Potassium activity and plasma membrane potentials in epithelial cells of toad bladder

Area of Science:

• Physiology
• Cell Biology
• Biophysics

Background:

• Intracellular potassium activity (aki) and membrane potentials are crucial for electrolyte transport.
• Understanding these parameters in toad bladder epithelium provides insights into epithelial function.

Purpose of the Study:

• To measure intracellular potassium activity (aki), mucosal and serosal membrane potentials (mEm, sEm), short-circuit current (Isc), and transepithelial potential difference in toad bladder epithelium.
• To investigate the effects of ouabain, rotenone, ethacrynic acid, vasopressin, and prostaglandin E1 on these parameters.

Main Methods:

• Utilized a potassium-sensitive liquid ion exchanger and microelectrodes for precise measurements.
• Measured aki, mEm, sEm, Isc, and transepithelial potential difference under basal and stimulated conditions.

Main Results:

• Basal aki was 41.2 +/- 0.5 mM, indicating significant bound or sequestered intracellular potassium.
• Serosal membrane potential (sEm) was lower than the potassium equilibrium potential (Eeq) and showed no direct relation.
• Vasopressin decreased aki and increased mEm; prostaglandin E1 increased aki and sEm. Ouabain and rotenone decreased aki, while ethacrynic acid affected Isc and potentials but not aki.

Conclusions:

• A substantial portion of intracellular potassium may be bound or sequestered within subcellular organelles.
• The observed changes in aki and membrane potentials provide valuable insights into the mechanisms of transcellular electrolyte transport in toad bladder epithelium.
• Hormonal regulation by vasopressin and prostaglandin E1 significantly impacts intracellular potassium dynamics and membrane potentials, influencing epithelial transport.