Abstract
Cardiac arrhythmias are often associated with mutations in ion channels or other proteins. To enable drug development for distinct arrhythmias, model systems are required that allow implementing patient-specific mutations. We assessed a muscular pump in Caenorhabditis elegans. The pharynx utilizes homologues of most of the ion channels, pumps and transporters defining human cardiac physiology. To yield precise rhythmicity, we optically paced the pharynx using channelrhodopsin-2. We assessed pharynx pumping by extracellular recordings (electropharyngeograms—EPGs), and by a novel video-microscopy based method we developed, which allows analyzing multiple animals simultaneously. Mutations in the L-type VGCC (voltage-gated Ca2+-channel) EGL-19 caused prolonged pump duration, as found for analogous mutations in the Cav1.2 channel, associated with long QT syndrome. egl-19 mutations affected ability to pump at high frequency and induced arrhythmicity. The pharyngeal neurons did not influence these effects. We tested whether drugs could ameliorate arrhythmia in the optogenetically paced pharynx. The dihydropyridine analog Nemadipine A prolonged pump duration in wild type, and reduced or prolonged pump duration of distinct egl-19 alleles, thus indicating allele-specific effects. In sum, our model may allow screening of drug candidates affecting specific VGCCs mutations, and permit to better understand the effects of distinct mutations on a macroscopic level.
Highlights
Cardiac arrhythmias constitute prevalent forms of heart disease
Spontaneous pump rate of the pharynx, in presence of bacteria, in pharyngeal muscle cells (PMCs)-ChR2 animals or wt, cultivated with or without the ChR2 chromophore all-trans retinal (ATR) was unaltered, indicating that PMCs were not affected by ChR2 expression (Fig. 1b)
The pump duration, i.e. period between E- and R peaks was much more reproducible between animals and between different pumps in pharynxes optically paced at 2 Hz (Fig. 1d), and in averaged, E-peak normalized traces, R-peaks were much less distributed in paced pharynxes (Fig. 1e)
Summary
Cardiac arrhythmias constitute prevalent forms of heart disease. Arrhythmias can affect heart rate, i.e. faster or slower than normal (tachycardia or bradycardia, with > 100 or < 60 beats per minute, respectively), or they disturb the regular rhythm and sequence of physiological events constituting a heartbeat, for example in aged hearts[6], or following damage (e.g. artery disease, heart attack)[7]. Long QT (LQT) syndromes involve a number of genes affecting the duration of the QT interval (prolonging it), like K+ channels, and the L-type VGCC, Cav1.2 (CACNA1C). The C. elegans feeding organ, the pharynx, is a rhythmically active muscular pump[15], with many properties similar to the vertebrate heart (and dissimilarities)[16]. By ChR2-mediated depolarization, we achieved pharynx pumping up to 6 Hz. Mutations in the L-type VGCC EGL-19 affected pump duration and ability of the pharynx to achieve high pump rates, similar to a LQT syndrome. Optogenetic pharynx pacing facilitates functional analysis of VGCC alleles in the context of a whole organ, and enables straightforward screening for novel anti-arrhythmogenic drugs
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