Kinetics of ionic transport across frog skin: two concentration-dependent processes

Area of Science:

• Physiology
• Biochemistry
• Membrane Transport

Background:

• Understanding ion transport in amphibian skin is crucial for osmoregulation.
• The frog skin model (Rana esculenta) is widely used to study epithelial transport.

Purpose of the Study:

• To characterize the kinetics of sodium and chloride influx in isolated frog skin.
• To elucidate the mechanisms underlying ion transport at varying external concentrations.

Main Methods:

• Measurement of sodium and chloride influxes across isolated frog skin.
• Analysis of transport kinetics using Michaelis-Menten models at diverse ionic concentrations.

Main Results:

• Sodium transport exhibits two Michaelis-Menten components, with a high-affinity system below 4 meq external sodium.
• Chloride transport also shows two saturating components, with a high-affinity system distinct from sodium's at low concentrations.
• At higher concentrations (>4 meq), a linked, low-affinity transport system for sodium and chloride emerges.

Conclusions:

• Low external ion concentrations involve high-affinity, potentially countertransport systems (Na+/H+ and Cl-/HCO3-).
• Higher external concentrations activate a coupled, lower-affinity transport system for sodium and chloride.
• These findings highlight the complex, concentration-dependent regulation of ion transport in amphibian skin.