Bicarbonate absorption by in vitro amphibian small intestine

Area of Science:

• Gastrointestinal Physiology
• Renal and Epithelial Transport
• Comparative Physiology

Background:

• The jejunum plays a crucial role in nutrient and electrolyte absorption.
• Understanding the mechanisms of bicarbonate absorption is vital for comprehending acid-base balance in the gut.

Purpose of the Study:

• To investigate the electrogenic absorption of bicarbonate (HCO3-) in the Amphiuma jejunum.
• To elucidate the specific transport mechanisms involved in jejunal HCO3- absorption.

Main Methods:

• Isolated jejunal segments from Amphiuma were bathed in chloride-free media.
• Electrical potentials and bidirectional isotope fluxes were measured under short-circuit conditions.
• Bicarbonate absorption rate was assessed using pH-stat titration and influenced by various inhibitors and ion substitutions.

Main Results:

• Jejunal segments generated a serosa-negative potential in the presence of HCO3-, indicating anion absorption.
• Short-circuit current and residual flux were consistent with active HCO3- absorption, unaffected by Na+ or Cl- replacement.
• Acetazolamide, anoxia, and 2,4-dinitrophenol inhibited both alkalinization and short-circuit current, while ouabain and K+ removal reduced absorption.

Conclusions:

• The Amphiuma jejunum actively absorbs HCO3- through an electrogenic mechanism.
• This process does not involve sodium-hydrogen exchange and is sensitive to metabolic inhibitors and ion gradients.
• Findings contribute to understanding intestinal ion transport and acid-base regulation in vertebrates.