Cyclical Changes in High-Energy Phosphates During the Cardiac Cycle by Pacing-Gated 31P Nuclear Magnetic Resonance

Abstract

number of studies of myocardial energy metabolism using 31 P nuclear magnetic resonance (NMR) have been done on in vitro 1-4 and in vivo [5][6][7] hearts. Cyclical changes in the concentration of adenosine triphosphate (ATP), phosphocreatine (PCr), and inorganic phosphate (Pi) during the cardiac cycle have also been studied using the subject's blood pressure or electrocardiogram (ECG)-gated 31 P NMR techniques. Several studies have demonstrated that cyclical changes in ATP, PCr, and Pi arise in vitro [8][9][10] and in vivo 11 in rat hearts. However, some investigators have not observed any cyclical changes in energy-related phosphate levels in in vitro 12 and in vivo 5,13-15 hearts. Controversy remains regarding the presence of cyclical changes in energy-related phosphate levels. Hoh et al performed electrophoretic analyses in pyrophosphate gels of intact myosin of adult rat myocardium. 16 Their study revealed the presence of 3 distinct components in ventricular myosin (V1, V2, and V3) and an association between the distribution of these myosin components and its adenosine triphosphatase (ATPase) activity.We have developed a pacing-gated NMR technique that is triggered by pulses for cardiac pacing. 10 This is a suitable method for determining cyclical changes in energy-related phosphate compounds in the cardiac cycle because the heart rate and the RF pulse repetition time maintain a constant relationship with pacing. The purpose of the present study was to determine whether cyclical changes in energy-related phosphate levels arise during the cardiac cycle in isolated rat hearts and are affected by differences in myosin isozyme composition. To perform these studies, we used pacing-gated 31 P NMR spectroscopy and manipulated the cardiac workload. Hypo-and hyperthyroid rats, in which myocardial contractility and myocardial energy use should differ as a result of varying myosin isozyme composition, were used in the studies. Methods AnimalsThe experiments were performed on hearts removed from 8-week-old male Wistar rats of the following groups: (1) normal rats (n=10); (2) hypothyroid rats (n=10), who had received 0.8 mg/ml 6-n-propyl-2-thiouracil (PTU; Sigma, St Louis, MO, USA) in drinking water for 21 days, 17 and (3) hyperthyroid rats (n=5), who had received daily intraperitoneal injections of 500 g/kg body weight 3,5,3'-triiodo-L-thyronine (T3; Sigma) for 5 days. 18 Heart PreparationRats were anesthetized intraperitoneally with pentobarbital (Nembutal 20-25 mg/100 g of body weight). The heart was rapidly excised and immersed in the buffer. The aorta was dissected free and mounted onto a Teflon cannula attached to a perfusion apparatus. The isolated, perfused rat heart was suspended in an NMR tube with an outer diameter measuring 15 mm. The heart was perfused in the Langendorff mode under isovolumic conditions at a constant temperature of 37°C and a constant hydrostatic perfusion pressure of 100 cmH2O. We used a modified KrebsHenseleit buffer solution containing 118.0 mmol/L NaCl, 4.7 Whether cyclical changes in e...

Application of the Principles of Systems Biology and Wiener's Cybernetics for Analysis of Regulation of Energy Fluxes in Muscle Cells in Vivo

“…The predictions from the mathematical modeling of feedback mechanisms of regulation of mitochondrial respiration in cardiac cells are consistent with the results of in vivo studies of isolated and perfused rat’s heart by using the pacing-gated 31 PRMS [164,165]. These studies, not very often discussed, showed that under conditions of metabolic homeostasis [meaning constant average values of high energy phosphate metabolites (Figure 6A)] cardiac contraction cycles are associated with small-scale oscillations in ATP, PCr and Pi concentrations, depending on heart workload and the intrinsic kinetic properties of myosin (Figure 6B).…”

“…(B) shows oscillations of relative PCr content during cardiac cycle in perfused rat’s heart under conditions of metabolic stability. The curve marked by empty circles (○) is refitted using experimental data received by Honda et al ., 2002 in gate-pacing in [165] (with permission), only the mean values of metabolites are shown. (C) The origin of the problem of the compartmentalization of adenine nucleotides and metabolic energy sensing in cardiac cells.…”

On the theoretical limits of detecting cyclic changes in cardiac high-energy phosphates and creatine kinase reaction kinetics usingin vivo31P MRS

“…Reaction velocities of myocardial ATP hydrolysis are not constant over the cardiac cycle, as suggested by older calorimetric studies indicating that about 75% of ATP consumption occurs during the systolic heart phase (11,12). Small changes in myocardial HEPs have been reported during the cardiac cycle in some perfused rat heart studies (13)(14)(15)(16)(17) and in one in vivo rat study (18), but the latter, to our knowledge, has not been reproduced (19). Cyclic changes in HEPs have not been observed in large animals or humans in vivo (20)(21)(22).…”

“…There has been much discussion about whether there are variations in HEPs during the cardiac cycle and, if so, whether they can be measured. Contradictory results have been published and hitherto no clear answer has arisen (13)(14)(15)(16)(17)(18)(19). The main focus of the current work was to investigate the flexibility of the CK reaction and the in vivo magnitude and accessibility of potential variations in HEPs and CK flux to detection by 31 P MRS methods.…”

Modular organization of cardiac energy metabolism: energy conversion, transfer and feedback regulation

“…Fluctuations of PCr and Cr were in the order of 8–15% during the different phases of the cardiac cycle (Honda et al . ). Inorganic phosphate, Pi, is not consumed by the myofibrillar MMCK reaction and therefore diffuses freely and enters mitochondrial matrix via its carrier (PiC).…”