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Biophys J, July 2001, p. 125-136, Vol. 81, No. 1

Modulation of Kv1.5 Potassium Channel Gating by Extracellular Zinc

Shetuan Zhang, Steven J. Kehl, and David Fedida

Department of Physiology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada

Zinc ions are known to induce a variable depolarizing shift of the ionic current half-activation potential and substantially slow the activation kinetics of most K+ channels. In Kv1.5, Zn2+ also reduces ionic current, and this is relieved by increasing the external K+ or Cs+ concentration. Here we have investigated the actions of Zn2+ on the gating currents of Kv1.5 channels expressed in HEK cells. Zn2+ shifted the midpoint of the charge-voltage (Q-V) curve substantially more (~2 times) than it shifted the V1/2 of the g-V curve, and this amounted to +60 mV at 1 mM Zn2+. Both Q1 and Q2 activation charge components were similarly affected by Zn2+, which indicated free access of Zn2+ to channel closed states. The maximal charge movement was also reduced by 1 mM Zn2+ by ~15%, from 1.6 ± 0.5 to 1.4 ± 0.47 pC (n = 4). Addition of external K+ or Cs+, which relieved the Zn2+-induced ionic current reduction, decreased the extent of the Zn2+-induced Q-V shift. In 135 mM extracellular Cs+, 200 µM Zn2+ reduced ionic current by only 8 ± 1%, compared with 71% reduction in 0 mM extracellular Cs+, and caused a comparable shift in both the g-V and Q-V relations (17.9 ± 0.6 mV vs. 20.8 ± 2.1 mV, n = 6). Our results confirm the presence of two independent binding sites involved in the Zn2+ actions. Whereas binding to one site accounts for reduction of current and binding to the other site accounts for the gating shift in ionic current recordings, both sites contribute to the Zn2+-induced Q-V shift.

Biophys J, July 2001, p. 125-136, Vol. 81, No. 1
© 2001 by the Biophysical Society   0006-3495/01/07/125/12  $2.00


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