Submitted on October 19, 2004
Accepted on March 13, 2005
Quantitative analysis of voltage-gated potassium currents from primary equine (Equus caballus) and elephant (Loxodonta africana) articular chondrocytes
A. Mobasheri1, T. C Gent1, M. D Womack1, S. D Carter1, P. D Clegg1, and R. Barrett-Jolley1*
1 Department of Veterinary Preclinical Sciences, Faculty of Veterinary Science, University of Liverpool, Liverpool, United Kingdom
* To whom correspondence should be addressed. E-mail: RBJ{at}liverpool.ac.uk.
In this comparative study, we have established in vitro models of both 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±0.04pS/pF (n=10) in equine chondrocytes, whereas that of elephant chondrocytes was significantly larger (0.8±0.4pS/pF, n =4, p
0.05). Steady-state activation parameters of elephant chondrocytes (V1/2 -22±6mV, k 11.8±3mV, n=4) were not significantly different to those of horse chondrocytes (V1/2 -12.5±4.3mV, k 12±2, n) =10). This suggests that there would be slightly more resting Kv activation in elephant chondrocytes than their equine counterparts. Kinetic analysis revealed both horse and elephant chondrocyte Kv currents had similar activation and inactivation parameters (with voltage steps to +30mV: approximately 3ms activation, >1s for inactivation). Pharmacological investigation of equine chondrocyte Kv currents showed them to be powerfully inhibited by the potassium channel blockers TEA and 4-AP (dissociation constants of 2.6±0.5mM
n=6, and 1.3±0.7mM respectively
n=5), but not dendrotoxin-I. Immunohistochemical studies using polyclonal antibodies to Kv1.1, Kv1.2, Kv1.3, Kv1.4 and 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 presented here 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 modelling of electro-mechanotransduction of fully differentiated articular chondrocytes in these and other species.
