Potassium microclimate at the mucosal surface of the proximal and the distal colon of guinea pig

Abstract

K⁺ concentrations were measured with K⁺ sensitive liquid ion exchanger microelectrodes in situ and in vitro in the mucus layer at the luminal cell surface of the proximal and the distal colon in guinea pig.

In a first series of experiments K⁺ concentrations were increased in the luminal solution from 0 to 70 mmol·l⁻¹; the serosal K⁺ concentrations were kept in vitro at 5.4 mmol·l⁻¹. In the proximal colon mean K⁺ concentration in the microclimate was in vitro 7.9±3.5 mmol·l⁻¹, and independent from mucosal concentrations. In the distal colon in vitro, and in situ in the proximal as well as in the distal colon, K⁺ concentrations in the microclimate were increased slightly when K⁺ concentrations were elevated in the luminal solution up to 70 mmol·l⁻¹.

In a second series of in vitro studies K⁺ concentrations were also altered in the serosal fluid. In the proximal and in the distal colon K⁺ concentrations increased linearily with elevated K⁺ concentrations in the serosal solutions.

A temporarily interrupted mucosal blood flow resulted in a significant increase in the K⁺ concentration in the microclimate.

A paracellular shunt pathway and a high preepithelial diffusion barrier for K⁺ would explain the observed K⁺ concentrations in the microclimate at the luminal cell surface.