H-NMR characterization of the human myocardium myoglobin and erythrocyte hemoglobin signals

Interaction of myoglobin with oleic acid

Previous studies have shown that palmitate (PA) can interact with myoglobin (Mb). The present study has investigated the interaction of the more soluble unsaturated fatty acid, oleic acid (OA). Indeed, (1)H NMR measurements of the Mb signal during OA titration also show signal changes consistent with specific and non-specific binding. At OA:Mb ratio<4:1, OA perturbs selectively the 8-heme methyl signal, consistent with a local and specific fatty acid-protein interaction. As OA:Mb ratio increases from 4:1 to 40:1, all hyperfine shifted MbCN signals decrease, consistent with a non-selective, global perturbation of the protein. The pH titration analysis indicates that the observed OA methylene signal in the presence of Mb reflects a non-specific interaction and does not originate from a shift in the lamella-micelle equilibrium. Given the OA interaction with Mb, a fatty acid flux model suggests that Mb can play a fatty acid transport role under certain physiological conditions.

Elevated carboxyhemoglobin in a marine mammal, the northern elephant seal

Low concentrations of endogenous carbon monoxide (CO), generated primarily through degradation of heme from heme-proteins, have been shown to maintain physiological function of organs and to exert cytoprotective effects. However, high concentrations of carboxyhemoglobin (COHb), formed by CO binding to hemoglobin, potentially prevent adequate O2 delivery to tissues by lowering arterial O2 content. Elevated heme-protein concentrations, as found in marine mammals, are likely associated with greater heme degradation, more endogenous CO production and, consequently, elevated COHb concentrations. Therefore, we measured COHb in elephant seals, a species with large blood volumes and elevated hemoglobin and myoglobin concentrations. The levels of COHb were positively related to the total hemoglobin concentration. The maximum COHb value was 10.4% of total hemoglobin concentration. The mean (± s.e.m.) value in adult seals was 8.7 ± 0.3% (N=6), while juveniles and pups (with lower heme-protein contents) had lower mean COHb values of 7.6 ± 0.2% and 7.1 ± 0.3%, respectively (N=9 and N=9, respectively). Serial samples over several hours revealed little to no fluctuation in COHb values. This consistent elevation in COHb suggests that the magnitude and/or rate of heme-protein turnover is much higher than in terrestrial mammals. The maximum COHb values from this study decrease total body O2 stores by 7%, thereby reducing the calculated aerobic dive limit for this species. However, the constant presence of elevated CO in blood may also protect against potential ischemia-reperfusion injury associated with the extreme breath-holds of elephant seals. We suggest the elephant seal represents an ideal model for understanding the potential cytoprotective effects, mechanisms of action and evolutionary adaptation associated with chronically elevated concentrations of endogenously produced CO.

Palmitate interaction with physiological states of myoglobin

BACKGROUND

Previous studies have shown that palmitate (PA) can bind specifically and non-specifically to Fe(III)MbCN. The present study has observed PA interaction with physiological states of Fe(II)Mb, and the observations support the hypothesis that Mb may have a potential role in facilitating intracellular fatty acid transport.

METHODS

1H NMR spectra measurements of the Mb signal during PA titration show signal changes consistent with specific and non-specific binding.

RESULTS

Palmitate (PA) interacts differently with physiological states of Mb. Deoxy Mb does not interact specifically or non-specifically with PA, while the carbonmonoxy myoglobin (MbCO) interaction with PA decreases the intensity of selective signals and produces a 0.15ppmupfield shift of the PAmethylene peak. The selective signal change upon PA titration provides a basis to determine an apparent PA binding constant,which serves to create a model comparing the competitive PA binding and facilitated fatty acid transport of Mb and fatty acid binding protein(FABP).

CONCLUSIONS

Given contrasting PA interaction of ligated vs. unligated Mb, the cellular fatty acid binding protein(FABP) and Mb concentration in the cell, the reported cellular diffusion coefficients, the PA dissociation constants from ligated Mb and FABP, a fatty acid flux model suggests that Mb can compete with FABP transporting cellular fatty acid.

GENERAL SIGNIFICANCE

Under oxygenated conditions and continuous energy demand, Mb dependent fatty acid transport could influence the cell's preference for carbohydrate or fatty acid as a fuel source and regulate fatty acid metabolism.

Myoglobin's old and new clothes: from molecular structure to function in living cells

Myoglobin, a mobile carrier of oxygen, is without a doubt an important player central to the physiological function of heart and skeletal muscle. Recently, researchers have surmounted technical challenges to measure Mb diffusion in the living cell. Their observations have stimulated a discussion about the relative contribution made by Mb-facilitated diffusion to the total oxygen flux. The calculation of the relative contribution, however, depends upon assumptions, the cell model and cell architecture, cell bioenergetics, oxygen supply and demand. The analysis suggests that important differences can be observed whether steady-state or transient conditions are considered. This article reviews the current evidence underlying the evaluation of the biophysical parameters of myoglobin-facilitated oxygen diffusion in cells, specifically the intracellular concentration of myoglobin, the intracellular diffusion coefficient of myoglobin and the intracellular myoglobin oxygen saturation. The review considers the role of myoglobin in oxygen transport in vertebrate heart and skeletal muscle, in the diving seal during apnea as well as the role of the analogous leghemoglobin of plants. The possible role of myoglobin in intracellular fatty acid transport is addressed. Finally, the recent measurements of myoglobin diffusion inside muscle cells are discussed in terms of their implications for cytoarchitecture and microviscosity in these cells and the identification of intracellular impediments to the diffusion of proteins inside cells. The recent experimental data then help to refine our understanding of Mb function and establish a basis for future investigation.

Oximetry with the NMR signals of hemoglobin Val E11 and Tyr C7

The NMR visibility of the signals from erythrocyte hemoglobin (Hb) presents an opportunity to assess the vascular PO₂ (partial pressure of oxygen) in vivo to gather insight into the regulation of O₂ transport, especially in contracting muscle tissue. Some concerns, however, have arisen about the validity of using the Val E11 signal as an indicator of PO₂, since its intensity depends on tertiary structural changes, in contrast to the quaternary structure changes associated with relaxed (R) and tense (T) transition during O₂ binding. We have examined the Val E11 and Tyr C7 signal intensity as a function of Hb saturation by developing an oximetry system, which permits the comparative analysis of the NMR and spectrophotometric measurements. The spectrophotometric assay defines the Hb saturation level at a given PO₂ and yields standard oxygen-binding curves. Under defined PO₂ and Hb saturation values, the NMR measurements have determined that the Val E11 signal, as well as the Tyr C7 signal, tracks closely Hb saturation and can therefore serve as a vascular oxygen biomarker.

Blood flow and metabolic regulation in seal muscle during apnea

In order to examine myoglobin (Mb) function and metabolic responses of seal muscle during progressive ischemia and hypoxemia, Mb saturation and high-energy phosphate levels were monitored with NMR spectroscopy during sleep apnea in elephant seals (Mirounga angustirostris). Muscle blood flow(MBF) was measured with laser-Doppler flowmetry (LDF). During six,spontaneous, 8–12 min apneas of an unrestrained juvenile seal, apneic MBF decreased to 46±10% of the mean eupneic MBF. By the end of apnea,MBF reached 31±8% of the eupneic value. The t1/2for 90% decline in apneic MBF was 1.9±1.2 min. The initial post-apneic peak in MBF occurred within 0.20±0.04 min after the start of eupnea. NMR measurements revealed that Mb desaturated rapidly from its eupenic resting level to a lower steady state value within 4 min after the onset of apnea at rates between 1.7±1.0 and 3.8±1.5% min–1, which corresponded to a muscle O2 depletion rate of 1–2.3 ml O2 kg–1 min–1. High-energy phosphate levels did not change with apnea. During the transition from apnea to eupnea, Mb resaturated to 95% of its resting level within the first minute. Despite the high Mb concentration in seal muscle, experiments detected Mb diffusing with a translational diffusion coefficient of 4.5×10–7 cm2 s–1,consistent with the value observed in rat myocardium. Equipoise PO2 analysis revealed that Mb is the predominant intracellular O2 transporter in elephant seals during eupnea and apnea.

Interaction of fatty acid with myoglobin

Upon titration with palmitate, the (1)H NMR spectra of metmyoglobin cyanide (MbCN) reveal a selective perturbation of the 8 heme methyl, consistent with a specific interaction of myoglobin (Mb) with fatty acid. Other detectable hyperfine shifted resonances of the heme group remain unchanged. Mb also enhances fatty acid solubility, as reflected in a more intense methylene peak of palmitate in Mb solution than in Tris buffer. Ligand binding analysis indicates an apparent palmitate dissociation constant (K(d)) of 43microM. These results suggest that Mb can bind fatty acid and may have a role in facilitating fatty acid transport in the cell.

Anisotropy and temperature dependence of myoglobin translational diffusion in myocardium: implication for oxygen transport and cellular architecture

Pulsed field gradient NMR methods have determined the temperature-dependent diffusion of myoglobin (Mb) in perfused rat myocardium. Mb diffuses with an averaged translational diffusion coefficient (DMb) of 4.24-8.37x10(-7)cm2/s from 22 degrees C to 40 degrees C and shows no orientation preference over a root mean-square displacement of 2.5-3.5 microm. The DMb agrees with the value predicted by rotational diffusion measurements. Based on the DMb, the equipoise diffusion PO2, the PO2 in which Mb-facilitated and free O2 diffusion contribute equally to the O2 flux, varies from 2.72 to 0.15 in myocardium and from 7.27 to 4.24 mmHg in skeletal muscle. Given the basal PO2 of approximately 10 mmHg, the Mb contribution to O2 transport appears insignificant in myocardium. In skeletal muscle, Mb-facilitated diffusion begins to contribute significantly only when the PO2 approaches the P50. In marine mammals, the high Mb concentration confers a predominant role for Mb in intracellular O2 transport under all physiological conditions. The Q10 of the DMb ranges from 1.3 to 1.6. The Mb diffusion data indicate that the postulated gel network in the cell must have a minimum percolation cutoff size exceeding 17.5 A and does not impose tortuosity within the diffusion root mean-square displacement. Moreover, the similar Q10 for the DMb of solution versus cell Mb suggests that any temperature-dependent alteration of the postulated cell matrix does not significantly affect protein mobility.

Myoglobin translational diffusion in rat myocardium and its implication on intracellular oxygen transport

Current theory of respiratory control invokes a role of myoglobin (Mb)-facilitated O2 diffusion in regulating the intracellular O2 flux, provided Mb diffusion can compete effectively with free O2 diffusion. Pulsed-field gradient NMR methods have now followed gradient-dependent changes in the distinct 1H NMR gamma CH3 Val E11 signal of MbO2 in perfused rat myocardium to obtain the endogenous Mb translational diffusion coefficient (D(Mb)) of 4.24 x 10(-7) cm2 s(-1) at 22 degrees C. The D(Mb) matches precisely the value predicted by in vivo NMR rotational diffusion measurements of Mb and shows no orientation preference. Given values in the literature for the Krogh's free O2 diffusion coefficient (K0), myocardial Mb concentration and a partial pressure of O2 that half saturates Mb (P50), the analysis yields an equipoise diffusion P(O2) of 1.77 mmHg, where Mb and free O2 contribute equally to the O2 flux. In the myocardium, Mb-facilitated O2 diffusion contributes increasingly more than free O2 diffusion when the P(O2) falls below 1.77 mmHg. In skeletal muscle, the P(O2) must fall below 5.72 mmHg. Altering the Mb P50 induces modest change. Mb-facilitated diffusion has a higher poise in skeletal muscle than in myocardium. Because the basal P(O2) hovers around 10 mmHg, Mb does not have a predominant role in facilitating O2 transport in myocardium but contributes significantly only when cellular oxygen falls below the equipoise diffusion P(O2).

Detection of myoglobin desaturation in Mirounga angustirostris during apnea

1H NMR solution-state study of elephant seal (Mirounga angustirostris) myoglobin (Mb) and hemoglobin (Hb) establishes the temperature-dependent chemical shifts of the proximal histidyl N(delta)H signal, which reflects the respective intracellular and vascular PO2 in vivo. Both proteins exist predominantly in one major isoform and do not exhibit any conformational heterogeneity. The Mb and Hb signals are detectable in M. angustirostris tissue in vivo. During eupnea M. angustirostris muscle maintains a well-saturated MbO2. However, during apnea, the deoxymyoglobin proximal histidyl N(delta)H signal becomes visible, reflecting a declining tissue PO2. The study establishes a firm methodological basis for using NMR to investigate the metabolic responses during sleep apnea of the elephant seal and to secure insights into oxygen regulation in diving mammals.

Oxygen supply and oxidative phosphorylation limitation in rat myocardium in situ

The 1H-NMR signal of the proximal histidyl-N(delta)H of deoxymyoglobin is detectable in the in situ rat myocardium and can reflect the intracellular PO2. Under basal normoxic conditions, the cellular PO2 is sufficient to saturate myoglobin (Mb). No proximal histidyl signal of Mb is detectable. On ligation of the left anterior descending coronary artery, the Mb signal at 78 parts/million (ppm) appears, along with a peak shoulder assigned to the corresponding signal of Hb. During dopamine infusion up to 80 microg. kg(-1) x min(-1), both the heart rate-pressure product (RPP) and myocardial oxygen consumption (MVO2) increase by about a factor of 2. Coronary flow increases by 84%, and O2 extraction (arteriovenous O2 difference) rises by 31%. Despite the increased respiration and work, no deoxymyoglobin signal is detected, implying that the intracellular O2 level still saturates MbO2, well above the PO2 at 50% saturation of Mb. The phosphocreatine (PCr) level decreases, however, during dopamine stimulation, and the ratio of the change in P(i) over PCr (DeltaP(i)/PCr) increases by 0.19. Infusion of either pyruvate, as the primary substrate, or dichloroacetate, a pyruvate dehydrogenase activator, abolishes the change in DeltaP(i)/PCr. Intracellular O2 supply does not limit MVO2, and the role of ADP in regulating respiration in rat myocardium in vivo remains an open question.

In vitro and in vivo studies of 1H NMR visibility to detect deoxyhemoglobin and deoxymyoglobin signals in myocardium

1H nuclear magnetic resonance (NMR) spectroscopy can be used noninvasively to detect the proximal histidyl N delta proton signals of deoxymyoglobin in the myocardium. However, the quantification of deoxymyoglobin is based on the assumption that the deoxymyoglobin signal detected is not contaminated by the deoxyhemoglobin signals contributed from the blood. The purpose of this study was to conduct in vitro and in vivo 1H NMR studies to examine the in vivo NMR visibility of deoxyhemoglobin in the myocardium. The results demonstrate that the NMR visibility of alpha and beta subunits of deoxyhemoglobin is sensitive to the pulse width for spin excitation because of short T2 relaxation times, and they are not NMR visible in the canine myocardium in vivo at 4.7 T when a 0.5-1.0 msec long Gaussian excitation pulse is used. Therefore, the resonance peak detected at approximately 72 ppm (relative to the water resonance) in the ischemic canine myocardium in vivo is dominated by deoxymyoglobin.

Cellular PO2 as a determinant of maximal mitochondrial O(2) consumption in trained human skeletal muscle

Previously, by measuring myoglobin-associated PO(2) (P(Mb)O(2)) during maximal exercise, we have demonstrated that 1) intracellular PO(2) is 10-fold less than calculated mean capillary PO(2) and 2) intracellular PO(2) and maximum O(2) uptake (VO(2 max)) fall proportionately in hypoxia. To further elucidate this relationship, five trained subjects performed maximum knee-extensor exercise under conditions of normoxia (21% O(2)), hypoxia (12% O(2)), and hyperoxia (100% O(2)) in balanced order. Quadriceps O(2) uptake (VO(2)) was calculated from arterial and venous blood O(2) concentrations and thermodilution blood flow measurements. Magnetic resonance spectroscopy was used to determine myoglobin desaturation, and an O(2) half-saturation pressure of 3.2 Torr was used to calculate P(Mb)O(2) from saturation. Skeletal muscle VO(2 max) at 12, 21, and 100% O(2) was 0.86 +/- 0.1, 1.08 +/- 0.2, and 1.28 +/- 0.2 ml. min(-1). ml(-1), respectively. The 100% O(2) values approached twice that previously reported in human skeletal muscle. P(Mb)O(2) values were 2.3 +/- 0.5, 3.0 +/- 0.7, and 4.1 +/- 0.7 Torr while the subjects breathed 12, 21, and 100% O(2), respectively. From 12 to 21% O(2), VO(2) and P(Mb)O(2) were again proportionately related. However, 100% O(2) increased VO(2 max) relatively less than P(Mb)O(2), suggesting an approach to maximal mitochondrial capacity with 100% O(2). These data 1) again demonstrate very low cytoplasmic PO(2) at VO(2 max), 2) are consistent with supply limitation of VO(2 max) of trained skeletal muscle, even in hyperoxia, and 3) reveal a disproportionate increase in intracellular PO(2) in hyperoxia, which may be interpreted as evidence that, in trained skeletal muscle, very high mitochondrial metabolic limits to muscle VO(2) are being approached.

Comparative analysis of NMR and NIRS measurements of intracellular PO2 in human skeletal muscle

1H NMR has detected both the deoxygenated proximal histidyl NdeltaH signals of myoglobin (deoxyMb) and deoxygenated Hb (deoxyHb) from human gastrocnemius muscle. Exercising the muscle or pressure cuffing the leg to reduce blood flow elicits the appearance of the deoxyMb signal, which increases in intensity as cellular PO2 decreases. The deoxyMb signal is detected with a 45-s time resolution and reaches a steady-state level within 5 min of pressure cuffing. Its desaturation kinetics match those observed in the near-infrared spectroscopy (NIRS) experiments, implying that the NIRS signals are actually monitoring Mb desaturation. That interpretation is consistent with the signal intensity and desaturation of the deoxyHb proximal histidyl NdeltaH signal from the beta-subunit at 73 parts per million. The experimental results establish the feasibility and methodology to observe the deoxyMb and Hb signals in skeletal muscle, help clarify the origin of the NIRS signal, and set a stage for continuing study of O2 regulation in skeletal muscle.

Observing the deoxy myoglobin and hemoglobin signals from rat myocardium in situ

1H NMR proximal histidyl NdeltaH signals of deoxy hemoglobin (Hb) and myoglobin (Mb) are distinguishable in the rat myocardium in situ. In the normoxic resting state, the blood and tissue pO2 is sufficient to saturate both Mb and Hb. No deoxy Mb or Hb signals are detected. Under 12% inspired O2, the erythrocyte Hb is partially desaturated and yields the alpha and beta proximal histidyl NdeltaH signals of deoxy Hb. The detection of the Hb signals clarifies the debate about the NMR visibility of erythrocyte Hb in vivo and augments the strategy to observe tissue pO2.

Myoglobin and hemoglobin rotational diffusion in the cell

The detection of the 1H NMR signal of myoglobin (Mb) in tissue opens an opportunity to examine its cellular diffusion property, which is central to its purported role in facilitating oxygen transport. In perfused myocardium the field-dependent transverse relaxation analysis of the deoxy Mb proximal histidyl NdeltaH indicates that the Mb rotational correlation time in the cell is only approximately 1.4 times longer than it is in solution. Such a mobility is consistent with the theory that Mb facilitates oxygen diffusion from the sarcoplasm to the mitochondria. The microviscosities of the erythrocyte and myocyte environment are different. The hemoglobin (Hb) rotational correlation time is 2.2 longer in the cell than in solution. Because both the overlapping Hb and Mb signals are visible in vivo, a relaxation-based NMR strategy has been developed to discriminate between them.

Regional myocardial oxygen tension: 19F MRI of sequestered perfluorocarbon

A novel noninvasive method of measuring local myocardial oxygen tension (pO2) in the perfused rat heart using 19F MRI is demonstrated. Tissue pO2 was determined on the basis of the 19F spin-lattice relaxation rate (R1) of perflubron (perfluorooctyl bromide) sequestered in the heart after IV infusion of an emulsion. Spectroscopic measurement of R1 was previously used to measure a global weighted average of oxygen status. 19F MRI now provides 3D spatial resolution indicating local cardiac pO2 under normally perfused, globally ischemic, and regionally ischemic conditions.

H-NMR signal of Arenicola marina myoglobin in vivo as an index of tissue oxygenation

Key questions on how intertidal animals adapt to hypoxic stress center on the high energy phosphate response to decreasing oxygenation. With recent 1H/31P-NMR techniques to monitor mammalian tissue metabolism, a novel approach has emerged to observe potentially the intracellular oxygen interaction in invertebrates. The present study indicates that Arenicola marina, a standard model for intertidal animals, exhibits a distinct set of Mb 1H-NMR signals in vivo, corresponding to the two isolated Mb isoforms. Specifically both deoxy-Mb I and deoxy-Mb II exhibit paramagnetically shifted signals at 93.4 ppm and 92.5 ppm at 25 degrees C, respectively, which arise from the proximal histidyl NdeltaH. These signals reflect the cellular oxygenation state and indicate clearly that the phosphotaurocyamine level begins to drop at the onset of anoxia and declines gradually to 50% of control after 3.5 h. 1H Mb spectra indicate protein heterogeneity originating from heme as well as structural disorder.

Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport

The assumption that cellular oxygen pressure (PO2) is close to zero in maximally exercising muscle is essential for the hypothesis that O2 transport between blood and mitochondria has a finite conductance that determines maximum O2 consumption. The unique combination of isolated human quadriceps exercise, direct measures of arterial, femoral venous PO2, and 1H nuclear magnetic resonance spectroscopy to detect myoglobin desaturation enabled this assumption to be tested in six trained men while breathing room air (normoxic, N) and 12% O2 (hypoxic, H). Within 20 s of exercise onset partial myoglobin desaturation was evident even at 50% of maximum O2 consumption, was significantly greater in H than N, and was then constant at an average of 51 +/- 3% (N) and 60 +/- 3% (H) throughout the incremental exercise protocol to maximum work rate. Assuming a myoglobin PO2 where 50% of myoglobin binding sites are bound with O2 of 3.2 mmHg, myoglobin-associated PO2 averaged 3.1 +/- .3 (N) and 2.1 +/- .2 mmHg (H). At maximal exercise, measurements of arterial PO2 (115 +/- 4 [N] and 46 +/- 1 mmHg [H]) and femoral venous PO2 (22 +/- 1.6 [N] and 17 +/- 1.3 mmHg [H]) resulted in calculated mean capillary PO2 values of 38 +/- 2 (N) and 30 +/- 2 mmHg(H). Thus, for the first time, large differences in PO2 between blood and intracellular tissue have been demonstrated in intact normal human muscle and are found over a wide range of exercise intensities. These data are consistent with an O2 diffusion limitation across the 1-5-microns path-length from red cell to the sarcolemma that plays a role in determining maximal muscle O2 uptake in normal humans.

Oximetry by dynamic nuclear polarization

This study describes quantitatively the effect of O2 on the dynamic nuclear polarization (DNP) of water protons. It is shown theoretically how DNP enhancement is altered by the paramagnetism of O2. The nonlinear effect of oxygen on the enhancement factor has been approximated by a first order expression that provides accurate predictions of the experimental results obtained with phosphate-buffered solutions of 2,2,6,6 tetramethyl-4-oxo-piperidine-N-oxyl. The proton relaxation rates and DNP line width were measured for nitroxide concentrations ranging from 0.5 to 10 mM and for oxygen partial pressures ranging from 0 to 760 mmHg. A method is suggested for the calculation of the nitroxide and oxygen concentrations of a sample, based on two measurements, one with on-resonance EPR irradiation, the other with slightly off-resonance irradiation. Although the correlation between the values for the actual and calculated oxygen concentrations is good, the accuracy of the calculated oxygen concentration values remains poor, because of the large number of parameters involved in this calculation.

1H nuclear magnetic resonance studies of sarcoplasmic oxygenation in the red cell-perfused rat heart

The proximal histidine N delta H proton of deoxymyoglobin experiences a large hyperfine shift resulting in its 1H nuclear magnetic resonance (NMR) signal appearing at approximately 76 ppm (at 35 degrees C), downfield of the diamagnetic spectral region. 1H NMR of this proton is used to monitor sarcoplasmic oxygen pressure in isolated perfused rat heart. This method monitors intracellular oxygenation in the whole heart and does not reflect oxygenation in a limited region. The deoxymyoglobin resonance intensity is reduced upon conversion of myoglobin to the ferric form by sodium nitrite. 1H resonances of the N delta H protons of the alpha and beta subunits of bovine deoxyhemoglobin do not interfere with the measurement of myoglobin deoxygenation in blood-perfused rat heart. We find that steady-state myoglobin deoxygenation is increased progressively (and reversibly) as oxygenation of the perfusing medium is decreased in both saline and red blood cell-perfused hearts at constant work output. An eightfold increase in the heart rate of the blood-perfused heart resulted in no change in the deoxymyoglobin signal intensity. Intracellular PO2 of myoglobin-containing cells is maintained remarkably constant in changing work states.

Myoglobin signal as an NMR tissue thermometer: implication for hyperthermia treatment of tumors

Measuring local tissue temperature is critical in establishing a rational approach for hyperthermia treatment of tumors. We have found that the heme signals of myoglobin provide a unique basis for NMR thermometry in vivo. In particular the 5-methyl heme signal of MbCN exhibits a sharp, temperature-dependent resonance that is distinguishable in the tissue spectrum. Its calibrated chemical shift can then reflect the local tissue temperature in vivo.