Basolateral membrane potential of a tight epithelium: ionic diffusion and electrogenic pumps

Area of Science:

• Physiology
• Membrane Transport
• Renal Physiology

Background:

• The basolateral membrane of the rabbit urinary bladder plays a crucial role in ion transport and maintaining cellular homeostasis.
• Understanding the specific ion contributions to membrane potential and conductance is essential for elucidating renal function.

Purpose of the Study:

• To investigate the roles of specific ions (potassium, chloride, sodium) in the basolateral membrane potential and conductance of the rabbit urinary bladder.
• To identify and characterize an electrogenic active transport process at the basolateral membrane.

Main Methods:

• Utilized conventional and ion-specific microelectrode techniques to measure intracellular ion activities and membrane potentials.
• Employed the polyene antibiotic nystatin to assess active transport mechanisms by altering apical membrane permeability.
• Analyzed ion selectivity and permeability ratios using the Goldman-Hodgkin-Katz equation.

Main Results:

• Intracellular potassium (K+) and chloride (Cl-) concentrations were determined, with Cl- in electrochemical equilibrium but K+ not.
• The basolateral membrane exhibited selective permeability, with a low sodium to potassium permeability ratio (PNa/PK = 0.044) and a chloride to potassium permeability ratio (PCl/PK = 1.17).
• A ouabain-sensitive, intracellular Na+-dependent hyperpolarization of the basolateral membrane was observed, indicating active transport.

Conclusions:

• The basolateral membrane potential is primarily a diffusion potential driven by K+ and Cl- permeability.
• Intracellular K+ is actively maintained against its electrochemical gradient.
• An electrogenic, ouabain-sensitive active transport system, likely involving Na+, is present at the basolateral membrane of the rabbit urinary bladder.