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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Quantitative analysis of voltage-gated potassium currents from primary equine (Equus caballus) and elephant (Loxodonta africana) articular chondrocytes

Faculty of Veterinary Science, University of Liverpool, Liverpool, United Kingdom

Submitted 19 October 2004 ; accepted in final form 13 March 2005

In this comparative study, we have established in vitro models of equine and elephant articular chondrocytes, examined their basic morphology, and characterized the biophysical properties of their primary voltage-gated potassium channel (Kv) currents. Using whole cell patch-clamp electrophysiological recording from first-expansion and first-passage cells, we measured a maximum Kv conductance of 0.15 ± 0.04 pS/pF (n = 10) in equine chondrocytes, whereas that in elephant chondrocytes was significantly larger (0.8 ± 0.4 pS/pF, n = 4, P 0.05). Steady-state activation parameters of elephant chondrocytes (V = –22 ± 6 mV, k = 11.8 ± 3 mV, n = 4) were not significantly different from those of horse chondrocytes (V = –12.5 ± 4.3 mV, k = 12 ± 2, n = 10). This suggests that there would be slightly more resting Kv activation in elephant chondrocytes than in their equine counterparts. Kinetic analysis revealed that both horse and elephant chondrocyte Kv currents had similar activation and inactivation parameters. Pharmacological investigation of equine chondrocyte Kv currents showed them to be powerfully inhibited by the potassium channel blockers tetraethylammonium and 4-aminopyridine but not by dendrotoxin-I. Immunohistochemical studies using polyclonal antibodies to Kv1.1–Kv1.5 provided evidence for expression of Kv1.4 in equine chondrocytes. This is the first electrophysiological study of equine or elephant chondrocytes. The data support the notion that voltage-gated potassium channels play an important role in regulating the membrane potential of articular chondrocytes and will prove useful in future modeling of electromechanotransduction of fully differentiated articular chondrocytes in these and other species.

cartilage; dendrotoxin; potassium channel; membrane potential; immunohistochemistry

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