Mechanical stretch of cardiac muscle modulates action potential propagation velocity, causing potentially arrhythmogenic conduction slowing. The mechanisms by which stretch alters cardiac conduction remain unknown, but previous studies suggest that stretch can affect the conformation of caveolae in myocytes and other cell types. We tested the hypothesis that slowing of action potential conduction due to cardiac myocyte stretch is dependent on caveolae. Cardiac action potential propagation velocities, measured by optical mapping in isolated mouse hearts and in micropatterned mouse cardiomyocyte cultures, decreased reversibly with volume loading or stretch, respectively (by 19±5% and 26±4%). Stretch-dependent conduction slowing was not altered by stretch-activated channel blockade with gadolinium or by GsMTx-4 peptide, but was inhibited when caveolae were disrupted via genetic deletion of caveolin-3 (Cav3 KO) or membrane cholesterol depletion by methyl-β-cyclodextrin. In wild-type mouse hearts, stretch coincided with recruitment of caveolae to the sarcolemma, as observed by electron microscopy. In myocytes from wild-type but not Cav3 KO mice, stretch significantly increased cell membrane capacitance (by 98±64%), electrical time constant (by 285±149%), and lipid recruitment to the bilayer (by 84±39%). Recruitment of caveolae to the sarcolemma during physiologic cardiomyocyte stretch slows ventricular action potential propagation by increasing cell membrane capacitance.

Digital PCR (dPCR) is emerging as an ideal platform for the detection and tracking of genomic variants in cancer due to its high sensitivity and simple workflow. The growing number of clinically-actionable cancer biomarkers creates a need for fast, accessible methods that allow for dense information content and high accuracy. Here, we describe a proof-of-concept amplitude modulation based multiplex dPCR assay capable of detecting 12 single nucleotide and indel variants in EGFR, KRAS, BRAF, and ERBB2, 14 gene fusions in ALK, RET, ROS1, NTRK1, and MET exon 14 skipping present in non-small cell lung cancer (NSCLC). We also demonstrate the use of multi-spectral target signal encoding to improve the specificity of variant detection by reducing background noise up to 11-fold. The assay reported an overall 100% PPA and 98.5% NPA compared to a sequencing-based assay in a cohort of 62 human FFPE samples. In addition, the dPCR assay rescued actionable information in 10 samples that failed to sequence, highlighting the utility of a multiplexed digital assay as a potential reflex solution for challenging NSCLC samples.

The timely appearance and proper functioning of pacemaker activity is a critical feature of heart physiology. Two main mechanisms have been proposed: (1) The ''voltage-clock'', where the hyperpolarization-activated funny current If causes diastolic depolarization that triggers action potential cycling; (2) The ''Ca2þ clock'', where cyclical release of Ca2þ from Ca2þ stores depolarizes the membrane during diastole via activation of the Naþ-Ca2þ exchanger (NCX). However, these pacemaker mechanisms remain highly controversial. Here, we used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) to study the embryonic pacemaker mechanisms of the human heart. Combined current-and voltage-clamp recording from the same hESC-CM and blocking If with zatebradine or ZD7288 and NCX with KB-R7943 or FRCRCF peptide revealed distinct pacemaker phenotypes. Results showed that the ''voltage clock'' and ''Ca2þ clock'' pacemakers can coexist in the same cell, but can also occur in a mutually exclusive fashion in other cell populations. Interestingly, all these pacemaker phenotypes shared a depolarizing drift of the maximal diastolic potential (MDP) following exposure of cells to blockers of the ''voltage'' and ''Ca2þ clocks'', suggesting that both mechanisms converge to a common pacemaking component. This MDP depolarization arises from inhibition of a previously unrecognized conductance in hESC-CMs. Remarkably, blockade of this conductance leads to depolarization of the MDP and suppresses pacemaker activity. Data are discussed on how this conductance plays a crucial role in human embryonic cardiac automaticity.

Digital PCR (dPCR) is an emerging platform for detecting genomic variants in cancer genomes due to its high sensitivity and fast time to result compared to massively parallel sequencing. However, translational oncology applications often require the measurement of more biomarkers than there are color channels available on dPCR platforms. One approach to address this is to split a sample across many wells and profile a subset of variants in each well. For input-limited samples, however, this results in fewer molecules being profiled in each well, resulting in a reduction in sensitivity and fewer samples processed per instrument run. ChromaCode has developed a research use only (RUO) high-definition digital PCR assay, for multiplexed detection of 14 DNA variants and 15 RNA fusion variants relevant in non-small cell lung cancer (NSCLC) samples. The assay is constructed using both amplitude modulation and multi-channel resilient signal encoding methods. Amplitude modulation enables different variants to generate a signal at different intensity levels in single color channel, allowing for greater than n targets in n color channels. In contrast, resilient encoding generates a signal in more than one color channel to create a form of error detecting code. DNA and RNA samples were obtained using a combination of synthetic templates, cell line nucleic acids, and commercially available reference materials. Samples were run with the HDPCR NSCLC RUO assay on the Thermo Fisher Absolute Q digital PCR system, and data analysis was performed with custom analysis algorithms. The HDPCR NSCLC RUO assay demonstrated a limit of detection as low as 10 variant copies in a 10,000 haploid human genome copy DNA background. By employing HDPCR technology on digital PCR systems, it is possible to build a comprehensive and sensitive research assay that quickly detects many genomic alterations relevant to NSCLC samples. Citation Format: Bryan Leatham, Katie McNall, Hari K. Subramanian, John Alvarado, Lucien Jacky, Mimi Wang, Aditya Rajagopal, Jerrod Schwartz. High-Definition Digital PCR (HDPCR™) enables sensitive measurement of DNA and RNA variants in non-small cell lung cancer samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2929.

e20603 Background: Digital PCR (dPCR) is an emerging technology platform for detecting genomic variants in cancer genomes due to its high sensitivity and fast time to results compared to sequencing. However, translational oncology applications often require the measurement of more biomarkers than there are color channels available on dPCR platforms. One approach to address this limitation with dPCR is to split a sample across many wells and profile a subset of variants in each well. For input-limited samples, however, this results in fewer molecules being profiled in each dPCR well, resulting in a reduction in sensitivity and fewer patient samples processed per instrument run. ChromaCode has developed a research use only (RUO) digital High Definition PCR (HDPCR) NSCLC assay, for multiplexed detection of 14 DNA variants and 15 RNA fusion variants relevant in non-small cell lung cancer samples. The assay is constructed using both amplitude modulation and multi-channel resilient signal encoding methods. Amplitude modulation enables different variants to generate a distinguishable signal at different intensity levels in a single color channel, allowing for multiple targets to be detected within that single-color channel. In addition, resilient encoding generates a signal in more than one color channel to create a form of error detection in the assay design. Methods: Assay benchmarking was performed using over 500 contrived human biological FFPE samples, consisting of synthetic DNA or RNA variants spiked into a background matrix of FFPE-extracted DNA or RNA; over 500 contrived human biological plasma samples, consisting of synthetic DNA or RNA variants spiked into a background matrix of plasma-extracted cell free DNA or RNA; and residual human biological FFPE and plasma NSCLC samples that were previously characterized using a targeted sequencing workflow. The samples were tested using the HDPCR NSCLC assay on the QuantStudio Absolute Q Digital PCR system, and data analysis was performed with custom analysis algorithms. Results: For the more than 500 contrived FFPE and plasma samples, the HDPCR NSCLC assay had high overall agreement with expectation across a range of mutant allele fractions for both DNA and RNA analytes (≥99% PPA and ≥99% NPA). For a set of N = 25 residual human biological FFPE samples, the assay was also highly concordant (100% PPA and 99% NPA) with a targeted panel sequencing comparator. The hands-on workflow time from isolation start to analysis complete was < 24 hours. Conclusions: The HDPCR NSCLC assay is a robust RUO tool for the sensitive and rapid detection of commonly targeted variants relevant to NSCLC samples. This technology could complement sequencing assays when there is a need for a rapid turnaround time or there are limited amounts of isolated nucleic acid.