Energy dependence of urinary bicarbonate secretion in turtle bladder

Area of Science:

• Physiology
• Renal Physiology
• Cellular Physiology

Background:

• Turtle bladders secrete acid (H+).
• Addition of bicarbonate (HCO3-) to the serosal side reduces net acid secretion.
• The driving forces for downhill HCO3- flow require characterization.

Purpose of the Study:

• To investigate the metabolic energy dependence of HCO3- flow across the turtle bladder.
• To determine the relationship between HCO3- transport and acid secretion.

Main Methods:

• Isolated turtle bladders were used under short-circuited conditions.
• HCO3- flux was measured using pH stat titration with a 20-mM HCO3- gradient.
• Effects of deoxygenation, metabolic inhibitors (dinitrophenol, cyanide, deoxyglucose), and substrates (pyruvate) were examined.

Main Results:

• Deoxygenation significantly reduced HCO3- flux, indicating dependence on oxidative metabolism.
• Metabolic inhibitors (dinitrophenol, cyanide, deoxyglucose) also inhibited HCO3- flux.
• Pyruvate increased HCO3- flux in substrate-depleted bladders, an effect abolished by deoxygenation.

Conclusions:

• The majority of downhill HCO3- flow is dependent on metabolic energy, primarily from oxidative sources.
• This energy-dependent HCO3- flow is likely the electroneutral component of HCO3- secretion coupled to Cl- absorption.