Possible epithelial sodium channels visualized by freeze-fracture

Area of Science:

• Avian physiology
• Epithelial transport
• Molecular biology

Background:

• The coprodeum is a key site for sodium (Na+) reabsorption in birds.
• Dietary sodium levels significantly influence ion transport in avian epithelia.

Purpose of the Study:

• To investigate the effect of low dietary sodium on Na+ transport in the hen coprodeum.
• To identify structural changes in the coprodeal epithelium associated with altered Na+ absorption.

Main Methods:

• Measurement of Na+ influx and Na+-diffusion potentials.
• Analysis of luminal cell membrane structure using freeze-fracture electron microscopy.

Main Results:

• A low Na+ diet induced significant Amiloride-sensitive Na+ absorption in the coprodeum.
• Freeze-fracture revealed a marked increase in rod-shaped particles in the luminal membrane of principal cells from birds on a low Na+ diet.
• These particles were virtually absent in birds on a high Na+ diet.

Conclusions:

• Dietary sodium restriction triggers the formation of specific Na+ channels in the hen coprodeum's luminal membrane.
• These newly formed Na+ channels are responsible for the enhanced Na+ influx and absorption observed under low Na+ conditions.
• The coprodeum efficiently adapts its structure to regulate Na+ balance in response to dietary intake.