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¹ Department of Civil Engineering and Joint Injury and Arthritis Research Group² Department of Physiology and Biophysics, The University of Calgary, Calgary, Alberta, Canada T2N 4 N1

The electrophysiological properties of acutely isolated canine articular chondrocytes have been characterized using patch-clamp methods. The ‘steady-state’ current–voltage relationship (I–V) of single chondrocytes over the range of potentials from –100 to +40 mV was highly non-linear, showing strong outward rectification positive to the zero-current potential. Currents activated at membrane potentials negative to –50 mV were time independent, and the I–V from –100 to –60 mV was linear, corresponding to an apparent input resistance of 9.3 ± 1.4 G (n= 23). The outwardly rectifying current was sensitive to the K⁺ channel blocking ion tetraethylammonium (TEA), which had a 50% blocking concentration of 0.66 mM (at +50 mV). The ‘TEA-sensitive’ component of the outwardly rectifying current had time- and membrane potential-dependent properties, activated near –45 mV and was half-activated at –25 mV. The reversal potential of the ‘TEA-sensitive’ current with external K⁺ concentration of 5 mM and internal concentration of 145 mM, was –84 mV, indicating that the current was primarily carried by K⁺ ions. The resting membrane potential of isolated chondrocytes (–38.1 ± 1.4 mV; n= 19) was depolarized by 14.8 ± 0.9 mV by 25 mM TEA, which completely blocked the K⁺ current of these cells. These data suggest that this voltage-sensitive K⁺ channel has an important role in regulating the membrane potential of canine articular chondrocytes.

(Received 27 November 2003; accepted after revision 10 March 2004; first published online 12 March 2004)
Corresponding author R. B. Clark: Department of Physiology and Biophysics, The University of Calgary, Calgary, Alberta, Canada T2N 4N1. Email: rclar{at}ucalgary.ca

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