Isoproterenol exacerbates a long QT phenotype in Kcnq1-deficient neonatal mice: possible roles for human-like Kcnq1 isoform 1 and slow delayed rectifier K+ current.
To determine whether the neonatal mouse can serve as a useful model for studying the molecular pharmacological basis of Long QT Syndrome Type 1 (LQT1), which has been linked to mutations in the human KCNQ1 gene, we measured QT intervals from electrocardiogram (ECG) recordings of wild-type (WT) and Kcnq1 knockout (KO) neonates before and after injection with the beta-adrenergic receptor agonist, isoproterenol (0.17 mg/kg, i.p.). Modest but significant increases in JT, QT, and rate-corrected QT (QTc) intervals were found in KO neonates relative to WT siblings during baseline ECG assessments (QTc = 57 +/- 3 ms, n = 22 versus 49 +/- 2 ms, n = 28, respectively, p < 0.05). Moreover, JT, QT, and QTc intervals significantly increased following isoproterenol challenge in the KO (p < 0.01) but not the WT group (p = 0.57). Furthermore, whole-cell patch-clamp recordings show that the slow delayed rectifier K+ current (IKs) was absent in KO but present in WT myocytes, where it was strongly enhanced by isoproterenol. This finding was confirmed by showing that the selective IKs inhibitor, L-735,821, blocked IKs and prolonged action potential duration in WT but not KO hearts. These data demonstrate that disruption of the Kcnq1 gene leads to loss of IKs, resulting in a long QT phenotype that is exacerbated by beta-adrenergic stimulation. This phenotype closely reflects that observed in human LQT1 patients, suggesting that the neonatal mouse serves as a valid model for this condition. This idea is further supported by new RNA data showing that there is a high degree of homology (>88% amino acid identity) between the predominant human and mouse cardiac Kcnq1 isoforms.
Department of Pharmacology, Georgetown University Medical Center, Washington, DC 20007, USA.
Bjorn C
BC
Knollmann
Mathew C
MC
Casimiro
Alexander N
AN
Katchman
Syevda G
SG
Sirenko
Tilmann
T
Schober
Qi
Q
Rong
Karl
K
Pfeifer
Steven N
SN
Ebert
D000200:Action Potentials / Q000187:drug effects; D000318:Adrenergic beta-Agonists / Q000009:adverse effects*; D000595:Amino Acid Sequence; D000818:Animals; D051668:Delayed Rectifier Potassium Channels; D006801:Humans; D007545:Isoproterenol / Q000009:adverse effects*; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000139:chemically induced*; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D010641:Phenotype; D015221:Potassium Channels / Q000172:deficiency* / Q000235:genetics / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D017386:Sequence Homology, Amino Acid
D000318:Adrenergic beta-Agonists; D051668:Delayed Rectifier Potassium Channels; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; C496910:Kcnq1 protein, mouse; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D007545:Isoproterenol