Alkaline secretion by amphibian duodenum. I. General characteristics.

Area of Science:

• Physiology
• Gastroenterology
• Ion Transport

Background:

• The bullfrog duodenum's role in alkali secretion is not fully understood.
• Investigating the mechanisms of intestinal bicarbonate transport is crucial for understanding digestive physiology.

Purpose of the Study:

• To elucidate the mechanisms of alkaline secretion in the bullfrog proximal duodenum.
• To determine the ionic and energetic basis of duodenal alkali transport.

Main Methods:

• Ussing chamber technique applied to isolated bullfrog proximal duodenum.
• Measurement of alkalinization rates, electrical parameters (potential difference, short-circuit current), and responses to various inhibitors and ion substitutions.

Main Results:

• Bullfrog duodenum secretes alkali at a stable rate, significantly reduced by anoxia and 2,4-dinitrophenol, indicating active transport.
• Alkaline secretion depends on nutrient bicarbonate and is partially dependent on nutrient sodium, acting in a facilitatory role.
• Secretion is electrogenic, not mediated by chloride, and independent of luminal pH or nutrient pH.

Conclusions:

• The amphibian duodenum transports alkali via active and passive mechanisms.
• Electrogenic alkaline secretion is partially dependent on nutrient sodium and involves endogenous bicarbonate secretion.
• Mechanisms like Cl--HCO3- exchange are not involved in this process.