Functional expression of an inactivating potassium channel cloned from human heart.
Recently a putative K+ channel with homology to the Shaker family of potassium channels has been cloned from human ventricular myocardium. However, proof that the cDNA encodes a K+ channel requires appropriate translation and expression of a functional ion-selective channel. Therefore, expression of this putative human K+ channel DNA was attempted by cytoplasmic injections of in vitro transcribed cRNA into Xenopus laevis oocytes and screening by two-electrode voltage-clamp methods. This resulted in expression of voltage-gated channels that rapidly inactivated (time constant of inactivation, 47.6 +/- 3.6 msec; 0 mV; n = 10) and were at least 50 times more selective for K+ than Na+ (Na+/K+ permeability ratio of 0.02). The channels showed voltage-dependent activation (half-maximal voltage, -34 +/- 0.7 mV; n = 5), and 50% of the channels were inactivated within 2 seconds when the membrane potential was clamped near -60 mV (half-maximal voltage, -62 +/- 7 mV; n = 10). The expressed protein resulted in a K+ current that had many properties similar to the 4-aminopyridine-sensitive calcium-insensitive component of the cardiac transient outward current that is observed in native cardiac myocytes and thus may serve as one molecular substrate for this current.
Po
S
S
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN.
Snyders
D J
DJ
Baker
R
R
Tamkun
M M
MM
Bennett
P B
PB
D000818:Animals; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D015870:Gene Expression; D006321:Heart / Q000502:physiology*; D006801:Humans; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D014982:Xenopus laevis
D015221:Potassium Channels; D004247:DNA