K⁴² and Cl³⁶ fluxes during ACh- and Ca-induced atrial fibrillation

¹ Department of Pharmacology, University of Mississippi School of Medicine, Jackson, Mississippi

K⁴² and Cl³⁶ fluxes are compared in fibrillation induced by ACh and Ca in isolated rabbit atria. An increased Na ion movement appears to be important in the initiation and maintenance of both types of arrhythmias. Inactivation of this Na movement could be the result of an increased K efflux and/or an increased Cl influx. Potassium appears to make the predominant contribution to Na inactivation initially in ACh-induced fibrillation. Data are presented which show that in Ca-induced fibrillation Cl influx is markedly increased over that seen in the ACh-induced arrhythmia. Potassium efflux is also increased in Ca-induced fibrillation but to a much less degree than in ACh-induced fibrillation. It was concluded that Cl plays a major role in Na inactivation in the Ca-induced arrhythmia and that Cl movement is extremely important in initiating and maintaining both arrhythmias.