Differential Sensitivity of Kir2 Inward-Rectifier Potassium Channels to a Mitochondrial Uncoupler: Identification of a Regulatory Site

Baltaev

et al. 2008

Cell Physiol Biochem

The Kir2 channels belong to a family of potassium selective channels with characteristic strong inward rectification. Heteromeric assemblies of Kir2.1, Kir2.2 and Kir2.3 channels underly membrane potential stabilizing currents in ventricular myocytes, neurons and skeletal muscle. Kir2 channels differ substantially in their sensitivity to extracellular pH. The extracellular histidine Kir2.3(H117) contributes to the pH dependence of K-channels containing Kir2.3. Here, we study the possibility of intramolecular interactions of the residue Kir2.3(H117) with conserved cysteines in close proximity to the selectivity filter. We engineered a cobalt coordination site and reduction/oxidation sensitivity in Kir2.3 by introduction of a cysteine into the putatively hydrogen bonding residue (Kir2.3(H117C)) confirming that this residue is in proximity to Kir2.3(C141). Using SCAM we determined the location of the Kir2.3(H117) in the outer pore mouth and incorporated these data into a 3D model. We conclude that formation of a hydrogen bond at low pH may stabilize the outer pore domain to favour the selectivity filter in a slightly distorted conformation thus reducing ion permeation. The data provide molecular insight into the unique pH regulation of inward rectifier channels.

Section: Introductionmentioning

confidence: 99%

Novel Insights into the Structural Basis of pH-Sensitivity in Inward Rectifier K+ Channels Kir2.3

Baltaev

et al. 2008

Cell Physiol Biochem

Journal Cellular Physiology

“…We previously reported an increase in K ir 2 channel activity in excised, inside-out membrane patches from oocytes pre-treated with FCCP (Collins et al, 2005). In the present study we took a closer look at this apparent recovery from FCCP because the conditions required for recovery could provide important clues to the mechanism.…”

Section: Mechanism Of Recovery From Fccpmentioning

confidence: 67%

“…In a previous study we found that the sensitivity of K ir 2 channels to FCCP was influenced by mutations that are known to alter PIP 2 sensitivity (Collins et al, 2005). This raised the possibility that FCCP inhibits K ir 2 channels by PIP 2 depletion.…”

Section: Evidence For An Endogenous Inhibitormentioning

confidence: 97%

“…We were previously unable to attenuate the inhibitory effect of FCCP on K ir 2.2 and K ir 2.3 by pre-injecting the oocytes with ATP (Collins et al, 2005). However, in the absence of a positive control this negative result did not rule out a role for ATP depletion as the mechanism of inhibition by FCCP, so we investigated this possibility further by using apyrase to directly deplete ATP.…”

Section: Evidence For An Endogenous Inhibitormentioning

confidence: 98%

“…Our previous mutagenesis studies suggested that phosphatidylinositol 4,5-bisphosphate (PIP 2 ) may be a link in this mechanism. However, the apparent recovery in isolated membrane patches of K ir 2 channels from inhibition by the mitochondrial uncoupler carbonyl cyanide ptrifluoromethoxyphenylhydrazone (FCCP) was inconsistent with a role of PIP 2 (Collins et al, 2005). The aim of the present study was to determine how much of the apparent recovery could be attributed to spontaneous ''run-up'' of the current.…”

mentioning

confidence: 93%

See 2 more Smart Citations

K_ir2.2 inward rectifier potassium channels are inhibited by an endogenous factor in Xenopus oocytes independently from the action of a mitochondrial uncoupler

Collins

Larson

2008

Self Cite

We previously showed inhibition of K(ir)2 inward rectifier K(+) channels expressed in Xenopus oocytes by the mitochondrial agents carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and sodium azide. Mutagenesis studies suggested that FCCP may act via phosphatidylinositol 4,5-bisphosphate (PIP(2)) depletion. This mechanism could be reversible in intact cells but not in excised membrane patches which preclude PIP(2) regeneration. This prediction was tested by investigating the reversibility of the inhibition of K(ir)2.2 by FCCP in intact cells and excised patches. We also investigated the effect of FCCP on K(ir)2.2 expressed in human embryonic kidney (HEK) cells. K(ir)2.2 current, expressed in Xenopus oocytes, increased in inside-out patches from FCCP-treated and untreated oocytes. The fraction of total current that increased was 0.79 +/- 0.05 in control and 0.89 +/- 0.03 in 10 microM FCCP-treated (P > .05). Following "run-up," K(ir)2.2 current was re-inhibited by "cramming" inside-out patches into oocytes. Therefore, run-up reflected not reversal of inhibition by FCCP, but washout of an endogenous inhibitor. K(ir)2.2 current recovered in intact oocytes within 26.5 h of FCCP removal. Injection of oocytes with 0.1 U apyrase completely depleted ATP (P < .001) but did not inhibit K(ir)2.2 and inhibited K(ir)2.1 by 35% (P < .05). FCCP only partially reduced [ATP] (P < .001), despite inhibiting K(ir)2.2 by 75% (P < .01) but not K(ir)2.1. FCCP inhibited K(ir)2.2 expressed in HEK cells. The recovery of K(ir)2.2 from inhibition by FCCP requires intracellular components, but direct depletion of ATP does not reproduce the differential inhibitory effect of FCCP. Inhibition of K(ir)2.2 by FCCP is not unique to Xenopus oocytes.

Cathet Cardio Intervent

Percutaneous saphenous vein graft intervention with sequential embolic protection devices: Complementing lesion anatomy with embolic protection device

Grow

Rab

2008

Saphenous vein graft (SVG) percutaneous coronary intervention (PCI) carries unique technical challenges requiring the utilization of embolic protection devices (EPDs) to reduce the adverse events associated with distal embolization. Distal embolization is a common and almost ubiquitous consequence of SVG PCI due to the soft and friable nature of the SVG lesions. We describe a case of revascularizing a SVG with tandem stenoses employing the use of two different EPDs that complemented their respective lesion's location within the SVG.