title: Overexpression of the Large-Conductance, Ca2+-Activated K+ (BK) Channel Shortens Action Potential Duration in HL-1 Cardiomyocytes.
abstract: Long QT syndrome is characterized by a prolongation of the interval between the Q wave and the T wave on the electrocardiogram. This abnormality reflects a prolongation of the ventricular action potential caused by a number of genetic mutations or a variety of drugs. Since effective treatments are unavailable, we explored the possibility of using cardiac expression of the large-conductance, Ca2+-activated K+ (BK) channel to shorten action potential duration (APD). We hypothesized that expression of the pore-forming α subunit of human BK channels (hBKα) in HL-1 cells would shorten action potential duration in this mouse atrial cell line. Expression of hBKα had minimal effects on expression levels of other ion channels with the exception of a small but significant reduction in Kv11.1. Patch-clamped hBKα expressing HL-1 cells exhibited an outward voltage- and Ca2+-sensitive K+ current, which was inhibited by the BK channel blocker iberiotoxin (100 nM). This BK current phenotype was not detected in untransfected HL-1 cells or in HL-1 null cells sham-transfected with an empty vector. Importantly, APD in hBKα-expressing HL-1 cells averaged 14.3 ± 2.8 ms (n = 10), which represented a 53% reduction in APD compared to HL-1 null cells lacking BKα expression. APD in the latter cells averaged 31.0 ± 5.1 ms (n = 13). The shortened APD in hBKα-expressing cells was restored to normal duration by 100 nM iberiotoxin, suggesting that a repolarizing K+ current attributed to BK channels accounted for action potential shortening. These findings provide initial proof-of-concept that the introduction of hBKα channels into a cardiac cell line can shorten APD, and raise the possibility that gene-based interventions to increase hBKα channels in cardiac cells may hold promise as a therapeutic strategy for long QT syndrome.
authors.affiliation: Department of Pharmacology & Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Stimers
authors.affiliation: Department of Pharmacology & Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Li
authors.initials: L
authors.lastname: Song
authors.affiliation: Department of Pharmacology & Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Rusch
authors.affiliation: Department of Pharmacology & Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Sung W
authors.initials: SW
authors.lastname: Rhee
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D017930:Genes, Reporter; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D016253:Microscopy, Immunoelectron; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000633:toxicity
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; C064719:iberiotoxin; D002118:Calcium