bluuebunny/crossref_metadata_2025 huggingface dataset:
A mediator derived from arginine mediates inhibitory junction potentials and relaxations in lower esophageal sphincter: an independent role for vasoactive intestinal peptide
Authors: Jury Jennifer , Ahmedzadeh Nahid , Daniel E. E.
Published: April 2011

This study provides mechanical and electrophysiological evidence to show that a metabolite of arginine, not vasoactive intestinal peptide (VIP), is the putative nonadrenergic noncholinergic (NANC) inhibitory mediator in canine and opossum lower esophageal sphincters (LES). Relaxations of spontaneous active tension by electrical field stimulation (FS) at parameters that induced tetrodotoxin (TTX)-sensitive responses were abolished by L-Nω-arginine methyl ester (L-NAME) at 10−4 M and restored by L-arginine (10−3 M) but not D-arginine (10−3 M). TTX-insensitive relaxations to 5-ms pulses were unaffected by L-NAME, L- or D-arginine. VIP (10−6 M) caused maximum relaxations of basal tension in both the opossum and canine LES. However these relaxations, unlike those from FS were unaffected by L-NAME. Methylene blue (5 × 10−5 M) increased basal tension of the LES in each species, and did not inhibit the relaxation to FS or VIP, but often increased the amplitudes of these responses due to the increase in basal tension. In parallel experiments NANC inhibition of body circular muscle from opossum esophagus was abolished by methylene blue. Electrophysiological studies using micro-electrodes revealed that NANC inhibition was associated with inhibitory junction potentials in the canine LES. These were inhibited by L-NAME and restored by L-arginine but not D-arginine. In contrast, 10−6 M VIP in canine LES did not induce any change in membrane potential during a 20-min superfusion. Sodium nitroprusside also hyperpolarized sphincteric muscle and its effects were not affected by L-NAME. We conclude that esophageal sphincter NANC nerve initiation of inhibitory junction potentials or relaxations depend on a mediator produced from L-arginine, like those of esophageal body circular muscle. This mediator resembles sodium nitroprusside in its actions. However, either the NANC mediator or the response to it differs in body circular muscle and LES since only the former was clearly sensitive to methylene blue. Moreover, TTX-insensitive relaxations to long pulse durations were not mediated by nitric oxide-related mechanisms because L-NAME had no effect on them.Key words: nitric oxide, vasoactive intestinal peptide, sphincter relaxation, inhibitory junction potentials.
Increased resting metabolic rate and lipid oxidation in exercise-trained individuals: evidence for a role of β-adrenergic stimulation
Authors: Tremblay Angelo , Coveney Serge , Després Jean-Pierre , Nadeau André , Prud'homme Denis
Published: April 2011

This study investigated the contribution of β-adrenergic stimulation to the increase in resting metabolic rate (RMR) and lipid oxidation observed in exercise-trained individuals. Nine trained and eight sedentary men were subjected to two testing sessions, during which these variables were measured before and for 3 h after the oral administration of propranolol or placebo. As expected, RMR and lipid oxidation were significantly higher in the trained subjects before the administration of propranolol and throughout the placebo test in comparison with sedentary controls. A significant decrease in RMR and lipid oxidation was induced by propranolol in the trained subjects, whereas no change was observed in the untrained group, and this effect of propranolol was sufficient to abolish the difference between the two groups at baseline and under the placebo condition. Propranolol also induced a significant reduction in heart rate and systolic blood pressure, but the response was comparable in the two groups. In conclusion, the results of this study show that β-adrenergic stimulation is involved in the increase in RMR and lipid oxidation observed in highly trained individuals. Moreover, the absence of a training–propranolol interaction effect on heart rate and systolic blood pressure suggests the existence of some dissociation between the metabolic and cardiovascular effects of prolonged exercise training.Key words: energy expenditure, propranolol, physical activity, catecholamines, heart rate, blood pressure.
Acute administration of bromocriptine abolishes the hyperprolactinemic response induced by submaximal exercise in man
Authors: Boisvert P. , Brisson G. R. , Péronnet F. , Gareau R.
Published: April 2011

The effective control of hypophysial prolactin (PRL) secretion with a pharmacological agent is a prerequisite for the investigation of the role of hyperprolactinemia observed during exercise. Using bromocriptine, a potent inhibitor of PRL secretion, this study established the proper experimental conditions whereby any significant increase in plasma PRL level can be prevented and basal circulating levels maintained during physical exercise. On three occasions at weekly intervals, 15 male adults, separated into two groups, exercised on an ergocycle (40 min at 65% [Formula: see text]) either 1 or 3 h after ingesting either placebo or 1.25 or 2.50 mg of bromocriptine mesylate (Parlodel; Sandoz Canada Inc., Dorval, Qué.). Under all conditions, the plasma PRL elevation observed during exercise after placebo was prevented by the administration of bromocriptine. Resting plasma PRL levels were maintained when exercise was performed 1 h after bromocriptine ingestion, but were significantly reduced when exercise was performed 3 h after administration of either bromocriptine dosages. Considering the primary and secondary effects observed, 1.25 mg of bromocriptine administered 1 h before exercise provides suitable experimental conditions to investigate the role of the increase in plasma PRL during physical exercise.Key words: prolactin, bromocriptine, exercise, heart rate, blood pressure.
Regulation of the M current: transduction mechanism and role in ganglionic transmission
Authors: Smith Peter A. , Chen Hsinyo , Kurenny Dmitry E. , Selyanko Alexander A. , Zidichouski Jeffrey A.
Published: April 2011

Slow excitatory postsynaptic potentials in sympathetic ganglia often involve suppression of a voltage-dependent potassium current termed the M current. This current is suppressed by the muscarinic action of acetylcholine, by peptides such as luteinizing hormone releasing hormone, and sometimes by α-adrenoceptor agonists. Activation of β-adrenoceptors sometimes produces weak potentiation. The voltage dependence of the M current is such that its suppression increases the excitability of ganglionic neurones. Since this sometimes leads to spontaneous discharge, activation of the slow excitatory postsynaptic potential mechanism (or modulation of M current) within a sympathetic ganglion produces effects that manifest in the autonomic outflow to the target organ. In frogs, M currents are present in the neurones of both paravertebral sympathetic ganglia and cardiac parasympathetic ganglia. Since the M current is suppressed by adrenaline in the parasympathetic ganglia and these ganglia often receive adrenergic fibres from sympathetic ganglia, this might reflect an important means of interaction between the two branches of the autonomic system. At the cellular level, M-current suppression is little affected by drugs that interfere with membrane phosphorylation–dephosphorylation processes. This observation is discussed in relationship to the current understanding of the transduction mechanism for agonist-induced M-current suppression.Key words: autonomic nerve, K+ channel, G protein, muscarinic mechanism, adrenergic mechanism.
Cellular metabolism regulating H and M currents in bullfrog sympathetic ganglia
Authors: Akasu Takashi , Tokimasa Takayuki
Published: April 2011

Much evidence has accumulated suggesting that neurons in autonomic and dorsal root ganglia possess voltage-dependent currents that link with transmitter receptors through intracellular signal transduction systems. The M current (IM), a voltage-dependent potassium current, was activated at potentials more positive than −65 mV, while the H current (IH), a voltage-dependent nonselective cationic current, was activated at potentials more negative than −50 mV. The hydrolyzable form of ATP was required to activate IM and IH. Intracellular application of calmodulin enhanced the amplitude of IM in a calcium-dependent manner. IM was reduced by W-7, a calmodulin antagonist, and by ML-9, an inhibitor of calmodulin-dependent protein kinase. IH was enhanced by intracellular loading with cyclic adenosine monophosphate (AMP) or bath application of forskolin and membrane-permeable cyclic AMP analogues. Isobutylmethylxanthine also increased the maximal conductance of IH. IH was depressed by H-8 but not by phorbol ester. It is concluded that the resting membrane conductance of these ganglion cells can be regulated by basal activities of calmodulin-dependent protein kinase and A kinase.Key words: peripheral neurons, M current, H current, calmodulin, adenylate cyclase.
Energy metabolism at the cellular level of the CNS
Authors: Hertz Leif , Peng Liang
Published: April 2011

Evidence is accumulating that interactions between different cell types are of paramount importance for CNS function, for example, release of the excitatory transmitter glutamate from neurons and its preferential uptake into astrocytes. Some information is also available about energy metabolism in different cell types, or more often in models of different cell types (e.g., synaptosomes, cultured neurons, cultured astrocytes). In this review an attempt is made not only to correlate information obtained with different cell models but also to integrate this information with in vivo data, with histochemical observations, and with results obtained using brain slices. The emerging patterns indicate that neurons, synaptosomes, and astrocytes are all capable of complete glycolysis and oxidation of glucose. Elevated extracellular concentrations of potassium, known to occur in vivo, enhance energy metabolism by mechanisms that differ between neurons and astrocytes and to a large extent serve to reaccumulate extracellular potassium ions into adjacent cells. Monoaminergic agonists also stimulate energy metabolism, but mainly or exclusively in astrocytes. Profound differences are found between the effects of excess potassium and of aminergic transmitters, suggesting that high potassium concentrations enhance neuronal–astrocytic interactions, whereas the monoamines may tend to dissociate metabolic events in neurons and in astrocytes.Key words: astrocytes, neurons, synaptosomes, potassium, noradrenaline.
Coupling among changes in energy metabolism, acid-base homeostasis, and ion fluxes in ischemia
Authors: Katsura Ken-ichiro , Ekholm Anders , Siesjö Bo K.
Published: April 2011

This article attempts correlating changes in cellular energy metabolism, acid-base alterations, and ion homeostasis in ischemia and other conditions. It is emphasized that loss of ion homeostasis, with thermodynamically downhill fluxes of K+, Ca2+, Na+, Cl−, and H+, occurs because energy production fails and (or) ion conductances are increased. In ischemia, energy failure is the leading event but, in hypoglycemia, activation of ion conductances is what precipitates energy failure. The initial event is a rise in K+e, at least in part caused by activation of K+ conductances modulated by Ca2+ or ATP/ADP ratio. Secondarily, this leads to release of excitatory amino acids and massive activation of unspecific cation (and anion) conductances. Production of H+ occurs in states characterized by energy failure (ischemia and hypoxia) or by alkalosis (hypocapnia and ammonia accumulation). H+ equilibrates between intra- and extra-cellular fluid via nonionic diffusion of lactic acid, and transmembrane fluxes of H+ or HCO3− via ion channels. Since the relationship between lactate and either pHi or pHe is linear, there are no abrupt pH shifts explaining why hyperglycemia worsens ischemic damage. The reversible insults seem to induce a sustained stimulation of H+ extrusion from cells giving rise to intracellular alkalosis and extracellular acidosis.Key words: energy metabolism, acid-base homeostasis, ion fluxes, ischemia.
Potassium and Sodium Transport and pH Regulation
Authors: Clausen Torben
Published: April 2011

The excitatory and metabolic events in nervous tissue lead to localized increases in extracellular potassium (K+) and intracellular hydrogen (H+) and calcium (Ca2+) ion concentrations. Even more pronounced increases are seen under pathological conditions and may interfere with the maintenance of cellular function and structure. Most presentations on the second day focussed on these processes and the mechanisms for the clearance of K+, H+, and Ca2+ from intra- or extra-cellular compartments. The essential role of glial cells was a returning theme. Extracellular K+ is transported into cells by the Na–K pump and by two other processes, Na–K–Cl2 cotransport and spatial buffering, which both depend on the operation of the Na–K pump. The clearance of H+ from the cytoplasm and into the extracellular space is mediated by Na+ gradient dependent processes, Na+/H+ antiport, Cl−/HCO3− exchange, and Na+–HCO3− cotransport. Also the clearance of cytoplasmic Ca2+ is to a large extent mediated by a Na+ gradient dependent process, the Na+/Ca2+ antiport. There is a wide divergence between the rates of Na–K pump mediated K+ influx measured in various cultures of glial and neuronal cells. There is a considerable need for systematic comparison between the functional capacity and the concentration of Na–K pumps in cell cultures and intact nervous tissue. It has not yet been ascertained whether K+ transport as measured in cultured astrocytes is representative for K+ transport in the in situ functioning astrocyte. In astrocytes, glutamate was shown to elicit a rapid intercellular propagation of a rise in cytoplasmic Ca2+. In neurons, the elevation of cytoplasmic Ca2+ during exposure to hypoxia, ischemia, or excitatory amino acids was described and related to cell damage. Cytoplasmic Ca2+ may be cleared by Na+/Ca2+ antiport as well as by a Ca2+-activated ATPase in the plasma membrane. The total concentration of this enzyme has not been quantified, and little is known about its energy requirements.Key words: potassium, glial cells, Na–K pump, calcium, sodium.
Intracellular pH in rat brain in vivo and in brain slices
Authors: LaManna Joseph C. , Griffith J. Keven , Cordisco Boris R. , Lin Chii-Wann , Lust W. David
Published: April 2011

Intracellular pH can be measured quantitatively in rat brain in vivo and in vitro using spectrophotometric detection of the vital dye neutral red. This method preserves spatial information and is compatible with microhistochemistry. The intracellular pH indicated by this method is in close agreement with that indicated by 31P-NMR spectroscopy. During ischemia, intracellular acidification is correlated with tissue lactate accumulation. The spatial distribution of pH values becomes more heterogeneous as the tissue becomes more acidic. Resuscitation from total cerebral ischemia produced by cardiac arrest results in rapid intracellular realkalinization. This realkalinization is at least partially inhibited by amiloride pretreatment. Some neuronal populations, especially in the hippocampal CA1 and CA4 regions, may become more acidic during ischemia and realkalinize more slowly after reperfusion than other tissue regions. The intracellular pH of hippocampal brain slice preparations is more alkaline than expected from in vivo studies. The intracellular pH of the brain slice can be acidified to near neutrality by specific inhibitors of the sodium/hydrogen ion exchanger.Key words: hippocampal brain slice, intracellular pH, neutral red, cardiac arrest and resuscitation, sodium/hydrogen ion exchanger.
Cell Swelling and Volume Regulation
Authors: Hoffmann Else K.
Published: April 2011

The extracellular space in the brain is typically 20% of the tissue volume and is reduced to at least half its size under conditions of neural insult. Whether there is a minimum size to the extracellular space was discussed. A general model for cell volume regulation was presented, followed by a discussion on how many of the generally involved mechanisms are identified in neural cells and (or) in astrocytes. There seems to be clear evidence suggesting that parallel K+ and Cl− channels mediate regulatory volume decrease in primary cultures of astrocytes, and a stretch-activated cation channel has been reported. The role of the different channels was discussed. A taurine leak pathway is clearly activated after cell swelling both in astrocytes and in neurones. The relations between the effect of glutamate and cell swelling were discussed. Discussion on the clearance of potassium from the extracellular space was continued. Neither the spatial buffering mechanism nor the role of the Na+/K+ pump was discussed here, but additional possibilities for K+ removal were discussed. At a high extracellular K+ concentration there is a possibility of channel-mediated KCl uptake by the glia cells, and a Na–K–2Cl cotransport system is present in astrocytes and seems to play a role at relatively low extracellular K+ concentrations (6–20 mM). The cotransport system is likely to be regulated, but little is known about its regulation in glia cells.Key words: volume regulation, astrocytes, taurine, K+ channels, Cl− channels.
Methods for determination of cell volume in tissue culture
Authors: Kimelberg H. K. , O'Connor E. R. , Sankar P. , Keese C.
Published: April 2011

In this paper we present an overview of methods for determining cell volume in both suspension and monolayer cultures. Data from the use of selected methods such as the Coulter counter system for suspension cultures and radiolabelled intracellular markers for substratum-attached, monolayer cultures are presented. The advantages, limitations, and conditions under which the different methods can be used are discussed. It is pointed out that there is a need for more direct physical methods for measuring dynamic changes in the cell volume of monolayer cultures without removing the cells from the substratum. Data from a method applicable to such cultures that measures extracellular impedance are presented.Key words: cell volume, monolayer cultures, extracellular impedance, radiolabelled intracellular markers, primary astrocyte cultures.
Mechanisms of glial swelling induced by glutamate
Authors: Schneider Gerd-Helge , Baethmann Alexander , Kempski Oliver
Published: April 2011

The mechanisms of glutamate-induced glial swelling have been studied using an in vitro model that permits detection of cell volume changes with high accuracy. The model allows for a close control of the extracellular environment to study in isolation the effect of defined extracellular alterations occurring in brain under pathophysiologic conditions. Glutamate was applied in concentrations between 50 μM and 10 mM to either C6 glioma cells or astrocytes from primary culture. Glutamate uptake was assessed by HPLC measurements of amino acids in the extracellular medium. Glutamate at all concentrations tested caused glial swelling, which, however, was moderate, with maximal average volume increases between 5.0 ± 1.92 and 18.38 ± 1.6% of control at 50 μM and 5 mM glutamate, respectively. Swelling was concentration dependent and correlated with glutamate uptake. After removal of all extracellular glutamate by glial uptake, cell volume spontaneously normalized. Pretreatment of the cells for 90 min with ouabain (1 mM) to abolish the extracellular/intracellular Na+ gradient, prevented glutamate-induced swelling. It is concluded that while glial cells readily accumulate glutamate from the extracellular environment to protect neurons from excitotoxic effects, swelling results from the increase of intracellular osmotic activity due to the uptake of Na+ and glutamate.Key words: glia, glutamate uptake, cell volume, ouabain.
Correlations between energy metabolism, ion transport, and water content in astrocytes
Authors: Olson James E. , Evers Julie A.
Published: April 2011

Energy metabolism, ion transport, and water content are interrelated in mechanisms of homeostasis of the brain intracellular and extracellular environment. The simplest model of cell homeostasis, the pump–leak hypothesis, incorporates basic relationships between these variables. Although this model accurately calculates steady-state cell volumes, ion concentrations, and metabolic rates, it fails to predict dynamic changes in these properties during elevated extracellular potassium, metabolic inhibition, and osmotic swelling. We have investigated relationships between ions, energy metabolism, and water content in cerebral astrocytes cultured from the neonatal rat. These cells swell more in hypoosmotic phosphate-buffered saline (PBS) containing NaCl than in hypoosmotic PBS with all NaCl replaced equiosmotically by sucrose. Unidirectional Na+ influx also is greater in cells suspended in hypoosmotic, compared with isoosmotic PBS. These data suggest that astrocytes possess a cell volume dependent mechanism of Na+ accumulation. The influx of Na+ during swelling may be coupled to metabolism via Na–K ATPase and may contribute to the sustained swelling of astrocytes observed in hypoosmotic swelling of the brain in situ.Key words: sodium, hypoosmolality, sodium–potassium adenosine triphosphatase, mathematical modeling.
Involvement of second messengers and protein phosphorylation in astrocyte swelling
Authors: Bender A. S. , Neary J. T. , Norenberg M. D.
Published: April 2011

In a hypoosmotic model of astrocyte swelling, we found that Ca2+ and intracellular signals such as diacylglycerol and inositol phosphate, as well as protein phosphorylation systems, are implicated in the generation and (or) modulation of volume regulatory processes. Cyclic AMP, which also has a significant effect on astrocyte volume regulation, in addition influences some of these second messengers.Key words: astrocyte, Ca2+-dependent protein kinases, Ca2+ influx, cell volume, cyclic AMP, inositol phosphates, protein phosphorylation.
Effect of vasopressin on brain swelling at the cellular level: do astrocytes exhibit a furosernide–vasopressin-sensitive mechanism for volume regulation?
Authors: Chen Ye , McNeill J. Robert , Hajek Ivan , Hertz Leif
Published: April 2011

Two sets of new observations are reported: (i) astrocytes in primary cultures show an increased potassium-induced swelling in the presence of 1–100 × 10−12 M vasopressin, whereas no similar phenomenon is found in primary cultures of neurons, and (ii) the furosemide-sensitive cotransport system for uptake of K+, Na+, and Cl−, which is known to exist in astrocytes, is absent in neurons. On the basis of these findings and observations by other investigators on transport of ions and water in the brain in vivo, a novel mechanism is suggested, according to which all boundaries of brain parenchymal tissue (perivascular astrocytic end-feet, glia limitans, and ependyma) in the absence of vasopressin are capable of performing a net uptake of K+, Na+, and Cl− without uptake of water, and that the resulting hyperosmolarity in the presence of vasopressin leads to water uptake (cell swelling), which causes a reduction in the amount of water in the interstitial fluid and thus an increase in extracellular concentrations of ions.Key words: astrocytes, furosernide, neurons, vasopressin, volume, water permeability.
Effect of erythromycin on D-galactose absorption and sucrase activity in rabbit jejunum
Authors: Navarro H. , Arruebo M. P. , Alcalde A. I. , Sorribas V.
Published: April 2011

Erythromycin, an antibiotic used in the treatment of infectious diseases, produces gastrointestinal side effects such as diarrhea. The mechanisms by which erythromycin produces these effects are not known. However, erythromycin has been shown to increase gastrointestinal motor activity and to inhibit intestinal neutral amino acid absorption. Both effects could contribute to the gastrointestinal side effects observed. Because the intestinal systems of amino acid and sugar transport present similar characteristics, the aim of the present work was to determine whether erythromycin also alters D-galactose absorption and sucrase activity in rabbit jejunum. The results show that erythromycin diminishes intestinal D-galactose absorption. This effect seems to be due to an action mainly located on the Na+-dependent sugar transport of the mucosal border of the intestinal epithelium. Erythromycin also inhibits the Na+–K+ ATPase activity of the enterocyte, which might explain the inhibition of the D-galactose Na+-dependent transport. However, a direct action of the erythromycin molecule on the Na+-dependent carrier cannot be excluded. Erythromycin did not alter sucrase activity.Key words: erythromycin, rabbit jejunum, D-galactose transport, sucrase activity.
Glucose-lowering effects of a new organic vanadium complex, bis(maltolato)oxovanadium(IV)
Authors: Yuen Violet G. , Orvig Chris , McNeill John H.
Published: April 2011

Inorganic vanadium has been shown, both in vivo and in vitro, to have insulin-mimetic properties. A new organic vanadium complex, bis(maltolato)oxovanadium(IV) (BMOV), was developed to increase the absorption of vanadium from the gastrointestinal tract, thereby reducing the dose of vanadium necessary to produce glucose-lowering effects. BMOV was administered in the drinking water for 25 weeks to control and streptozotocin-induced diabetic, male Wistar rats. BMOV treatment produced a stable euglycemic state in 70% of diabetic treated animals. The other 30% of the diabetic treated animals demonstrated fluctuations in glucose control over the entire study period. The initial effective dose of BMOV was 0.45 mmol/kg, which decreased to an effective maintenance dose of 0.18 mmol/kg, significantly lower than the dose of inorganic vanadium salts used in previous studies. BMOV treatment did significantly reduce fluid consumption levels in control treated animals after 10 weeks of therapy; however, the food consumption for control treated animals was only intermittently lower than that for controls. Plasma cholesterol and triglyceride levels were normalized with BMOV treatment for all diabetic treated animals, without a concomitant increase in plasma insulin levels. An oral glucose tolerance test demonstrated that glucose homeostasis in control-treated animals occurred at significantly lower plasma insulin levels than in control animals. BMOV effectively produced the glucose-lowering effects at significantly lower dose than previously used for inorganic vanadium salts, without any overt signs of toxicity.Key words: bis(maltolato)oxovanadium(IV), streptozotocin-induced diabetes, diabetes treatment.
Sarcoplasmic reticulum Ca-release channel and ATP-synthesis activities are early myocardial markers of heart failure produced by rapid ventricular pacing in dogs
Authors: O'Brien Peter James , Moe Gordon W. , Nowack Linda M. , Grima Etienne A. , Armstrong Paul W.
Published: April 2011

The contraction–relaxation cycle of the heart is dependent on a cycle of ATP production and utilization and a cycle of Ca uptake and Ca release by the sarcoplasmic reticulum (SR). Heart failure (HF) is associated with abnormalities of myocardial Ca and ATP cycling, but the time course of their development is unknown. This study tested the hypothesis that, compared with ATP-utilizing and Ca-uptake activities, decreases in ATP-synthesis and Ca-release activities occurred earlier in the development of HF and persisted longer during recovery from HF. HF was induced by right ventricular pacing of dogs at 250 beats/min. Dogs were studied after 1 week of pacing (n = 8, early HF), at HF (n = 11, severe HF), and 4 weeks after cessation of pacing (n = 9) and were compared with dogs not subjected to pacing. At early HF, there were decreased activities (p < 0.05) of the SR Ca-release channel (rate constant from 199 ± 36 × 10−4 to 90 ± 16 × 10−4 s−1), mitochondrial ATP synthesis (from 11.2 ± 2.4 to 7.0 ± 2.2 international units (IU)/g), and creatine kinase (CK) from 2028 ± 266 to 1811 ± 79 IU/g). The decreased Ca-channel activity was due to a 32% decrease in maximal activity (rate constant from 249 ± 50 × 10−4 to 170 ± 29 × 10−4 s−1) and to a 2-fold increase (from 19.1 ± 12.4 to 42.0 ± 14.2%) in inhibition of maximal channel activity (p < 0.05). At severe HF, Ca-uptake (rate constant from 407 ± 41 × 10−4 to 296 ± 77 × 10−4 s−1) and ATP-utilization activities also became depressed (from 27.2 ± 3.3 to 20.3 ± 1.9 IU/g), and CK further decreased to 1321 ± 241 IU/g (p < 0.05). Four weeks after cessation of pacing, only total Ca-cycling (sum of Ca uptake and Ca release), Ca-uptake, and CK activities were significantly recovered (p < 0.05). Left ventricular ejection fraction was significantly correlated with total Ca cycling (n = 12, r = 0.68, p < 0.02), Ca-channel inhibition (n = 12, r = −0.60, p < 0.04), and basal ATPase (n = 11, r = 0.69, p < 0.02). We conclude that biochemical measurements of ATP- and Ca-cycling activities correlate with myocardial performance, and that compared with ATP-utilization and Ca-uptake activities, inhibition of ATP synthesis and Ca release occurs earlier in the development of HF and persists longer during recovery from HF.Key words: Ca-release channel, sarcoplasmic reticulum, rapid ventricular pacing, congestive heart failure, Ca ATPase pump, mitochondria.
α2-Adrenergic mediation of the effects of angiotensin II on rat renal artery in vitro
Authors: Ajikobi David O. , Cupples William A.
Published: April 2011

Angiotensin II (ANG II) is a major influence on renal blood flow, acting directly on the renal vasculature and upon other controllers. In vivo observations suggest that ANG II affects renal artery resistance, although explicit in vitro studies have produced negative results. To resolve this issue, potential interactive effects of ANG II on renal artery in vitro were tested. Renal arteries were harvested from ketamine-anesthetized Sprague–Dawley rats and perfused in vitro at constant flow. Resistance was determined from the axial pressure drop while downstream pressure was held constant at ≈80 mmHg (1 mmHg = 133.3 Pa). ANG II, per se, had only a trivial effect on arterial diameter (−5.5 ± 1.5% at 10−7 M ANG II) and failed to affect resistance at concentrations ranging from 10−11 to 10−7 M. Norepinephrine caused strong concentration-dependent constriction, increasing resistance from 0.32 ± 0.04 to 1.86 ± 0.73 mmHg∙mL−1∙min at 10−6 M and 3.27 ± 0.88 mmHg∙mL−1∙min at 10−5 M. In the presence of 10−8 M ANG II, these responses were significantly increased to 3.31 ± 1.00 and 5.02 ± 1.22 mmHg∙mL−1∙min, respectively. Similarly, in the presence of 10−6 M norepinephrine, ANG II caused significant, concentration-dependent constriction of renal artery. In a separate experiment, 10−7 M yohimbine, a relatively specific antagonist of α2-adrenergic receptors, reversed the resistance increment due to ANG II, but not that due to norepinephrine. When yohimbine was applied before norepinephrine and ANG II, it did not affect the response to norepinephrine, but again blocked potentiation of the response by ANG II. The results indicate that, as occurs in some other vascular beds, ANG II "uncovers" vascular constriction that is mediated by α2-adrenergic receptors.Key words: vascular, resistance, interaction, norepinephrine, yohimbine.
Tyrosine kinase inhibitors and the contractile action of G-protein-linked vascular agonists
Authors: Laniyonu A. A. , Saifeddine M. , Yang S.-G. , Hollenberg M. D.
Published: April 2011

In a porcine coronary artery helical strip preparation, the tyrosine kinase inhibitors genistein and tyrphostin (AG82) attenuated the contractile actions of angiotensin II, arginine vasopressin, epidermal growth factor – urogastrone, noradrenaline, and prostaglandin F2aα, under conditions where contractions due to acetylcholine and KCl were not affected. Both genistein and tyrphostin also caused a selective inhibition of angiotensin II action in rat aorta helical strips, without affecting KCl-mediated contractions. The IC50 values for the inhibition of contraction in the porcine coronary artery were in the range of 2–5 μM for genistein and 8–15 μM for tyrphostin. Comparable IC50 values were observed for the inhibitory effects of genistein on angiotensin II and prostaglandin F2α action in the rat aorta, whereas much higher tyrphostin concentrations (IC50 ≥ 40μM) were required to block angiotensin II action in this preparation. Angiotensin II caused an elevation of phosphotyrosyl protein (antiphosphotyrosine Western blot) in the porcine coronary artery, which was reversed by genistein. In addition, porcine coronary artery derived membrane and cytosolic fractions exhibited sarcoma virus related tyrosine kinase activity, which was inhibited by both genistein and tyrphostin. Our data (i) document the selective inhibition by genistein and tyrphostin of the contractile action of some, but by no means all, G-protein-linked vascular agonists in porcine and rat arterial preparations, (ii) establish the presence of sarcoma virus related tyrosine kinase activity in the porcine coronary artery, and (iii) demonstrate angiotensin II mediated increases in phosphotyrosyl protein content in porcine coronary artery tissue. These data support the hypothesis that selected G-protein-linked contractile vascular agonists may act in part via the stimulation of nonreceptor tyrosine kinases. The data also indicate the complex actions of the tyrosine kinase inhibitors, even for the same agonist acting in vascular preparations obtained from different species.Key words: epidermal growth factor, genistein, tyrosine kinase, tyrphostin, vascular contractility.
Effect of nitroprusside and endothelium-derived products on slow-twitch skeletal muscle function in vitro
Authors: Murrant C. L. , Woodley N. E. , Barclay J. K.
Published: April 2011

We tested the hypothesis that the products of endothelial cells alter the force developed by skeletal muscle. Since these products have a very short half-life and are produced in a low concentration, we developed a superfused muscle preparation in which the mouse soleus (SOL) was superfused at 10.5 mL/min with Krebs–Henseleit buffer (KH) (27 °C; pH 7.4), gassed with 95% O2 – 5% CO2. To evaluate this preparation, we compared the superfused muscles with muscles submerged in a bath. All muscles were stimulated at 50 Hz for 500 ms once every 30 s. Submerged SOL developed 275 ± 15 mN/mm2, while the superfused muscles developed 271 ± 15 mN/mm2. Both submerged and superfused SOL consistently increased rest tension to a 3-mL bolus of 25 mM caffeine and decreased developed force when exposed to a 3-mL bolus of 30 mM diprotonated phosphate (pH 6.4). We then exposed superfused SOL to 3-mL bolus injections of KH, 1 μM acetylcholine, 30 mM nitroprusside (a source of nitric oxide), and the supernatant from dishes of cultured endothelial cells from rabbit aorta challenged with acetylcholine. Nitroprusside and the supernatant significantly improved force maintenance, compared with KH and acetylcholine, respectively. Since the supernatant should contain products of endothelial cells, these products appear to have a positive effect on contractile function in slow-twitch skeletal muscle that is similar to the effect of nitric oxide.Key words: superfused slow-twitch skeletal muscle, tetanic contractions, sodium nitroprusside, caffeine, inorganic phosphate, cultured endothelial cells.
Gender differences in cardiovascular responses to the cold hand pressor test and facial cooling
Authors: Kilgour R. D. , Carvalho J.
Published: April 2011

To test the hypothesis that changes in systemic vascular resistance (SVR) contribute to the differences in arterial blood pressure responses between men and women to local cold pressor tests, nine normotensive men (25.9 ± 5.9 years old) and women (24.4 ± 5.9 years old) performed the cold hand pressor test (CPT; 6 min in 5 °C water) in the supine position. A subgroup of men (n = 5) and women (n = 5) from the CPT were exposed to 6 min of facial cooling (FC) by circulating cold water (5 °C) through a perfusion mask. Using standard auscultatory techniques, pre-experimental systolic and diastolic blood pressures were found to be significantly higher (p ≤ 0.05) in males than females. During the initial 2 min of CPT and FC, both males and females experienced similar relative increases in pressure. Thereafter, only the males maintained an elevated pressor response, whereas the females progressively declined. The gender-related trends in blood pressure can be explained by differences in SVR, with the males exhibiting significantly greater changes in SVR than females during min 4–6 in CPT. Heart rate increased (p ≤ 0.05) in both groups, with the greater rise occurring in females at each minute of CPT. Throughout FC, the changes in SVR were similar between groups, with the exception of the 6-min value being greater than baseline in men but not women. No differences in heart rate or cardiac output were observed between groups during FC. In general, the results indicate that men respond with greater and more prolonged peripheral adjustments (e.g., rise in SVR), whereas females are more like "cardiac" responders, with greater increases in heart rate and an attenuated blood pressure response to CPT.Key words: cold pressor test, facial cooling, gender, systemic vascular resistance, heart rate.
Gastric inhibitory polypeptide and glucagon-like peptide-1(7–36) amide exert similar effects on somatostatin secretion but opposite effects on gastrin secretion from the rat stomach
Authors: Jia X. , Brown J. C. , Kwok Y. N. , Pederson R. A. , McIntosh C. H. S.
Published: April 2011

Previous studies on the isolated perfused stomach have shown that gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1(7–36) amide (GLP-1(7–36) amide) stimulate release of somatostatin (somatostatin-like immunoreactivity, SLI). GIP produced a paradoxical increase in gastrin secretion, whereas GLP-1(7–36) was inhibitory. In the current study, the actions of synthetic (sp) and native (np) porcine and synthetic human (sh) GIP, G LP-1(7–36), and GLP-1(7–37) on SLI and gastrin secretion were compared using a gradient perfusion of peptide. All peptides increased SLI secretion at a threshold concentration of ~ 50 pmol/L (p < 0.05). The initial rate of increase in response to spGIP (119 ± 39 pg/min) was greater than with other forms of GIP or GLP-1. Maximal increases obtained with the two porcine peptides did not differ. Gastrin secretion was increased by concentrations of spGIP and npGIP similar to those increasing SLI secretion, but the maximal response to shGIP was lower. In contrast to GIP-induced increases, both GLP-1 (7–36) and GLP-1 (7–37) suppressed gastrin secretion. It is concluded that human and porcine GIP, GLP-1 (7–36), and GLP-1 (7–37) all stimulate SLI secretion but with different maximal effects, and GIP stimulates gastrin secretion whereas both forms of GLP-1 inhibit gastrin secretion.Key words: somatostatin, gastrin, gastric inhibitory polypeptide, glucagon-like peptide-1, gastric secretion.
The antiadrenergic effect of cyclopentyladenosine on myocardial contractility is reduced in vivo in diabetic rats
Authors: Romano Fred D. , Kopp Stephen J. , Daar June T. , Smith Cynthia A.
Published: April 2011

The aim of this study was to test the hypothesis that the antiadrenergic action of adenosine is reduced in diabetes. This was determined by evaluating the effect of experimental diabetes mellitus on the in vivo myocardial antiadrenergic action of cyclopentyladenosine, an adenosine A1- receptor agonist. Changes in heart rate and ventricular performance in response to infusion of dobutamine, a β1-adrenergic agonist, were determined in the absence and presence of cyclopentyladenosine, in anesthetized, 10- to 12-week male diabetic (60 mg/kg streptozotocin), insulin-treated diabetic and control rats. Intravenous dobutamine (16 μg/kg) increased +dP/dtmax and −dP/dtmax in control rats from 7 706 ± 553 and 5 449 ± 403 mmHg/s (1 mmHg = 133.3 Pa) to 19 170 ± 465 and 8 855 ± 317 mmHg/s, respectively. In diabetic rats dobutamine increased +dP/dtmax and −dP/dtmax from 5 733 ± 541 and 4 016 ± 426 to 15 015 ± 1 521 and 7 039 ± 809 mmHg/s, respectively. Cyclopentyladenosine significantly attenuated dobutamine-stimulated increases in +dP/dtmax and −dP/dtmax in both control and diabetic rats in a dose-dependent (0.1–3.0 μg/kg) manner. Cyclopentyladenosine potency to attenuate dobutamine-enhanced +dP/dtmax was reduced significantly (p < 0.05) in diabetic rats compared with controls (ID50, 1.07 vs. 0.59 μg/kg, respectively) with no change in efficacy. The magnitude of cyclopentyladenosine inhibition of dobutamine-enhanced −dP/dtmax was greater in control than diabetic rats (81 vs. 54%, respectively), but ID50 values were not different. Insulin treatment of diabetic rats prevented the observed changes. These data suggest that the antiadrenergic action of adenosine is compromised in diabetes and that this may contribute to the development of diabetic cardiomyopathy.Key words: adenosine, dobutamine, ventricle, left ventricular pressure, streptozotocin.
Regulation of myosin light chain kinase: kinetic mechanism, autophosphorylation, and cooperative activation by Ca2+ and calmodulin
Authors: Sobieszek Apolinary
Published: April 2011

Phosphorylation of the regulatory light chain of myosin catalyzed by myosin light-chain kinase (MLCK) is the key reaction in the regulation of actin–myosin interaction in smooth muscle. It is shown that this reaction is of an ordered type, whereby kinase first binds ATP and then the light chain, and following phosphate transfer, the phosphorylated light chain is released before ADP. The MLCK also phosphorylates itself, and this intramolecular autophosphorylation is Ca2+ and calmodulin (CaM) dependent. It has, however, no pronounced effect on the kinase activity or on its affinity for Ca2+ and CaM. With the aim of understanding the cooperativity of MLCK activation, the activity of the kinase was systematically measured as a function of different ligands involved. In these measurements the isolated light chain and intact filamentous myosin, as well as native actomyosin, were used as substrates. The activation of the kinase by Ca2+ was positively cooperative but only at relatively low CaM levels. The activation by CaM (at saturating Ca2+ levels) was also cooperative, even though noncooperative activation would be expected from the established 1:1 binding stoichiometry between CaM and the kinase. This cooperativity was shown to result from time-dependent changes in the MLCK that take place during incubation with Ca2+ and CaM before addition of ATP in phosphorylation assays. As a result, activity of the kinase as a function of its concentration at constant CaM was biphasic: there was optimum activity at a ratio of 1:1 CaM to kinase and almost complete inhibition of the activity at a three- to six-fold excess of the kinase over CaM. The modification required 10–15 min preincubation (with Ca2+ and CaM) and could be explained by a dimerization of the kinase, demonstrated by the use of a zero-length cross-linker.Key words: kinetic mechanism, autophosphorylation, calcium and calmodulin activation, cooperativity, myosin light chain kinase, smooth muscle.
Is phosphorylation the main physiological action of myosin light chain kinase?
Authors: Ebashi Setsuro , Kuwayama Hideto
Published: April 2011

The 155-kDa component of bovine stomach, which exhibits a strong actomyosin (AM) activating activity and a relatively weak myosin light chain kinase (MLCK) activity, has a strong affinity for the actin filament and the actin-binding site is confined to an 80 amino acid residue on its N-terminal side. This affinity may play a crucial role in AM activation. Some reagents preferentially abolish either the AM-activating effect or MLCK activity. In conclusion, MLCK of the 155-kDa component does not play a fundamental role in activating the AM system as far as the in vitro system is concerned. The possible mechanism of AM activation by the component is discussed.Key words: myosin light chain kinase, phosphorylation of myosin light chain, leiotonin, wortmannin, beryllium sulfate.
Regulation of vascular smooth muscle contraction: myosin light chain phosphorylation dependent and independent pathways
Authors: Zhang Yawen , Moreland Suzanne , Moreland Robert S.
Published: April 2011

Ca2+-dependent myosin light chain (MLC) phosphorylation is an important step in the initiation of smooth muscle contraction. However, MLC phosphorylation alone cannot account for all aspects of contractile regulation, suggesting the involvement of other elements. In this article we present evidence obtained from Triton X-100 detergent skinned and intact tissue which demonstrates that vascular smooth muscle contraction can be initiated by a Ca2+-dependent mechanism that does not require prior MLC phosphorylation. We show that Ca2+ can initiate contractions supported by cytidine triphosphate (CTP) and that these contractions are inhibited by calmodulin antagonists, suggesting a Ca2+–calmodulin dependence of force distinct from that for MLC phosphorylation. Evidence is presented to demonstrate that carotid medial fibers contain a mitogen-activated protein (MAP) kinase which is activated by Ca2+ and may catalyze caldesmon phosphorylation. Based in part on our results and those of other investigators, we propose that direct Ca2+–calmodulin binding to caldesmon or phosphorylation of caldesmon by a Ca2+-dependent MAP kinase disinhibits caldesmon. Disinhibition of caldesmon allows an inherent basal level of actin-activated myosin ATPase activity to be expressed. The result is the slow development of force.Key words: mitogen-activated protein kinase, caldesmon, Triton X-100, detergent-skinned fibers, cytidine triphosphate, calmodulin.
Caidesmon and calponin phosphorylation in regulation of smooth muscle contraction
Authors: Gerthoffer William T. , Pohl Jennifer
Published: April 2011

Recent studies of the smooth muscle contractile system indicate that Ca2+-dependent phosphorylation of the 20-kDa myosin light chains, modulation of phosphoprotein phosphatases, and phosphorylation of thin-filament proteins are all potential features of contractile system regulation. The thin-filament proteins caidesmon and calponin are known to inhibit actomyosin ATPase in vitro and actin sliding velocity in the in vitro motility assay. Inhibition of actomyosin ATPase is relieved by phosphorylation of caldesmon or calponin. The notion that caldesmon and calponin phosphorylation – dephosphorylation is important in the living smooth muscle cell was tested using canine tracheal smooth muscle strips labeled with 32P. We found that both caldesmon and calponin phosphorylation increased in response to stimulation with carbachol. Carbachol induced a biphasic increase in [Ca2+]i in canine tracheal smooth muscle, an early transient increase in myosin phosphorylation, which decayed to 0.4 mol Pi/mol light chain, and a rapid transient increase in tissue shortening velocity. Relative changes in caidesmon phosphorylation correlate best with force development and the [Ca2+]i transient, both of which follow a similar time course. Calponin phosphorylation appears to be a rapid transient event more similar to the transient increase in unloaded shortening velocity. Our results are consistent with a potential role for both caldesmon and calponin phosphorylation in regulating smooth muscle contraction.Key words: calcium, caldesmon, calponin, colon, myosin, phosphorylation, smooth muscle, trachea.