A voltage-dependent and a voltage-independent potassium channel in brown adipocytes of the rat.
Single-channel recordings of a voltage-dependent potassium channel in brown adipocytes of the rat confirm recordings of macroscopic currents. Single-channel conductance (gamma) is 8 pS at 20 degrees C in KF solution inside vs. a modified Ringer's solution outside. With KCl solution outside, gamma is 17 pS for outward currents and 21 pS for inward currents. The majority of the channels inactivate with a time constant around 200 ms; deactivation occurs within milliseconds. The channel is blocked by tetraethylammonium (TEA) with an inhibiting constant of 1.8 mM. The type of block is fast. Selectivity sequence for monovalent cations is K+ > Rb+ >> NH4+ >> Li+ > or = Na+ approximately Cs+. Cs+ at the outside causes a voltage-dependent block of inward currents. This channel is remarkably similar to the delayed rectifier of the F-type in the node of Ranvier. Occasionally, an additional K+ channel was found. This channel is voltage-insensitive, not blocked by 10 mM TEA, and has not been recorded in brown adipocytes before. Physiological relevance of this channel could be the steady-state membrane potential.
Russ
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Institut für Zoologie, Universität Regensburg, Germany.
Ringer
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Siemen
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D017667:Adipocytes / Q000502:physiology*; D002001:Adipose Tissue, Brown / Q000502:physiology*; D000818:Animals; D002414:Cations, Monovalent / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004553:Electric Conductivity; D005260:Female; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008962:Models, Theoretical; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D011189:Potassium Chloride / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002414:Cations, Monovalent; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D011189:Potassium Chloride