Acid- and Volume-Sensitive Chloride Currents in Human Chondrocytes

Area of Science:

• Cell biology
• Physiology
• Biochemistry

Background:

• Chondrocytes maintain cell volume (CV) and pH despite environmental changes.
• Osteoarthritis (OA) involves cartilage dehydration and acidification, impairing chondrocyte function and survival.
• Volume-sensitive anion channels are implicated in OA pathogenesis.

Purpose of the Study:

• To investigate the impact of hypotonicity and extracellular acidification on chondrocyte chloride conductances and CV regulation.
• To elucidate the role of volume-sensitive outwardly rectifying (VSOR) and acid-sensitive outwardly rectifying (ASOR) Cl- currents in chondrocyte response to osmotic and pH stress.

Main Methods:

• Patch clamp electrophysiology to measure Cl- currents and membrane potentials in human chondrocytes.
• BCECF fluorescence for intracellular pH assessment.
• Coulter method for CV measurements and resazurin assay for cell viability.

Main Results:

• Hypotonic swelling activated VSOR currents and induced regulatory volume decrease (RVD), inhibited by DCPIB.
• Extracellular acidification (pH ≤ 5.0) activated ASOR currents, depolarized cells, and suppressed RVD.
• Under combined stress, VSOR and ASOR currents coactivated, with VSOR diminishing over time, leaving a pure ASOR phenotype.

Conclusions:

• Extracellular acidification impairs chondrocyte CV regulation by deactivating VSOR currents.
• Suppressed RVD and altered Cl- conductance under acidic conditions compromise chondrocyte viability.
• These findings highlight the contribution of impaired ion channel function to OA progression.