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PubMed1996

Regulation of oxygen diffusion in hypoxic isolated cardiac myocytes.

In the normal beating heart, oxygen pressure (PO2) gradients between capillary blood and intracellular space are so large that cytosolic PO2 may decline to around PO2 at half saturation of myoglobin (2-5 Torr). Hence, a decrease in capillary blood PO2 of a few Torr would easily deplete oxygen in mitochondria if PO2 gradients are unchanged. The aim of the present study was to demonstrate, in a single isolated cardiac myocyte of the rat, a mechanism that reduces PO2 gradients in hypoxia so that oxygenation of the intracellular space would be sustained. Using a newly developed microspectrophotometric device, we were able to follow changes in cytosolic PO2 of an individual ventricular myocyte in an hypoxic medium. For extracellular PO2 of 4.4 Torr, we found an elevation (2.1 Torr) of the cytosolic PO2 when oxygen consumption of the cell was abolished by 2 mM NaCN, thus demonstrating PO2 gradients from extracellular medium to cytosolic space in a single individual cardiomyocyte. The magnitude of these PO2 gradients was reduced as extracellular PO2 was further lowered, and they were no longer detectable for extracellular PO2 of 0.6 Torr. To further elucidate physiological effects of the PO2-dependent changes in PO2 gradients demonstrated above, we conducted a simulation of ischemia in a single cardiac myocyte. The stop-flow procedure (simulated ischemia) quickly decreased cytosolic PO2 from 7.3 to 1.8 Torr in 5 min, while the rate of fall of PO2 considerably decreased when the cytosolic PO2 decreased to < 2 Torr. Consequently, even 30 min after the onset of the stop flow, cytosolic PO2 was significantly higher than that of the anoxic perfusion. These results together suggest that in severe hypoxia oxygenation of the intracellular space might be partially maintained by relative elevation of cytosolic PO2, resulting from progressive decrease in PO2 gradients from extracellular space to cytosol.

Animals↗
PubMed1993

Transport, distribution space and intracellular concentration of the anti-inflammatory drug niflumic acid in the perfused rat liver.

Transport and distribution space of niflumic acid in the perfused rat liver were investigated employing the multiple-indicator dilution technique with constant infusion of the drug (step input). Niflumic acid permeated the cell membrane in both directions at very high rates and its distribution in the cellular space was flow-limited; at least at 37 degrees, the rates of influx and efflux could not be measured. Dissociation of the niflumic acid-albumin complex also occurred at very high rates. The apparent space of distribution of niflumic acid in the liver depended on the concentration of the drug and varied between 4.37 (1 mM) and 43.5 (10 microM) times the water space; even with 90% extracellular binding to albumin, the apparent space of distribution of niflumic acid was 5.1 times greater than the water space. The high apparent spaces of distribution reflected the high intracellular concentrations. The ratio of intracellular bound plus free concentration to the extracellular bound plus free concentration (Ci/Ce) varied between 6.62 (1 mM portal niflumic acid) and 71.0 (10 microM portal niflumic acid). Metabolic transformation depended on the concentration of the free form. Intracellular binding is probably the major reason for the high concentration of the drug in the hepatic tissue.

Animals↗
PubMed1957

Calcium equilibrium in muscle.

1. A study of the calcium equilibrium in isolated frog muscle has been attempted. 2. When sartorius muscles were immersed in Ca(45) Ringer's solution, the surface phase took up the Ca(45) in about 1 minute; the extracellular water space and connective tissue in about 30 minutes; and the intracellular space in about 300 minutes. 3. The percentages of total calcium in the whole muscle immersed in Ringer's solution was as follows: 10 per cent in the surface phase; 12 per cent in the extracellular water space; 17 per cent in the dry connective tissue; 24 per cent in the intracellular space; and 37 per cent as non-exchangeable calcium. 4. The exchange constants of isolated frog sartorius muscle to calcium has been determined. The flux of intracellular calcium in the steady state was approximately 0.8 mM/(liter hr). 5. It appears that there is a calcium pump pushing calcium out of the cell against an electrochemical gradient of about 4 cal./mM of calcium. However, since the flux is low, the maximum energy required per hour to pump calcium out of the cell against this high gradient is only about 2 cal./kg. muscle or about 1 per cent of the resting energy.

Animals↗
PubMed1995

Restricted diffusion of an 19F-labelled organic acid in human erythrocytes analyzed by 19F pulsed field gradient NMR.

The diffusion coefficient of an 19F-labelled organic acid (3-trifluoromethylhippurate: TFMH) was measured in intact human red blood cells (RBCs) and sealed right-side-out ghosts at 22.5 +/- 0.05 degrees C. Diffusion coefficients were measured using stimulated echo and spin-echo pulsed field gradient sequences. The apparent diffusion coefficient (Da) of TFMH in the intracellular space was much smaller than in the extracellular medium. This was due to restricted diffusion of intracellular TFMH since i) the intracellular Da decreased when the diffusion time was increased, and ii) the smaller Da component disappeared when the membrane was permeabilized with saponin. From the intracellular Da values obtained over a range of diffusion times, from 5 ms to 1 s, the apparent radius of the diffusion barrier was estimated to be 3 +/- 1.1 micron assuming spherical geometry. Despite the high protein concentration in the intracellular space of the intact RBC, the intracellular values of Da were similar to the values obtained in the ghosts at the same diffusion times. We therefore conclude that the small diffusion coefficient of intracellular TFMH is mainly explained by the restricted diffusion due to the cell boundary.

Biological Transport↗
PubMed2005

Kinetics of glucose transport and sequestration in lactating bovine mammary glands measured in vivo with a paired indicator/nutrient dilution technique.

To quantify kinetics of mammary glucose utilization in vivo, 24 paired glucose and extracellular indicator (p-aminohippuric acid) dilution curves across intact bovine mammary glands were obtained after bolus injections into the external iliac artery. Dilution curves were analyzed using a compartmental capillary, convolution integration model. Four candidate submodels of glucose transport and metabolism in capillary supply zones were fit to the glucose dilution curves and evaluated. Model I, with one extracellular compartment for glucose and first-order unidirectional uptake, failed, indicating that efflux of glucose from the intracellular space could not be ignored. Model II, with first-order exchanges between extracellular and intracellular compartments and sequestration from the latter, was overdefined because unidirectional clearance of glucose was at least five times the blood flow rate and 20 times the net clearance rate. Model III, combining extracellular and intracellular space into one compartment, was superior in its goodness-of-fit to curves and identifiability of parameters. Michaelis-Menten parameters of sequestration were not identifiable. Parameters of the optimal compartmental capillary, convolution integration model were applicable to both the dynamics of injected glucose dilution and the steady-state background arteriovenous difference of glucose. Glucose sequestration followed first-order kinetics between 0 and 7 mM extracellular glucose with an average rate constant of 0.006 s(-1) or a clearance of 44 ml/s. The ratio of intracellular to extracellular glucose distribution space was 0.34, which is considerably lower than the expected intracellular volume and suggests an intracellular occlusion compartment with which extracellular glucose rapidly exchanges.

Animals↗
PubMed1980

Sulfated proteoglycan accumulation during development of the embryonic chick limb bud studied by electron microscopic autoradiography.

Cartilage cells are characterized by a high concentration of extracellular sulfated proteoglycan. Electron microscopic autoradiography was used to compare the incorporation of sulfate into proteoglycan by limb-bud chondrogenic and myogenic cells. From stage 19 to stage 21 there was no significant difference between the cartilage- and muscle-forming regions in the number of silver grains over either the extracellular space or the intracellular space. From stage 22 to 25 the number of extracellular silver grains was significantly greater in the chondrogenic region than in the myogenic region, but the number of intracellular silver grains was the same. Since most of the silver grains were intracellular, no significant difference in the total number of grains was found between the two tissues. Stage-26 and -27 embryos showed a significantly greater number of silver grains over both the cells and the extracellular space in the cartilage region than in the muscle region. Thus, the first step of cartilage differentiation involves a decrease in the extracellular deposition of sulfated proteoglycan in the myogenic region rather than an increase in deposition in the chondrogenic region between stage 22 and 25. After stage 25 there is an increase in sulfated proteoglycan synthesis in the chondrogenic region to the myogenic region.

Animals↗
PubMed1988

Measurement of local cerebral protein synthesis in vivo: influence of recycling of amino acids derived from protein degradation.

A quantitative autoradiographic method for the determination of local rates of protein synthesis in brain in vivo is being developed. The method employs L-[1-14C]leucine as the radiolabeled tracer. A comprehensive model has been designed that takes into account intracellular and extracellular spaces, intracellular compartmentation of leucine, and the possibility of recycling of unlabeled leucine derived from steady-state degradation of protein into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the steady-state precursor pool distribution space for labeled leucine to that of unlabeled leucine. The values obtained were 0.58 in whole brain and 0.47 in liver. These results indicate that there is significant recycling of unlabeled amino acids derived from steady-state protein degradation in both tissues. Any method for the determination of rates of cerebral protein synthesis in vivo with labeled tracers that depends on estimation of precursor pool specific activity in tissue from measurements in plasma must take this recycling into account.

Amino Acids↗
PubMed1981

A scanning electron microscopy study of the invasion of leaflets of a bloat-safe and a bloat-causing legume by rumen microorganisms.

A newly developed technique using ruthenium red to detect foci of bacterial digestion in mounts of whole leaflets that had been incubated with rumen bacteria was used to compare the digestion of alfalfa, a bloat-causing legume, and sainfoin, a bloat-safe legume. When whole leaflets were suspended in an artificial rumen medium and inoculated with rumen bacteria, massive bacterial adhesion and proliferation were noted at the stomata of alfalfa leaflets after 6 h of incubation, whereas only a few isolated bacteria adhered near the stomata of sainfoin leaflets After 22 h of incubation, the epidermal layers of alfalfa leaflets had peeled away in many areas, revealing an extensive bacterial invasion of the underlying mesophyll tissue in which large bacterial microcolonies had formed in intercellular spaces, and in intracellular spaces in several areas where plant cell walls had broken down. After 22 h of incubation, the surface of sainfoin leaflets resembled that of alfalfa leaflets at 6 h, with bacterial microcolonies adhering to the area surrounding the stomata, but without sloughing of the epidermis. Uninoculated control leaflets of both species showed no surface alteration but part of their normal bacterial flora had proliferated to form microcolonies on the surface after 22 h incubation. Dry matter loss due to leaching or bacterial digestion when whole leaflets of legumes were suspended in an artificial rumen medium, alone or with rumen bacteria, was significantly higher in the bloat-causing group. Values of leaching and of bacterial digestion were positively correlated. We conclude that reported differences in plant anatomy, and in cell wall chemistry, produce distinct rates or organic nutrient release from legume leaflets, and that these same differences produce an equally distinct susceptibility of leaflets to bacterial invasion, plant cell rupture, and the consequent release of intracellular plant components. The rate of release of organic nutrients from legume leaflets may be important in the etiology of foamy pasture bloat. This technique of in vitro digestion of whole leaflets followed by ruthenium red staining shows some promise of providing a rapid and qualitative test to distinguish, within a species, cultivars that may differ in their bloat-related characteristics.

Animal Feed↗
PubMed2002

Biexponential diffusion attenuation in the rat spinal cord: computer simulations based on anatomic images of axonal architecture.

Water diffusion in neurological tissues is known to possess multicomponent diffusion behavior. The fractions of fast and slow apparent diffusion components have often been attributed to the volume fractions of extracellular space (ECS) and intracellular space (ICS) although diffusion fractions are at variance with the tissue compartment volume ratios. In this article this puzzle was examined with a finite difference diffusion simulation model on the basis of optical images from sectioned rat spinal cord. Here the results show that assignment of fractions obtained from biexponential fits of fast and slow diffusion attenuation to ECS and ICS volume ratios is not correct. Rather, the observed multicomponent diffusion behavior is caused by motional restriction and limited intercompartmental water exchange in that at long diffusion times diffusion attenuation is shown to become monoexponential. Although the measured apparent diffusion fractions also depend on T2 relaxation time of water protons in the various compartments, the sensitivity to T2 is small and thus T2 differences are unlikely to explain the mismatch between apparent diffusion fractions and cellular volume fractions.

Animals↗
PubMed1986

Na+-dependent p-aminohippurate transport at the basolateral side of the isolated perfused rat kidney.

The uptake of p-amino[3H]hippurate by isolated perfused rat kidney was studied to characterize the mechanism which was responsible for organic anion transport process. A rapid injection multiple indicator dilution technique and the distributed two-compartment model of Sawada et al. (Computer Methods Programs Biomed., 20 (1985) 51) were employed. Some characteristics of a carrier-mediated transport from the antiluminal space to the intracellular space for p-aminohippurate at the basolateral side were demonstrated: the uptake was stimulated by the countertransport effect and showed Na+ dependency. These findings are consistent with p-amino[3H]hippurate's being taken up into the isolated rat basolateral membrane vesicle by Na+-dependent carrier-mediated transport (J. Pharmacol. Exp. Ther. 227 (1983) 122). It is suggested that the multiple indicator dilution technique is a sensitive new method to study the mechanisms of renal tubular transport in the living kidney as an organ.

Aminohippuric Acids↗
PubMed2003

T2 mapping of muscle.

Muscle activation produces increases in magnetic resonance ( T(2)) signal intensity leading to recruitment images that demonstrate spatial patterns and intensity of muscle activation. These T(2) activation maps are useful for visualizing and quantifying various aspects of muscle function. Activity-dependent changes in T(2) result from an increase in the T(2) relaxation time of muscle water. The current state of investigation indicates that the mechanism of increased T(2) results from osmotically driven shifts of muscle water that increase the volume of the intracellular space and from intracellular acidification resulting from the end products of metabolism. Although the spatial resolution of magnetic resonance imaging is still insufficient to map territories of individual motor units, it is possible to demonstrate nonuniform activation between subregions or compartments of muscle. Taken together, the attributes of the T(2) mapping technique hold great potential for demonstrating aberrant muscle activation patterns in pathology and positive adaptation to exercise or rehabilitative intervention.

Biomechanical Phenomena↗
PubMed1999

Review of mechanisms by which electrical stimulation alters the transmembrane potential.

Electrical stimuli pace, cardiovert, or defibrillate the heart by changing transmembrane potential (deltaVm). Recent simulation studies provide insights into mechanisms by which stimuli establish deltaVm. This review attempts a nonmathematical description of these mechanisms. We start with the cable model in which the intracellular core conductor is bounded by a highly resistive and capacitive membrane that separates the intracellular and extracellular spaces. Intracellular and extracellular resistances are assumed to vary linearly with position. Although this model predicts anodal extracellular stimuli hyperpolarize adjacent tissue and cathodal extracellular stimuli depolarize that tissue, it fails to reproduce regions of opposite deltaVm distant from the electrodes. We then consider the sawtooth model in which microscopic discontinuities in intracellular resistance represent gap junctions. While model studies with such discontinuities demonstrate large deltaVm at cell ends, experimental validation of such deltaVm remains elusive. Extending the analysis to the two- and three-dimensional syncytium, we also consider the bidomain model in which intracellular, extracellular, and interstitial currents are explicitly characterized. Differences in resistance to these currents gives rise to virtual electrodes, which are experimentally observed regions of large deltaVm that arise distant from the stimulating electrode. Distant deltaVm regions are also evident when macroscopic discontinuities in intracellular resistance are introduced into the bidomain model. Such discontinuities are associated with clefts or scars that give rise to "secondary sources." Albeit the cable model offers remarkable insight the bidomain model and the concept of secondary sources provide a more complete understanding of membrane excitation, especially when combined into a unifying activating function.

Action Potentials↗
PubMed1990

Role of glucagon in disposal of an amino acid load.

Amino acids stimulate the release of glucagon and insulin. To assess the role of aminogenic hyperglucagonemia, we have studied, in healthy young males, the effects of basal (less than 100 pg/ml) and high (200-400 pg/ml) plasma glucagon concentrations on amino acid metabolism during intravenous infusion (0.5 g.h-1.4 h) of a mixture of 15 amino acids. Basal plasma glucagon concentrations were obtained by infusion of somatostatin (0.5 mg/h) plus glucagon (0.25 ng.kg-1.min-1) and high plasma glucagon concentrations by infusion of somatostatin plus glucagon (3.0 ng.kg-1.min-1) or by infusion of amino acids alone. All studies were performed under conditions of euglycemic (83-91 mg/dl) hyperinsulinemia (50-80 microU/ml). Hyperglucagonemia significantly increased 1) net amino acid transport from the extracellular into the intracellular space (by approximately 4%), 2) net degradation of amino acids entering the intracellular space (by approximately 40%), and 3) conversion of degraded amino acids into glucose from 0-10% (basal glucagon) to 70-100% (high glucagon). Hyperglucagonemia did not affect the amount of amino acids excreted in the urine (approximately 4%). We conclude that glucagon plays an important role in the disposition of amino acids by increasing their inward transport, their degradation, and their conversion into glucose.

Adult↗
PubMedDate not supplied

[Oxygen metabolism (based on polarographic data) in patients with thyroid diseases].

The results are presented of the studies of oxygen metabolism in the muscular tissue of patients with the thyroid goiter formation. An original method of the polarographic study allows one to observe the process of oxygen transport not only from the intracellular space into the cell, but also from the blood channel into the intracellular space. Oxygen utilization curve was recorded after prolonged ischemia (15 minutes) the oxygen recovery curve was noted, according to which the oxygen recovery rate coefficient, allowing to judge the circulation time and the vascular wall permeability, was counted by analogy with oxygen utilization rate determination. The ratio of these coefficients was used as an index for the tissue supplying with oxygen. The data are presented of studying 105 patients with different forms of the thyroid goiter formation. The informativeness of the utilization rate coefficient is examined for evaluating oxygen consumption by tissues. This index was practically equal in patients with diffuse toxic goiter, nodose euthyroid goiter and in the controls. At the same time the coefficient of oxygen recovery rate and the coefficient ratio of oxygen recovery and utilization rates were significantly elevated in patients with diffuse toxic goiter (1.3 +/- 0.21, 4.33 +/- 0.76) in comparison with the patients suffering from nodose euthyroid goiter (0.72 +/- 0.2, 2,95 +/- 0.66) and the controls (0.67 +/- 0.18, 1.8 +/- 0.37). In the patients with diffuse toxic goiter these indices returned to normal (0.44 +/- 0.11, 1.57 +/- 0.63) following the preoperative preparation.

Biological Transport↗
PubMed1981

Serum potassium levels during and after terbutaline.

The intravenous infusion of terbutaline is associated with decreased levels of serum potassium. The duration of this hypokalemia has not been reported. Therefore, serum potassium levels were measured in dogs before during and for 3 hours after a 2-hour intravenous infusion of 0.5 micrograms/kg/min of terbutaline. Serum potassium levels decreased significantly during the infusion and returned to near preinfusion levels within 3 hours after the infusion was stopped. The mechanism for the decrease in the serum potassium is most likely a shift of the potassium ion from the extracellular space to the intracellular space.

Adult↗
PubMed1994

Acute onset of hypokalemia and muscular weakness in four hyperthyroid cats.

Sudden onset of muscular weakness and ventroflexion of the neck were identified in 4 hyperthyroid cats. In each cat, the onset of clinical signs was associated with an acute decrease in serum potassium concentration. The cause for hypokalemia was undetermined, but could have resulted from deficits in total body potassium content or shifts of potassium from the extracellular space into the intracellular space. The 4 cats responded to administration of potassium. Hyperthyroid cats may be prone to disturbances in potassium homeostasis. Clinicians should be aware of potential changes in potassium homeostasis during the treatment of cats with hyperthyroidism.

Acute Disease↗
PubMed1979

Distribution of tryptophan and tyrosine in unipolar affective disorders as defined by multicompartmental analysis.

As requirements for tryptophan for synthesis of protein and 5-hydroxytryptamine were comparable in rat brain, during depletion of tryptophan there could be competition between the two pathways for the amino acid. This implied that tryptophan should be rate-limiting for protein synthesis and this was found in the short term when concentrations of the amino acid were reduced in rats. Multicompartmental studies of tryptophan and tyrosine in controls and patients subject to unipolar depression defined two main pools of the amino acid provisionally assigned to extracellular and intracellular spaces. For tyrosine, mean values for the extracellular space were comparable to those of controls. The concentration of tyrosine was low in the intracellular space in both depressed and recovered patients, but the raised fractional clearance rates for this compartment during depression had returned to normal on remission. Plasma tryptophan concentrations were significantly reduced in depression with intermediate values after recovery. This suggested that the procedure used may have been mildly stressful and that this had evoked an idiosyncratic response to the stress in the depressed patients, which was characterized by inability to maintain concentrations of this amino acid in plasma. The findings for both amino acids may have a bearing on the aetiology of unipolar affective disorder.

Adult↗
PubMed1971

Determination of extracellular space and intracellular electrolytes in rat liver in vivo.

1. Uptake of a number of isotopically labelled extracellular tracers by rat liver in vivo was studied.2. A residual intravascular space of 3.0-3.5% following exsanguination was measured by use of [(51)Cr]red cells. This space was significantly greater than that of skeletal muscle and was also greater in nephrectomized as compared to intact rats.3. [(131)I]albumin and polyvinylpyrolidine (PVP) were found to distribute initially in a space of 6-7% and this was followed by a delayed rise that was greater for PVP. The extravascular portion of this space is termed the large-molecule accessible space and is believed to correspond to the histological space of Disse.4. [(14)C]sucrose and inulin initially distribute in a space of 10-12% followed by a continued late increase. This initial space is termed the small molecule accessible space and is thought to include most of interstitial space.5. (36)Cl(-) and stable Na(+) and Cl(-) spaces were constant at 19-21% and can be used to put an upper limit on extracellular space.6. Operationally, the 1 hr inulin space in the nephrectomized rat was felt to be the best indicator of extracellular space.7. Total electrolytes were measured and intracellular values of 22, 165 and 22 m-mole/l. cell water for Na(+), K(+) and Cl(-), respectively, were calculated.8. By use of [(14)C]DMO, an intracellular pH of 7.25 and an intracellular HCO(3) (-) of 13 m-mole/l. cell water were calculated.

Albumins↗