Modulation of potassium channel gating by coexpression of Kv2.1 with regulatory Kv5.1 or Kv6.1 α-subunits

Abstract

We have determined the effects of coexpression of Kv2.1 with electrically silent Kv5.1 or Kv6.1 α-subunits in Xenopus oocytes on channel gating. Kv2.1/5.1 selectively accelerated the rate of inactivation at intermediate potentials (−30 to 0 mV), without affecting the rate at strong depolarization (0 to +40 mV), and markedly accelerated the rate of cumulative inactivation evoked by high-frequency trains of short pulses. Kv5.1 coexpression also slowed deactivation of Kv2.1. In contrast, Kv6.1 was much less effective in speeding inactivation at intermediate potentials, had a slowing effect on inactivation at strong depolarizations, and had no effect on cumulative inactivation. Kv6.1, however, had profound effects on activation, including a negative shift of the steady-state activation curve and marked slowing of deactivation tail currents. Support for the notion that the Kv5.1’s effects stem from coassembly of α-subunits into heteromeric channels was obtained from biochemical evidence of protein-protein interaction and single-channel measurements that showed heterogeneity in unitary conductance. Our results show that Kv5.1 and Kv6.1 function as regulatory α-subunits that when coassembled with Kv2.1 can modulate gating in a physiologically relevant manner.

Fluorescence measurements reveal stoichiometry of K + channels formed by modulatory and delayed rectifier α-subunits

“…Modulatory ␣-subunits influence all gating transitions investigated, with the most striking effects concerning inactivation (7,9,10,13). Thus, Kv9.3 is thought to selectively enhance closedstate inactivation and inhibit open-state inactivation of Kv2.1 (9), conferring to the heteromeric channels unique functional properties, and supporting a distinct role for them in electrical signaling.…”

“…When expressed in heterologous systems, modulatory ␣-subunits are unable to form homomeric channels but selectively interact with delayed rectifier subunits of the Kv2 subfamily to form heteromeric channels with unique functional properties that can be correlated with a number of native channels (e.g., 12). The functional properties of some of these heteromeric channels have been described in detail (9,12,13), and structural determinants of the regulatory function of modulatory ␣-subunits have been identified (14,15). However, the stoichiometry and geometric arrangement of their assembly with Kv2 subunits are unknown.…”

Kv2.1 and silent Kv subunits underlie the delayed rectifier K+ current in cultured small mouse DRG neurons

“…Thus, heterotetrameric K v 2/silent K v currents can be distinguished from homotetrameric K v 2 currents based on the voltage dependence of inactivation. In most cases, inactivation is slowed, and the voltage dependence is shifted into hyperpolarized direction, by up to 40 mV (3,11,13,20,25,28,29,37,42). In our case, both the ScTx-as well as anti-Kv2.1-sensitive current clearly displayed two components in their voltage dependence of inactivation (Figs.…”

Voltage-dependent K + channels in pancreatic beta cells: Role, regulation and potential as therapeutic targets

“…Subunits of these families have not been shown to form functional channels alone, but rather associate with members of the Kv1-4 families as modulator α-subunits (Table 1) [46,47,48,49,104]. Kv2.1 in particular, is often a target for these modulatory subunits, which have been shown to alter this channel's biophysical properties including kinetics of activation and inactivation, voltage-dependencies of activation and inactivation, and recovery times [47,48,105,106,107,108]. One recent study shows mRNA expression in human pancreas of Kv10.1 and 11.1, which can form heterotetrameric channels with, and modulate the properties of, Kv2.1 [47].…”