bluuebunny/crossref_metadata_2025 huggingface dataset:
L-641,953 (R-8-fluoro-dibenzo[b, f]thiepin-3-carboxylic acid-5-oxide): a novel thromboxane–prostaglandin endoperoxide antagonist
Authors: Hall R. A. , Rokach J. R. , Bélanger P. , Bianchi L. , Ethier D. , Ford-Hutchinson A. W. , Girard Y. , Hamel P. , Hamel R. , Lord A. , Yusko P.
Published: April 2011

The effects of L-641,953 (R-8-fluoro-dibenzo[b, f)thiepin-3-carboxylic acid-5-oxide) have been studied on pulmonary and other smooth muscle preparations in vitro and in vivo. When studied in vitro on guinea-pig tracheal chains, L-641,933 produced significant shifts in the dose–response curves to the prostaglandin endoperoxide analogues, U-44069 (pA2 7.06) and U-46619 (pA2 7.14), and prostaglandin (PG) F2α (pA2 6.33) had minimal activity against contractions induced by histamine (pA2 4.38), 5-hydroxytryptamine (pA2 4.63), and acetylcholine (pA2 4.56) and slightly enhanced relaxation induced by PGE2. When tested on the guinea-pig gall bladder strip in vitro, L-641,953 antagonized contractions induced by U-44069 (pA2 7.03) but was less active against those induced by PGF2α (pA2 6.03), PGE1 (pA2 5.62), and histamine (pA2 4.84). When tested in vitro on the guinea-pig pulmonary artery, L-651-953 significantly antagonized contractions induced by U-44069 (pA2 7.04), U-46619 (pA2 7.14), and PGF2α (pA2 7.16) but was less effective against contractions induced by histamine (pA2 4.19). Schild analysis indicated that L-641,953 was fully competitive against contractions of either the guinea-pig tracheal chain induced by U-46619 or the guinea-pig pulmonary artery induced by U-44069 and U-46619. When tested on human platelets in vitro L-641,953 inhibited aggregation induced by U-44069 (IC50 1.3 × 10−6 M) but not ADP. In vivo L-641,953 administered i.v. inhibited increases in pulmonary resistance induced by U-44069 (ED50 0.026 mg/kg) but not histamine in the guinea pig and U-44069 (ED50 0.15 mg/kg) but not histamine or PGF2α in the dog. When L-641,953 was administered by the intraduodenal route to dogs (3 mg/kg) significant inhibition of bronchoconstriction induced by U-44069 or arachidonic acid was observed with a duration of action [Formula: see text]. It is concluded that L-641,953 is a novel, relatively selective, and orally active antagonist of the thromboxane–prostaglandin endoperoxide receptor.
Phlorizin increases the permeability of intestinal mucosal membrane to sodium
Authors: Dinda P. K. , Beck I. T.
Published: April 2011

We reported previously that when jejunal transmural glucose transport was inhibited by phlorizin the ratio of Na:giucose transport increased from 2.0:1 (in controls) to 3.3:1. To elucidate the mechanism of this increased ratio of Na:glucose transport, in the present study we have investigated the effect of phlorizin on Na uptake by brush border membrane vesicles and by everted sacs of hamster jejunum. In experiments on membrane vesicles the following observations were made. The time course of Na uptake showed that the control vesicles were in complete equilibrium with a Na-containing (100 mM) medium between 30 and 90 min incubation. In these periods of incubation, the vesicles incubated with phlorizin presumably also equilibrated with the medium, but lost their intravesicular Na during Millipore filtration and washing, and consequently the residual Na content was lower than that of controls. This effect of phlorizin was concentration dependent, and appeared to be unrelated to Na-coupled glucose transport, because it was also observed in the absence of glucose. This loss of Na during Millipore filtration and washing was also observed (i) when vesicles were equilibrated in a Na-containing solution in the absence of phlorizin and then exposed to a similar solution containing phlorizin, or (ii) when vesicles were equilibrated in a Na-containing solution in the presence of phlorizin and then washed repeatedly following Millipore filtration. Preincubation of vesicles for 10 min in a Na- and glucose-free solution containing phlorizin followed by incubation for 30–90 s in solutions containing 1 mM glucose and various concentrations of Na (from 10 to 100 mM) caused an increase in Na uptake from all concentrations of Na. After similar preincubation, when jejunal everted sacs were incubated for 15 s in a Na- and glucose-containing medium, Na uptake by the sacs increased. These findings suggest that phlorizin causes an increase in permeability of mucosal membrane of the enterocyte to Na. This may cause a rapid dissipation of Na gradient and an increase in the ratio of Na:glucose transport. The dissipation of Na gradient may be an additional mechanism for phlorizin-induced inhibition of intestinal sugar transport.
Modification of sodium channel currents by lanthanum and lanthanide ions in human heart cells
Authors: Bustamante J. Omar
Published: April 2011

I examined the effects of 100 μM extracellular lanthanum and lanthanide ions on the fast transmembrane sodium channel currents of human heart cell segments. The experiments were conducted under control of the transmembrane electrical and chemical gradients. Lanthanum and lanthanide ion exposure decreased the amplitude and increased the inactivation time constant of the sodium current. Only a transient increase occurred for the activation time constant of the sodium current. The dependence of peak sodium current on excitatory and holding potentials (steady-state activation and inactivation curves, respectively) was transiently shifted to less negative potentials during the first 3 min of exposure, as if these cations were momentarily neutralizing the effective negative charges at the extracellular side of the membrane. The curves then returned to their original position and only the inactivation curves continued shifting progressively towards a limit at more negative membrane potentials. Membrane capacitance was always reduced and this may explain these late effects in terms of changes in membrane dielectric properties and free and bound charges, in addition to traditional screening and binding concepts. These effects were related to the electronic structure of these ions.
Excitation–contraction coupling in myocardium: implications of calcium release and Na+–Ca2+ exchange
Authors: Keurs Henk E. D. J. ter , Schouten Vincent J. A. , Bucx Jeroen J. , Mulder Barbara M. , Tombe Peter P. de
Published: April 2011

In this paper, we present evidence in support of the hypothesis that electrogenic Na+–Ca2+ exchange is responsible for three phenomena in rat cardiac muscle: (i) the slow repolarization phase of the action potential, (ii) the time course of the mechanical recovery process, and (iii) the development of triggered arrhythmias. It was shown that the duration of the slow phase of repolarization of the action potential varies in proportion to the Na+ concentration gradient and inversely with the Ca2+ concentration gradient over the cell membrane. This suggested that Na+–Ca2+ exchange can generate a current of sufficient magnitude to maintain the membrane depolarized at a level of −60 mV. The mechanical restitution process of rat cardiac trabeculae was shown to exhibit three phase. The first phase, α, probably reflects rapid transport of calcium in the sarcoplasmic reticulum from the uptake sites to the release sites. After the initial increase of force during α, force rises further during phase β and then declines during phase γ. During all phases, force increases with the extracellular calcium concentration. β is accelerated by preceding extrasystoles, while an increase of the heart rate causes force to increase at approximately the same rate but to a higher level during phase β. These observations are compatible with a model in which the sarcoplasmic reticulum sequesters calcium from the cytosol, while the membrane of the sarcoplasmic reticulum is assumed to exhibit also a small leak of calcium into the cytosol. Net influx of calcium into sarcoplasmic reticulum during phase β diminishes with time after the heart beat, while the cytosolic calcium concentration gradually decreases as a result of the concerted activities of the Na+–K+ pump and Na+–Ca2+ exchanger. Cytosolic calcium decreases in 1.5 min after the last contraction sufficiently to cause a net calcium loss from the sarcoplasmic reticulum during the ensuing phase γ. In damaged trabeculae we observed triggered arrhythmias that were always preceded by propagating spontaneous contractions. Propagation of spontaneous contractions was consistent with spontaneous calcium release in the region of damage of the trabeculae as a result of a calcium overload of the sarcoplasmic reticulum. Calcium release in the damaged area causes calcium-induced calcium release in adjacent sites as a result of diffusion of calcium. Propagation velocity of the spontaneous contraction was consistent with this model. The occurrence of arrythmias was consistent with the hypothesis that the release of calcium during this process leads to a depolarization as a result of electrogenic Na+–Ca2+ exchange. The triggered action potential adds to the calcium load of the cells and thereby causes another spontaneous calcium release to repeat the cycle.
The pH dependence of the contractile response of fatigued skeletal muscle
Authors: Mainwood G. W. , Renaud J. M. , Mason M. J.
Published: April 2011

Following a period of intense repetitive stimulation (e.g., brief tetanic stimuli every second for 3 min), muscle isometric tension development is reduced by about 80%. This suppression is reversible at a high external pH (8.0) with a half time of 15–20 min, but if the external pH is low (6.4) or the buffer concentration is low, recovery is prevented. Inhibition of recovery is associated with a slowed rate of lactate loss, which may suggest that intracellular lactacidosis is the cause of the inhibition. Alternatively, a low external pH may affect recovery from fatigue quite independently of its effect on lactate efflux. The possibility that surface membrane properties are changed by fatigue in a pH-dependent fashion was examined by measuring the cable properties and action potentials of fatigued fibres at different external pH values. A low external pH during recovery from fatigue was shown to result in a prolonged membrane depolarization of 10–12 mV, an increased transmembrane resistance, and a prolonged action potential. At a high external pH transmembrane resistance is lowered by fatigue, the depolarization lasts only about 10–15 min, and there is a smaller effect on the action potential. While the fatigued fibre membrane does show a changed response that is dependent on external pH, it is not clear that this could be related to the suppression of contraction. Direct measurements of intracellular pH show a fall of about 0.4 to 0.5 pH units in the surface fibres following fatigue. This results from the lactic acid generated during activity. It is now clear that lactate crosses the membrane in association with protons and at least part of this flux is mediated by a specific carrier mechanism. Efflux is limited by the transmembrane pH gradient, which in turn depends on the extracellular buffer concentration in the diffusion limited space around the fibres. Intracellular lactacidosis in resting muscles can be generated by a reversal of the normal flux. Fibres can be loaded with lactate (L) by increasing the extracellular [H+][L−] product with a resultant fall in intracellular pH. Lactate loads similar to those seen in fatigued muscle simulate some but not all of the responses seen in the postfatigue state. The twitch is prolonged with a slow relaxation phase, an increased time to peak tension but with an increase in peak tension. The effects are reversible but usually result in a reduced contractile response following the washout. Tetanic tension is reduced, but the effect is small compared with that seen in fatigue. Relaxation from the tetanus is also slowed by the intracellular lactacidosis in a reversible fashion. It is concluded that intracellular lactacidosis is not the main cause of the suppressed tension found in the type of fatigue studied here but that the acidosis slows relaxation and may also prevent or slow some step in the transition from the fatigued to the normal state.
Membranes, calcium, and coupling
Authors: Eisenberg R. S.
Published: April 2011

Every eukaryotic cell contains systems linking the extracellular space and internal membrane compartments. These systems allow cells to communicate and, ultimately they allow the nervous system to control most of the cytoplasmic activity. In skeletal muscle, this system is called "excitation–contraction coupling." While much is known of the early and late steps in coupling, the critical link between the cell (i.e., here the T system) membrane and sarcoplasmic reticulum membrane is not known. Electrical coupling cannot easily account for experimental results; here we show that the Ca2+ influx is not causally related to the excitation–contraction coupling. The most likely mechanism seems to be a variant of the "remote control model" in which a voltage change and accompanying charge movement in the T membrane activates an enzyme tethered to the cytoplasmic leaflet of the T membrane but spanning part of the T – sarcoplasmic reticulum gap.
Differentiation of mechanisms for mobilization of calcium in smooth muscle
Authors: Weiss George B. , Karaki Hideaki , Murakami Kazuyasu
Published: April 2011

Techniques to dissociate different sites or stores important for Ca2+ entry or release in smooth muscle include washouts of 45Ca in cold La3+-substituted solutions, Scatchard-coordinate plots of Ca2+ uptake, substitution of Sr2+ for Ca2+, and both desaturation and rate coefficient plots. Rabbit aortic smooth muscle is particularly useful because Ca2+ mobilization components can be clearly separated. Other vascular preparations investigated (e.g., renal vessels, coronary arteries) appear to have similar components, but their relative importance varies. Respiratory smooth muscle also has similar Ca2+ mobilization components, but they are less readily dissociated by techniques employed in vascular smooth muscles. In guinea pig trachea, cold La3+ washouts do not retain cellular Ca2+ as well as in other preparations; use of other experimental approaches including the Ca2+ channel entry stimulator, CGP 28392, can demonstrate different Ca2+ uptake mechanisms for K+-stimulated and agonist-induced Ca2+ uptake. In rabbit aorta, CGP 28392 potentiates tension increases elicited with lower concentrations of added K+ but has no effect on norepinephrine-induced contraction. A general model illustrating different Ca2+ entry mechanisms present in three types of smooth muscle provides examples drawn from a spectrum of possible variations in smooth muscle specificity for Ca2+ mobilization.
Mg2+–Ca2+ interaction in contractility of vascular smooth muscle: Mg2+ versus organic calcium channel blockers on myogenic tone and agonist-induced responsiveness of blood vessels
Authors: Altura B. M. , Altura B. T. , Carella A. , Gebrewold A. , Murakawa T. , Nishio A.
Published: April 2011

Contractility of all types of invertebrate and vertebrate muscle is dependent upon the actions and interactions of two divalent cations, viz., calcium (Ca2+) and magnesium (Mg2+) ions. The data presented and reviewed herein contrast the actions of several organic Ca2+ channel blockers with the natural, physiologic (inorganic) Ca2+ antagonist, Mg2+, on microvascular and macrovascular smooth muscles. Both direct in vivo studies on microscopic arteriolar and venular smooth muscles and in vitro studies on different types of blood vessels are presented. It is clear from the studies done so far that of all Ca2+ antagonists examined, only Mg2+ has the capability to inhibit myogenic, basal, and hormonal-induced vascular tone in all types of vascular smooth muscle. Data obtained with verapamil, nimopidine, nitrendipine, and nisoldipine on the microvasculature are suggestive of the probability that a heterogeneity of Ca2+ channels, and of Ca2+ binding sites, exists in different microvascular smooth muscles; although some appear to be voltage operated and others, receptor operated, they are probably heterogeneous in composition from one vascular region to another. Mg2+ appears to act on voltage-, receptor-, and leak-operated membrane channels in vascular smooth muscle. The organic Ca2+ channel blockers do not have this uniform capability; they demonstrate a selectivity when compared with Mg2+. Mg2+ appears to be a special kind of Ca2+ channel antagonist in vascular smooth muscle. At vascular membranes it can (i) block Ca2+ entry and exit, (ii) lower peripheral and cerebral vascular resistance, (iii) relieve cerebral, coronary, and peripheral vasospasm, and (iv) lower arterial blood pressure. At micromolar concentrations (i.e., 10–100 μM), Mg2+ can cause significant vasodilatation of intact arterioles and venules in all regional vasculatures so far examined. Although Mg2+ is three to five orders of magnitude less potent than the organic Ca2+ channel blockers, it possesses unique and potentially useful Ca2+ antagonistic properties.
Pretreatment of human platelet membranes with trypsin abolishes GTP but not Na+ effects on α2-adrenoreceptor–agonist interactions
Authors: Periyasamy Sankaridrug , Somani Pitambar
Published: April 2011

The affinity of many types of membrane-bound receptors coupled negatively to adenylate cyclase is regulated by divalent and monovalent cations and by guanine nucleotides (GTP). We used α2-adrenoreceptors of human platelets as a model system to find out the effect of limited proteolysis with trypsin on the regulation of the α2-adrenoreceptor–agonist interactions by GTP and Na+. We found that partial proteolysis of the membranes with trypsin for 3 min at 35 °C reduced specific [3H]yohimbine binding to platelet membranes to 40–50% of control. The following characteristics of the receptors remaining after proteolysis were similar to those of untreated membranes: affinity for the agonist and antagonists, stereospecificity, and kinetic properties. Trypsin also did not modify the ability of the receptor's change from a high to low affinity state in the presence of Na+. These findings suggested that the capability of the receptors to recognize the ligand and their ability to undergo a conformational change in the presence of the agonist were retained despite a reduction in the total number of receptors by trypsin. However, the modulation of the receptor–agonist interactions by GTP or Mg2+ was lost in the trypsin-pretreated membranes, while the modulation by Na+ remained intact. It is suggested that the loss of GTP or Mg2+ effects on receptor–ligand interactions produced by trypsin may be due to trypsin-induced disruption of subunits (αi, βγ) interactions of Gi protein.
Cardiovascular effects of mycotoxin T-2 after topical application in rats
Authors: Magnuson B. A. , Schiefer H. B. , Hancock D. S. , Bhatti A. R.
Published: April 2011

Evidence has been mounting that trichothecenes cause cardiac lesions and cardiovascular effects in general. T-2 toxin, dissolved in dimethyl sulfoxide, was applied in doses of 0, 1.0, 2.0 mg/kg to the skin of Sprague–Dawley rats. Twenty-four hours later, the cardiac function of the animals was assessed, followed by killing and histological examination. It was found that the arterial blood pressure values were lower in the 2.0 mg/kg group, the peak intraventricular pressure was lower in both the 1.0 and 2.0 mg/kg groups, and the resting systolic and diastolic blood pressure values of the 2.0 mg/kg group were lower than the 0 and 1.0 mg/kg groups. The 1.0 and 2.0 mg/kg groups had significantly lower epinephrine-stimulated intraventricular pressure values, indicating reduced contractility. Extended Q–T intervals in electrocardiograms of the 1.0 and 2.0 mg/kg groups suggested also impaired contractility. The histological examination gave equivocal results. It is concluded that topical applications of small doses of T-2 toxin have a noticeable negative effect on cardiovascular function.
Binding of [14,15-3H]14,15-dihydroforskolin to rat liver membranes: comparison with the stimulatory effect of forskolin on adenylate cyclase
Authors: Schmidt Kurt , Baer Hans P. , Shariff Azim , Ayer William A. , Browne Lois
Published: April 2011

The binding of [14,15-3H]14,15-dihydroforskolin ([3H]DHF) to rat liver membranes has been further characterized and was compared with the stimulatory effect of forskolin on adenylate cyclase. The binding equilibrium dissociation constant (KD) for 14,15-dihydroforskolin obtained in inhibition experiments was 0.6 μM, with a maximal binding capacity (Bmax) of 114 pmol/mg protein. A similar KD value (0.5 μM) was derived from kinetics studies that revealed very rapid association and dissociation reactions. For structure–activity relationship studies several forskolin derivatives were synthesized and tested for their ability to inhibit [3H]DHF binding and increase adenylate cyclase activity. Among the tested compounds, forskolin itself was the most potent agonist (KI = 0.2 μM). Further modification of the molecule in position 7 and (or) 1 decreased or abolished its agonist properties in both adenylate cyclase and binding studies. [3H]DHF binding was not affected by several nucleotides, carbohydrates, lectins, and hormone receptor agonists including isoproterenol, glucagon, and adenosine, but the steroids 17-β-estradiol, progesterone, and testosterone showed slight inhibitory effects at unphysiologically high concentrations, [3H]DHF binding and forskolin-stimulated adenylate cyclase were sensitive to heat and N-ethylmaleimide treatment. Forskolin protected adenylate cyclase against inactivation by heat but not by N-ethylmaleimide. Preincubation of the membrane with trypsin decreased [3H]DHF binding. The results presented in this study demonstrate that the binding sites identified with [3H]DHF have a high specificity for forskolin and provide evidence that these binding sites are involved in the stimulation of adenylate cyclase by forskolin.
Dose-dependent effects of phencyclidine on hippocampal CA1 neurons
Authors: Kujtan Peter W. , Carlen Peter L.
Published: April 2011

The dose-dependent effects of phencyclidine were examined in guinea pig hippocampal slices using intracellular and extracellular recordings. Orthodromically evoked population potentials from the CA1 cell body layer were enhanced by low doses (0.2–0.4 μM) and depressed by high doses (0.01–10 mM). Medium doses of the drug (2.0–10.0 μM) showed little effect. Intracellular recordings from CA1 pyramidal neurons gave similar dose-dependent results. Low doses increased spontaneous firing rates and caused silent cells to fire. Medium doses both increased and decreased firing rates, whereas high doses depressed firing rates. Large transient depolarizing shifts were seen in some phencyclidine-treated cells at medium and high doses. Phencyclidine effects took 15–30 min to develop and were only partially reversible after a washout of up to 1 h.
Tip size of ion-exchanger based K+-selective microelectrodes. II. Effects on measurement of evoked [K+]0 transients
Authors: Ransom Bruce R. , Carlini Walter G. , Yamate Carol L.
Published: April 2011

Double-barreled ion-exchanger based K+-selective microelectrodes (K+ ISMs) of a variety of tip diameters were used to provide an experimental test of predictions that microelectrode tip induced tissue damage influences the magnitude of measured [K+]0 increases. The measured magnitude of stimulation induced [K+]0 rises in the rat optic nerve depended on the tip diameter of the measuring K+ ISM; smaller tipped K+ ISMs tended to measure larger rises of [K+]0 than bigger tipped K+ ISMs. When stimulated [K+]0 increases were simultaneously recorded with 2 K+ ISMs of different tip size, the smaller tipped K+ ISM recorded [K+]0 increases that were, on average, 14% larger than the increases measured by the bigger tipped K+ ISM. In view of these results, and those presented in the previous paper, investigators should standardize the tip sizes of the ISMs used in their experiments.
Ability of the Ca2+ -selective microelectrodes to measure fast and local Ca2+ transients in nerve cells
Authors: Levy Simon , Tillotson Douglas
Published: April 2011

The ability of the Ca2+-selective microelectrode to measure fast Ca2+ transients intracellularly is reviewed. In vitro, Ca microelectrodes can respond to Ca2+ injections with time to peaks as small as 40 ms. We present methods to improve the dynamic response of Ca microelectrodes and to make Ca-buffered solutions in high ionic strength. Examples of measurements of intracellular free Ca2+ ([Ca2+]i) transients in Aplysia neurons and in Limulus photoreceptors are shown. To show the validity of those measurements, simultaneous recordings of the Arsenazo III (AIII) absorbance and of the Ca-selective electrode potential were made in voltage-clamped neurons of the abdominal ganglion of Aplysia californica. Pressure injection of AIII to a concentration of 300–500 μM induced a rise in resting [Ca2+]i; injection of higher [AIII] led to buffering of [Ca2+]i transients. Both techniques responded to changes in resting [Ca2+]i in the same direction except that AIII showed an increase in absorbance in 0 [Ca2+]o. Voltage-clamp pulses transiently increased both the AIII absorbance and the Ca2+ electrode potential. Reducing or increasing the driving force for Ca2+ entry changed the magnitude of both signals in the right direction. Examples of spatial localization of [Ca2+]i increases and Ca2+ gradients within the cytoplasm were demonstrated using the Ca electrode. The use of optical techniques to measure local [Ca2+]i changes is briefly reviewed.
Transmembrane K+, Na+, and Cl− permeability and conductance changes in the frog sartorius fibres following ouabain and zero [K+]o treatment
Authors: Hinke J. A. M.
Published: April 2011

Changes in the K+, Na+, and Cl− permeabilities (P) and conductances (g) of the intact frog sartorius fibre membrane following ouabain or zero [K+]o treatment were calculated from intrafibre activity and whole muscle electrolyte changes. Conventional equations relating ionic fluxes to resting potential (E), ionic gradient potential, and internal and external ionic activities were used. Both treatments produced a three- to five-fold increase in PNa and gNa. In addition, ouabain produced a fivefold increase in PK (and gK) and a small decrease in PCl (and gCl), whereas zero [K+]o produced a 60% reduction in PK, a 90% reduction in gK, and a threefold increase in PCl (and gCl). When the two treatments were combined, the P and g changes were paradoxical, suggesting that the ouabain-induced increase in gK and the zero [K+]o-induced decrease in gK were occurring but in different channels (or carriers). During ouabain treatment, E reflects mainly the transmembrane K+ gradient potential; during zero [K+]o treatment, E reflects mainly the Cl− gradient potential. Despite channel (or carrier) specificity, it appears that all three ionic permeabilities are altered during the perturbations.
Direct measurement of intracellular pH in identified glial cells and neurones of the leech central nervous system
Authors: Schlue Wolf-R. , Deitmer Joachim W.
Published: April 2011

Neutral carrier pH-sensitive double-barrelled microelectrodes were used to investigate intracellular pH (pHi) in leech neuropile glial cells and in Retzius neurones. The mean pHi of the glial cells was 6.87 ± 0.13 (± SD, n = 27) in HEPES-buffered saline (pHo 7.4) and 7.18 ± 0.19 (n = 13) in solutions buffered with 2% CO2 – 11 mM[Formula: see text]. The distribution of H+ ions in both the glia and neurones was found not to be in electrochemical equilibrium. To investigate pHi regulation, the pHi was decreased by exposure to CO2 or by adding and then removing NH4Cl. Acidification by any method was followed by a recovery to normal pHi values within minutes. The pHi recovery from acidification in neuropile glial cells in HEPES-buffered saline and [Formula: see text] buffered saline was, however, blocked by removing external Na. In [Formula: see text]-free solutions the diuretic amiloride (2 mM) reduced the rate of pHi recovery. In the presence of [Formula: see text], the rate of acid efflux was stimulated; the stilbene 4-acetamido-4′-isothiocyanatostilbene-2,3′-disulfonic acid (SITS; 0.5 mM) slowed pHi recovery. In HEPES buffered and [Formula: see text] buffered solutions pHi regulation in neurones was inhibited by removing external Na. In [Formula: see text]-free solutions amiloride reduced the rate of pHi recovery considerably. In the presence of [Formula: see text], SITS or amiloride slowed but did not completely block pHi recovery. We conclude that leech glial cells and neurones have two mechanisms of pHi regulation, one being Na+–H+ exchange and the other Na+ and [Formula: see text] dependent.
pH regulation in the vertebrate central nervous system: microelectrode studies in the brain stem of the lamprey
Authors: Chesler Mitchell
Published: April 2011

Studies of intracellular pH (pHi) in nervous tissue are summarized and recent investigation of intracellular and extracellular pH (pHo) in the isolated brain stem of the lamprey is reviewed. In the lamprey, pHi regulation was studied in single reticulospinal neurons using double-barrel ion-selective microelectrodes (ISMs). In nominally [Formula: see text]-free HEPES-buffered media, acute acid loading was followed by a spontaneous recovery of pHi requiring 10–20 min and was associated with a prolonged rise in intracellular Na+. The recovery of pHi was blocked by 1–2 mM amiloride. Amiloride also caused a small rise in pHo. Substitution of external Na+ caused a slow intracellular acidification and extracellular alkalinization. Return of external Na+ reversed these effects. Transition from HEPES to [Formula: see text]-buffered media increased the rate of acid extrusion during recovery of pHi. Recovery in [Formula: see text]-buffered media was inhibited by 4,4′-diisothio-cyanostilbene-2,2′-disulfonic acid and was slowed after exposure to Cl−-free media. Following inhibition of acid extrusion by amiloride, transition to [Formula: see text] media restored pHi recovery. These data indicate that lamprey neurons recover from acute acid loads by both Na+–H+ exchange and an independent [Formula: see text]-dependent mechanism. Evidence for [Formula: see text]-dependent acid extrusion in other vertebrate cells and the protocols of pHi studies using ISMs are discussed.
Regulation of potassium levels by Müller cells in the vertebrate retina
Authors: Newman Eric A.
Published: April 2011

The membrane properties of Müller ceils, the principal glial cells of the vertebrate retina, have been characterized in a series of physiological experiments on freshly dissociated cells. In species lacking a retinal circulation (tiger salamander, rabbit, guinea pig), the end-foot of the Müller cell has a much higher K+ conductance than do other cell regions. In species with retinal circulation (mouse, cat, owl monkey) the K+ conductance of the end-foot is greater than the conductance of the proximal process of the cell. In these species, however, the K+ conductance of the soma and distal process is equal to, or greater than, the end-foot conductance. Müller cells also possess four voltage-dependent ion channels, including an inward rectifying K+ channel. These membrane specializations may aid in the regulation of extracellular K+ levels by Müller cells in the retina. High end-foot conductance shunts excess K+ out through the end-foot, where it diffuses into the vitreous humor. In vascularized retinae, excess K+ may also be transferred to the ablumenal wall of capillaries, where it could be transported into the blood.
Bicarbonate and ammonia changes in brain during spreading depression
Authors: Kraig R. P. , Cooper A. J. L.
Published: April 2011

An alkaline, followed by an acid-going transient, characterizes acid-base changes in the interstitial space during spreading depression in a variety of brain structures. In rat, such changes are associated with a significant rise in brain lactate content. How brain proton buffers behave during spreading depression is unknown. Techniques to significantly improve the response time of gas permeable membrane semimicroelectrodes for carbon dioxide and ammonia are reported. Measurements with such electrodes, when coupled to measurements of hydrogen ion concentration (from microelectrodes), permit rapid changes to be determined in bicarbonate concentration or ammonia and ammonium ion concentration, respectively. Bicarbonate concentration fell from 30 ± 1 (n = 16) to 14 ± 1 mM (n = 16) during spreading depression. On the other hand, ammonia concentration rose from 2.3 ± 0.1 to 4.4 ± 0.3 μM (n = 17) while ammonium ion concentration rose from 116 ± 11 (n = 17) to 382 ± 30 μM (n = 17) during spreading depression. Bicarbonate changes probably reflect titration of brain bicarbonate stores by accumulated lactic acid. Similar physicochemical changes do not explain the rise in ammonia and ammonium ion concentrations. Instead, elevation of the latter can only result from an increase in ammonia content of the interstitial space.
A slow wave frequency complex of the canine small intestine during the fasting state
Authors: Pousse A. , Mendel C. , Aprahamian M. , Kachelhoffer J. , Balboni G. , Plas A.
Published: April 2011

The electrical activity of the duodenum and proximal jejunum was studied in conscious healthy dogs implanted with unipolar silver electrodes. A computerized method was used for the calculation of the mean frequency of the slow wave for each consecutive minute of the electromyographic signal. A "slow wave frequency complex" was identified in the fasted animals. It was characterized by an increase of the mean frequency of the slow wave which ranged, from one dog to another, between 1 and 3 cycles/min. The complex lasted about 30 min. It consisted of two distinct phases: a phase of increasing frequency of the slow wave which lasted about one-third of the total duration of the complex and a phase of progressive return of the frequency to its precomplex value. Each phase III of the migrating myoelectric complex occurring in both the duodenum and the jejunum was associated with one slow wave frequency complex. The phase III began a few minutes before the start of the slow wave frequency complex and ended a few minutes before the slow wave frequency reached its maximum. Ectopic phase III which occurred in the jejunum but not in the duodenum were not associated with slow wave frequency complexes. The slow wave frequency complex was never seen in the fed dogs.
Sodium-dependent D-glucose transport in brush-border membrane vesicles from isolated rat small intestinal villus and crypt epithelial cells
Authors: Freeman H. J. , Johnston G. , Quamme G. A.
Published: April 2011

Differentiation and maturation of enterocytes occur with migration from the crypt to villus compartments. To investigate the effect of epithelial cell differentiation on sodium-dependent D-glucose transport, brush-border membrane vesicles were prepared from small intestinal epithelial cell suspensions selectively isolated from villus and crypt populations. Enterocytes were isolated with a morphologically monitored sequential cell dissociation method. Thymidine kinase, sucrase, and alkaline phosphatase activities were measured as differentiation markers of specific cell populations. Brush-border membrane vesicles were purified and their kinetic characteristics defined with a rapid filtration method under conditions of a zero-trans, 100 mM cis-NaSCN gradient. Typical "overshoot" phenomena characteristic of sodium D-glucose cotransport were observed for both villus (five- to eight-fold equilibrium values) and crypt brush-border membrane vesicles (two- to four-fold equilibrium values). Kinetics analyses of the initial D-glucose flux in brush-border membrane vesicles suggested the presence of at least two sodium-dependent D-glucose carriers in the villus and only a single carrier in the crypt compartments. These data indicate that sodium D-glucose cotransport occurs in brush-border membranes of both villus and crypt populations. Moreover, quantitative and qualitative differences between these two membrane populations suggest that epithelial D-glucose transport processes are differentiation dependent and reflect the degree of enterocyte development.
Interactions of reproductive steroids, osmotic pressure, and glucose on thermosensitive neurons in preoptic tissue slices
Authors: Boulant J. A. , Silva N. L.
Published: April 2011

The preoptic area contains thermosensitive neurons, thought to be important in thermoregulation, and steroid-sensitive neurons, thought to be involved in reproduction. The preoptic area also contains osmosensitive neurons, considered important in water balance, and glucosensitive neurons, thought to function in the regulation of glucose. If these various neurons belong to separate populations, one might predict that most osmosensitive, glucosensitive, and steroid-sensitive neurons constitute the population of temperature-insensitive neurons rather than thermosensitive neurons. To test this hypothesis, single unit activity was recorded in preoptic tissue slices prepared from male rats. In addition to temperature changes, neuronal responses were examined with various perfusion media containing testosterone or estradiol (30 pg/mL), low glucose (1.0 mM), and increased osmotic pressure (309 mosmol/kg). It was found that the steroid-sensitive, osmosensitive, and glucosensitive neurons were not confined to the temperature-insensitive neurons; but that nearly half of the thermosensitive neurons responded to these nonthermal stimuli. This lack of specificity was also observed between osmosensitive and glucosensitive neurons; however, most of the steroid-sensitive neurons were highly specific for either estradiol or testosterone. Although these findings do not suggest a strong functional specificity for preoptic neurons, they do support studies emphasizing interactions between regulatory systems.
Multimodal responses of preoptic and anterior hypothalamic neurons to thermal and nonthermal homeostatic parameters
Authors: Hori Tetsuro , Kiyohara Toshikazu , Nakashima Toshihiro , Shibata Masaaki , Koga Hisao
Published: April 2011

The hypothesis that thermosensitive neurons in the preoptic anterior hypothalamic nuclei (POAH) have a principal role in central thermoregulation is based on numerous findings, suggesting correlations between the activity of thermosensitive neurons and thermoregulatory responses. Such relationships have been observed during thermal (local and peripheral) and pharmacological stimulation, during modulation of neural inputs from extra-POAH brain regions, and during actual thermoregulatory responses. Recent studies using in vitro slice preparations and conscious animals have revealed that 40–70% of POAH thermosensitive neurons respond to nonthermal homeostatic parameters such as local osmolality, blood pressure, and nonthermal emotional stimuli. About two-thirds of the POAH thermosensitive neurons, which responded in monkeys during bar press thermoregulatory tasks, changed their activity during bar press feeding behavior. A high degree of convergence of thermal and nonthermal homeostatic signals on the POAH neurons, together with abundant neural connections between the POAH and divergent areas of the brain, suggests that POAH thermosensitive neurons may be involved in the coordination of thermoregulation and nonthermal autonomic and behavioral responses controlled from the hypothalamus.
Vasopressin and fever: evidence supporting the existence of an endogenous antipyretic system in the brain
Authors: Naylor A. M. , Cooper K. E. , Veale W. L.
Published: April 2011

Vasopressin administered into the ventral septum exerts a dose-related antipyresis. This site of action is similar in a number of species. The fever-reducing properties of vasopressin are both site and neuropeptide specific. Evidence supporting a role for endogenous vasopressin in fever suppression is the demonstration that the release of the peptide from the ventral septal area is altered during fever: the amount released correlates negatively with febrile changes in body temperature. In addition, changes in the concentration of vasopressin in the septum and amygdala have been demonstrated immunocytochemically during fever: an activation of vasopressinergic neurons occurs which is similar to that observed in pregnant animals at term when fever is absent. Specific antibodies directed against vasopressin or specific vasopressin antagonist analogues (e.g., d(CH2)5Tyr(Me)AVP) enhanced the febrile response to a pyrogen challenge when injected into the ventral septum. The same antagonist also can antagonize the antipyretic effect of exogenously administered vasopressin. The use of relatively specific antagonists and agonists of vasopressin, directed against the V1 and V2 subtypes of the peripheral vasopressin receptor, suggests that the central receptor responsible for the antipyretic effect of vasopressin may resemble the V1 subtype. Recent experiments using electrophysiological techniques have demonstrated the existence of thermoresponsive units in the ventral septal area whose activity may be altered by vasopressin which is possibly derived from the paraventricular nucleus and bed nucleus of the stria terminalis. Electrical stimulation of one of these cell groups in the paraventricular nucleus can reduce the fever evoked by systemic administration of bacterial pyrogen in the rabbit. Collectively, these data strongly support the hypothesis that a system of endogenous antipyresis involving vasopressin exists in the brain. There also may exist another antipyretic system in the brain involving α-melanotropin. This peptide is antipyretic when injected into the dorsal septum and concentrations of α-melanotropin are altered in this area of the brain during fever. Further, passive immunoneutralization using antiserum specific to α-melanotropin results in prolonged fever. A possible connection between the two systems has not yet been investigated. However, in future studies the mechanisms and significance of such a system will be investigated further.
Effect of capsaicin upon afferent and efferent mechanisms of nociception and temperature regulation in birds
Authors: Sann Holger , Harti Gerhard , Pierau Friedrich-Karl , Simon Eckhart
Published: April 2011

(1) Acute capsaicin effects on nociception in the conscious chicken were tested by close arterial injection. The threshold dose to elicit nocifensive and autonomic responses was 50 μg, i.e., two to three orders of magnitude higher than in mammals but four times lower than in pigeons. (2) Foot withdrawal from hot water remained unchanged after capsaicin was injected either intravenously in the chicken at a cumulative dose of 600 mg/kg or perineurally at a dose of 100 μg into the sciatic nerve of pigeons. (3) Temperature regulation and body temperature in the chicken were not affected by subcutaneous injection of capsaicin, but intravenous infusion at rates of 2–5 or 10–13 mg∙min−1∙kg−1 transiently lowered body temperature by 1.5 °C and stimulated panting and sometimes vasodilatation of the comb. Repeated capsaicin infusion produced temporary tachyphylaxia but no permanent desensitization. (4) A cumulative dose of 1 g/kg body weight capsaicin reduced the relationship between breathing frequency and respiratory evaporative heat loss in the duck. This deficit was compensated by more pronounced panting and, thus, did not indicate any impairment of temperature regulation. (5) Injection of capsaicin into the sciatic nerve depleted substance P in the dorsal horn of rats. Similar treatment in pigeons caused an increase of substance P immunoreactivity in the dorsal horn. (6) The effects of high capsaicin doses in birds indicate only low susceptibility of afferent neural mechanisms. Some of the effects may be due to a capsaicin action upon efferent neural mechanisms.
A comparison of the febrile responses of the Brattleboro and Sprague–Dawley strains of rats to endotoxin and endogenous pyrogens
Authors: Stitt John T. , Shimada Steven G.
Published: April 2011

The febrile responses of homozygous (di/di) Brattleboro rats, to both intravenous endogenous pyrogen and to a lipopolysaccharide endotoxin, were compared with those of normal Sprague–Dawley rats. There were no detectable differences between the fever curves of the two strains in response to endogenous pyrogen. Brattleboro rats, which are deficient in the neuropeptide arginine vasopressin (AVP), displayed fevers that were both qualitatively and quantitatively indistinguishable from those of normal Sprague–Dawley rats that do not suffer from congenital diabetes insipidus. It is concluded that the absence of AVP-containing cells in Brattleboro rats is not an important factor in determining the nature of their febrile responses to endogenous pyrogen. More remarkable, however, were the divergent febrile responses of the two strains to intravenously injected endotoxin. Normal rats displayed hypothermic responses, whereas the Brattleboro rats became febrile. By 2 h after the injection of endotoxin, body temperatures in both strains had returned to normal. Three hours after the rats had been exposed to endotoxin, both strains were found to be totally refractory to endogenous pyrogen. However, when both strains of rats were tested to endogenous pyrogen 3 days later, their febrile responses were more than double the magnitude of their intitial control responses. These alterations in the febrile responsiveness of rats occurring at different times after the injection of endotoxin appear to be related to the effects that endotoxin has on the cells of the reticuloendothelial system, over the same time course.
Responses of baboons to traditionally pyrogenic agents
Authors: Zurovsky Y. , Laburn Helen , Mitchell D. , MacPhail A. P.
Published: April 2011

It is not clear whether baboons develop fever in response to endotoxin or other pyrogens. We injected various pyrogens intravenously in 12 unrestrained baboons (Papio ursinus) and measured their body temperature using intra-abdominal radio-telemeters. Serum iron concentration was also measured. The baboons developed fever after injection of killed Staphylococcus aureus (5 × 107 organisms/kg). No significant fever was measured after injection of lipopolysaccharide (Salmonella typhosa) (0.1, 8, 40, and 100 μg/kg), bovine serum albumin (4 mg/kg), killed Salmonella minnesota (5 × 107 organisms/kg), and killed Salmonella typhi (5 × 107 organisms/kg). A significant decrease in serum iron concentration was found only after injection of S. aureus and lipopolysaccharide, 100 μg/kg. The phagocytic synthesis of interleukin-1 following pyrogen stimulation in baboons and some other primates appears to differ from that in man and in nonprimates.
Overlapping distributions of receptors for atrial natriuretic peptide and angiotensin II visualized by in vitro autoradiography: morphological basis of physiological antagonism
Authors: Mendelsohn F. A. O. , Allen A. M. , Chai S. Y. , Sexton P. M. , Figdor R.
Published: April 2011

Atrial natriuretic peptides exert actions on many key organs involved in blood pressure and water and electrolyte balance. Many of these actions result in a physiological antagonism of angiotensin. To investigate the morphological basis of this interaction, we have mapped the distribution of receptors for atrial natriuretic peptide and angiotensin II in a number of target organs, using 125I-labelled rat atrial natriuretic peptide (99–126) and 125I-labelled [Sar1,Ile8]angiotensin II. In the kidney both atrial natriuretic peptide and angiotensin II receptors were observed overlying glomeruli, vasa recta bundles (high densities), and the outer cortex (moderate density). In the other tissues studied, atrial natriuretic peptide and angiotensin II receptors were codistributed in the adrenal zona glomerulosa, cerebral circumventricular organs including the subfornical organ, organum vasculosum of the lamina terminalis and area postrema, and the external plexiform layer of the olfactory bulb. The concurrent distribution of specific receptors for both peptides at these sites provides the basis for atrial natriuretic peptide to exert a functional antagonism of the actions of angiotensin II on blood pressure and water and electrolyte homeostasis at multiple sites.