Mapping the block of a cloned human inward rectifier potassium channel by dofetilide.
Dofetilide, a methanesulfonanilide derivative, is a potent class III antiarrhythmic drug. Like other members of this class of K+ channel blockers, the sites in the channel to which the drug binds are unknown, although high and low affinity binding has been reported in cardiomyocytes. The most sensitive K+ channel target for dofetilide seems to be IKr, the rapid component of the repolarizing delayed rectifier K+ current. However, block of other K+ channels occurs at higher concentrations and is of special interest in regard to toxicity. Recently, we have demonstrated that hIRK, a cloned inward rectifier K+ channel (IRK) isolated from human atrium and expressed heterologously in Xenopus oocytes, is blocked by dofetilide. We report the localization of a site that is critical for dofetilide block in hIRK. We used chimeric constructs between hIRK and ROMK1, a related inward rectifier that is drug resistant. Substitution of hIRK-M2, the second putative transmembrane spanning segment of IRKs, with ROMK1-M2 increased unblocking of dofetilide by 10-20-fold in hIRK. Site-directed mutagenesis further pinpointed the effects to a single hydrophobic residue (I177) in M2. A reduction in hydrophobicity by the point mutation I177C increased recovery from block > 10-fold (1.17 sec in wild-type to 0.112 sec at -80 mV at physiological K+ concentrations), leading us to suggest that hydrophobic interactions are essential for dofetilide block in hIRK. A similar mechanism may explain dofetilide block in other ion channels, including IKr.
Kiehn
J
J
Rammelkamp Center for Research, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA.
Wible
B
B
Lacerda
A E
AE
Brown
A M
AM
D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001665:Binding Sites; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010627:Phenethylamines / Q000494:pharmacology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors; D012995:Solubility; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000494:pharmacology*
D000889:Anti-Arrhythmia Agents; D010627:Phenethylamines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011993:Recombinant Fusion Proteins; D013449:Sulfonamides; C063533:dofetilide