Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB015

Poster Communications

Proarrythmic effects of β-adrenergic stimulation in a pharmacological model of LQT3 in the absence of action potential prolongation.

E. Lubenko2, N. Pomeroy2, P. Jolly2, C. Shewell2, M. E. Hardy1,2

1. Faculty of Life Sciences, University of Bradford, Bradford, West Yorkshire, United Kingdom. 2. Faculty of Biological Sciences, University of Leeds, LS2 9JT, Leeds, United Kingdom.

Long QT syndrome type 3 (LQT3) is a congenital cardiac channelopathy associated with sudden death. Dysfunction in the cardiac sodium channel results in delayed repolarisation of the action potential. β-blockers are the first line of treatment, although their efficacy has been questioned and the role of β-adrenergic stimulation in cardiac arrhythmias occurring in LQT3 is not fully understood. We aimed to evaluate the effects of β-adrenergic stimulation alongside the influence of pacing rate on proarrhythmic parameters in the ventricular action potential. Experiments were conducted with local ethical approval and in accordance with UK Home Office and European Parliament Directive 2010/63/EU guidelines on the use of animals in research. Firstly, monophasic ventricular action potentials were recorded from Langendorff perfused Wistar rat hearts, stimulated for 60 s at 6, 9 and 12 Hz consecutively. The pacing protocol was performed in the absence or presence of 100 nM isoproterenol (ISO), before and 15 min after the addition of 50ng/l anthopleurin-A (AP-A). Control hearts underwent a time-matched protocol in the absence of any drugs/toxin. Owing to the high incidence of non-recoverable arrhythmia in AP-A+ISO treated hearts, an additional group was studied with 5 min between pacing protocols. Statistics were performed using ANOVA or Student t-tests. Data is expressed as means ± SEM. Secondly an in silico experiment was made using LabHEART - a computational model of the rabbit ventricular myocyte. As a surrogate for LQT3, background sodium conductance was increased from 114 µS/µF to 300 µS/µF at pacing rates of 1, 2 and 3 Hz. Increasing the pacing rate from 6 to 12 Hz did not significantly alter action potential duration at 90% repolarisation (APD90) in control hearts (36.61 ± 12.54 to 32.34 ± 15.97 ms, n = 6, N.S.). AP-A did not cause prolongation of APD90 at any of the pacing frequencies measured (33.40 ± 13.25 to 27.64 ± 11.30 ms at 6 Hz, 32.37 ± 11.25 to 17.35 ± 10.92 ms at 12 Hz, n = 6, N.S.). The addition of ISO did not have a significant effect on APD90 in either control or AP-A treated hearts (time matched data: Con 31.96 ± 23.21 ms, n = 6, AP-A 27.64 ± 13.25 ms, n = 6, ISO ISO+AP-A 35.83 ± 11.7 ms, n=4 N.S.). Despite an absence of APD prolongation, only 50% hearts treated with AP-A alone and 17% AP-A+ISO did not go into irreversible fibrillation before completion of pacing protocols, compared to 100% control hearts. In labHEART, APD90 increased from 218 ms to 226 ms at 1Hz and from 225 ms to 257 ms at 3 Hz. At the higher sodium conductance, simulation of a supramaximal dose of ISO altered the APD90 to 216 ms and 189 ms at 1 and 3 Hz, respectively. These results show that 50 ng/l AP-A does not cause action potential prolongation in isolated rat hearts. Despite this, ISO in addition to AP-A does increase arrhythmogenic risk. This suggests that β-stimulation in LQT3 may have proarrhythmic consequences by mechanisms independent of APD prolongation.

Where applicable, experiments conform with Society ethical requirements