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A study was performed to compare the baseline and protein kinase A (PKA)-dependent troponin I (TnI) phosphorylation in left ventricular myocytes from hearts of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Phosphorylation of TnI by PKA was believed to reduce myofilament Ca2+ sensitivity. Results indicated that after activation of the beta-adrenergic mechanism, PKA-dependent TnI phosphorylation from the SHR group was greater than in WKY coupled with decreased Ca2+ sensitivity of actomyosin ATPase activity.

A study was initiated to determine effects of mitochondrial metabolism on mitochondrial calcium (Ca) uptake during physiological processes. Mensuration of changes in the left ventricular function, pyruvate dehydrogenase (PDH) activity and mitochondrial Ca content was done in perfused hamster hearts frozen during systole. Results indicated that no relevant change was seen in mitchondrial Ca content during isoproterenol activation and increased perfusion pressure.

People with newly-discovered mutations in the gene for cardiac troponin T may have few symptoms of hypertrophic cardiomyopathy but nevertheless have a high risk of sudden death. Hypertrophic cardiomyopathy is a type of heart disease. Researchers used DNA analysis to detect mutations in the genes for the heart muscle proteins alpha tropomyosin and cardiac troponin T in 27 families and 126 people with a family history of hypertrophic cardiomyopathy. Five families and six people had a mutation in the gene for cardiac troponin T. Only one person had a mutation in the gene for alpha tropomyosin. Eight mutations in the cardiac troponin T gene could be linked to hypertrophic cardiomyopathy and five have never been described before. Death rates were higher in young patients with a mutation in cardiac troponin T, and more died suddenly, compared to patients with the more common mutation in the heavy chain of beta cardiac myosin. However, many of the patients with the cardiac troponin T mutation had no clinical signs of heart disease.

Abstract Background Reliability of real-time PCR (RT-qPCR) data is dependent on the use of appropriate reference gene(s) for normalization. To date, no validated reference genes have been reported for normalizing gene expression in human myocardium. This study aimed to identify validated reference genes for use in gene expression studies of failed and non-failed human myocardium. Methods Bioinformatic analysis of published human heart gene expression arrays (195 failed hearts, 16 donor hearts) was used to identify 10 stable and abundant genes for further testing. The expression stability of these genes was investigated in 28 failed and 28 non-failed human myocardium samples by RT-qPCR using geNorm software. Results Signal recognition particle 14 kDa (SRP14), tumor protein, translationally-controlled 1 (TPT1) and eukaryotic elongation factor 1A1 (EEF1A1) were ranked the most stable genes. The commonly used reference gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was ranked the least stable of the genes tested. The normalization strategy was tested by comparing RT-qPCR data of both normalized and raw expression levels of brain natriuretic peptide precursor (NPPB), a gene known to be up-regulated in heart failure. Non-normalized levels of NPPB exhibited a marginally significant difference between failed and non-failed samples (p = 0.058). In contrast, normalized NPPB expression levels were significantly higher in heart-failed patients compared with controls (p = 0.023). Conclusion This study used publicly available gene array data to identify a strategy for normalization involving two reference genes in combination that may have broad application for accurate and reliable normalization of RT-qPCR data in failed and non-failed human myocardium.

Reiser, Peter J., Michael A. Portman, Xue-Han Ning, and Christine Schomisch Moravec. Human cardiac myosin heavy chain isoforms in fetal and failing adult atria and ventricles. Am J Physiol Heart Circ Physiol 280: H1814-H1820, 2001.--The goal of this study was to test the hypothesis that the relative amounts of the cardiac myosin heavy chain (MHC) isoforms MHC-[Alpha] and MHC-[Beta] change during development and transition to heart failure in the human myocardium. The relative amounts of MHC-[Alpha] and MHC-[Beta] in ventricular and atrial samples from fetal (gestational days 47-110) and nonfailing and failing adult hearts were determined. The majority of the fetal right and left ventricular samples contained small relative amounts of MHC-[Alpha] (mean [is less than] 5% of total MHC). There was a small significant decrease in the level of [MHC-[Alpha] in the ventricles between 7 and 12 wk of gestation. Fetal atria expressed predominantly MHC-[Alpha] (mean [is greater than] 95%), with MHC-[Beta] being detected in most samples. The majority of adult nonfailing right and left ventricular samples had detectable levels of MHC-[Alpha] ranging from 1 to 10%. Failing right and left ventricles expressed a significantly lower level of [MHC-[Alpha]. [MHC-[Alpha] comprised -90% of the total MHC in adult nonfailing left atria, whereas the relative amount of MHC-[Alpha] in the left atria of individuals with dilated or ischemic cardiomyopathy was -50%. The differences in MHC isoform composition between fetal and nonfailing adult atria and between fetal and nonfailing adult ventricles were not statistically significant. We concluded that the MHC isoform compositions of fetal human atria are the same as those of nonfailing adult atria and that the ventricular MHC isoform composition is different between adult nonfailing and failing hearts. Furthermore, the marked alteration in atrial MHC isoform composition, associated with cardiomyopathy, does not represent a regression to a pattern that is uniquely characteristic of the fetal stage. development; myocardium; dilated cardiomyopathy; ischemic cardiomyopathy

BACKGROUND: Genome-wide association studies have identified 23 loci for atrial fibrillation (AF), but the mechanisms responsible for these associations, as well as the causal genes and genetic variants, remain undefined. METHODS: To identify the effect of common genetic variants on gene expression that might explain the mechanisms linking genome-wide association loci with AF risk, we performed RNA sequencing of left atrial appendages from a biracial cohort of 265 subjects. RESULTS: Combining gene expression data with genome-wide single nucleotide polymorphism data, we found that approximately two-thirds of the expressed genes were regulated in cis by common genetic variants at a false discovery rate of <0.05, defined as cis-expression quantitative trait loci. Twelve of 23 reported AF genome-wide association loci displayed genome-wide significant cis-expression quantitative trait loci, at PRRX1 (chromosome 1q24), SNRNP27 (1q24), CEP68 (2p14), FKBP7 (2q31), KCNN2 (5q22), FAM13B (5q31), CAV1 (7q31), ASAH1 (8p22), MYOZ1 (10q22), C11ORF45 (11q24), TBX5 (12q24), and SYNE2 (14q23), suggesting that altered expression of these genes plays a role in AF susceptibility. Allelic expression imbalance was used as an independent method to characterize the cis-control of gene expression. One thousand two hundred forty-eight of 5153 queried genes had cis-single nucleotide polymorphisms that significantly regulated allelic expression at a false discovery rate of <0.05. CONCLUSIONS: We provide a genome-wide catalog of the genetic control of gene expression in human left atrial appendage. These data can be used to confirm the relevance of genome-wide association loci and to direct future functional studies to identify the genes and genetic variants responsible for complex diseases such as AF. [ABSTRACT FROM AUTHOR]

Two-pore K+ (K2p) channels have been described in modulating background conductance as leak channels in different physiological systems. In the heart, the expression of K2p channels is heterogeneous with equivocation regarding their functional role. Our objective was to determine the K2p expression profile and their physiological and pathophysiological contribution to cardiac electrophysiology. Induced pluripotent stem cells (iPSCs) generated from humans were differentiated into cardiomyocytes (iPSC-CMs). mRNA was isolated from these cells, commercial iPSC-CM (iCells), control human heart ventricular tissue (cHVT), and ischemic (iHF) and nonischemic heart failure tissues (niHF). We detected 10 K2p channels in the heart. Comparing quantitative PCR expression of K2p channels between human heart tissue and iPSC-CMs revealed K2p1.1, K2p2.1, K2p5.1, and K2p17.1 to be higher expressed in cHVT, whereas K2p3.1 and K2p13.1 were higher in iPSC-CMs. Notably, K2p17.1 was significantly lower in niHF tissues compared with cHVT. Action potential recordings in iCells after K2p small interfering RNA knockdown revealed prolongations in action potential depolarization at 90% repolarization for K2p2.1, K2p3.1, K2p6.1, and K2p17.1. Here, we report the expression level of 10 human K2p channels in iPSC-CMs and how they compared with cHVT. Importantly, our functional electrophysiological data in human iPSC-CMs revealed a prominent role in cardiac ventricular repolarization for four of these channels. Finally, we also identified K2p17.1 as significantly reduced in niHF tissues and K2p4.1 as reduced in niHF compared with iHF. Thus, we advance the notion that K2p channels are emerging as novel players in cardiac ventricular electrophysiology that could also be remodeled in cardiac pathology and therefore contribute to arrhythmias. [ABSTRACT FROM AUTHOR]