Fibrillation and potassium influx.

Absolute influx and efflux of potassium-42 have been measured in isolated rabbit atria during acetylcholine-induced fibrillation. The efflux of potassium was increased three to four times; influx was not changed. The data are interpreted as indicating that an inhibition of active K uptake is not involved in the initiation of fibrillation, and that the process results from a marked increase in Na permeability.