bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca and Na selectivity of the active membrane of rabbit AV nodal cells
Authors: Akiyama T. , Fozzard H. A.
Published: December 2017

The atrioventricular (AV) node is thought to have a slow ionic channel. These experiments were designed to measure the relative contributions of Na and Ca ions to inward currents in the AV nodal cells of rabbit heart superfused with Tyrode solution. The effects of tetrodoxin (TTX), Mn2+, and verapamil observed in this study were in agreement with reports by others. The overshoot of AV nodal (N) cells was related to external Ca, with a slope of 12 mV/decade, unchanged by addition of TTX. Similar dependence of overshoot on external Na was seen, with a slope of 20 mV/decade. The slope did not change on addition of TTX. Total removal of either Na or Ca from the solution abolished excitability. Using a constant field equation, we estimated relative permeability (P) of the membrane at the time of maximal overshoot to be PCa/PNa congruent to 60 similar to or approximately 100 and PK/PNa congruent to 1. Relative contributions of these ions to the currents were estimated as ICa congruent to 17%, INa congruent to 33% (inward currents), and IK congruent to 50% (outward current). In conclusion, AV nodal cells have "slow inward-current channels" that are selective for Ca over Na ions.
Myasthenia in frogs immunized against cholinergic-receptor protein
Authors: Nastuk W. L. , Niemi W. D. , Alexander J. T. , Chang H. W. , Nastuk M. A.
Published: December 2017

Frogs immunized with cholinergic-receptor protein developed myasthenia in 116--175 days. The muscular weakness was overcome by subcutaneous administration of 20 microgram of neostigmine. Electromyograms showed a decline in action potential amplitude during a 2-Hz train. Nerve stimulation evoked subthreshold end-plate potentials (EPPs) averaging 10.4 +/- 7.4 mV, but at many junctions no EPP was obtained. Miniature EPP amplitude had a modal value of 0.15 mV compared with 0.35 mV for the controls. The corresponding means were 0.24 +/- 0.23 mV and 0.48 +/- 0.23 mV. Microperfusion with edrophonium (5 mg/l) increased the amplitude of EPPs and miniature end-plate potentials (MEPPS). Postjunctional response tested with 20 muM carbamylcholine was 56% of control. Postjunctional response by carbamylcholine iontophoresis gave 19 +/- 22 mV/nC compared with 76 +/- 50 mV/nC for the controls. The data indicate that the neuromuscular transmission deficits in receptor-immunized frogs are mainly postsynaptic in origin, but there may be additional presynaptic contributions. This amphibian model of myasthenia gravis offers many opportunities and advantages in the study of receptor-immunized animals.
Inhibition of short-circuit current by triaminopyrimidine in isolated toad urinary bladder
Authors: Fanestil D. D. , Vaughn D. A.
Published: December 2017

The organic cation 2,4,6-triaminopyrimidine (TAP) produced inhibition of short-circuit current (SCC) when added to either the mucosal or serosal surface of the isolated urinary bladder of the toad. Fifty percent inhibition was produced by 10(-3) M TAP in the mucosal solution at pH 6.8 when the mucosal [Na+] was 113 mM. The actions of TAP resemble those produced by amiloride in several ways: a) inhibition of SCC by mucosal application is rapid; b) the mucosal inhibition is fully reversible; c) high concentrations in the serosal solutions produce irreversible inhibition; and d) the concentration required to produce 50% inhibition from the mucosal side is reduced when mucosal [Na+] is reduced. It is postulated that mucosal application of TAP and amiloride inhibit short-circuit current in high-resistance epithelia via action at a common locus.
pH regulation in barnacle muscle fibers: dependence on extracellular sodium and bicarbonate
Authors: Boron W. F. , McCormick W. C. , Roos A.
Published: December 2017

Intracellular pH (pHi) regulation was studied in barnacle muscle fibers with pH-sensitive microelectrodes. The cells were acid loaded, and the subsequent recovery of pHi was monitored. The rate of recovery was reduced by one-third when external Na+ ([Na+]o) was replaced by Li+, but recovery was completely abolished when Na+ was replaced by choline or N-methyl-D-glucamine. In other experiments, varying amounts of Na+ were replaced by choline, and the acid extrusion rate, derived from the recovery rate of pHi, was calculated at a single value of pHi, 6.80. The dependence of the acid extrusion rate on [Na+]o could be described by Michaelis-Menten kinetics; at pHo (extracellular) = 8.0 and [HCO3-]o (extracellular) = 10 mM, the apparent Km and Vmax were 59 mM and 1.3 mmol x l(-1) x min-1. When [HCO3-]o was reduced to 2.5 mM at the same pHo, Km did not change significantly, but Vmax was substantially reduced. On the other hand, when pHo was reduced to 7.4 at constant [HCO3-]o, Vmax changed only slightly, but Km increased substantially. In similar experiments, we examined the dependence of the acid extrusion rate on [HCO3-]o. At pHo = 8.0 and [Na+]o = 440 mM, the apparent Km and Vmax were 4.1 mM and 2.1 mmol x 1-1 x min-1. When pHo was reduced to 7.4, Vmax was not altered, but Km substantially increased. The kinetic data are discussed in terms of the role of pHo, [Na+]o, and [HCO3-]o in the pHi-regulating system.
Physiological and biochemical effects of iron deficiency on rat skeletal muscle
Authors: McLane J. A. , Fell R. D. , McKay R. H. , Winder W. W. , Brown E. B. , Holloszy J. O.
Published: December 2017

Young rats were made iron deficient by feeding them a low-iron diet for 8 wk. Iron deficiency resulted in a 50% decrease in cytochrome c and cytochrome oxidase and a 26% decrease in mitochondrial glycerol-3-phosphate dehydrogenase activity in skeletal muscle. Respiratory capacity of muscle homogenates was reduced 55%. After 8 days of iron treatment, respiratory capacity, cytochrome c, cytochrome oxidase, and glycerol-3-phosphate dehydrogenase had returned 50% toward normal. Maximum O2 uptake of contracting hindlimb muscles averaged 8.5 mumol O2.min-1.g-1 in control, 4.3 mumol O2.min-1.g-1 in iron-deficient, and 6.2 mumol O2.min-1.g-1 in the 8-day-iron-repleted rats. Muscle fatigue during 10 min of stimulation was greater in the iron-deficient group. Lactate concentration in red muscle was higher in iron-deficient than in control rats after stimulation. The muscle fatigue and lactate responses returned 50% toward normal during 8 days of iron treatment. We conclude that iron deficiency results in a decrease in skeletal muscle capacity for aerobic metabolism and, by this mechanism, increases susceptibility to fatigue.
Effect of weak acids on pH regulation and anion transport in barnacle muscle fibers
Authors: Keifer D. W.
Published: December 2017

The intracellular pH (pHi) of barnacle muscle fibers was measured with microelectrodes while the fibers were exposed to the weak acids, propionic acid (98 mM), or 5,5-dimethyloxazolidine-2,4-dione (DMO) (100 mM), at extracellular pH (pH0) 7.8. Both propionate and DMO caused an initial drop in pHi, followed by a partial recovery to the final steady pHi of 7.16. In the presence of 6 mM HCO3(-) (pH0 7.8), the final pHi was 7.31 for either weak acid. In other experiments, pHi was initially lowered by temporarily exposing the fiber to NH4Cl-containing solution. The rate of subsequent pHi recovery at pHi 6.84 was expressed as an H+ equivalent flux. In the absence of HCO3(-), the H+ equivalent flux was stimulated (two- to threefold) by both propionate and DMO. Part of this stimulation was due to the reduced Cl- concentration in the external solution when the anion of the weak acid is substituted for Cl-. Another part of the stimulation may have been due to the increased buffering in the intracellular unstirred layer. HCO3(-) greatly stimulated (ninefold) the H+ equivalent flux, but in the presence of HCO3(-), propionate and DMO had no additional effect. There is no evidence from the present work indicating that either propionate or DMO anions acted as substrates for operation of the anion exchange mechanism (Cl-/Cl- and HCO3(-)/Cl-). Since exposure of the cell to either of the weak acids lowered pHi and since the rate of anion exchange fluxes is known to increase when pHi is lowered, propionate most likely stimulated anion fluxes indirectly by lowering pHi.
Metabolic cooperativity between epithelial cells and adipocytes of mice
Authors: Bartley J. C. , Emerman J. T. , Bissell M. J.
Published: December 2017

We have demonstrated that glycogen and lipid synthesis in adipocytes is modulated by the lactational state and that this modulation in mammary adipocytes requires the presence of the adjacent epithelial cells. Glycogen and lipid synthesis from [14C]glucose was measured in mammary fat pads cleared of epithelium, in abdominal fat pads, and in adipocytes from both sources and from intact mammary gland of mature virgin, pregnant, and lactating mice. Accumulation of glycogen, the activity of glycogen synthase, and the lipogenic rate in abdominal and mammary adipocytes remained high during pregnancy but decreased to insignificant levels by early lactation. The depressant effects of lactation were observed solely in those mammary adipocytes isolated from intact glands. The presence of mammary epithelial cells was also required to effect the stimulated lipogenesis in mammary adipocytes during pregnancy, We conclude that the metabolic activity of adipocytes is modulated both during pregnancy and lactation to channel nutrients to the mammary epithelial cell. The fact that the changes occur in mammary adipocytes only when epithelial cells are present indicates that local as well as systemic factors are operating in these modulations.
Specific binding of nerve growth factor to normal and denervated canine heart
Authors: Wells D. J. , Strehlo B. L. , Kaye M. P.
Published: December 2017

Preparations of membranes from normal and surgically denervated canine heart were tested for binding of radiolabeled nerve growth factor. Specific binding was detected in both normal and denervated hearts. Binding was nonsaturable and complex for normal atria and ventricles and denervated atria but appeared to be saturable for denervated ventricles. Nerve growth factor bound per microgram of protein was lower in denervated ventricles than normal ventricles, whereas slightly higher binding to denervated atria than normal atria was observed. This binding could not be displaced by cytochrome c, insulin, or epidermal growth factor. The data indicate that a large part of binding to normal ventricles could be due to nerve terminals attached to the heart, but specific binding detected in the denervated ventricles may be an intrinsic property of the tissue itself. These sites may serve as storage or uptake sites to direct sympathetic innervation in the developing or reinnervating myocardium.
Mechanism of activation of isolated rabbit aorta by PGH2 analogue U-44069
Authors: Loutzenhiser R. , van Breemen C.
Published: December 2017

The effects of a stable analogue of PGH2 on 45Ca fluxes and tension were studied in the isolated rabbit aorta. U-44069 produced maximal tension responses at a concentration of 10(-7) M. The analogue increased smooth muscle Ca2+ content and increased the unidirectional 45Ca influx. U-44069 also induced contractions of reduced magnitude in the absence of external Ca2+ and caused a transient stimulation of 45Ca efflux, suggesting that the analogue releases intracellularly bound Ca2+. Both the contractile response in CA2+-free media and the stimulation of 45Ca efflux were greatly attenuated by prior exposure to norepinephrine. The analogue-induced contractions in Ca2+-free media were also prevented by prior exposure to histamine but not angiotensin II. D-600 completely blocked the U-44069-induced gain in calcium content (IC50 = 10(-6) M) but inhibited the contractile response by only 40%. It was concluded that the PGH2 analogue activates rabbit aorta by activating a CA2+ influx pathway and releasing a fraction of the intracellular Ca2+ pool that is sensitive to norepinephrine and other agonists.
Stretch-induced growth in chicken wing muscles: effects on hereditary muscular dystrophy
Authors: Ashmore C. R.
Published: December 2017

Skeletal muscle growth induced by passive stretch was characterized in the Patigialis muscle of chicks with hereditary muscular dystrophy. When the muscle of 6-wk-old chicks was stretched for 1 wk, the effects on muscle growth and on muscle pathology were variable, but in general few differences between stretched and unstretched muscles were observed. However, when the muscle of 1-wk-old chicks was stretched for 6 wk, the effects on muscle growth and on prevention of pathology were dramatic. Similar to results obtained previously when normal chick muscles were stretched [Holly et al., Am. J. Physiol. 238 (Cell Physiol. 7): C62-C71, 1980; Barnett et al., Am. J. Physiol. 239 (Cell Physiol. 8): C39-C46, 1980], stretched dystrophic muscle increased in weight (200%), cross-sectional area (107%), and fiber cross-sectional area (82%). DNA concentration, which is severalfold higher in unstretched dystrophic muscle compared with unstretched normal muscle, fell to values not different from normal values after being stretched. Nuclei per square millimeter also were the same for stretched dystrophic and stretched normal muscle. Histograms indicated that stretching induced a fiber distribution in dystrophic muscle qualitatively similar to that found in stretched normal muscle. Cytochemical observations revealed a dramatic protective effect of stretch against the progressive pathology of dystrophy. It is concluded that stretch of muscle applied to newly hatched dystrophic chicks is a powerful deterrent of symptoms characteristic of hereditary muscular dystrophy. Stretch imposed after the symptoms of dystrophy are apparent provides little, if any, protection.
Bath osmolality: effect on water permeability of epithelial tissue
Authors: Lau Y. T. , Parsons R. H. , Feeney G. A. , Walker K. L.
Published: December 2017

When hyperosmotic gradients from 100 to 500 mosM are used to produce a water flux, the water permeability of live and potassium cyanide (KCN)-poisoned frog skin decreases with increasing osmotic gradients. In addition, as the total bath osmolality (corium + epithelial) increases there is a reduction in tissue water. Examination of the tissue cellular and extracellular compartments shows that cell shrinkage caused by the increasing hyperosmolality of the bathing medium correlates with the decrease in osmotic permeability. When the bath osmolality is held constant and cell volume decreases, there is a decrease in the water permeability. High potassium in the external bathing medium causes cell swelling that is associated with an increase in water permeability. These data support the hypothesis that a number of conditions known to affect the water permeability of frog skin do so partly or wholly as a result of a change in the cell volume, which either directly or indirectly alters the osmotic permeability of a rate limiting barrier, possibly the cell membrane.
Importance of molecular size and hydrogen bonding in vasopressin-stimulated urea transport
Authors: Petrucelli R. J. , Eggena P.
Published: December 2017

We have employed a variety of urea and thiourea analogues to elucidate further the vasopressin-stimulated urea transport mechanism. In the urea series there was a progressive inhibition of tracer urea transport as cylindrical radius of analogue increased from 2.9 to 3.5 A. Above 3.8 A no inhibition was found. Thiourea analogues were more potent inhibitors for comparable cylindrical radii, and compounds greater than 3.8 A again were not inhibitory. Inhibition was comparable when the inhibitor was moving in the same or opposite directions. Urea transport and its inhibition were preserved in bladders fixed with glutaraldehyde. Osmotic water flow, tritiated water flow, and uric acid transport were not affected by any analogues tested. Analogues of urea and thiourea affected the transport of labeled methylurea and thiourea in a manner similar to their effect on urea. We therefore propose that the urea transport mechanism is a channel with a cylindrical radius between 3.5 and 3.8 A that is capable of interaction with the moving species by hydrogen bonding. This model can account for the selectivity of the vasopressin-stimulated urea transport, its inhibition by urea and thiourea analogues, the facilitated transport of urea, inhibition of tracer urea flux from either the cis or the trans position, and finally the preservation of the urea transport machinery following glutaraldehyde fixation.
An ATP- and Ca2+-regulated Na+ channel in isolated intestinal epithelial cells
Authors: Kimmich G. A. , Randles J.
Published: December 2017

When isolated intestinal epithelial cells are treated with 2 mM ATP, the unidirectional influx of Na+ to those cells increases from values near 50 to rates over 200 nmol . min-1 . mg protein-1. Calcium influx increases from 1 to 40 nmol . min-1 . mg protein-1. Within 2 min, the total cell Na+ increases two- to threefold, and total Ca+ increases about fivefold. The cells lose a major part of their capability for accumulating sugars during this interval. About 2 min after the time of ATP addition the normal permeability for Na+ and Ca2+ is restored, at which time the previously accumulated ions are rapidly extruded on a net basis until control levels are attained and the cells regain their usual sugar transport capability. The "repair" process requires Ca2+ in the incubation medium and is dependent on cellular uptake of Ca2+. Chlorpromazine (0.5 mM) blocks the Ca2+ entry route and the restoration of normal Na+ permeability. The Na+ entry route is selectively blocked by 4-acetamido-4'-isocyanostilbene-2,2'-disulfonic acid. The data show that ATP induces the influx of Na+ and Ca2+ by two different routes, which can be selectively inhibited. These ion flux routes may be involved in the events that allow intestinal tissue to convert from an absorptive state to a state in which net ion secretion occurs.
Polyamine metabolism and function
Authors: Pegg A. E. , McCann P. P.
Published: December 2017

Polyamines are ubiquitous organic cations of low molecular weight. The content of these amines is closely regulated by the cell according to the state of growth. The reactions responsible for the biosynthesis and interconversion of the polyamines and their precursor putrescine are described and the means by which polyamine content can be varied in response to exogenous stimuli are discussed. The role of polyamines in the cell cycle, cell division, tissue growth, and differentiation is considered. Recent studies using highly specific inhibitors of polyamine biosynthesis such as alpha-difluoromethylornithine to prevent accumulation of polyamines have indicated that the synthesis of polyamines is intimately associated with these processes. Such inhibitors have great potential for investigation of the cellular role of polyamines.
Chloride transport in glands of frog skin
Authors: Thompson I. G. , Mills J. W.
Published: December 2017

The effects of beta-adrenergic stimulation on the bidirectional fluxes of Na+ and Cl- across the frog skin glands were determined. Isoproterenol elicited net serosal-to-mucosal fluxes of both Na+ (JNanet) and Cl- (JClnet) equal to 0.19 +/- 0.05 (SE) and 0.57 +/- 0.05 mueq X cm-2 X h-1, respectively. The residual current (JClnet - JNanet) of 0.38 +/- 0.05 mueq X cm-2 X h-1 closely approximates the isoproterenol-induced short-circuit current of 0.30 +/- 0.04 mueq X cm-2 X h-1. Furosemide added to the serosal side prior to isoproterenol inhibited the isoproterenol-induced net fluxes of both Na+ and Cl-. The addition of dibutyryl cAMP and 3-isobutyl-1-methylxanthine to the serosal side mimicked the action of isoproterenol by stimulating glandular short-circuit current. We conclude that an active Cl(-)-transport mechanism resides in the frog skin glands and is 1) stimulated by a beta-adrenergic agonist (its action is mimicked by cAMP) and 2) inhibited by the loop diuretic furosemide.
Na+-K+-ATPase in rat vascular smooth muscle cell grown in vitro
Authors: Aviv A. , Higashino H. , Hensten D. , Bauman J. W. , Lubit B. W. , Searle B. M.
Published: December 2017

This study has focused on the characteristics of the Na+-K+-ATPase in in vitro preparations of vascular smooth muscle cells (VSMCs) derived from the rat carotid artery. The maximum velocity of enzyme reaction (Vmax) for the specific activity of the enzyme in the VSMCs' preparations was 2.36 +/- 0.04 (SE) mumol Pi X mg cell protein-1 X h-1 or 0.82 +/- 0.02 mumol Pi X 10(6) cells-1 X h-1. The activation of the enzyme by potassium, sodium and ATP has been investigated. The half-maximal values for potassium and sodium activation of the enzyme in the preparations were 1.18 and 10-20 meq/l, respectively. The respective Vmax values for potassium and sodium activation were reached at concentrations of 4-10 and 80-100 meq/l. The Michaelis constant for ATP was 0.83 mM. Calcium exerted a potent inhibition on the activity of the enzyme (I50 at 1 mM). It has been concluded that the Na+-K+-ATPase kinetic pattern in in vitro preparations of VSMCs is quite similar to that observed in homogenates or subcellular fractions of other tissues.
Alpha 1-adrenergic stimulation of hamster brown adipocyte respiration
Authors: Schimmel R. J. , McCarthy L. , McMahon K. K.
Published: December 2017

Respiration was increased approximately 5-fold with 0.05 microM norepinephrine and to a maximum of 10-fold by 0.30 microM norepinephrine. Prazosin, an alpha-adrenergic blocking agent highly selective for alpha 1-type receptors, partially inhibited the response to norepinephrine (0.05 microM) by 20-25% at a concentration of 0.10-1 microM. In contrast, when the stimulus for respiration was provided by isoproterenol or 3-isobutyl-1-methylxanthine, prazosin was without effect up to a concentration of 10 microM. Yohimbine, an alpha-adrenergic blocking drug preferential for alpha 2-receptors, did not influence norepinephrine-stimulated oxygen uptake. Respiration was increased two- to fourfold by phenylephrine or methoxamine, agents preferential for alpha 1-adrenergic receptors but not at all by clonidine, an agent preferential for alpha 2-adrenergic receptors. The stimulatory effect of phenylephrine on oxygen uptake was fully blocked by prazosin but not propranolol. Removal of extracellular calcium with ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid prevented phenylephrine stimulation of respiration but was without effect when isoproterenol was the stimulus. These results support the participation of alpha 1-adrenergic receptors in control of respiration and are consistent with the possibility that changes in cell calcium are intimately involved in this response.
Evidence for active Na+ transport by cultured monolayers of pulmonary alveolar epithelial cells
Authors: Goodman B. E. , Fleischer R. S. , Crandall E. D.
Published: December 2017

Primary cultured type II alveolar epithelial cells grown to confluence on nonporous surfaces form many small fluid-filled hemicysts or domes. These domes are generally thought to result from active transport of solutes from the medium above the cell monolayer to the substratum, with water following passively. We have investigated the characteristics of active transport by primary cultured monolayers of type II alveolar epithelial cells from rat lungs. Changes in dome density were measured after exposure to metabolic inhibitors, Na+ or Cl- transport inhibitors, and low-Na+ or low-Cl- culture media. Metabolic and Na+ transport inhibitors, and low-Na+ medium, lead to disappearance of domes, whereas Cl- transport inhibitors and low-Cl- medium seem to have no effect on dome density. These results suggest the presence of a Na+-dependent active transepithelial transport process across the monolayer, which is responsible for the formation of domes. This finding implies that absorption of fluid by mammalian alveolar epithelium in vivo may be important in the maintenance of normal lung fluid balance.
FMLP-induced enzyme release from neutrophils: a role for intracellular calcium
Authors: Chandler D. , Meusel G. , Schumaker E. , Stapleton C.
Published: December 2017

The ability of the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (FMLP) to stimulate beta-glucuronidase release and 45Ca2+ release from rabbit neutrophils was studied. FMLP stimulated enzyme release from cytochalasin B-treated cells either in the presence or the absence of extracellular calcium. Depletion of cell calcium, by exposure to either ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid or the calcium ionophore A23187, blocked the ability of FMLP to stimulate enzyme release and 45Ca2+ release in the absence of extracellular calcium. The ability of A23187 to lower the 45Ca2+ content of neutrophils, to block FMLP-stimulated 45Ca2+ release, and to inhibit FMLP-stimulated enzyme release in the absence of calcium was dose dependent over the same concentration range (10(-8) to 10(-6) M A23187) for all three actions. In contrast, FMLP stimulated enzyme release from A23187-treated cells, provided that extracellular calcium was present. This secretory response was normal as judged by cell ultrastructure and FMLP dose-response relationships. It is concluded that A23187 depletes a pool of intracellular calcium usually released by FMLP and that release of calcium from this pool is necessary for initiation of enzyme secretion in the absence of extracellular calcium.
Sarcolemmal Na+-K+-ATPase activity in diabetic rat heart
Authors: Pierce G. N. , Dhalla N. S.
Published: December 2017

Heart sarcolemmal membranes were isolated by the hypotonic shock-LiBr treatment from rats with chronic diabetes induced by a streptozotocin (65 mg/kg, iv) injection. Sarcolemmal Mg2+-dependent ATPase activity was elevated, whereas 5'-nucleotidase and K+-p-nitrophenylphosphatase activities in diabetic heart were depressed in comparison to control preparations. Although patent Na+-K+-ATPase and patent ouabain-sensitive Na+-K+-ATPase activities were unaltered, latent Na+-K+-ATPase activities, as determined in membranes after alamethicin or deoxycholate treatments, were found to be significantly depressed in diabetic animals. A depression in the latent Na+-K+-ATPase activity in diabetic preparations was also observed in membranes prepared by the sucrose density gradient method. Insulin-treated diabetic rats were observed to have normalized latent Na+-K+-ATPase activities. Total phospholipid content did not differ, but cholesterol content of the sarcolemmal membranes was significantly increased in diabetic heart preparations. Sarcolemmal Na+-K+-ATPase activity in diabetic heart was more resistant to treatments with filipin, an agent known to bind with cholesterol residues. These results suggest that chronic experimental diabetes is associated with some defects in sarcolemmal enzymatic activities and composition.
Vasoconstrictor-evoked prostaglandin synthesis in cultured vascular smooth muscle
Authors: Hassid A. , Williams C.
Published: December 2017

We investigated the hypothesis that vasopressin, angiotensin II, and norepinephrine stimulate the synthesis of vasodilatory prostaglandins in cultured vascular smooth muscle cells from rat mesenteric arteries. The major prostaglandin synthesized by subcultured vascular smooth muscle cells was PGI2 (measured as its stable metabolite 6-keto-PGF1 alpha) followed by 1/20th to 1/40th as much PGF2 alpha and PGE2. Vasopressin and angiotensin II dose dependently increased prostaglandin synthesis with a half-maximal stimulatory concentration of the order of 1 X 10(-8) M for both peptides. However, vasopressin could provoke the synthesis of two to three times as much PGI2 as angiotensin II, at maximally effective concentrations. Vasopressin's ability to provoke prostaglandin synthesis depended on its pressor activity as demonstrated by the ability of a potent antipressor analogue of vasopressin, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine] arginine vasopressin, to completely inhibit vasopressin-provoked prostaglandin synthesis. Moreover, 1-desamino-8-D-arginine vasopressin, an analogue having full antidiuretic but no pressor activity was much less effective than vasopressin as a prostaglandin-stimulatory agent. Unlike peptide vasoconstrictors, norepinephrine (10(-9) to 10(-5) M) had no ability to stimulate prostaglandin synthesis in vascular smooth muscle cells. We conclude that the potent vasodilator PGI2, released from vascular smooth muscle cells, may buffer the peptide-induced vasoconstriction.
Forskolin stimulation of acid and pepsinogen secretion in isolated gastric glands
Authors: Chew C. S.
Published: December 2017

Forskolin, a specific diterpene activator of adenylate cyclase in intact cells and cellular homogenates, was used to examine the relationship among adenosine 3',5'-cyclic monophosphate (cAMP) metabolism, gastric acid, and pepsinogen secretion in isolated gastric glands. This agent was found to stimulate [14C]aminopyrine (AP) accumulation and respiration, both measurements of which are indexes of parietal cell acid secretory responsiveness and pepsinogen secretion, which is a measure of chief cell activity. Forskolin also increased cAMP content and activated cAMP-dependent protein kinase in the glands. The histamine H2-receptor antagonist, cimetidine, inhibited forskolin-stimulated increases in AP accumulation and respiration when submaximal concentrations of forskolin were used but had not effect on the other response parameters. Forskolin also potentiated the action of the muscarinic agonist, carbachol, in both the presence and absence of cimetidine. Since there was a close kinetic and temporal correlation between the secretory response parameters and cAMP-dependent protein kinase activation, it appears that cAMP plays an important role in the mediation of gastric acid and pepsinogen secretion. The inhibitory action of cimetidine on forskolin-stimulated AP accumulation and respiration suggest that forskolin potentiates the action of endogenous histamine present in the glands. Forskolin potentiation of carbachol in the presence of maximum inhibitory concentrations of cimetidine indicates that previously observed potentiating interactions between carbachol and histamine, secretagogues which appear to act via cAMP-independent and cAMP-dependent mechanisms, respectively, involve intracellular events that occur subsequent to the binding of these agents to their respective receptors and subsequent to an increase in intracellular cAMP content.
Activity of circular muscle of rat uterus at different times in pregnancy
Authors: Bengtsson B. , Chow E. M. , Marshall J. M.
Published: December 2017

During pregnancy, circular muscle activity changes from weak irregular contractions at midterm to strong regular contractions at term. The present study was designed to determine if this change is related to contractile ability or to membrane electrical events. Myometrial segments were taken from rats on days 16–17, 18–19, 20, and 21 (term) of gestation. Contractile ability was estimated as the maximum force elicited by 121 mM KCl or 0.6 mM acetylcholine. The K- and acetylcholine-induced contractions were significantly greater than spontaneous and no different at midterm and term. Electrical activity was measured with intracellular electrodes. Between days 16 and 21, action potentials evolved from single, plateau-type to repetitive spike trains. Plateau potentials were associated with small contractions and repetitive spikes with larger contractions. On day 21, there was a transient increase in membrane potential and cessation of spontaneous activity. Before delivery, the membrane potential declined and spontaneous spike trains appeared and triggered large contractions. Conclusion: the change in circular muscle activity during pregnancy is related to electrical events and not to contractile ability.
Some effects of lead at mammalian neuromuscular junction
Authors: Pickett J. B. , Bornstein J. C.
Published: December 2017

The effect of lead on transmitter release was investigated in a rat phrenic nerve-hemidiaphragm preparation using conventional microelectrode techniques. Lead reduced the number of quanta released by a nerve stimulus (m) in a dose-dependent fashion. As extracellular Ca2+ concentration ([Ca2+]o) was varied in the absence of lead, a linear relationship between ln(m) and ln([Ca2+]o) was obtained. Lead shifted the relationship between ln(m) and ln([Ca2+]o) to the right without altering the slope. This suggested lead competed with Ca2+, which was confirmed by using a modified Lineweaver-Burk plot. Lead inhibits Ca2+ entry into frog sympathetic preganglionic nerve terminals, and a similar mechanism may underlie this present finding; such a mechanism, however, could not explain all the observed actions of lead. Lead increased the frequency of spontaneous quantal release in a dose-dependent manner, and 10(-4) M lead doubled the magnitude of facilitation of evoked release seen with five stimuli at 60 Hz. It is suggested that these effects result from inhibition of some, or all, of the nerve terminal's Ca2+ sequestration mechanisms.
Responses of chick renal cell to parathyroid hormone: effect of vitamin D
Authors: Liang C. T. , Balakir R. A. , Barnes J. , Sacktor B.
Published: December 2017

The in vitro incubation of chick renal cells with parathyroid hormone (PTH) resulted in the inhibition of Na+-dependent phosphate uptake when the cells were isolated from 1,25-dihydroxycholecalciferol 1,25-dihydroxycholecalciferol [1,25-(OH)2D3]-repleted chicks but not when the cells came from vitamin D-deficient animals. Na+-independent phosphate and Na+-dependent alpha-methylglucoside uptakes were not affected by PTH and the vitamin D status of the bird. The activation of chick renal cell adenylate cyclase by PTH was significantly blunted when the enzyme was from vitamin D-deficient animals relative to the activation of the enzyme from repleted cockerels. This alteration was due to a change in maximum velocity of the system rather than an effect on the affinity for hormone. The response of adenylate cyclase to other hormones, e.g., prostaglandin E2, and activators, e.g., 5' -guanylyl-imidodiphosphate and forskolin, was not affected by the vitamin D status of the animal. PTH had little effect in activating protein kinase in cells from vitamin D-deficient chicks. In cells from vitamin D-sufficient birds, PTH caused a fourfold increase in adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Dibutyryl cAMP inhibited Na+-dependent phosphate uptake by cells from 1,25-(OH)2D3-repleted animals, but the cyclic nucleotide had no effect on phosphate uptake in cells from vitamin D-depleted chicks. This finding suggests that the loss of PTH receptor sites known to be concomitant with the secondary hyperparathyroidism associated with vitamin D deficiency is only a partial explanation for the failure of PTH to inhibit phosphate uptake in cells from vitamin D-deficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Epithelial properties of human colonic carcinoma cell line Caco-2: electrical parameters
Authors: Grasset E. , Pinto M. , Dussaulx E. , Zweibaum A. , Desjeux J. F.
Published: December 2017

Human colonic carcinoma Caco-2 cells grown in vitro undergo epithelial differentiation. Electrical measurements showed that they form resistant monolayers of polarized cells. On millipore filters, transepithelial electrical resistance (154 +/- 6.5 omega X cm2) was accompanied by a small potential difference (0.29 +/- 0.02 mV, serosal side positive) and by short-circuit current (1.9 +/- 0.14 microA X cm-2), both of which were ouabain sensitive. Micropuncture of domes formed on plastic supports under standard culture conditions revealed electrical polarity similar to that of filter-grown cells (0.8 +/- 0.2 mV, serosal side positive) combined with a highly negative cytoplasm (-57 +/- 1 mV) and very marked cell asymmetry (76% of total electrical cell resistance was located in the mucosal membrane). These parameters were not affected by the diuretic amiloride nor the hormone aldosterone, suggesting that sodium conductance is very limited in the mucosal membrane. Addition to the mucosal side of the ionophore nystatin or amphotericin B unmasked the possibility of high electrical transport activity. Electrical measurements made it possible to define the epithelial properties of Caco-2 cells, which may resemble those of colonic crypt or fetal cells. These measurements also confirmed that functional differentiation is homogeneous in Caco-2 cells. It is suggested that dome cell micropuncture may be useful in investigating the functional properties of other dome-forming cell lines.
Comparison of subunits of cardiac, brain, and kidney Na+-K+-ATPase
Authors: McDonough A. , Schmitt C.
Published: December 2017

Na+-K+-ATPase is in low abundance in cardiac tissue. Therefore, we utilized antibodies to detect the cardiac Na+-K+-ATPase subunits and to compare their characteristics with those of kidney and brain Na+-K+-ATPase subunits. By using crude preparations of heart membranes as well as purified sarcolemmal membranes from guinea pig hearts, we resolved peptides by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, blotted them onto diazotized paper, and detected Na+-K+-ATPase subunits with antibodies generated against highly purified kidney Na+-K+-ATPase holoenzyme. We tested the hypothesis that the two families of ouabain-binding affinities described in heart are due to two forms of alpha-subunit, analogous to the two forms with different affinities for ouabain described in brain. Although the antibodies did detect two forms of catalytic subunit in brain (alpha and alpha +), only one form of alpha was detected in the heart membranes, with the same electrophoretic mobility as kidney alpha. Cardiac beta-subunit could also be detected with the antikidney antibodies. It had a similar electrophoretic mobility to that described for kidney beta, whereas brain beta had a higher mobility.
Temperature-dependent physiological stability of rat skeletal muscle in vitro
Authors: Segal S. S. , Faulkner J. A.
Published: December 2017

Stability of rat skeletal muscle contractile properties with time in vitro as a function of incubation temperature was characterized. Female Sprague-Dawley rats (8 wk, 148 g) were anesthetized with pentobarbital sodium (40 mg/kg, ip). Intact soleus (SOL) and extensor digitorum longus (EDL) muscles of 70- to 90-mg mass were removed and studied at incubation temperatures of 20, 25, 30, 35, and 40 degrees C. The average muscle thickness was 2.0 mm. Each muscle was studied at one temperature only. At 5, 15, 30, 45, and 60 min following immersion in an oxygenated Krebs-Ringer bicarbonate solution, isometric contractile properties were measured. Peak twitch tension, maximum tetanic tension, and rate of tension development of both SOL and EDL muscles were stable with time at 20 and 25 degrees C but decreased with time as a function of bath temperature above 25 degrees C. The calculated critical radius for O2 diffusion declined from 1.19 mm at 20 degrees C to 0.51 mm at 40 degrees C. For SOL and EDL muscles incubated at 25 degrees C, the histochemical demonstration of glycogen content was similar to that of fresh muscles, whereas muscles incubated at 40 degrees C showed staining for glycogen only in peripheral fibers. Observed and calculated results both infer a progressively larger hypoxic core at incubation temperatures above 25 degrees C.
Effects of acidosis on rat muscle metabolism and performance during heavy exercise
Authors: Spriet L. L. , Matsos C. G. , Peters S. J. , Heigenhauser G. J. , Jones N. L.
Published: December 2017

The metabolism and performance of a perfused rat hindquarter preparation was examined during heavy exercise in three conditions: control (C), metabolic acidosis (MA, decreased bicarbonate concentration), and respiratory acidosis (RA, increased CO2 tension). A one-pass system was used to perfuse the hindquarters for 30 min at rest and 20 min during tetanic stimulation via the sciatic nerve. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and biopsies were taken pre- and postperfusion. Initial isometric tensions were similar in all conditions, but the rate of tension decay was largest in acidosis; the 5-min tensions for C, MA, and RA were 1,835 +/- 63, 1,534 +/- 63, and 1,434 +/- 73 g, respectively. O2 uptake in C was greater than in MA and RA (23.4 +/- 1.3 vs. 17.0 +/- 1.4 and 16.5 +/- 2.3 mumol X min-1), paralleling the tension findings. Hindquarter lactate release was greatest in C, least in MA, and intermediate in RA. Acidosis resulted in less muscle glycogen utilization and lactate accumulation than during control. Muscle creatine phosphate utilization and ATP levels were unaffected by acidosis. Acidosis decreased the muscle's ability to generate isometric tension and depressed both aerobic and anaerobic metabolism. During stimulation in this model lactate left the muscle mainly as a function of the production rate, although a low plasma bicarbonate concentration at pH 7.15 depressed muscle lactate release.
Roles of cell geometry and cellular viscosity in red cell passage through narrow pores
Authors: Reinhart W. H. , Chien S.
Published: December 2017

The relative roles of two fundamental determinants of red cell deformability, namely cell size and cellular viscosity, in affecting red cell passage through narrow channels have been assessed by determining the filterability of red cells subjected to osmotic variations. Suspensions of red cells (10(6) cells/microliter) in eight different osmolalities ranging from 172 +/- 3 (mean +/- SD) to 665 +/- 28 mosmol/kg H2O were filtered through polycarbonate sieves with three different pore diameters (2.6 +/- 0.2, 4.5 +/- 0.6, and 6.9 +/- 0.8 micron). The mean corpuscular volume varied inversely with osmolality and ranged from 149 +/- 9 to 67 +/- 10 fl; the mean corpuscular hemoglobin concentration varied directly with osmolality and ranged from 23.7 +/- 0.8 to 55.9 +/- 3.9 g/dl. The filtration data were analyzed with a theoretical model to derive the parameter beta, which is the ratio of resistance in a pore bearing a red blood cell to that in a pore filled with the suspending medium alone. For each pore size, beta showed a V-shaped relationship with osmolality; the optimum osmolality for minimum beta varied inversely with the pore size. For the small 2.6-micron pores, the minimum beta was attained following hyperosmotic shrinkage of the red cells at 400 mosmol/kg H2O, whereas passage through the large 6.9-micron pores was facilitated by hypoosmotic swelling of the red cells in about 200 mosmol/kg H2O. Red cell filtration through small pores is more sensitive to alterations in cell volume, whereas that through large pores is primarily determined by changes in cellular viscosity.(ABSTRACT TRUNCATED AT 250 WORDS)
Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport
Authors: Restrepo D. , Kimmich G. A.
Published: December 2017

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.
Intracellular Ca2+ levels and amylase secretion in Quin 2-loaded mouse pancreatic acini
Authors: Powers R. E. , Johnson P. C. , Houlihan M. J. , Saluja A. K. , Steer M. L.
Published: December 2017

Dispersed mouse pancreatic acini were loaded with the Ca2+-sensitive fluorescence probe Quin 2. Stimulation with carbamylcholine or cholecystokinin-octapeptide (CCK-OP) resulted in a rapid increase in Quin 2 fluorescence, which returned to a lower and sustained plateau level within 2 min of secretagogue stimulation. The magnitude of the initial rise in fluorescence intensity and of amylase secretion were closely related to the concentration of agonist used. Maximal fluorescence changes and amylase secretion were noted with 1 X 10(-5) M carbamylcholine and 1 X 10(-9) M CCK-OP, whereas both responses were half maximal in the presence of 5 X 10(-7) M carbamylcholine and approximately 1 X 10(-10) M CCK-OP. The resting cytosolic free Ca2+ concentration, as measured by the intensity of Quin 2 fluorescence, was calculated to be 1.03 +/- 0.12 X 10(-7) M. Cytosolic free Ca2+ rose to 1.3 +/- 0.3 X 10(-6) M after addition of 1 X 10(-5) M carbamylcholine and 1.25 +/- 0.21 X 10(-6) M following 1 X 10(-9) M CCK-OP. Amylase secretion, but not the Quin 2 fluorescence response, was attenuated at higher secretagogue concentrations. Both secretagogue-induced Quin 2 fluorescence and amylase secretion were inhibited by secretagogue antagonists. Removal of Ca2+ from the extracellular medium resulted in a 48.8 +/- 2.0% reduction of carbamylcholine-induced Quin 2 fluorescence. Following addition of carbamylcholine, CCK-OP was unable to stimulate a second increase in Quin 2 fluorescence without the intervening addition of a cholinergic antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of prostaglandins in hypoxia-stimulated erythropoietin production
Authors: Kurtz A. , Jelkmann W. , Pfeilschifter J. , Bauer C.
Published: December 2017

The role of prostaglandins in the mediation of hypoxia-stimulated erythropoietin (Ep) production by cultured rat renal mesangial cells was examined. It was found that an increase in prostaglandin E2 (PGE2) production accompanied the rise in Ep due to hypoxia (2% O2). The hypoxia-stimulated increase in Ep production was abolished in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M). When PGE2 (10(-6) M was added simultaneously with indomethacin, however, no diminution in hypoxia-stimulated Ep production was observed. Addition of arachidonic acid (AA, 10(-5) M), PGE2 (10(-6) M), or PGI2 (10(-4) M) enhanced Ep production under normoxic conditions (20% O2), while PGF2 alpha (10(-6) M) had no effect on Ep production. AA, PGE2, and PGI2 were found to stimulate adenosine 3',5'-cyclic monophosphate formation by the cultured mesangial cells. Enhancement of adenylate cyclase activity by forskolin (10(-5) M) also increased Ep production in the cell cultures. Our results suggest that hypoxia-stimulated Ep production by cultured mesangial cells is mediated by prostaglandins with subsequent stimulation of adenylate cyclase activity.