Regulatory volume decrease in a renal distal tubular cell line (A6). I. Role of K+ and Cl-

Area of Science:

• Cell Physiology
• Epithelial Transport
• Ion Channel Function

Background:

• A6 epithelial cells are a model system for studying cell volume regulation.
• Understanding the mechanisms of regulatory volume decrease (RVD) is critical for cell homeostasis.
• The role of specific ions and conductive pathways in RVD requires further elucidation.

Purpose of the Study:

• To investigate the ion conductances involved in regulatory volume decrease (RVD) in A6 epithelial cells.
• To identify the specific ion transporters and channels facilitating cell volume regulation.
• To characterize the conductive pathways for chloride and potassium excretion during osmotic challenges.

Main Methods:

• Measurement of cell thickness (Tc) to monitor cell volume changes.
• Exposure to reduced basolateral osmolality (260 to 140 mosmol/kg) with transepithelial Na+ transport inhibited by amiloride.
• Ion substitution experiments (Cl-, SO4(2-), gluconate, NO3(-)) and application of channel blockers (NPPB, Ba2+, quinine).

Main Results:

• Regulatory volume decrease (RVD) was observed in Cl--containing media but was reduced with SO4(2-) or gluconate substitution.
• Chloride (Cl-) excretion through a conductive pathway, insensitive to NPPB, was implicated in RVD.
• Potassium (K+) excretion via conductive pathways, blocked by Ba2+ and quinine, and influenced by membrane potential, was essential for RVD.

Conclusions:

• Cell volume regulation in A6 cells is mediated by conductive pathways for both chloride and potassium excretion.
• A Cl- conductive pathway, insensitive to NPPB, plays a significant role in RVD.
• Apical K+ conductive pathways, modulated by basolateral membrane potential, are critical for efficient RVD.