Ion transport across amphibian lung

Area of Science:

• Physiology
• Comparative Biology
• Toxicology

Background:

• Amphibian lungs offer a simple model for studying epithelial transport.
• Alveolar epithelium dominates lung barrier permeability and bioelectric properties.

Purpose of the Study:

• To investigate the transport mechanisms of the amphibian alveolar epithelium.
• To determine the bioelectric properties and ion permeability of the frog lung.

Main Methods:

• Excised bullfrog lungs were mounted as planar sheets.
• Transmural electrical potential difference and resistance were measured.
• Unidirectional fluxes of various ions and molecules were assessed using short-circuit current analysis and voltage clamping.

Main Results:

• Frog lungs exhibited a transmural potential difference (20 mV) and resistance (700 omega cm2).
• Asymmetrical fluxes of 36Cl-, Br-, I-, and SCN- were observed, indicating active secretion.
• Net chloride flow matched short-circuit current and was inhibited by metabolic inhibitors, suggesting active transport.
• Other ions and molecules (Na+, K+, Ca+, HCO3-, TcO4-, SO42-, p-aminohippurate, gluconate, dinitrophenolate, water) showed passive diffusion patterns.

Conclusions:

• The frog alveolar epithelium actively secretes halide and pseudohalide anions.
• These findings aid in understanding lung barrier function and the impact of airborne environmental agents on pulmonary health.