Potassium-induced contracture and calcium exchange in the guinea pig's taenia coli

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

High potassium (40 mm)-induced tension declined after calcium concentration in the medium (Ca₀) was reduced below 1.25 mm, reaching equilibrium level which was dependent on Ca₀. High K applied after reduction of Ca₀ (0.156–0.94 mm) caused a transient tension rise followed by decline to the same equilibrium level as above. In the presence of 2,4-dinitrophenol (0.3 mm), a transient contraction occurred after high K followed by a decline to a low equilibrium tension which was not dependent on Ca₀ (0.156–2.5 mm). Rate constants of Ca⁴⁵ outflow were not markedly affected by high K. Ca⁴⁵ uptake and exchangeable fraction of cellular Ca increased with high K. Results suggest the release of Ca during K contracture.