Improving the hERG model fitting using a deep learning-based method.

The hERG channel is one of the essential ion channels composing the cardiac action potential and the toxicity assay for new drug. Recently, the comprehensive in vitro proarrhythmia assay (CiPA) was adopted for cardiac toxicity evaluation. One of the hurdles for this protocol is identifying the kinetic effect of the new drug on the hERG channel. This procedure included the model-based parameter identification from the experiments. There are many mathematical methods to infer the parameters; however, there are two main difficulties in fitting parameters. The first is that, depending on the data and model, parametric inference can be highly time-consuming. The second is that the fitting can fail due to local minima problems. The simplest and most effective way to solve these issues is to provide an appropriate initial value. In this study, we propose a deep learning-based method for improving model fitting by providing appropriate initial values, even the right answer. We generated the dataset by changing the model parameters and trained our deep learning-based model. To improve the accuracy, we used the spectrogram with time, frequency, and amplitude. We obtained the experimental dataset from https://github.com/CardiacModelling/hERGRapidCharacterisation. Then, we trained the deep-learning model using the data generated with the hERG model and tested the validity of the deep-learning model with the experimental data. We successfully identified the initial value, significantly improved the fitting speed, and avoided fitting failure. This method is useful when the model is fixed and reflects the real data, and it can be applied to any in silico model for various purposes, such as new drug development, toxicity identification, environmental effect, etc. This method will significantly reduce the time and effort to analyze the data.

Cell-cell contacts via N-cadherin induce a regulatory renin secretory phenotype in As4.1 cells.

The lack of a clonal renin-secreting cell line has greatly hindered the investigation of the regulatory mechanisms of renin secretion at the cellular, biochemical, and molecular levels. In the present study, we investigated whether it was possible to induce phenotypic switching of the renin-expressing clonal cell line As4.1 from constitutive inactive renin secretion to regulated active renin secretion. When grown to postconfluence for at least two days in media containing fetal bovine serum or insulin-like growth factor-1, the formation of cell-cell contacts via N-cadherin triggered downstream cellular signaling cascades and activated smooth muscle-specific genes, culminating in phenotypic switching to a regulated active renin secretion phenotype, including responding to the key stimuli of active renin secretion. With the use of phenotype-switched As4.1 cells, we provide the first evidence that active renin secretion via exocytosis is regulated by phosphorylation/dephosphorylation of the 20 kDa myosin light chain. The molecular mechanism of phenotypic switching in As4.1 cells described here could serve as a working model for full phenotypic modulation of other secretory cell lines with incomplete phenotypes.

Variability, Mean, and Baseline Values of Metabolic Parameters in Predicting Risk of Type 2 Diabetes.

CONTEXT: The effect of baseline (B) and alteration of metabolic parameters (MPs), including plasma glucose (PG) testing, insulin resistance surrogates, and lipid profile and their mutual interactions on the development of type 2 diabetes mellitus (T2DM), has not been investigated systematically. OBJECTIVE: To access the association of the past variability (V), past mean (M), and B values of various MPs and their mutual interaction with the risk of T2DM. METHODS: A community-based, longitudinal analysis was conducted using the Korean Genome and Epidemiology Study comprising 3829 nondiabetic participants with completed MPs measurements during 3 biannually visits who were followed over the next 10 years. Outcomes included the incidence of T2DM during follow-up. RESULTS: Among predictors, PG concentrations measured during the oral glucose tolerance test were the most prominent T2DM determinants, in which the M of the average value of fasting PG (FPG), 1-hour, and 2-hour PGs had the strongest discriminative power (hazard ratios and 95% CI for an increment of SD: 3.00 (2.5-3.26), AUC: 0.82). The M values of MPs were superior to their B and V values in predicting T2DM, especially among postload PGs. Various mutual interactions between indices and among MPs were found. The most consistent interactants were the M values of high-density lipoprotein cholesterol and the M and V values of FPG. The findings were similar in normal glucose tolerance participants and were confirmed by sensitivity analyses. CONCLUSION: Postload PG, past alteration of measurements, and mutual interactions among indices of MPs are important risk factors for T2DM development.

Development of a Portable Respiratory Gas Analyzer for Measuring Indirect Resting Energy Expenditure (REE).

OBJECTIVE: A rapidly growing home healthcare market has resulted in the development of many portable or wearable products. Most of these products measure, estimate, or calculate physiologic signals or parameters, such as step counts, blood pressure, or electrocardiogram. One of the most important applications in home healthcare is monitoring one's metabolic state since the change of metabolic state could reveal minor or major changes in one's health condition. A simple and noninvasive way to measure metabolism is through breath monitoring. With breath monitoring by breath gas analysis, two important indicators like the respiratory quotient (RQ) and resting energy exposure (REE) can be calculated. Therefore, we developed a portable respiratory gas analyzer for breath monitoring to monitor metabolic state, and the performance of the developed device was tested in a clinical trial. Approach. The subjects consisted of 40 healthy men and women. Subjects begin to measure exhalation gas using Vmax 29 for 15 minutes. After that, subjects begin to measure exhalation gas via the developed respiratory gas analyzer. Finally, the recorded data on the volume of oxygen (VO2), volume of carbon dioxide (VCO2), RQ, and REE were used to validate correlations between Vmax 29 and the developed respiratory gas analyzer. RESULTS: The results showed that the root-mean-square errors (RMSE) values of VCO2, VO2, RQ, and REE are 0.0315, 0.0417, 0.504, and 0.127. Bland-Altman plots showed that most of the VCO2, VO2, RQ, and REE values are within 95% of the significance level. CONCLUSIONS: We have successfully developed and tested a portable respiratory gas analyzer for home healthcare. However, there are limitations of the clinical trial; the number of subjects is small in size, and the age and race of subjects are confined. The developed portable respiratory gas analyzer is a cost-efficient method for measuring metabolic state and a new application of home healthcare.

The mean of fasting, 1-h, and 2-h plasma glucose levels is superior to each separate index in predicting diabetes.

AIMS: The fasting, 1-h, and 2-h plasma glucose (PG) levels during oral glucose tolerance test represent different glucose metabolic functions. We examined whether averaging these PG indices (GLUM0.60.120) results in a better predictor of future type 2 diabetes (T2DM). METHODS: 7533 participants were followed up biannually for 12 years. Hazard ratios (HRs), area under the curve (AUC) of the receiver-operating characteristic, and the net reclassification index (NRI) for T2DM were calculated to compare the discriminative ability of GLUM0.60.120 versus other PG indices. RESULTS: The adjusted HRs and 95% confidence intervals for an increase in SD of GLUM0.60.120 was 2.50 (2.36-2.65) and 1.88 (1.73-2.04) in T2DM-free and normal glucose tolerance (NGT) participants, respectively. The AUC of GLUM0.60.120 was higher than that of fasting PG, 1-h, and 2-h PG values for T2DM-free (0.79 versus 0.67, 0.77, and 0.73) and NGT (0.73 versus 0.65, 0.72, and 0.61). The model using GLUM0.60.120 improved the classification of the models with fasting PG, 1-h, and 2-h PG values (NRI: 0.369, 0.272, and 0.282 for T2DM-free and 0.249, 0.131, and 0.351 for NGT participants with all p < 0.001). CONCLUSIONS: The mean of fasting, 1-h, and 2-h PG levels predicts future T2DM better than each index.

In silico models for evaluating proarrhythmic risk of drugs.

Safety evaluation of drugs requires examination of the risk of generating Torsade de Pointes (TdP) because it can lead to sudden cardiac death. Until recently, the QT interval in the electrocardiogram (ECG) has been used in the evaluation of TdP risk because the QT interval is known to be associated with the development of TdP. Although TdP risk evaluation based on QT interval has been successful in removing drugs with TdP risk from the market, some safe drugs may have also been affected due to the low specificity of QT interval-based evaluation. For more accurate evaluation of drug safety, the comprehensive in vitro proarrhythmia assay (CiPA) has been proposed by regulatory agencies, industry, and academia. Although the CiPA initiative includes in silico evaluation of cellular action potential as a component, attempts to utilize in silico simulation in drug safety evaluation are expanding, even to simulating human ECG using biophysical three-dimensional models of the heart and torso under the effects of drugs. Here, we review recent developments in the use of in silico models for the evaluation of the proarrhythmic risk of drugs. We review the single cell, one-dimensional, two-dimensional, and three-dimensional models and their applications reported in the literature and discuss the possibility of utilizing ECG simulation in drug safety evaluation.

Teaching cardiac excitation-contraction coupling using a mathematical computer simulation model of human ventricular myocytes.

To understand the excitation-contraction (E-C) coupling of cardiomyocytes, including the electrophysiological mechanism of their characteristically long action potential duration, is one of the major learning goals in medical physiology. However, the integrative interpretation of the responses occurring during the contraction-relaxation cycle is challenging due to the dynamic interaction of underlying factors. Starting in 2017, we adopted the mathematical computer simulation model of human ventricular myocyte (Cardiac E-C_Sim), hypothesizing that this educational technology may facilitate students' learning of cardiac physiology. Here, we describe the overall process for the educational application of Cardiac E-C_Sim in the human physiology practicum of Seoul National University College of Medicine. We also report the results from questionnaires covering detailed assessment of the practicum class. The analysis of results and feedback opinions enabled us to understand how the students had approached the problem-solving process. As a whole, the students could better accomplish the learning goals using Cardiac E-C_Sim, followed by constructive discussions on the complex and dynamic mechanisms of cardiac E-C coupling. We suggest that the combined approach of lecture-based teaching and computer simulations guided by a manual containing clinical context would be broadly applicable in physiology education.

Seasonal effects on resting energy expenditure are dependent on age and percent body fat.

Seasonal variation in resting energy expenditure (REE) is still under debate. This study investigated seasonal changes in REE and relevant factors among Korean adults. A total of 867 healthy volunteers (385 men and 482 women) aged 20-69 years were divided into four seasonal groups and subgroups based on age, body mass index (BMI), and percent body fat (PBF) quartiles. REE, body composition, glucose metabolism, thyroid hormones, and catecholamines were measured. The seasonal factor contributed to REE independent of anthropometric indices, with additional variation decreasing from 6% to 2% among younger and older persons, respectively. The adjusted REE in the winter was 5.4-13.9%, 7.8-14.3%, and 8.6-11.9% higher than that in the summer in the age, BMI, and PBF subgroups, respectively. T3 and log-transformed norepinephrine (NElog) were higher, whereas log-transformed epinephrine (EPIlog) was lower in the winter compared to the summer. The magnitude of the winter-summer difference in REE and T3 and of the summer-winter difference in EPIlog were reduced three-fold between the lowest and highest intervals of age and PBF, whereas the difference in NElog was constant across all age and PBF intervals. There was no obvious change in seasonal differences in REE or its relevant biomarkers across BMI intervals. In summary, season is an independent predictor of REE and its effect is attenuated by the increment of age and PBF but not BMI.

A Novel Nicotinamide Adenine Dinucleotide Correction Method for Intracellular Ca2+ Measurement with Fura-2-Analog in Live Cells.

To measure [Ca2+] quantitatively, fura-2 analogs, which are ratiometric fluoroprobes, are frequently used. However, dye usage is intrinsically limited in live cells because of autofluorescence interference, mainly from nicotinamide adenine dinucleotide (NADH). More specifically, this is a major obstacle when measuring the mitochondrial [Ca2+] quantitatively using fura-2 analogs because the majority of NADH is in the mitochondria. If the fluorescent dye concentration is the same, a certain excitation intensity should produce the same emission intensity. Therefore, the emission intensity ratio of two different excitation wavelengths should be constant. Based on this principle, a novel online correction method of NADH signal interference to measure [Ca2+] was developed, and the real signal intensity of NADH and fura-2 can be obtained. Further, a novel equation to calculate [Ca2+] was developed with isosbestic excitation or excitation at 400 nm. With this method, changes in mitochondrial [Ca2+] could be successfully measured. In addition, with a different set of the excitation and emission wavelengths, multiple parameters, including NADH, [Ca2+], and pH or mitochondrial membrane potential (Ψm), could be simultaneously measured. Mitochondrial [Ca2+] and Ψm or pH were measured using fura-2-FF and tetramethylrhodamine ethyl ester (TMRE) or carboxy-seminaphtorhodafluor-1 (carboxy-SNARF-1).

Koreans Do Not Have Higher Percent Body Fat than Australians: Implication for the Diagnosis of Obesity in Asians.

OBJECTIVE: It has been assumed that, for a given BMI, Asians have higher percent body fat (PBF) than Caucasians. As a result, it has been suggested that the BMI threshold for diagnosing obesity in Asians be lowered to less than 30 kg/m2 . This study sought to compare PBF between Koreans and Australians. METHODS: Whole-body fat mass and PBF were measured in 1,211 Koreans and 1,006 Australians using dual-energy x-ray absorptiometry (Lunar Prodigy; GE Healthcare, Madison, Wisconsin). The two groups were then matched for age and BMI by the propensity score method. RESULTS: For a given age and BMI, Koreans had lower PBF than Australians, and the difference was statistically significant in women (mean difference: -2.13%; 95% CI: -2.61% to -1.65%) but not in men (difference: -0.54%; 95% CI: -1.22% to 0.14%). Matched-pair analysis (423 pairs of women and 208 pairs of men) also showed that Korean women had statistically lower PBF than their Australian counterparts (P < 0.001). CONCLUSIONS: In individuals aged 60 years and older, Koreans do not have higher PBF than Australians after adjusting for BMI. These results suggest that there is no evidence for lowering the BMI threshold for the diagnosis of obesity in elderly Koreans.

Toward a grey box approach for cardiovascular physiome.

The physiomic approach is now widely used in the diagnosis of cardiovascular diseases. There are two possible methods for cardiovascular physiome: the traditional mathematical model and the machine learning (ML) algorithm. ML is used in almost every area of society for various tasks formerly performed by humans. Specifically, various ML techniques in cardiovascular medicine are being developed and improved at unprecedented speed. The benefits of using ML for various tasks is that the inner working mechanism of the system does not need to be known, which can prove convenient in situations where determining the inner workings of the system can be difficult. The computation speed is also often higher than that of the traditional mathematical models. The limitations with ML are that it inherently leads to an approximation, and special care must be taken in cases where a high accuracy is required. Traditional mathematical models are, however, constructed based on underlying laws either proven or assumed. The results from the mathematical models are accurate as long as the model is. Combining the advantages of both the mathematical models and ML would increase both the accuracy and efficiency of the simulation for many problems. In this review, examples of cardiovascular physiome where approaches of mathematical modeling and ML can be combined are introduced.

Three-Dimensional Heart Model-Based Screening of Proarrhythmic Potential by in silico Simulation of Action Potential and Electrocardiograms.

The proarrhythmic risk is a major concern in drug development. The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative has proposed the JTpeak interval on electrocardiograms (ECGs) and qNet, an in silico metric, as new biomarkers that may overcome the limitations of the hERG assay and QT interval. In this study, we simulated body-surface ECGs from patch-clamp data using realistic models of the ventricles and torso to explore their suitability as new in silico biomarkers for cardiac safety. We tested seven drugs in this study: dofetilide (high proarrhythmic risk), ranolazine, verapamil (QT increasing, but safe), bepridil, cisapride, mexiletine, and diltiazem. Human ventricular geometry was reconstructed from computed tomography (CT) images, and a Purkinje fiber network was mapped onto the endocardial surface. The electrical wave propagation in the ventricles was obtained by solving a reaction-diffusion equation using finite-element methods. The body-surface ECG data were calculated using a torso model that included the ventricles. The effects of the drugs were incorporated in the model by partly blocking the appropriate ion channels. The effects of the drugs on single-cell action potential (AP) were examined first, and three-dimensional (3D) body-surface ECG simulations were performed at free Cmax values of 1×, 5×, and 10×. In the single-cell and ECG simulations at 5× Cmax, dofetilide, but not verapamil or ranolazine, caused arrhythmia. However, the non-increasing JTpeak caused by verapamil and ranolazine that has been observed in humans was not reproduced in our simulation. Our results demonstrate the potential of 3D body-surface ECG simulation as a biomarker for evaluation of the proarrhythmic risk of candidate drugs.

The ion channel activator CyPPA inhibits melanogenesis via the GSK3ß/ß-catenin pathway.

Research into materials that inhibit melanogenesis in skin has gained interest. Screening for such compounds in B16F10 cells revealed that cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA), a positive modulator of small-conductance Ca2+-activated K+ channels, is a strong inhibitor of melanogenesis. We investigated the anti-melanogenic activity of CyPPA and the molecular mechanism by which CyPPA reduced melanin production in normal human melanocytes (NHM). CyPPA treatment resulted in a significant concentration-dependent reduction in melanin content without significant cytotoxicity; treatment likewise resulted in a significant time-dependent reduction in tyrosinase (TYR) activity. Treatment with CyPPA also decreased transcription of melanogenesis-related genes, including the gene encoding microphthalmia-associated transcription factor (MITF). In addition, visual evaluation of the MelanoDerm™ human skin model revealed significantly lower melanin content in the CyPPA-treated condition than in the untreated control. CyPPA was determined to modulate glycogen synthase kinase-3ß (GSK3ß) activity, thereby leading to a decrease in ß-catenin/MITF expression. Thus, CyPPA acts as a melanogenesis inhibitor by modulating the GSK3ß/ß-catenin/MITF pathway.

Body weight difference between dual-energy X-ray absorptiometry and multi-frequency bioelectrical impedance analysis attenuates the equivalence of body-composition assessment.

BACKGROUND/OBJECTIVES: Low agreement of body-composition analysis (BCA) using dual-energy X-ray absorptiometry (DXA) and multi-frequency bioelectrical impedance analysis (MF-BIA) has been reported. We examined whether this discrepancy is influenced by the precision of body weight (BW) measurement using DXA. SUBJECTS/METHODS: This cross-sectional study enrolled 1353 participants aged 53-83 years. A whole-body DXA scan and an eight-polar tactile-electrode impedance-meter using four electronic frequencies of 5, 50, 250, and 500 kHz were employed for BCA. The level of agreement between BW estimated using DXA and actual BW (WgtA) was calculated. The agreement of BCA parameters using DXA and MF-BIA across WgtA groups was also assessed. RESULTS: DXA incorrectly estimated BW, especially in men. In total, 13.5%, 5.1%, and 5.6% of the participants had BW bias levels of 2%, 3%, and ≥4%, respectively. Correlations of BCA parameters measured using DXA and MF-BIA, including body fat mass, percent body fat, and lean body mass (LBM), were gradually reduced, whereas the root mean square error was increased in accordance with the reduction in WgtA. DXA provided a lower LBM amount compared to MF-BIA and this difference increased significantly across groups with poor WgtA. CONCLUSIONS: Lower WgtA greatly contributed to the difference in BCA measured using DXA and MF-BIA.

Pulmonary Function Difference in Sasang Constitutional Types.

The purpose of this study was to determine the differences in pulmonary function among Sasang constitutional types in young adults. The Sasang Constitutional Analysis Tool (SCAT), pulmonary function tests (PFTs), and cardiopulmonary exercise tests were conducted in 417 participants from 2009 to 2015. Subjects with the Tae-Eum (TE) type had significantly higher inspiratory capacity (IC) and inspiratory reserve volume (IRV) values than those with the So-Yang (SY) and So-Eum (SE) types (P < 0.0001). The TE and SY types showed higher forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1) values than the SE type (P < 0.0001). An increase in IRV and a decrease in expiratory reserve volume (ERV) in TE type males remained even after adjusting for covariate factors. These results indicate that young adults with the TE type have weaker lung function than those with the other constitutional types, suggesting its innate physiological pulmonary features.

Anthropometry-based estimation of body heat capacity in individuals aged 7-69 years: the Size Korea Survey 2010.

Although our previously developed anthropometry-based calculation of heat capacity (HC) for adults appeared to be precise and valid, its use in children and adolescents may be associated with bias. This study investigated a large dataset from the Size Korea survey, a national anthropometric survey conducted in 2010, to revalidate our previous HC equation and to develop another one that is appropriate for children and adolescents. We enrolled 12,766 participants aged 7-69 years with body composition data measured by multi-frequency bioelectrical impedance analysis. Age was associated with HC in children aged 7-19 years (R2 = 0.58) but not in adults (R2 = 0.007). Linear regression was appropriate to describe the relationship between HC and body surface area (BSA) in adults, whereas the regression in children and adolescent was quadratic. The previously developed HC equation had high reliability (intra-class correlation coefficient = 0.995) and predictive power (accurate prediction rate = 86.1%) in the >20 age group. The model composed of sex, body weight, BSA, and BSA2 was appropriate for the prediction of HC in young individuals aged 7-19 years. In conclusion, anthropometric-based modelling is a simple, reliable, and useful method for the calculation of HC.

Lower cellular metabolic power can be an explanation for obesity trend in Tae-Eum type: hypothesis and clinical observation.

BACKGROUND: Those classified as Tae-Eum (TE)-type people in Sasang constitutional medicine (SCM) are prone to obesity. Although extensive clinical observations have confirmed this tendency, the underlying physiological mechanisms are unknown. Here, we propose a novel hypothesis using integrative physiology to explain this phenomenon. METHODS: Hypoactive lung function in the TE type indicates that respiration is attenuated at the cellular level-specifically, mitochondrial oxygen consumption. Because a functional reduction in cellular energy metabolism is suggestive of intrinsic hypoactivity in the consumption (or production) of metabolic energy, we reasoned that this tendency can readily cause weight gain via an increase in anabolism. Thus, this relationship can be derived from the graph of cellular metabolic power plotted against body weight. We analyzed the clinical data of 548 individuals to test this hypothesis. RESULTS: The statistical analysis revealed that the cellular metabolic rate was lower in TE-type individuals and that their percentage of obesity (body mass index >25) was significantly higher compared to other constitutional groups. CONCLUSION: Lower cellular metabolic power can be an explanation for the obesity trend in TE type people.

Body composition and personality traits in so-Yang type males.

BACKGROUND: The purpose of the present study was to examine the body composition of So-Yang type males according to Sasang constitutional medicine, which is popular in Korea. Different Sasang constitutional types are associated with different muscle distributions, body shapes, and disease susceptibilities. We used the Sasang Personality Questionnaire (SPQ) as a measure of the temperament of each Sasang type. METHODS: In total, 953 subjects aged over 20 years were recruited in Korea. We collected anthropometric parameters and bioimpedence information from the subjects and administered the SPQ. A logistic regression was conducted to calculate propensity scores. RESULTS: The percentage of skeletal muscle mass in So-Yang (SY) and non-So-Yang (non-SY) males was 45.8 ± 2.7 and 44.2 ± 3.3, respectively, before matching and 45.8 ± 2.6 and 44.9 ± 3.0, respectively, after propensity score matching. The extracellular water (ECW)/intracellular water (ICW) and extracellular water (ECW)/total body water (TBW) ratios and SPQ scores were significantly different between the SY and non-SY types. CONCLUSIONS: This study suggested that the SY type may be significantly and independently associated with body composition and could be associated with personality.

Neuronal nitric oxide synthase modulation of intracellular Ca2+ handling overrides fatty acid potentiation of cardiac inotropy in hypertensive rats.

Cardiac neuronal nitric oxide synthase (nNOS) is an important molecule that regulates intracellular Ca2+ homeostasis and contractility of healthy and diseased hearts. Here, we examined the effects of nNOS on fatty acid (FA) regulation of left ventricular (LV) myocyte contraction in sham and angiotensin II (Ang II)-induced hypertensive (HTN) rats. Our results showed that palmitic acid (PA, 100 µM) increased the amplitudes of sarcomere shortening and intracellular ATP in sham but not in HTN despite oxygen consumption rate (OCR) was increased by PA in both groups. Carnitine palmitoyltransferase-1 inhibitor, etomoxir (ETO), reduced OCR and ATP with PA in sham and HTN but prevented PA potentiation of sarcomere shortening only in sham. PA increased nNOS-derived NO only in HTN. Inhibition of nNOS with S-methyl-L-thiocitrulline (SMTC) prevented PA-induced OCR and restored PA potentiation of myocyte contraction in HTN. Mechanistically, PA increased intracellular Ca2+ transient ([Ca2+]i) without changing Ca2+ influx via L-type Ca2+ channel (I-LTCC) and reduced myofilament Ca2+ sensitivity in sham. nNOS inhibition increased [Ca2+]i, I-LTCC and reduced myofilament Ca2+ sensitivity prior to PA supplementation; as such, normalized PA increment of [Ca2+]i. In HTN, PA reduced I-LTCC without affecting [Ca2+]i or myofilament Ca2+ sensitivity. However, PA increased I-LTCC, [Ca2+]i and reduced myofilament Ca2+ sensitivity following nNOS inhibition. Myocardial FA oxidation (18F-fluoro-6-thia-heptadecanoic acid, 18F-FTHA) was comparable between groups, but nNOS inhibition increased it only in HTN. Collectively, PA increases myocyte contraction through stimulating [Ca2+]i and mitochondrial activity in healthy hearts. PA-dependent cardiac inotropy was limited by nNOS in HTN, predominantly due to its modulatory effect on [Ca2+]i handling.