bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic requirements for anaerobic active Cl and Na transport in the bullfrog cornea
Authors: Reinach P. S. , Schoen H. F. , Candia O. A.
Published: December 2017

In the bullfrog cornea, the relationships between the rates of aerobic and anaerobic glycolysis and active Cl and Na transport were studied. In NaCl Ringer (glucose-free), the short-circuit current (SCC) declined much more slowly under aerobic than under anaerobic conditions. The aerobic lactate effluxes in glucose-free and glucose-rich NaCl Ringer were 0.08 and 0.23 micromol/h.cm2, respectively. The transition to anoxia caused these values to increase significantly and was accompanied by depletion of endogenous glycogen in glucose-free Ringer. In Na2SO4 Ringer, amphotericin B (10(-5) M) stimulation of the aerobic SCC was not dependent on the presence of glucose but under anoxia, SCC stimulation required glucose. In Na2SO4 (glucose-rich) Ringer, amphotericin B stimulated the aerobic lactate efflux from 0.26 to 0.36 mumol/h.cm2 and anoxia increased it to 0.55 micromol/h.cm2. In NaCl Ringer, the addition of either 0.5 mM adenosine or 1 mM ATP with 26 mM glucose restored the anaerobic-inhibited SCC and lactate efflux of glucose-depleted corneas. The results show that the reactions of glycolysis are a sufficient energy source for supporting active Na and Cl transport.
Myofibrillar ATPase activity in rat heart after chronic propranolol administration
Authors: Dowell R. T.
Published: December 2017

A previous study has shown that chronic chemical sympathectomy brought about by 6-hydroxydopamine injections results in a dpression in myocardial contractile function which is accompanied by reduced myofibrillar ATPase activity. To determine whether chronic beta-adrenergic receptor blockade elicits similar alterations in cardiac contractile-protein ATPase activity, adult rats were given twice-daily injections of propranolol 7 days/wk for 2 wk. Effective beta-adrenergic receptor blockade was verified by the lack of hemodynamic responsiveness to isoproterenol infusion. Myofibrils were prepared from left ventricular tissue and analyzed for ATPase activity. Myofibrillar ATPase activity was 295 +/- 8 nmol Pi.mg-1.min-1 in controls. Enzyme activity was not significantly different in propranolol-injected rats. The results demonstrate that chronic propranolol administration does not alter the ATPase activity of cardiac myofibrils. Therefore, it seems likely that the altered contractile-protein enzymatic properties resulting from chronic chemical sympathectomy do not occur as the result of a reducted level of cardiac beta-adrenergic receptor stimulation.
Coupling between oxidative metabolism and active transport in the midgut of tobacco hornworm
Authors: Mandel L. J. , Moffett D. F. , Riddle T. G. , Grafton M. M.
Published: December 2017

Active K transport (Isc) in the midgut of tobacco hornworm Manduca sexta has been shown to be highly dependent on oxidative metabolism. However, the oxygen consumption rate (rO2) was not altered by conditions that drastically affect Isc. Respiration was normally maximal, inasmuch as uncouplers did not increase rO2. This rate could be maintained without any added substrate probably by oxidation of endogenous substrates. Additional succinate increased rO2 by 17%. Simultaneous monitoring of Isc and the redox level of the respiratory chain components demonstrated that 1) succinate (5 mM) reduced all the respiratory enzymes while increasing Isc by 17%; 2) sesamol (5 mM), a mitochondrial uncoupler, reoxidized all respiratory enzymes and inhibited Isc by about 50%; 3) cyanide (1 mM) fully reduced the cytochromes and completely inhibited Isc. These redox responses indicate that the mitochondria in this tissue are normally coupled, even if respiration is maximal and is not modulated by active transport. Mitochondria isolated from the midgut show coupling and respiratory control by ADP, appearing to behave like mitochondria from other tissues. Therefore, a cytoplasmic constraint must exist in this tissue that continually elicits an unmodulated maximal respiratory rate.
Potassium exchange in the whole cell, cytoplasm, and nucleus of amphibian oocytes
Authors: Frank M. , Horowitz S. B.
Published: December 2017

Potassium isotope exchange was studied in whole oocytes, with and without ovarian follicles, and in oocyte cytoplasm and nucleus. Cryomicrodissection was used to prevent solute redistribution during nuclear and cytoplasmic separation. Manual follicle removal causes a small decrease in the K+ of the preparation. No effect of follicle removal is seen on 42K+ exchange. Whole oocyte exchange is multiphasic and reflects the presence of two intracellular K+ fractions. One of these fractions is present in both nucleus and cytoplasm. It exhibits first-order exponential kinetics, apparently established at the cell membrane. The second fraction is restricted to cytoplasm and exchanges at an imperceptible rate. The fractions differ in pre- and posthibernation oocytes. These observations clarify the mechanism whereby nuclear/cytoplasmic K+ concentration asymmetries are maintained and the mechanisms responsible for the high K+-activity coefficient previously reported in these cells.
Effect of lactate and palmitate on substrate utilization of isolated rat soleus
Authors: Pearce F. J. , Connett R. J.
Published: December 2017

The effects of exogenous lactate and palmitate on the metabolism of rat soleus muscle were studied. In the presence of glucose and insulin, the addition of 8 mM lactate resulted in a decrease in the oxidation of both glucose and other substrates. Lactate accounted for 70% of the oxygen consumption under these conditions. Glycogen accumulation and the incorporation of exogenous palmitate into triglycerides were stimulated by lactate addition, whereas the utilization of exogenous glycerol was depressed. The addition of 1 mM palmitate in either the presence or absence of lactate resulted in an inhibition of both glycolysis and the utilization of exogenous glucose. The results are discussed in terms of the effect of lactate levels on recovery from exercise.
Monosaccharide transport across microvillous membrane of human placenta
Authors: Johnson L. W. , Smith C. H.
Published: December 2017

Transport through the microvillous membrane of the syncytium is the first step in placental transfer of nutrients. We have therefore studied glucose transport by isolated microvillous membrane vesicles. Transport occurred by selective and rapid facilitated diffusion, which was inhibited by phloridzin, phloretin, cytochalasin B, and HgCl2. Nonmediated diffusion of the substrate was found by three independent methods to be very slow. Competition studies showed that aldohexoses in the C-1 chair conformation were the preferred substrates. Transport was independent of sodium gradients and was not modulated by insulin. However, several steroids inhibited transport including estriol and progesterone, which are abundant in utero. Kinetic analysis by equilibrium exchange demonstrated a Km of 31 mM and a Vmax of 120 nmol . s-1 . mg protein-1. The Km and Vmax suggest a large capacity in relation to calculated fetal needs. In consequence of this capacity, intrasyncytial concentrations of glucose are probably maintained near those of maternal blood. Augmentation of transport at this membrane by hormones or other agents is unlikely to increase fetal supply of glucose, but down regulation by steroids may serve a regulatory function.
Cold adaptation in the rat: increased brown fat peroxisomal beta-oxidation relative to maximal mitochondrial oxidative capacity
Authors: Nedergaard J. , Alexson S. , Cannon B.
Published: December 2017

Brown fat hypertrophy in the rat resulting from cold adaptation is shown here to involve increased mitochondrial, peroxisomal, and lysosomal enzyme activities. Mitochondrial activity in homogenates of brown fat was estimated as cytochrome c oxidase. After 4 wk in the cold (+5 C), the total activity was 3-fold higher than in control rats, although the specific activity was somewhat lower. Peroxisomal activity was followed as cyanide-insensitive palmitoyl-CoA-dependent NAD+ reduction (palmitoyl-CoA oxidase) and as catalase. The total activity of both palmitoyl-CoA oxidase and catalase was more than 10-fold higher than in controls and the specific activity about 3-fold higher. Acid phosphatase, used as a lysosomal marker, showed a 6-fold higher total activity and almost twice as high specific activity. The relatively greater increase in peroxisomes and lysosomes compared with mitochondria indicates an involvement in thermogenesis also for these organelles.
Membrane permeability to the molecular and ionic forms of DMO in barnacle muscle
Authors: Keifer D. W. , Roos A.
Published: December 2017

The time course of the intracellular pH (pHi) of barnacle muscle fibers was followed using microelectrodes while the fibers were exposed to 15 mM of the weak acid 5,5-dimethyloxazolidine-2,4-dione (DMO) at pH 6.5. The rapid initial fall in pHi was used to determine the membrane permeability to the DMO molecule, while the much slower fall during the subsequent plateau phase yielded the permeability to the DMO ion. This experimental approach and the mathematical treatment of the data can be used to obtain the membrane permeabilities to other weak acids or bases. We found values of 1.9 X 10(-4) cm/s for the permeability to the DMO molecule and 1.5 X 10(-7) cm/s for the permeability to the ion, assuming the fiber to be a cylinder. Thus the permeability of the neutral form is about 10(3) times that of the ionized form. At commonly encountered conditions of pHi = 7.3, outside pH = 7.5, and membrane potential = -52 mV, this permeability ratio introduces an error of only -0.01 to -0.02 into the determination of pHi based on the distribution of DMO.
Nonspatial determinants of electrograms in guinea pig ventricle
Authors: Holland R. P. , Arnsdorf M. F.
Published: December 2017

Theory states that the extracellularly recorded potential (epsilon) is determined by spatial and nonspatial factors. Spatial factors include the boundary between areas with different transmembrane voltages (Vm) and the relationship of the boundary to the extracellular electrode. Nonspatial factors include the Vm across the boundary [transmembrane potential gradient (TPG)] and a conductivity term (C sigma). Few studies have investigated the nonspatial factors experimentally due to the difficulty in separating the nonspatial from the spatial determinants. Our model rendered the spatial factors constant, permitted the simultaneous recording of epsilon and Vm, and allowed the manipulation of Vm and C sigma across the boundary. Epsilon and the TPG were related predictably with changes in [K+]o, [Na+]o, temperature, conduction, stimulus rate or prematurity, and hypoxia. In the presence of a constant TPG, epsilon could be affected by a change in C sigma caused by hypoxia and a metabolic poison. The effects of the nonspatial determinants on epsilon could be modeled using electrical circuit analogues. Nonspatial determinants must be considered in studies using electrocardiographic measures as an index of ischemia.
Role of cyclic GMP in cholinergic activation of Na-K pump in duck salt gland
Authors: Stewart D. J. , Sen A. K.
Published: December 2017

Na-K-ATPase will hydrolyze an alternate substrate, p-nitrophenylphosphate (pNPP). The hydrolysis is ouabain sensitive and occurs at an external site on the cell membrane, thereby allowing measurement of Na-K-ATPase activity in the intact cell. pNPP hydrolysis was monitored in salt gland slices incubated in a bicarbonate-buffered Ringer solution. Methacholine-stimulated pNPP hydrolysis was inhibited by either atropine or ouabain. The hydrolysis was also dependent on the presence of calcium and sodium in the Ringer solution. cGMP stimulated ouabain-sensitive pNPP hydrolysis at concentrations from 10(-8) M to 10(-4) M with an optimum at 10(-5) M. cAMP did not produce a significant activation of pNPP hydrolysis. The effect of cGMP ws not dependent on either sodium or calcium in the Ringer solution and was not inhibited by atropine. Hydrolysis of pNPP promoted by either methacholine or cGMP occurred under conditions where no net influx of Na+ into the cells could occur. Sodium-pump activation during cholinergic stimulation, therefore, does not depend on an elevation of cell sodium but must occur by another mechanism. cGMP appears to play a direct role in that mechanism.
Pulmonary absorption of amino acids in the rat: evidence of carrier transport
Authors: Lin Y. J. , Schanker L. S.
Published: December 2017

To investigate the absorption of nonmetabolized amino acids from the rat lung, 0.1 ml of Krebs-Ringer phosphate solution containing either 14C-labeled 1-aminocyclopentanecarboxylic acid (cycloleucine) or alpha-aminoisobutyric acid (AIB) was administered to anesthetized animals by way of a catheter introduced through a tight-fitting tracheal cannula. After various times, lungs were removed and assayed for the amount of amino acid that remained. Cycloleucine appeared to be absorbed by a combination of at least two processes: saturable carrier-type transport and a nonsaturable process. The saturable process was inhibited to varying degrees by a number of L- and D-amino acids but not by D-ornithine, betaine, 3-O-methyl-D-glucose, phenol red, disodium cromoglycate, or tetraethylammonium. The nonsaturable process appeared to be too rapid to be accounted for by diffusion alone, thus suggesting interaction with a second carrier system of high capacity. Although AIB was a weak inhibitor of cycloleucine transport, it appeared to be absorbed solely by a nonsaturable process at a rate consistent with diffusion through aqueous membrane channels.
GDP binding to rat brown fat mitochondria: effects of thyroxine at different ambient temperatures
Authors: Sundin U.
Published: December 2017

Reports on a reciprocal relationship between sympathetic-nerve and experimentally induced changes in thyroid-hormone activity called into question the proposed role of thyroxine in the changes seen in the brown fat after cold adaptation. Rats reared at +30, +22, and +5 degrees C received daily injections of thyroxine (1 mg/kg). After 3 wk of treatment, the thermogenic state of the tissue was assessed by measuring the capacity of the brown fat mitochondria to bind guanosine 5'-diphosphate (GDP). GDP-inhibited mitochondrial swelling, brown adipose tissue (BAT) wet weights, and mitochondrial yields were also measured. The control animals showed a linear increase in GDP binding between +30 and +5 degrees C. Thyroxine was found to lower the GDP binding markedly at +5 degrees C, less so at +22 degrees C, while no effect was evident at +30 degrees C. The values at +22 and +30 degrees C were identical. The other parameters studied all confirmed these results. The conclusion made is that the thyroxine-induced rise in basal metabolic rate lowers the critical temperature and reduces the demand for nonshivering thermogenesis. This is reflected in the reduced GDP binding and hence heating capacity of the brown fat mitochondria.
Transport properties of toad kidney epithelia in culture
Authors: Perkins F. M. , Handler J. S.
Published: December 2017

The characteristics of a continuous line of toad kidney epithelial cells (A6) are described. These cells form a monolayer epithelium of high transepithelial electrical resistance (about 5,000 omega . cm2). The cells generate a transepithelial potential difference (apical surface negative) of about 9 mV. The short-circuit current is equivalent to net sodium flux. Net sodium flux is stimulated by aldosterone and by analogues of cAMP. The stimulation is readily reversible. Neither urea permeability nor osmotic water flow is altered by analogues of cAMP. Amiloride eliminates 90% of the short-circuit current. Thus A6 cells form an epithelium with several differentiated properties including hormonal regulation of transport.
Application of 31P-NMR spectroscopy to the study of striated muscle metabolism
Authors: Meyer R. A. , Kuchmerick M. J. , Brown T. R.
Published: December 2017

This review presents the principles and limitations of phosphorus nuclear magnetic resonance (31P-NMR) spectroscopy as applied to the study of striated muscle metabolism. Application of the techniques discussed include noninvasive measurement of high-energy phosphate, intracellular pH, intracellular free Mg2+, and metabolite compartmentation. In perfused cat biceps (fast-twitch) muscle, but not in soleus (slow-twitch), NMR spectra indicate a substantially lower (1 mM) free inorganic phosphate level than when measured chemically (6 mM). In addition, saturation and inversion spin-transfer methods that enable direct measurement of the unidirectional fluxes through creatine kinase are described. In perfused cat biceps muscle, results suggest that this enzyme and its substrates are in simple chemical equilibrium.
Cytosolic free calcium levels in rabbit proximal kidney tubules
Authors: Murphy E. , Mandel L. J.
Published: December 2017

Cytosolic free Ca levels were measured in isolated rabbit proximal kidney tubules using a previously described null-point method (19). Control values for cytosolic free Ca levels averaged 0.45 +/- 0.09 microM (n = 13). Addition of 1 microM A23187, an agent expected to increase ionized Ca levels, resulted in an eightfold increase in the null point. Total mitochondrial Ca content was determined by measuring the fluorocyanocarbonylphenylhydrazine-releasable Ca. 80% of the total cell Ca was found to be mitochondrial. These results suggest that the mitochondria play an important role in the regulation of cytosolic free Ca levels in mammalian proximal kidney tubules.
Mechanics and energetics of muscle contraction in normal and dystrophic chickens
Authors: Polinski W. J. , Rall J. A.
Published: December 2017

Energy liberation and isometric force generation were compared at 25 degrees C in isolated normal (n = 15) and dystrophic (n = 18) posterior latissimus dorsi muscles (PLD) from 16- to 33-day-old chickens. Twitch-energy liberation in dystrophic muscle decreased by 27 +/- 6%, and force per cross-sectional area decreased by 26 +/- 11%. Tetanic energy liberation in dystrophic PLD was depressed by 32 +/- 10% compared with a 22 +/- 9% reduction in peak force per cross-sectional area plus a 26 +/- 3% reduction in ability to maintain force. Normalizing results using the force-time integral demonstrates an unaltered force generation per unit energy liberation in dystrophic PLD (7 +/- 11% difference from normal). Kinetic properties of the mechanical responses were not significantly different in normal compared with dystrophic PLD. Dystrophic PLD demonstrated hyperexcitability to nerve transection and electrical stimulation. Although force-generating capacity is reduced in dystrophic PLD, coupling of force production to energy utilization appears unaltered.
Transient responses and continuous behavior of active smooth muscle during controlled stretches
Authors: Meiss R. A.
Published: December 2017

Controlled length changes were imposed on mesotubarium superius and ovarian ligament smooth muscles from the reproductive tracts of female rabbits in constant estrus. Stretches of up to 35% of the muscle length were applied during isometric contraction, relaxation, and steady-state force levels. Force was continuously monitored and was plotted as a function of length. During constant velocity stretches there was an initial steep rise in force, a rapid downward deviation from the initial slope, and a long region with a constant upward slope. Stretches made during contraction showed smaller initial rises in force and steeper linear portions than did identical comparison stretches made during relaxation. The value of the slope was independent of the prior developed force, but it did depend on whether the muscle was contracting or relaxing. During contraction and steady-state force levels, the slope was independent of the stretch rate, but it was strongly rate dependent during relaxation. Changes in the stretch rate during stretch caused associated changes in muscle force; the relationship was curvilinear and was exaggerated during relaxation. The findings are placed in the context of a sliding-filament--cross-bridge hypothesis.
Differentiated function in cultured epithelia derived from thick ascending limbs
Authors: Burg M. , Green N. , Sohraby S. , Steele R. , Handler J.
Published: December 2017

Medullary thick ascending limbs were dissected from rabbit kidney and cultured on thin collagen membranes. The collagen membranes were supported by a special device that limited the exposed surface area to a disk 1 mm in diameter. The cells usually proliferated to form a confluent epithelial monolayer covering the collagen membrane within 8-10 days. Transepithelial voltage was measured between bridges immersed in the solutions bathing the bottom of the collagen membrane and the apical (upper) surface of the epithelium. The voltage typically was oriented positive toward the apical surface and persisted for a few weeks. Furosemide but not amiloride reduced the voltage reversibly. Both the orientation of the voltage and its reduction by furosemide are characteristic of thick ascending limbs. Therefore, the observed voltage supports the identification of the epithelial cells in culture and is evidence of differentiated function.
Effects of 2-n-butyl-methylenedioxyindene on skeletal muscle mechanics and energetics
Authors: Burchfield D. M. , Rall J. A. , Rahwan R. G.
Published: December 2017

Mechanical and energetic effects of 2-n-butyl-3-dimethylamino-5,6-methylenedioxyindene (2-butyl-MDI) were investigated in isolated frog semitendinosus muscles at 0 degrees C. Previous research on various tissues suggested that this compound functions as an intracellular Ca2+ antagonist. The effects of 2-butyl-MDI (2 X 10(-4) M) with respect to time were progressive and reversible with exposures of 30 min or less. A 30-min exposure to the agent significantly decreased twitch and tetanus force and energy liberation, increased the twitch-to-tetanus ratio, prolonged kinetics of force development, induced a stimulus frequency-dependent tetanic fatigue, and decreased contractile economy (measured as force per unit energy liberation). Energy associated with Ca2+ cycling, activation heat, was depressed by 31 +/- 4%. The significant reduction of activation heat production by 2-butyl-MDI suggests that the quantity of Ca2+ released by the sarcoplasmic reticulum upon stimulation is reduced. However, the complexity of the results summarized above suggests multiple sites and/or modes of action for the agent.
Metabolism of l-lactate by LLL-PK1 renal epithelia
Authors: Mullin J. M. , Cha C.-J. M. , Kleinzeller A.
Published: December 2017

Page C41: J. M. Mullin, C.-J. M. Cha, and A. Kleinzeller. “Metabolism of l-lactate by LLL-PK1 renal epithelia.” Page C43: discussion, second sentence should read: Glutamate then serves as the amino donor in transaminations to yield alanine, which derives its [14C]labeled carbons from pyruvate, and from aspartate, which then feeds into urea synthesis.
Effect of thyrotoxicosis on sarcoplasmic reticulum in rat skeletal muscle
Authors: Kim D. H. , Witzmann F. A. , Fitts R. H.
Published: December 2017

The effect of thyrotoxicosis on the capacity of fragmented sarcoplasmic reticulum (FSR) and crude homogenate (CH) to sequester Ca2+ was determined in rat muscle for the slow-twitch type I soleus (SOL), the fast-twitch type IIA deep region of the vastus lateralis (DVL),and the fast-twitch type IIB superficial region of the vastus lateralis (SVL). The maximal rate of Ca2+ uptake (Vmax) and Km were determined in both the CH and FSR preparations, and the total Ca2+ uptake capacity of the CH was determined. In the slow SOL, thyrotoxicosis increased the Vmax (8.20 +/- 0.96 vs. 15.70 +/- 0.92 mumol Ca2+ . g wet muscle-1 . min-1) and the total Ca2+ uptake (17.62 +/- 1.30 vs. 27.13 +/- 2.16 mumol Ca2+ . g wet muscle-1) of the CH preparation. Thyrotoxicosis increased the FSR yield 2.3-fold in the slow-twitch SOL; however, the kinetic characteristics (Vmax and Km) of these vesicles were not altered. Thyrotoxicosis had no effect on the CH and FSR preparations in either the type IIA or type IIB sample. These results can be explained by a thyroid hormone-mediated increase in the quantity of the sarcoplasmic reticulum in type I muscle and suggest no effect on the hormone on the qualitative nature of the Ca2+-enzyme interaction.
Effects of extracellular calcium removal and anoxia on isolated rat myocytes
Authors: Cheung J. Y. , Thompson I. G. , Bonventre J. V.
Published: December 2017

Calcium-tolerant myocytes were isolated from adult rat ventricles by successive perfusion and incubation with buffer containing collagenase and hyaluronidase. Greater than 70% of the cells excluded trypan blue, maintained normal morphology, and contracted in response to an externally applied electric field. We have characterized metabolic defects present in isolated calcium-tolerance myocytes when exposed to low concentrations of extracellular calcium under aerobic and anaerobic conditions. In control cells exposed to 1.25 mM Ca2+, the following metabolic parameters were measured (in mumol/g protein): adenosine triphosphate (ATP) 28.8 +/- 3.3, creatine phosphate (CrP) 49.1 +/- 7.5, intracellular Na+ 37.7 +/- 8.1, intracellular K+ 352.9 +/- 49.3, cellular Ca2+ 12.3 +/- 1.8, as well as rate of protein synthesis 0.34 +/- 0.03 mumol . g protein-1 . h-1. In aerobic cells incubated in medium without added Ca2+, the corresponding values (in mumol/g protein) were ATP 27.9 +/- 4.4, CrP 25.3 +/- 4.3, intracellular Na+ 130.9 +/- 23.1, intracellular K+ 217.2 +/- 32.0, cellular Ca2+ 3.9 +/- 1.0, and rate of protein synthesis 0.09 +/- 0.02 mumol . g protein-1 . h-1. These data indicated major metabolic aberrations in myocytes exposed to medium low in Ca2+ (less than 10 microM). Metabolic depression was most severe in cells incubated in the absence of both Ca2+ and O2. It is postulated that Ca2+ removal resulted in an increase in Na+ and K+ permeability, causing a net gain of intracellular Na+ and loss of intracellular K+. These ionic shifts might stimulate the activity of membrane-associated Na+-K+-ATPase, accounting for lower levels of CrP.
5-HT-stimulated arachidonic acid release from labeled phosphatidylinositol in blowfly salivary glands
Authors: Litosch I. , Saito Y. , Fain J. N.
Published: December 2017

In blowfly salivary glands, breakdown of phosphatidylinositol has been linked to the activation of hormone-sensitive Ca2+ channels. Addition of 5-hydroxytryptamine to blowfly salivary glands stimulated the breakdown of phosphatidylinositol prelabeled with 32P or [3H]arachidonic acid. This was associated with a transient accumulation of [3H]arachidonic-labeled diglyceride. There was no appreciable effect of 5-hydroxytryptamine on breakdown of phosphatidylethanolamine or phosphatidylcholine labeled with 32P or [3H]arachidonic acid, indicating that phosphatidylinositol was the immediate source of diglyceride. Extracellular Ca2+ was necessary for [3H]arachidonic acid but not 32P loss from phosphatidylinositol. Addition of arachidonic acid to salivary glands did not stimulate salivary gland secretion or 45Ca flux. In contrast, 5-hydroxytryptamine stimulated both salivary gland secretion and 45Ca flux. These results indicate that, although [3H]arachidonic acid is incorporated into phosphatidylinositol and its release from this phospholipid is increased by 5-hydroxytryptamine, the liberated arachidonic acid does not stimulate salivary gland secretion or 45Ca flux.
Regulation of polyamine content in cultured fibroblasts
Authors: Bethell D. R. , Hibasami H. , Pegg A. E.
Published: December 2017

The content of putrescine and of the polyamines (spermidine and spermine) and the activities of their biosynthetic enzymes were measured in 3T3 mouse fibroblasts and SV40-transformed mouse fibroblasts over the entire period from subculturing in fresh medium until confluence. The transformed cells had a substantially higher content of putrescine and spermidine than the 3T3 cells and higher activities of all of the biosynthetic enzymes. However, the ratio of spermine synthase to spermidine synthase was higher in the 3T3 cells, which correlated with their higher spermine-to-spermidine ratio. All of the biosynthetic enzymes increased in activity during cell growth. Ornithine decarboxylase increased 20-fold with a maximum at 24-36 h after culturing whereas S-adenosylmethionine decarboxylase increased 3-fold at the same time. Spermidine synthase increased 10- to 16-fold during the growth period whereas spermine synthase increased 2- to 3-fold. The relative enzyme activities and the changes in total polyamine content suggested that 1) the activity of S-adenosylmethionine decarboxylase limited the production of the polyamines and 2) the relative amounts of spermidine and spermine synthase determined the predominant polyamine that the available decarboxylated S-adenosylmethionine is used to synthesize. When 3T3 cells become quiescent at confluence, there was a substantial fall in the intracellular spermidine level because of a greatly increased excretion of spermidine into the medium. Spermine content also fell because there was an increased conversion of spermine into spermidine, which was then excreted. The specific excretion of spermidine did not occur with the transformed SV-3T3 cells.
A sensitive photoelectric force transducer with a resonant frequency of 6 kHz
Authors: Chiu Y. L. , Asayama J. , Ford L. E.
Published: December 2017

A displacement-type photoelectric force transducer with a projection arm and a resonant frequency of 6 kHz is described. A vane on a moving element partially interrupts a light beam shining on a pair of phototransistors. Movement of the vane causes changes in the phototransistor currents, which are amplified to give an overall sensitivity of 10 mV/mg. Most of the half of each phototransistor not under the vane is covered by a mask, the edge of which is parallel to the edge of the vane. This increases the sensitivity of the transducer so that stiffer moving elements can be used. Compliance of the transducer at the tip of the projection arm is about 10 micrometers/g. The inertia of the lightweight moving element is minimized by having it rotate about a twisting strip hinge. The equivalent mass of the moving element at the tip, 6 mm from the pivot, is about 0.9 mg. The principal advantages of the transducer over other types is that it is nearly impervious to moisture.
Insulin depolarization of rat hepatocytes in primary monolayer culture
Authors: Wondergem R.
Published: December 2017

Rat hepatocytes in primary monolayer culture demonstrated two stable states of transmembrane potential (Em). Low potentials ranging from -10 to -15 mV followed impalements with glass microelectrodes, and in some cells low potentials increased spontaneously or in response to a train of intermittent current (5 nA) to stable potentials of -50 mV, which were comparable to hepatocyte Em in vivo. Adding insulin at 20 mU/ml depolarized the stable higher Em 22.4 +/- 2.6 mV (n = 6) over an 11-min interval, and input resistance increased 21.4 +/- 4.7 M omega (n = 6) during the depolarization. The insulin effect was dose dependent, because adding insulin at 0.2 mU/ml depolarized the stable high Em 5.0 +/- 1.5 mV (n = 3) and increased input resistance 6.3 +/- 1.8 M omega (n = 3). In one experiment the Em repolarized 32 min after insulin was washed out. Adding metabolic inhibitors KCN (1 mM) and 2,4-dinitrophenol (10 and 1 mM) and increasing external potassium (60 mM, with external sodium reduced equivalently) also depolarized Em, but they did not increase input resistance. Thus insulin depolarized hepatocytes from a stable high Em, which is equivalent to the Em of liver in vivo, to a stable low Em, which occurs in hepatocytes in primary monolayer culture. This hormone action is consistent with changes in membrane ion conductance, and it further demonstrates that these cells can sustain two stable states of Em.
Activation energy for water transport in toad bladder
Authors: Eggena P.
Published: December 2017

Activation energies (Ea) for water movement across vasopressin-(ADH) sensitive epithelia have been reported to be about 10 kcal/mol (1, 12). The present study shows that measurements of Ea for osmotic water flow across toad bladders are unreliable, because a temperature change induces marked alterations in membrane permeability to water within a 2.5-min interval. Thus bladders equilibrated with ADH either at room temperature or at 33 degrees C and then suddenly subjected to a lower temperature were found to exhibit a marked increase in membrane permeability to water. This observation suggests that there is a rapid turn-over of water permeability sites and that sudden exposure to cold inhibits the removal more than the induction of sites by ADH. To stabilize ADH-induced water channels for Ea measurements, bladders were exposed to ADH at room temperature, fixed with glutaraldehyde, and subjected to osmotic gradients at different temperatures. The Ea values for osmotic water flow across these ADH-permeabilized, glutaraldehyde-fixed bladders were 5.1 (4-12 degrees C), 4.3 (12-21 degrees C), 3.6 (21-36 degrees C), and 3.6 kcal/mol (30-38 degrees C). Ea values for shear viscosity of water in these temperature ranges were calculated to be 4.7, 4.2, 4.1, and 3.6 kcal/mol, respectively. The close correlation between Ea values for bulk water viscosity and osmotic water flow across the bladder wall suggests that an equivalent number of hydrogen bonds must be broken to achieve an increase in water flow through ADH-induced channels and an increase in fluidity of water in bulk solution.
Localization and properties of bovine photoreceptor 5'-nucleotidase
Authors: Yu L. W. , Fager R. S.
Published: December 2017

The main light-activated enzyme of the vertebrate photoreceptor is cGMP phosphodiesterase, whose product is GMP. GMP would be broken down to guanosine by the enzyme 5'-nucleotidase on the cytoplasmic (extradiscal) surface of the disks. The presence of 5'-nucleotidase on the cytoplasmic surface was verified by using sucrose continuous gradients to show its association with the photoreceptors and by using disk preparation and concanavalin A binding to demonstrate its presence on the extradiscal surface. Further studies using detergents and freeze-thaw showed that an even higher 5'-nucleotidase activity is present on the intradiscal surface; however, it is the smaller cytoplasmic surface activity that is potentially relevant to the physiology. The 5'-nucleotidase on the extradiscal surface is light insensitive, has a broad optimal pH range, shows a divalent cation dependence, and is competitively inhibited by nucleoside di- and triphosphates. When the data determined experimentally were extrapolated to physiological conditions, we obtained a decay time constant for GMP breakdown by 5'-nucleotidase in the range of 0.4 to 1.06 s. This time constant is in the range of the time constants of the fall of rod cell receptor potential, suggesting a possible role for GMP level in visual transduction.
Volume-responsive sodium movements in dog red blood cells
Authors: Parker J. C.
Published: December 2017

As dog red blood cells are shrunken in vitro, their sodium permeability increases progressively. Some new features of this volume-responsive transport process are described. Retardation of sodium movements in shrunken cells occurs when chloride is replaced by the more conductive anions: nitrate or thiocyanate. Micromolar concentrations of amiloride or quinidine inhibit the increment of sodium flux associated with a reduction in cell volume. In the presence of a large outwardly directed sodium gradient, dog red blood cells can progressively alkalinize the medium in which they are suspended. This pH change is stimulated by cell shrinkage, reversed by cell swelling, retarded when chloride is replaced by nitrate or thiocyanate, and inhibited by micromolar concentrations of amiloride or quinidine. The similarities between the shrinkage-associated sodium flux and the alkalinization phenomenon suggest that the mechanism responsible for increased sodium permeability in shrunken cells can be made to operate as a sodium-hydrogen exchanger.
Sodium gradient-driven transport processes in ATP-depleted renal tubules
Authors: Blumenthal S. S. , Ware R. A. , Kleinman J. G.
Published: December 2017

The effects of directed Na+ gradients on proximal tubule cell transport processes were examined in suspensions of rabbit renal tubules depleted of ATP. Cells of high-Na+ content were generated by suspending the tubules in high-Na+ media, whereas low-Na+ cells were produced by incubating tubules in Na+-free media. Resuspension of the high-Na+ tubules in Na+-free media caused a fall in cell pH simultaneous with a fall in cell Na+. Resuspending the low-Na+ cells in Na+-replete media led to a rise in cell pH, in parallel with the rise in cell Na+. Removing HCO-3 and CO2 augmented and amiloride inhibited the increase in cell pH generated by the inward Na+ gradient. Low-Na+ tubules exposed to an inwardly directed Na+ gradient also concentrated the sugar analogue alpha-methylglucoside, and this uptake was blocked by phlorizin. These findings demonstrate the suitability of ATP-depleted renal tubules for the study of linked transport processes by providing evidence for the existence of the proximal luminal transport processes, Na+-H+ exchange, and Na+-sugar cotransport in this preparation.
Phosphagen and metabolite content during contraction in porcine carotid artery
Authors: Krisanda J. M. , Paul R. J.
Published: December 2017

Previous studies (Paul, R. J. Chemical energetics of vascular smooth muscle. In: Handbook of Physiology: The Cardiovascular System. Bethesda, MD: Am. Physiol. Soc., 1980, p. 201-235) have shown that vascular oxygen consumption reaches a steady state at approximately twice the basal rate during maintenance of isometric contraction. The time course of the attainment of a metabolic steady state, the metabolic signal for the observed increase in respiration, and the contribution of endogenous phosphagens to the energetics of isometric contraction are not known with certainty. To this end, the time course of the tissue content of ATP, ADP, AMP, phosphocreatine (PCr), inorganic phosphate (Pi), and lactate were measured during a KCl-induced isometric contraction in porcine carotid artery and compared with values in the basal state. Oxygenated unpoisoned strips were frozen at 0, 0.5, 1, and 15 min of contraction, and tissue extracts were analyzed using analytical isotachophoresis. No statistically significant changes from the basal levels of ATP and PCr were measured. A small but significant increase in ADP was seen at all times. An increase in Pi of 1.25 mumol/g was observed at 0.5 min, which decreased in time. Tissue lactate content increased by 1.79 mumol/g after 1 min of contraction. The calculated range of cellular free ADP (ADPfree), 44-123 microM, may be sufficient to saturate oxidative phosphorylation. This and the apparent lack of change of ADPfree from basal during contraction suggest that it does not play a role in the coordination of metabolism and contractility. From as early as 0.5 min, when less than 40% of peak isometric force is attained, intermediary metabolism provides the total ATP required for contraction.
Functional compartmentalization of oxidative and glycolytic metabolism in vascular smooth muscle
Authors: Paul R. J.
Published: December 2017

The metabolism of vascular smooth muscle is characterized by an unusual component of aerobic glycolysis. Lactate production, even under fully oxygenated conditions, is of similar magnitude to the rate of oxygen consumption when compared on a molar basis. Although the underlying mechanisms are unknown, the ratio of glycolytic to oxidative metabolism has been suggested to be an index of vascular myopathy. Measurements of the rate of O2 consumption (JO2), lactate production (Jlac), and isometric force in porcine coronary arteries were made under conditions known to alter both active force (delta Po) and Na+-K+ transport. As previously reported, JO2 was strongly correlated with delta Po; Jlac, however, was correlated with conditions that alter Na+-K+ transport. Under conditions known to inhibit Na+-K+ transport (10(-5) M ouabain, absence of extracellular K+ or Na+), Jlac was inhibited even though delta Po and JO2 were increased. The coupling of Na+-K+ transport with aerobic glycolysis was not dependent on tonicity or the major anion species, nor was it an effect simply on tissue lactate permeability as indicated by studies of tissue lactate content. Metabolic measurements made at similar levels of delta Po indicate that Jlac is markedly inhibited by ouabain, whereas JO2 shows little effect. Thus the unusual aerobic glycolysis observed in vascular smooth muscle appears to be linked to Na+-K+ transport processes and not to some nonspecific metabolic deficiency. Experiments on both systemic and pulmonary arteries from rat, rabbit, dog, and pig indicate that these results are not limited solely to porcine coronary vessels.
Effects of amino acid methyl esters on cardiac lysosomes and protein degradation
Authors: Long W. M. , Chua B. H. , Lautensack N. , Morgan H. E.
Published: December 2017

Perfusion of rat hearts as Langendorff preparations for 20 min with buffer containing 15 mM glucose and either 10 mM methionine methyl ester or 10 mM leucine methyl ester decreased 1) latency of beta-N-acetylglucosaminidase, 2) buoyant density of cardiac lysosomes, 3) the rate of proteolysis, and 4) heart rate and coronary flow. A significant inhibitory effect on proteolysis was not observed during this brief exposure of insulin-treated hearts to the methyl esters. The effects of the methyl esters were reversible when they were washed away. Heart rate and coronary flow returned to control values within 5 min. After 90 min of recovery, lysosomes distributed on Percoll gradients in dense and buoyant bands that were indistinguishable from control hearts. The reversibility of these effects correlated with the net release of either methionine or leucine from hearts exposed to the corresponding methyl ester. During recovery, rates of proteolysis returned toward those observed in control hearts. In insulin-treated hearts, methionine methyl ester inhibited proteolysis during the recovery period, but leucine methyl ester had no effect. These results indicate that exposure to amino acid methyl esters led to swelling of cardiac lysosomes and inhibition of protein degradation. These effects appeared to be related to the amount of free amino acid that was retained.
Volume-induced anion conductance in human B lymphocytes is cation independent
Authors: Grinstein S. , Clarke C. A. , Rothstein A. , Gelfand E. W.
Published: December 2017

Peripheral blood T lymphocytes swollen in hypotonic media regain normal size by releasing internal KCl through activation of conductive K+ and Cl- pathways. In contrast, no regulatory volume decrease (RVD) is observed in tonsillar B lymphocytes. The volume-induced K+ permeability is minimal in these cells, but little was known about the effect of swelling on anion transport and its coupling to cation translocation. The induction of an anion-conductive pathway on swelling of B cells was demonstrated in the following way: 1) when an exogenous cation ionophore was added, hypotonic swelling was followed by secondary volume changes, the direction of which was dictated by the electrochemical gradients of the diffusible ions; 2) the rate of 36Cl efflux was markedly increased by swelling; and 3) upon swelling, the membrane potential approached the Cl- equilibrium potential. Quinine, which blocks K+ transport and RVD in swollen T cells, has no effect on volume-induced anion fluxes. Consequently, secondary volume changes could be elicited by gramicidin in cells pretreated with quinine. It can be concluded that in B cells, swelling leads to activation of a conductive Cl- permeability but not of K+ permeability. These and other findings support the view that the Cl- pathway functions independently of the K+ pathway.
Exogenous substrate utilization by isolated myocytes from chronically diabetic rats
Authors: Chen V. , Bagby G. J. , Spitzer J. J.
Published: December 2017

The effect of chronic streptozotocin-induced diabetes on the utilization of exogenous substrates by freshly isolated, Ca2+-tolerant nonbeating myocytes was investigated. The rates of glucose (5 or 25 mM) and lactate (1 mM) oxidation were significantly reduced in myocytes of diabetic rats, whereas palmitate (0.4 or 1 mM) oxidation was similar to the controls. Glucose oxidation in diabetic (but not in control) and palmitate oxidation in control (but not in diabetic) myocytes were increased by raising the respective substrate concentrations in the medium to levels found in vivo in diabetic rats. Inhibition of glucose and lactate oxidation in the presence of competing substrates were generally similar between control and diabetic myocytes. However, the inhibitory effect of glucose on lactate oxidation was greater in control cells. The rate of palmitate oxidation was diminished by glucose in the controls, but this was not observed in the diabetic myocytes. Oxygen consumption by the myocytes of diabetic rats was below that of control cells when lactate or palmitate was present in the medium. ATP and phosphocreatine contents were similar in the myocytes of diabetic and control rats. All the observed changes in myocytes prepared from diabetic rats were reversed by in vivo insulin treatment.
Role of particle interaction on distribution of liver lysosomes in colloidal silica
Authors: Surmacz C. A. , Wert J. J. , Mortimore G. E.
Published: December 2017

Rat liver mitochondrial-lysosomal fractions were separated on gradients of colloidal silica. Lysosomal enzymes were distributed bimodally. The dense peak (1.117 g/ml) was nearly free from contaminants; beta-N-acetyl-D-glucosaminidase was enriched nearly 60-fold. By contrast, the buoyant peak (1.085 g/ml) co-sedimented with mitochondria, microsomes, peroxisomes, and Golgi particles. Decreasing the amount of protein layered on the gradient medium or dispersing a full sample through it shifted lysosomal marker from the buoyant to the dense peak. Thus the majority of lysosomes in the two peaks appeared to have equivalent densities. Electron microscopic examination of particles separated from gradients with layered samples showed that the dense peak contained most of the dense bodies, whereas the buoyant peak was relatively enriched in autophagic vacuoles. Dispersion, however, shifted autophagic vacuoles from the buoyant to the dense peak without affecting the distribution of dense bodies. We conclude that the bulk of buoyant particles act as a sieve to retard the density equilibration of autophagic vacuoles without specifically affecting other lysosomal enzyme-containing components.
Development and activation of brown fat in rats with pheochromocytoma PC 12 tumors
Authors: Ricquier D. , Mory G. , Nechad M. , Combes-George M. , Thibault J.
Published: December 2017

To study the neurohormonal determinism of cellular growth and differentiation and mitochondrial development in brown adipose tissue (BAT), this organ was analyzed in rats bearing uncloned or cloned (PC 12) pheochromocytoma; comparison was made with cold adaptation. Both uncloned and PC 12 tumors induced an enlargement of tissue weight and DNA total content, although smaller than during cold adaptation. The following striking modifications were observed in rats bearing PC 12 tumors: strong vasodilation, increase in protein and phospholipid percentage, alteration of the fatty acid composition of phospholipids, increase in mitochondrial protein, large increase of the GDP binding to isolated mitochondria, and marked rise in specific amount of 32,000-dalton uncoupling protein (ascertained using immunological approach). It is concluded that secretions of PC 12 tumors can induce the same alterations in BAT as does the sympathetic system during cold adaptation of animals. An important contribution of norepinephrine to these effects is evidenced, but a specific function of other trophic factors secreted by PC 12 cells and by sympathetic nerves can be postulated.