Acid secretion in isolated guinea pig colon.

Area of Science:

• Gastroenterology
• Physiology
• Cell Biology

Background:

• The colon's role in ion transport and acid-base balance is crucial for digestive health.
• Mechanisms of acid secretion in the distal colon are not fully elucidated.

Purpose of the Study:

• To investigate the mechanisms and localization of acid secretion in the guinea pig distal colon.
• To identify the transporters and enzymes involved in colonic acid secretion.

Main Methods:

• Ussing chamber experiments on isolated guinea pig distal colon segments.
• Measurement of acid secretion rates using pH stat systems.
• Pharmacological inhibition using methazolamide, ouabain, and vanadate; ion-free solutions were employed.

Main Results:

• Significant acid secretion (1.0-1.5 mumol X cm-2 X h-1) was observed in the middle and distal colon, absent proximally.
• Acid secretion was linked to serosal alkalinization, inhibited by carbonic anhydrase inhibitor methazolamide, and abolished by K+-free conditions.
• Mucosal H+-ATPase activity was indicated by inhibition with ouabain and vanadate, and maintained at low mucosal pH.

Conclusions:

• The guinea pig distal colon actively secretes acid, likely via CO2 hydration and subsequent H+ release.
• Carbonic anhydrase and an H+-ATPase sensitive to ouabain mediate this acid secretion.
• This finding highlights a novel physiological role for the distal colon in acid-base regulation.