Abstract 242: Priming for Action: Interventions That Promote IKs-Channel Opening Restore Defective cAMP-Dependent Upregulation in Long-QT1 Syndrome

Abstract

Introduction: Patients with the KCNQ1 mutation A341V show a high incidence of sympathetically-triggered ventricular tachyarrhythmias and sudden cardiac death. A341V decreases basal IKs and disrupts cAMP-dependent upregulation. The latter can be rescued by the phosphomimetic substitution KCNQ1 S27D. We hypothesize that A341V imposes a different conformational state of the IKs channel, which prevents full phosphorylation of KCNQ1 S27 and therefore loss of upregulation. We have now examined whether different strategies that promote channel opening can rescue cAMP-dependent upregulation. Methods: Chinese hamster ovary cells were transfected with wild type (WT) and heterozygous KCNQ1 A341V, with KCNE1 and Yotiao. In the absence and presence of cAMP/okadaic acid (OA), we examined IKs responses to (1) the KCNQ1 I346-K358 short peptide (shown to unlock the closed state of IKs through its binding to the endogenous S4-S5L of KCNQ1), (2) the double mutant A341V/L353K (L353K was previously shown to promote constitutive current), and (3) the channel activator ML277 (1 μmol/L). Results: As previously shown, WT but not A341V IKs was upregulated by intrapipette cAMP/OA. The unlocking effect of the I346-K358 peptide and the constitutive conduction by the co-presence of L353K facilitated mutant IKs enhancement by cAMP/OA (+61% and +71%, respectively), along with a -10 mV shift of the IV curve. Similar results were found for the IKs activator ML277. In baseline conditions, ML277 increased both WT and A341V IKs by approximately 60%. The IKs response to ML277 in cells stimulated with cAMP/OA was amplified more than twofold in WT, but strikingly also in A341V channels. This larger ML277 effect is thus likely explained by an augmented cAMP-dependent regulation of A341V IKs. Conclusions: Pharmacological and molecular interventions that promote IKs-channel opening rescue (at least partly) from defective cAMP-dependent upregulation by the hot spot mutation A341V. Our results suggest novel therapeutic strategies to restore the beta-adrenergic control of repolarization in long-QT1 syndrome.