Active transport of the chloride ion by the colon - abstract

ABSTRACT

The present data represent some results of our continuing studies on the mechanisms of electrolyte transport in the colon. Trained dogs with chronic isolated segments of colon were used, and the transport of chloride ion was studied by instilling the following electrolyte solutions into the colon sodium chloride (154 mEq/L, 100 mEq/L), Mannitol (5 percent) choline choride (100 mEq/L), lithium chloride (100 mEq/L), lithium chloride (60 mEq/L) plus potassium chloride (40 mEq/L), lithium chloride (75 mEq/L) plus sodium bicarbonate (75 m Eq/L). All solutions were made isotonic whenever necessary by the addition of mannitol and all contained the non-absorbable maker polyethylene glycol (PEG). Samples of colonic fluid were taken at intervals over a six-hour period following the instillation of solution into the isolated colonic segment. The samples were analysed for Na, K, Cl, HCO3 - pH, osmolality and PEG. The electrical potential difference across the colon was measured in several experiments. Chloride ion transport was also studied following the administration of Diamax or Aldosterone, mucosa. There was no evidence of active water transport. The mucosa is normally electrically negative with respect to serosa; however, in the presence of choline chloride the mucosa becomes electrically positive with respect to serosa. Our data also show that the chloride ion is actively transported against both an electrical and a chemical gradient. In addition chloride can be transported in the absence of sodium, but in the presence of sodium can be transported more rapidly than that ion. Chloride transport is to some extent linked to sodium transport and also to bicarbonate transport (AU)