31P NMR spectroscopy, chemical analysis, and free Mg2+ of rabbit bladder and uterine smooth muscle

Creatine Kinase Equilibration and ΔGATP over an Extended Range of Physiological Conditions: Implications for Cellular Energetics, Signaling, and Muscle Performance

In this report, we establish a straightforward method for estimating the equilibrium constant for the creatine kinase reaction (CK Keq″) over wide but physiologically and experimentally relevant ranges of pH, Mg2+ and temperature. Our empirical formula for CK Keq″ is based on experimental measurements. It can be used to estimate [ADP] when [ADP] is below the resolution of experimental measurements, a typical situation because [ADP] is on the order of micromolar concentrations in living cells and may be much lower in many in vitro experiments. Accurate prediction of [ADP] is essential for in vivo studies of cellular energetics and metabolism and for in vitro studies of ATP-dependent enzyme function under near-physiological conditions. With [ADP], we were able to obtain improved estimates of ΔGATP, necessitating the reinvestigation of previously reported ADP- and ΔGATP-dependent processes. Application to actomyosin force generation in muscle provides support for the hypothesis that, when [Pi] varies and pH is not altered, the maximum Ca2+-activated isometric force depends on ΔGATP in both living and permeabilized muscle preparations. Further analysis of the pH studies introduces a novel hypothesis around the role of submicromolar ADP in force generation.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

NAD+ repletion improves muscle function in muscular dystrophy and counters global PARylation

Neuromuscular diseases are often caused by inherited mutations that lead to progressive skeletal muscle weakness and degeneration. In diverse populations of normal healthy mice, we observed correlations between the abundance of mRNA transcripts related to mitochondrial biogenesis, the dystrophin-sarcoglycan complex, and nicotinamide adenine dinucleotide (NAD⁺) synthesis, consistent with a potential role for the essential cofactor NAD⁺ in protecting muscle from metabolic and structural degeneration. Furthermore, the skeletal muscle transcriptomes of patients with Duchene's muscular dystrophy (DMD) and other muscle diseases were enriched for various poly[adenosine 5'-diphosphate (ADP)-ribose] polymerases (PARPs) and for nicotinamide N-methyltransferase (NNMT), enzymes that are major consumers of NAD⁺ and are involved in pleiotropic events, including inflammation. In the mdx mouse model of DMD, we observed significant reductions in muscle NAD⁺ levels, concurrent increases in PARP activity, and reduced expression of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme for NAD⁺ biosynthesis. Replenishing NAD⁺ stores with dietary nicotinamide riboside supplementation improved muscle function and heart pathology in mdx and mdx/Utr^-/- mice and reversed pathology in Caenorhabditis elegans models of DMD. The effects of NAD⁺ repletion in mdx mice relied on the improvement in mitochondrial function and structural protein expression (α-dystrobrevin and δ-sarcoglycan) and on the reductions in general poly(ADP)-ribosylation, inflammation, and fibrosis. In combination, these studies suggest that the replenishment of NAD⁺ may benefit patients with muscular dystrophies or other neuromuscular degenerative conditions characterized by the PARP/NNMT gene expression signatures.

Mitochondrial NAD(P)H In vivo: Identifying Natural Indicators of Oxidative Phosphorylation in the (31)P Magnetic Resonance Spectrum

Natural indicators provide intrinsic probes of metabolism, biogenesis and oxidative protection. Nicotinamide adenine dinucleotide metabolites (NAD(P)) are one class of indicators that have roles as co-factors in oxidative phosphorylation, glycolysis, and anti-oxidant protection, as well as signaling in the mitochondrial biogenesis pathway. These many roles are made possible by the distinct redox states (NAD(P)(+) and NAD(P)H), which are compartmentalized between cytosol and mitochondria. Here we provide evidence for detection of NAD(P)(+) and NAD(P)H in separate mitochondrial and cytosol pools in vivo in human tissue by phosphorus magnetic resonance spectroscopy ((31)P MRS). These NAD(P) pools are identified by chemical standards (NAD(+), NADP(+), and NADH) and by physiological tests. A unique resonance reflecting mitochondrial NAD(P)H is revealed by the changes elicited by elevation of mitochondrial oxidation. The decline of NAD(P)H with oxidation is matched by a stoichiometric rise in the NAD(P)(+) peak. This unique resonance also provides a measure of the improvement in mitochondrial oxidation that parallels the greater phosphorylation found after exercise training in these elderly subjects. The implication is that the dynamics of the mitochondrial NAD(P)H peak provides an intrinsic probe of the reversal of mitochondrial dysfunction in elderly muscle. Thus, non-invasive detection of NAD(P)(+) and NAD(P)H in cytosol vs. mitochondria yields natural indicators of redox compartmentalization and sensitive intrinsic probes of the improvement of mitochondrial function with an intervention in human tissues in vivo. These natural indicators hold the promise of providing mechanistic insight into metabolism and mitochondrial function in vivo in a range of tissues in health, disease and with treatment.

Na(+)-independent Mg(2+) transport sensitive to 2-aminoethoxydiphenyl borate (2-APB) in vascular smooth muscle cells: involvement of TRPM-like channels

Magnesium is associated with several important cardiovascular diseases. There is an accumulating body of evidence verifying the important roles of Mg²⁺-permeable channels. In the present study, we estimated the intracellular free Mg²⁺ concentration ([Mg²⁺]_i) using ³¹P-nuclear magnetic resonance (³¹P-NMR) in porcine carotid arteries. pH_i and intracellular phosphorus compounds were simultaneously monitored. Removal of extracellular divalent cations (Ca²⁺ and Mg²⁺) in the absence of Na⁺ caused a gradual decrease in [Mg²⁺]_i to ∼60% of the control value after 125 min. On the other hand, the simultaneous removal of extracellular Ca²⁺ and Na⁺ in the presence of Mg²⁺ gradually increased [Mg²⁺]_i in an extracellular Mg²⁺-dependent manner. 2-aminoethoxydiphenyl borate (2-APB) attenuated both [Mg²⁺]_i load and depletion caused under Na⁺- and Ca²⁺-free conditions. Neither [ATP]_i nor pH_i correlated with changes in [Mg²⁺]_i. RT-PCR detected transcripts of both TRPM6 and TRPM7, although TRPM7 was predominant. In conclusion, the results suggest the presence of Mg²⁺-permeable channels of TRPM family that contribute to Mg²⁺ homeostasis in vascular smooth muscle cells. The low, basal [Mg²⁺]_i level in vascular smooth muscle cells is attributable to the relatively low activity of this Mg²⁺ entry pathway.

Heart slice NMR

Nuclear magnetic resonance (NMR) spectroscopy of the heart is normally carried out using whole heart preparations under coronary perfusion. In such preparations, either radical changes in ionic composition of the perfusate or applications of numerous drugs would affect coronary microcirculation. This report communicates the first (31)P NMR spectroscopy study using a heart slice preparation (left ventricular slices) superfused with extracellular medium. The ratio of phosphocreatine concentration to ATP concentration was approximately 2.1. Also, intracellular pH and Mg(2+) concentration ([Mg(2+)](i)), estimated from the chemical shifts of inorganic phosphate and ATP, were comparable with those under retrograde perfusion. [Mg(2+)](i) was significantly increased by the removal of extracellular Na(+), supporting the essential role of Na(+)-coupled Mg(2+) transport in Mg(2+) homeostasis of the heart. Heart slice preparation could also be used to evaluate the potency of cardiac drugs, regardless of their possible effects on coronary microcirculation.

Magnesium regulates ADP dissociation from myosin V

Processivity in myosin V is mediated through the mechanical strain that results when both heads bind strongly to an actin filament, and this strain regulates the timing of ADP release. However, what is not known is which steps that lead to ADP release are affected by this mechanical strain. Answering this question will require determining which of the several potential pathways myosin V takes in the process of ADP release and how actin influences the kinetics of these pathways. We have addressed this issue by examining how magnesium regulates the kinetics of ADP release from myosin V and actomyosin V. Our data support a model in which actin accelerates the release of ADP from myosin V by reducing the magnesium affinity of a myosin V-MgADP intermediate. This is likely a consequence of the structural changes that actin induces in myosin to release phosphate. This effect on magnesium affinity provides a plausible explanation for how mechanical strain can alter this actin-induced acceleration. For actomyosin V, magnesium release follows phosphate release and precedes ADP release. Increasing magnesium concentration to within the physiological range would thus slow both the ATPase activity and the velocity of movement of this motor.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Ca2+-dependent modulation of intracellular Mg2+ concentration with amiloride and KB-R7943 in pig carotid artery

It has long been recognized that magnesium is associated with several important diseases, including diabetes, hypertension, cardiovascular, and cerebrovascular diseases. In the present study, we measured the intracellular free Mg2+ concentration ([Mg2+]i) using 31P nuclear magnetic resonance (NMR) in pig carotid artery smooth muscle. In normal solution, application of amiloride (1 mm) decreased [Mg2+]i by approximately 12% after 100 min. Subsequent washout tended to further decrease [Mg2+]i. In contrast, application of amiloride significantly increased [Mg2+]i (by approximately 13% after 100 min) under Ca2+-free conditions, where passive Mg2+ influx is facilitated. The treatments had little effect on intracellular ATP and pH (pHi). Essentially the same Ca2+-dependent changes in [Mg2+]i were produced with KB-R7943, a selective blocker of reverse mode Na+-Ca2+ exchange. Application of dimethyl amiloride (0.1 mM) in the presence of Ca2+ did not significantly change [Mg2+]i, although it inhibited Na+-H+ exchange at the same concentration. Removal of extracellular Na+ caused a marginal increase in [Mg2+]i after 100-200 min, as seen in intestinal smooth muscle in which Na+-Mg2+ exchange is known to be the primary mechanism of maintaining a low [Mg2+]i against electrochemical equilibrium. In Na+-free solution (containing Ca2+), neither amiloride nor KB-R7943 decreased [Mg2+]i, but they rather increased it. The results suggest that these inhibitory drugs for Na+-Ca2+ exchange directly modulate Na+-Mg2+ exchange in a Ca2+-dependent manner, and consequently produce the paradoxical decrease in [Mg2+]i in the presence of Ca2+.

Magnesium abnormalities of skeletal muscle in dermatomyositis and juvenile dermatomyositis

OBJECTIVE

To characterize abnormalities in magnesium levels in the muscles of patients with dermatomyositis (DM) and juvenile dermatomyositis (JDM) and to evaluate the beneficial effects of prednisone and immunosuppressive therapy in elevating free magnesium (Mg(2+)) and ATP-bound magnesium (Mg-ATP).

METHODS

The study groups consisted of 12 adult patients with DM and 10 juvenile patients with JDM. The 2 control groups were 11 normal adults and 6 healthy children. Levels of total ATP in the quadriceps muscles of the subjects were determined during rest, exercise, and recovery, using noninvasive P-31 magnetic resonance spectroscopy (MRS). Concentrations of the biologically active free Mg(2+) and the enzymatically active Mg-ATP complex were determined from the spectroscopy data by calculation of the chemical shifts of the beta-phosphate peak of ATP.

RESULTS

Mg-ATP levels in DM and JDM myopathic muscles were at least 37% lower than those in normal muscles during rest, exercise, and recovery from exercise (P < 0.0005). Free Mg(2+) levels were normal in DM and JDM myopathic muscles at rest, but were significantly lower than control values during exercise and recovery (P < 0.029 and P < 0.005 for DM and JDM, respectively). Prednisone and immunosuppressive therapy partially reversed the magnesium abnormalities, as evidenced by elevation of the levels of Mg-ATP and free Mg(2+).

CONCLUSION

Low levels of Mg-ATP and free Mg(2+) are concordant with weakness and fatigue observed in DM and JDM patients. Immunosuppressive therapy alleviates, in part, the magnesium deficits in the diseased muscles. Therefore, Mg-ATP and free Mg(2+) may play a significant role in the pathophysiology of these diseases.

Phosphocholine and phosphoethanolamine during chick embryo myogenesis: a (31)P-NMR study

Elevated contents of phosphoethanolamine (Etn-P) and/or phosphocholine (Cho-P), a common feature of most tumours with respect to normal counterparts, may also occur in non-cancerous proliferating tissues. The significance of these alterations in relation to cell proliferation, differentiation and maturation is scarcely understood. In this work, the Cho-P and Etn-P pools were measured by (31)P-NMR in extracts of chick embryo pectoral muscle at different days of development. The average concentration of these metabolites exhibited the highest values (respectively, 1.5 and 3.0 micromol/mg DNA) on days 9-11 and decreased at later stages of myogenesis. While, however, Cho-P maintained substantial levels (above 1.0 micromol/mg DNA) also during myotube formation (days 11-18) and stepwise decreased (to about 0.5 micromol/mg DNA) upon fibres' maturation, Etn-P gradually decreased between day 11 and hatching time (down to about 0.2 micromol/mg DNA). These results demonstrate that significant changes may occur in the steady-state pools of these metabolites during normal in vivo cellular development and differentiation, and are consistent with: (a) high rates of phospholipid biosynthesis reported in the literature for proliferating myoblasts; (b) sustained phosphatidylcholine synthesis maintained also during myoblast fusion; and (c) decreased requirement of phospholipid synthesis in the last phase of in ovo myofibre maturation.

Effect of Mg2+ on stress, myosin phosphorylation, and ATPase activity in detergent-skinned swine carotid media

Smooth muscle contraction has a relatively high requirement for free magnesium (Mg2+). In this study we examined the effect of Mg2+ concentration ([Mg2+]) on Ca2+-dependent stress development and stress maintenance, myosin ATPase activity, and myosin light chain (MLC) phosphorylation levels in Triton X-100 detergent-skinned fibers of the swine carotid media. Increasing [Mg2+] in a stepwise fashion from 0.1 to 6 mM 1) decreased the magnitude and Ca2+ sensitivity of stress development but augmented the amount of stress maintained without proportional MLC phosphorylation, 2) produced a greater decrease in the Ca2+ sensitivity of MLC phosphorylation than that of stress development, and 3) decreased myosin ATPase activity. These findings demonstrate that Mg2+ differentially modulates the MLC phosphorylation-dependent development of stress and the MLC phosphorylation-independent maintenance of stress. We suggest that increases in [Mg2+] enhance stress maintenance by increasing [MgADP], thus increasing the number of cross bridges in a force-generating state, and by a direct effect on the pathway responsible for Ca2+-dependent, MLC phosphorylation-independent contractions.

Cytoplasmic free concentrations of Ca2+ and Mg2+ in skeletal muscle fibers at rest and during contraction

This review summarizes estimates for cytoplasmic-free concentrations of Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) at rest and during contraction of skeletal muscles, from which substantial quantitative information about them has been accumulated. Although the estimates of resting [Ca2+]i in the literature widely differ, which is because of the variety of difficulties related to different methodologies used, recent studies suggest that estimates of resting [Ca2+]i of approximately 0.05-0.1 microM are likely to be correct. Following action potential propagation, the Ca2+ release from the sarcoplasmic reticulum causes a transient rise of [Ca2+]i (Ca2+ transient). The large peak amplitude and brief time course of the Ca2+ transients have been established only recently by studies with low-affinity Ca2+ indicators developed in the past decade. These technical improvements in [Ca2+]i measurements have made it possible to study relationships between [Ca2+]i and force in intact muscle fibers. In the second part of this review, various estimates of [Mg2+]i in the resting muscle are discussed. Relatively recent estimates of the [Mg2+]i level appear to be about 1.0 mM. Using the current knowledge of concentrations and reaction properties of intracellular Ca2+-Mg2+ binding sites, we constructed a model for dynamic Mg2+ movement following Ca2+ transients. The model predicts that with a train of action potentials, the sustained rise of [Ca2+]i produces an elevation of [Mg2+]i of about 200 microM.

Capillary electrophoretic measurement of tissue metabolites

A method for the measurement of tissue metabolites from rabbit urinary bladder using capillary electrophoresis (CE) has been developed. The method generates a reproducible electropherogram containing > 20 peaks, including NAD, NADH, lactate, UDP-glucose, phosphocreatine, creatine, ATP, ADP, GTP, and UTP, from < 20 nl of extract solution generated from 1.1 nl (or approximately 1.2 micrograms) of tissue in < 40 min. Multiple samples from the same bladder produce SE comparable with enzymatic or nuclear magnetic resonance (NMR) measurements of metabolites: phosphorus-NMR measurement requires 10(6) more tissue than CE; individual enzymatic measurements using 100 microliters/sample require 2,000 microliters, a 10(5) greater volume than required by CE for the same number of metabolites. CE detects about three times more peaks than phosphorus-NMR on a similar time scale. Comparable measurements using enzymatic analysis would require approximately 10 times longer. The combination of minimal tissue volume requirements, rapid measurement, and reproducibility makes CE a valuable tool in the investigation of simultaneous changes in multiple metabolites from minute tissue samples.

Neuroprotective effects of MgSO4 and MgCl2 in closed head injury: a comparative phosphorus NMR study

Previous studies have shown that free magnesium levels decline after traumatic brain injury and that magnesium salt administration improves posttraumatic outcome. These earlier studies, however, have been limited to models of injury that do not produce a significant degree of diffuse axonal injury and have used either MgSO4 or MgCl2 as the magnesium salt. The present study compares the neuroprotective efficacy of MgSO4 and MgCl2 in a severe model of diffuse axonal injury in rats using phosphorus nuclear magnetic resonance spectroscopy and the rotarod test to monitor effects on metabolism and neurologic outcome, respectively. Both MgSO4 and MgCl2 given as a bolus of 100 micromoles/kg at 30 min after severe, closed head injury significantly improved brain intracellular free magnesium concentration and neurologic outcome. These findings suggest that both salts penetrate the blood-brain barrier after brain trauma, enter injured tissue, and subsequently improve neurologic outcome.

Consequences of metabolic inhibition in smooth muscle isolated from guinea-pig stomach

1. In smooth muscle isolated from the guinea-pig stomach, cyanide (CN) and iodoacetic acid (IAA) were applied to block oxidative phosphorylation and glycolysis, respectively. Effects of IAA on generation of spontaneous mechanical and electrical activities were systematically investigated by comparing those of CN. Spontaneous activity ceased in 10-20 min during applications of 1 mM IAA. On the other hand, application of 1 mM CN also reduced the spontaneous activity, but never terminated it. In the presence of CN the negativity of the resting membrane potential was slightly reduced. 2. When spontaneous activity ceased with IAA, the resting membrane potential was not significantly affected. Also, before ceasing, the amplitude and duration of the spontaneous electrical activity were significantly reduced. The amplitude of the electrotonic potential was, however, not changed by IAA. Further, glibenclamide did not prevent the effects of IAA. These results suggest that, unlike cardiac muscle, activation of metabolism-dependent K+ channels in stomach smooth muscle does not seem to play a major role in reducing and terminating spontaneous activity during metabolic inhibition. 3. Carbachol-induced contraction transiently increased, and subsequently decreased gradually during application of IAA. 4. After 50 min application of IAA, when there was no spontaneous activity, the concentrations of phosphocreatine (PCr) and ATP measured with 31P nuclear magnetic resonance decreased to 60 and 80% of the control, respectively, while inorganic phosphate (Pi) concentration paradoxically fell to below detectable levels. During subsequent prolonged application of IAA, high-energy phosphates steadily decreased. On the other hand, after 50 min CN application, [PCr] and [ATP] decreased to approximately 30 and 80% of the control, respectively, while [Pi] increased by 2.6-fold. 5. In the presence of either CN or IAA, spontaneous mechanical and electrical activities were reduced or eliminated, although amounts of high-energy phosphates sufficient to contract smooth muscle remained. It can be postulated that some mechanism(s) related to energy metabolism, but not including ATP-sensitive K+ channels, plays an important role in generating spontaneous activity in guinea-pig stomach smooth muscle. During metabolic inhibition the energy metabolism-dependent mechanism(s) would preserve high-energy phosphates, and consequently cell viability, by stopping spontaneous activity.

Predicted changes in concentrations of free and bound ATP and ADP during intracellular Ca2+ signaling

High Ca2+ concentrations can develop near Ca2+ sources during intracellular signaling and might lead to localized regulation of Ca2+-dependent processes. By shifting the amount of Ca2+ and other cations associated with ATP, local high Ca2+ concentrations might also alter the substrate available for membrane-associated and cytoplasmic enzymes. To study this, simultaneous equations were solved over a range of Ca2+ and Mg2+ concentrations to determine the general effects of Ca2+ on the concentrations of free and Ca2+- and Mg2+-bound forms of ATP. To obtain a more specific picture of the changes that might occur in smooth muscle cells, mathematical models of Ca2+ diffusion and regulation were used to predict the magnitude and time course of near-membrane Ca2+ transients and their effects on the free and bound forms of ATP near the membrane. The results of this work indicate that changes in free Ca2+ concentration over the range of 50 nM-100 microM would result in significant changes in free ATP concentration, MgATP concentration, and the CaATP-to-MgATP concentration ratio.

Apparent Mg2+-adenosine 5-triphosphate dissociation constant measured with Mg2+ macroelectrodes under conditions pertinent to 31P NMR ionized magnesium determinations

Using Mg2+ macroelectrodes based on the sensor ETH 7025 and accurate Mg2+-EDTA buffer solutions, the apparent Mg2+-ATP dissociation constant (Kapp) was measured at 25 and 37 degrees C in background solutions mimicking the cationic intracellular milieu of muscle cells. The mean +/- SD (in microM) at 25 degrees C was 157.0 +/- 13 (n = 4), 127.5 +/- 12.0 (n = 11), 101.0 +/- 9.0 (n = 4) and at 37 degrees C was 106.6 +/- 9.6 (n = 4), 87.4 +/- 4.9 (n = 4), 78.1 +/- 2.0 (n = 4) at pH values of 6.7, 7.2, and 7.7, respectively. The dependence of Kapp at 25 degrees C on the ionic strength was also measured, the mean +/- SD (microM) being 61.9 +/- 2.2 (n = 3), 127.5 +/- 12 (n = 11), and 243.0 +/- 11.8 (n = 3) at ionic strengths of 0. 087, 0.156 (normal background), and 0.3 m, respectively. These values are larger than the Kapp values most commonly used in the literature (87.4 microM compared to 38 microM at pH 7.2 and 37 degrees C) to estimate the [Mg2+]i in 31P NMR experiments, attributed to the difficulties in setting the [Mg2+]i without the use of Mg2+ buffer solutions. If these new values are used, the literature values for [Mg2+]i estimated by 31P NMR increase by a factor of around 1.5, making them similar to values obtained by direct Mg2+ microelectrode measurements.

The effects of temperature, pH, and magnesium on the diffusion coefficient of ATP in solutions of physiological ionic strength

Intracellular diffusive transport of adenosine triphosphate (ATP) is critical to cellular metabolism. Physical models predict that diffusion coefficients (D) of small molecules are functions of temperature and viscosity of the diffusive environment. Therefore, changes in body temperature, commonly experienced by poikilotherms, are expected to result in changes in the rate of intracellular ATP transport. However, it has been postulated that changes in the electrical charge of ATP may influence the interaction between ATP and the cytosol and that the temperature sensitivity of DATP may deviate from the predicted relationship. To investigate the effects of changes in electrical charge on the temperature sensitivity of DATP, we measured DATP under various conditions of temperature, pH, and pMg2+. Changes in pH and pMg2+ were used to alter the net charge of ATP, and DATP was measured in solutions of physiological ionic strength. Results showed a positive correlation between DATP and temperature; DATP = 1.75 +/- 0.09, 3.68 +/- 0.14, and 4.64 +/- 0.13 (mean +/- S.E.M.) x 10(-6) cm2/s at 5 degrees C, 25 degrees C, and 40 degrees C, respectively. Changes in pH and pMg2+ did not significantly influence DATP, and the change in DATP with respect to temperature was similar to that predicted on the basis of changes in temperature and viscosity of the aqueous medium.

Minimal cost per twitch in rattlesnake tail muscle

Sound production is one of the most energetically costly activities in animals. Minimizing contraction costs is one means of achieving the activation rates necessary for sound production (20-550 Hz) (refs 1-3) without exceeding energy supplies. Rattlesnakes produce a sustained, high-frequency warning sound by extremely rapid contraction of their tailshaker muscles (20-90 Hz) (refs 4,5). The ATP cost per twitch is only 0.015 micromol ATP per g muscle per twitch during rattling, as measured by in vivo magnetic resonance. The reduced volume density of myofibre (32%) in tailshaker muscle is consistent with contraction cost being minimized (crossbridge cycling), in contrast to the contractile costs of vertebrate locomotory and asynchronous insect flight muscle. Thus tailshaker muscle is an example of sound-producing muscle designed for 'high frequency, minimal cost'. The high rates of rattling are achieved by minimizing contractile use of ATP, which reduces the cost per twitch to among the lowest found for striated muscle.

31P NMR studies of human soleus and gastrocnemius show differences in the J gamma beta coupling constant of ATP and in intracellular free magnesium

Localized proton decoupled 31P in vivo NMR spectroscopy of the human calf muscle was performed using a 1.5-T whole-body imager and the slice selective two-dimensional chemical-shift-imaging (2D-CSI) technique. The 31P-31P coupling constants and the chemical shifts of ATP were compared in gastrocnemius and soleus. Significant differences were found in the coupling constant J gamma beta: (18.1 +/- 0.7) Hz versus (17.1 +/- 0.6) Hz (means +/- SD, P < 10-5). Differences were also observed in the chemical shift separation delta alpha beta between the alpha- and beta-ATP signal: (8.498 +/- 0.023) ppm versus (8.522 +/- 0.222) ppm (p < 0.001) in gastrocnemius and soleus, respectively. A higher [MgATP]/[ATPfree] ratio and a significantly higher level of intracellular free magnesium of (0.52 +/- 0.06) mM in gastrocnemius versus (0.46 +/- 0.05) mM in soleus (p < 0.001) can be derived based on delta alpha beta and KDMgATP. Heterogeneity needs to be taken into account in clinical studies on magnesium by NMR methods in calf muscle. The coupling constant J gamma beta provides additional information, possibly on enzymatic processes, and correlates with [Mg2+free]. The detailed analysis of muscles with different fiber type characteristics lends support to the significance of this parameter in evaluating metabolism. The data reported can be used as prior knowledge for fits in which the coupling constants are set to a fixed value.

Transgenic animals as models in the study of the neurobiological role of polyamines

Natural polyamines, putrescine, spermidine and spermine, exhibit a number of neurophysiological and metabolic effects in brain preparations. In the in vitro studies, several specific sites of action have been identified such as ion channels, transmitter release and Ca2+ homeostasis. Polyamines have been linked to the development of neuronal degeneration caused by, for instance, epileptic seizures and stroke. The role of endogenous polyamines in the functioning brain is not clear, however. We review the work carried out using state-of-the-art transgenic animal models for polyamine research. A number of transgenic mouse lines carrying human ornithine decarboxylase, spermidine synthase and S-adenosylmethionine decarboxylase gene have been generated. Of these animals those with ornithine decarboxylase transgene show an extensive and constitutive expression of the enzyme in the brain with an exceedingly high putrescine concentration, a phenotype that is not encountered under physiological conditions. In this article we review the neurometabolic, behavioural and histological data that has been obtained from these transgenic mice.

Responses of mouse fast and slow skeletal muscle to streptozotocin diabetes: myosin isoenzymes and phosphorous metabolites

A condition similar to insulin-dependent diabetes mellitus (IDDM) was induced in male CD-1 mice by injection of streptozotocin (STZ). Five weeks after treatment, the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles were isolated for analysis. Phosphorous metabolites were quantified by 31P-NMR and HPLC, native myosin was characterized electrophoretically, and activities of metabolic enzymes were measured spectrophotometrically. Relative to control animals, STZ-diabetes resulted in a significant 32% decrease in the FM1 isoform of myosin in EDL and a 24% decrease in IM myosin of SOL. Mass-specific activities of phosphofructokinase, citrate synthase, and cytochrome oxidase were significantly lower in SOL from STZ-diabetic mice than in controls by 23, 18, and 36%, respectively. Intracellular ATP was significantly lower in SOL from STZ-diabetic mice than in controls (3.44 +/- 0.20 mumol g-1 wet weight vs. 4.61 +/- 0.20 mumol g-1, respectively), as was creatine phosphate (11.98 +/- 0.80 mumol g-1 wet weight vs. 14.22 +/- 0.44 mumol g-1). In contrast to results from SOL, there were no significant changes in phosphorus metabolites or enzyme activity in EDL. These results show that the effects of IDDM on levels of phosphorus containing metabolites and maximal activities of key regulatory enzymes in muscle are markedly fiber-type specific. It is suggested that the muscle type-specific effects of STZ-diabetes may be a consequence of differential accumulation of intracellular fatty acids.

31P NMR study of phosphorus containing metabolites in the uterus of hamster: changes during the estrous cycle and the effect of hormonal manipulation

Changes in the concentrations of phosphorus containing metabolites were monitored by 31P NMR in the uteri of hamsters during the estrous cycle. Concentrations of phosphocreatine (PCr) and ATP were significantly increased in estrus animals compared to diestrus animals. Concentrations of these metabolites were also increased in immature female hamsters and ovariectomized (OVX) adult hamsters treated with estradiol indicating that estradiol was responsible for this effect. However, the steroid hormones progesterone and testosterone did not increase the concentrations of the phosphorus containing metabolites. Further, immature female hamsters also following treatment with estradiol showed an initial decline in phosphomonoester (PME), PCr, ATP and inorganic phosphate but by 24 h of treatment the concentrations returned to control levels. The NMR study also revealed that the intracellular pH of the hamster uterus was around 7.4 all through the estrous cycle.

pHi, [Ca2+]i, and myosin phosphorylation in histamine- and NH4(+)-induced swine carotid artery contraction

We examined the interaction among changes in pHi, [Ca2+]i, myosin light-chain phosphorylation, and contraction in arterial smooth muscle stimulated by histamine, NH4+, Tris+, and/or changes in extracellular pH (pHo). We loaded swine carotid medial tissues with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein to measure pHi or aequorin to measure [Ca2+]i. Incubation of tissues in NH4+ increased pHi, [Ca2+]i, myosin phosphorylation, and force. Washout of NH4+ decreased pHi and transiently further increased in [Ca2+]i and force. Incubation of tissues in a similar concentration of Tris+ or increasing pHo also increased pHi; however, there were only modest changes in [Ca2+]i and force. Increasing extracellular pH coincidentally with washout of NH4+ prevented the decrease in pHi but did not affect the NH4+ washout-induced contraction. These data suggest that NH4+ altered [Ca2+]i and contraction by mechanisms other than its effects on pHi. The type of pH buffer did not affect the [Ca2+]i, myosin phosphorylation, or stress response to histamine stimulation. The time course of changes in pHi was much slower than the time course of histamine-induced changes in [Ca2+]i, myosin phosphorylation, and stress. Addition of 10 mmol/L NH4+ concurrently with histamine aborted the histamine-induced decrease in pHi and significantly slowed the histamine-induced increase in [Ca2+]i, myosin phosphorylation, and stress. There was little effect on histamine-induced increases in [Ca2+]i, myosin phosphorylation, or contraction when three other protocols aborted the histamine-induced decrease in pHi. These data show that incubation in NH4+ can alter [Ca2+]i and contraction in both unstimulated and histamine-stimulated smooth muscle. However, these effects were not caused by NH4(+)-dependent changes in pHi.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of phospholipase C with neomycin improves metabolic and neurologic outcome following traumatic brain injury

Activation of phospholipase C has been implicated as a factor in the development of irreversible tissue damage following injury to the central nervous system. We have used phosphorus magnetic resonance spectroscopy and a battery of postinjury motor function tests to characterize the role that phospholipase C activity may play in determining biochemical and neurologic outcome following traumatic brain injury in rats. Moderate (2.7 atmospheres) fluid percussion induced lateral brain injury caused a decline in free magnesium concentration, phosphorylation potential, and increased mitochondrial rate of oxidative phosphorylation. Neurologic motor score at 24 h and 1 week posttrauma in these animals was consistent with moderate injury. In contrast, treatment with the phospholipase C inhibitor neomycin B (15 mg/kg i.v.) immediately prior to injury significantly improved free magnesium status, bioenergetic state and neurological outcome (P < 0.01) after injury. We propose that phospholipase C activated second messenger pathways affecting magnesium homeostasis are involved in determining outcome after brain injury.

[Ca2+]i signaling in pregnant human myometrium

The purpose of the present study was to determine the changes in intracellular ionized calcium concentration ([Ca2+]i) or [Ca2+]i sensitivity accompanying spontaneous and agonist-induced contraction of human myometrium at term pregnancy, as well as to quantify the response to three prototypical agonists: 1) oxytocin, 2) vasopressin, and 3) phenylephrine. Uterine biopsies were obtained at the time of cesarean section from patients who delivered at or near full-term gestation. These preparations were used to measure isometric force development and [Ca2+]i levels with the luminescent calcium indicator aequorin. Concentration-response relationships were determined with respect to isometric force development in the presence of the agonist. [Ca2+]i-force relationships were determined with respect to spontaneous phasic contractions, as well as agonist-induced phasic and tonic contractions. The results provide evidence that the phasic nature of term human myometrium is due to 1) the resting [Ca2+]i level being less than the calcium threshold for contractions and 2) the inability of the tissue to maintain high [Ca2+]i levels for prolonged periods of time. In addition, calcium-independent mechanisms of regulation were suggested by the relatively minor calcium sensitizing action of oxytocin and the observation that relaxation of tonic contractions preceded the fall in [Ca2+]i levels.

Effect of pH on intracellular free Mg2+ in isolated adult rat cardiomyocytes

Changes in intracellular pH (pHi) alters the cytosolic concentrations of many electrolytes including Ca2+ and Na+. The present studies determined the effect of pHi on intracellular Mg2+ ([Mg2+]i) activity in isolated adult rat ventricular myocytes. Intracellular magnesium, [Mg2+]i, and calcium, [Ca2+]i, concentrations were measured with microfluorometry. Basal intracellular [Mg2+]i was 634 +/- 27 microM, n = 42 cells, and was not changed following electrical stimulation (0.5 Hz/s) which resulted in transient increases in [Ca2+]i and cell contractions. An NH4Cl pulse was used to rapidly alkalize and acidify the cytosol. Intracellular Mg2+ concentration within single cells decreased by 129 +/- 13 microM with rapid alkalinization of pH from basal levels of 7.1 to 7.6 following a NH4+ pulse. Removal of NH4Cl bathing solution resulted in cytosolic acidification, pH 6.9, and an increase in [Mg2+]i, from 467 +/- 47 to 569 +/- 41 microM. Intracellular [Ca2+] rose with acidification 80 +/- 4 to 149 +/- 19 nM, n = 5, and returned to normal levels, 89 +/- 5 nM, following recovery of pHi. Intracellular acidosis following exposure to 5% CO2/20 mM HCO3- solutions resulted in a significant increase in [Mg2+]i, to 778 +/- 63 microM. These results indicate that intracellular pH may have significant effects on [Mg2+]i in adult cardiomyocytes.

Regulation of the Ascaris major sperm protein (MSP) cytoskeleton by intracellular pH

The development and locomotion of the amoeboid sperm of the nematode, Ascaris suum, depend on precise control of the assembly of their unique major sperm protein (MSP) filament system. We used fluorescence ratio imaging of cells loaded with BCECF to show that intracellular pH (pHi) is involved in controlling MSP polymerization in vivo. Spermatogenesis is marked by a cycle of MSP assembly-disassembly-reassembly that coincides with changes in pHi. In spermatocytes, which contain MSP in paracrystalline fibrous bodies, pHi was 6.8, 0.6 units higher than in spermatids, which disassemble the fibrous bodies and contain no assemblies of MSP filaments. Activation of spermatids to complete development resulted in rapid increase in pHi to 6.4 and reappearance of filaments. Treatment of spermatocytes with weak acids caused the fibrous bodies to disassemble whereas incubation of spermatids in weak bases induced MSP assembly. The MSP filaments in spermatozoa are organized into fiber complexes that flow continuously rearward from the leading edge of the pseudopod. These cells established a pseudopodial pH gradient with pHi 0.15 units higher at the leading edge, where fiber complexes assemble, than at the base of the pseudopod, where disassembly occurs. Acidification of these cells caused the MSP cytoskeleton to disassemble and abolished the pH gradient. Acid removal resulted in reassembly of the cytoskeleton, re-establishment of the pH gradient, and re-initiation of motility. MSP assembly in sperm undergoing normal development and motility and in cells responding to chemical manipulation of pHi occurs preferentially at membranes. Thus, we propose that filament assembly in sperm is controlled by pH-sensitive MSP-membrane interaction.

Mg2+ buffering in cultured chick ventricular myocytes: quantitation and modulation by Ca2+

To characterize the Mg2+ buffering of cultured chick ventricular myocytes, cytosolic Mg2+ was increased by liberating Mg2+ normally chelated by ATP upon total depletion of ATP content. Because the total Mg content and cell volume remained constant during this time, the difference between the amount of Mg2+ liberated (2.7 mM) and the 0.9 mM increase in cytosolic Mg2+ activity measured fluorometrically with mag-fura-2 indicates a sizable Mg2+ buffering. A new term, the Mg2+ buffer coefficient (BMg), was derived to quantify this buffering. We also determined that cytosolic Mg2+ activity increased by only 0.6 mM in cells acutely exposed to zero external Ca2+ during ATP depletion. In the absence of extracellular Ca2+, the basal cytosolic Ca2+ activity (alpha Ca2+i) was reduced by 72%, whereas the increase in alpha Ca2+i induced by ATP depletion was substantially blunted; no difference in either the time course of adenine nucleotide changes or the Ca and Mg content was observed. The BMg value calculated for these cells indicates that Mg2+ buffering is substantially greater in the absence of extracellular Ca2+ (2.5) than when extracellular Ca2+ is present (1.4), indicating that alpha Ca2+i affects cytosolic Mg2+ activity in ventricular myocytes. Therefore the Mg2+ buffering of ventricular myocytes appears to be comprised of at least two components: 1) a Ca(2+)-insensitive adenine nucleotide pool and 2) a Ca(2+)-sensitive nonadenine nucleotide pool.

Nuclear magnetic resonance characterization of secondary mechanisms following traumatic brain injury

Much of the injury that occurs following a traumatic insult to the central nervous system is the result of physiological and biochemical processes initiated by the primary traumatic event. These processes occur over a period of hours to days following the insult, and although a number of factors have been identified as being associated with this secondary injury process, their role and interrelationship with one another is unclear. Nuclear magnetic resonance spectroscopy has been utilized to characterize many of these secondary factors and their relationship to eventual neurological outcome. In particular, the role of high energy phosphates, pH, lactic acid, excitatory amino acids, and magnesium has been investigated, along with pharmacotherapies directed toward altering the status of these factors following traumatic injury. This review critically examines the role that each of these factors may play in the secondary injury process, and proposes a scheme which theoretically accounts for the interrelationships among the various factors.

Phosphorus 31 magnetic resonance spectroscopy of perifused human placental villi under varying oxygen concentrations

OBJECTIVE

Initial phosphorus magnetic resonance spectroscopy observations on the oxygen metabolism of placental villi from normal term pregnancies are described.

STUDY DESIGN

Villi were suspended in medium and perifused within a custom-designed 30 mm nuclear magnetic resonance probe in a superconducting vertical nuclear magnetic resonance magnet where pH, temperature, and oxygenation were monitored.

RESULTS

Phosphorus resonances were observed from adenosine triphosphate, phosphomonoesters. inorganic phosphate, and phosphodiesters. No phosphocreatine signal was observed. The placental villus tissue responded to an increase in oxygen concentration of the perifusate with a rise in the adenosine triphosphate level and a concomitant decline in the inorganic phosphate and the phosphomonoester signals.

CONCLUSION

The changes observed reflect continuing dynamic glycolysis and oxidative phosphorylation. The absence of a phosphocreatine peak suggests that aerobic pathways not driven by creatine kinase are important for placental metabolism. Our system demonstrates dynamic oxygen metabolism in perifused viable placental villus tissue by means of magnetic resonance spectroscopy.

Calcium ion homeostasis in smooth muscle

Ca2+ plays an important role in the regulation of smooth-muscle contraction. In this review, we will focus on the various Ca(2+)-transport processes that contribute to the cytosolic Ca2+ concentration. Mainly the functional aspects will be covered. The smooth-muscle inositol 1,4,5-trisphosphate receptor and ryanodine receptor will be extensively discussed. Smooth-muscle contraction also depends on extracellular Ca2+ and both voltage- and Ca(2+)-release-activated plasma-membrane Ca2+ channels will be reviewed. We will finally discuss some functional properties of the Ca2+ pumps that remove Ca2+ from the cytoplasm and of the Ca2+ regulation of the nucleus.

The actions of extracellular magnesium on isolated human detrusor muscle function

The effects of increasing the extracellular magnesium concentration ([Mg]) on the in vitro mechanical and electrophysiological properties of isolated human detrusor smooth muscle have been investigated. Raising extracellular Mg reduced the magnitude of the electrically-induced phasic contractions as well as spontaneous contractions. A similar increase in the [Mg] reduced the magnitude of the inward Ca2+ current associated with the action potential as well as shifting the activation curve to more positive potentials. Spontaneous oscillations of intracellular Ca2+ could be observed in some isolated cells and such activity was also abolished by raising the extracellular [Mg]. It is proposed that the contractile effects of raised extracellular Mg are mediated by an action on the inward Ca2+ current and that these observations suggest a means whereby normal and abnormal detrusor contractions might be effectively regulated.

Tightly-bound divalent cation of actin

Actin is known to undergo reversible monomer-polymer transitions that coincide with various cell activities such as cell shape changes, locomotion, endocytosis and exocytosis. This dynamic state of actin filament self-assembly and disassembly is thought to be regulated by the properties of the monomeric actin molecule and in vivo by the influence of actin-associated proteins. Of major importance to the properties of the monomeric actin molecule are the presence of one tightly-bound ATP and one tightly-bound divalent cation per molecule. In vivo the divalent cation is thought to be Mg2+ (Mg-actin) but in vitro standard purification procedures result in the preparation of Ca-actin. The affinity of actin for a divalent cation at the tight binding site is in the nanomolar range, much higher than earlier thought. The binding kinetics of Mg2+ and Ca2+ at the high affinity site on actin are considered in terms of a simple competitive binding mechanism. This model adequately describes the published observations regarding divalent cation exchange on actin. The effects of the tightly-bound cation, Mg2+ or Ca2+, on nucleotide binding and exchange on actin, actin ATP hydrolysis activity and nucleation and polymerization of actin are discussed. From the characteristics that are reviewed, it is apparent that the nature of the bound divalent cation has a significant effect on the properties of actin.

Nuclear magnetic resonance spectroscopy study on energy metabolism, intracellular pH, and free Mg2+ concentration in the brain of transgenic mice overexpressing human ornithine decarboxylase gene

We have generated a transgenic mouse line strikingly overexpressing the human ornithine decarboxylase (ODC) gene in their brain. Brain ODC activity was increased in the transgenic animals by a factor of 70 in comparison with their nontransgenic littermates. The content of brain putrescine, the product of ODC, was greater than 60 mumol/g of tissue in the transgenic mice, whereas in the normal animals it was below the level that could be detected by an HPLC method. The concentrations of the higher polyamines (spermidine and spermine) were not significantly different from control values. 31P nuclear magnetic resonance (31P NMR) spectroscopy analyses revealed a significantly reduced (40%) free Mg2+ concentration as calculated from the chemical shift differences of the nucleoside triphosphate alpha and beta peaks in the brains of the transgenic animals. The lower free Mg2+ concentration in the brains of ODC transgenic mice was not a consequence of altered intracellular pH or changes in cellular high-energy metabolites. 1H NMR showed no differences in brain choline/N-acetylaspartate and total creatine/N-acetylaspartate ratios between the two animal groups. These ODC transgenic animals may serve as models in vivo for studies on cerebral postischemic events and on epilepsy, as polyamines are supposed to be involved in these processes.

Vascular oxidative metabolism under different metabolic conditions

Control of respiration in vascular smooth muscle was examined while the metabolic state of the tissue was manipulated. During KCl-induced contractures in the presence of 5 mM glucose, oxygen consumption increased by 10 nmol/per min g without any decrease in phosphocreatine (PCr) or ATP as determined by 31P-NMR indicating a control of respiration which does not involve changes in high-energy phosphates (e.g., ADP, phosphorylation potential). However, when aortae with resting tone in the absence of substrate were then provided with 5 mM 2-deoxyglucose as the sole substrate, oxygen consumption increased 7.4 nmol/min per g while PCr decreased by more than 50% (resulting in a 2-fold increase in the calculated free ADP) with no change in tension from resting tone. During a subsequent KCl induced contracture in the presence of 2-deoxyglucose, oxygen consumption increased an additional 7.2 nmol/min per g while PCr continued to decline. Therefore, at least two mechanisms of respiratory control may exist in sheep aorta, one dependent and the other independent of changes in high-energy phosphates.

Flosequinan, a vasodilator with a novel mechanism of action

1. The mechanism of action of flosequinan was investigated in ferret aortic smooth muscle by the simultaneous measurement of aequorin luminescence and isometric force. 2. The control calcium-force curve was obtained by plotting the calibrated aequorin luminescence against the force from potassium-depolarized muscles. Flosequinan relaxed potassium-depolarized muscles by causing parallel changes in [Ca2+]i and force with no shift in the control [Ca2+]i-force relationship. 3. The [Ca2+]i-force relationship in the presence of a maximally effective concentration of phenylephrine was significantly shifted to the left of that for the control, potassium-depolarized muscle. Flosequinan relaxed the phenylephrine-contracted muscle by causing a large decrease in force with only a minimal decrease in [Ca2+]i, resulting in an apparent rightward shift of the [Ca2+]i-force relationship, toward the control curve. 4. In comparison, sodium nitroprusside caused relaxation of either the potassium- or phenylephrine-induced contraction solely by a decrease in [Ca2+]i with no shift in either calcium-force relationship. 5. Milrinone caused no significant rightward shift of the calcium-force relationship during phenylephrine- or potassium-induced contractions, but when milrinone was added in the absence of vasoconstrictors, relaxation was obtained with no significant decrease in [Ca2+]i. 6. Flosequinan appears to differ in mechanism of action from both nitroprusside and milrinone. It relaxes depolarization-mediated contractions solely by decreasing [Ca2+]i but also appears to be capable of reversing the apparent calcium sensitizing action of phenylephrine.

Phosphorus 31 magnetic resonance spectroscopy of human placenta and quantitation with perchloric acid extracts

Phosphorus 31 magnetic resonance spectroscopic studies of fresh placental tissue are reported that indicate resonances for adenosine triphosphate, inorganic phosphate, sugar phosphates-phosphomonoesters, and phosphodiesters. Perchloric acid extract methods were used to further characterize and quantitate phosphorous metabolites in term human placentas by phosphorus 31 magnetic resonance spectroscopy. The perchloric acid extracts give enhanced resolution of phosphorus signals and allow identification of other phosphorus metabolites including small amounts of phosphocreatine. Emphasis was placed on quantitating adenosine triphosphate levels in the acid extracts with the use of the external reference standard hexachlorocyclotriphosphazene in a coaxial capillary system. Adenosine triphosphate levels measured in this way ranged from 0.404 to 0.709 mumol per gram wet weight. Comparison with an internal standard method with phosphocreatine is also reported. Contribution to the measured high-energy phosphate pool from blood in the highly vascularized tissue was found to be relatively large and could range from 30% to 50% of the total adenosine triphosphate measured.