Characterization of the Rapidly Activating Delayed Rectifier Potassium Current, I Kr, in HL-1 Mouse Atrial Myocytes

Department of Physiology, Shiga University of Medical Science, Otsu, Japan.
Journal of Membrane Biology (Impact Factor: 2.46). 06/2010; 235(2):73-87. DOI: 10.1007/s00232-010-9257-2
Source: PubMed


HL-1 is the adult murine cardiac cell line that can be passaged repeatedly in vitro without losing differentiated phenotype. The present study was designed to characterize the rapidly activating delayed rectifier potassium current, I (Kr), endogenously expressed in HL-1 cells using the whole-cell patch-clamp technique. In the presence of nisoldipine, depolarizing voltage steps applied from a holding potential of -50 mV evoked the time-dependent outward current, followed by slowly decaying outward tail current upon return to the holding potential. The amplitude of the current increased with depolarizations up to 0 mV but then progressively decreased with further depolarizations. The time-dependent outward current as well as the tail current were highly sensitive to block by E-4031 and dofetilide (IC(50) of 21.1 and 15.1 nM, respectively) and almost totally abolished by micromolar concentrations of each drug, suggesting that most of the outward current in HL-1 cells was attributable to I (Kr). The magnitude of I (Kr) available from HL-1 cells (18.1 +/- 1.5 pA pF(-1)) was sufficient for reliable measurements of various gating parameters. RT-PCR and Western blot analysis revealed the expression of alternatively spliced forms of mouse ether-a-go-go-related genes (mERG1), the full-length mERG1a and the N-terminally truncated mERG1b isoforms. Knockdown of mERG1 transcripts with small interfering RNA (siRNA) dramatically reduced I (Kr) amplitude, confirming the molecular link of mERG1 and I (Kr) in HL-1 cells. These findings demonstrate that HL-1 cells possess I (Kr) with properties comparable to those in native cardiac I (Kr) and provide an experimental model suitable for studies of I (Kr) channels.

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    • "As noted, we have observed marked variation in the magnitude of outward K+ currents in HL-1 cells under these conditions. Indeed, we have been able to elicit robust Ca2+ transients in otherwise quiescent cells by perfusing the cells with an inhibitor of the delayed-rectifier K+ channels (E-4031, 10 μM; Graves and Wondergem, unpublished observations); which are prevalent in HL-1 cells [8,33]. Thus, variation among HL-1 cells in the strength of repolarizing K+ current during action potentials or in cells at rest may account for the different rates and amplitudes of Ca2+ transients as well as [Ca2+i. "
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