Comparative views of electrophysiological parameters of large intestinal segments in pig, sheep, pony, guinea pig and rat.

This study gives a comparative analysis of certain electrical parameters across various segments of the large intestine in pigs, sheep, ponies, rats, and guinea pigs. Its findings reveal significant variations across different species and intestinal segments, providing a better understanding of the electrogenic transport mechanisms within the large intestine.

Study Overview

The study aimed to measure and compare two main electrophysiological parameters – short circuit current (ISC) and transepithelial conductance (gt) – across different parts of the large intestine, namely the caecum, and the proximal and distal colon in five different species.

• The ISC represents the electric current generated by the active transport of ions across the cell membrane, responsible for the electrogenic transport mechanisms.
• The gt measures how easily ions can move through the epithelial cells of the colon.

Findings

The observed differences in ISC values between different species and intestinal segments demonstrate the heterogeneity of transport mechanisms employed within the large intestine.

• In certain parts of the large intestine, including the caecum in pigs, sheep and ponies, as well as the proximal colon in guinea pigs and all segments of the rat hindgut, there were no significant indications of a high level of electrogenic sodium (Na) transport.
• However, in all other intestinal segments, the application of amiloride (a sodium transport inhibitor) caused a marked decrease in ISC, indicating a higher level of electrogenic Na transport.
• Electrogenic Na transport appears to be the highest in the distal colon of sheep and in both the proximal and distal colon of pigs. Guineas pigs and pony’s distal colon also showed significant, but somewhat lower, levels.

The results revealed that the epithelium of the pony’s caecum has the lowest transepithelial conductance (gt), meaning it allows the least amount of ions to pass through.

• Sheep was the only exception where gt values were considerably different from other species.
• The rat proximal colon, on the other hand, had the highest conductance, allowing ions to pass through more freely than any other tested segment or species.
• In pigs, sheep, and ponies, the gt values were similar in both the proximal and distal colon. Guinea pig’s values were slightly lower, while rat’s values were much lower.