. Visualization and quantification of whole rat heart laminar structure using highspatial resolution contrast-enhanced MRI. Am J Physiol Heart Circ Physiol 302: H287-H298, 2012. First published October 21, 2011; doi:10.1152/ajpheart.00824.2011.-It has been shown by histology that cardiac myocytes are organized into laminae and this structure is important in function, both influencing the spread of electrical activation and enabling myocardial thickening in systole by laminar sliding. We have carried out high-spatial resolution three-dimensional MRI of the ventricular myolaminae of the entire volume of the isolated rat heart after contrast perfusion [dimeglumine gadopentate (Gd-DTPA)]. Four ex vivo rat hearts were perfused with Gd-DTPA and fixative and high-spatial resolution MRI was performed on a 9.4T MRI system. After MRI, cryosectioning followed by histology was performed. Images from MRI and histology were aligned, described, and quantitatively compared. In the three-dimensional MR images we directly show the presence of laminae and demonstrate that these are highly branching and are absent from much of the subepicardium. We visualized these MRI volumes to demonstrate laminar architecture and quantitatively demonstrated that the structural features observed are similar to those imaged in histology. We showed qualitatively and quantitatively that laminar architecture is similar in the four hearts. MRI can be used to image the laminar architecture of ex vivo hearts in three dimensions, and the images produced are qualitatively and quantitatively comparable with histology. We have demonstrated in the rat that: 1) laminar architecture is consistent between hearts; 2) myolaminae are absent from much of the subepicardium; and 3) although localized orthotropy is present throughout the myocardium, tracked myolaminae are branching structures and do not have a discrete identity. myocardium; magnetic resonance imaging; ventricles; small animal imaging MYOCARDIAL STRUCTURE IS CENTRALLY important to cardiac mechanical function in health and disease (6), and myolaminar sliding is thought to be the principle mechanism of myocardial thickening in systole (10). Myolaminar structure has recently been shown to substantially influence the spread of activation in the myocardium (8,20).The myocardium is structured as stacked laminae of myocytes 4 -6 cells thick (ϳ80 -120 m), also known as myolaminae or sheets (24). These laminae are organized together in a complex fashion in which there are some regions of abrupt transmural change in laminar organization. The long axes of the myocytes, which make up the laminae, have a regular helical organization: the orientation of their long axes (with respect to the cardiac short axis) varies through ϳ120°trans-murally from endocardium to epicardium (33). The average orientation of the long axes of neighboring myocytes is known as the fiber-orientation (16). The myocardium therefore has regular lower order fiber architecture, with a more irregular and locally distinct higher order laminar arc...

Heart failure is the final common pathway of various cardiac pathologies and is associated with sudden cardiac death, mostly caused by ventricular arrhythmias. In this paper we briefly review the electrophysiological remodeling and the alterations in intracellular calcium handling, and the resulting arrhythmogenic mechanisms associated with heart failure. Intercellular uncoupling and fibrosis are identified as a major arrhythmogenic factors. Diet and ventricular wall stretch are discussed as modulating factors. Finally, emphasis is placed on the hitherto poorly studied aspects of right ventricular failure. This article is part of a Special Issue entitled: Heart failure pathogenesis and emerging diagnostic and therapeutic interventions.

Pulmonary hypertension provokes right heart failure and arrhythmias. Better understanding of the mechanisms underlying these arrhythmias is needed to facilitate new therapeutic approaches for the hypertensive, failing right ventricle (RV). The aim of our study was to identify the mechanisms generating arrhythmias in a model of RV failure induced by pulmonary hypertension. Rats were injected with monocrotaline to induce either RV hypertrophy or failure or with saline (control). ECGs were measured in conscious, unrestrained animals by telemetry. In isolated hearts, electrical activity was measured by optical mapping and myofiber orientation by diffusion tensor-MRI. Sarcoplasmic reticular Ca(2+) handling was studied in single myocytes. Compared with control animals, the T-wave of the ECG was prolonged and in three of seven heart failure animals, prominent T-wave alternans occurred. Discordant action potential (AP) alternans occurred in isolated failing hearts and Ca(2+) transient alternans in failing myocytes. In failing hearts, AP duration and dispersion were increased; conduction velocity and AP restitution were steeper. The latter was intrinsic to failing single myocytes. Failing hearts had greater fiber angle disarray; this correlated with AP duration. Failing myocytes had reduced sarco(endo)plasmic reticular Ca(2+)-ATPase activity, increased sarcoplasmic reticular Ca(2+)-release fraction, and increased Ca(2+) spark leak. In hypertrophied hearts and myocytes, dysfunctional adaptation had begun, but alternans did not develop. We conclude that increased electrical and structural heterogeneity and dysfunctional sarcoplasmic reticular Ca(2+) handling increased the probability of alternans, a proarrhythmic predictor of sudden cardiac death. These mechanisms are potential therapeutic targets for the correction of arrhythmias in hypertensive, failing RVs.

Benoist D, Stones R, Drinkhill M, Bernus O, White E. Arrhythmogenic substrate in hearts of rats with monocrotaline-induced pulmonary hypertension and right ventricular hypertrophy. Am J Physiol Heart Circ Physiol 300: H2230 -H2237, 2011. First published March 11, 2011 doi:10.1152/ajpheart.01226.2010.-Mechanisms associated with right ventricular (RV) hypertension and arrhythmias are less understood than those in the left ventricle (LV). The aim of our study was to investigate whether and by what mechanisms a proarrhythmic substrate exists in a rat model of RV hypertension and hypertrophy. Rats were injected with monocrotaline (MCT; 60 mg/kg) to induce pulmonary artery hypertension or with saline (CON). Myocardial levels of mRNA for genes expressing ion channels were measured by real-time RT-PCR. Monophasic action potential duration (MAPD) was recorded in isolated Langendorff-perfused hearts. MAPD restitution was measured, and arrhythmias were induced by burst stimulation. Twenty-two to twenty-six days after treatment, MCT animals had RV hypertension, hypertrophy, and decreased ejection fractions compared with CON. A greater proportion of MCT hearts developed sustained ventricular tachycardias/fibrillation (0.83 MCT vs. 0.14 CON). MAPD was prolonged in RV and less so in the LV of MCT hearts. There were decreased levels of mRNA for K ϩ channels. Restitution curves of MCT RV were steeper than CON RV or either LV. Dispersion of MAPD was greater in MCT hearts and was dependent on stimulation frequency. Computer simulations based on ion channel gene expression closely predicted experimental changes in MAPD and restitution. We have identified a proarrhythmic substrate in the hearts of MCT-treated rats. We conclude that steeper RV electrical restitution and rate-dependant RV-LV action potential duration dispersion may be contributing mechanisms and be implicated in the generation of arrhythmias associated with in RV hypertension and hypertrophy. electrical restitution; fibrillation; action potentials INCREASED PULMONARY ARTERIAL pressure increases loading on the right ventricle (RV), which can lead to electrical, mechanical, and structural remodeling. In humans, pulmonary artery hypertension (PAH) is a disease that can be unstable and RV failure is a common outcome (4, 13, 38). The QT interval and QT dispersion of the ECG have been reported to be increased (19,20), and the shift in ECG derived ventricular gradient [reflecting action potential duration (APD) dispersion] has been related to increased RV load (17). Such changes in electrical activity have been linked to arrhythmias (1, 39), and PAH is associated with arrhythmias in patients (11). RV pathophysiology is in general understudied compared with the left ventricle (LV; Ref. 38), and the mechanisms that underlie RV changes in electrical activity in response to hypertension are not well understood.The monocrotaline (MCT)-induced model of pulmonary arterial hypertension and RV hypertrophy is well established (e.g., Refs. 14, 23). MCT is a pyrrolizidine alkaloid from...

Typical high-temperature, short-time (HTST) pasteurization encompasses a lower heat treatment and shorter refrigerated shelf life compared with ultra-pasteurization (UP) achieved by direct steam injection (DSI-UP) or indirect heat (IND-UP). A greater understanding of the effect of different heat treatments on flavor and flavor chemistry of milk is required to characterize, understand, and identify the sources of flavors. The objective of this study was to determine the differences in the flavor and volatile compound profiles of milk subjected to HTST, DSI-UP, or IND-UP using sensory and instrumental techniques. Raw skim and raw standardized 2% fat milks (50 L each) were processed in triplicate and pasteurized at 78°C for 15 s (HTST) or 140°C for 2.3 s by DSI-UP or IND-UP. Milks were cooled and stored at 4°C, then analyzed at d 0, 3, 7, and 14. Sensory attributes were determined using a trained panel, and aroma active compounds were evaluated by solid-phase micro-extraction or stir bar sorptive extraction followed by gas chromatography-mass spectrometry, gas chromatography-olfactometry, and gas chromatography-triple quad mass spectrometry. The UP milks had distinct cooked and sulfur flavors compared with HTST milks. The HTST milks had less diversity in aroma active compounds compared with UP milks. Flavor intensity of all milks decreased by d 14 of storage. Aroma active compound profiles were affected by heat treatment and storage time in both skim and 2% milk. High-impact aroma active compounds were hydrogen sulfide, dimethyl trisulfide, and methional in DSI-UP and 2 and 3-methylbutanal, furfural, 2-heptanone, 2-acetyl-1-pyrroline, 2-aminoacetophenone, benzaldehyde, and dimethyl sulfide in IND-UP. These results provide a foundation knowledge of the effect of heat treatments on flavor development and differences in sensory quality of UP milks.

This study shows that localized structural alterations underlie a significant subset of previously unexplained sudden cardiac death. In the other subset, Purkinje electrical pathology seems as a dominant mechanism.

Gouda cheese is a washed-curd cheese that is traditionally produced from bovine milk and brined before ripening for 1 to 20 mo. In response to domestic and international demand, US production of Gouda cheese has more than doubled in recent years. An understanding of the chemical and sensory properties of Gouda cheese can help manufacturers create desirable products. The objective of this study was to determine the chemical and sensory properties of Gouda cheeses. Commercial Gouda cheeses (n = 36; 3 mo to 5 yr; domestic and international) were obtained in duplicate lots. Volatile compounds were extracted by solid-phase microextraction and analyzed by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Composition analyses included pH, proximate analysis, salt content, organic acid analysis by HPLC, and color. Flavor and texture properties were determined by descriptive sensory analysis. Focus groups were conducted to document US consumer perception followed by consumer acceptance testing (n = 149) with selected cheeses. Ninety aroma-active compounds in Gouda cheeses were detected by solid-phase microextraction/gas chromatography-olfactometry. Key aroma-active volatile compounds included diacetyl, 2- and 3-methylbutanal, 2-methylpropanal, methional, ethyl butyrate, acetic acid, butyric acid, homofuraneol, δ-decalactone, and 2-isobutyl-3-methoxypyrazine. Aged cheeses had higher organic acid concentrations, higher fat and salt contents, and lower moisture content than younger cheeses. Younger cheeses were characterized by milky, whey, sour aromatic, and diacetyl flavors, whereas aged cheeses were characterized by fruity, caramel, malty/nutty, and brothy flavors. International cheeses were differentiated by the presence of low intensities of cowy/barny and grassy flavors. Younger cheeses were characterized by higher intensities of smoothness and mouth coating, whereas aged cheeses were characterized by higher intensities of fracture and firmness. American consumers used Gouda cheese in numerous applications and stated that packaging appeal, quality, and age were more important than country of origin or nutrition when purchasing Gouda cheeses. Young and medium US cheeses ≤6 mo were most liked by US consumers. Three distinct consumer segments were identified with distinct preferences for cheese flavor and texture. Findings from this study establish key differences in Gouda cheese regarding age and origin and identify US consumer desires for this cheese category.

ance is a cardinal symptom of right ventricular heart failure (RV HF) and skeletal muscle adaptations play a role in this limitation. We determined regional remodeling of muscle structure and mitochondrial function in a rat model of RV HF induced by monocrotaline injection (MCT; 60 mg·kg Ϫ1 ; n ϭ 11). Serial sections of the plantaris were stained for fiber type, succinate dehydrogenase (SDH) activity and capillaries. Mitochondrial function was assessed in permeabilized fibers using respirometry, and isolated complex activity by blue native gel electrophoresis (BN PAGE). All measurements were compared with saline-injected control animals (CON; n ϭ 12). Overall fiber cross-sectional area was smaller in MCT than CON: 1,843 Ϯ 114 vs. 2,322 Ϯ 120 m 2 (P ϭ 0.009). Capillary-to-fiber ratio was lower in MCT in the oxidative plantaris region (1.65 Ϯ 0.09 vs. 1.93 Ϯ 0.07; P ϭ 0.03), but not in the glycolytic region. SDH activity (P ϭ 0.048) and maximal respiratory rate (P ϭ 0.012) were each ϳ15% lower in all fibers in MCT. ADP sensitivity was reduced in both skeletal muscle regions in MCT (P ϭ 0.032), but normalized by rotenone. A 20% lower complex I/IV activity in MCT was confirmed by BN PAGE. MCT-treatment was associated with lower mitochondrial volume density (lower SDH activity), quality (lower complex I activity), and fewer capillaries per fiber area in oxidative skeletal muscle. These features are consistent with structural and functional remodeling of the determinants of oxygen supply potential and utilization that may contribute to exercise intolerance and reduced quality of life in patients with RV HF. bioenergetics; exercise; mitochondrial complex I; respirometry; monocrotaline AN INCREASE IN PULMONARY ARTERIAL pressure increases the loading on the right ventricle of the heart. If sustained, pulmonary arterial hypertension (PAH) results in right ventricular hypertrophy and ultimately to right ventricular heart failure (RV HF), the major cause of death in sufferers of PAH (5, 21). Mortality rates of patients with PAH and RV HF are very high: 20 to 40% in the first 3 years after diagnosis (5). PAH and HF are characterized by a reduced tolerance to muscular exercise despite new therapies (2,19,21,33). Interestingly, the reduction in the maximal oxygen uptake (V O 2max ) is a better predictor of mortality than the central hemodynamic deficit or other traditional risk factors (36). Consequently, correction of the central blood flow limitation by heart transplantation does not consistently resolve functional limitations in patients with HF (43), supporting the view that skeletal muscle remodeling plays an important role in exercise intolerance and mortality in many chronic disease states including PAH and RV HF (17,33,54).A common observation in patients with LV (32) and RV (33) HF is muscle atrophy and weakness, that contributes to a loss of power generating capacity. This may be accompanied by a shift in muscle fiber type expression away from fatigueresistant type I fibers, towards type II (33, 42, 44) and changes i...