Biology subjects

Posnack, N. G.

Publications and source records attributed to Posnack, N. G..

10 recordsLinked to original sources

bioRxiv2026

Patient-Specific Heart Rate Modulates Developmental Electrophysiology in Transcriptomic-Guided In Silico Models of Pediatric Human Atrial Cardiomyocytes

Cardiac electrophysiology adapts throughout pediatric development, driven by factors including age-associated ion channel expression changes and decreasing heart rate. Our prior transcriptomic-guided simulations of human atrial cardiomyocytes predicted developmental-associated changes in electrophysiology biomarkers at a fixed pacing rate, leaving the contribution of age- and patient-specific heart rate unresolved. In this study, we incorporated intrinsic heart rate into gene expression-guided computational models to predict the interaction between developmental maturation and pacing rate to shape atrial electrophysiology. Virtual patient-specific populations of atrial cardiomyocytes were generated from the right atrial cardiomyocyte gene expression data from 117 patients, spanning neonates to young adults. We simulated each population at pacing rates corresponding to each patients intrinsic ECG-based heart rate and at fixed rates corresponding to the patient cohort minimum, median, and maximum. Action potential and calcium transient biomarkers were quantified, and partial least squares regression assessed key biomarker dependencies. For intrinsic-rate pacing conditions, action potential duration at 50% and 90% repolarization increased with age, whereas early repolarization shortened; maximum upstroke velocity increased, resting membrane potential became more negative, and alternans prevalence decreased. Developmental differences persisted during fixed-rate pacing conditions, indicating that differences were not explained solely by the faster heart rates of younger patients. Notably, intrinsic-rate simulations exhibited stronger age associations for upstroke velocity and alternans than fixed-rate simulations. Sensitivity analyses indicated that electrophysiological phenotypes arose from interactions among ionic conductances, calcium handling, age, and heart rate. Collectively, we find that pediatric atrial electrophysiology reflects both intrinsic developmental remodeling and rate-dependent modulation.

biophysics↗

bioRxiv2024

Connecting Transcriptomics with Computational Modeling to Reveal Developmental Adaptations in the Human Pediatric Myocardium

BackgroundNearly 1% or 1.3 million babies are born with congenital heart disease (CHD) globally each year - many of whom will require palliative or corrective heart surgery within the first few years of life. A detailed understanding of cardiac maturation can help to expand our knowledge on cardiac diseases that develop during gestation, identify age-appropriate cardiovascular drug therapies, and inform clinical care decisions related to surgical repair, myocardial preservation, or postoperative management. Yet, to date, our knowledge of the temporal changes that cardiomyocytes undergo during postnatal development is largely limited to animal models. MethodsRight atrial tissue samples were collected from n=117 neonatal, infant, and pediatric patients undergoing correct surgery due to (acyanotic) CHD. Patients were stratified into five age groups: neonate (0-30 days), infant (31-364 days), toddler to preschool (1-5 years), school age (6-11 years), and adolescent to young adults (12-32 years). We measured age-dependent adaptations in cardiac gene expression, and used computational modeling to simulate action potential and calcium transients. ResultsEnrichment of differentially expressed genes (DEG) was explored, revealing age-dependent changes in several key biological processes (cell cycle, cell division, mitosis), cardiac ion channels, and calcium handling genes. Gene-associated changes in ionic currents exhibited both linear trends and sudden shifts across developmental stages, with changes in calcium handling (INCX) and repolarization (IK1) most strongly associated with an age-dependent decrease in the action potential plateau potential and increase in triangulation, respectively. We also note a shift in repolarization reserve, with lower IKr expression in younger patients, a finding likely tied to the increased amplitude of IKs triggered by elevated sympathetic activation in pediatric patients. ConclusionThis study provides valuable insights into age-dependent changes in human cardiac gene expression and electrophysiology among patients with CHD, shedding light on molecular mechanisms underlying cardiac development and function across different developmental stages.

cell biology↗

bioRxiv2024

Electroanatomical Adaptations in the Guinea Pig Heart from Neonatal to Adulthood

BackgroundElectroanatomical adaptations during the neonatal to adult phase have not been comprehensively studied in preclinical animal models. To explore the impact of age as a biological variable on cardiac electrophysiology, we employed neonatal and adult guinea pigs, which are a recognized animal model for developmental research. MethodsHealthy guinea pigs were categorized into three age groups (neonates, n=10; younger adults, n=13; and older adults, n=26). Electrocardiogram (ECG) recordings were collected in vivo from anesthetized animals (2-3% isoflurane). A Langendorff-perfusion system was employed for optical assessment of epicardial action potentials and calcium transients, using intact excised heart preparations. Optical data sets were analyzed and metric maps were constructed using Kairosight 3.0. ResultsThe allometric relationship between heart weight and body weight diminishes with age, as it is strongest at the neonatal stage (R2 = 0.84) and completely abolished in older adults (R2 = 1E-06). Neonatal hearts exhibit circular activation waveforms, while adults show prototypical elliptical shapes. Neonatal conduction velocity (40.6{+/-}4.0 cm/s) is slower than adults (younger adults: 61.6{+/-}9.3 cm/s; older adults: 53.6{+/-}9.2 cm/s). Neonatal hearts have a longer action potential duration (APD) and exhibit regional heterogeneity (left apex; APD30: 68.6{+/-}5.6 ms, left basal; APD30: 62.8{+/-}3.6), which was absent in adult epicardium. With dynamic pacing, neonatal hearts exhibit a flatter APD restitution slope (APD70: 0.29{+/-}0.04) compared to older adults (0.49{+/-}0.04). Similar restitution characteristics are observed with extrasystolic pacing, with a flatter slope in neonatal hearts (APD70: 0.54{+/-}0.1) compared to adults (Younger adults: 0.85{+/-}0.4; Older adults: 0.95{+/-}0.7). Finally, neonatal hearts display unidirectional excitation-contraction coupling, while adults exhibit bidirectionality. ConclusionThe transition from neonatal to adulthood in guinea pig hearts is characterized by transient changes in electroanatomic properties. Age-specific patterns can influence cardiac physiology, pathology, and therapies for cardiovascular diseases. Understanding postnatal heart development is crucial to evaluating therapeutic eligibility, safety, and efficacy. What is KnownAge-specific cardiac electroanatomical characteristics have been documented in humans and some preclinical animal models. These age-specific patterns can influence cardiac physiology, pathology, and therapies for cardiovascular diseases. What the Study AddsCardiac electroanatomical characteristics are age-specific in guinea pigs, a well-known preclinical model for developmental studies. Age-dependent adaptations in cardiac electrophysiology are readily observed in the electrocardiogram recordings and via optical mapping of epicardial action potentials and calcium transients. Our findings reveal unique activation and repolarization characteristics between neonatal and adult animals. Graphical AbstractAge-dependent adaptations in the guinea pig heart include adjustments in allometric scaling and cardiac electrophysiology. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/577234v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@5fcdaforg.highwire.dtl.DTLVardef@1b8acc3org.highwire.dtl.DTLVardef@1567089org.highwire.dtl.DTLVardef@1f63c4a_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2023

Toxins in plastic: Evidence for the cardiodepressive effects of di-2-ethylhexylphthalate (DEHP)

Di-2-ethylhexylphthalate (DEHP) is commonly used in the manufacturing of plastic materials, including intravenous bags, blood storage bags, and medical-grade tubing. DEHP can leach from plastic medical products, which can result in inadvertent patient exposure. DEHP concentrations were measured in red blood cell (RBC) units stored between 7-42 days (23-119 g/mL). Using these concentrations as a guide, Langendorff-perfused rat heart preparations were acutely exposed to DEHP. Sinus activity remained stable with lower doses of DEHP (25-50 g/mL), but sinus rate declined by 43% and sinus node recovery time prolonged by 56.5% following 30-minute exposure to 100 g/ml DEHP. DEHP exposure also exerted a negative dromotropic response, as indicated by a 69.4% longer PR interval, 108.5% longer Wenckebach cycle length, and increased incidence of atrioventricular uncoupling. Pretreatment with doxycycline partially rescued the effects of DEHP on sinus activity, but did not ameliorate the effects on atrioventricular conduction. DEHP exposure also prolonged the ventricular action potential and effective refractory period, but had no measurable effect on intracellular calcium transient duration. Follow-up studies using hiPSC-CM confirmed that DEHP slows electrical conduction in a time (15 min - 3 hours) and dose-dependent manner (10-100 g/mL). Previous studies have suggested that phthalate toxicity is specifically attributed to metabolites of DEHP, including mono-2-ethylhexyl phthalate (MEHP). This study demonstrates that DEHP exposure also contributes to cardiac dysfunction in a dose- and time-dependent manner. Future work is warranted to investigate the impact of DEHP (and its metabolites) on human health, with special consideration for clinical procedures that employ plastic materials.

pharmacology and toxicology↗

bioRxiv2023

KairoSight-3.0: Validated Optical Mapping Software to Characterize Cardiac Electrophysiology, Excitation-Contraction Coupling, and Alternans

BackgroundCardiac optical mapping is an imaging technique that measures fluorescent signals across a cardiac preparation. Dual optical mapping of voltage-sensitive and calcium-sensitive probes allow for simultaneous recordings of cardiac action potentials and intracellular calcium transients with high spatiotemporal resolution. The analysis of these complex optical datasets is both time intensive and technically challenging; as such, we have developed a software package for semi-automated image processing and analysis. Herein, we report an updated version of our software package (KairoSight-3.0) with features to enhance characterization of cardiac parameters using optical signals. MethodsTo test software validity and applicability, we used Langendorff-perfused heart preparations to record transmembrane voltage and intracellular calcium signals from the epicardial surface. Isolated hearts from guinea pigs and rats were loaded with a potentiometric dye (RH237) and/or calcium indicator dye (Rhod-2AM) and fluorescent signals were acquired. We used Python 3.8.5 programming language to develop the KairoSight-3.0 software. Cardiac maps were validated with a user-specified manual mapping approach. ResultsManual maps of action potential duration (30 or 80% repolarization), calcium transient duration (30 or 80% reuptake), action potential and calcium transient alternans were constituted to validate the accuracy of software-generated maps. Manual and software maps had high accuracy, with >97% of manual and software values falling within 10 ms of each other and >75% within 5 ms for action potential duration and calcium transient duration measurements (n=1000-2000 pixels). Further, our software package includes additional cardiac metric measurement tools to analyze signal-to-noise ratio, conduction velocity, action potential and calcium transient alternans, and action potential-calcium transient coupling time to produce physiologically meaningful optical maps. ConclusionsKairoSight-3.0 has enhanced capabilities to perform measurements of cardiac electrophysiology, calcium handling, and the excitation-contraction coupling with satisfactory accuracy. Graphical Abstract Demonstrating Experimental and Data Analysis WorkflowCreated with Biorender.com O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=148 SRC="FIGDIR/small/538926v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@619850org.highwire.dtl.DTLVardef@156cd35org.highwire.dtl.DTLVardef@1ba772aorg.highwire.dtl.DTLVardef@e57084_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2023

The Impact of Chronic Phthalate Exposure on Rodent Anxiety and Cognition

There is a growing importance for environmental contributions to psychiatric disorders and understanding the impact of the exposome (i.e., pollutants and toxins). Increased biomonitoring and epidemiological studies, for example, suggest that daily phthalate chemical exposure contribute to neurological and behavioral abnormalities, however these mechanisms remain poorly understood. The current study therefore aimed to examine the effects of chronic phthalate exposure on rodent anxiety behaviors, cognition, and the impact on hypothalamic-pituitary{-} adrenal (HPA)-axis function. Adult male mice (C57BL6/J) were administered mono-2-ethylhexyl phthalate (MEHP) via drinking water (1 mg/ml), and anxiety-like behavior, cognition combined with HPA- axis and inflammatory assays were assessed after 3 weeks of MEHP exposure. MEHP-treated mice exhibited enhanced generalized anxiety-like behaviors, as demonstrated by reduced time spent in the open-arm of the elevated plus maze (EPM) and center exploration in the open field (OF). Tests of spatial, cognition and memory function were unchanged. Following MEHP administration, circulating levels of corticosterone and pro{-} inflammatory cytokines were significantly increased, while at the tissue level, MEHP-dependent reductions in glucocorticoid metabolism genes 11{beta}-hydroxysteroid dehydrogenase (11{beta}-HSD) 1 and 2. These data suggest that chronic MEHP exposure leads to enhanced generalized-anxiety behaviors independent of rodent measures of cognition and memory, which maybe driven by MEHP-dependent effects on HPA-axis and peripheral glucocorticoid metabolism function.

pharmacology and toxicology↗

bioRxiv2021

Bisphenol S and bisphenol F are less disruptive to cardiac electrophysiology and potentially safer for use in medical products, as compared to bisphenol A

BackgroundBisphenol A (BPA) is a high-production volume chemical that is commonly used to manufacture consumer and medical-grade plastic products. Due to its ubiquity, the general population can incur daily environmental exposure to BPA, while heightened BPA exposure has been reported in intensive care patients and industrial workers. Due to health concerns, structural analogues are being explored as replacements for BPA. ObjectiveThis study aimed to examine the direct nongenomic effects of BPA on cardiac electrophysiology and compare its safety profile to recently developed alternatives, including BPS (bisphenol S) and BPF (bisphenol F). MethodsWhole-cell voltage-clamp recordings were performed on cell lines transfected with Nav1.5, hERG, or Cav1.2. Results of single channel experiments were validated by conducting electrophysiology studies on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) and intact, whole heart preparations. ResultsOf the chemicals tested, BPA was the most potent inhibitor of both fast (INa-P) and late (INa-L) sodium channel (IC50 = 55.3 and 23.6 M, respectively), L-type calcium channel (IC50 = 30.8 M) and hERG channel current (IC50 = 127 M). The inhibitory effects of BPA and BPF on L-type calcium channels were supported by microelectrode array recordings, which revealed shortening of the extracellular field potential (akin to QT interval). Further, BPA and BPF exposure impaired atrioventricular conduction in intact, whole heart experiments. BPS did not alter any of the cardiac electrophysiology parameters tested. DiscussionResults of this study demonstrate that BPA and BPF exert an immediate inhibitory effect on cardiac ion channels, and that BPS may be a safer alternative. Intracellular signaling or genomic effects of bisphenol analogues were not investigated; therefore, additional mechanistic studies are necessary to fully elucidate the safety profile of bisphenol analogues on the heart.

pharmacology and toxicology↗

bioRxiv2020

Potential consequences of the red blood cell storage lesion on cardiac electrophysiology

The red blood cell (RBC) storage lesion is a series of morphological, functional and metabolic changes that RBCs undergo following collection, processing and refrigerated storage for clinical use. Since the biochemical attributes of the RBC unit shifts with time, transfusion of older blood products may contribute to cardiac complications, including hyperkalemia and cardiac arrest. We measured the direct effect of storage age on cardiac electrophysiology and compared with hyperkalemia, a prominent biomarker of storage lesion severity. Donor RBCs were processed using standard blood banking techniques. The supernatant was collected from RBC units (sRBC), 7-50 days post-donor collection, for evaluation using Langendorff-heart preparations (rat) or human stem-cell derived cardiomyocytes. Cardiac parameters remained stable following exposure to fresh sRBC (day 7: 5.9+0.2 mM K+), but older blood products (day 40: 9.7+0.4 mM K+) caused bradycardia (baseline: 279{+/-}5 vs day 40: 216{+/-}18 BPM), delayed sinus node recovery (baseline: 243{+/-}8 vs day 40: 354{+/-}23 msec), and increased the effective refractory period of the atrioventricular node (baseline: 77+2 vs day 40: 93+7 msec) and ventricle (baseline: 50+3 vs day 40: 98+10 msec) in perfused hearts. Beating rate was also slowed in human cardiomyocytes after exposure to older sRBC (-75+9%, day 40 vs control). Similar effects on automaticity and electrical conduction were observed with hyperkalemia (10-12 mM K+). This is the first study to demonstrate that older blood products directly impact cardiac electrophysiology, using experimental models. These effects are likely due to biochemical alterations in the sRBC that occur over time, including, but not limited to hyperkalemia. Patients receiving large volume and/or rapid transfusions may be sensitive to these effects. New & noteworthyWe demonstrate that red blood cell storage duration time can have downstream effects on cardiac electrophysiology, likely due to biochemical alterations in the blood product. Hyperkalemia and cardiac arrest have been reported following blood transfusions, but this is the first experimental study to show a direct correlation between storage duration and cardiac function. Infant and pediatric patients, and those receiving large volume and/or rapid transfusions may be sensitive to these effects.

physiology↗

bioRxiv2019

Age-dependent changes in electrophysiology and calcium handling: implications for pediatric cardiac research

RationaleThe heart continues to develop and mature after birth and into adolescence. Accordingly, cardiac maturation is likely to include a progressive refinement in both organ morphology and function during the postnatal period. Yet, age-dependent changes in cardiac electrophysiology and calcium handling have not yet been fully characterized.\n\nObjectiveThe objective of this study, was to examine the relationship between cardiac maturation, electrophysiology, and calcium handling throughout postnatal development in a rat model.\n\nMethodsPostnatal rat cardiac maturation was determined by measuring the expression of genes involved in cell-cell coupling, electrophysiology, and calcium handling. In vivo electrocardiograms were recorded from neonatal, juvenile, and adult animals. Simultaneous dual optical mapping of transmembrane voltage and calcium transients was performed on isolated, Langendorff-perfused rat hearts (postnatal day 0-3, 4-7, 8-14, adult).\n\nResultsYounger, immature hearts displayed slowed electrical conduction, prolonged action potential duration and increased ventricular refractoriness. Slowed calcium handling in the immature heart increased the propensity for calcium transient alternans which corresponded to alterations in the expression of genes encoding calcium handling proteins. Developmental changes in cardiac electrophysiology were associated with the altered expression of genes encoding potassium channels and intercalated disc proteins.\n\nConclusionUsing an intact whole heart model, this study highlights chronological changes in cardiac electrophysiology and calcium handling throughout postnatal development. Results of this study can serve as a comprehensive baseline for future studies focused on pediatric cardiac research, safety assessment and/or preclinical testing using rodent models.

physiology↗

bioRxiv2019

Simultaneous Dual Optical Mapping of the Heart Using a Single Excitation, Single Camera Approach

BackgroundOptical mapping of transmembrane voltage and intracellular calcium is a powerful tool for investigating cardiac physiology and pathophysiology. However, simultaneous dual mapping of two fluorescent probes remains technically challenging. We introduce a novel, easy-to-use approach that requires a path splitter, single camera and excitation light to simultaneously acquire voltage and calcium signals from whole heart preparations, which can be applied to other physiological models - including neurons and isolated cardiomyocytes.\n\nResultsComplementary probes were selected that could be excited with a single wavelength light source. Langendorff-perfused hearts (rat, swine) were stained and imaged using a sCMOS camera outfitted with an optical path splitter to simultaneously acquire two emission fields at high spatial and temporal resolution. Voltage (RH237) and calcium (Rhod2) signals were acquired concurrently on a single sensor, resulting in two 384x256 images at 814 frames per second. At this frame rate, the signal-to-noise ratio was 47 (RH237) and 85 (Rhod2). Imaging experiments were performed on small rodent hearts, as well as larger pig hearts with sufficient optical signals. In separate experiments, each dye was used independently to assess crosstalk and demonstrate signal specificity. Additionally, the effect of ryanodine on myocardial calcium transients was validated - with no measurable effect on the amplitude of optical action potentials. To demonstrate spatial resolution, ventricular tachycardia was induced -resulting in the novel finding that spatially discordant calcium alternans can be present in different regions of the heart, even when electrical alternans remain concordant. The described system excels in providing a wide field of view and high spatiotemporal resolution for a variety of cardiac preparations.\n\nConclusionsWe report the first multiparametric mapping system that simultaneously acquires calcium and voltage signals from cardiac preparations, using a path splitter, single camera and excitation light. This approach eliminates the need for multiple cameras, excitation light patterning or frame interleaving. These features can aid in the adoption of dual mapping technology by the broader cardiovascular research community, and decrease the barrier of entry into panoramic heart imaging, as it reduces the number of required cameras.

bioengineering↗