A large-conductance voltage-dependent potassium channel in cultured pig articular chondrocytes

Abstract

 The patch-clamp techniques were used to study voltage-dependent potassium channels in cultured pig articular chondrocytes. A predominant single-channel conductance of 125 pS was found. These channels were reversibly blocked by tetraethylammonium. In cell-attached patches, transient increases in the channel activity were observed, and defined as a switching between low and high activity modes (LAM and HAM). Open-time distributions could be described with two kinetics components (in LAM and HAM) having similar time constants (fast τ₁ and slow τ₂). In HAM, the area of the slow component was larger. The mean burst length was significantly longer in HAM than in LAM. In both modes, the burst-length distributions were fitted with a sum of three exponentials. In LAM and HAM, the time constants τ₁ and τ₂ were indistinguishable from those of the open-time distributions. The slowest time constant, τ₃, was strongly voltage dependent, and was significantly longer in HAM than in LAM. In both LAM and HAM, the ensemble currents were characterised by a rapid rising phase followed by fast and profound inactivation. The activation kinetics were similar, but the inactivation was faster in HAM. In the outside-out configuration no evidence for mode switching was found. The kinetics of the rising phase of the ensemble currents were also similar to those observed using the cell-attached configuration, but the channels did not inactivate. In the whole-cell configuration, the mode switching was not present. The inactivation time constant showed a large scattering, and was much slower than that measured in the cell-attached patch mode. These currents were blocked by tetraethylammonium and 4-aminopyridine. Our results indicate that intracellular factors are involved in controlling the mode switching and the kinetics of the inactivation of potassium channels in pig articular chondrocytes.