Phosphorylated compounds and function in isolated hearts: a 31P-NMR study

Abstract

The potential role of phosphorylated compounds in the control of myocardial cell respiration was investigated by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Isolated isovolumic rat hearts, perfused with a 9 mM glucose, 2 mM pyruvate medium at a constant beating rate (6 Hz) and temperature (37 degrees C), were subjected to changes in work load by varying the calcium concentration ([Ca2+]) in the perfusion fluid from 0.5 to 1.0, 1.5, or 2.0 mM. Each change in left ventricular developed pressure (LVDP) induced by the [Ca2+] change was accompanied by alterations in the inorganic phosphate-to-creatine phosphate ratio ([Pi]/[PCr]), with the ATP level remaining constant. The relationship between [Pi]/[PCr] and LVDP followed a Michaelis-Menten pattern with an apparent Michaelis constant (Km) of 0.09 and a maximal LVDP of 91 mmHg. This Km corresponded to intracellular concentrations of 1.2 mM for Pi and 13.0 mM for PCr. The calculated [ADP] and phosphorylation potential corresponding to these values were 44 microM and 151,000 M-1, respectively. All these values are close to those estimated under in situ physiological conditions. These results support the assumption that in the rat heart, as in skeletal muscle, mitochondrial activity could be controlled by changes in phosphorylated compound concentrations under normoxic conditions.

Energy metabolism response to calcium activation in isolated rat hearts during development and regression of T3-induced hypertrophy

“…The features of our protocol were discussed in details in a previous paper [18]. In brief, we observed stepwise changes in intracellular PCr and Pi contents in response to external calcium increase under our experimental conditions (presence of pyruvate 2 raM, low workload, adequate oxygen and substrate deliveries) and in contrast with the observations reported under other experimental conditions [26,27].…”

“…The PCr surface was corrected taking into account the saturation factor previously obtained with fully relaxed spectra. The myocardial PCr, Pi andATP contents were expressed as percentages of PCr + Pi + ATP which was assumed to be constant during the whole experiment as demonstrated previously [ 18]. These percentages were converted intoconcentrations using the 13P-ATP peak of the first spectrum as an internal standard with a concentration equal to the ATP concentration determined biochemically.…”

“…The aim of this study was precisely to evaluate the ability of the myocardial cell to respond to acute changes in energy demand after T3-treatment. For this purpose we used the experimental protocol established in our laboratory [18] in which the phosphorylated compound concentrations of the isolated heart are changing with the workload when the calcium coneentration in the perfusion fluid was increased. We used 31P-NMR spectroscopy to evaluate the free cytosolic phosphorylated compound concentrations (ATP, PCr, Pi) of the perfused heart and we followed the changes in concentration of these compounds when the external calcium concentration was stepwise increased.…”

Study of ischemic myocardial buffering capacity in perfused rat heart through rapidly interleaved 1H and 31P MRS measurements

“…It has been reasoned that during ischemia, the collapse of the proton gradient would inhibit lactate efflux and thus explain the high intracellular lactate accumulation observed (22). In our experiment, the lactate concentration of the myocardium (assuming 0.6 ml/g wet weight) (23) was over 20 times that of the perfusate (see Table 1). Efflux of lactate into the extracellular space would not significantly affect the experimental measurements of lactate content because the perfusate was contained within the coil volume.…”

Complementarity of magnetic resonance spectroscopy, positron emission tomography and single photon emission tomography for the in vivo investigation of human cardiac metabolism and neurotransmission

“…31p is the most commonly used nucleus in cardiac spectroscopy because of the abundance of high-energy phosphate compounds and their fundamental importance in myocardial energetics and function (Aussedat et al 1991 ;Chatham et al 1990;Fralix and Balaban 1989;Humphrey and Garlic 1991 ;Kitakaze et al 1988;Kupriyanov etal. 1987;Lewandowski etal.…”