bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of Ionic Channels by Deoxycholate in Frog and Human Cell Lines
Authors: Maurício A. C. , Ferreira K. T. G.
Published: May 2004

Humans, after extensive ileal resection, frequently suffer from diarrhoea, which may be due to an increased delivery of deoxycholate (DOC) to the large intestine. In the frog skin the addition of DOC (0·5 mM) to the apical side induced the activation of amiloride‐sensitive Na+ channels and an increase in the unidirectional Cl− fluxes. Here we used two established cell lines (A6 and Caco2) to study the effect of DOC on ion channels at cell and membrane level using the patch‐clamp technique. In A6 cells subcultured directly on Petri dishes and studied in the whole‐cell configuration, DOC induced an increase in cell conductance of 110·3 ± 4 pS pF−1 (N= 8) which was reduced to 89 ± 14 pS pF−1 (N= 8) by the addition of DIDS (0·5 mM). The absolute values of these two effects were not statistically different (P < 0·2). In Caco2 cells, the addition of DOC (0·5 mM) induced, after 1 min, an increase in cell conductance of 583 ± 16 pS pF−1 (N= 8) which was reduced to 560·4 ± 16 pS pF−1 (N= 8) by DIDS (0·5 mM) and N‐phenylanthranilic acid (DPC; 0·5 mM). The two values were not statistically different (P < 0·4). In Caco2 cells subcultured under the same conditions, DOC induced an increase in cell conductance of 1710 ± 64 pS pF−1 (N= 6). Subsequent addition of amiloride (0·1 mM) reduced the cell conductance to 1558 ± 33 pS pF−1 (N= 6). These two mean values were statistically different allowing for an error of the second kind < 0·05. In cells in which DOC produced a conductance increase of 1010 ± 10 pS pF−1, gadolinium (0·5 mM) induced a fall in cell conductance of 1800 ± 10 pS pF−1. In Caco2 cells, addition of DOC (0·5 mM) to the bath reversibly induced the appearance of or an increase in channel activity in patches studied in cell‐attached and excised inside‐out configuration. In inside‐out experiments (N= 13) DOC (0·5 mM) induced the appearance of channel activity with conductances and reversal potentials (Er) of 27·7 ± 1·9 pS and 0·8 ± 5·7 mV, respectively. In cell‐attached patches (N= 13) these values were 24·9 ± 4·4 pS and ‐18·1 ± 6·4 mV. In excised inside‐out patches from Caco2 cells, subjected to electrochemical gradients for Na+, K+ and Cl−, (+85, ‐85 and 0 mV, respectively), addition of DOC also induced an increase in the baseline conductance and a shift in the reversal potential from values around +25 mV to values around 0 mV. Bile salts activated both anionic and cationic channels and did not require the presence of intracellular factors for these effects. We suggest that they act at the membrane level.
Regulatory Role of cAMP in Transport of Na+, Cl− and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium
Authors: Gäbel Gotthold , Butter Heidrun , Martens Holger
Published: May 2004

Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short‐chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl−, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium‐coupled transport mechanisms in short‐circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0·1 mM) significantly reduced mucosal‐to‐serosal sodium transport, leading to a reduction of net transport. The theophylline‐ or theophylline‐forskolin‐induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short‐chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline‐forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline‐forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 μM) led to a theophylline‐sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride‐sensitive Na+‐H+ exchange and/or basolateral Na+‐K+‐ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.
Cardiac Electrophysiological Effects of Platelet‐Derived Substances
Authors: Flores N. A. , Botchway A. N. S. , Stavrou B. M. , Sheridan D. J.
Published: May 2004

The ability of the heart to function as an efficient pump is critically dependent on an adequate blood supply to the myocardium. When myocardial blood supply is reduced (ischaemia), contractile function of the heart is impaired and its cellular electrophysiological properties are profoundly altered. Prolonged ischaemia may result in cell necrosis which, if irreversible, leads to cell death (infarction) and predisposes the heart to ventricular arrhythmias, which in turn may be fatal. In man, myocardial ischaemia is the consequence of narrowing or occlusion of a coronary artery and is usually a manifestation of coronary artery disease which is often associated with thrombosis.
Drug Extrusion, 125I− Efflux and the Control of Intracellular [Ca2+] in Drug‐Resistant Ovarian Epithelial Cells
Authors: McAlroy H. L. , Bovell D. L. , Plumb J. A. , Thompson P. , Wilson S. M.
Published: May 2004

Experiments were undertaken using an ovarian adenocarcinoma cell line (A2780) and a drug‐resistant strain (A2780.ad) derived from this line. P‐glycoprotein could not be detected in A2780 cells but was essentially ubiquitous in A2780.ad cells, although removing the selective pressure for drug resistance led to reduced expression. However, the amount of P‐glycoprotein present was used to predict the capacity of these cells to extrude rhodamine‐123 (R‐123) and their resistance to adriamycin, a cytotoxic drug. This accords with the role of P‐glycoprotein as a drug pump. Although hypotonic solutions increased anion efflux from A2780 and A2780.ad cells, larger responses occurred in the parental line. Moreover, R‐123 extrusion and anion efflux appeared to be mutually independent processes and so these data do not support the view that P‐glycoprotein is involved in the control of volume‐sensitive anion channels. Hypotonic solutions increased intracellular free calcium ([Ca2+]i) in drug‐resistant cells but not in the parental line, and so establishing a drug‐resistant strain may affect the control of [Ca2+]i during osmotic swelling. This could account for effects that were previously attributed to P‐glycoprotein.
The Effects of Caffeine on the Kinetics of O2Uptake, CO2Production and Expiratory Ventilation in Humans During the On‐Transient of Moderate and Heavy Intensity Exercise
Authors: Bell C. , Kowalchuk J. M. , Paterson D. H. , Scheuermann B. W. , Cunningham D. A.
Published: May 2004

In order to test the hypothesis that glycogen sparing observed early during exercise following caffeine ingestion was a consequence of tighter metabolic control reflected in faster VO2 kinetics, we examined the effect of caffeine ingestion on oxygen uptake (VO2), carbon dioxide production (VCO2) and expiratory ventilation (VE) kinetics at the onset of both moderate (MOD) and heavy (HVY) intensity exercise. Male subjects (n= 10) were assigned to either a MOD (50 % VO2,max, n= 5) or HVY (80 % VO2,max, n= 5) exercise condition. Constant‐load cycle ergometer exercise was performed as a step function from loadless cycling 1 h after ingestion of either dextrose (placebo, PLAC) or caffeine (CAFF; 6 mg (kg body mass)−1). Alveolar gas exchange was measured breath‐by‐breath. A 2‐ or 3‐component exponential model, fitted through the entire exercise transient, was used to analyse gas exchange and ventilatory data for the determination of total lag time (TLT: the time taken to attain 63 % of the total exponential increase). Caffeine had no effect on TLT for VO2 kinetics at either exercise intensity (MOD: 36 ± 14 s (PLAC) and 41 ± 10 s (CAFF); HVY: 99 ± 30 s (PLAC) and 103 ± 26 (CAFF) (mean ±s.d.)). TLT for VE was increased with caffeine at both exercise intensities (MOD: 50 ± 20 s (PLAC) and 59 ± 21 s (CAFF); HVY: 168 ± 35 s (PLAC) and 203 ± 48 s (CAFF)) and for VCO2 during MOD only (MOD: 47 ± 14 s (PLAC) and 53 ± 17 s (CAFF); HVY: 65 ± 13 s (PLAC) and 69 ± 17 s (CAFF)). Contrary to our hypothesis, the metabolic effects of caffeine did not alter the on‐transient VO2 kinetics in moderate or heavy exercise. VCO2 kinetics were slowed by a reduction in CO2 stores reflected in pre‐exercise and exercise end‐tidal CO2 pressure (PET,CO2) and plasma PCO2 which, we propose, contributed to slowed VE kinetics.
Isometric and Concentric Performance of Electrically Stimulated Ankle Plantar Flexor Muscles in Intact Rat
Authors: Willems Mark E. T. , Stauber William T.
Published: May 2004

The relationship between muscle force and ankle position during isometric and pre‐loaded slow concentric contractions (angular velocity, 0.52 rad s−1; range of motion, 1.22 rad) and the recovery of isometric force following concentric contractions at different velocities were determined for electrically stimulated plantar flexor muscles in intact rats. Pre‐loaded refers to the isometric contraction which immediately precedes the concentric contraction. Ankle position was controlled by a dynamometer and force was recorded under the sole of the foot. The peak isometric force (19.2 N) was nearly constant at all ankle positions (range of motion, 1.57 rad). The muscle length and distal fibre length of gastrocnemius medialis at ankle positions between 0.79 rad and 2.01 rad were increased by 12.6% and 20.3%, respectively. During slow concentric contractions, the force progressively decreased (23.1 ± 2.1%); the force decreased by only 6.3 ± 0.9% during sustained isometric contractions of similar duration (3400 ms). The recovery of isometric force following concentric contractions with similar stimulation frequencies (80 Hz) was velocity dependent (i.e. more rapid at higher velocities). It is concluded that pre‐loaded slow concentric contractions of the plantar flexor muscles in intact rats do not follow the same relationship as that of isometric force and ankle position. Our results in intact rats show that the force output of electrically stimulated ankle plantar flexor muscles measured under the sole of the foot can be used to study the physiological properties of skeletal muscle working in situ.
The Role of Na+−H+ Exchange in Fluid and Solute Transport in the Rat Efferent Ducts
Authors: Hansen L. A. , Clulow J. , Jones R. C.
Published: May 2004

In vivo microperfusion techniques were used to investigate the role of Na+‐H+ exchange in the efferent ducts of the rat. Individual efferent ducts were perfused with a Krebs‐Ringer bicarbonate solution (KRB) containing 0, 1, 3, 5 or 7·5 mM amiloride. Concentrations of 1‐5 mM amiloride inhibited fluid reabsorption from the efferent ducts in a linear dose‐dependent manner with an apparent Km of 3 mM. Inhibition was maximal at 5 mM with reabsorption reduced by about 70%. The effects of amiloride were completely reversible and there was little effect of amiloride on luminal osmolality and concentrations of Na+, Cl− or K+. It is concluded that Na+‐H+ exchange is one of the principal mechanisms responsible for fluid and electrolyte reabsorption in the efferent ducts and offers a means by which the efferent ducts are able to achieve flow‐dependent, autoregulated fluid reabsorption.
Comparison of Step and Ramp Voltage Clamp on Background Currents in Guinea‐Pig Ventricular Cells
Authors: Spindler A. J. , Noble S. J. , Noble D.
Published: May 2004

Isolated cardiac ventricular myocytes from guinea‐pig were used to investigate the effect of voltage clamp protocols on background Na+ current (ib.Na) and inward rectifier current (iK1). Using long (4 s) clamp pulses and very long step clamps, the i‐V relations showed that removal of Na+ reduces the amplitude and shifts the voltage dependence of iK1 (Spindler et al. 1998). Ramp clamps, however, gave more complicated results, with slower ramps more often giving the same results as steps and pulses. Both iK1 itself and, during faster ramps, other currents show hysteresis, so masking the steady‐state changes. Using pulses, TTX had no effect on steady‐state current. Small differences occurred in the ramps, but even at fast ramp speeds the effects are very much smaller than in Purkinje tissue. Only part of ib,Na is TTX sensitive and the effect does not occur in all cells.
Mechanically Induced Potentials in Fibroblasts from Human Right Atrium
Authors: Kamkin A. , Kiseleva I. , Wagner K. D. , Lammerich A. , Bohm J. , Persson P. B. , Günther J.
Published: May 2004

It has been shown that cardiac fibroblasts of the human heart are electrically non‐excitable and mechanosensitive. The resting membrane potential of these cells is ‐15.9 ± 2.1 mV and the membrane resistance is 4.1 ± 0.1 GΩ. Rhythmic contractions of the myocardium associated with stretch of the surrounding tissue produce reversible changes in the membrane potential of cardiac fibroblasts. These mechanically induced potentials (MIPs) follow the rhythm of myocardial contractions. Simultaneous recording of the action potential of cardiomyocytes and MIPs of cardiac fibroblasts demonstrates a delay of 40.0 ± 0.4 ms after the action potential before the appearance of the MIP. Contraction produces a MIP which is more positive or more negative than the reversal potential ‐ the membrane potential due to current injection at which the MIP reverses its direction. Regardless of the initial orientation of the MIP, intracellular polarization increases the amplitude towards the reversal potential if the background MIP had depolarized the membrane or away from the reversal potential if the initial background MIP had hyperpolarized the membrane. Artificial intracellular polarization changed the amplitude but not the frequency of the MIP. The pool of electrically non‐excitable mechanosensitive cells, which change their electrical activity during contraction and relaxation of the heart, may play a role in the mechano‐electrical feedback mechanism which has to be taken into account in the normal function of the heart as well as in pathological processes.
Sweat Ethanol Concentrations are Highly Correlated with Co‐Existing Blood Values in Humans
Authors: Buono Michael J.
Published: May 2004

This study compared the concentration of ethanol, both absolute and relative to water content, in sweat and blood. Ten male volunteers consumed approximately 13 mmol (kg body weight)−1 of ethanol. Blood and sweat samples were collected approximately 1, 2 and 3 h following ingestion. Sweat was collected following pilocarpine iontophoresis using an anaerobic technique that prevented ethanol evaporation. In addition, the water content of sweat and blood samples was determined. The correlation between sweat and blood ethanol, expressed in mmol l−1, was r= 0.98. The slope of the relationship was 0.81. When corrected for the water content in each sample, and expressed as mmoles per litre of water, the correlation remained very high (r= 0.97) while the slope increased to 1.01. These results suggest that rapid and complete equilibrium of ethanol occurs across the sweat gland epithelium.
Mg‐Atp Binding: Its Modification by Spermine, the Relevance to Cytosolic Mg2+ Buffering, Changes in the Intracellular Ionized Mg2+ Concentration and the Estimation of Mg2+ by 31P‐NMR
Authors: Lüthi Daniel , Günzel Dorothee , McGuigan John A. S.
Published: May 2004

It is now generally accepted that the intracellular ionized magnesium concentration ([Mg2+]i) in muscle cells is around 1 mmol l−1; in heart muscle this means that from the total some 90‐95% is bound (see McGuigan et al. 1991a). Although binding will include sequestration by intracellular organelles, a large part of the binding is by ATP in the cytosol and an equilibrium exists in the cytosol between free ATP, ionized magnesium and Mg‐ATP. The extend of this equilibrium depends on the equilibrium constant of the reaction, which is a function of pH, temperature and ionic strength. This equilibrium constant is also important in the estimation of [Mg2+]i using 31P‐NMR. In this method the difference between the α and β peaks of ATP is measured and from this shift and the equilibrium constant between Mg2+ and ATP in the cytosol, the [Mg2+]i can be calculated (Vink, 1993).
Role of Nitric Oxide in Indomethacin‐Induced Gastric Mucosal Dysfunction in the Rat
Authors: Gürbüz Vildan , Alican Inci , Yegen Berrak Ç. , Bozkurt Ayhan , Oktar Berna , Haklar Goncagül , Yüksel Meral , Kurtel Hizir
Published: May 2004

The present study was undertaken to explore the role of nitric oxide (NO) in the pathogenesis of experimental non‐steroidal anti‐inflammatory drug (NSAID)‐induced gastropathy. We assessed the role of NO inhibition and donation in indomethacin‐induced gastric mucosal dysfunction. The stomach was perfused with vehicle (control) for 20 min, followed by indomethacin (10 mg ml−1 in 1.25% sodium bicarbonate, pH 8.4) for 120 min. NG‐nitro‐l‐arginine methyl ester (l‐NAME, 5 and 10 mg kg−1, i.v. bolus), l‐arginine, D‐arginine (100 mg kg−1i.v. bolus, 10 mg kg−1 h−1, 2 h infusion) and the NO donor glyceryl trinitrate (GTN) were given at the same time (20, 40 and 80 μg kg−1 min−1, 15 min infusion) as perfusion with indomethacin was started. Epithelial permeability was quantified by measuring blood‐to‐lumen clearance of 51Cr‐labelled EDTA. Indomethacin caused a 20‐fold increase in 51Cr‐EDTA leakage compared with that of the control group. Treatment with l‐NAME or l‐arginine did not affect the indomethacin‐induced alterations in mucosal permeability. Administration of GTN (20 μg kg−1 min−1) significantly reduced the indomethacin‐induced mucosal dysfunction. By contrast, higher doses of GTN (80 μg kg−1 min−1) exacerbated epithelial dysfunction induced by indomethacin. Elevated levels of carbonyls and myeloperoxidase (MPO) observed after indomethacin administration were significantly reduced, to the control values, when GTN (20 μg kg−1 min−1) was administered along with indomethacin. These data suggest that NO from exogenous sources can exert a dual action on the integrity of the gastric mucosa challenged by indomethacin. Low doses of GTN can prevent mucosal dysfunction induced by indomethacin, while higher doses of GTN may exacerbate the increases in epithelial permeability.
Identification of Calcium‐Activated Potassium Channels in Cultured Equine Sweat Gland Epithelial Cells
Authors: Huang Yu , Ko Wing‐Hung , Chung Yiu‐Wa , Wong P. Y. D.
Published: May 2004

The patch‐clamp recording technique was used to examine the properties of the K+ channels in cultured equine sweat gland epithelial cells. With symmetric K+ solutions (140 mM), a single population of K+ channels was identified with a slope conductance of 187 pS and a reversal potential of around 0 mV. The channel was selective for K+ over Na+. Channel activity was increased by membrane depolarization. A 10‐fold increase in [Ca2+]i produced an approximate 60 mV negative shift in the open state probability (Popen)‐voltage curve. Externally applied tetraethylammonium ions (TEA+) caused a rapid and flickery block of the channel and reduced the unitary current amplitude. TEA+ bound to the blocking site with stoichiometry of 1:1 and with a dissociation constant (Kd) of 186 ± 27 μM at +40 mV. A weak voltage dependence of Kd was observed. Iberiotoxin (100 nM) reduced Popen but had no effect on single‐channel conductance. Neither glibenclamide (10 μM) nor intracellular adenosine 5′‐triphosphate (ATP, 1 mM) altered channel activity. In addition, ATP, when applied extracellularly, transiently activated the channel by increasing Popen. Channel activity was low around the resting membrane potential in the intact epithelia, indicating that these channels might not contribute to the resting K+ conductance. However, the channel could be activated in a regulated manner. The K+ channels may play a role in transepithelial fluid secretion in sweat gland.
Physiological Society Symposium: Atherosclerosis ‐ From Molecule to Man
Authors: Maxwell Andrew J. , Tsao Philip S. , Cooke John P.
Published: May 2004

This symposium paper has already been published as a Review Article in Experimental Physiology, volume 83, pp. 573‐584.
Candidate Genes Involved in Vascular Matrix Remodelling in Atherogenesis
Authors: Henney Adriano M.
Published: May 2004

One of the earliest events in the formation of an atherosclerotic lesion is the adherence of circulating monocytes to the vascular endothelium, through which they then gain entry to the sub‐intimal tissue. This early lesion subsequently evolves over a number of years to form an atherosclerotic plaque, through the migration and proliferation of cells, the accumulation of lipid in the vessel wall and through the extensive deposition and modification of a connective tissue matrix. Pathological studies have described a wide spectrum of structural architecture in atherosclerotic plaques which suggests that, with time, the vascular connective tissue matrix is extensively modified during atherogenesis. This process of vascular connective tissue remodelling, where matrix macromolecules are both deposited and degraded, is controlled by a complex network of cell‐cell and cell‐matrix interactions, involving the secretion of a wide variety of growth factors and cytokines and chemokines.
Molecular Modelling of the Biosynthesis of the Rna‐Editing Enzyme Apobec‐1, Responsible for Generating the Alternative forms of Apolipoprotein B
Authors: Scott James , Navaratnam Naveenan , Carter Charles
Published: May 2004

We discovered in 1987 that the shorter form of apolipoprotein B (B48) synthesized in the intestine is due to the action, previously unrecognized in mammalian cells, of an mRNA‐editing process, and more recently we demonstrated that this was due to a specific enzyme (APOBEC‐1) with cytidine deaminase activity. We show here, by sequence alignment, molecular modelling and mutagenesis, that APOBEC‐1 is a cytidine deaminase, responsible for editing apoB mRNA, and that is related in crystal structure to the cytidine deaminase of Escherichia coli (ECCDA). The two enzymes are both homodimers with composite active sites formed with loops from each monomer. In the sequence of APOBEC‐1, three gaps compared with ECCDA match the size and contour of the minimal RNA substrate. We propose a model in which the asymmetric binding of one active site to the substrate cytidine which is positioned by the downstream binding of the product uridine and that this helps to target the other active site for deamination.
Effect of Extracellular Cations on the Inward Rectifying K+ Channels Kir2.1 and Kir3.1/Kir3.4
Authors: Owen J. M. , Quinn C. C. , Leach R. , Findlay J. B. C. , Boyett M. R.
Published: May 2004

The effects of Ba2+, Mg2+, Ca2+ and Na+ as blocking ions were investigated in 90 and 10 mM extracellular K+ solutions on the cloned inward rectifying K+ channel Kir2.1 expressed in Xenopus oocytes. Some data were also obtained using another inward rectifying K+ channel Kir3.1/Kir3.4. The addition of Ba2+ caused a concentration‐, voltage‐ and time‐dependent block of both channels. Decreasing the extracellular K+ concentration augmented the block. The data suggest that Ba2+ blocks the channels by binding to a site within the channel pore and that the electrical binding distance, δ, of the site is significantly different for Kir2.1 and Kir3.1/Kir3.4 (∼ 0·38 and ∼ 0·22, respectively). Mg2+ and Ca2+ caused an instantaneous concentration‐ and voltage‐dependent block of both channels. With Kir2.1, decreasing the K+ concentration augmented the block. The voltage dependence of the block was less than that of Ba2+ (δ, ∼ 0·1), indicating a more superficial binding site for these ions within the channel pore. The affinity of the channels for Mg2+ and Ca2+ was ∼ 1000‐fold lower than that for Ba2+. Addition of Na+ resulted in a concentration‐, voltage‐ and time‐dependent block of Kir2.1, similar to that observed with Ba2+. The competition between the blocking cations (for Kir2.1: Ba2+, Mg2+, Ca2+; for Kir3.1/Kir3.4: Ba2+) and extracellular K+ suggests that the binding sites for the blocking cations may be sites to which K+ binds as part of the normal passage of K+ through the channels. It is possible that under normal physiological conditions naturally occurring extracellular cations may partly block the two inward rectifying K+ channels.
Breast Growth and the Urinary Excretion of Lactose During Human Pregnancy and Early Lactation: Endocrine Relationships
Authors: Cox David B. , Kent Jacqueline C. , Casey Tammy M. , Owens Robyn A. , Hartmann Peter E.
Published: May 2004

Breast volume and morphology of eight subjects were measured before conception and at intervals throughout pregnancy until 1 month of lactation. Breast volume before conception ranged from 293 to 964 ml. At the end of pregnancy the volume of breast tissue had increased by 145 ± 19 ml (mean ±s.e.m., n= 13 breasts, range 12‐227 ml) with a further increase to 211 ± 16 ml (n= 12 breasts, range 129‐320 ml) by 1 month of lactation. Urinary excretion of lactose increased at 22 weeks of pregnancy, signalling the capacity of the breast to synthesize lactose at this time. During pregnancy, both the change in breast volume and the change in cross‐sectional area of the areola were related to the concentration of human placental lactogen in the plasma. The growth of the nipple and the rate of excretion of lactose were related to the concentration of prolactin in the plasma. During the first 3 days after birth, the rate of excretion of lactose was related to the rate of excretion of progesterone. There was no relationship between the growth of the breast during pregnancy and the amount of milk produced at 1 month of lactation.
Breast Volume and Milk Production During Extended Lactation in Women
Authors: Kent Jacqueline C. , Mitoulas Leon , Cox David B. , Owens Robyn A. , Hartmann Peter E.
Published: May 2004

Quantitative measurements were made of relative breast volume and milk production from 1 month of lactation until 3 months after weaning, and the storage capacity of the breasts was calculated. The increase in breast tissue volume from before conception until 1 month of lactation was maintained for the first 6 months of lactation (means ±s.e.m.) (190·3 ± 13·1 ml, number of breasts, nb= 46). During this period of exclusive breast‐feeding, 24 h milk production from each breast remained relatively constant (453·6 ± 20·1 g, nb= 48), and storage capacity was 209·9 ± 11·0 ml (nb= 46). After 6 months, breast volume, milk production and storage capacity all decreased. There was a relationship between 24 h milk production and the storage capacity of the breasts, and these both appeared to be responding to infant demand for milk. At 15 months of lactation, the 24 h milk production of each breast was substantial (208·0 ± 56·7 g, nb= 6), even though the breasts had returned to preconception size. This was associated with an apparent increased efficiency of the breast (milk production per unit breast tissue) after 6 months, which may have been due to redistribution of tissues within the breast. The possible causes of the decrease in breast volume are discussed.
Comparison of Microvascular Filtration in Human Arms with and without Postmastectomy Oedema
Authors: Stanton A. W. B. , Holroyd B. , Mortimer P. S. , Levick J. R.
Published: May 2004

Oedema is caused by impaired lymphatic drainage and/or increased microvascular filtration. To assess a postulated role for the latter in postmastectomy oedema, filtration was studied in the forearms of 14 healthy subjects and 22 patients with chronic, unilateral arm oedema caused by surgical and radiological treatment for breast cancer. A new non‐contact optical device (the Perometer) and a conventional mercury strain gauge were used simultaneously to record forearm swelling rates caused by microvascular filtration during applied venous congestion. Filtration rate (FR) per 100 ml tissue was measured over 10‐15 min at a venous pressure of 30 cmH2O, a pressure reached in the dependent forearm (FR30), and then at 60 cmH2O (FR60). Apparent filtration capacity of 100 ml soft tissue (CFCa) was calculated from FR60 ‐ FR30/30, after adjustment for bone volume. The Perometer and strain gauge gave similar results in normal and oedematous arms. Mean CFCa in healthy subjects was (3·8 ± 0·4) × 10−3 ml (100 ml)−1 cmH2O−1 min−1, close to literature values. In the patients, FR30 was 47% lower in the oedematous forearm than in the opposite, unaffected forearm (P= 0·04). FR60 showed a similar trend but did not reach significance (P= 0·15). The values of CFCa of (2.2 ± 0.5) × 10−3 ml (100 ml)−1 cmH2O−1 min−1 in the oedematous arm and (2.8 ± 0.5) × 10−3 ml (100 ml)−1 cmH2O−1 min−1 in the unaffected arm were not significantly different (P= 0.47). When differences in arm volume on the two sides were taken into account, the total fluid load on the lymphatic system of the oedematous forearm was (411.0 ± 82.2) × 10−3 ml min−1 at 30 cmH2O and (1168 ± 235.6) × 10−3 ml min−1 at 60 cmH2O, similar to the normal side, namely (503.7 ± 109.3) × 10−3 ml min−1 and (1063 ± 152.0) × 10−3 ml min−1, respectively (P >= 0·50). The filtration capacity of the entire oedematous forearm (CFCa scaled up by total soft tissue volume), (25.4 ± 6.2) × 10−3 ml cmH2O−1 min−1, was not significantly greater than that of the normal forearm, (18.3 ± 2.6) × 10−3 ml cmH2O−1 min−1 (P= 0.40). The results indicate that no major change occurs in the microvascular hydraulic permeability‐area product of the forearm, or in the total filtration load on the lymph drainage system during dependency, in the arm with postmastectomy oedema compared with the normal arm. This argues against a significant haemodynamic contribution to postmastectomy oedema.
Insulin Sensitivity, Clearance and Release in Kininogen‐Deficient Rats
Authors: Damas Jacques , Bourdon Victor , Lefebvre Pierre J.
Published: May 2004

Insulin sensitivity of kininogen‐deficient rats was compared with that of normal rats using euglycaemic hyperinsulinaemic glucose clamping. Anaesthetized animals were infused with 2‐50 mU kg−1 min−1 of insulin and the glucose infusion rates needed to maintain euglycaemia were determined. Maximum glucose uptake, insulin sensitivity index and insulin clearance were reduced in kininogen‐deficient rats. Captopril increased the amount of glucose needed to maintain euglycaemia during infusion of 2 and 10 mU kg−1 min−1 of insulin in normal rats, but had no effect in kininogen‐deficient rats. Anaesthetized rats of both strains were given an intraperitoneal injection of glucose and the evolution of blood glucose was followed for 120 min. The peak increase was higher in kininogen‐deficient rats. Similar larger increases in blood glucose were observed after glucose injection in normal rats previously treated with HOE 140, a bradykinin B2 receptor antagonist. After glucose injection, plasma insulin increased in both groups of rats but reached lower levels in kininogen‐deficient animals. These results suggest that bradykinin is involved not only in the clearance of glucose and insulin by the tissues during insulin infusion but also that bradykinin can affect the release of insulin after a glucose load.
The Relaxant Effects of Parathyroid Hormone(1‐34) and Parathyroid Hormone‐Related Protein(1‐34) on Ovine Reticulo‐Ruminal Smooth Muscle in Vivo
Authors: Care A. D. , Abbas S. K. , Harmeyer J. , Boivin R.
Published: May 2004

The motility of the reticulo‐rumen has been measured in trained, conscious sheep using inflated balloons temporarily introduced to selected regions of that forestomach. The frequency and amplitude of the contractions of the reticulum and both the A and B waves of contraction of the rumen were measured under the same conditions before, during and after the administration of an i.v. bolus of either parathyroid hormone (PTH(1‐34)) or PTH‐related protein (PTHrP(1‐34)) followed by its i.v. infusion. These two peptides are known to share a common receptor in other organs, e.g. the kidney. In this study they both showed an inhibitory effect on reticulo‐ruminal motility. The effect of PTHrP(1‐34) on the rate of ruminal blood flow was also examined and a significant reduction observed, after a transient increase. The secretion of endogenous PTH(1‐34) was stimulated by a 32 % reduction in the plasma calcium ion concentration induced by an i.v. infusion of sodium citrate. Associated with this were significant reductions in reticulo‐ruminal motility, e.g. the reduction in the mean amplitude of the reticular contractions reflected the reduction in plasma calcium ion concentration. When the PTH(1‐34)/PTHrP(1‐34) receptor was blocked with [Asn10,Leu11,D‐Trp12]PTHrP(7‐34) before and during the induction of hypocalcaemia, all but one of the parameters of reticulo‐ruminal motility were normalized. Indeed, by the day following the administration of this blocking agent, all these parameters had returned to their normal range. It is concluded that stimulation of the PTH(1‐34)/PTHrP(1‐34) receptor in reticulo‐ruminal smooth muscle reduces the motility of this tissue and may play a role in the depression of motility of the digestive tract which is characteristic of clinical milk fever in the dairy cow.
Effect of Temperature on Muscle Metabolism During Submaximal Exercise in Humans
Authors: Starkie Rebecca L. , Hargreaves Mark , Lambert Donna L. , Proietto Joseph , Febbraio Mark A.
Published: May 2004

To study the effect of temperature on muscle metabolism during submaximal exercise, six endurance‐trained men had one thigh warmed and the other cooled for 40 min prior to exercise using water‐perfused cuffs. One cuff was perfused with water at 50‐55°C (HL) with the other being perfused with water at 0°C (CL). With the cuffs still in position, subjects performed cycling exercise for 20 min at a work load corresponding to 70% VO2,peak (where VO2,peak is peak pulmonary oxygen uptake) in comfortable ambient conditions (20‐22°C). Muscle biopsies were obtained prior to and following exercise and forearm venous blood was collected prior to and throughout the exercise period. Muscle temperature (Tmus) was not different prior to treatment, but treatment resulted in a large difference in pre‐exercise Tmus (difference = 6·9 ± 0·9°C; P < 0·01). Although this difference was reduced following exercise, it was nonetheless significant (difference = 0·4 ± 0·1°C; P < 0·05). Intramuscular [ATP] was not affected by either exercise or muscle temperature. [Phosphocreatine] decreased (P < 0·01) and [creatine] increased (P < 0·01) with exercise but were not different when comparing HL with CL. Muscle lactate concentration was not different prior to treatment nor following exercise when comparing HL with CL. Muscle glycogen concentration was not different when comparing the trials before treatment, but the post‐exercise value was lower (P < 0·05) in HL compared with CL. Thus, net muscle glycogen use was greater during exercise with heating (208 ± 23 vs. 118 ± 22 mmol kg−1 for HL and CL, respectively; P < 0·05). These data demonstrate that muscle glycogen use is augmented by increases in intramuscular temperature despite no differences in high energy phosphagen metabolism being observed when comparing treatments. This suggests that the increase in carbohydrate utilization occurred as a direct effect of an elevated muscle temperature and was not secondary to allosteric activation of enzymes mediated by a reduced ATP content.
Effects of Acute and Chronic Starvation on Central and Peripheral Noradrenaline Turnover, Blood Pressure and Heart Rate in the Rat
Authors: El Fazaa S. , Somody L. , Gharbi N. , Kamoun A. , Gharib C. , Gauquelin‐koch G.
Published: May 2004

When faced with stress, an organism calls upon several mechanisms to maintain biological homeostasis. The cardiovascular system is the first to respond usually with an increase in arterial pressure and tachycardia. Therefore we investigated the central and peripheral sympathetic responses to acute and chronic starvation in Wistar rats. The noradrenaline (NA) turnover rate was determined in different catecholaminergic nuclei (A1, A2, A5, A6) as well as the arterial blood pressure and heart rate modifications. During acute starvation (3 days of starvation), the NA turnover was increased in the A1 and rostral A2 nuclei as well as in ventricles and kidneys and decreased in the A6 nucleus. During chronic starvation (4 consecutive cycles of 3 days of starvation plus 1 day of feeding), the NA turnover was increased in the A5 and caudal A2 nuclei as well as in ventricles and atria and decreased in the A1 nucleus and kidneys. The arterial blood pressure revealed a gradual decrease during the first 3 days of fasting but the heart rate was not modified. We conclude that starvation should be considered as an unusual state of stress because of the absence of locus coeruleus response (A6 nucleus) despite its well‐defined role in stress reactions. One of the manifestations of these central and peripheral noradrenergic changes is the change in blood pressure during the starvation‐feeding cycles.
High Activity K+ Channels in Rat Hippocampal Neurones Maintained in Culture
Authors: Wann K. T. , Goodwin P. A. , Richards C. D.
Published: May 2004

A channel was identified in cell‐attached recordings in rat hippocampal neurones maintained in culture. This channel, which was highly active at the resting membrane potential, was present in most (73%) patches studied. The channel was characterized by long duration openings and a high open probability (Po, mean value 0·73 at ‐70 mV) at negative patch potentials with mild voltage dependence over the range ‐40 to ‐120 mV. It showed inward rectification. There were up to five active channels in cell‐attached recordings in experiments where the cells were bathed in sodium‐containing Locke solution. The single channel conductances in cell‐attached recordings with 140 or 40 mM K+ in the patch pipette were 26 and 12 pS, respectively. The channel was therefore selective for K+ over Na+. The channel was not permeable to Rb+ ions. The single channel conductance was 24 pS in excised inside‐out patches bathed in symmetrical K+ (140 mM) solutions. Examination of the channel kinetics revealed that both the open and closed time distributions could be fitted by the sum of three exponentials, there being no pronounced voltage sensitivity between ‐60 and ‐120 mV. The 26 pS K+ channel was insensitive to extracellular TEA, apamin, 4‐AP and dequalinium. Neither was it sensitive to intracellular Ca2+. Extracellular Ba2+ was effective in reversibly blocking the channel, the IC50 being 2.0 mM. There was no obvious effect of bath application of the K+ channel opener, lemakalim, or a cAMP analogue. This channel appears to contribute a significant proportion (at least 30%) of the resting conductance in these neurones.
Effects of Variations in Live Weight Gain on Bone Growth and Composition and on Markers of Bone Turnover in Lambs
Authors: Nicodemo M. L. F. , Scott D. , Buchan W. , Duncan A. , Robins S. P.
Published: May 2004

Growing lambs were fed the same diet at intakes supporting mean live weight gains of 0·1, 0·2 and 0·3 kg day−1, representing slow, intermediate and fast growth groups, respectively. The effects on bone growth and composition, and on blood and urinary bone marker concentrations or excretion rates were monitored. Compared with the slow‐growing lambs, the higher intake group grew twice as fast, had higher rates of bone growth (indicated by external metatarsal length), and larger and heavier bones at slaughter. Bones from fast‐growing animals had higher collagen and deoxypyridinoline concentrations, and lower Ca:collagen, Ca:P and pyridinoline : deoxypyridinoline ratios, indicating a less mature bone compared with the slow‐growing lambs. Bone growth rate had no effect on plasma osteocalcin, bone‐specific alkaline phosphatase or growth hormone concentrations, nor on the urinary excretion of pyridinoline and deoxypyridinoline. The results for plasma markers may be explained by an increase in blood volume linked with increased body weight.
The Use of a Deuterium Tracer Technique to Follow the Fate of Fluids Ingested by Human Subjects: Effects of Drink Volume and Tracer Concentration and Content
Authors: Lambert C. P. , Ball D. , Leiper J. B. , Maughan R. J.
Published: May 2004

Deuterium oxide (2H2O) has been added to drinks as a tracer for water to estimate the availability to the body water pool of ingested fluids, but doubts have been raised as to the reliability of the method. The present investigation evaluated the effects of systematic variations in the volume of fluid consumed and the amount and concentration of added tracer on the rate of accumulation of tracer in arterialized blood after ingestion of a labelled drink. Three separate experiments were undertaken. In expt 1, six healthy men ingested on separate occasions 200, 400 and 800 ml of a dilute glucose‐electrolyte solution: all test drinks contained the same concentration (40 g l−1) of 2H2O. In expt 2, six healthy men ingested 200, 400 and 800 ml of the same glucose‐electrolyte drink: each drink contained 8 g of 2H2O so that the concentration, but not the amount, of 2H2O differed between treatments. In expt 3, six healthy men ingested 400 ml of the same drink on three separate occasions: each drink contained 8, 16 or 32 g of tracer so that amount and concentration of 2H2O both varied. Arterialized venous blood samples were collected for the determination of deuterium (2H) concentration before ingestion of the test drink and at intervals for 120 min after ingestion. All trials for each of the experiments were conducted in the morning after an overnight fast and trials were in randomized order and separated by 7 days. In expt 1, the blood 2H concentration at all time points from 2 min after ingestion of the test drink onwards was higher for the drink containing 32 g 2H2O than for the drink containing 16 g 2H2O, which in turn was higher than after ingestion of the drink containing 8 g of 2H2O. In expt 2, no significant differences between treatments were observed at any time. In expt 3, the rate of 2H accumulation was greater after ingestion of the drink containing 32 g of 2H2O than after either of the other two drinks, and the 2H accumulation rate was greater after ingestion of the drink containing 16 g of 2H2O than after the drink containing 8 g of 2H2O. When data from all three experiments were combined, significant correlations were observed between the rate of accumulation of 2H in the circulation (p.p.m. min−1) and the amount (rs= 0.75, P < 0.001) and concentration (rs= 0.69, P < 0.001) of 2H2O in the test drink, but there was no relationship (rs= 0.09, P= 0.5) between the rate of 2H accumulation in the blood and the volume of the drink consumed. The results suggest that the rate of tracer accumulation in the blood after ingestion of different volumes of test drinks is not a reliable indication of the availability of the ingested fluid, but that the method gives at least a qualitative measure of the sum of the effects of gastric emptying and intestinal water absorption.
Energy Metabolism of Rat Skeletal Muscle Modulated by the Rate of Perfusion Flow
Authors: Štefl Bohumír , Mejsnar Jiří A. , Janovská Alena
Published: May 2004

In order to advance our understanding of the phenomenon of flow‐induced increases in the metabolism of the relaxed muscle, the metabolic rate of the isolated rat gracilis muscle was investigated at 28°C in vitro. The muscle was perfused with cell‐free Krebs‐Henseleit bicarbonate buffer containing 5% bovine serum albumin and 5 mM glucose, saturated with a gas mixture of 95% O2 and 5% CO2 and simultaneously superfused with a medium saturated with a low O2 gas mixture (1% O2, 5% CO2 and 94% N2). Two different perfusion flow rates (0·054 and 0·100 ml min−1) have been used. Their influence on oxygen consumption and lactate production has been measured. After a 100 min perfusion period, the muscle was freeze‐clamped and analysed for ATP, phosphocreatine, creatine, lactate, pyruvate, inorganic phosphate and glycogen content. The energy state of the cell and the proportions of glycolytic and mitochondrial fluxes of ATP synthesis were evaluated. During perfusion at the low flow rate of 0·054 ml min−1, the oxygen uptake was 45 ± 9 nmol min−1 (g wet wt)−1, accompanied by a dominance of anaerobic glycolytic synthesis of ATP over mitochondrial ATP synthesis, even though the total delivery of oxygen to muscle was three times higher than oxygen consumption. Increasing the perfusion flow rate to 0·100 ml min−1 increased the oxygen uptake to 120 ± 6 nmol min−1 (g wet wt)−1, thus leading to a prevalence of mitochondrial ATP synthesis over glycolytic ATP synthesis. The inner stores of glycogen served as the main substrate of energy metabolism and the role of exogenous substrates in the flow‐stimulated increase of oxygen uptake was negligible. The increase in perfusion rate also enhanced the energy state of the muscle fibres, which was expressed either as the creatine charge or as the value of the change of Gibbs free energy of ATP hydrolysis. Data indicate that the change of perfusion flow rate per se, apart from oxygen and exogenous substrate supply, elicits changes in the regulation of energy metabolism within non‐contracting skeletal muscle under open microcirculation.
Blockage of Mouse Muscle Nicotinic Receptors by Serotonergic Compounds
Authors: García‐Colunga Jesús , Miledi Ricardo
Published: May 2004

Xenopus laevis oocytes were used to analyse the effects of serotonin (5‐hydroxytryptamine, 5‐HT) and serotonergic agents on ionic currents elicited by the activation of mammalian muscle nicotinic acetylcholine receptors (AChRs). 5‐HT as well as other serotonergic agents, such as ketanserin, 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT), methysergide, spiperone, or fluoxetine alone (up to 1 mM), did not elicit membrane currents in Xenopus oocytes expressing AChRs, but they reversibly reduced the current elicited by acetylcholine (ACh‐current). Serotonin was applied before, together with or after ACh application, and its effects were examined on desensitizing and non‐desensitizing ACh‐currents. 5‐HT reduced the amplitude and accelerated the desensitization of the desensitizing currents. In contrast, non‐desensitizing currents were reduced in amplitude but their time course was not significantly affected. With the same concentration of 5‐HT the inhibition was stronger on desensitizing than on non‐desensitizing ACh‐currents. For example, 100 μM 5‐HT reduced the peak of a desensitizing ACh‐current to 0·48 ± 0·06 (peak current ratio) and after 40 s the current was reduced to a ratio of 0·25 ± 0·04, whereas a non‐desensitizing ACh‐current was reduced to a ratio of 0·66 ± 0·01. All the serotonergic agents tested inhibited the ACh‐currents rapidly and reversibly, suggesting that they are acting directly on the AChRs. The half‐inhibitory concentration, IC50, of 5‐HT acting on non‐desensitizing currents elicited by 250 nM ACh was 247 ± 26 μM and the Hill coefficient was [sim]0.88, suggesting a single site for the interaction of 5‐HT with the receptor. It appears that 5‐HT inhibits AChRs non‐competitively because neither the half‐effective concentration of ACh, EC50, for ACh‐current nor the Hill coefficient were affected by 5‐HT. Furthermore, the extent of inhibition of 5‐HT on AChRs did not depend on the nicotinic agonist (suberyldicholine, ACh or nicotine). The inhibition of AChRs by serotonergic agents was voltage‐dependent. The electrical distance of the binding site for 5‐HT was [sim]0.75, whereas for the other serotonergic agents tested it was [sim]0.22, suggesting that ketanserin, 8‐OH‐DPAT, methysergide, spiperone and fluoxetine act within the ion channel, but at a site more external than that for 5‐HT. These substances inhibited the ACh‐current more potently than 5‐HT. We conclude that 5‐HT and serotonergic agents inhibit, in a non‐competitive manner, the ACh‐current in muscle AChRs by blocking the open receptor‐channel complex. Moreover, 5‐HT appears to promote the desensitized state of the receptor when the current is elicited by high ACh concentrations.