Disopyramide block of K(ATP) channels is mediated by the pore-forming subunit.
The class Ia antiarrhythmic agent disopyramide blocks native ATP-sensitive K+ (K(ATP)) channels at micromolar concentrations. The K(ATP) channel is a complex of a pore-forming inwardly rectifying K+ channel (Kir6.2) and a sulfonylurea receptor (SUR). The aim of the present study was to further localize the site of action of disopyramide. We have used a C-terminal truncated form of Kir6.2 (Kir6.2delta26), which--in contrast to Kir6.2--expresses independently of SUR. Kir6.2delta26 channels were expressed in African green monkey kidney COS-7 cells, and enhanced green fluorescent protein (EGFP) cDNA was used as a reporter gene. EGFP fluorescence was visualized by a laser scanning confocal microscope. Disopyramide applied to the cytoplasmic membrane surface of inside-out patches inhibited Kir6.2delta26 channels half-maximally at 7.1 microM (at pH 7.15). Lowering the intracellular pH to 6.5 potentiated the inhibition of Kir6.2delta26 channels by disopyramide. These observations suggest that disopyramide directly blocks the pore-forming Kir6.2 subunit, in particular at reduced intracellular pH values that occur under cardiac ischaemia.
Federal Institute for Drugs and Medical Devices, Berlin, Federal Republic of Germany. j.zuenkler@bfarm.de
B J
BJ
Zünkler
S
S
Kühne
I
I
Rustenbeck
T
T
Ott
A G
AG
Hildebrandt
D000818:Animals; D019556:COS Cells; D018076:DNA, Complementary / Q000235:genetics; D004206:Disopyramide / Q000494:pharmacology*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects; D018613:Microscopy, Confocal; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying; D013453:Sulfonylurea Compounds / Q000494:pharmacology; D014162:Transfection
D018076:DNA, Complementary; D008164:Luminescent Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D013453:Sulfonylurea Compounds; D049452:Green Fluorescent Proteins; D004206:Disopyramide