellular medium of the syncytium 1 · 25, 1 · 36 and 1 · 43 fold and reduces that of the electrogenic membrane 1 · 13, 1 · 12 and 1 · 23 fold respectively. It is concluded that ACh increases the resistance of the intercellular contacts in the s.a. node.