External K⁺ relieves the block but not the gating shift caused by Zn²⁺ in human Kv1.5 potassium channels

Abstract

Changing the extracellular concentration of divalent cations can have dramatic effects on the behaviour of electrically excitable membranes as illustrated by the lowering or raising of the threshold for cell firing caused by hypo-or hypercalcaemia, respectively (Frankenhaeuser & Hodgkin, 1957). Voltage-clamp analyses have shown that the divalent cation-induced change of excitability can be linked to a shift of the voltage dependence of channel gating. For example, an elevation of the external concentration of Ca 2+ ([Ca 2+ ] o ) produces a depolarizing shift of the midpoint (V 1/2 ) of the activation curves of both voltage-gated Na + and K + channels of the squid giant axon (Hille et al. 1975;Hahin & Campbell, 1983 1. We used the whole-cell recording technique to examine the effect of extracellular Zn 2+ on macroscopic currents due to Kv1.5 channels expressed in the human embryonic kidney cell line HEK293.2. Fits of a Boltzmann function to tail current amplitudes showed that 1 mM Zn 2+ shifted the half-activation voltage from _10.2 ± 0.4 to 21.1 ± 0.7 mV and the slope factor increased from 6.8 ± 0.4 to 9.4 ± 0.7 mV. The maximum conductance in 1 mM Zn 2+ and with 3.5 mM K + o was 33 ± 7 % of the control value.3. In physiological saline the apparent K D for the Zn 2+ block was 650 ± 24 µM and was voltage independent. A Hill coefficient of 1.0 ± 0.03 implied that block is mediated by the occupation of a single binding site. 6. We propose that the gating shift and the block caused by Zn 2+ are mediated by two distinct sites and that the blocking site is located in the external mouth of the pore.

Zinc Inactivates Melastatin Transient Receptor Potential 2 Channels via the Outer Pore

“…The most common effect of extracellular Zn 2ϩ is allosteric modulation, potentiating or inhibiting channel activity (32,33). Examples are numerous, including K V (34,35), Na V (36,37), Ca V (38,39), ionotropic receptors for ␥-aminobutyric acid (40,41), glycine (42), 5-hydroxytryptamine (43), glutamate (44,45) and ATP (46 -48), two-pore K ϩ channels (49,50), acid-sensitive ion channels and epithelial Na ϩ channels (51,52), and TRPM1 channel (53).…”

SCAM analysis reveals a discrete region of the pore turret that modulates slow inactivation in Kv1.5

“…Inhibition of WT Kv1.5 by H ϩ or Zn 2ϩ is antagonized either by raising [K ϩ ] o or by the R487V mutation (25,51). Similarly, the [K ϩ ] o dependence of Kv1.5 H463G currents is mitigated by the R487V mutation as implied in Fig.…”

Episodic ataxia type 1 mutation F184C alters Zn2+-induced modulation of the human K+ channel Kv1.4-Kv1.1/Kvβ1.1

“…The molecular determinants of these binding sites are unknown. Recent studies of Kv1.5 channels have shown that Zn 2ϩ may act on two distinct binding sites, one of which is located within the pore turret (32,67,68). It is possible that at least one Zn 2ϩ binding site is also located within the pore turret of the Kv1.4-1.1 channel, since the amino acid sequence of this region is similar to that of the Kv1.5 channel.…”