Abstract
The electrophysiological properties of voltagedependent potassium channels from freshlydissociated rat articular chondrocytes were studied.The resting membrane potential (-42.7±2.0 mV) wassignificantly depolarized by increasing concentrationsof external potassium. No change was observed whenexternal chloride concentration was varied. Additionof TEA, 4AP, α-Dendrotoxin and charybdotoxindepolarized resting membrane potential. Whole cellpatch clamp studies revealed the presence ofoutwardly rectifying currents whose kinetic andpharmacological properties suggest the expressionof voltage dependent potassium channels. Two kindsof currents were observed under the sameexperimental conditions. The first one, most frequentlyobserved (80%), starts activating near -50 mV, withV<sub>1/2</sub>=-18 mV, G<sub>max</sub>=0.30 pS/pF. The second kind wasobserved in only 10% of cases; It activates near -40mV, with<sub>1/2</sub>=+28.35 mV, G<sub>max</sub>=0.28 pS/pF pA/pF anddoes not inactivates. Inactivating currents weresignificantly inhibited by TEA (IC<sub>50</sub>=1.45 mM), 4AP(IC<sub>50</sub>=0.64 mM), CTX (IC<sub>50</sub>≈10 nM), α-Dendrotoxin(IC<sub>50</sub> < 100 nM) and Margatoxin (IC<sub>50</sub>=28.5 nM). Theseresults show that rat chondrocytes express voltagedependent potassium currents and suggest a role ofvoltage-dependent potassium channels in regulatingmembrane potential of rat chondrocytes.
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