bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation and inactivation characteristics of the sodium permeability in muscle fibres from Rana temporaria
Authors: Collins Carol A. , Rojas E. , Suarez‐Isla B. A.
Published: December 2014

1. The steady‐state and kinetic characteristics of the processes of activation and inactivation of the Na+ permeability, PNa, were measured in cut skeletal muscle fibres from Rana temporaria under voltage‐clamp conditions.

2. The specific resistance, rss, in series with the surface sarcolemma, was estimated as 6 Ω cm2 by measuring the initial value of the membrane potential transient in response to current pulses under current‐clamp conditions. To reduce the error in the potential across the sarcolemma introduced by rss, Na+ currents were recorded using positive feed‐back compensation, in the presence of tetrodotoxin (2·4‐5 n
m).

3. PNa(t) was fitted with m3h kinetics assuming a voltage‐dependent delay, δt, to the start of the activation process.

4. The PNa—Vp curve exhibited saturation at potentials more positive than 30 mV. m∞, calculated as (PNa, ∞/P̄Na)⅓ as a function of Vp, was a sigmoid curve with a mid point at ‐35 mV. The slope, dm∞/dVp, at this point was 0·032 mV−1.

5. Using a double‐pulse protocol a non‐exponential time course for the development of fast inactivation at small depolarizations was observed.

6. The time constant for activation, τm, as a function of Vp, and τh as a function of Vp, could be fitted with an approximately bell‐shaped function, maximum of 430 μs at ‐43 mV and 925 μs at ‐78 mV respectively, at 15 °C.

7. The mid‐point potential of the h∞—Vl curve occurred at ‐58 mV, and h∞ approached 1 for V1 values more negative than ‐103 mV.

8. Using a double‐pulse procedure the development of a slow inactivation of the Na+ current was demonstrated. Its time course could be described in terms of a single exponential function, time constant equal to 0·58 s. The recovery from slow inactivation could be described by a similar exponential for recovery times smaller than 1 s.
Adrenergic mechanisms and chemoreception in the carotid body of the cat and rabbit
Authors: Folgering H. , Ponte J. , Sadig T.
Published: December 2014

1. The effect of β‐adrenergic and dopaminergic agonists and antagonists on the chemoreceptor response to graded hypoxia and hypercapnia was tested in nineteen cats and ten rabbits anaesthetized either with chloralose—urethane or pentobarbitone sodium, paralysed with pancuronium bromide and artificially ventilated.

2. The inhibitory action of dopamine was confirmed. The inhibition following intra‐arterial bolus injection was blocked by haloperidol; dopamine then excited and this excitation was blocked with propranolol. Adrenaline or noradrenaline caused a transient inhibition followed by a marked excitation. The inhibition was blocked with haloperidol and the excitation blocked with propranolol or metoprolol. Isoprenaline excited without inhibition and this was blocked with propranolol or metoprolol.

3. A novel finding was that the chemoreceptor response to hypoxia was markedly reduced or even abolished with propranolol or metoprolol. The response was enhanced with a constant infusion of isoprenaline, adrenaline or noradrenaline in proportion to the degree of hypoxia, an effect mimicked by raising CO2. The chemoreceptor response to hypoxia was similarly enhanced by haloperidol and depressed by a constant infusion of dopamine in proportion to the degree of hypoxia.

4. The effect of these drugs on the chemoreceptor response to hypercapnia was less constant. In the majority of tests the aminergic agonists and antagonists caused a parallel shift of the CO2 response curves in the same direction as the O2 response curves and by amounts proportional to the degree of hypoxia. In some tests these drugs caused a change in the slope of the CO2 response curves but only if Pa, O2 was less than 60 mmHg.

5. One interpretation of these results is that hypoxia exerts a presynaptic action, causing the release of noradrenaline and dopamine from Type I cells, and that these substances act upon aminergic receptors on the sensory fibre, causing a change in potential and discharge frequency proportional to the rates of dopamine and noradrenaline release.

6. An additional or alternative interpretation is that O2 and CO2 (the latter most probably acting on intracellular pH) alter the sensitivity of the aminergic receptors to their agonists.
Control of the antral motor response to feeding by gastric acid secretion in rats.
Authors: Bueno L , Ferre J P , Fioramonti J , Ruckesbusch M
Published: December 2014

1. The motor response of the antrum to feeding was examined in relation to gastric acid content in six adult rats fitted with electrodes and strain gauges on the antrum, two of them also having a small cannula in the fundus. 2. After fasting overnight, feeding was accompanied by an immediate increase in antral activity of seventeen to nineteen strong contractions lasting 5.33 +/‐ 1.15 min. Both the duration and amplitude of this antral motor response were increased 2 hr after ingestion of cimetidine (20 mg/kg) or 60 min after intramuscular administration of the same dose of proglumide. 3. By contrast, the response to feeding was reduced by 43% in duration and by 58% in amplitude during an intravenous infusion of pentagastrin (5 mg/kg per hr) and disappeared after an infusion of HCl into the stomach. The area under the curve of the pressure developed by the gauge, used as a motility index, was nearly doubled when the pH of the gastric contents increased from 3.1 to 5.7 and was halved when the pH decreased from 3.1 to 2.2. 4. In normal or inhibitory gastric acid secretion, the blockade of the antral motor response to feeding appeared when the total acid content of the gastric juice reached 35‐70 mu equiv/ml. 5. The results indicated that the rate of gastric secretion is of paramount importance in regulating the magnitude of the antral motor response to feeding. It is suggested that the vagally stimulated antral motility is rapidly counteracted by the increased acid secretion.
Water repellency induced by pulmonary surfactants.
Authors: Hills B A
Published: December 2014

1. Pure cotton fabric was partially carboxylated to produce a tough, porous, hydrophilic sub‐phase to stimulate the epithelial membrane of the alveolar wall from a permeability standpoint. 2. Two of the predominant pulmonary surfactants, dipalmitoyl lecithin (DPL) and dipalmitoyl phosphatidylethanolamine (DPPE), were found to inhibit wetting of this synthetic membrane and of human cutaneous epithelium as manifest by a large contact angle. 3. When treated with DPL at physiological concentrations, the porous synthetic membrane was found to support a head of saline well in excess of systolic pulmonary artery pressure with no penetration and could do so for periods well in excess of 1 hr; untreated control samples allowed almost immediate fluid filtration. 4. Filtration could be initiated in the DPL‐treated membranes by wetting the reverse side, confirming that the threshold pressure for fluid penetration was afforded by capillarity and, hence, by water repellency induced by the surfactant. 5. Water repellency induced by the amphoteric surfactants occurring naturally in the lung is discussed as a possible factor contributing to the pressure threshold to be exceeded for alveolar oedema to form. 6. Evidence is reviewed and several advantages discussed for the implied concept of an essentially dry lining to the alveolus with a discontinuous liquid layer largely confined to convex corners which could slowly resolve any oedema by surface forces.
The action of serotonin on excitatory nerve terminals in lobster nerve‐muscle preparations.
Authors: Glusman S , Kravitz E A
Published: December 2014

1. The action of serotonin on excitatory transmission in the opener muscle of the dactyl of the lobster walking leg was examined by intracellular recording techniques. 2. Serotonin, at concentrations as low as 5 x 10(‐9) M, caused a sustained increase in the size of the excitatory junctional (synaptic) potential (e.j.p.). When serotonin was washed out of the bath the e.j.p. declined in two steps (T 1/2 approximately equal to 1‐2 min; T 1/2 approximately equal to 30 min) to the control size. The increased e.j.p. size was predominantly due to a serotonin‐induced increase in the release of quanta of excitatory transmitter with nerve stimulation. 3. The increase in transmitter release did not require nerve stimulation or the presence of Na+ or Ca2+ ions in the bathing medium during the period of serotonin treatment. 4. Three types of experiments suggested that a part of the action of serotonin on excitatory nerve terminals might involve a long‐term metabolic change within terminals, possibly involving the buffering or storage of Ca2+ ions. First, serotonin increased the frequency of spontaneous release of transmitter in both normal saline (26 mM‐Ca2+) and saline with very low levels of Ca2+ (less than 10(‐8) M). Secondly, serotonin greatly potentiated increases in miniature excitatory junctional potential frequency induced by the loading of the nerve terminal with Na+ either by veratridine or by inhibition of the Na+ pump or by the addition of the Na‐ionophore monensin in low‐Ca2+ salines. Thirdly, in some experiments, serotonin treatment produced a partial restoration of the nerve‐evoked release of transmitter in the low‐Ca2+ medium (less than 10(‐8) M).
Calcium efflux from the rat neurohypophysis
Authors: Nordmann Jean J. , Zyzek Evelyne
Published: December 2014

1. Calcium efflux from isolated rat neurophypophyses has been studied. Curve fitting of the wash‐out curves suggests three phases with t½ of ca. 3, 15 and 130 min.

2. The slow component of the 45Ca efflux is attributed to efflux of intracellular Ca. On the basis of the temperature sensitivity of the Ca efflux, the activation energy has been calculated to be approximately 12,000 cal/mole, corresponding to a Q10 of ca. 2·0.

3. Ca efflux decreased by approximately 32% when external Na was replaced by choline. Lio, in the presence or absence of Cao, was as effective as Nao in stimulating the Ca efflux.

4. The curve relating Ca efflux to [Na]o or [Li]o is sigmoid and suggests that at least two Na (or Li) ions are necessary to activate the efflux of each Ca ion. Cao does not modify the absolute Na‐dependent Ca efflux but decreases the affinity for Na of the site involved in Ca extrusion.

5. Removal of Cao decreased the Ca efflux by ca. 44% in Na‐free media. The apparent affinity for Cao of the Cao‐activated Ca efflux (KmCao = 20 μM) is greatly decreased by the presence of 150 mM‐Na (KmCao = 0·8 mM).

6. Lanthanum decreased the total Ca efflux by ca. 60% and totally abolished the Nao‐activated and Cao‐activated Ca efflux.

7. Vanadate reduced the Ca efflux remaining in Na‐, Ca‐free saline by 73%.

8. Elevation of Nai with ouabain did not modify the rate of loss of 45Ca.

9. Increased concentration of Ko stimulated transiently the 45Ca loss. The time course of this increase depends on the Cao concentration ([Ca]o).

10. Cyanide or CCCP (carbonyl cyanide m‐chlorophenylhydrazone) increased transiently the Ca efflux. The increase induced by cyanide could only be observed when the neural lobes had been over‐loaded with 45Ca.

11. Membrane destruction induced by high temperature eliminated the effect of [Na]o and [Ca]o on 45Ca efflux.

12. In 150 mM‐Na‐containing saline, half‐maximum activation of 45Ca uptake occurs in the 0·2‐0·4 mM [Ca]o range.

13. The Ca efflux from isolated pituicytes was not affected by removal of Nao.

14. In conclusion we show that Ca efflux from neurosecretory nerve terminals can be subdivided into three components of approximately the same magnitude, one which is activated by Nao, another by Cao and a third component which is independent of Nao and Cao.
Characterization of the fast sodium current in isolated rat myocardial cells: simulation of the clamped membrane potential.
Authors: Bodewei R , Hering S , Lemke B , Rosenshtraukh L V , Undrovinas A I , Wollenberger A
Published: December 2014

1. The fast sodium inward current of freshly isolated single rat myocardial cells was studied by means of the internal perfusion‐voltage clamp method. 2. The voltage dependence of this current did not differ from the current‐voltage characteristics of the fast sodium inward current described for other excitable cells and tissues. 3. The time constant of inactivation of the Na+ current of the isolated myocardial cells ranged between 5.2 msec at ‐58 mV and 0.5 msec at +18 mV. The activation time constant ranged from 0.3 msec at ‐55 mV to 70 microseconds at +10 mV. 4. The reactivation time constant of the maximum sodium current at a holding potential of ‐100 mV was found to be 21 +/‐ 5 msec. 5. A mathematical model was developed for the simulation and analysis of the influence of the series and shunt resistances on the time response of the membrane potential. The results of the modelling make it clear that control of the series and shunt resistances in any given experiment is a conditio sine qua non for a valid analysis of the kinetic parameters of the sodium inward current. 6. Sodium currents with delayed activation kinetics must be regarded as an indication of insufficient control of the membrane potential.
The reflex respiratory effects on cats of breathing through a tube.
Authors: Marsh J , Nye P C
Published: December 2014

1. In anaesthetized cats, breathing air through an external dead space (a tube, 20‐40 ml.) stimulated ventilation in excess of that expected from the end‐tidal gases. 2. The stimulatory effect remained after bilateral vagotomy. 3. The stimulatory effect was reduced or abolished after bilateral section of the carotid sinus nerves. 4. The stimulatory effect was abolished by bilateral section of both the vagi and the sinus nerves. 5. Recording from chemoreceptor afferents in the sinus nerve showed that, although the tube increased mean discharge frequency, this increase was insufficient to account for the stimulation of ventilation observed. 6. Some feature of chemoreceptor discharge other than its mean level, possibly related to its wave form, may explain the effect.
The effects of alanine, glucose and starch ingestion on the ketosis produced by exercise and by starvation.
Authors: Koeslag J H , Noakes T D , Sloan A W
Published: December 2014

1. Several investigators have found that the development of post‐exercise ketosis is not counteracted by glucose ingestion. Post‐exercise ketosis might therefore have more in common with diabetic ketoacidosis than with starvation ketosis. 2. The effects of ingesting 100 g of glucose, alanine or starch were therefore studied in subjects rendered hyperketonaemic by prolonged running on a low carbohydrate diet, or by 65 h of starvation. These substances were also ingested by normal post‐prandial subjects. 3. The runners developed post‐exercise ketosis (1.81 +/‐ S.D. 0.81 mmol/l), which was counteracted by alanine and glucose, but only minimally by starch. 4. Fasting caused a variable ketosis (2.19 +/‐ S.D. 1.63 mmol/l), also counteracted by glucose and less by starch, but alanine caused vomiting. 5. Glucose and alanine lowered the blood ketone body levels of the post‐prandial subjects. 6. The rising ketone body levels in starvation and after exercise were accompanied by simultaneous increases in the plasma insulin/glucagon ratios; in both, glucose ingestion increased the ratio further, while alanine decreased it. 7. It is concluded that there is no essential difference between established post‐exercise and starvation ketosis, and that the blood fuel‐hormone changes do not correlate with the changes in blood ketone body concentrations.
Motor units and immunohistochemistry of cat soleus muscle after long periods of cross‐reinnervation
Authors: Lewis D. M. , Rowlerson Anthea , Webb Sandra N.
Published: December 2014

1. Cat soleus (slow twitch) was cross‐reinnervated with nerve to flexor hallucis or digitorum longus muscle (fast twitch). More than 3 years later motor unit isometric contractions and muscle immunohistochemistry and histochemistry were investigated. All muscles differed from normal fast or slow muscle.

2. The motor units could be divided into two groups: one with fast twitches and low tetanic tension, the other with slow twitches and high tension. This is the reverse of the relation between motor unit twitch time and tetanic tension in normal muscle (fast or slow).

3. Motor unit twitch time to peak decreased with axonal conduction velocity, as in normal muscle, but so did tetanic tension, which is abnormal.

4. Twitch—tetanus ratio increased with twitch time to peak in the group of slow units but not in the fast group (although the range of ratios was as great).

5. A tetanus depressed the twitch tension of slow motor units and potentiated fast ones as in normal muscle but the potentiation was often accompanied by an abnormal prolongation of the twitch.

6. The mean conduction velocity of axons was slightly higher than at 6 months' reinnervation but below the normal value for fast muscle.

7. Antibody to slow myosin was bound strongly to Type I fibres but not to Type II fibres, confirming the histochemical division of fibres into Types I and II.

8. More than 95% of the fibres were oxidative, with Type I predominating over Type II a in the ratio of about 2:1.

9. The higher tension of the slow motor units was the result of three factors: the number of fibres per motor unit was at least three times that in the fast; Type I fibres had cross‐sectional areas little less than Type II (a and b together) and were estimated to develop more tension per unit area. All three findings were different from those in normal fast muscle.

10. One flexor hallucis longus muscle was self‐reinnervated and examined histochemically. This muscle was abnormal in that a large majority of the fibres were Type I.
Comparison of gastrin bioactivity and immunoreactivity of antral extracts from man, pig and cat.
Authors: Blair E L , Grund E R , Lund P K , Reed J D , Sanders D J
Published: December 2014

1. The gastrin bioactivity and immunoreactivities of human, porcine and feline antral extracts were compared. 2. Human and porcine had similar activities but cat had much less. 3. The ratio of gastrin bioactivity to immunoreactivity was much greater with feline antral extracts than with human and porcine extracts.
Prenatal onset and maternal modifications of the circadian rhythm of plasma corticosterone in blind infantile rats.
Authors: Hiroshige T , Honma K , Watanabe K
Published: December 2014

1. In order to clarify the manner in which maternal nursing modifies the circadian rhythm of plasma corticosterone in blind pups, specified schedules of maternal nursing were imposed on blind pups and the hormone rhythm was followed individually. 2. Two groups of blinded pups were continuously nursed, alternately by two mother rats having different circadian phases of lactating period. In both groups, phase angles of the original mother were predominantly reflected in the phase of the pups' hormone rhythm. 3. When the maternal nursing was limited only during the light period (L nursing), it caused no detectable effect on the pups' hormone rhythm. 4. In contrast, when the maternal nursing was limited only during the dark period (D nursing), approximately one half of the pups at the fourth post‐natal week showed a bimodal pattern of hormone rhythm. A second peak appearing 180 degrees out of phase to the first peak disappeared by the sixth or eight post‐natal week. 5. It is concluded that the circadian oscillation underlying the plasma corticosterone rhythm starts to function prenatally and the original mother (probably, a prenatal LD cycle) primarily determines the phase angle of the circadian oscillation in blind pups. The maternal nursing does not entrain the pups' circadian oscillation, but does modify transiently the overt hormone rhythm, probably through a discord between maternal nursing and pups' feeding phases.
The role of intracellular chloride in hyperpolarizing post‐synaptic inhibition of crayfish stretch receptor neurones
Authors: Deisz R. A. , Lux H. D.
Published: December 2014

1. The intracellular Cl− activity (aCli) of isolated crayfish stretch receptor neurones was measured using liquid ion exchanger Cl−‐selective micro‐electrodes. The potential developed due to the difference between the normal extracellular Cl− activity (aClo) and aCli (VCl) was compared with the simultaneously measured reversal potential of the inhibitory post‐synaptic potential (Ei.p.s.p.) to further clarify the ionic basis of the i.p.s.p..

2. In normal Ringer solution, VCl (63·3 ± 2·3 mV) was found to be close to the resting membrane potential (Em, 62·6 ± 3·9 mV) while Ei.p.s.p. (74·5 ± 1·9 mV) was more negative than either. The VCl value corresponds to an apparent aCli of 12·7 ± 1·3 mM, which is about 4 mM more than required for a Cl− governed Ei.p.s.p. of 74·5 mV.

3. Reducing aClo caused smaller changes in VCl than predicted for passive Cl− re‐distributions. On complete removal of extracellular Cl− (Clo−), VCl increased to 84·6 ± 2·7 mV, equivalent to an apparent aCli of about 5 mM‐Cl−. This value can be used as an estimate of the level of intracellular interference on the Cl−‐selective micro‐electrode.

4. Increasing extracellular K+ (K0+) decreased both VCl and Ei.p.s.p.. Decreasing Ko+ had the converse effect. The time course of the changes in VCl and Ei.p.s.p. was much the same. The difference between VCl and Ei.p.s.p. decreased to about 3 mV in high Ko+, and increased to about 30 mV in low Ko+. This variation in the difference between Ei.p.s.p. and VCl is consistent with the assumption that anions other than Cl− contribute to the recorded VCl rather than another ion contributes to the inhibitory current.

5. Application of 5 mM‐NH4+ or of frusemide (6 × 10−4 M) decreased VCl and Ei.p.s.p.. The difference between VCl and Ei.p.s.p. was also decreased.

6. We conclude that aCli is lower than predicted from a passive distribution and thus the chloride equilibrium potential (ECl) is more negative than Em. If a constant intracellular interference equivalent to about 4 mM‐Cl− is assumed to contribute to the recorded VCl, ECl was approximately equal to Ei.p.s.p. in all the experimental conditions. Therefore we suggest that the i.p.s.p. is solely generated by Cl− ions.
Mechanisms of relaxation induced by activation of β‐adrenoreceptors in smooth muscle cells of the guinea‐pig mesenteric artery
Authors: Itoh Takeo , Izumi Hidetaka , Kuriyama Hirosi
Published: December 2014

Relaxation of smooth muscle cells induced by activation of β‐adrenoceptors was investigated in intact and skinned muscles of the guinea‐pig mesenteric artery.

1. In concentrations over 10−7 M, isoprenaline reduced the resting tone of intact preparations and also the amplitude of K contractions. When Ca was applied after previous superfusion with Ca‐free solution, the amount of Ca accumulated into storage sites was increased by isoprenaline in polarized and depolarized ([K]o 128 mM) muscles. The amount of Ca stored increased even further when procaine and isoprenaline were applied simultaneously during store loading.

2. Isoprenaline increased the concentration of cyclic AMP as determined by radioimmunoassay. Application of isoprenaline at a concentration of 10−7 M increased cyclic AMP from 2.2±0.3 to 2.8±0.6 p‐mole/mg wet weight and at 10−6 M increased it to 4.5±0.8 p‐mole/mg wet weight after 5 min incubation (n = 4).

3. Application of cyclic AMP (3 × 10−6 M) with cyclic AMP‐dependent protein kinase (50 μg/ml.) had no effect on the pCa—tension relationship in the skinned muscles. However, an increased concentration of cyclic AMP (> 10−5 M) suppressed the Ca‐induced concentration only in the presence of protein kinase. This protein kinase (50 μg/ml.) alone had no effect on the Ca‐induced contraction.

4. In skinned fibres, the Ca store could be loaded by applying low concentrations of Ca. If cyclic AMP (3 × 10−6 M) with protein kinase (50 μg/ml.) was applied during the loading procedure, the amount of Ca accumulated by the store increased if the loading solution contained 10−6 M‐Ca applied for 2 min or less, but if the loading solution was applied for 3 min, or if higher Ca concentrations were used, the presence of cyclic AMP with protein kinase decreased the store size, suggesting that a Ca‐induced Ca‐release mechanism was also being activated.

5. In skinned muscles, accumulation of Ca into the store site in the presence of cyclic AMP (3 × 10−6 M) with protein kinase (50 μg/ml.) was further accelerated by simultaneous applications of procaine (5 mM), as here the Ca‐induced Ca‐release mechanism was suppressed.

6. These results indicate that activation of β‐adrenoceptors by isoprenaline increases the amount of cyclic AMP in the intact muscles, and leads to an increase in Ca accumulation into the store site. In the skinned muscles, the Ca‐induced Ca‐release mechanism is activated by cyclic AMP and the Ca receptor for contraction (leiotonin C or calmodulin) is somewhat suppressed. These effects of exogenously applied cyclic AMP require the presence of protein kinase. The relaxation following β‐adrenoceptor activation is more likely to involve Ca extrusion from the cell and accumulation of Ca in internal storage sites than suppression of the binding of calmodulin with the myosin light chain kinase.
The spatial distribution of synchronization of intercostal motoneurones in the cat
Authors: Kirkwood P. A. , Sears T. A. , Stagg D. , Westgaard R. H.
Published: December 2014

1. The three different types of synchronization of intercostal motoneurones which were described in the preceding paper (Kirkwood, Sears, Tuck & Westgaard, 1982) were studied for motoneurones of the same segment or for different segmental separations (up to five segments) and for motoneurones on opposite sides of the same segment.

2. The strength of synchronization declined with segmental separation for all three categories, although the rate of decline was more variable for broad‐peak synchronization than for the two other types. Short‐term synchronization was undetectable for separations greater than three or four segments but clear peaks were still visible in the cross correlation histograms for high‐frequency oscillation (h.f.o.) or broad‐peak synchronization at a segmental separation of five. Synchronization between motoneurones on opposite sides of the cord was generally weak although less so for broad‐peak or h.f.o. components.

3. The decline in strength of short‐term synchronization with segmental separation could not be explained by temporal dispersion of impulses in presynaptic axons.

4. A time shift was observed in the position of the cross‐correlation histogram peak which was dependent on segmental separation and equivalent to a mean descending conduction velocity of 28 m/s in the assumed common input. This figure is similar to the mean conduction velocity of bulbospinal respiratory neurones derived from published values.

5. We conclude that the short‐term synchronization in these preparations is generated by the bulbospinal respiratory neurones and that the majority of their axons do not branch to make strong synaptic connexions to motoneurones over more than three to four segments.

6. Interpretations of the different distributions of the other types of synchronization are discussed.
Effect of potassium depolarization on sodium‐dependent calcium efflux from goldfish heart ventricles and guinea‐pig atria
Authors: Busselen P.
Published: December 2014

1. 45Ca fluxes were studied in normal and potassium‐depolarized goldfish ventricles as a function of the external Na concentration. Some of the experiments were also performed on guinea‐pig auricles.

2. When the external K concentration was increased from 5·4 to 142 mM, keeping osmolarity constant by adding 137 mM‐Li or choline (hyperosmotically) to the low K solution, the 45Ca efflux was reversibly inhibited, whereas the [3H]sucrose efflux was unaffected.

3. Goldfish ventricles, which have been depolarized with 142 mM‐K for 100 min, repolarized within 20 min, from ca. ‐15 mV to ca. ‐70 mV, following the application of 5·4 mM‐K. This repolarization was independent of the presence of external Na. During the repolarization the 45Ca efflux was reactivated. This reactivation, however, depended on the external Na concentration. Comparable results were obtained in guinea‐pig atria.

4. A similar repolarization and Na‐dependent reactivation of 45Ca efflux was obtained in goldfish ventricles superfused with 10−6 M‐Ca2+ (4·5 mM‐Ca, 5 mM‐EGTA, pH 7·1), provided that the 45Ca washout was started in high K.

5. In 10−6 M‐Ca2+, 137 mM‐Na, 5·4 mM‐K and 137 mM‐choline goldfish ventricles depolarized to about ‐25 mV within 80 min. If the choline was now replaced by 137 mM‐K, the membrane potential moved to ca. ‐15 mV, and under these conditions the 45Ca efflux was slightly increased.

6. Following Na‐free perfusion for 100 min, and at normal external Ca concentrations, the 45Ca efflux from goldfish ventricles was stimulated by the addition of Na. The curve relating this stimulation to the external Na concentration had a sigmoidal shape and was shifted to the right by K‐depolarization. In guinea‐pig atria the inhibition of the Na‐stimulated Ca efflux by depolarization was of a non‐competitive type.

7. Following a Na‐free incubation of 100 min and a subsequent period of 20 min in 137 mM‐Na, the intracellular Na content of goldfish ventricular cells was some 20% lower in K‐depolarized cells than in cells at the resting potential.

8. 45Ca influx in goldfish ventricles in the presence of 137 or 68·5 mM‐Na was not significantly changed by K‐depolarization.

9. The results show that the Na‐dependent fraction of Ca efflux is inhibited by high external K. The effect is probably due to depolarization, which may be an argument in favour of electrogenic n Na+‐1 Ca2+ exchange, with n ≥ 3.
Biochemical evidence for re‐use of noradrenergic storage vesicles in the guinea‐pig heart
Authors: Wakade Arun R. , Wakade Taruna D.
Published: December 2014

1. The present investigation was specifically aimed to study the question of re‐use of sympathetic storage vesicles of the isolated guinea‐pig heart.

2. Tetraethylammonium (TEA, 20 mM) caused a massive enhancement of noradrenaline (NA) overflow upon transmural stimulation of the heart. The enhancement was inversely related to the frequency of stimulation, and maximum amounts (expressed per pulse) overflowed upon stimulation with one pulse. After one pulse the overflow reached a maximum level in about 20 sec and gradually declined to a basal level in about 80 sec.

3. Enhanced overflow of NA by TEA and intermittent stimulation was accompanied by reduction in ventricular NA content. Reduction was inversely related to the frequency of stimulation. Almost 50% reduction occurred 15 min after TEA and stimulation (1 Hz), and reached a maximum value (80%) in 60‐70 min.

4. Substantially higher quantities of NA were recovered in the perfusion fluid than were lost from the heart after TEA plus stimulation.

5. Reduction in NA content effected by TEA plus stimulation (for 70 min) was not accompanied by any decrease in dopamine‐β‐hydroxylase.

6. After incubation with 6 μ
m‐NA, the normal ventricular portions showed a net accumulation of NA (0·87 μg/g). Tissue NA content was not changed upon incubation with 6 μ
m‐dopamine or 25 μM‐L‐DOPA (L‐3,4‐dihydroxyphenylalanine).

7. Partially depleted stores of ventricular NA (by TEA and stimulation) were restored to a significant extent by exogenous NA, dopamine or L‐DOPA. The process of partial depletion of and repletion with NA was repeated two times in the same tissue. Restoring effects of NA, dopamine and L‐DOPA on the NA stores of the partially depleted ventricle were almost completely blocked by desipramine.

8. Newly retained NA or that synthesized from L‐DOPA in a partially depleted ventricle was released upon electrical stimulation. The release was totally dependent on Ca.

9. The capacity of a partially depleted tissue to take up and retain exogenous NA remained identical to that of a normal ventricle, provided the tissue was stimulated in the presence of TEA for only 10 min rather than for 70 min.

10. Our conclusion is that the functional integrity of the noradrenergic storage vesicles of cardiac sympathetic nerves remains normal after exocytotic release of their transmitter substance. One possibility is that these vesicles can be re‐utilized by the terminal region of the neurone to synthesize, store and release their transmitter substance.
Constrictor actions of acetylcholine, 5‐hydroxytryptamine and histamine on bovine coronary artery inner and outer muscle
Authors: Garland C. J. , Keatinge W. R.
Published: December 2014

1. In bovine coronary arteries, cholinesterase staining showed an extensive cholinergic innervation at the adventitia—media junction, and some cholinesterase in the outer but not inner smooth muscle.

2. Acetylcholine or methacholine caused large, atropine‐sensitive contractions of outer muscle but caused little contraction of inner muscle.

3. Fluorescence microscopy for monoamines and for histamine, supported by chemical assays, showed no adrenergic innervation but showed numerous fluorescent cells in the adventitia and the outer 50% of the media which stained as mast cells and contained large amounts of histamine and noradrenaline and some dopamine, but little 5‐hydroxytryptamine (5‐HT).

4. 5‐hydroxytryptamine (acting by D receptors) and histamine (acting by H1 receptors) in high concentrations caused large contractions, of similar size, in inner and outer muscle. In given submaximal concentrations they generally caused more contraction of outer than inner muscle, particularly in the case of histamine, provided that imipramine or desipramine was present to inhibit uptake of the agents by mast cells which were present in the outer part of the artery wall.

5. Without blockade of uptake, 5‐HT applied to the arteries in submaximal concentrations caused less contraction of outer than inner muscle; histamine still caused significantly more contraction of outer than inner muscle.

6. The findings indicate that the cholinergic constrictor nerves of these arteries, unlike adrenergic constrictor nerves of other systemic arteries, act almost solely on outer muscle of the vessel wall; and that mast cells give considerable protection against constriction by 5‐HT, but little against histamine, reaching the vessel from its adventitial surface.
Adrenal catecholamine output in response to stimulation of the splanchnic nerve in bursts in the conscious calf.
Authors: Edwards A V
Published: December 2014

1. Different patterns of stimulation have been applied to the peripheral end of the right splanchnic nerve, below behavioural threshold, in conscious 2‐5 week‐old calves. 2. The effects of continuous stimulation at 4 Hz for 10 min were compared with those of stimulation at 40 Hz in 1 s bursts at 10 s intervals for the same period. Delivering the same total number of impulses in the form of bursts in this way increased the output of both adrenaline and noradrenaline and this increase was statistically significant in the case of adrenaline (P less than 0.02) but not noradrenaline. 3. The effects of stimulation in 1 s bursts at 10 s intervals for 2‐3 min were investigated over the frequency range 10‐150 Hz and compared with the effects of continuous stimulation over the range 1‐15 Hz obtained previously in conscious calves of the same age (Edwards, Furness and Halle, 1980). The output of adrenaline but not noradrenaline was found to significantly greater in response to stimulation in bursts at frequencies of up to 40 Hz than when the equivalent number of impulses were delivered at a constant rate (P less than 0.02). 4. It is concluded that the release of catecholamines from the adrenal gland is maximal at relatively high frequencies (40‐100 Hz) when the impulses are delivered in bursts.
Modulation of neuromuscular transmission by endogenous and exogenous prostaglandins in the guinea‐pig mesenteric artery
Authors: Kuriyama Hirosi , Makita Yuji
Published: December 2014

1. At concentrations of 2·8 × 10−8‐2·8 × 10−6 M, prostaglandins (PGs; PGE1, PGE2 and PGF2α) had no effect on membrane potential and resistance of smooth muscles of the guinea‐pig mesenteric artery. PGs (2·8 × 10−8 M) suppressed the contraction evoked by perivascular nerve stimulation, but did not suppress the contraction evoked by direct muscle stimulation.

2. PGs (2·8 × 10−8 M) suppressed the e.j.p.s evoked by repetitive perivascular nerve stimulation but preserved the facilitation process of e.j.p.s evoked by any given stimulus frequency (0·1‐1·0 Hz).

3. The relationships between e.j.p. amplitudes and [Ca]o plotted on log scales in the presence or absence of PGE2 were not parallel. High concentrations of [Ca]o prevented the inhibitory actions of PGs on the amplitude of e.j.p.s.

4. PGE2 did not suppress the activity of nerve fibres contributing to the generation of e.j.p.

5. Indomethacin (10−6 M) enhanced the amplitude of e.j.p.s and the frequency of miniature e.j.p.s with no change in the membrane potential and resistance of smooth muscles; these actions of indomethacin were suppressed by PGE2 (2·8 × 10−8 M).

6. Phentolamine (10−7 M) enlarged and yohimbine (10−7 M) reduced the amplitude of the first e.j.p. evoked by a train stimulation, but the maximum amplitude of e.j.p., after the facilitation was completed, was in both cases much larger than that observed in the control. The enhancement of the transmission process was also suppressed by PGs (2·8 × 10−8 M).

7. The results indicate that in the guinea‐pig mesenteric artery, PGs mainly suppress chemical transmitter release from nerve terminals due to interactions with Ca influx, but not due to interaction with presynaptic α‐adrenoceptors. Endogenous PG may act as a regulator substance in neuromuscular transmission.
Ungulate cardiac Purkinje fibres: the influence of intracellular pH on the electrical cell‐to‐cell coupling
Authors: Reber Walter R. , Weingart Robert
Published: December 2014

1. Passive electrical properties of sheep cardiac Purkinje fibres were assessed by performing linear cable analysis. In a separate set of experiments pHi was monitored using recessed‐tip pH‐sensitive micro‐electrodes.

2. In Tris‐buffered Tyrode solution (nominally CO2‐free), the pHi was 7·27, in bicarbonate‐buffered solution equilibrated with 6% CO2, the mean pHi was 7·02.

3. Application of 15 mM‐NH4Cl produced a rapid intracellular alkalinization (0·19 pH units), followed by a slower acidification. Removal of NH4Cl gave rise to a slow and transient intracellular acidification (0·5 pH units).

4. The biphasic and transient shift in pHi, induced by the NH4Cl treatment, was accompanied by a change of the inside longitudinal resistance per unit fibre length, ri, displaying a similar time course. The increase in pHi produced a maximum decrease in ri of 16·4%, while the decrease in pHi yielded a maximum increase in ri of 30·4%.

5. Changing from bicarbonate‐buffered Tyrode solution equilibrated with 6% CO2 to Tris‐buffered Tyrode solution led to an increase in pHi (0·26 pH units). A subsequent change to bicarbonate‐buffered Tyrode solution equilibrated with 15% CO2 produced a decrease in pHi (0·48 pH units). Both changes were sustained.

6. This CO2 protocol gave rise to corresponding changes in ri; the intracellular alkalosis was associated with a decrease in ri (21·2%), and the intracellular acidosis was accompanied by an increase in ri (30%).

7. Based on recent findings showing an interaction between pHi and pCai (Hess & Weingart, 1980), it is concluded that the changes in ri are directly caused by protons and not indirectly via secondary changes of the [Ca2+]i.

8. The pHi‐dependent changes in ri are likely to reflect alterations of the nexal resistance, rn, because the cytoplasmic resistance, rc, has the inverse sensitivity to pHi.

9. Unlike pCai, pHi would seem to be able to modify the cell‐to‐cell coupling by increasing or decreasing ri over a rather narrow range, without ever producing electrical uncoupling.

10. Because of basic differences in the action of calcium and protons on the cell‐to‐cell coupling (magnitude of the effect, operative concentration range), it is tempting to conclude that there is more than one kind of binding site which controls the nexal conductance.
Evidence for a slowly exchangeable pool of calcium in the pancreatic beta cell plasma membrane.
Authors: Gylfe E , Hellman B
Published: December 2014

1. Exposure to media deprived of Ca2+ resulted in prompt and transient stimulation of 45Ca efflux from beta cell‐rich pancreatic islets microdissected from ob/ob‐mice and to some extent also from the isolated neurohypophysis. 2. Particular high efflux rates were reached when the Ca2+‐deficient medium contained EGTA, but there was no effect of the chelator on the total amount of radioactivity mobilized from the islets. 3. The removal of extracellular Ca2+ was less effective in promoting the 45Ca efflux in the absence of Na+ and no stimulatory response was seen in the presence of 1 mM‐La3+. 4. The 45Ca washout was stimulated whether or not the media used for the loading or subsequent perifusion of the islets were supplemented with 20 mM‐D‐glucose. However, there was no response to a second exposure to a Ca2+‐deficient medium even subsequent to redistribution of intracellular calcium induced by temporary lowering of the temperature. 5. It is suggested that the islet 45Ca released by the removal of extracellular Ca2+ originates from a distinct plasma membrane pool which is exchanged slowly compared to most of the calcium at the beta cell periphery.
Passive rubidium fluxes mediated by Na‐K‐ATPase reconstituted into phospholipid vesicles when ATP‐ and phosphate‐free
Authors: Karlish S. J. D. , Stein W. D.
Published: December 2014

1. Phospholipid vesicles reconstituted with Na—K‐ATPase from pig kidney, show slow passive pump‐mediated 86Rb fluxes in the complete absence of ATP and phosphate.

2. The Rb fluxes are inhibited in vesicles prepared from enzyme pre‐treated with either ouabain or vanadate ions. Rb fluxes through Na—K pumps oriented inside‐out or right‐side out by comparison with the normal cellular orientation can be distinguished by effects of vanadate on one or both sides of the vesicle.

3. 86Rb uptake into Rb‐loaded vesicles represents a 86Rb—Rb exchange. The maximal rate of exchange through inside‐out and right‐side out oriented pumps is equal, suggesting a random arrangement of the pumps across the vesicle membrane. This Rb—Rb exchange is half‐saturated on inside‐out and right‐side out pumps at about 0·6 and 0·2 mM‐external Rb respectively.

4. 86Rb uptake into Rb‐free vesicles represents a net Rb flux. The Rb uptake through inside‐out pumps has a maximal rate about equal to the Rb—Rb exchange, half‐saturates at an external Rb concentration of roughly 0·5 mM, and shows evidence for co‐operativity. Net Rb uptake through right‐side out pumps is very slow, and half‐saturates at roughly 0·1 mM external Rb.

5. K ions at low concentrations in the exterior medium stimulate 86Rb uptake, but at high concentrations, inhibit. Na ions in the exterior medium always inhibit 86Rb uptake. The result suggests that K ions are transported in co‐operative fashion together with Rb ions, while Na ions block the Rb fluxes.

6. The presence of Rb congeners at the vesicle interior raises the 86Rb uptake through inside‐out pumps with the decreasing order of effectiveness: Li > Na > Cs > K > Rb. Stimulation by Na ions involves a Rb—Na exchange.

7. Turnover numbers were estimated from parallel measurement of Na/K pump mediated fluxes and amount of covalent phosphoenzyme. In units of moles of ion per mole of phosphoenzyme per second at 20 °C the following values were obtained: ATP‐dependent Na—Rb exchange, 43; (ATP+phosphate)‐stimulated Rb—Rb exchange, 7. For (ATP+phosphate)‐independent fluxes: Rb—Rb exchange 0·25; net Rb uptake 0·15 and Rb—Na exchange 0·65.

8. Mg ions in the exterior medium inhibited both net and exchange Rb fluxes through inside‐out pumps in a manner antagonistic with respect to Rb. Mg and vanadate ions inhibit the Rb fluxes in a synergistic fashion.

9. The results are interpreted in terms of a model in which net and exchange 86Rb fluxes occur via conformational transitions between form E1 which binds Rb at the cytoplasmic face of the protein, the form E2 (Rb)occ containing occluded Rb ions and a form E2 which binds Rb at the extracellular face of the protein. A kinetic analysis allows us to identify rate‐limiting steps of the transport cycle by making use of our transport data in combination with values of rate‐constants for conformational transitions observed directly in isolated Na—K‐ATPase.
The effect of peripheral nerve lesions and of neonatal capsaicin in the rat on primary afferent depolarization
Authors: Wall Patrick D.
Published: December 2014

1. In anaesthetized adult rats with intact peripheral nerves, a conditioning orthodromic volley in myelinated afferents produces a prolonged increase in the excitability of the terminals of the afferents which have carried the orthodromic volley and in the terminals of their passive neighbours. This phenomenon, primary afferent depolarization, p.a.d., is shown by the antidromic stimulation of afferents with a micro‐electrode in the dorsal horn and by recording the antidromic volley on a cut peripheral nerve.

2. If a peripheral nerve is cut and ligated, the size of the myelinated afferent volley generated by stimulation proximal to the cut and measured on dorsal roots is not affected for 14 days after the cut (Wall & Devor, 1981). Similarly the size of the volleys ascending the cord in axons from cord cells remains unaffected.

3. If a peripheral nerve is cut and tested after 7‐14 days, it produces a markedly decreased p.a.d. on itself and on its neighbours.

4. If a nerve is crushed rather than cut, it produces a normal p.a.d. on itself and its neighbours after 7‐14 days.

5. In animals treated neonatally with capsaicin, there is a severe loss of unmyelinated afferents. Testing the effect of an orthodromic volley in myelinated afferents on the excitability of myelinated afferent central terminals shows that there is a strongly decreased p.a.d. in these animals.

6. It is concluded that primary afferent depolarization is sensitive to peripheral nerve lesions and that it may be particularly dependent on the integrity of the unmyelinated afferents in spite of the fact that p.a.d. is measured as a phenomenon of myelinated afferents acting on myelinated afferents.