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R S Balaban

Publications and source records attributed to R S Balaban.

At least 109 records · Page 6Linked to original sources
PubMed1990

Effects of tissue absorbance on NAD(P)H and Indo-1 fluorescence from perfused rabbit hearts.

The effects of tissue optical absorbance on intracellular NAD(P)H and Indo-1 fluorescence emission have been evaluated in the perfused rabbit heart. These results demonstrate that the tissue optical absorbance significantly modifies the emission characteristics of these fluorophores. This tissue 'inner filter' effect, observed with both probes, changed as a function of tissue oxygenation and redox state in a wavelength-dependent manner. Pathlength calculations from these results indicate that this inner filter effect could occur with a mean pathlength of 310 microns due to the extremely high extinction coefficient of heart tissue. It is concluded that tissue optical absorbance significantly affects the fluorescent emission characteristics of both intrinsic and extrinsic probes in the intact heart, under a variety of conditions. Several potential methods of correcting for these tissue inner filter effects are discussed.

Animals↗
PubMed1990

NMR spectral analysis of kinetic data using natural lineshapes.

An automated rapid data analysis scheme for NMR spectroscopy time course studies is presented. This method uses a high signal-to-noise reference spectrum collected at the beginning of a time course as a lineshape model to analyze subsequent low signal-to-noise data collected with higher time resolution. The method is fast (approximately 1 s to evaluate two peaks in a 2K spectrum) and easily implemented on NMR spectrometer computers. An application of this method to spectroscopic studies on the heart is provided.

Humans↗
PubMed1990

The effect of cardiopulmonary bypass on brain and heart metabolism: a 31P NMR study.

The development of a large animal preparation using 31P nuclear magnetic resonance (NMR) spectroscopy for the study of cerebral and myocardial metabolism during cardiopulmonary bypass (CPB) is reported. The effect of normothermic CPB on myocardial and cerebral metabolism was evaluated. Adolescent sheep were used which have low levels of 2,3-diphosphoglycerate, a compound which can interfere with the calculation of intracellular pH and inorganic phosphate content. CPB was performed using standard procedures modified for the presence of a high magnetic field and limited access to the animal. High quality 31P NMR data were obtained from the brains and hearts of these animals before and during normothermic CPB. These results demonstrate that the initiation of normothermic CPB does not change high energy phosphate levels or intracellular pH. In particular, the decreased myocardial oxygen demand associated with CPB is not associated with improvement in the levels of adenosine triphosphate or phosphocreatine. The measurements of energy metabolism and intracellular pH of the brain and heart during CPB were possible within the constraints of the NMR experiment without compromising the CPB procedure. Combining NMR and CPB techniques permits future studies of cerebral and myocardial metabolism, especially those relating to ischemia.

Adenosine Triphosphate↗
PubMed1990

Renal distribution and metabolism of [2H9]choline. A 2H NMR and MRI study.

Trimethylamines are required as substrates in the biosynthesis of a number of important molecules in the cell. Herein, we describe the use of choline, deuterated in its 9 methyl positions, as an NMR label for following the distribution and metabolism of methyl groups after intravenous choline infusion. Deuterium (2H) NMR spectroscopy of the rabbit kidney in vivo revealed a linear uptake of infused choline that was directly proportional to the rate of infusion. The sensitivity limit for the spectroscopic studies in vivo was in the order of 100 microM for a 2 min data collection. After the infusion, 2H NMR imaging of the kidney in vivo demonstrated high trimethylamine concentrations in both the cortex and inner medulla but not in the outer medulla. The inner medullary fraction, however, was more labile to diuresis induced by furosemide. Companion high resolution 2H NMR studies of extracts revealed a cortex betaine/choline concentration ratio of 0.69 +/- 0.05 (mean +/- SEM, n = 3) before furosemide administration. Following furosemide infusion, the cortex betaine/choline concentration ratio was 3 +/- 1 (n = 6). Thus, 2H renal images following furosemide treatment can be interpreted as metabolic maps of betaine distribution. In addition, extraction studies revealed high concentrations of labelled choline and betaine in the liver. These data demonstrate that 2H-labelled choline is an effective marker of choline methyl metabolism in vivo and should provide a unique tool for the investigation of this important substrate.

Animals↗
PubMed1990

Control of mitochondrial respiration in the heart in vivo.

After reviewing the controversies in the literature surrounding the regulation of oxidative phosphorylation, a unifying theory to integrate the disparate results would be welcome. Following the traditional biochemical approach to identifying sites of control, one searches for the rate-limiting step in a series of reactions (i.e. a biochemical pathway) that, presumably, will not be at equilibrium. This approach has not succeeded in locating a reaction in cardiac respiratory control that is singularly rate-limiting and may actually be contributing to, rather than clarifying, the problem. There are two major criticisms of this approach. First, even if the step is in disequilibrium, it does not prove that it is rate-limiting (26). Second, a reaction near equilibrium can contribute to regulation of a system (37). In a complex, multiple-reaction integrated pathway such as mitochondrial respiration there are many steps that could potentially share the control of the overall system. Thus this pathway easily lends itself to the possibility of multiple sites of control, each of which could contribute by varying degrees to regulation. In Figure 3 we present one possible network (undoubtedly incomplete) for the distributed control of respiration, which incorporates contributions by the cellular redox state (supply), phosphate metabolite concentrations (either kinetic or thermodynamic), and oxygen. The coordination of the dehydrogenases, phosphate metabolites, and myosin ATPase activity (work) may be orchestrated by a second messenger. Calcium is an attractive candidate for this role (15) as it simultaneously can modulate reducing equivalent supply via the dehydrogenases and ATP use by the myofibrils. The theory of shared control along the path of respiration is not new (37), and has been gaining support from a variety of laboratories (3, 9, 26). Applying this concept to the experimental setting, the relative control strengths for various steps in oxidative phosphorylation have been reported for isolated mitochondria (26). The control coefficients for respiration in isolated myocytes or hearts in vivo remain unknown at this time. If control of respiration occurs at multiple sites, it could account for much of the disagreement in the literature. Experimental conditions, whether intentional or inadvertent, that saturate one or more control mechanisms will increase the relative effect of the other regulatory sites on the remaining range of mitochondrial function. If, for example, the medium surrounding isolated myocytes is such that the cytosolic redox state and pO2 are very high, the phosphate metabolite concentrations could logically be expected to be a major factor influencing the observed rate of oxidative phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Regulation of the predominant renal medullary organic solutes in vivo.

The predominant organic solutes of the renal medulla have been hypothesized to osmotically balance extracellular NaCl and protect macromolecular function from the adverse effects of urea. The evidence for their long- and short-term physiologic significance in vivo has been reviewed. The organic solutes decrease acutely in response to diuresis with a time course similar to that observed for inorganic ion fluxes and therefore probably play an important role in short-term volume regulation. However, because organic solutes are slow to accumulate (even in the presence of high urea and sodium concentrations), their significance to the short-term physiologic function of renal medullary epithelia is in doubt and needs further investigation. The organic solutes may be more important to the long-term function and survival of renal medullary cells.

Animals↗
PubMed1990

Regulation of oxidative phosphorylation in the mammalian cell.

The cell is capable of maintaining a steady-state flux of energy from mitochondrial oxidative phosphorylation, producing ATP, to the cytosolic adenosinetriphosphatases (ATPases), performing work. Considerable effort has been devoted to investigating the individual mechanisms involved in these two processes. However, less effort has been directed toward learning how these reactions of energy metabolism interact through the cytosol to maintain the observed steady state in the intact cell. The "classical" model for the cytosolic interaction of these two processes involves the feedback of ATP hydrolysis products, ADP and Pi, from the ATPases to oxidative phosphorylation. This model is based on data from isolated mitochondria in which the rate of oxidative phosphorylation is controlled by the concentration of ADP and Pi. Yet, recent data from intact tissues with high oxidative phosphorylation capacities (i.e., heart, brain, and kidney) indicate that the cytosolic concentration of ADP and Pi do not change significantly with work. These data imply that this simple feedback model is not adequate to explain the regulation of energy metabolism in these tissues. Other sites within the oxidative phosphorylation process must be playing a regulatory role or the kinetics of ATP synthesis must be very different than currently believed to establish the steady state. This review covers the potential sites within oxidative phosphorylation which may be regulated through cytosolic transducers to result in the necessary feedback network regulating the steady-state flow of energy in the cell. These sites will include substrate delivery to the cytochrome chain, the processes involved in the phosphorylation of ADP to ATP, and the delivery of oxygen.

Adenosine Triphosphatases↗
PubMed1990

Sodium-23 nuclear magnetic resonance imaging of the rabbit kidney in vivo.

The mechanism by which the mammalian kidney generates a concentration gradient of sodium from cortex to papilla is still not entirely understood. Studies of how the kidney as an organ generates this gradient have been hampered by the lack of a noninvasive method for monitoring the intrarenal sodium distribution. Herein, we demonstrate the value of sodium-23 nuclear magnetic resonance (23Na-NMR) imaging to nondestructively assess the intrarenal sodium distribution. 23Na-NMR images were obtained from a surgically exposed kidney preparation that showed the two-dimensional distribution of sodium in the rabbit kidney. In the antidiuretic kidney this gradient resulted in papillary sodium concentrations that were approximately threefold higher than cortical values. Serial 23Na-NMR images obtained during saline infusion demonstrated the kinetics by which the sodium gradient increases with diuresis. The half-time for 23Na washout of the medulla of the kidney was approximately 6 min with this protocol. In addition, a three-dimensional data set of the sodium distribution of the kidney was obtained with voxel dimensions of 1.5 mm3 by use of a three-dimensional 23Na-NMR imaging technique. Without surgical exposure, 23Na-NMR images of the rabbit kidney were collected under completely noninvasive conditions by use of a surface coil. The 23Na-NMR signal from the kidney was easily detected; however, to obtain images of comparable signal-to-noise ratio to the surgically exposed kidney, spatial and temporal resolution were significantly reduced.

Animals↗
PubMed1990

Phosphorus-31 nuclear magnetic resonance analysis of transient changes of canine myocardial metabolism in vivo.

The time course of the relative myocardial phosphocreatine and adenosine triphosphate contents (PCr/ATP) during step changes in heart rate in vivo was studied in 14 dogs using 31P nuclear magnetic resonance (NMR) to determine if transient changes in the high energy phosphates occur with changes in cardiac work. Coronary sinus blood flow (CF), oxygen consumption (MVO2), and NMR data were simultaneously measured during brief (approximately 3 min), paced increases in heart rate in these open chest animals. 31P spectra were collected with a time resolution of 15-16 s (PCr signal to noise 22-41:1). Paced tachycardia associated with increased CF and MVO2 had no significant transient or sustained effect on PCr/ATP. Higher heart rates, associated with decreased CF and blood pressure, caused rapid decreases of PCr/ATP that were reversible upon return to control rates. These data indicate that there are no transient changes in 31P metabolites (on a 15-16-s time base) during step changes in cardiac work associated with increased CF. This lack of change demonstrates that ATP hydrolysis and production are closely matched and that the feedback mechanism linking these processes occurs rapidly with no detectable transient change in the phosphate metabolites. In contrast, when the CF response to tachycardia is insufficient PCr is quickly depleted. This latter result suggests that the PCr/ATP ratio may be a sensitive, rapidly responding indicator of coronary supply/demand mismatching in vivo.

Adenosine Triphosphate↗
PubMed1990

Intermittent hypothermic asanguineous cerebral perfusion (cerebroplegia) protects the brain during prolonged circulatory arrest. A phosphorus 31 nuclear magnetic resonance study.

A system has been developed for the nuclear magnetic resonance spectroscopic evaluation of cerebral high-energy phosphate levels during hypothermic total circulatory arrest and reperfusion by means of cardiopulmonary bypass in large animals. The use of intermittent hypothermic asanguineous cerebral perfusion, termed cerebroplegia, for the preservation of cerebral high-energy phosphates during a 2-hour period of hypothermic total circulatory arrest and reperfusion has been evaluated. Cardiopulmonary bypass was used to achieve deep hypothermia (12 degrees to 15 degrees C) during 2 hours of circulatory arrest and reperfusion. Juvenile sheep were divided into two groups. Group 1 animals (n = 8) (no cerebroplegia) served as the control group. In group 2 animals (n = 7), cerebroplegia was established by intermittent bilateral carotid artery infusion of a hypothermic oxygenated asanguineous cardioplegic solution. Nuclear magnetic resonance spectroscopy recorded changes in cerebral adenosine triphosphate, creatine phosphate, and intracellular pH. Adenosine triphosphate, creatine phosphate, and pH were higher in the group 2 animals for all points during the arrest period and until 60 minutes after reperfusion (p less than 0.05). Electroencephalographic activity returned after 36 minutes of reperfusion in group 2, but it did not return until 117 minutes in group 1 (p less than 0.05). In summary, cerebral high-energy phosphates and pH were maintained and the electroencephalographic signal returned more rapidly during circulatory arrest with the institution of cerebroplegia. These studies suggest that cerebroplegia is protective of the brain during circulatory arrest.

Acid-Base Equilibrium↗
PubMed1989

Control of mitochondrial respiration in the heart in vivo.

The role of the hydrolysis products of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and inorganic phosphate (Pi), in the control of myocardial respiration was evaluated in vivo using 31P NMR. These studies were conducted to evaluate whether increases in the ATP hydrolysis products can be detected through the cardiac cycle or during increases in cardiac work. 31P NMR data acquisitions gated to various portions of the cardiac cycle (50 msec time resolution) revealed that cytosolic ATP, ADP and Pi did not change over the course of the cardiac cycle. These metabolites were also monitored during steady-state increases in cardiac work in conjunction with measurements of coronary blood flow and oxygen consumption. No changes were observed during 2 to 3 fold increases in myocardial oxygen consumption induced by various methods. These results demonstrate that the cytosolic ATP, ADP, and Pi concentrations remain relatively constant throughout the cardiac cycle and during physiological increases in cardiac work and oxygen consumption. Furthermore, it is shown that ADP and Pi cannot be solely responsible for the regulation of cardiac respiration in vivo based on the in vitro Km values of these compounds for oxidative phosphorylation. It is concluded that other mechanisms, working in concert with the simple kinetic feedback of ATP hydrolysis products, must be present in the cytosol to provide control of myocardial respiration in vivo.

Adenosine Diphosphate↗
PubMed1989

Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo.

In this study the exchange between 1H magnetization in "free" water (1Hf) and that in a pool with restricted motion (1Hr) was observed in tissues in vivo using NMR saturation transfer methods. Exchange between these two pools was demonstrated by a decrease in the steady-state magnetization and relaxation times of 1Hf with radiofrequency irradiation of 1Hr. The pseudo-first-order rate constant for the movement of magnetization from 1Hf to 1Hr was approximately 1 s-1 in kidney and approximately 3 s-1 in skeletal muscle in vivo. Proton NMR imaging demonstrated that this exchange was tissue specific and generated a novel form of NMR image contrast. The extent of exchange between 1Hf and 1Hr as well as the topological correlation of the exchange with relaxation weighted images suggests that this pathway is a major determinant of the observed relaxation properties of water 1H in vivo.

Animals↗
PubMed1989

Improvement in 31P NMR signal-to-noise for ATP in vivo using homonuclear decoupling.

The efficiency of 31P homonuclear decoupling in vivo is demonstrated. In low-field clinical situations, when JPP is equal to or greater than delta v, significant improvements in the precision of measuring the ATP resonance area can be expected upon decoupling due to the increase in signal-to-noise produced upon collapse of the J coupling. The sensitivity loss due to time sharing between the decoupler and receiver is discussed.

Adenosine Diphosphate↗
PubMed1989

Linear drive birdcage coil for 23Na human head studies at 1.5 T.

Progress in the development of non-proton NMR applications in medical research has been hampered by the generally low sensitivity of these nuclides as well as the lack of instrumentation readily available for studying these spins. For example, custom head coils suitable for sodium imaging of the human head are either not available or very expensive, making research startup costs high or impossible. Herein the detailed design and construction of a research 23Na head coil for MRI imaging is presented. 23Na NMR images collected with the coil are presented as well as a discussion of design modifications for other nuclides.

Head↗
PubMed1989

Nicotinamide adenine dinucleotide fluorescence spectroscopy and imaging of isolated cardiac myocytes.

Nicotinamide adenine dinucleotide (NADH) plays a critical role in oxidative phosphorylation as the primary source of reducing equivalents to the respiratory chain. Using a modified fluorescence microscope, we have obtained spectra and images of the blue autofluorescence from single rat cardiac myocytes. The optical setup permitted rapid acquisition of fluorescence emission spectra (390-595 nm) or intensified digital video images of individual myocytes. The spectra showed a broad fluorescence centered at 447 +/- 0.2 nm, consistent with mitochondrial NADH. Addition of cyanide resulted in a 100 +/- 10% increase in fluorescence, while the uncoupler FCCP resulted in a 82 +/- 4% decrease. These two transitions were consistent with mitochondrial NADH and implied that the myocytes were 44 +/- 6% reduced under the resting control conditions. Intracellular fluorescent structures were observed that correlated with the distribution of a mitochondrial selective fluorescent probe (DASPMI), the mitochondrial distribution seen in published electron micrographs, and a metabolic digital subtraction image of the cyanide fluorescence transition. These data are consistent with the notion that the blue autofluorescence of rat cardiac myocytes originates from mitochondrial NADH.

Animals↗
PubMed1989

Experimental preparations and models for MRS.

Magnetic resonance spectroscopy (MRS) has been most extensively applied to the study of animal models and not humans. The major reason for this extensive animal research is due to the nature of the early magnetic resonance high-field magnets, which only permitted the study of isolated cells, tissues, or small animals. However, equally important was the necessity of using animal models in the investigation of both the MRS technique itself and the actual biochemistry and physiology it interrogates. The advantages and disadvantages of various experimental models for magnetic resonance spectroscopy (MRS) research are presented, along with guidelines for choosing an appropriate model for a given experimental requirement.

Disease Models, Animal↗