Intracellular pH and bicarbonate activities in rabbit colon

Area of Science:

• Physiology
• Cell Biology
• Gastroenterology

Background:

• The rabbit colon actively absorbs chloride ions.
• A proposed mechanism involves a chloride-bicarbonate exchange in the mucosal cell membrane.
• This exchange could lead to bicarbonate accumulation above electrochemical equilibrium.

Purpose of the Study:

• To test the chloride-bicarbonate exchange model in rabbit colon.
• To measure intracellular pH and bicarbonate activity.
• To determine if bicarbonate accumulation energizes chloride absorption.

Main Methods:

• Utilized a novel hydrogen ion-selective liquid membrane microelectrode for precise intracellular pH measurement.
• Employed conventional open-tipped microelectrodes to measure mucosal cell membrane electrical potential difference.
• Calculated intracellular bicarbonate activity and electrochemical potential gradients.

Main Results:

• Average intracellular pH was 6.9 +/- 0.1, indicating active hydrogen ion extrusion.
• Intracellular bicarbonate activity averaged 8 +/- 1 mM.
• The electrochemical potential gradient for bicarbonate across the mucosal membrane was -28 +/- 2 mV, showing accumulation above equilibrium.

Conclusions:

• Intracellular bicarbonate is concentrated above electrochemical equilibrium in rabbit colon epithelium.
• The energy from bicarbonate exiting the cell may drive chloride entry.
• This supports a mechanism where bicarbonate accumulation energizes active transepithelial chloride absorption.