Characterization of a delayed rectifier potassium current in chicken growth plate chondrocytes.
With the use of the whole cell arrangement of the patch-clamp technique, an outward-directed time-dependent potassium current was identified in cultured chicken growth plate chondrocytes. This delayed rectifier potassium current (IK) activated with a sigmoidal time course during voltage steps to potentials positive to -40 mV. The half-maximal voltage required for current activation was determined to be -8 mV. The reversal potential (Erev) for IK, measured using deactivating tail currents, was -72 mV in the presence of 140 mM internal and 5 mM external [K+] solutions. Changes in external [K+] caused Erev to shift in a manner expected for a potassium-selective channel. In addition, increasing external [K+] from 5 to 50 mM caused the slope conductance of the tail currents to increase twofold. The chondrocyte IK was inhibited by the potassium-channel blocker 4-aminopyridine (4-AP) at concentrations of 0.5-4 mM and by the scorpion venom toxin charybdotoxin (CTX; 10 nM) but was unaffected by 10 mM tetraethylammonium (TEA). Addition of 20 microM ZnCl2 reduced IK in a voltage-dependent manner with the greatest inhibition found to occur at potentials near the threshold for current activation. Reduction of IK by ZnCl2 was accompanied by a slowing in the kinetics of IK activation. On the basis of the gating and pharmacological properties of this current, it is suggested that the chondrocyte channel belongs to a superfamily of K+ channels found in bone and immune system cells. The chondrocyte K+ channel may contribute to the unusually high [K+] found in the extracellular fluid of growth plate cartilage.
Walsh
K B
KB
Department of Pharmacology, University of South Carolina School of Medicine, Columbia 29208.
Cannon
S D
SD
Wuthier
R E
RE
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002356:Cartilage / Q000166:cytology / Q000502:physiology*; D002478:Cells, Cultured; D018999:Charybdotoxin; D002645:Chickens; D002712:Chlorides / Q000494:pharmacology; D004553:Electric Conductivity; D006132:Growth Plate / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000502:physiology*; D012604:Scorpion Venoms / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology; D017967:Zinc Compounds
D002712:Chlorides; D012604:Scorpion Venoms; D017967:Zinc Compounds; D018999:Charybdotoxin; C016837:zinc chloride; D015761:4-Aminopyridine; D015032:Zinc; D011188:Potassium