Potassium transport in isolated guinea pig ileum

¹ Department of Pharmacology, School of Medicine, Vanderbilt University, Nashville, Tennessee

A study was carried out to characterize the transport of potassium ions across the smooth muscle membrane of the isolated guinea pig ileum. The relative magnitudes of unidirectional ion fluxes were followed by employing the radioactive tracer K⁴². In unstimulated tissues both the efflux and influx of potassium were found to be proportional to the total quantities of exchangeable ion present in the tissue and in the surrounding medium respectively. The addition of approximately 7.5 x 10^–6 m pilocarpine, a concentration which produced a maximal contraction of longitudinal smooth muscle, increased potassium efflux about 100–150%, whereas potassium influx was markedly impeded. Cocaine (about 9 x 10^–4 m) blocked the enhancement of potassium efflux induced by pilocarpine, but did not alter potassium efflux in the untreated tissue. The data suggest that the movements of potassium in excited smooth muscle fibers reflect, to a large extent, a permeability change either to sodium ions or some other ion species which exert a depolarizing influence on the cell membrane.