TBAK-1 and TASK-1, two-pore K + channel subunits: kinetic properties and expression in rat heart

Activation of the platelet-activating factor (PAF) receptor leads to a decrease in outward current in murine ventricular myocytes by inhibiting the TASK-1 channel. TASK-1 carries a background or "leak" current and is a member of the two-pore domain potassium channel family. Its inhibition is sufficient to delay repolarization, causing prolongation of the action potential duration, and in some cases, early after depolarizations. We set out to determine the cellular mechanisms that control regulation of TASK-1 by PAF. Inhibition of TASK-1 via activation of the PAF receptor is protein kinase C (PKC)-dependent. Using isoform-specific PKC inhibitor or activator peptides in patch clamp experiments, we now demonstrate that activation of PKC⑀ is both necessary and sufficient to regulate murine TASK-1 current in a heterologous expression system and to induce repolarization abnormalities in isolated myocytes. Furthermore, site-directed mutagenesis studies have identified threonine 381, in the C-terminal tail of murine TASK-1, as a critical residue in this regulation.Regulation of cardiac function depends on the appropriate cumulative activity of numerous ion channels in individual cardiomyocytes that are responsible for the sequential depolarization-repolarization cycle known as the action potential (AP). 1 Although the major currents contributing to the AP have been described (1), additional small currents at specific points of low conductance in the AP cycle are sufficient to induce repolarization abnormalities in isolated cells (2, 3) and therefore arrhythmias in situ. These arrhythmias may contribute to the electrical abnormalities that lead to sudden death after myocardial infarction, which persists as the number one cause of death in the United States. We have focused on one channel that has been proposed to contribute to cardiac arrhythmias, TASK-1, a member of the recently described family of two-pore domain potassium channels (4).The two-pore domain K channel family is composed of at least 15 different members. These channels are widely distributed in excitable tissue, primarily in the brain and heart, and in general are responsive to environmental cues such as temperature, pH, and stretch (5, 6). Several are also regulated by lipids such as arachidonic acid or platelet-activating factor (PAF) (7-9). PAF is an inflammatory phospholipid that has been linked to arrhythmogensis in isolated canine ventricular myocytes (10). We have recently shown that PAF regulates the TASK-1 channel and determined that the arrhythmogenic effect of the stable PAF analog, carbamyl-platelet-activating factor (C-PAF) in mouse cardiomyocytes, is due to the inhibition of TASK-1 current in a protein kinase C (PKC)-dependent manner (2).In this study, we elucidate the molecular mechanism of the C-PAF effect on TASK-1 current by identifying the ⑀ isoform of PKC (PKC⑀) as a critical component in PAFR signaling. In addition, using site-directed mutagenesis, we have tentatively identified the critical residue that is the target for PKC in the mu...

Section: Discussionmentioning

confidence: 99%

Activation of Protein Kinase C ϵ Inhibits the Two-pore Domain K+ Channel, TASK-1, Inducing Repolarization Abnormalities in Cardiac Ventricular Myocytes

Besana

Barbuti

Tateyama

et al. 2004

“…In this respect, TASK-3 differs from the other 2P K ϩ channels such as TASK-1/TBAK (26,27), TASK-2 (6), TRAAK (5), and also from most two-transmembrane-domain inward rectifier channels. The pronounced increase in open probability of TASK-3 with depolarization is also a novel finding.…”

Section: Properties Of Gptask-3 Currents In Xenopusmentioning

confidence: 99%

TASK-3, a Novel Tandem Pore Domain Acid-sensitive K+Channel

Rajan¹,

Wischmeyer²,

Liu³

et al. 2000

286

298

Tandem pore domain acid-sensitive K ؉ channel 3 (TASK-3) is a new member of the tandem pore domain potassium channel family. A cDNA encoding a 365-amino acid polypeptide with four putative transmembrane segments and two pore regions was isolated from guinea pig brain. An orthologous sequence was cloned from a human genomic library. Although TASK-3 is 62% identical to TASK-1, the cytosolic C-terminal sequence is only weakly conserved. Analysis of the gene structure identified an intron within the conserved GYG motif of the first pore region. Reverse transcriptase-polymerase chain reaction analysis showed strong expression in brain but very weak mRNA levels in other tissues. Cellattached patch-clamp recordings of TASK-3 expressed in HEK293 cells showed that the single channel currentvoltage relation was inwardly rectifying, and open probability increased markedly with depolarization. Removal of external divalent cations increased the mean single channel current measured at ؊100 mV from ؊2.3 to ؊5.8 pA. Expression of TASK-3 in Xenopus oocytes revealed an outwardly rectifying K ؉ current that was strongly decreased in the presence of lower extracellular pH. Substitution of the histidine residue His-98 by asparagine or tyrosine abolished pH sensitivity. This histidine, which is located at the outer part of the pore adjacent to the selectivity filter, may be an essential component of the extracellular pH sensor.

“…The Mechanism of Regulation of Acid-sensitive K2P Channels by Extracellular Acidification-Although the effects of extracellular acidification on TASK-1 and TASK-3 K ϩ channels have been extensively studied, the mechanism of how low pH o affects these channels is not well understood (2). Previous studies showed that lowered pH o changes single channel properties such as open probability and/or unitary current of TASK-1 and TASK-3 K ϩ channels (7,8,17). In this study, we show that lowered pH o also modulates the selectivity filter and then influences ion selectivity of TWIK-1, TASK-1, and TASK-3 K ϩ channels.…”

Section: Dynamic Ion Selectivity Of Acid-sensitive Twik and Task Kmentioning

confidence: 99%

“…Site-directed mutagenesis studies have identified the conserved histidine that is primarily responsible for the pH o sensitivity in TWIK-1, TASK-1, and TASK-3 K ϩ channels (4,7,8). Two related hypotheses have been proposed to interpret the mechanism of how lowered pH o results in inhibition of TASK-1 and TASK-3 K ϩ channels: a pore-blocking mechanism by protons or proton-induced inhibition of the channel gating (2), based on the effects of lowered pH o on open probability and/or unitary current (6,8,9,17). These hypotheses face a challenge in interpreting the [K ϩ ] o dependence of low pH o -induced inhibition of the channels (2).…”

mentioning

confidence: 99%

Acid-sensitive TWIK and TASK Two-pore Domain Potassium Channels Change Ion Selectivity and Become Permeable to Sodium in Extracellular Acidification

Zhang

Zhou

et al. 2012