FIG. 2.

Temperature-dependent contribution of the Na⁺/K⁺ pump electrogenic current to the chondrocyte resting membrane potential. The superimposed I-V curves in (A) were generated using our published model of the chondrocyte resting potential as shown, assuming a temperature of 23°C and measured and estimated ionic concentrations within the chondrocyte matrix. The analogous superimposed I-V curves shown in (B) were generated using the same model after the Na⁺/K⁺ pump current was adjusted to pathophysiological temperature (37°C) based on a Q₁₀ of 3.0 and the channel-mediated background currents were adjusted using a Q₁₀ of 1.2. The two records of membrane potential in (C) illustrate the significant but relatively small effect of the electrogenic current due to the Na⁺/K⁺ pump at 23°C contrasted with the much larger hyperpolarization generated by this pump current at 37°C. As shown, the additional Na⁺/K⁺ pump current simulated at pathophysiological temperature in the chondrocyte matrix hyperpolarizes the chondrocyte resting membrane potential by ∼25 mV (approximately -67 mV at 23°C and approximately -92 mV at 37°C).