bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of intraluminal flow rate on glomerulotubular balance in the proximal tubule of the rat kidney
Authors: Romano G , Favret G , Federico E , Bartoli E
Published: December 2014

To differentiate intraluminal from peritubular factors in mediating the glomerulotubular balance, single nephron filtration rate (SNGFR) and reabsorption were measured by total collection from the last proximal segment before, and during, externally applied mechanical compression of an early proximal convolution of ninety‐three rat nephrons. SNGFR fell from 55.6 +/− 2.3 nl min‐1 during control conditions to 34.5 +/− 2.0 nl min‐1 during compression (P < 0.0001) in sixty tubules (‘responders’). Absolute reabsorption fell from 41.8 +/− 2.0 to 28.4 +/− 1.8 nl min‐1 (P < 0.0001), while percentage reabsorption rose from 75 +/− 2 to 82 +/𠈒 2% (P < 0.0001). These effects were reversible and independent of whether the compression was applied before or after the control collection. In thirty‐three proximal tubules the compression procedure was not successful (‘non‐responders’), SNGFR remaining unchanged (36.1 +/− 2.9 vs. 36.9 +/− 2.9 nl min‐1, P > 0.3). Absolute and percentage reabsorptions rose slightly, albeit significantly, from 26.1 +/− 2.1 to 30.7 +/− 2.4 nl min‐1 (P < 0.0001) and from 75 +/− 3 to 85 +/− 2% (P < 0.0001). Thus, the response of reabsorption to changes in intraluminal flow is composed of two different adaptive mechanisms. The slowing of flow is present in both sets of tubules and causes a slight increase in resorption; the change in filtration per se is present only in the first set of responders, and causes an SNGFR‐dependent consensual change in resorption.
The effect of taurine on the activation osmolality of the osmosensitive current in single ventricular myocytes of rabbits
Authors: Leem CH , Ho WK , Earm YE
Published: December 2014

An osmosensitive current was identified in rabbit ventricular cells and the effects of taurine on osmotic stress were examined. The osmosensitive current was measured with the whole‐cell patch clamp technique and all known currents were blocked using Ba2+, Cd2+, Ni2+, diltiazem, ouabain, Cs+ and tetraethyl ammonium. When hyposmotic solution (200 mosmol/kg) was applied, the background current increased gradually. This osmosensitive current was dependent on Cl‐. When the conductance of the activated current reached three times the control conductance, the osmolality was arbitrarily named the activation osmolality. The activation osmolality was regarded as an indication of cell volume expansion. With 20 mM taurine in the pipette solution, the activation osmolality was lowered significantly. With high [Na+] (32.5 mM) in the pipette solution, the effect of taurine in reducing the activation osmolality was larger than that in low [Na+] (2.5 mM). From these results, we conclude that taurine reduces the activation osmolality and this effect is more pronounced in the presence of high [Na+] in the pipette solution. It is suggested that Na+−dependent taurine transport could be involved in reducing osmotic stress.
Intrinsic hydrogen ion buffering in rat CNS neurones maintained in culture
Authors: Amos BJ , Richards CD
Published: December 2014

The intrinsic proton buffering power (beta 1) of individual rat hippocampal and neocortical neurones maintained in culture has been investigated using the fluorescent dye 2', 7'‐bis(carboxymethyl)‐5, 6‐(carboxyfluorescein) (BCECF). The steady‐state intracellular pH (pH1) was estimated to be 7.03 +/− 0.04 (n = 22) in Hepes‐buffered media and beta 1 estimated from the addition and removal of weak bases was ca 10 mM (pH unit)‐1 at pH1 values near to 7. Estimates of beta 1 made from butyric acid challenges were inconsistent with estimates made at the same pH1, using NH4Cl withdrawal. However, estimating beta 1 with butyrate in the presence of the monocarboxylate ion transport inhibitor alpha‐cyano‐hydroxy‐cinnamate (CHC) yielded beta 1 values commensurate with those measured using NH4Cl. Application of CHC alone lead to a rapid fall in pH1, suggesting a significant contribution of the monocarboxylate transporter to pH1 regulation. beta 1 was also estimated from a step increase in extracellular P(CO2). This yielded a value of 11 mM at an average pH1 of 7.1, which is similar to that of the other estimates reported here. beta 1 was found to increase with decreasing pH1: each unit drop in pH1 increased buffering power by about 60%. Blockade of pH1 regulation did not significantly affect estimates of beta 1. The change in buffering power with pH could be closely modelled from the known concentrations of free amino acids and organic phosphates.
Nitric oxide and release of the peptide VIP from parasympathetic terminals in the submandibular gland of the anaesthetized cat
Authors: Edwards AV , Tobin G , Ekstrom J , Bloom SR
Published: December 2014

The role of nitric oxide (NO) in mediating various submandibular responses to stimulation of the parasympathetic innervation has been investigated in anaesthetized cats, in which N omega‐nitro‐L‐arginine methyl ester (L‐NAME; 30 mg kg‐1 I.A.) was used to block the synthesis of NO. L‐NAME significantly reduced the vasodilator response and the flow of saliva, together with the output of salivary protein that occurred during stimulation of the chorda lingual nerve (20 Hz for 1 s at 10 s intervals), without significantly reducing the output of vasoactive intestinal peptide (VIP) from the gland. The results show that NO is implicated not only in the release of VIP, as established previously, but also in mediating its actions following release in the submandibular gland of the cat.
Cholecystokinin‐8 and vasoactive intestinal polypeptide stimulate exocrine pancreatic secretion via duodenally mediated mechanisms in the conscious pig
Authors: Kiela P , Zabielski R , Podgurniak P , Midura M , Barej W , Gregory P , Pierzynowski SG
Published: December 2014

The effects of local and peripheral administration of cholecystokinin‐8 (CCK‐8) and vasoactive intestinal polypeptide (VIP) on basal pancreatic secretion were investigated in conscious pigs. Five pigs (20 +/− 2 kg, mean +/− S.E.M.) were chronically fitted with a T‐shaped cannula in the duodenum, and catheters in the pancreatic duct, jugular vein, and right gastroepiploic artery. The arterial catheter was inserted against the bloodstream with its tip opposite the duodenal branch(es) of the right gastroepiploic artery, so that all injected peptides would reach the duodenal arterial circulation excluding the pancreas. Pancreatic secretion during basal conditions (i.e. after an overnight fast) exhibited a characteristic cyclic pattern (cycle duration, 70 +/− 4.2 min). Secretion volume oscillated between 0.2 +/− 0.04 and 4.0 +/− 0.9 ml kg‐1 h‐1 (P < 0.001), trypsin output between 9.6 +/− 1.9 and 29.1 +/− 4.1 U kg‐1 h‐1 (P < 0.001) and protein output between 0.36 +/− 0.08 and 9.2 +/Ȓ 1.7 mg kg‐1 h‐1 (P < 0.001). Infusion into the jugular vein for 1 min, during the trough of pancreatic secretion, of either CCK‐8 (15 pmol kg‐1 min‐1) or VIP (7 pmol kg‐1 min‐1) did not stimulate pancreatic secretion. However, local infusion of an identical dose of CCK‐8 or VIP into the duodenal arterial circulation increased the volume, protein output and trypsin output of the pancreatic juice (P < 0.05 to < 0.001). These results indicate that CCK‐8 and VIP can stimulate the exocrine pancreas by a duodenally mediated mechanism.
Reflex vascular responses from aortic arch, carotid sinus and coronary baroreceptors in the anaesthetized dog
Authors: McMahon NC , Drinkhill MJ , Hainsworth R
Published: December 2014

In chloralose‐anaesthetized dogs, pressure applied to coronary, carotid and aortic baroreceptors were changed independently and the resulting reflex vascular responses were determined. Increases in pressure to each group of baroreceptors resulted in reflex vasodilatation; the maximal responses to distension of carotid and coronary baroreceptors were significantly larger than those to aortic receptors, but not different from each other. Increases in pressure in all three regions induced maximal responses at similar times from the onset of the pressure stimulus. However, the time for recovery of vascular resistance following a decrease in baroreceptor pressure differed. Vasoconstriction following a period of coronary hypertension occurred slowly, requiring 70 s for 90% of the response to develop. This was significantly longer than the corresponding times for carotid and aortic receptors (about 28 s). The rate of vasoconstriction in response to coronary baroreceptor unloading was influenced by the period for which the pressure stimulus was applied and vasoconstriction was even slower when the pressure stimulus had been maintained for 8 min. The mechanism responsible for delaying the vasoconstriction following a period of coronary hypertension is not known, but this effect may have important implications for the control of arterial blood pressure.
A dopamine transporter in human erythrocytes: modulation by insulin
Authors: Azoui R , Cuche JL , Renaud JF , Safar M , Dagher G
Published: December 2014

Red blood cells are capable of transport and accumulation of catecholamines. The aim of this paper is to characterize the catecholamine transport system in the human red blood cell and in particular that of dopamine. Dopamine, noradrenaline and adrenaline enter the red blood cell by a similar process, which shows saturation kinetics with Vmax values of 0.54 +/− 0.12, 0.48 +/− 0.08 and 0.63 +/− 0.13 mumol (1 cells)‐1 min‐1, respectively, and K(m) values of 15.62 +/− 1.19, 5.81 +/− 1.19 and 12.00 +/− 2.97 nM, respectively. Observations based on the dependence of dopamine influx on the transmembrane H+ gradient, and the effect of transport inhibitors such as DMA (dimethyl‐amiloride), DIDS (4,4'‐diisothiocyanatostilbene 2,2'‐disulphonic acid), reserpine, GBR 12909 (1‐(2‐(di(4‐fluoro‐phenyl)‐methoxy)‐ethyl)‐4‐(3‐phenylpropyl)piperazine) , GBR 12935 (1‐(2‐(diphenyl‐methoxy)‐ethyl)‐4‐(3‐phenyl‐propyl)piperazine), and cyanine suggest that catecholamine transport is not mediated by the Na(+)‐H+ exchanger, the anion exchanger or a system similar to that responsible for dopamine uptake in either synaptosomes or the proximal tubule. However, choline inhibits the influx of dopamine with an IC50 value of 17 microM and stimulates the efflux of dopamine with a K(m) value of 8.20 microM. These results strongly suggest that dopamine is transported by the choline exchanger previously reported to be present in red blood cells. Probenecid inhibits dopamine uptake with an IC50 of 0.63 microM. The presence of insulin receptors in human red blood cells, and the relationship between insulin and catecholamine levels in the plasma led us to investigate the effect of insulin on catecholamine transport. In fasting subjects, dopamine, adrenaline and noradrenaline influxes were higher than in fed subjects. Furthermore, the addition of exogenous insulin to red blood cells from fasting subjects significantly reduced the influx of catecholamines while no effect was observed when insulin was added to red blood cells obtained from fed subjects. The present study shows that catecholamines, and in particular dopamine, are transported in red blood cells via an exchanger which is possibly the choline transport system. The activity of this transporter is regulated by insulin. These results support a role for red blood cells as a storage pool for circulating catecholamines.
Changes in the intracellular free amino acid pool in human saphenous vein tissue culture
Authors: Suleiman MS , Wallace D , Birkett S , Angelini GD
Published: December 2014

The aim of this work was to investigate the effect of tissue culture on the intracellular amino acid pool in both freshly isolated and surgically prepared saphenous vein segments taken from patients undergoing coronary artery bypass surgery (number of patients, n = 8). Viability of freshly isolated vein rings, indicated by ATP concentration, was maintained in culture (321 +/− 41 vs. 277 +/‐ 31 nmol (g wet wt)‐1, 0 vs. 14 days). The initial decrease in ATP concentration in surgically prepared rings was significantly reversed following 14 days in culture from 135 +/− 26 to 201 +/− 18 nmol (g wet wt)‐1 (P < 0.05). Freshly isolated vein rings maintained their intracellular free amino acid pool during the 14 days in culture (from 166 +/− 25 to 166 +/− 23 mumol (g protein)‐1). Surgical preparation of vein rings induced a decrease in the intracellular free amino acid pool (from 166 +/− 25 to 87 +/− 15 mumol (g protein)‐1, P < 0.05). This decrease was partially reversed after 14 days in culture (140 +/− 19 mumol (g protein)‐1). Although the total amino acid pool in both types of vein rings after 14 days in culture was similar, there were variations in individual amino acid concentrations. Freshly isolated rings showed an increase in glutamine concentration and a decrease in alanine and aspartate concentrations after 14 days in culture. Surgically prepared vein rings showed a decrease in aspartate concentration and an increase in concentrations of glutamine, asparagine, glutamate and glycine. The changes in individual intracellular free amino acid concentrations, which were largely determined by the corresponding concentrations in the medium, indicates that culture media should be supplemented with taurine, aspartate and alanine.
Molecular biology of the amiloride‐sensitive epithelial Na+ channel
Authors: Lingueglia E , Voilley N , Lazdunski M , Barbry P
Published: December 2014

The amiloride‐sensitive epithelial Na+ channel is formed by the assembly of three homologous subunits, alpha, beta and gamma. The channel is characterized by its sensitivity to amiloride and to some amiloride derivatives, such as phenamil and benzamil, by its small unitary conductance (approximately 5 pS), by its high selectivity for lithium and sodium, and by its slow kinetics. The alpha‐, beta‐, and gamma‐proteins share significant identity with degenerins, a family of proteins found in the mechanosensory neurons and interneurons of the nematode Caenorhabditis elegans. They are also homologous to FaNaCh, a protein from Helix aspersa nervous tissues, which corresponds to a neuronal ionotropic receptor for the Phe‐Met‐Arg‐Phe‐NH2 peptide. All these proteins contain a large extracellular loop, located between two transmembrane alpha‐helices. The NH2 and COOH terminal segments are cytoplasmic and contain potential regulatory segments that are able to modulate the activity of the channel. Accordingly, in Liddle syndrome, in which patients develop a form of genetic hypertension, mutations within the cytoplasmic COOH terminal of the beta‐ and gamma‐chains of the epithelial Na+ channel lead to a hyperactivity of the channel. Epithelial Na+ channel activity is tightly controlled by several distinct hormonal systems, including corticosteroids and vasopressin. In kidney and colon, aldosterone is the major sodium‐retaining hormone, acting by stimulation of Na+ reabsorption through the epithelium. In the distal colon from steroid‐treated animals, a large increase in beta‐ and gamma‐subunit transcription is observed, whereas the alpha‐subunit remains constitutively transcribed. In kidney, RNA levels of the three subunits are not altered by aldosterone, suggesting that other mechanisms control Na+ channel activity in that tissue. In lung, the glucocorticoids are positive regulators of the channel activity, especially around birth, and act via an increased transcription of the three subunits.
Role of mitochondria‐rich cells in epithelial chloride uptake
Authors: Larsen EH , Christoffersen BC , Jensen LJ , Sorensen JB , Willumsen NJ
Published: December 2014

Uptake of NaCl by amphibian tight epithelia, such as skin, urinary bladder and collecting duct, requires considerable thermodynamic work. By calculation it is demonstrated that NaCl absorption from dilute external solutions ([NaCl] approximately 1 mM) demands more energy than can be provided by the Na(+)−K(+)‐ATPase alone. Thus, in addition to the Na+ pump, another transport ATPase must be involved. Previously, we have suggested that the other transport ATPase is an apical proton pump in mitochondria‐rich (MR) cells. By driving an apical Cl(−)−HCO3− exchange, a rheogenic H+ pump would energize entrance of Cl‐ across the apical membrane. Since Cl− channels are present in the basolateral membrane, the net result would be a transcellular active rheogenic uptake of Cl‐, and secretion of H+ and HCO3‐. At higher external concentrations, the Cl− uptake by MR cells is driven by the Na+ pump‐generated transepithelial electrical potential difference, which also requires the presence of apical Cl− channels. Electrophysiological methods have been developed by which we have been able to study the polarity of single MR cells and identify apical and basolateral transport systems. We have verified the existence of rheogenic H+ pumps in the apical membrane and Cl− channels in both membranes.
Comparison of ultra‐slow, voltage‐dependent inactivation of the cardiac L‐type Ca2+ channel with Ca2+ or Ba2+ as the charge carrier in ferret ventricular myocytes
Authors: McMorn SO , Harrison SM , Zang WJ , Boyett MR
Published: December 2014

The whole‐cell patch clamp technique was used to investigate the effect of different charge carriers upon ultra‐slow voltage‐dependent inactivation of L‐type Ca2+ channel current in ferret ventricular myocytes at 37 degrees C. Intracellular Ca2+ was buffered with 10 mM EGTA and the membrane potential held at ‐40 mV. With Ba2+ as the charge carrier, the L‐type current decayed throughout 20 s pulses to 0 mV as a result of ultra‐slow voltage‐dependent inactivation. In contrast, with Ca2+ as the charge carrier, there was no such slow decay of the current as the current decayed almost completely in the first approximately 100 ms as a result of Ca(2+)‐dependent inactivation. However, with Ca2+ as the charge carrier it is still possible that ultra‐slow voltage‐dependent inactivation occurs. A conditioning‐test pulse protocol and a second protocol were used to test for the development of ultra‐slow inactivation during 20 or 30 s pulses to 0 mV with Ca2+ as the charge carrier. Ultra‐slow inactivation did occur and it was qualitatively similar to that with Ba2+ as the charge carrier. The onset of ultra‐slow inactivation with Ca2+ as the charge carrier could be described by the sum of two exponentials with time constants of 0.3 and 6.7 s. Recovery from ultra‐slow inactivation with Ca2+ as the charge carrier was also measured with a conditioning‐test pulse protocol and was best described by the sum of two exponentials with time constants of 0.5 and 6.2 s. We conclude that ultra‐slow inactivation of the L‐type current does occur with the physiological charge carrier, Ca2+, but it is normally masked by Ca(2+)‐dependent inactivation.
The effects of 5‐hydroxydopamine on salivary flow rates and protein secretion by the submandibular and parotid glands of rats
Authors: Abe K , Itoh T , Tashiro M , Okina A , Gao C , Nakamura H , Nose T , Inoue H , Yu SF
Published: December 2014

The secretory effects of 5‐hydroxydopamine (5‐OHDA) were tested in Nembutal‐anaesthetized adult male Sprague‐Dawley rats injected I.V. over a wide range of doses, with and without various autonomic antagonists and Ca2+ channel blockers. Polyacrylamide disc gel (15%) and iso‐electric focusing (IEF) electrophoresis by the PhastSystem were used to separate and determine the types of protein in submandibular saliva. Amylase activity of parotid saliva was determined by the blue dextran method. Salivation by the submandibular glands following application of 5‐OHDA was completely abolished by both prazosin and propranolol, whereas salivation by the parotid glands was completely abolished by propranolol alone. Following application of 5‐OHDA, there was a dose‐related increase in flow rates and total output of protein, but not in the protein concentration and amylase activity, from both salivary glands. The effect of 5‐OHDA on submandibular saliva was significantly reduced by alpha‐adrenoceptor blockers, but not by beta‐adrenoceptor and cholinergic blockers, nor by any Ca2+ channel blocker. The effect of 5‐OHDA on the parotid gland was not significantly altered by atropine and phentolamine. However, after pretreatment with reserpine, a 95% reduction was observed in the salivation from the submandibular gland. This implies that 5‐OHDA is mostly acting indirectly via release of noradrenaline. The proteins in submandibular saliva following treatment with 5‐OHDA alone or 5‐OHDA in combination with beta‐adrenoceptor blockers were mainly of the alpha‐type, whereas after treatment with 5‐OHDA in combination with alpha‐adrenoceptor blockers they were of the beta‐type. The alpha‐type was found in saliva after treatment with each of three Ca2+ channel blockers.
Tetrahydrobiopterin and GTP cyclohydrolase I in a rat model of endotoxic shock: relation to nitric oxide synthesis
Authors: Hattori Y , Nakanishi N , Kasai K , Murakami Y , Shimoda S
Published: December 2014

Induction of the inducible isoform of nitric oxide synthase (iNOS) in various types of cells is implicated as the cause of septic shock. We evaluated the concentration of tetrahydrobiopterin (BH4), a cofactor of NOS, in plasma and various other tissues of rats treated with lipopolysaccharide (LPS; 10 mg/kg I.V.). The activity of GTP cyclohydrolase I (GTPCH), the first and rate‐limiting enzyme in the de novo synthesis of BH4, in rat tissues was also determined. Three hours after administration of LPS, rats showed plasma levels of BH4 and NOx (NO3‐ and NO2‐) that were elevated by 137 and 206%, respectively. GTPCH was expressed in liver and, to a lesser extent, in the lung, heart and kidney of control rats. In control rats, although a high concentration of BH4 was detected in the liver, its level was lower in lung, heart, kidney and aorta. Three hours after LPS administration, a significant increase in BH4 concentration and/or GTPCH activity was observed in all tissues examined except the liver. Our results demonstrate that the de novo synthesis of BH4 is upregulated by LPS in the rat in vivo, which may, at least in part, account for the increases in plasma level and tissue concentration of BH4 after the administration of LPS.
Blunting the rise in body temperature reduces muscle glycogenolysis during exercise in humans
Authors: Febbraio MA , Snow RJ , Stathis CG , Hargreaves M , Carey MF
Published: December 2014

To examine the effect of blunting the rise in body temperature on exercise metabolism, seven endurance‐trained men cycled for 40 min at 65% of maximal oxygen consumption (VO2,max) in an environmental chamber at either 20 degrees C and 20% relative humidity (RH) (T20) or 3 degrees C and approximately 50% RH (T3). The trials were conducted in random order at least 1 week apart. Mean oxygen consumption (VO2) during exercise was not different when comparing the two trials. In contrast, the mean respiratory exchange ratio (RER) was lower (P < 0.05) at T20 compared with T3. Heart rate, rectal temperature and plasma catecholamines were higher (P < 0.05) during exercise at T20 compared with T3, as was post‐exercise muscle temperature (P < 0.01). Muscle and blood lactate and blood glucose concentrations were not significantly different when comparing T20 with T3. Net muscle glycogen utilization was greater (P < 0.05) at T20 compared with T3. These results suggest that glycogenolysis in contracting skeletal muscle is reduced during exercise when the rise in body core temperature is attenuated. These changes in carbohydrate metabolism appear to be influenced by alterations in muscle temperature and/or sympatho‐adrenal activity.
Two components of the delayed rectifier potassium current, IK, in rabbit sino‐atrial node cells
Authors: Lei M , Brown HF
Published: December 2014

The delayed rectifier current was studied in rabbit isolated sino‐atrial (SA) node cells using the whole‐cell voltage clamp technique with amphotericin‐permeabilized patches. The envelope of tails test indicated that in SA node cells the decay of IK (IK.tall) comprises two distinct current components similar to the specific fast and slow components of IK (IKr and JKs) that have been found in atrial and ventricular myocytes. Dofetilide, a Class III antiarrhythmic agent and a selective blocker of IKr. separated the delayed rectifier current into drug‐sensitive current (IKr) and drug‐insensitive current (IKs). The dofetilide‐sensitive current activated rapidly and it showed two components of deactivation, the larger of which was very slow, while the dofetilide‐insensitive current activated more slowly and deactivated quickly. The effects of propofol, an IKs blocker, on the delayed rectifier current were also investigated. The results show that IKs contributes to IK.tall and that the more positive the membrane potential, the more the contribution of IKs. The ratio of IKs to IKr in tail currents at ‐40 mV after a 1 s clamp pulse to +40 mV was 0.3‐0.4:1. Dofetilide slowed spontaneous activity, suggesting that IKr contributes to the pacemaker activity of the SA node cell.
Inward rectification of the large conductance potassium channel in smooth muscle cells from rabbit pulmonary artery
Authors: Snetkov VA , Gurney AM , Ward JP , Osipenko ON
Published: December 2014

Large conductance Ca(2+)‐dependent K+ channels were studied in smooth muscle cells enzymatically dissociated from rabbit pulmonary artery. The current‐voltage relationship of single channels recorded in cell‐attached patches revealed strong inward rectification, which disappeared after patch excision. Cell permeabilization with saponin, beta‐escin or equinatoxin II also removed rectification. These observations imply the existence of fast open channel block by an intracellular substance(s). Application to the cytosolic side of inside‐out patches of Na+ ions, mono‐ di‐ and trinucleotides, taurine, reduced and oxidized forms of glutathione, or peptides extracted from pulmonary artery smooth muscle, did not reproduce the inward rectification. Patch treatment with either alkaline phosphatase or protein kinase A alpha‐subunit, which strongly affected open state probability, was also incapable of reducing the outward single channel current. Mg2+ ions applied from the cytosolic side induced concentration‐ and voltage‐dependent block of the outward single channel currents with a Kd of 7.9 +/‐ 2.3 mM, resulting in inward rectification qualitatively similar to that observed in cell‐attached patches. An increase in the Mg2+ concentration of the intracellular solution induced a significant decrease in the outward whole‐cell current at depolarized potentials. Another putative endogenous channel blocker, the polyamine putrescine, was not effective. However, its metabolites spermidine and spermine reduced the amplitude of the outward single channel current with Kd values of 4.9 +/‐ 0.6 and 1.4 +/‐ 0.4 mM, respectively. Pre‐incubation of the cells with the irreversible inhibitor of polyamine synthesis difluoromethylornithine abolished the rectification in the cell‐attached patches. These results suggest that intracellular polyamines may underlie at least part of the inward rectification of the Ca2+ activated K+ channel in this tissue, but that intracellular Mg2+ is unlikely to play a major role.
The effect of climatic heat stress on intermittent supramaximal running performance in humans
Authors: Maxwell NS , Aitchison TC , Nimmo MA
Published: December 2014

The purpose of this study was to test the hypothesis that intermittent supramaximal running would be negatively affected when performed in a hot humid environment. Twelve physically active, male volunteers took part in this study. The exercise model was performed under three environmental trial conditions, randomly assigned and separated by 1 week. This included performing: (a) a standardized warm‐up in the cool environment and a repeated sprint test in the cool environment (CC); (b) a standardized warm‐up in the cool environment and a repeated sprint test in a hot, humid environment (CH); and (c) a standardized warm‐up in a hot, humid environment and a repeated sprint test in a hot, humid environment (HH). The repeated sprint test involved 20 s runs, each at increasing‐intensity, with 100s passive recovery between successive sprints. Capillary blood samples were taken post‐warm‐up and at 1, 3 and 6 min post‐repeated sprint test for the determination of plasma lactate, ammonia and glucose concentrations and the percentage change in plasma volume. Rectal, aural and mean skin temperature were measured continuously throughout each trial condition. Sweat loss was estimated from the change in body mass. Sweat loss was significantly greater in the HH trial than in the CH trial and in the CH trial than in the CC trial (P < 0.0001). Performance was significantly better in the CC trial than in the CH and HH trials (CC vs. CH and HH: 151 +/‐ 4 vs. 144 +/‐ 5 and 140 +/‐ 5 s, respectively, P = 0.02). For the post‐exercise data, significant differences were found between the CC and the CH and HH trials in rectal (P = 0.007), aural (P < 0.001) and mean skin temperatures (P < 0.001). No significant differences were found in post‐repeated sprint test lactate and ammonia concentrations, or in plasma volume among trial conditions, but glucose concentrations were higher in the CH and HH trials than in the CC trial (P = 0.005). No significant differences were found in performance, body temperature or any blood measurement between the CH and HH trials. Intermittent supramaximal running performance was detrimentally affected by a hot, humid environment, resulting in performance being significantly less in the CH and HH trials than in the CC trial.
Hypothalamic and plasma total nitrate/nitrite concentrations in spontaneously hypertensive rats
Authors: Alaghband‐Zadeh J , Das I , Hanson MR , MacGregor CA , de Wardener HE , Laycock JF
Published: December 2014

Stable end‐products of nitric oxide (NO) metabolism, nitrates and nitrites, were measured in hypothalamic extracts and plasma samples of Okamoto spontaneously hypertensive (SH) rats. The mean total nitrate/nitrite concentration was significantly lower in the hypothalami of SH rats compared with the normotensive Wistar Kyoto (WKY) control animals (P < 0.01). In contrast, their plasma concentrations were significantly higher (P < 0.05). These results indicate that the hypertensive state in SH rats is associated with a diminished production of hypothalamic NO, while the raised plasma nitrate/nitrite levels could reflect an increased compensatory endothelial NO synthase activity in these animals compared with the WKY controls.
Effects of acetylcholine on a slow voltage‐activated non‐selective cation current mediated by non‐nicotinic receptors on isolated Ascaris muscle bags
Authors: Martin RJ , Valkanov MA
Published: December 2014

Isolated muscle bags from the parasitic nematode Ascaris suum were prepared by collagenase treatment and dissection. Single bags were mounted in a V‐shaped plastic pipette for voltage clamp application and intra‐ and extracellular perfusion. With ‘physiological’ intra‐ and extracellular solutions, depolarizing voltage steps from near the normal resting membrane potential, ‐40 mV, produced in leak‐corrected currents, a slowly activating outward current at potentials more positive than ‐20mV. At the end of the depolarizing pulse there was a slow inward tail current with a reversal potential near ‐20mV. Hyperpolarizing voltage steps produced an outward current relaxation and an outward tail current with the same reversal potential. The observations can be explained by the presence in the bag of a non‐selective cation channel current, Ibcat, that activates spontaneously at the holding potential; depolarization increases opening of the channel and hyperpolarization decreases opening. Bath‐applied acetylcholine in concentrations greater than 10(−7) M produced an increase in the amplitude of Ibcat. The effect of acetylcholine was not antagonized or prevented by 100 microM tubocurarine, suggesting the presence of a non‐nicotinic acetylcholine receptor. Atropine (100 microM) had no detectable influence on the effect of acetylcholine but the FMRFamide peptide, PF1, in concentrations > 1 microM, reduced the amplitude of Ibcat. Ibcat was maintained when Cs+ was used to replace intra‐ and extracellular cations, showing that the channels were permeable to Cs+. It is concluded that the bag membrane possesses a slow voltage‐activated non‐selective cation channel current, Ibcat. The effect of acetylcholine in the presence of nicotinic antagonist indicates the presence of non‐nicotinic acetylcholine receptors on the bag membrane. The effect of PF1 indicated the presence of PF1 receptors on the bag membrane.
Mechanical behaviour of rat skeletal muscle during fatiguing stretch‐shortening cycles
Authors: Ettema GJ
Published: December 2014

The effects of muscle fatigue on the mechanical efficiency of muscle work performance were studied in situ, in stretch‐shortening cycles that resembled physiological conditions. The experiments were performed on the medial gastrocnemius muscles of seven rats. To calculate efficiency, a simple Hill‐type model was used, consisting of the contractile component (CC) and the series elastic component (SEC). Mechanical efficiency was defined as the external work done by the muscle‐tendon complex divided by the external work done upon the muscle‐tendon complex plus work done by the CC. The fatiguing protocol consisted of a l Hz stretch‐shortening cycle with a 0.3 duty factor (i.e. the muscle was stimulated for 300 ms in each cycle). In total, 240 cycles were imposed. The mechanical performance (work, force and mechanical efficiency) was determined throughout the fatiguing process. Fatigue reduced muscle power and force production to approximately 17 and 30%, respectively. SEC stiffness increased, but did not have any effect on muscle performance and probably reflects altered cross‐bridge characteristics. Mechanical efficiency was enhanced during the imposed stretch‐shortening cycles from 0.74 to 0.83. As a result of the lower peak forces, proportionally less series elastic energy was wasted during the relaxation period of each strength‐shortening cycle in the fully fatigued muscles. These results indicate that, in vivo, the timing of muscle contractions in the fresh and the fatigued state may be different in order to perform muscle work efficiently. After a period of 30 min recovery, the condition of the muscles had (partially) returned to the fresh state in all aspects.
The role of carotid chemoreceptors in the effects of hypoxia on renal blood flow in the late gestation sheep fetus
Authors: Green LR , Bennet L , Robson S , Hanson MA
Published: December 2014

Previous studies of the effect of hypoxia on fetal renal haemodynamics have demonstrated a fall, a rise or no change in renal blood flow (RBF). The underlying mechanisms are not understood but involve a balance between neural vasoconstrictor and opposing vasodilator mechanisms. Since carotid chemoreflex mechanisms contribute to vasoconstriction in other fetal vascular beds and in the adult renal vasculature, we examined their effects on RBF during 1 h of acute hypoxia in late gestation fetal sheep (n = 12). Renal blood flow was measured continuously and urine collected at 15 min intervals. Seven fetuses underwent bilateral section of the carotid sinus nerves (CSD fetuses). During hypoxia CSD fetuses showed a transient initial rise in RBF (P < 0.05) and then a subsequent fall (P < 0.05) to levels comparable with that recorded in intact fetuses. There was no change in urine output in either intact or CSD fetuses during hypoxia. Thus the initial fall in RBF during hypoxia is a carotid chemoreflex but other mechanisms, e.g. vasoconstrictor hormones, contribute to the sustained response.
Intracellular pH and H+ buffering capacity in guinea‐pigs with left ventricular hypertrophy induced by constriction of the thoracic aorta
Authors: Wallis WR , Wu C , Sheridan DJ , Fry CH
Published: December 2014

Intracellular pH (pHi) was measured in left ventricular myocytes from hearts hypertrophied by constriction of the thoracic aorta. There was a continuous relation between an increase in heart‐to‐body weight ratio and a decrease in pHi (mean +/− S.D., 7.06 +/ࢤ 0.18 pH units in control hearts vs. 6.87 +/− 0.17 pH units in hypertrophied hearts). Intracellular H+ buffering capacity (beta) increased as pHi fell, but the value of beta was independent of hypertrophy per se.
Adrenal independence of fluid and electrolyte reabsorption in the ductuli efferentes testis of the rat
Authors: Man SY , Clulow J , Hansen LA , Jones RC
Published: December 2014

The ductuli efferentes testis (efferent ducts) of the rat were studied to determine whether fluid and electrolyte reabsorption by the ducts is under the control of adrenal mineralocorticoids. Testicular fluid output and the rate of fluid reabsorption by the ducts were determined in sham‐operated controls and in rats which had been adrenalectomized 10 days previously, adrenalectomized 10 days previously and given aldosterone therapy (75 micrograms kg‐1 day‐1 S.C.) from day 3 to day 10 post adrenalectomy, and in rats given injections of the aldosterone antagonist, spironolactone, for 10 days (10 mg kg‐1 day‐1 S.C.). The values for testicular fluid output and fluid flow from the efferent ducts (means +/‐ S.E.M.) in the sham‐operated rats were 36.0 +/‐ 7.8 and 1.23 +/‐ 0.12 microliters h‐1, respectively, resulting in an estimate of fluid reabsorption by the efferent ducts of 94.8 +/‐ 1.6% of the testicular fluid output. None of the treatments resulted in a significant change in testicular fluid output or in fluid reabsorption from the efferent ducts. Similarly, the treatments did not significantly alter the osmolality or electrolyte concentrations in fluid samples from the rete testis or the distal end of the efferent ducts (sham‐operated values for rete testis and efferent duct fluid, respectively, were: osmolality, 311.2 +/‐ 1.7 and 302.7 +/‐ 5.7 mosmol kg‐1; [Na+], 151.2 +/‐ 5.6 and 150.8 +/‐ 8.1 mmol l‐1; [Cl‐], 147.9 +/‐ 6.6 and 126.7 +/‐ 2.2 mmol l‐1; [K+], 15.2 +/‐ 0.7 and 13.5 +/‐ 2.4 mmol l‐1). It is concluded that, like the homologous proximal tubule of the metanephric kidney, fluid reabsorption from the efferent ducts is independent of adrenal mineralocorticoid control.
Role of nuclear factor‐kappa B in atherogenesis
Authors: Brand K , Page S , Walli AK , Neumeier D , Baeuerle PA
Published: December 2014

Transcription factors of the nuclear factor‐kappa B (NF‐kappa B)/Rel family have an important function in the regulation of a variety of genes involved in the inflammatory and proliferative responses of cells. Recent studies strongly indicate that the inducible transcription factor NF‐kappa B is involved in the pathogenesis of atherosclerosis. Activated NF‐kappa B is present in the fibrotic thickened intima‐media and atheromatous areas of the atherosclerotic lesion, within smooth muscle cells, macrophages and endothelial cells, whereas little or no activated NF‐kappa B can be detected in vessels lacking atherosclerosis. A variety of molecules have been identified in the atherosclerotic environment that are able to activate NF‐kappa B in vitro. Furthermore, an increased expression of numerous genes known to be regulated by NF‐kappa B has been found in the atherosclerotic lesion. Possible functional implications for activated NF‐kappa B in atherogenesis are discussed here. The activation and role of NF‐kappa B in atherosclerosis may provide a model for the involvement of the transcription factor in human chronic inflammatory disease.
Metabolic and clonogenic consequences of ischaemia reperfusion insult in solid tumours
Authors: Parkins CS , Hill SA , Stratford MR , Dennis MF , Chaplin DJ
Published: December 2014

Tumour cell survival is intimately related to blood vessel function and so the tumour vasculature represents a novel target for cancer therapy. We have investigated a murine tumour model in which a metal clamp was used to occlude the vascular supply temporarily and then removed to allow reperfusion. This allows the study of ischaemia‐reperfusion as a model system for investigating tumour response to metabolic and oxidative stress. Recent studies have shown that prolonged reduction of tumour blood flow results in a deterioration of the hypoxic and acidic microenvironment found within tumours which leads to cytotoxicity. This cytotoxicity is dramatically enhanced if these cells are subsequently reperfused. It was the aim of the present study to determine the relative contribution of cytotoxicity occurring during the ischaemic period and that occurring during reperfusion. Although significant reductions in tumour energy status were induced during the clamping period itself, these were poorly correlated with the degree of tumour cytotoxicity. Relative vascular perfusion, measured using a radiolabelled tracer, remained significantly depressed below the control value following clamp removal. The degree of recovery of perfusion was also dependent upon the clamp duration. Relative tumour perfusion at 1 h after clamp removal was 70.1 +/‐ 14.6 and 50.5 +/‐ 6.3% of control values after a 1 or 3 h clamp, respectively, and showed no significant further increase when measured at 24 h after clamp removal. Tumour cytotoxicity following ischaemia reperfusion insult was modulated by administering the anti‐oxidant enzymes superoxide dismutase or catalase intravenously just before clamp removal. These enzymes are restricted to the vascular compartment, where it is proposed that they modulate the concentration of oxygen free radicals released during reperfusion and by neutrophil oxidative burst. Reperfusion injury to the tumour was enhanced by administration of an inhibitor of nitric oxide synthase, nitro‐L‐arginine, probably owing to enhanced neutrophil adhesion and oxidative burst. Conversely, reperfusion injury to the tumour was reduced by administration of a nitric oxide donor, diethylamine nitric oxide. The murine model reported in this paper shows that ischaemia‐reperfusion damage mediated by oxygen free radical formation provides a model system for investigating tumour response to oxidative stress at the level of the vascular endothelium.
Electrochemical detection of K(+)‐evoked quantal secretory events from isolated rat type I carotid body cells
Authors: Hatton CJ , Peers C
Published: December 2014

Using amperometric techniques, electrochemical events associated with vesicular transmitter release were recorded from isolated rat type I carotid body cells when exposed to a solution containing 50 mM K+. Events were enhanced in amplitude by preloading cells with the catecholamine precursor, L‐beta‐3,4‐dihydroxyphenylalanine (L‐DOPA). K(+)‐evoked secretion was abolished by the non‐selective Ca2+ channel blocker Cd2+ (100 microM) and markedly reduced by the L‐type Ca2+ channel blocker nifedipine (5 microM). Our results indicate that secretion from isolated rat type I cells can be monitored electrochemically and we demonstrate a major role for L‐type Ca2+ channels in mediating K(+)‐evoked secretion.
Transcellular openings through frog microvascular endothelium
Authors: Neal CR , Michel CC
Published: December 2014

Reconstructions from serial ultrathin sections of microvascular endothelium suggest that gaps, which are induced by a range of stimuli, may pass through endothelial cells as well as between them. To address the possibility that the transcellular gaps are not artefacts of aldehyde fixation, we have reconstructed fourteen gaps, induced by the ionophore A23187, in frog mesenteric microvessels where the primary fixative was osmium tetroxide. All fourteen gaps were transcellular. The different actions of osmium tetroxide and glutaraldehyde lead us to consider that it is highly unlikely that transcellular gaps are fixation artefacts.
Effect of adrenaline and alpha‐agonists on net rate of liquid absorption from the pleural space of rabbits
Authors: Zocchi L , Raffaini A , Agostoni E
Published: December 2014

Indirect evidence supporting a solute‐coupled liquid absorption from the pleural space of rabbits has recently been provided; moreover, the beta 2‐adrenoceptor agonist terbutaline has been found to increase this absorption. In this study the effect of adrenaline and alpha‐adrenoceptor agonists on net rate of liquid absorption (Jnet) from albumin Ringer hydrothoraces of various sizes has been determined in anaesthetized rabbits. In hydrothoraces with adrenaline (5 x 10(‐6) M) the relationship between Jnet and volume of liquid injected was displaced upwards by 0.09 ml h‐1 relative to that in control hydrothoraces (P < 0.01). This displacement did not occur with lower adrenaline concentrations or after pretreatment with the beta‐blocker propranolol. Hence, this increase in Jnet is mediated by stimulation of beta‐receptors. It seems to be caused by an increase in solute‐coupled liquid absorption, since beta‐agonists inhibit lymphatic activity while, at relatively high concentrations, they may increase active transport. Conversely, the strong stimulation of lymphatic alpha‐receptors that should occur with adrenaline after beta‐blockade may fail to increase lymphatic drainage, because it has been shown that the increase in contraction frequency of lymphatics may be balanced by the decrease in their stroke volume. Arterial blood pressure during the hydrothoraces with adrenaline was unchanged. In hydrothoraces with the alpha 2‐agonist clonidine (5 x 10(‐6) M; a less potent agent than adrenaline) the slope of the relationship between Jnet and volume injected increased by 26% (P < 0.01), while its origin did not change. This increase in slope did not occur with a lower clonidine concentration or after pretreatment with the alpha‐blocker phentolamine. Hence, it is caused by stimulation of alpha 2‐receptors, which probably lead to an increase in lymphatic drainage related to liquid load. In hydrothoraces with the alpha 1‐agonist phenylephrine (5 x 10(‐6) or 10(‐7) M) Jnet was simlar to control values.
Beta‐agonist‐induced activation of Na+ absorption and KCl release in rat fetal distal lung epithelium: a study of cell volume regulation
Authors: Nakahari T , Marunaka Y
Published: December 2014

The effects of terbutaline (a selective beta 2‐adrenoceptor agonist) on cell volume and ion transport in rat fetal distal lung epithelial (FDLE) cells were studied. In FDLE cells, benzamil (1 microM) induced cell shrinkage, while cell volume was increased by 1 mM quinine or 2 mM Ba2+ but was not affected by 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoic acid (NPPB, 20 microM). Terbutaline (10 nM) induced transient cell swelling, which was suppressed by benzamil, while 10 microM terbutaline induced initial rapid cell shrinkage followed by delayed slow cell shrinkage, which was suppressed by 1 mM quinine or 20 microM NPPB but not by 2 mM Ba2+. Application of benzamil enhanced the cell shrinkage induced by 10 microM terbutaline. These observations suggest that: (1) benzamil‐blockable Na(+)ࢤpermeable channels and quinine‐ and Ba(2+)ࢤblockable K+ channels contribute to maintenance of cell volume of FDLE cells; (2) terbutaline at both 10 nM and 10 microM activates benzamil‐blockable Na(+)ࢤpermeable channels; (3) quinine‐blockable K+ channels are activated by 10 microM terbutaline; and (4) NPPB‐blockable Cl‐ channels are responsible for Clࢤ movement in cell volume changes induced by terbutaline. The present study demonstrates that the cellular mechanisms of volume change induced by terbutaline are closely related to activation of Na+ absorption and KCl release.