Potassium microclimate at the mucosal surface of the proximal and the distal colon of guinea pig
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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.
Key wordsGuinea pig Colon Potassium Microclimate Mucus layer Preepithelial barrier
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