bluuebunny/crossref_metadata_2025_split huggingface dataset:
Respiratory modulation of baroreceptor and chemoreceptor reflexes affecting heart rate through the sympathetic nervous system
Authors: Davis Anne L. , McCloskey D. I. , Potter Erica K. 
Published: December 2014

1. Brief stimuli were delivered to the carotid body chemoreceptors or the carotid sinus baroreceptors at different phases of the respiratory cycle in anaesthetized dogs. Chemoreceptor stimulation was achieved by injecting small volumes (0·2‐0·5 ml.) of warmed saline equilibrated with CO2 near to the carotid bodies on both sides. Baroreceptor stimulation was achieved by injecting larger volumes (2‐5 ml.) of saline equilibrated with air into the region of the carotid bifurcation on both sides, after first clamping the common carotid arteries.2. When the vagus nerves were intact, but sympathetic nervous effects on heart rate were blocked by administration of propranolol, there was a prompt and pronounced bradycardia evoked when either baroreceptor or chemoreceptor stimuli were given in expiration, but little or no change in heart rate when they were given in inspiration.3. When the vagus nerves were cut, but sympathetic nervous function was intact, respiratory modulation of both baroreceptor and chemoreceptor reflex effects on heart rate could still be demonstrated. The bradycardia evoked by either stimulus was more marked for stimuli given in expiration than for stimuli given in inspiration. A complementary response pattern for brief decreases in baroreceptor stimulation (carotid occlusions) was demonstrated: the tachycardia evoked by occlusions timed during inspiration was greater than that evoked by occlusions timed during expiration. All the reflex effects were mediated by the sympathetic system because they were abolished by administration of propranolol.4. Typically, the sympathetic reflex effects were slight in comparison with the vagal reflexes evoked by either chemoreceptor or baroreceptor stimuli.
Effects of adrenoceptor stimulating and blocking agents on carotid body chemosensory inhibition
Authors: Llados F. , Zapata P. 
Published: December 2014

1. The effects of α‐ and β‐adrenoceptor agonists and antagonists on chemosensory discharges originating from carotid bodies in situ were studied in anaesthetized cats.2. Noradrenaline (NA) injections commonly resulted in increased frequency of carotid nerve chemosensory discharge, an effect ascribed to reduced blood flow through the glomus, and reduced or eliminated by α‐adrenergic block.3. NA injections occasionally produced an initial reduction of chemosensory discharge frequency, which was however less intense and of shorter duration than that caused by dopamine. This effect of NA is not mediated by α‐adrenoceptors, since it is not blocked by dibenamine, but probably by low affinity for dopamine receptors.4. Dopamine and apomorphine‐elicited chemosensory inhibition were not affected by low doses of phenoxybenzamine, which blocked NA‐evoked hypertensive reactions.5. Higher doses of phenoxybenzamine and dibenamine produced a displacement to the right of dose—response curves for dopamine‐ and apormorphine‐elicited chemosensory inhibition. However, this interference by α‐adrenergic blockers was attributed to the resultant hypotension, since it was reversed upon restoration of blood pressure.6. Isoprenaline, a β‐adrenergic agonist, did not induce chemosensory inhibition, whilst β‐adrenergic blockers (propranolol and dichloroisoproterenol) did not modify dopamine‐ and apomorphine‐elicited chemosensory inhibition.7. These results provide further support for the hypothesis that chemosensory inhibition could be mediated by specific dopamine receptors, distinct from α‐ and β‐adrenoceptors.
Carotid and cardiopulmonary baroreceptor control of splanchnic and forearm vascular resistance during venous pooling in man
Authors: Abboud Francois M. , Eckberg Dwain L. , Johannsen U. James , Mark Allyn L. 
Published: December 2014

1. This study evaluated the contribution of carotid and cardiopulmonary baroreceptors to reflex splanchnic and forearm vascular adjustments during venous pooling in man. We compared (a) responses to lower body suction which produces venous pooling with (b) responses to lower body suction plus simultaneous application of neck suction. The rationale was that simultaneous application of neck suction, which stretches carotid baroreceptors, would minimize the contribution of carotid baroreceptors to circulatory adjustments produced by lower body suction.2. Lower body suction at 40 mmHg decreased central venous pressure and arterial pulse pressure and increased forearm vascular resistance (plethysmography), splanchnic vascular resistance (indocyanine green dye clearance), and heart rate. Simultaneous application of neck suction prevented the tachycardia and most of the splanchnic vasoconstriction during lower body suction, but did not significantly attenuate the forearm vasoconstriction.3. The major findings in this study are first, that the splanchnic vasoconstrictor response during venous pooling is mediated primarily through carotid baroreceptors, and secondly, that carotid and cardiopulmonary baroreceptors produce strikingly contrasting and non‐uniform regional vascular responses during venous pooling. Cardiopulmonary baroreceptors exert the predominant influence on forearm vascular resistance, but appear to have only a minor influence on splanchnic vascular resistance. Carotid baroreceptors produce most of the splanchnic vasoconstriction during venous pooling. but have a minor role in the forearm vasoconstriction.
Separate and combined effects of ouabain and extracellular potassium on renin secretion from rat renal cortical slices
Authors: Churchill Monique C. , Churchill Paul C. 
Published: December 2014

1. Renin secretion of rat renal cortical slices was measured as a function of extracellular K and ouabain concentrations in the incubation medium.2. A sigmoid relationship was found between renin secretion and log K concentration over the range 1·0‐4·0 m
M. Secretion was maximal at about 2·25 m
M‐K and half‐maximal at about 1·43 m
M‐K.3. In media containing 4·0 m
M‐K, ouabain at 10−8, 10−7, and 10−6
M did not affect renin secretion. Higher concentrations of ouabain inhibited secretion. A sigmoid relationship was found between% inhibition of secretion and log ouabain concentration (10−6‐10−3
M). Inhibition was half‐maximal at 2·3 × 10−5
M and complete at 10−3
M‐ouabain.4. Lowering extracellular K concentration from 4·0 to 2·25 m
M shifted the dose‐effect curve of ouabain to the left. At 2·25 m
M‐K, inhibition of renin secretion was half‐maximal at 10−5
M‐ouabain.5. The inhibitory effect of 2 × 10−5
M‐ouabain (twice the dose for 50% inhibition) in media containing 2·25 m
M‐K was nearly identical to the combined effect of lowering K to 1·43 m
M (the concentration required for 50% inhibition) and adding 10−5
M‐ouabain. This observation suggests that ouabain and low extracellular K act at a common site, presumably on Na, K‐ATPase activity, to inhibit renin secretion.6. Neither 10−3
M‐ouabain nor K‐free medium inhibited renin secretion when the concentration of free Ca in the medium was lowered to < 10−8
M. Therefore it is proposed that as a result of Na, K‐ATPase inhibition, (a) intracellular Na increases, (b) intracellular Ca increases via Na‐Ca exchange, provided that extracellular Ca exceeds 10−8
M, and that (c) Ca accumulation, in some unknown manner, inhibits renin secretion from rat renal cortical slices.
The mechanism of drinking induced by parenteral hyperoncotic solutions in the pigeon and in the rat
Authors: Kaufman Susan , Kaesermann Hans‐Peter , Peters Georges 
Published: December 2014

1. In pigeons, the
I.V. injection of 0·3‐1·3 ml. of 50% (w/w) solutions of either polyethylene glycol (mol.wt. 20,000) or dextran (mol.wt. 40,000) induced reliable, rapid dose‐dependent drinking responses. The amount of water drunk in response to
I.V. polyethylene glycol was greater than that in response to
I.P. polyethylene glycol and twice that in response to
I.V. dextran.
I.V. polyethylene glycol induced a diuresis following the onset of drinking.2. The dipsogenic effect of
I.P. polyethylene glycol solutions in the pigeon was depressed by
I.V. isotonic NaCl solution 1 hr before offering water but was increased by simultaneous
I.V. hyperoncotic polyethylene glycol solution.3. In contrast, in rats, the subcutaneous injection of 25% (w/w) polyethylene glycol (mol.wt. 20,000; 1·25‐10·0 ml./kg body wt.) induced reliable drinking responses, while the same doses of polyethylene glycol, injected
I.V., did not induce drinking consistently. The volume of water drunk by rats in response to subcutaneous polyethylene glycol was smaller per unit dose than that drunk by
I.P. injected pigeons.4. The results suggest that receptors for drinking induced by extracellular dehydration in the pigeon could be situated in the extravascular interstitial section of the extracellular compartment.
Calcium‐mediated inactivation of calcium current in Paramecium
Authors: Brehm Paul , Eckert Roger , Tillotson Douglas 
Published: December 2014

1. The Ca current seen in response to depolarization was investigated in Paramecium caudatum under voltage clamp. Inactivation of the current was measured with the double pulse method; a fixed test pulse of an amplitude sufficient to evoke maximal inward current was preceded by a conditioning pulse of variable amplitude (0‐120 mV).2. The amplitude of the current recorded during the test pulse was related to the potential of the conditioning pulse. Reduction of test pulse current was taken as an index of Ca current inactivation. The current recorded during a test pulse showed a progressive decrease to a minimum as the potential of the conditioning pulse approached +10 to +30 mV. Further increase in conditioning pulse amplitude was accompanied by a progressive restoration of the test pulse current. Conditioning pulses near the calcium equilibrium potential had only a slight inactivating effect on the test pulse current.3. Injection of a mixture of Cs and TEA which blocked late outward current had essentially no effect on the inward current or its inactivation.4. Elevation of external Ca from 0·5 to 5 m
M was accompanied by increased inactivation of the test pulse current. The enhanced inactivation of the test pulse current was approximately proportional to the increase in current recorded during the conditioning pulse.5. Following injection of the Ca chelating agent, EGTA, the inactivation of the test pulse current was diminished; in addition, the transient inward current relaxed slightly more slowly, and the transient was followed by a steady net inward current.6. The time course of recovery from inactivation in the double pulse experiment approximated a single exponential having a time constant of 80‐110 msec. Injection of EGTA shortened the time constant by as much as 50%.7. It is concluded that interference with the entry of Ca or enhanced removal of intracellular free Ca2+ interferes with the process of Ca current inactivation, while enhanced entry of Ca promotes the process of inactivation. While the mechanism of inactivation is unknown, arguments are presented that the accumulation of intracellular Ca influences the Ca channel conductance.
Role of calcium and albumin in the autoregulation of renal perfusate flow
Authors: Baker S. , Cohen A. J. , Fray J. C. S. , Laurens N. J. 
Published: December 2014

1. We investigated the role of calcium and albumin on the perfusate flow in isolated perfused rat kidneys. The initial perfusion medium was Krebs‐Henseleit bicarbonate solution with 1.82 m
m‐calcium without albumin. Perfusate flow autoregulation occurred above 100 mmHg.2. Raising albumin concentration to 20 and 60 g/l. abolished autoregulation and increased perfusate flow.3. Keeping ionized calcium at 1.82 m
m restored autoregulation in medium containing 20 and 60 g albumin/l. However, in 60 g albumin/l. autoregulation occurred at a significantly higher flow.4. 1.82 m
m‐ionized calcium appears to be a critical level for autoregulation of flow in these experiments, for autoregulation was not obtained in 60 g albumin/l. medium containing 1.80 m
m‐ionized calcium. On the other hand, autoregulation occurred in medium containing 1.83 m
m‐ionized calcium, but at a lower perfusate flow.5. Raising albumin concentration to 120 g/l. increased perfusate flow from 14.6±0.8 to 20.8±0.7 ml./min.g (n = 5, P < 0.01) in the presence of 1.82 m
m‐total calcium, and from 11.6±1.0 to 15.8±0.7 ml./min.g (n = 5, P < 0.01) in 1.82 m
m‐ionized calcium. The effect of raising albumin concentration was reversible.6. Removing the capsule from the kidneys abolished the increased flow in response to raising albumin concentration.7. We conclude that (a) the mechanism for the autoregulation of renal perfusate flow in isolated perfused kidneys is critically dependent on an extremely narrow range of ionized calcium concentration in the perfusion medium, below this range, autoregulation is not achieved; above it, however, autoregulation is achieved, but during intense vasoconstriction; (b) raising albumin concentration in the perfusion medium increases perfusate flow and abolishes autoregulation by lowering extracellular ionized calcium and by raising intrarenal tissue pressure.
Conduction block in rat myelinated fibres following acute exposure to antigalactocerebroside serum
Authors: Lafontaine Serge , Rasminsky Michael , Saida Takahiko , Sumner Austin J. 
Published: December 2014

1. We have observed conduction in single rat spinal ventral root nerve fibres following acute topical application of anti‐galactocerebroside serum.2. Conduction of nerve impulses was initially slowed and subsequently blocked at the site of serum exposure.3. Conduction block occurred within as little as 1 hr in more slowly conducting (20‐30 m/sec) myelinated fibres but occurred later in fibres conducting more rapidly.4. Conduction block was preceded by a rise in internodal conduction time from the normal 20 μsec to about 200 μsec.5. At nodes exposed to serum, conduction block was invariably associated with greatly decreased depolarization; this was contrasted with nodes exposed to local anaesthetic or tetrodotoxin where conduction block occurred despite nodal depolarization well beyond threshold potential.6. Nodal capacitance and resistance were estimated from simultaneous recordings of membrane current and extracellular potential at blocked nodes exposed to local anaesthetic or tetrodotoxin (normal nodes) and at blocked nodes exposed to anti‐galactocerebroside serum.7. For normal fibres of internodal length 0·8‐1·1 mm, an upper limit estimate for average nodal capacitance was 2·6 ± 0·3 pF and a lower limit estimate for average nodal resistance was 55 ± 10 MΩ. There was an order of magnitude increase in the capacitance of nodes at which conduction block occurred following exposure to anti‐galactocerebroside serum.8. We conclude that the early conduction block caused by anti‐galactocerebroside serum is due to paranodal demyelination and that acute paranodal demyelination is sufficient to cause conduction block.
Is action potential duration of the intact dog heart related to contractility or stimulus rate?
Authors: Drake Angela J. , Noble Mark I. M. , Schouten Vincent , Seed Anthony , Keurs Henk E. D. J. Ter , Wohlfart Bjorn 
Published: December 2014

1. The contractility (maximum rate of rise of left ventricular pressure) and action potential duration were measured in intact closed‐chest anaesthetized dogs with complete atrioventricular dissociation and β‐adrenergic blockade.2. Measurements were confined to test beats following a 1 sec interval. Prior to the test interval (priming period) a variety of potentiating stimulus trains were introduced.3. When the frequency of stimulation was increased in the priming period (frequency potentiation), there was an inverse relationship between action potential duration and contractility of the test beat.4. When the test beat was potentiated by a single beat terminating the priming period with one short interval (post‐extrasystolic potentiation), there was no relationship between the action potential duration and contractility of the test beat.5. Paired pulse stimulation was used for any given frequency to vary contractility by short interval potentiation. For any given frequency of stimulation there was no relationship between action potential duration and contractility of the test beat. For any given value of contractility, action potential duration decreased with increased frequency of stimulation.6. The introduction of a high frequency train caused a step decrease in action potential duration on the first beat of the train. This was followed by a further slow decline in action potential duration with a time course of over 3 min. These two changes could be dissociated by the introduction during the train of one second interval test pulses, which only showed the slow shortening.7. The lack of a consistent relationship between action potential duration and contractility of the test beat disagrees with the hypothesis that repolarization is controlled by the activator calcium responsible for the contractility. The action potential shortening associated with increased frequency is related to the frequency change per se.8. The slow time course of change in action potential duration following an increase in stimulation frequency suggests that these changes are caused by the accumulation of an ion or metabolite, or possibly by changes of activity of the electrogenic Na+—K+ pump.
Injection of guanosine and adenosine nucleotides into Limulus ventral photoreceptor cells
Authors: Bolsover S. R. , Brown J. E. 
Published: December 2014

1. Several nucleotide and nucleotide analogues had striking effects when pressure‐injected into Limulus ventral photoreceptor cells. The poorly hydrolysable GTP analogues guanosine 5′‐0‐(3‐thiotriphosphate) (GTPγS), guanylyl imidodiphosphate (Gpp[NH]p) and guanylyl (β, γ methylene) diphosphonate (Gpp[CH2]p) produced large increases in the frequency of ‘discrete events’ that were recorded from photoreceptors in darkness. This effect was only observed after the injected cell was exposed to light. Injection of the ATP analogue ATPγS had effects similar to those of the GTP analogues.2. We conclude that GTPγS, Gpp[NH]p, Gpp[CH2]p and ATPγS act at a common site to cause a light‐dependent, long‐term activation of the excitation mechanism of the photoreceptor.3. Injection of GTP or GDP at pH 4.8 was followed by a smooth, transient depolarization that was observed neither when GTP at pH 7.5 was injected nor when ATP, 5′GMP or 2‐[N‐morpholino] ethane sulphonic acid (MES) were injected at pH 4.8. The reversal potential of the current induced by GTP injection was significantly more positive than the reversal potential of the light‐induced current.4. We conclude that GTP injection induces changes of membrane conductance either in addition to, or different from, the light‐induced change of membrane conductance.5. Injection of the ATP analogue adenylyl imidodiphosphate (App[NH]p), and the pyrophosphate analogue imidodiphosphate (p[NH]p) produced a drastic decrease in the sensitivity of photoreceptors to light. This decrease in sensitivity was partially reversed when the concentration of calcium ions in the bathing medium was reduced.6. We suggest that App[NH]p and p[NH]p injections act by increasing the cytoplasmic concentration of calcium ions.
Effect of age, potassium depletion and denervation on specific displaceable [3H]ouabain binding in rat skeletal muscle in vivo
Authors: Clausen Torben , Hansen Otto , Kjeldsen Keld , Nørgaard Aage 
Published: December 2014

1. Following intraperitoneal injection of [3H]ouabain in rats, the isotope is rapidly distributed in blood plasma available for binding to the Na‐K‐ATPase in the plasma membranes of most tissues. In skeletal muscle tissue excised and washed 4 × 30 min in ice‐cold buffer, 95% of the 3H activity retained was shown to be [3H]ouabain using a specific binding assay.2. The [3H]ouabain bound to soleus and extensor digitorum longus (e.d.l.) muscles in vivo and retained following wash‐out in the cold showed the same saturation characteristics as those determined when binding took place in vitro.3. In soleus and e.d.l. muscles obtained from 28‐day‐old rats, the number of [3H]ouabain binding sites measured in vivo was 583±19 and 720±22 pmol/g wet wt., respectively, i.e. in good agreement with previous and present results obtained in vitro.4. In vivo measurements showed that 7 days after denervation, the number of [3H]ouabain binding sites in soleus and e.d.l. muscles was reduced by 22 and 13%, respectively.5. In the age interval from 28 to 85 days, the number of [3H]ouabain binding sites in soleus was found to decrease by 58%. Following I.P. injection of [3H]ouabain, the 85‐day‐old rats showed a more pronounced and sustained rise in plasma 3H activity, which in part can be due to the reduced capacity for [3H]ouabain binding in skeletal muscle.6. K depletion induced by the administration of K‐deficient diet for 3 weeks reduced [3H]ouabain binding by 63% in soleus muscles. In the K‐depleted animals, the plasma 3H activity measured 15 min after I.P. injection of [3H]ouabain was 77% higher than in controls receiving the same dose per kg body weight.7. The present in vivo results provide further support for the idea that increased digitalis toxicity due to increasing age or K depletion is related to reduced binding capacity for digitalis glycosides in skeletal muscle.
Numerical Analysis of the Tapping Atomic Force Microscopy on a Viscoelastic Sample
Authors: Carmichael Ben , Frey Gary , Mahmoodi S. Nima 
Published: December 2014

Mechanical characterization of thin samples is now routine due to the prominence of the Atomic Force Microscope. Advances in amplitude modulation techniques have allowed for accurate measurement of a sample’s elastic properties by interpreting the changes in the vibration of a cantilevered beam in intermittent contact. However, the nonlinearities associated with contact complicate attempts to find an accurate time-history for the beam. Furthermore, the inclusion of viscous effects, common to soft samples, puts an explicit solution even farther from reach.
A numerical method is proposed that analyzes the time-history and frequency response of a microcantilever beam with a viscoelastic end-condition. The mathematics can be simplified by incorporating the viscoelastic end-condition into the equation of motion directly by modeling it as a distributed load. A forcing function can then be derived from the Standard Linear Solid model of viscoelasticity and implemented in the non-conservative work term of Hamilton’s principle. The Galerkin method can separate the resulting nonlinear equation of motion into time and space components. Performing a numerical analysis of the time factor equation provide the beam’s response over time. The results demonstrate the distinctive effects of viscoelasticity and periodic contact on the beam’s motion and provide the framework for the determination of viscous properties using dynamic techniques.