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Human Kir2.1 channel carries a transient outward potassium current with inward rectification

  • Ion Channels, Receptors and Transporters
  • Published:
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Abstract

We have previously reported a depolarization-activated 4-aminopyridine-resistant transient outward K+ current with inward rectification (I to.ir) in canine and guinea pig cardiac myocytes. However, molecular identity of this current is not clear. The present study was designed to investigate whether Kir2.1 channel carries this current in stably transfected human embryonic kidney (HEK) 293 cells using whole-cell patch-clamp technique. It was found that HEK 293 cells stably expressing human Kir2.1 gene had a transient outward current elicited by voltage steps positive to the membrane potential (around −70 mV). The current exhibited a current–voltage relationship with intermediate inward rectification and showed time-dependent inactivation and rapid recovery from inactivation. The half potential (V 0.5) of availability of the current was −49.4 ± 2.1 mV at 5 mM K+ in bath solution. Action potential waveform clamp revealed two components of outward currents; one was immediately elicited and then rapidly inactivated during depolarization, and another was slowly activated during repolarization of action potential. These properties were similar to those of I to.ir observed previously in native cardiac myocytes. Interestingly, inactivation of the I to.ir was strongly slowed by increasing intracellular free Mg2+ (Mg2+ i , from 0.03 to 1.0, 4.0, and 8.0 mM). The component elicited by action potential depolarization increased with the elevation of Mg2+ i . Inclusion of spermine (100 μM) in the pipette solution remarkably inhibited both the I to.ir and steady-state current. These results demonstrate that the Mg2+ i -dependent current carried by Kir2.1 likely is the molecular identity of I to.ir observed previously in cardiac myocytes.

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Acknowledgment

The study was supported in part by a grant from Sun Chieh Yeh Heart Foundation. We appreciate Dr. Carol A. Vandenberg in University of California at Santa Barbara, CA, USA, for providing us human Kir2.1 channel gene. The authors thank Ms Hai-Ying Sun for the excellent technical support and Dr. G. Droogmans in the Department of Physiology, KU Leuven, Leuven, Belgium for the excellent Cabuf software which makes it possible to accurately calculate free Mg2+ concentrations in pipette solutions.

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Authors and Affiliations

  1. Department of Medicine and Research Centre of Heart, Brain, Hormone and Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China

    De-Yong Zhang, Chu-Pak Lau & Gui-Rong Li

  2. Department of Physiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China

    Gui-Rong Li

  3. Department of Medicine, L8-01, Laboratory Block, FMB, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China

    Gui-Rong Li

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  1. De-Yong Zhang
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Correspondence to Gui-Rong Li.

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Zhang, DY., Lau, CP. & Li, GR. Human Kir2.1 channel carries a transient outward potassium current with inward rectification. Pflugers Arch - Eur J Physiol 457, 1275–1285 (2009). https://doi.org/10.1007/s00424-008-0608-0

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