bluuebunny/crossref_metadata_2025 huggingface dataset:
Action potential duration and the inotropic response to reduced extracellular potassium in guinea‐pig ventricular myocytes
Authors: White E , Terrar DA
Published: December 2014

The mechanism of the inotropic effect of a reduction of extracellular potassium from 5.4 to 2.7 mM was investigated in myocytes isolated from guinea‐pig ventricle. Action potentials were recorded using intracellular microelectrodes and cell shortening was measured by analysis of a video image. Changes in cytosolic calcium transients were estimated from calcium‐activated currents under voltage‐clamp conditions. The aim was to determine whether the prolongation of action potential duration which was observed to occur in low potassium might contribute to the increased shortening and increase in calcium‐activated current under these conditions. Using a voltage‐clamp waveform to mimic the waveform of the action potential, it was found that reduction of potassium caused a marked increase in cell shortening and of calcium‐activated current in the absence of prolongation of the ‘action potential’ waveform. No change in inward calcium current was detected when extracellular potassium was reduced. The sensitivity to strophanthidin appeared to be increased under these conditions. We conclude that prolongation of the action potential is not a major factor contributing to the increased cell shortening and to the increased cytosolic calcium transient when extracellular potassium is reduced.
The effects of feeding diets containing either NaHCO3 or NH4Cl on indices of bone formation and resorption and on mineral balance in the lamb
Authors: Abu Damir H , Scott D , Loveridge N , Buchan W , Milne J
Published: December 2014

The effects of diet‐induced changes in blood acid‐base status on mineral retention has been studied in lambs fed diets containing either 1% NH4Cl or 2% NaHCO3. Balance measurements using 45Ca and 32P showed no difference between them in the amounts of dietary Ca and P absorbed from the gut. Retention of both minerals, however, was lower and their excretion in urine higher in those fed the acid diet. Plasma Ca and P levels were unaffected but parathyroid hormone and 1,25‐dihydroxyvitamin D3 levels were higher in lambs on this diet while measurements of tartrate‐resistant acid phosphatase and alkaline phosphatase levels in rib samples indicated an increase in osteoclast and a reduction in osteoblast activity in these lambs. Cell‐mediated changes in bone turnover together with changes in urinary mineral loss would thus appear to be the major factors contributing to the lower rates of mineral retention seen in lambs fed acid diets.
Glucagon 1‐21 reduces intestinal epithelial cell proliferation in parenterally fed rats
Authors: Goodlad RA , Ghatei MA , Bloom SR , Wright NA
Published: December 2014

The hypothesis that glucagon 1‐21 (G1‐21) is trophic to the gastrointestinal tract was investigated in the hypoplastic intestine of intravenously maintained rats. Three groups of eight rats were fed parenterally for three days and then were infused with either 0, 20 or 80 micrograms rat‐1 day‐1 of G1‐21 for 3 days. No significant effect on the weight of the stomach, caecum or colon was observed, but both the weight and crypt cell production rate of the small intestine were significantly decreased by G1‐21. Plasma enteroglucagon was also decreased by G1‐21 treatment. It is concluded that G1‐21 does not have a trophic effect on the gastrointestinal tract, and, in fact, has an antiproliferative effect on the small intestine, which could in turn be modulated by decreased levels of endogenous enteroglucagon.
Undershoots of intracellular sodium and the strength of contraction when the sodium‐potassium pump of isolated sheep Purkinje fibres is reactivated by potassium
Authors: Levi AJ , Boyett MR
Published: December 2014

We have recorded changes of membrane current, intracellular Na+ activity (aiNa), intracellular pH (pHi) and the strength of contraction in voltage‐clamped sheep Purkinje fibres during and after inhibition of the Na(+)‐K+ pump. The pump was inhibited by the removal of K+ from the bathing solution and this resulted in a rise in aiNa. On return of K+ to the bathing medium to reactivate the Na(+)‐K+ pump there was a fall of aiNa to below its control value after which aiNa slowly returned to its control value over the next 20 min. This ‘undershoot‘ of aiNa was seen in 69% of contracting fibres and 78% of quiescent fibres, and the mean (+/‐ S.D.) values of the undershoot in contracting and quiescent fibres were 0.66 +/‐ 0.15 and 0.9 +/‐ 0.35 mM, respectively. The undershoot of aiNa was observed regardless of whether the Na(+)‐K+ pump was reactivated with Rb+ or K+. It was not voltage dependent over the potential range studied (‐95 to ‐45 mV) and was not accompanied by a change of intracellular pH. The undershoot of aiNa could be the result of a long‐lasting increase in Na+ efflux or a long‐lasting decrease in Na+ influx. Zero [K+]o resulted in the loss of one Na+ current, the pacemaker current i(f), but when K+ was returned to the bathing medium i(f) recovered rapidly and is therefore unlikely to be responsible for the long‐lasting undershoot of aiNa. This conclusion was confirmed by the use of Cs+: although Cs+ blocked i(f), it did not block the undershoot of aiNa. The undershoot of aiNa was accompanied by (and, via Na(+)‐Ca2+ exchange, was presumably the cause of) an undershoot of the force of contraction. Undershoots are not only seen after reactivation of the Na(+)‐K+ pump: in a variety of different preparations, similar undershoots in aiNa and twitch force have been reported after a decrease in the frequency of stimulation. The undershoot of aiNa may be the result of novel feedback mechanism for the control of aiNa: the control of Na+ influx by aiNa.
Variations in [3H]ouabain binding of porcine skeletal muscle associated with feeding
Authors: Dauncey MJ , Burton KA , Morovat A
Published: December 2014

The maximal ouabain binding capacity (Bmax) of longissimus dorsi muscle has been determined over a 24 h period in young pigs living at 12 degrees C. Animals were fed once a day and Bmax was estimated at 4, 8, 12 or 24 h after a large meal. Mean values of Bmax +/‐ S.E.M. (pmol ouabain/g wet wt muscle) of 548 +/‐ 78 and 556 +/‐ 57 at 4 and 24 h after feeding were significantly greater than those of 383 +/‐ 24 and 393 +/‐ 30 at 8 and 12 h after feeding (P less than 0.02). The extent to which these differences represent apparent or real changes in numbers of ouabain binding sites and, hence, in Na+,K(+)‐ATPase concentration is discussed.
Primary culture of collecting duct cell epithelium from neonate rabbit kidney in monolayer
Authors: White S , Reeve H
Published: December 2014

Cortical collecting duct cells from rabbit neonate kidney capsula fibrosa explants were grown in low (0.1%) serum medium on permeable culture supports. We found that over a period of 3–4 days in culture, the cells migrated from the explants, to form monolayers. The cells in monolayer displayed morphology similar to adult collecting duct cells. Approximately 24% of cells grown in monolayer were found to bind a specific beta‐cell‐probe, peanut agglutinin. Single cells were isolated by brief exposure to 0 Ca(2+)−Mg2+ solutions and the whole‐cell clamp technique was used to measure macroscopic currents. The whole‐cell conductance of 1.35 +/− 0.1 nS was reduced to 0.9 +/− 0.2 nS in the presence of 100 microM‐amiloride. We conclude that these cells express cell membrane properties consistent with those of the collecting duct and that it may be a useful model for the study of cellular transport mechanisms and the factors controlling development of collecting duct cell types.
Mechanosensitive cells in the atrium of frog heart
Authors: Kohl P , Kamkin AG , Kiseleva IS , Streubel T
Published: December 2014

Mechanosensitive cells were found in the sinus venosus and right atrium of the frog heart. Their intracellular membrane potentials were studied in spontaneously beating hearts and in artificially stretched preparations. Membrane resistance was indirectly proportional to the stretch applied. The electrophysiological data and distribution of these cells in the heart led to the conclusion that they are cardiac fibroblasts.
An olfactory‐submandibular salivary reflex in humans
Authors: Lee VM , Linden RW
Published: December 2014

In a previous study we concluded that there is no olfactory‐parotid salivary reflex in humans (Lee & Linden, 1991). The present study examines the olfactory‐submandibular salivary reflex. Bilateral submandibular saliva was collected using custom‐made collection devices for each of nine subjects. Salivary flow was measured in response to six appetizing odours: peppermint, vanilla, chocolate, beef, tomato and lemon. A significant increase in salivary flow was seen in response to each. There was no significant response to distilled water. We conclude that an olfactory‐submandibular salivary reflex does exist in humans.
Cholecystokinin‐induced c‐fos expression in the rat brain stem is influenced by vagal nerve integrity
Authors: Fraser KA , Davison JS
Published: December 2014

Exogenous cholecystokinin (CCK) activates brain stem neurons in the area postrema and nucleus of the tractus solitarius, primarily in regions where vagal afferent fibres terminate. The present experiments show that vagal sensory fibres mediate CCK‐induced c‐fos in brain stem neurons, based on the findings that perivagal capsaicin pre‐treatment in seven out of eight cases reduced or ablated c‐fos expression in these regions.
Heart rate changes evoked by hypoxia in the anaesthetized, artificially ventilated cat
Authors: O'Donnell CP , Bower EA
Published: December 2014

Reflex changes in heart rate evoked by hypoxia were investigated in cats anesthetized with chloralose and ventilated by positive pressure during administration of vecuronium or gallamine. In five cats receiving vecuronium and with aortic pressure stabilized, systemic hypoxia (arterial O2 pressure (Pa, O2) 34.9 mmHg) reduced heart rate by 55.8 +/− 7.5 beats min‐1 (mean +/− S.E.M.). After administration of atropine, hypoxia (Pa, O2 32.1 mmHg) increased heart rate by 28.2 +/− 3.4 beats min‐1. After subsequent bilateral ablation of carotid sinus and vagus nerves, hypoxia (Pa, O2 31.9 mmHg) increased heart rate by 7.1 +/− 1.8 beats min‐1. The cardiac accelerator response to hypoxia was further examined in groups of cats treated with gallamine and atropine. In four vagotomized cats, local perfusion of both carotid sinuses with hypoxic blood (Pa, O2 37.7 mmHg) increased heart rate by 15.5 +/− 2.3 beats min‐1. In the same cats, systemic hypoxia (Pa, O2 38.3 mmHg) increased heart rate by 16.4 +/− 2.3 beats min‐1. The heart rate increment in cats which had undergone either bilateral adrenalectomy or cardiac sympathectomy was similar to the increment in unoperated cats. The increment was significantly less in cats which had both adrenal glands and cardiac sympathetic nerves ablated. It is concluded that stimulation of the carotid bodies in the cat excites both parasympathetic and sympathetic cardiac nerves simultaneously.
Inhibition in the rat of nitric oxide synthesis in vivo does not attenuate the hypotensive action of acetylcholine, ATP or bradykinin
Authors: O'Shaughnessy KM , Newman CM , Warren JB
Published: December 2014

The hypotensive action of acetylcholine in vivo may be dependent on the release of the novel vasorelaxant, endothelium‐derived relaxing factor (EDRF)/nitric oxide (NO), by the vascular endothelium. However, using two different inhibitors of NO synthesis, NG‐monomethyl‐L‐arginine (L‐NMMA, 100 mg/kg) and NG‐nitro‐L‐arginine methyl ester (L‐NAME, 100 mg/kg), we have been unable to attenuate the hypotensive action of intravenous (i.v.) boluses of acetylcholine in anesthetized rats. L‐NMMA also failed to alter the hypotensive effect of i.v. bradykinin and adenosine triphosphate (ATP). NO generation by a column of cultured endothelial cells was, however, completely abolished by L‐NMMA. The hypotensive effect of acetylcholine was not affected by glibenclamide at a dose which blocks the effect of i.v. cromakalim, a drug which opens ATP‐sensitive K+ channels. The rapid hypotensive response to i.v. bolus acetylcholine, ATP and bradykinin remains unexplained.
Electrophysiological influences of the parietal cortex and dorso‐medial thalamic nucleus on the prefrontal cortex of the cat
Authors: Criado JM , Fuente AJ , Patino A , Riolobos AS , Yajeya J
Published: December 2014

Lesion studies have shown that the functional integrity of prefrontal and posterior parietal cortex is necessary for complex behavioural performance. Recordings were made from 137 prefrontal cells in awake cats. Parietal cortex stimulation affected fifty‐four cells (39.5%); thirty‐four (63%) increased and twenty (37%) decreased their discharge frequency. Thalamic stimulation affected forty‐seven cells; twenty‐eight increased their discharge and nineteen decreased it. These responses suggest firstly that the organization between parietal and prefrontal cortex is similar to that in monkeys, and secondly that prefrontal cortex has an integrative role.
Prolactin secretion in sheep after dehydration followed by restraint or administration of ovine corticotrophin‐releasing factor
Authors: Matthews SG , Parrott RF
Published: December 2014

Plasma concentrations of prolactin were measured in male sheep (wethers, n = 8) during 120 min exposure to mild physical stress (restraint), and also following I.V. injection of 30 micrograms ovine corticotrophin‐releasing factor (CRF), when the animals were water replete and when they had been deprived of water for 48 h. Restraint stress produced a small increase in prolactin secretion (n.s.) when the animals were euhydrated and a large increase (P less than 0.001) when they were dehydrated. Administration of CRF had no effect on prolactin concentrations in either experimental condition. In a further study in which euhydrated animals (n = 6) were subjected to restraint while receiving infusions of vasopressin (1 microgram/h), there was no enhancement of basal or stress‐induced prolactin secretion. Thus, dehydration enhances stress‐induced prolactin release in sheep through a process that does not involve a pituitary action of CRF or circulating vasopressin.
Influence of short‐chain fatty acids on ammonia absorption across the rumen wall in sheep
Authors: Bodeker D , Shen Y , Kemkowski J , Holler H
Published: December 2014

The effects of short‐chain fatty acids (SCFA) on ammonia net absorption from the sheep rumen in vivo and on ammonia transport across rumen wall mucosa in vitro were studied. Ammonia net absorption was directly, though in a non‐linear manner, correlated with the SCFA concentration in the artificial rumen fluid. Almost 70% of total ammonia absorption was dependent upon the presence of SCFA when 12 mmol l‐1 ammonia and 67.5 mmol l‐1 SCFA were present. Lactic acid was ineffective. Incubation experiments showed that mucosal disappearance and serosal appearance of ammonia were reduced by 38% and 32%, respectively, when SCFA (63 mmol l‐1) were replaced by lactic acid. The SCFA effect was independent of the type of SCFA used. In part of the experiments up to 54% of the ammonia taken up by the tissue was not recovered in the serosal incubation solution and must have been metabolized in the mucosa.
Is there a calcium paradox in isolated bovine aortic endothelial cells?
Authors: Gillespie JI , Johnson C , Nicholls J , Lynch M , Greenwell
Published: December 2014

When bovine aortic endothelial (BAE) cells are superfused with a solution containing low calcium (approximately 10 nM) and subsequently exposed to a solution containing normal Ca2+ (2 mM) a large transient increase in intracellular calcium is seen. This elevation in [Ca2+]i is similar to that described as the calcium paradox in cardiac cells. If the cells are exposed to the agonist, ATP, during the period in low‐Ca2+ solution the paradoxical rise in [Ca2+]i is increased. Removal of external Na+ from the low‐Ca2+ solution reduces the rise in [Ca2+]i on returning to 2mM‐Ca2+ solution. These data are consistent with the presence of a calcium paradox in these cells and with the hypothesis that the underlying mechanism involves the loading of the cell with Na+ during the period in low Ca2+. This process may occur as a result of the altered selectivity of the ATP‐activated Ca2+ influx mechanism.
The effect of tachykinins on sheep bronchomotor tone
Authors: Corcoran BM , Haigh AL
Published: December 2014

The mammalian tachykinin neuropeptides substance P (SP) and neurokinin A (NKA) are present in the airways of several species and are involved in control of bronchomotor tone. We investigated the effect of SP and NKA on various respiratory and cardiovascular parameters in anaesthetized sheep. Dose‐dependent decrease in dynamic compliance (Cdyn) and increase in respiratory resistance (RL) occurred with intravenous administration of SP. The predominant effect of NKA was on Cdyn with little or no effect on RL. Consequently SP is a more potent bronchoconstrictor than NKA in the sheep and affects both central and peripheral airway tone. The sensitivity to SP and NKA and the order of potency found suggests the NK‐1 receptor predominates in sheep airways. Atropine and the ganglion blocker hexamethonium markedly reduced the bronchoconstriction caused by SP. SP and NKA were equipotent in causing a significant reduction in respiratory rate. SP caused a fall in mean blood pressure while NKA caused mild vasoconstriction. Neither peptide affected heart rate. We concluded that SP is a more potent bronchoconstrictor than NKA in the sheep and that the mechanism of action is mainly indirect involving modulation of postganglionic cholinergic nerve endings.
Measurement of intracellular pH in isolated bovine articular chondrocytes
Authors: Wilkins RJ , Hall AC
Published: December 2014

Cartilage is an avascular tissue, the cells of which are exposed to reduced extracellular pH. The synthesis of cartilage matrix by chondrocytes is pH‐sensitive and therefore control of intracellular pH (pHi) is important. We have measured the pHi of chondrocytes in MOPS‐buffered saline (pH 7.4) using the fluorescent dye 2',7'‐bis‐2‐(carboxyethyl)‐5(6)‐carboxyfluorescein. Mean pHi was 7.10 +/‐ 0.04 (+/‐ S.E.M., n = 22), and intracellular buffering power was 30 +/‐ 4 mmol l‐1 (pH unit)‐1 when pHi was displaced over the range 7.4‐7.8 (n = 13). Recovery from acid load was blocked by 100 microM‐ethylisopropylamiloride or by removal of extracellular Na+, indicating that these cells possess the Na(+)‐H+ antiporter.
Evidence for presynaptic depression of monosynaptic excitation in neonatal rat motoneurones by (1S,3S)‐ and (1S,3R)‐ACPD
Authors: Pook PC , Sunter DC , Udvarhelyi PM , Watkins JC
Published: December 2014

Both the (1S,3S) and (1S,3R) stereoisomers of 1‐aminocyclopentane‐1,3‐dicarboxylate (ACPD), but not the (1R,3R) or (1R,3S) isomers, potently depress the fastest (presumed monosynaptic) component of dorsal root‐evoked ventral root potentials in hemisected isolated spinal cord of the newborn rat. This effect is not due to antagonism of known excitatory amino acid (EAA) receptors on motoneurones and may reflect an action of the two ACPD isomers at presynaptic EAA receptors of the L‐2‐amino‐4‐phosphonobutyrate (L‐AP4) type.
The effect of luminal flow in rabbit carotid artery on transmural fluid transport
Authors: Lever MJ , Tarbell JM , Caro CG
Published: December 2014

The steady‐state flow of fluid across the wall of the isolated rabbit common carotid artery has been measured in the presence and absence of flow within the lumen of the vessel. The perfusate solution contained either 10 or 40 mg ml‐1 albumin and transmural flux was measured by monitoring the rate of movement of fluid into a chamber enclosing the artery. Vasomotion was minimized by the inclusion of the vasodilator sodium nitrite in both the perfusate and the outer bathing solution. A relatively slow luminal flow caused a reversible increase in the transmural flux by 20‐30% relative to the value in the absence of flow. The mechanism responsible for the increase is not clear, but since it was not affected by the H1 antagonist, mepyramine, it would not appear to have been mediated by histamine release.
Cholinergic mechanisms for secretin release after intraduodenal alkalinization in the anaesthetized rabbit
Authors: Garcia LJ , Montero A , Minguela A , Calvo JJ , Lopez MA
Published: December 2014

Exocrine pancreatic response to duodenal perfusion with alkaline solutions (pH 11.4) was studied in the anaesthetized rabbit; secretin and vasoactive intestinal polypeptide (VIP) levels in portal plasma were measured and the contribution of cholinergic mechanisms was also evaluated. Intraduodenal perfusion of sodium carbonate stimulated flow rate and bicarbonate output to a maximum of 322 +/− 44 and 609 +/− 105% respectively compared with basal levels. Significant increases of plasma secretin levels, with a maximum of 267 +/− 38% as compared with basal, were also observed. A lower increase in VIP levels (maximum of 151 +/− 12%) was seen. All these effects, except the VIP response, were substantially inhibited by atropine. Our results show that exocrine pancreatic response to intraduodenal sodium carbonate is specifically focused on hydroelectrolytic secretion. Keeping in mind what occurs after intraduodenal alkaline phosphate buffer administration (at the same pH as sodium carbonate: 11.4) it seems that about 50% of the pancreatic response to sodium carbonate may be ascribed to pH and the remaining 50% to the carbonate anion. Moreover, this response would mainly be mediated by secretin, whose release can be facilitated by a cholinergic reflex.
Effects of the beta‐adrenergic agonist, ritodrine, and insulin on plasma potassium concentrations in fetal lambs
Authors: Bassett JM , Bomford J , Hanson C , Mott JC , Weeding CM
Published: December 2014

Prolonged infusion of the beta 2‐adrenergic agonist, ritodrine, into sheep during late pregnancy decreased maternal plasma K+ from 3.6 to 2.5 mmol l‐1 during the first 6‐8 h of infusion, as it does during tocolysis in women. This decrease was not accompanied by significant change in fetal plasma K+ concentration. Ritodrine infusion (1‐3.5 micrograms kg‐1 min‐1) directly into the fetus also did not decrease fetal plasma K+ significantly. In contrast, insulin (2.5 mU kg‐1 min‐1), infused together with glucose (3.6 mg kg‐1 min‐1) directly into the fetus decreased fetal plasma K+ concentration by 0.8 mmol l‐1 within 1 h. The results suggest immaturity in beta 2‐adrenergic receptor regulation of electrogenic K+ uptake by muscle in fetal lambs.
Intracellular sodium and potassium activities of skeletal muscle fibres of hypothyroid rats
Authors: MacDermott M
Published: December 2014

In soleus muscle fibres of hypothyroid rats, the membrane potential (Vm) and the intracellular K+ activity (aKi) were significantly lower than in control muscles. These results are consistent with the well‐documented decrease in the number of Na(+)‐K+ pumps which occurs in hypothyroid muscles. aNai was unchanged in the hypothyroid muscles but this may reflect a change in passive Na+ fluxes which has been reported to occur in association with changes in the number of pump units.
Effect of intraduodenal HCl and soybean extract on pancreatic juice secretion during atropinization and cold vagal blockade in calves
Authors: Zabielski R , Kato S , Pierzynowski SG , Mineo H , Podgurniak P , Barej W
Published: December 2014

In order to elucidate the mechanisms by which intraduodenal hydrochloric acid (HCl) and soybean extract influence exocrine pancreatic secretion in the young ruminant, we conducted experiments repeatedly on six conscious calves with and without blockade of the extrinsic and intrinsic neural pathways. In the absence of blockade, each of the two stimuli increased the juice volume, the HCl effect being far stronger than that of soybean extract. Intrinsic cholinergic blockade by atropinization blocked the stimulatory work of soybean extract on pancreatic secretion and on HCl‐stimulated protein but had a weak effect on the amount of juice evoked by HCl. Temporary vagal blockade by chilling virtually abolished the excitatory effects of both soybean extract and HCl. With or without blockade, duodenal HCl resulted in a noteworthy increase in plasmal secretin and a slight increase in cholecystokinin (CCK). With alimentary proteins, acidification of the duodenum was responsible for both the composition and secretion of pancreatic juice in young calves, generally via neural pathways. Atropine‐sensitive nerves of the pancreas totally regulate the intestinal phase of pancreatic juice secretion allied with intraduodenal protein, whereas HCl‐dependent excitation of the exocrine pancreas takes place partly via atropine‐resistant nerves. However, as hardly any pancreatic juice was secreted independently of the vagi, the vagi are deemed to govern all the postprandial regulatory mechanisms of the exocrine pancreas in the young calf.
Effect of stage of lactation and milk accumulation on mammary cell differentiation in lactating bats
Authors: Wilde CJ , Kerr MA , Knight CH , Racey PA , Burnett A
Published: December 2014

Mammary cell differentiation was measured in lactating pipistrelle bats (Pipistrellus pipistrellus) by assay of key enzyme activities, and by determination of protein and lactose synthesis rates in short‐term tissue cultures. By these criteria, mammary cell differentiation did not change significantly with stage of lactation, but depended on the extent to which the gland was filled with milk. Key enzyme activities and in vitro synthesis rates were significantly higher in glands suckled immediately before tissue collection, compared with contralateral glands that were engorged with milk. This indicates that mammary cell differentiation in the lactating bat is regulated locally within each gland by a mechanism sensitive to milk accumulation, to the extent that, unlike other species, this obscures any underlying effect of stage of lactation.
FMRFamide‐related peptides potentiate transmission at the squid giant synapse
Authors: Cottrell GA , Lin JW , Llinas R , Price DA , Sugimori M , Stanley EF
Published: December 2014

The stellate ganglion of the squid Loligo pealli contains the neuropeptides Phe‐Met‐Arg‐Phe‐NH2 (FMRFamide), Phe‐Leu‐Arg‐Phe‐NH2 (FLRFamide) and at least one N‐terminally extended FMRFamide‐related peptide that is yet to be fully characterized. Both local application and arterial perfusion of FLRFamide potentiate transmission at the giant synapse. The N‐terminally related peptide Ser‐Asp‐Pro‐Phe‐Leu‐Arg‐Phe‐NH2 (SDPFLRFamide) produced a similar effect. The threshold for both the tetra‐ and the hepta‐peptides was less than 10 microM. Potentiation could be detected as an increase in rate of rise of the EPSPs, as an increase in amplitude of the EPSP in the absence of spikes, or under voltage clamp as an increase in the EPSC. The effect was most pronounced when the synapse was fatigued by high frequency stimulation. Another molluscan peptide, eledoisin and also leucine enkephalin were without effect. In the absence of any detectable effects of FLRFamide on the resting membrane potential of either pre‐ or postsynaptic terminals or on the presynaptic spike, it is suggested that the peptide influences transmitter mobilization. However, the peptide could also exert small changes in preterminal calcium currents, which so far we have been unable to detect.
Cytoplasmic bridges and gap junctions in an insect cell line (Aedes albopictus)
Authors: Bukauskas FF , Kempf C , Weingart R
Published: December 2014

Cell pairs of an insect cell line (Aedes albopictus, clone C6/36) were used study simultaneously the diffusional and electrical properties of intercellular junctions. Diffusion studies involved injection of fluorescent molecules into one cell of a cell pair and visual inspection of their intercellular redistribution. Electrical measurements involved a dual voltage clamp method and whole‐cell recording with patch pipette. The voltage clamp protocol was aimed at examining the dependency of the junctional conductance, gj, on membrane potential, Vm. Cell pairs exhibiting a voltage‐dependent gj were found to allow intercellular diffusion of Lucifer Yellow CH (molecular mass, 443 Da), but not of FITC‐dextran (molecular mass, 4,400 Da). This response pattern is consistent with the presence of gap junctions in the intercellular junctions. Cell pairs showing no voltage dependence of gj were found to permit intercellular diffusion of both Lucifer Yellow CH and FITC‐dextran (dextran labelled with fluorescein isothiocyanate). This behaviour is compatible with the presence of cytoplasmic bridges connecting the two adjacent cells. Hence, in culture the cells investigated express two kinds of intercellular structures, gap junctions and cytoplasmic bridges.
Evidence for a possible role of 5‐hydroxytryptamine in the genesis of fatigue in man: administration of paroxetine, a 5‐HT re‐uptake inhibitor, reduces the capacity to perform prolonged exercise
Authors: Wilson WM , Maughan RJ
Published: December 2014

Seven healthy subjects exercised to exhaustion on a bicycle ergometer at a power output corresponding to 70% of maximum oxygen uptake after administration of either a placebo or 20 mg of paroxetine, a serotonin re‐uptake inhibitor. Exercise time after paroxetine (median 94 min; range 84‐127 min) was less (P < 0.05) than after placebo (median 116 min; range 86‐133 min). The metabolic and cardiorespiratory responses to exercise were the same in both trials. This result supports the suggestion that there is a central component to fatigue which is mediated by the activity of serotoninergic neurones.
Phase‐dependent properties of the cardiac sarcoplasmic reticulum oscillator in cat right atrium: a mechanism contributing to dysrhythmias induced by Ca2+ overload
Authors: Rubenstein DS , Zbilut JP , Webber CL  , Lipsius SL
Published: December 2014

These experiments analyse the phase‐dependent properties of spontaneous oscillations of the sarcoplasmic reticulum (SR) induced by Ca2+ overload. Right atrial tissue was loaded with intracellular Ca2+ by exposure to a modified Tyrode solution containing 50% of normal Na+ and 0.5 mM K+. Verapamil (2 microM) was added to block regenerative activity. Intracellular Ca2+ overload elicited spontaneous, rhythmic voltage and tension oscillations that were phase locked 1:1. Voltage and tension oscillations were abolished by exposure to low (0.9 mM) external Ca2+, 1 microM ryanodine, or 10 mM caffeine, indicating that both voltage and tension oscillations resulted from spontaneous oscillations in SR Ca2+ release. Single pulses of nerve‐stimulated ACh release elicited phase shifts in both voltage and tension oscillations. Sinusoidal current was used as a periodic stimulus to drive membrane voltage and elicit periodic voltage oscillations. Stimulated voltage oscillations entrained spontaneous tension oscillations 1:1 in a range of frequencies close to the basic spontaneous SR oscillatory cycle length, or 2:1 at frequencies close to one‐half the spontaneous SR oscillatory cycle length. Stimulation frequencies between these two regions entrained tension oscillations in predictable fixed coupled ratios (4:3, 3:2) and resulted in Wenckeback‐like voltage patterns. Stimulation frequencies between phase‐locked regions resulted in complex coupling relationships and irregular voltage patterns. Exposure to 1 microM ryanodine, 0.9 mM external Ca2+, or 10 mM caffeine abolished irregular voltage patterns and tension. We conclude that the SR oscillator exhibits phase‐dependent sensitivity to perturbations at the surface membrane. As a result, external perturbations can elicit phase differences between spontaneous SR oscillations and membrane voltage that cause either phase‐locked or irregular voltage patterns. These findings identify an intracellular mechanism that may contribute to the development of cardiac dysrhythmias resulting from intracellular Ca2+ overload.
The regulation of intracellular Mg2+ in guinea‐pig heart, studied with Mg(2+)‐selective microelectrodes and fluorochromes
Authors: Buri A , Chen S , Fry CH , Illner H , Kickenweiz E , McGuigan JA , Noble D , Powell T , Twist VW
Published: December 2014

Because of the reported presence of a Na(+)−Mg2+ exchanger in guinea‐pig but not in ferret myocardium, the Mg2+ extrusion mechanism in guinea‐pig myocardium has been reinvestigated using Mg(2+)‐ and Na(+)− selective microelectrodes and the fluorochromes mag‐fura‐2 and ‐5. The mean [Mg2+]i measured with microelectrodes in trabeculae or papillary muscles was 0.72 mmol/l (n = 22, thirteen experiments; range 0.42‐1.23 mmol/l). Increasing [Mg2+]o from 0.5 mmol/l to either 10.5 or 20 mmol/l caused small increases in [Mg2+]i. Decreasing [Na+]o by 50% had no effect on the [Mg2+]i and there was no change in [Na+]i on increasing [Mg2+]o from 0.5 to 10.5 mmol/l. Varying pHo or changing pHi with NH4Cl did not influence the [Mg2+]i. In vitro calibration of mag‐fura‐2 and ‐5 using the ratio method gave values for K'd (experimentally determined dissociation constant) of 22.2 +/− 2.7 (mean +/− S.D., n = 7) and 25.7 +/− 1.3 (n = 4) mmol/l respectively. Mag‐fura‐2 reacted to physiological concentrations of Ca2+ and mag‐fura‐5 to changes in pH. In isolated myocytes, Na+ removal gave an apparent increase of [Mg2+]i with mag‐fura‐2 but not with mag‐fura‐5. However, when the pHi was altered with NH4Cl mag‐fura‐5 showed an apparent decrease in [Mg2+]i on application and an apparent increase on removal, with a time course similar to the pHi changes. It is concluded that Mg2+ extrusion in guinea‐pig myocardium is not via a Na(+)−Mg2+ exchanger. The use of mag‐fura‐2 and ‐5 are limited in their application because of Ca2+ and H+ sensitivity respectively.
Na(+)−H+ exchanger in isolated epithelial tracheal cells from sheep. Involvement in tracheal proton secretion
Authors: Acevedo M , Steele LW
Published: December 2014

The presence of a Na(+)−H+ exchanger in isolated tracheal epithelial cells has been tested. Sodium uptake in tracheocytes was found to increase when the intracellular medium was made acidic. Micromolar 5‐(N‐ethyl‐N‐isopropyl) amiloride (EIPA) concentrations reduced the sodium uptake in acidified cells. Intracellular pH was studied using the fluorescent indicator, 2',7'‐bis‐(2‐carboxyethyl)‐5‐(and‐6)‐carboxyfluorescein (BCECF). The rate of recovery from an acidifying pulse was partially dependent on the presence of extracellular sodium. EIPA decreased the initial rate of pH recovery from acidification in the presence but not in the absence of external sodium. These results suggest the existence of a Na(+)−H+ exchanger in sheep tracheocytes, and of some other Na(+)−independent proton extruding mechanism(s). Proton secretion into the tracheal lumen was studied in whole tracheae bathed in bicarbonate‐free solutions by a 'pH stat' technique. The rate of proton secretion was significantly decreased by the addition of EIPA to the luminal solution, suggesting the involvement of an apically located Na(+)−H+ exchanger in proton secretion in sheep trachea.
The role of adenosine in hypoxic pulmonary vasoconstriction in the anaesthetized rat
Authors: Thomas T , Marshall JM
Published: December 2014

In nine artificially ventilated rats anaesthetized with Saffan, systemic hypoxia induced a tachycardia followed by a bradycardia, a fall in systemic arterial pressure and an increase in pulmonary artery pressure (PPA) indicating pulmonary vasoconstriction. This increase in PPA was abolished by the adenosine receptor antagonist 8‐phenyltheophylline (8‐PT, 10 mg kg‐1 I.V.). Further, in seven rats the Pa,O2 achieved during hypoxia was greater after 8‐PT than before (38 vs. 40 mmHg). We suggest that adenosine makes a major contribution to hypoxia‐induced pulmonary vasoconstriction in the rat. The better maintenance of Pa,O2 during hypoxia may reflect improved perfusion of well‐ventilated alveoli.
Potassium loss from skeletal muscle during exercise in man: a radioisotope study
Authors: Qayyum MS , Freemantle CA , Carey CJ , Page BC , Soper N , Paterson DJ , Robbins PA
Published: December 2014

Muscle potassium (K+) content decreases during exercise. Previous studies, in humans, have used measurements of arteriovenous plasma potassium concentration differences (AV delta[K+]) and/or muscle biopsy to measure the loss of muscle K+ during exercise. In the current study a non‐invasive method was developed to measure skeletal muscle K+ before and after exercise, using an isotope of K+, potassium‐43 (43K+). Twelve subjects performed single‐leg extension exercise for 2 h at 50% of their maximum predicted heart rate. The level of radioactivity from the quadriceps femoris was determined before exercise and during two periods post‐exercise. After correction for counts arising outside the exercised muscle, we estimate a decrease in muscle K+ content of 3.2 +/− 1.55% (mean +/− S.E.M.) following exercise. The muscle K+ was not restored following 75 min of recovery. The decrease in muscle K+ following exercise in our study is considerably less than that suggested by previous studies using AV delta[K+] measurements but not so dissimilar from results obtained using muscle biopsy. We conclude that a small but significant loss of K+ occurs following prolonged dynamic exercise, and that complete recovery of muscle K+ is slow.
Periodic fluctuations in pancreatic secretion and duodenal motility investigated in neonatal calves
Authors: Zabielski R , Onaga T , Mineo H , Kato S
Published: December 2014

To clarify the relative timing of clinical changes in duodenal motility and pancreatic secretion in newborn calves, we recorded duodenal electrical and mechanical activity and analysed pancreatic secretion and migrating myoelectric complex (MMC). In eight calves integrated recordings were derived from sites near the duodenal bulb and pancreatic accessory duct orifice, and pancreatic juice was sampled after an overnight fast, after a feed, and during reversible cold vagal blockade. Peak secretion coincided with duodenal irregular spiking activity and the nadir with absence of spiking. Feeding elicited electrical and mechanical hyperactivity in the duodenum, dissipated the MMC temporarily, and dramatically increased the juice volume and bicarbonate and protein outputs. Periodic fluctuations in secretion started shortly after a feed, as did recovery of the duodenal myoelectric complexes. Cold vagal blockade reversibly disrupted the synchronous changes in duodenal motility and pancreatic secretory activity, though the close association was not totally obliterated. In milk‐fed calves interdigestive pancreatic secretion apparently rises and falls in phase with migrating myoelectric complexes of the proximal duodenum and the vagus is largely, though not exclusively, responsible for co‐ordinating these changes.
Volume‐sensitive KCl co‐transport and taurine fluxes in horse red blood cells
Authors: Gibson JS , Ellory JC , Culliford SJ , Fincham DA
Published: December 2014

Potassium (using 86Rb+ as a tracer), amino acid and taurine fluxes were measured in horse red blood cells (RBCs). No volume‐sensitive component of alanine and glycine transport was observed, and although volume‐sensitive taurine fluxes were observed in most animals, their absolute magnitudes were small. K+ fluxes, however, were shown to be particularly volume sensitive; they were stimulated by cell swelling and inhibited by cell shrinkage. Sizeable fluxes were present at normal cell volumes. The volume‐sensitive K+ flux was Cl‐ dependent and was abolished by Cl‐ replacement with methylsulphate. The Cl(−)‐dependent K+ fluxes in horse red blood cells were stimulated by lowering in external pH to 6.9 and by treatment with the sulphydryl‐reacting agent, N‐ethylmaleimide. They were inhibited by the potent K(+)‐Cl‐ co‐transport inhibitor, DIOA, ([(dihydroindenyl)oxy]alkanoic acid) but were insensitive to the Na(+)‐K(+)‐Cl‐ co‐transport inhibitors, frusemide and bumetanide. A Cl‐ channel inhibitor, 5‐nitro‐2‐(phenylpropyl‐amino)‐benzoate (NPPB), produced partial inhibition. These results suggest that regulatory volume decrease in horse red blood cells is achieved predominantly by volume‐sensitive K+ efflux mediated via a K(+)‐Cl‐ co‐transport system with similar properties to those observed in the red blood cells of other species. The significance of these findings and their rheological consequences are discussed.
Measurements of intracellular Ca2+ in cultured human myometrial smooth muscle cells bathed in low Na+ solutions
Authors: Morgan JM , Lynn S , Gillespie JI , Greenwell
Published: December 2014

In cultured human myometrial smooth muscle cells, removal of external Na+ activates repetitive increases in intracellular Ca2+ ([Ca2+]i). The Ca2+ transients persist in isotonic K+ solutions which suggests that the activity does not arise from regenerative changes in membrane potential. In nominally Ca(2+)‐free solution, the activity disappears after a few cycles suggesting the involvement of internal stores. On Na+ removal, a background influx of Ca2+ may be responsible for activating the cyclical release of Ca2+ from internal stores. The absence of any effect of caffeine on resting [Ca2+]i suggests that the classical cardiac type of Ca(2+)‐induced‐Ca(2+)‐release mechanism is not operating in these cells.
The neuropeptide Phe‐Met‐Arg‐Phe‐NH2 (FMRFamide) increases levels of inositol 1,4,5‐trisphosphate in the tentacle retractor muscle of Helix aspersa
Authors: Falconer SW , Carter AN , Downes CP , Cottrell GA
Published: December 2014

The C3 neurone, which acts as a motoneurone for the tentacle retractor muscle in Helix aspersa, contains both Phe‐Met‐Arg‐Phe‐NH2 (FMRFamide) and acetylcholine (ACh). Each of these transmitter substances evokes contraction of the isolated muscle. FMRFamide induces a delayed rise in tension followed by phasic contractions. Unlike the response to ACh, this response is not associated with a depolarization of the muscle cells. Here we show that FMRFamide stimulates the inositol phosphate second messenger system in the muscle and causes a significant increase in total inositol trisphosphate (InsP3) levels. The isomer which releases intracellular Ca2+ stores, inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3), is increased in a similar proportion to the total InsP3. The production of Ins(1,4,5)P3 is therefore likely to be involved in the response of the muscle to FMRFamide and may account for the oscillatory nature of the mechanical response. The N‐terminally extended heptapeptide pGlu‐Asp‐Pro‐Phe‐Leu‐Arg‐Phe‐NH2 (pQDPFLRFamide), which relaxes the muscle, had no acute effect on InsP3 levels. Indirect evidence also indicates that intracellular Ca2+ stores are required for the generation of the FMRFamide response.
Carbon dioxide‐sensitive superior laryngeal nerve afferents in the anaesthetized cat
Authors: Bradford A , Nolan P , O'Regan RG , McKeogh D
Published: December 2014

The effects of CO2 on laryngeal receptors were studied in ten anaesthetized, paralysed, artificially ventilated cats using a preparation in which the upper airway was isolated in situ and artificially ventilated. This allowed CO2 to be confined to the upper airway and enabled responses to CO2 to be recorded whilst the larynx was being ventilated under physiological conditions. Single‐unit afferent activity was recorded from the superior laryngeal nerve and the pressure and thermal sensitivity of receptors determined. Carbon dioxide responses were tested by switching from upper airway ventilation with room air to mixtures containing 5 and 9% CO2 with 21% O2 in N2. Fibres were classified into two broad groups, tonic and quiescent, depending on their level of activity when the larynx was not being ventilated. All tonic fibres responded to either positive or negative pressure. Quiescent fibres were either positive or negative pressure receptors, cold receptors or had no response to pressure or cold airflow. The majority of all categories of fibres were significantly affected by CO2 in a reversible and usually concentration‐dependent manner. Tonic fibres were inhibited, regardless of pressure sensitivity. Quiescent negative and positive pressure receptors were excited and inhibited respectively whilst cold receptors and fibres with no response to occlusion were excited. Laryngeal hypoxia and systemic asphyxia and hypercapnia had no effect on receptor activity. We conclude that the majority of laryngeal receptors are sensitive to CO2 and that this receptivity may be important in the control of ventilation and upper airway muscle activity.
Correlation between spontaneous bursts of activity recorded from the dorsal roots in an isolated hamster spinal cord preparation
Authors: Chen Y , Bagust J , Kerkut GA , Tyler AW
Published: December 2014

At a temperature of 25‐27 degrees C spontaneous antidromic activity has been demonstrated in lumbar and thoracic dorsal roots of an isolated spinal cord preparation taken from the golden hamster. A characteristic pattern of bursts of action potentials has been identified, which develops within 1‐2 h following dissection and persists for more than 8 h. Simultaneous recordings made from pairs of dorsal roots have revealed correlations between the patterns of spontaneous activity in dorsal roots separated by up to sixteen segments longitudinally and across the cord. The strongest correlations were found between pairs of adjacent roots on the same side of the cord which produced a cross‐correlation histogram having a single peak with a mode close to 0 ms. As the separation between the roots was increased the cross‐correlation histogram became bimodal, with peaks equidistant on either side of 0 ms. Activity recorded in ipsilateral and contralateral pairs of roots supplying the same spinal segment also produced bimodal cross‐correlation histograms. Transverse sectioning of the cord did not abolish spontaneous activity in any of the spinal roots examined, although there was a progressive reduction in the frequency of the bursts of spontaneous activity with shorter lengths of cord. These results suggest that each spinal segment is capable of generating spontaneous activity, and that there is a system by which adjacent segments are linked, allowing the activity to spread up and down the cord from the point of origin. The networks associated with the spread of dorsal root activity and primary afferent depolarization (PAD) in the spinal cord are discussed.
Activity of inspiratory neurones of the ambiguus complex during cough in the spontaneously breathing decerebrate cat
Authors: Dawid‐Milner MS , Lara JP , Milan A , Gonzalez‐Baron S
Published: December 2014

In spontaneously breathing, decerebrate cats, extracellular recordings in the intermediate region of the ambiguus complex have been used to characterize the activity of inspiratory laryngeal motoneurones (ILMNs) during mechanical stimulation of tracheal irritant receptors. Laryngeal resistance was measured using an isolated larynx in situ. The effect of tracheal stimulation was analysed successfully in twenty‐seven neurones. Eleven were ILMNs and sixteen inspiration‐related neurones. Inspiration‐related neurones increased their phasic discharge frequency during tracheal stimulation while ILMNs fired tonically, during both the inspiratory and the expiratory efforts of the cough. The tonic discharge of ILMNs coincided with a decrease of laryngeal resistance.