Acidification and sodium entry in frog skin epithelium

Area of Science:

• Physiology
• Comparative Physiology
• Epithelial Transport

Background:

• The relationship between external acidification and sodium (Na+) uptake in frog skin is complex.
• Previous in vivo studies suggested a correlation between net Na+ absorption and net acidification.

Purpose of the Study:

• To investigate the relationship between external acidification and Na+ uptake in isolated frog skin (Rana catesbeiana, Rana temporaria, and Caudiververa caudiververa).
• To determine the factors controlling acidification in frog skin epithelium.

Main Methods:

• Utilized the pH-stat technique to measure acidification under short-circuit and open-circuit conditions.
• Examined the effects of amiloride and varying external Na+ concentrations.
• Assessed the role of metabolically produced CO2 in acidification.

Main Results:

• External acidification in isolated frog skins is not directly coupled to Na+ or anion transport.
• Acidification can be inhibited by amiloride, but only at high external Na+ concentrations.
• Acidification rate is partially controlled by metabolic CO2 production.
• The in vivo correlation between Na+ absorption and acidification could not be replicated in vitro, even after salt depletion stress.

Conclusions:

• External acidification in isolated frog skin is a complex process not directly driven by Na+ or anion transport.
• Metabolic CO2 production plays a role in regulating frog skin acidification.
• The in vitro frog skin model does not replicate the in vivo relationship between Na+ absorption and acidification, suggesting other physiological factors are involved in whole animals.