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Short QT Syndrome (SQTS) is a novel clinical entity characterized by markedly rapid cardiac repolarization and lethal arrhythmias. A mutation in the Kir2.1 inward rectifier K+ channel (D172N) causes one form of SQTS (SQT3). Pharmacologic block of Kir2.1 channels may hold promise as potential therapy for SQT3. We recently reported that the anti-malarial drug chloroquine blocks Kir2.1 channels by plugging the cytoplasmic pore domain. In this study, we tested whether chloroquine blocks D172N Kir2.1 channels in a heterologous expression system and if chloroquine normalizes repolarization properties using a mathematical model of a human ventricular myocyte. Chloroquine caused a dose- and voltage-dependent reduction in wild-type (WT), D172N and WT-D172N heteromeric Kir2.1 current. The potency and kinetics of chloroquine block of D172N and WT-D172N Kir2.1 current were similar to WT. In silico modeling of the heterozygous WT-D172N Kir2.1 condition predicted that 3 μM chloroquine normalized inward rectifier K+ current magnitude, action potential duration and effective refractory period. Our results suggest that therapeutic concentrations of chloroquine might lengthen cardiac repolarization in SQT3. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Inwardly-rectifying K+ channel subunits are not homogenously expressed in different cardiac tissues. In ventricular myocytes (VM) the background current-voltage relation is dominated by IK1, carried by channels composed of Kir2.x subunits, which is less important in atrial myocytes (AM). On the other hand in AM a large G protein gated current carried by Kir3.1/3.4 complexes can be activated by stimulation of muscarinic M2 receptors (IK(ACh)), which is assumed to be marginal in VM. Recent evidence suggests that total current carried by cardiac inward-rectifiers (IK(ATP), IK(ACh), IK1) in both, AM and VM is limited, due to K+ accumulation/depletion. This lead us to hypothesize that in conventional whole celI recordings IK(ACh) in VM is underestimated as a consequence of constitutive IK1. In that case a reduction in density of IK1 should be paralleled by an increase in density of IK(ACh). Three different experimental strategies have been used to test for this hypothesis: (i) Adenovirus-driven expression of a dominant-negative mutant of Kir2.1, one of the subunits supposed to form IK1 channels, in VM caused a reduction in IK1-density by about 80 %. In those cells IK(ACh) was increased about 4 fold. (ii) A comparable increase in IK(ACh) was observed upon reduction of IK1 caused by adenovirus-mediated RNA interference.(iii) Ba2+ in a concentration of 2 μM blocks IK1 in VM by about 60 % without affecting atrial IK(ACh). The reduction in IK1 by 2 μM Ba2+ is paralleled by a reversible increase in IK(ACh) by about 100%. These data demonstrate that the increase in K+ conductance underlying ventricular IK(ACh) is largely underestimated, suggesting that it might be of greater physiological relevance than previously thought. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Inwardly-rectifying K+ channel subunits are not homogenously expressed in different cardiac tissues. In ventricular myocytes (VM) the background current-voltage relation is dominated by IK1, carried by channels composed of Kir2.x subunits, which is less important in atrial myocytes (AM). On the other hand in AM a large G protein gated current carried by Kir3.1/3.4 complexes can be activated by stimulation of muscarinic M2 receptors (IK(ACh)), which is assumed to be marginal in VM. Recent evidence suggests that total current carried by cardiac inward-rectifiers (IK(ATP), IK(ACh), IK1) in both, AM and VM is limited, due to K+ accumulation/depletion. This lead us to hypothesize that in conventional whole celI recordings IK(ACh) in VM is underestimated as a consequence of constitutive IK1. In that case a reduction in density of IK1 should be paralleled by an increase in density of IK(ACh). Three different experimental strategies have been used to test for this hypothesis: (i) Adenovirus-driven expression of a dominant-negative mutant of Kir2.1, one of the subunits supposed to form IK1 channels, in VM caused a reduction in IK1-density by about 80 %. In those cells IK(ACh) was increased about 4 fold. (ii) A comparable increase in IK(ACh) was observed upon reduction of IK1 caused by adenovirus-mediated RNA interference.(iii) Ba2+ in a concentration of 2 μM blocks IK1 in VM by about 60 % without affecting atrial IK(ACh). The reduction in IK1 by 2 μM Ba2+ is paralleled by a reversible increase in IK(ACh) by about 100%. These data demonstrate that the increase in K+ conductance underlying ventricular IK(ACh) is largely underestimated, suggesting that it might be of greater physiological relevance than previously thought. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The weak inward rectifier potassium channel ROMK is important for water and salt reabsorption in the kidney. Here we identified Golgin-160 as a novel interacting partner of the ROMK channel. By using yeast two-hybrid assays and co-immunoprecipitations from transfected cells, we demonstrate that Golgin-160 associates with the ROMK C-terminus. Immunofluorescence microscopy confirmed that both proteins are co-localized in the Golgi region. The interaction was further confirmed by the enhancement of ROMK currents by the co-expressed Golgin-160 in Xenopus oocytes. The increase in ROMK current amplitude was due to an increase in cell surface density of ROMK protein. Golgin-160 also stimulated current amplitudes of the related Kir2.1, and of voltage-gated Kv1.5 and Kv4.3 channels, but not the current amplitude of co-expressed HERG channel. These results demonstrate that the Golgi-associated Golgin-160 recognizes the cytoplasmic C-terminus of ROMK, thereby facilitating the transport of ROMK to the cell surface. However, the stimulatory effect on the activity of more distantly-related potassium channels suggests a more general role of Golgin-160 in the trafficking of plasma membrane proteins. [ABSTRACT FROM AUTHOR]