Adaptation to respiratory acidosis in the turtle bladder

Area of Science:

• Physiology
• Cell Biology
• Renal Function

Background:

• Respiratory acidosis, induced by elevated partial pressure of carbon dioxide (pCO2), affects physiological processes.
• The turtle bladder is a model for studying ion transport and cellular adaptation.
• Carbonic anhydrase plays a crucial role in acid-base balance and ion secretion.

Purpose of the Study:

• To investigate the effects of in vivo respiratory acidosis on turtle bladder function and cell morphology.
• To determine if acidosis alters hydrogen ion (H+) or bicarbonate ion (HCO3-) secretion rates.
• To examine changes in carbonic anhydrase-expressing cells and their subtypes.

Main Methods:

• Turtles were exposed to hypercapnic chambers to induce respiratory acidosis for 4 and 48 hours.
• Blood pH, pCO2, and bicarbonate levels were measured.
• In vitro H+ secretion was assessed using reverse short-circuit current, and HCO3- secretion using pH stat.
• Fluorescence microscopy and specific stains (6-carboxyfluorescein, rhodamine 123, acridine orange, 3,3'-diethyloxacarbocyaninine iodide, NBD-taurine) were used to analyze cell morphology and carbonic anhydrase subtypes.

Main Results:

• Respiratory acidosis significantly lowered blood pH and elevated pCO2.
• In vitro H+ secretion increased significantly after 48 hours of acidosis.
• The total number of carbonic anhydrase cells increased, but HCO3(-)-secreting (beta subtype) cells did not.
• In vitro exposure to 1% CO2 increased H+ secretion and carbonic anhydrase cells, which was blocked by SITS.

Conclusions:

• In vivo respiratory acidosis enhances H+ secretion in the turtle bladder.
• CO2 exposure appears to shift mucosal cells towards a carbonic anhydrase phenotype, potentially increasing alpha-carbonic anhydrase cells.
• The adaptation may involve the production or recruitment of alpha-carbonic anhydrase cells rather than an increase in beta cells.