Modulation of antidiuretic hormone-dependent capacitance and water flow in toad urinary bladder

Area of Science:

• Physiology
• Cell Biology
• Membrane Transport

Background:

• Antidiuretic hormone (ADH) regulates water reabsorption in the kidney.
• Apical membrane area changes are hypothesized to mediate ADH-dependent water permeability.

Purpose of the Study:

• To investigate the relationship between ADH-dependent water permeability and apical membrane area changes.
• To examine how different conditions affect water flow and membrane capacitance.

Main Methods:

• Measurements of water flow (Jv) and capacitance (delta C) in toad urinary bladder.
• Experiments conducted under varying ADH concentrations, osmotic gradients, and chemical treatments (hydrazine, NH4Cl, CO2).
• Assessment of responses to 8-bromo-adenosine 3',5'-cyclic monophosphate (cAMP) and serosal Na removal.

Main Results:

• Water flow and capacitance changes were similar at low ADH concentrations but diverged at higher concentrations.
• The osmotic gradient influenced the decrease in capacitance at high ADH levels.
• Hydrazine and NH4Cl modulated water flow and capacitance differently, with NH4Cl's effect dependent on the osmotic gradient.
• Mucosal CO2 significantly inhibited both water flow and capacitance, and also blocked cAMP-induced responses.
• Serosal Na removal diminished cAMP-dependent water flow and capacitance.

Conclusions:

• Confirms a strong correlation between ADH-dependent water permeability and apical membrane capacitance.
• Suggests that under certain conditions, membrane can be retrieved from the apical surface without a corresponding decrease in water permeability.
• Highlights the complex regulatory mechanisms of water transport in response to ADH and other stimuli.