Plasma potassium concentration dependency of the potassium secretion in the mouse distal colon

Abstract

Potassium secretion in the colon involves the basolateral, bumetanide-sensitive Na⁺/K⁺/2Cl⁻ cotransporter and the apical TEA-sensitive K⁺ channel. This study investigated whether increasing plasma K⁺ concentration directly affects the rate of colonic K⁺ secretion, in addition to activating it indirectly through aldosterone. [Methods] Isolated distal colon of the mouse fed on a normal diet or high-K⁺ diet was mounted in Ussing chamber and short-circuit current (Isc) was determined. [Results] In animals fed on control diet, serosal bumetanide or increasing K⁺ concentration in the serosal side from 3 mM to 7 mM had no effect on Isc under basal condition. The addition of isoproterenol (5 μM, serosal) caused a decrease in Isc, a magnitude of which became larger as serosal K⁺ concentration was increased. The Isc decrease that was stimulated by isoproterenol and dependent on serosal K⁺ concentration was largely inhibited by mucosal TEA (10 mM), indicating that it represent K⁺ secretion. In animals fed on high-K⁺ diet, Isc under basal condition was significantly increased by serosal bumetanide, suggesting the presence of on-going K⁺ secretion. However the increase in serosal K⁺ concentration did not affect Isc. On the other hand, When K⁺ secretion was stimulated by isoproterenol, the increase in serosal K⁺ concentration stimulated TEA-sensitive Isc decrease. [Conclusion] Under certain conditions, the colonic K⁺ secretion is enhanced as the plasma K⁺ concentration increases, thereby probably contributing to the homeostatic K⁺ regulation in the body. [Jpn J Physiol 55 Suppl:S114 (2005)]