Biology subjects

Kucera, J. P.

Publications and source records attributed to Kucera, J. P..

3 recordsLinked to original sources

bioRxiv2024

Computational Modeling of Effects of PKP2 Gene Therapy on Ventricular Conduction Properties in Arrhythmogenic Cardiomyopathy

BackgroundPatients with arrhythmogenic cardiomyopathy (ACM) due to pathogenic variants in PKP2, the gene for the desmosomal protein plakophilin-2, are being enrolled in gene therapy trials designed to replace the defective allele via adeno-associated viral (AAV) transduction of cardiac myocytes. Evidence from experimental systems and patients indicates that ventricular myocytes in PKP2 ACM have greatly reduced electrical coupling at gap junctions and reduced Na+ current density. In previous AAV gene therapy trials, <50% of ventricular myocytes have generally been transduced. MethodsWe used established computational models of ventricular cell electrophysiology to define the effects of varying levels of successful gene therapy on conduction in patients with PKP2 ACM. Conduction velocity and development of conduction block were analyzed in tissue constructs composed of cells with levels of electrical coupling and Na+ current density observed in experimental studies. ResultsWe observed a non-linear relationship between conduction velocity and the proportion of transduced cells. Conduction velocity increased only modestly when up to 40% of myocytes were transduced. Conduction block did not occur in tissue constructs with moderate levels of uncoupling (0.10 or 0.15 of normal) as this degree of coupling was sufficient to allow electrotonic current to pass through diseased cells. Thus, low levels of transduction, likely to occur in phase 1 clinical trials, do not appear to pose a major safety concern. However, our models did not incorporate potential effects of fibrosis and immune signaling, both of which will presumably be present in PKP2 ACM patients undergoing gene therapy. ConclusionsThe extent of successful ventricular myocyte transduction anticipated to be achieved in PKP2 AAV gene therapy trials will likely not restore conduction velocity to levels sufficient to decrease risk of reentrant arrhythmias. What is Known- Patients with arrhythmogenic cardiomyopathy due to pathogenic variants in PKP2 (the gene for the desmosomal protein plakophilin-2) are now being enrolled in gene therapy trials. - Experimental and clinical observations indicate that patients with arrhythmogenic cardiomyopathy have slow ventricular conduction with a propensity to conduction block due to source-sink mismatch. - <50% of ventricular myocytes are usually transduced after adeno-associated viral gene therapy. What the Study Adds- At anticipated levels of successful transduction of ventricular myocytes, little change in conduction velocity will be achieved in patients with arrhythmogenic cardiomyopathy due to variants in PKP2. - Higher levels of transduction could produce conditions that increase risk of conduction block, especially in the presence of areas of non-conducting fibrofatty scar tissue.

physiology↗

bioRxiv2022

Nano-scale solution of the Poisson-Nernst-Planck (PNP) equations in a fraction of two neighboring cells reveals the magnitude of intercellular electrochemical waves

The basic building blocks of the electrophysiology of cardiomyocytes are ion channels integrated in the cell membranes. Close to the ion channels there are very strong electrical and chemical gradients. However, these gradients extend for only a few nano-meters and are therefore commonly ignored in mathematical models. The full complexity of the dynamics is modelled by the Poisson-Nernst-Planck (PNP) equations but these equations must be solved using temporal and spatial scales of nano-seconds and nano-meters. Here we report solutions of the PNP equations in a fraction of two abuttal cells separated by a tiny extracellular space. We show that when only the potassium channels of the two cells are open, a stationary solution is reached with the well-known Debye layer close to the membranes. When the sodium channels of the left cell are opened, a very strong and brief electrochemical wave emanates from the channels. If the extracellular space is sufficiently small and the number of sodium channels is sufficiently high, the wave extends all the way over to the neighboring cell and may therefore explain cardiac conduction even at very low levels of gap junctional coupling.

biophysics↗

bioRxiv2019

Modelling depolarization delay, sodium currents, and electrical potentials in cardiac transverse tubules

T-tubules are invaginations of the lateral membrane of striated muscle cells that provide a large surface for ion channels and signaling proteins, thereby supporting excitation-contraction coupling. T-tubules are often remodeled in heart failure. To better understand the electrical behavior of T-tubules of cardiac cells in health and disease, this study addresses two largely unanswered questions regarding their electrical properties: (1) the delay of T-tubular membrane depolarization and (2) the effects of T-tubular sodium current on T-tubular potentials.\n\nHere, we present an elementary computational model to determine the delay in depolarization of deep T-tubular membrane segments as the narrow T-tubular lumen provides resistance against the extracellular current. We compare healthy tubules to tubules with constrictions and diseased tubules from mouse and human, and conclude that constrictions greatly delay T-tubular depolarization, and diseased T-tubules depolarize faster than healthy ones due to tubule widening. We moreover model the effect of T-tubular sodium current on intraluminal T-tubular potentials. We observe that extracellular potentials become negative during the sodium current transient (up to -50 mV in constricted T-tubules), which feedbacks on sodium channel function (self-attenuation) in a manner resembling ephaptic effects that have been described for intercalated discs where opposing membranes are very close together.\n\nThese results show that (1) the excitation-contraction coupling defects seen in diseased cells cannot be explained by T-tubular remodeling alone; and (2) the sodium current may modulate intraluminal potentials. Such extracellular potentials might also affect excitation-contraction coupling.

physiology↗