TWIK-2, an Inactivating 2P Domain K+ Channel

Abstract

We cloned human and rat TWIK-2 and expressed this novel 2P domain K ؉ channel in transiently transfected COS cells. TWIK-2 is highly expressed in the gastrointestinal tract, the vasculature, and the immune system. Rat TWIK-2 currents are about 15 times larger than human TWIK-2 currents, but both exhibit outward rectification in a physiological K ؉ gradient and mild inward rectification in symmetrical K ؉ conditions. TWIK-2 currents are inactivating at depolarized potentials, and the kinetic of inactivation is highly temperature-sensitive. TWIK-2 shows an extremely low conductance, which prevents the visualization of discrete single channel events. The inactivation and rectification are intrinsic properties of TWIK-2 channels. In a physiological K ؉ gradient, TWIK-2 is half inhibited by 0.1 mM Ba 2؉ , quinine, and quinidine. Finally, cysteine 53 in the M1P1 external loop is required for functional expression of TWIK-2 but is not critical for subunit self-assembly. TWIK-2 is the first reported 2P domain K ؉ channel that inactivates. The base-line, transient, and delayed activities of TWIK-2 suggest that this novel 2P domain K ؉ channel may play an important functional role in cell electrogenesis.

Molecular Background of Leak K+Currents: Two-Pore Domain Potassium Channels

“…The current deviated from that of an ideal background channel as the activity was influenced by the membrane potential. About 50% of TWIK-2 inactivated slowly ( ϳ2 s) at strong depolarization (steady-state half inactivation at ϩ65 mV) (270), while the remaining fraction showed background K ϩ current properties (270). The inactivation was also modified by the extracellular K ϩ concentration.…”

“…Coexpression of TWIK-1 and TWIK-2 subunits also failed to induce K ϩ current (279). Interestingly, rat TWIK-2 produced 15-fold higher currents than the human channel in COS-7 cells; thus rat TWIK-2 was more readily characterized (270). According to these (sometimes contradictory) reports, the expression of TWIK-2 may also be limited in the different expression systems (with the possible exception of rat TWIK-2).…”

A disulphide-linked heterodimer of TWIK-1 and TREK-1 mediates passive conductance in astrocytes

“…Previous studies showed that a disulphide bridge is not required for the formation of TWIK-2 (ref. 28) or TASK-2 (ref. 29) homodimers.…”

Glucose Inhibition Persists in Hypothalamic Neurons Lacking Tandem-Pore K+Channels

“…They are only moderately inhibited by Ba 2ϩ , the most sensitive being TWIK1 (Kcnk1, K 2P 1.1) and TWIK2 (KCNK6, K 2P 6.1), with Ba 2ϩ concentrations inhibiting 50% of the max currents (IC 50 ) around 100 M (Lesage et al, 1996;Patel et al, 2000). Ba 2ϩ IC 50 for TASK1 and TASK3 are much more important and comprised between 300 M and 3 mM (for review, see Goldstein et al, 2005).…”