Interaction between cell sodium and the amiloride-sensitive sodium entry step in rabbit colon

Area of Science:

• Physiology
• Cell Biology
• Renal and Epithelial Physiology

Background:

• The short-circuit current (Isc) and transepithelial conductance (Gt) of the rabbit colon are affected by ouabain and amphotericin B.
• Amiloride-sensitive sodium (Na) entry is crucial for transepithelial Na transport.

Purpose of the Study:

• To investigate the regulation of the amiloride-sensitive Na entry step in rabbit colon.
• To elucidate the role of intracellular Na concentration in modulating Na transport.

Main Methods:

• Short-circuit current (Isc) and transepithelial conductance (Gt) measurements in rabbit colon.
• Exposure of Na-depleted tissues to 140 mM Na in the presence and absence of ouabain or amphotericin B.
• Analysis of amiloride-sensitive Na entry and its dependence on intracellular Na.

Main Results:

• Ouabain abolished Isc and decreased Gt, while amphotericin B increased both.
• Amiloride-sensitive Na entry was blocked by elevated intracellular Na in the presence of ouabain or amphotericin B.
• Sudden exposure of Na-depleted tissues to 140 mM Na caused a rapid increase and subsequent decline in amiloride-sensitive Isc and Gt, indicating a negative feedback mechanism regulated by intracellular Na.

Conclusions:

• The conductance of the amiloride-sensitive Na entry step is inversely regulated by intracellular Na concentration.
• A parallel cellular compartment with a large Na capacity likely mediates negative feedback on Na entry permeability.
• This system allows for rapid initiation and steady-state achievement of active transepithelial Na transport.