Electrogenic bicarbonate secretion in the turtle bladder: apical membrane conductance characteristics

Area of Science:

• Cell Physiology
• Ion Transport Mechanisms
• Epithelial Biology

Background:

• Electrogenic bicarbonate (HCO3-) secretion is linked to increased short-circuit current (Isc), apical membrane capacitance (Ca), and apical membrane conductance (Ga).
• The ionic basis for the increase in Ga and its regulatory role in HCO3- secretion remain to be fully elucidated.

Purpose of the Study:

• To investigate the ionic basis of the increased apical membrane conductance (Ga) during electrogenic bicarbonate secretion.
• To determine if changes in Ga regulate the rate of electrogenic bicarbonate secretion.

Main Methods:

• Utilized impedance analysis techniques to measure membrane electrical parameters in hemibladders.
• Stimulated electrogenic bicarbonate secretion using cyclic adenosine monophosphate (cAMP).
• Varied chloride concentrations in solutions and applied the anion channel blocker anthracene-9-carboxylic acid (9-AA).

Main Results:

• A significant apical chloride (Cl-) conductance was observed in control hemibladders.
• The cAMP-induced increase in Ga comprises a Cl(-)-conductive component and a HCO3- conductance.
• Anthracene-9-carboxylic acid (9-AA) reduced both Ga and Isc in cAMP-stimulated hemibladders.

Conclusions:

• Electrogenic bicarbonate secretion involves parallel apical conductances to Cl- and HCO3-.
• The apical membrane conductance (Ga) plays a crucial role in regulating the rate of electrogenic bicarbonate secretion (Isc).
• Changes in apical membrane ionic permeability, particularly for Cl- and HCO3-, are key to regulating bicarbonate secretion.