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This Article Full Text Full Text (PDF) All Versions of this Article: 295/5/H1867    most recent 433.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Imredy, J. P. Articles by Salata, J. J. Search for Related Content PubMed PubMed Citation Articles by Imredy, J. P. Articles by Salata, J. J.

Modeling of the adrenergic response of the human I_Ks current (hKCNQ1/hKCNE1) stably expressed in HEK-293 cells

Safety and Exploratory Pharmacology, Safety Assessment, Merck Research Laboratories, West Point, Pennsylvania

Submitted 24 April 2008 ; accepted in final form 28 July 2008

Stable coexpression of human (h)KCNQ1 and hKCNE1 in human embryonic kidney (HEK)-293 cells reconstitutes a nativelike slowly activating delayed rectifier K⁺ current (HEK-I_Ks), allowing β-adrenergic modulation of the current by stimulation of endogenous receptors in the host cell line. HEK-I_Ks was enhanced two- to fourfold by isoproterenol (EC₅₀ = 13 nM), forskolin (10 µM), or 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (50 µM), indicating an intact cAMP-dependent ion channel-regulating pathway analogous to the PKA-dependent regulation observed in native cardiac myocytes. Activation kinetics of HEK-I_Ks were accurately fit with a novel modified second-order Hodgkin-Huxley (H-H) gating model incorporating a fast and a slow gate, each independent of each other in scale and adrenergic response, or a "heterodimer" model. Macroscopically, β-adrenergic enhancement shifted the current activation threshold to more negative potentials and accelerated activation kinetics while leaving deactivation kinetics relatively unaffected. Modeling of the current response using the H-H model indicated that observed changes in gating could be explained by modulation of the opening rate of the fast gate. Under control conditions at nearly physiological temperatures (35°C), rate-dependent accumulation of HEK-I_Ks was observed only at pulse frequencies exceeding 3 Hz. Rate-dependent accumulation of I_Ks at high pulsing rate had two phases, an initial staircaselike effect followed by a slower, incremental accumulation phase. These phases are readily interpreted in the context of a heterodimeric H-H model with two independent gates with differing closing rates. In the presence of isoproterenol after normalizing for its tonic effects, rate-dependent accumulation of HEK-I_Ks appeared at lower pulse frequencies and was slightly enhanced (25%) over control.

slowly activating cardiac delayed rectifer potassium current; human embryonic kidney-293 cells; β-adrenergic modulation; KCNQ1; KCNE1