FIG. 1.

Modeling of the chondrocyte resting membrane potential and demonstration of the effects of temperature on the electrogenic current generated by the Na⁺/K⁺ pump in a human chondrocyte preparation. (A, B) Present an illustration of the structure and function of the electrogenic sodium-potassium ATPase whose role in chondrocyte electrophysiology is investigated here; each pump turnover results in 3 Na⁺ ions' expulsion from and 2 K⁺ ions' inclusion into the cell, generating a net outward current. (C) Shows an illustrated schematic of the mathematical model of the chondrocyte resting membrane potential used here, as previously published.³⁸ (D) Explores the steady-state voltage dependence of the electrogenic pump Na⁺/K⁺ pump current density, given through our previously published model.³⁸ Strong temperature dependence is revealed, and the steady-state current at healthy joint temperature (23°C, black trace), as well as at pathophysiological temperature (37°C, red trace), is illustrated. Both I-V curves also show the curvilinear waveform that is due to the intrinsic voltage dependence of the Na⁺/K⁺ pump in mammalian cells. Intracellular and extracellular ion concentrations as initial modeling conditions are assumed (as previously) to be those measured in synovial fluid (as shown in inset).