bluuebunny/crossref_metadata_2025 huggingface dataset:
Secretagogue‐evoked changes in intracellular free magnesium concentrations in rat pancreatic acinar cells.
Authors: Lennard R , Singh J
Published: December 2014

1. This study employs the fluorescent dye Mag‐Fura‐2 acetoxymethyl ester (AM) to measure intracellular free magnesium concentration [Mg2+]i in isolated rat pancreatic acinar cells. Initially a number of protocols were investigated to develop optimal loading conditions for the dye Mag‐Fura‐2 AM. The procedure yielding cells which showed minimal dye loss and no adverse compartmentalization was adopted for subsequent experiments. 2. The mean resting [Mg2+]i is 1.39 +/‐ 0.08 mM (n = 39). 3. Acetylcholine (ACh), cholescystokinin‐octapeptide (CCK8), carbamylcholine chloride evoked marked reduction in [Mg2+]i in pancreatic acinar cells compared to resting values in the absence of secretagogues. The ACh‐evoked decrease in [Mg2+]i was abolished by pre‐treatment with atropine. In contrast, noradrenaline, adrenaline and histamine had no significant effect on [Mg2+]i. 4. In acinar cells loaded with the Ca(2+)‐sensitive dye, Fura‐2 acetoxymethyl ester (AM), ACh stimulation resulted in a marked elevation in intracellular free Ca2+ concentration [Ca2+]i. This response was blocked by pre‐treatment with atropine. 5. Atomic absorption spectrophotometry was used to measure Mg2+ levels in effluent samples from pancreatic segments. Stimulation of pancreatic segments with ACh resulted in a marked elevation in Mg2+ concentrations (net efflux). On removal of ACh, Mg2+ concentration returned to resting level followed by a small net influx of Mg2+ into pancreatic tissue. 6. The results demonstrate that secretagogue‐evoked alteration in [Mg2+]i may occur concurrently with Mg2+ release from pancreatic tissue.
Regulation of intracellular free magnesium concentration in the taenia of guinea‐pig caecum.
Authors: Nakayama S , Tomita T
Published: December 2014

1. In the taenia isolated from the guinea‐pig caecum, changes in free intracellular magnesium concentration ([Mg2+]i) were measured based on the separation of the chemical shift of the alpha‐ and beta‐peaks of ATP obtained with nuclear magnetic resonance (NMR). 2. When external Mg2+ was increased from 1.2 to 12 and 40 mM, [Mg2+]i increased from 0.34 +/‐ 0.05 to 0.39 +/‐ 0.07 and 0.61 +/‐ 0.18 mM (n = 3), respectively, in 125‐150 min. In the absence of Ca2+, the increase was greater, i.e. [Mg2+]i reached 0.92 +/‐ 0.05 (n = 3) and 3.37 mM (n = 1), respectively. 3. In Ca(2+)‐ and Mg(2+)‐free solution, [Mg2+]i decreased to about 10 microM in 100 min. This decrease was not affected by substitution of Na+ with K+, but the recovery of [Mg2+]i on Mg2+ readmission was slower in the absence of Na+. This recovery was prevented by Ca2+ (2.4 mM), but Na+ readmission produced full recovery of [Mg2+]i in the presence of Ca2+. 4. When Na+ was substituted with K+ in the absence of Ca2+, [Mg2+]i increased from 0.38 +/‐ 0.01 mM to 0.56 +/‐ 0.04 mM (n = 4) in 100 min. Substitution of Na+ with N‐methyl‐D‐glucamine produced a much greater increase (to 2.1 mM in 100 min). Removal of the external K+ in the absence of Ca2+ also increased [Mg2+]i to 0.66 +/‐ 0.11 mM (n = 4) in 150 min, but no clear change was observed in the presence of Ca2+. Full recovery of [Mg2+]i could be produced in normal solution even when the intracellular phosphocreatine and ATP concentrations were 70‐80% of the control. 5. It is concluded that in the smooth muscle of the guinea‐pig taenia caeci an Na(+)‐Mg2+ exchange process and possibly also an ATP‐driven Mg2+ pump are playing important roles in maintaining free [Mg2+]i at about 0.3 mM under the physiological condition. In addition to this, Ca2+ inhibits both Mg2+ efflux and influx, probably by reducing the membrane permeability to Mg2+ and by competing with Mg2+ in the Na(+)‐Mg2+ exchange of the plasma membrane.
Adenosine 5'‐triphosphate increases acetylcholine channel opening frequency in rat skeletal muscle.
Authors: Lu Z , Smith D O
Published: December 2014

1. The effects of extracellular adenosine 5'‐triphosphate (ATP) on the acetylcholine (ACh) channel opening activity was studied in dissociated rat skeletal muscle cells using patch‐clamp recording techniques in cell‐attached configuration. 2. With 10 microM‐ATP in the recording pipette, the spontaneous opening frequency on the the alpha‐bungarotoxin‐sensitive ACh channel increased significantly from 0.3 to 4.7 s‐1, although the opening frequency was not as high as that activated by very low (0.4 microM) ACh concentrations (64 s‐1). 3. Spontaneous ACh channel openings, and ATP‐associated and ACh‐activated channel openings had similar single‐channel conductances, 55, 59 and 56 pS, respectively. 4. ATP‐associated events and spontaneous ACh channel opening events had similar mean channel open durations (0.6 ms); however, these values were considerably shorter than the duration of ACh‐activated events (2 ms). 5. Pre‐treatment with alpha‐bungarotoxin (100 nM) blocked spontaneous ACh channel openings, ATP‐associated openings and ACh‐activated openings. 6. When delivered through a separate drug pipette after the formation of a gigaseal, ATP increased ACh‐activated single‐channel open probability in a dose‐dependent fashion. 7. The increase in channel open probability was due primarily to the increase in channel opening frequency. ATP did not significantly alter the mean channel open duration or the single‐channel conductance. 8. The ATP analogue adenosine‐5'‐O‐(3‐thiotriphosphate) (ATP‐gamma‐S) also enhanced ACh‐activated channel open probability with relatively less potency. ADP, AMP and adenosine (up to 1 mM) did not significantly increase ACh channel open probability. 9. It is concluded that ATP in the micromolar range facilitates both spontaneous and agonist‐activated ACh channel opening. The facilitation is due to ATP itself and not to products of ATP hydrolysis. The facilitatory actions of ATP on ACh channels are manifested by the increase in the channel opening frequency, and they may be mediated by an intracellular second messenger.
Vestibular and cerebellar modulation of expiratory motor activities in the cat.
Authors: Huang Q , Zhou D , St John W M
Published: December 2014

1. The purpose of our investigation was to evaluate the hypothesis that components of the vestibular and cerebellar systems regulate efferent respiratory‐modulated activities of cranial and spinal nerves. The hypothesis was based upon the observation that spinal neural activities during expiration are greatly altered subsequent to a change in posture. 2. In decerebrate and paralysed cats, efferent activities were recorded from the central cut ends of the phrenic nerve, intercostal nerve, branch of the intercostal nerve innervating the triangularis sterni, cranial iliohypogastric (abdominal) nerve and recurrent laryngeal nerve. 3. Animals were artificially ventilated. Those with intact vagi were ventilated by a servo‐respirator which produced changes in lung volume in parallel with alterations in integrated activity of the phrenic nerve. Animals with bilateral vagotomy were ventilated with a standard respirator. 4. Aspiration of the entire cerebellar cortex did not produce alterations in levels of neural activities; the respiratory frequency was increased modestly. Following ablation of the ventrolateral portion of corpus medullare and cerebellar peduncles, expiratory activities of spinal nerves were completely eliminated whereas inspiratory activities were not greatly altered. Results were similar in animals having either intact or sectioned vagi. 5. Electrical stimulation or chemical stimulation by glutamate of regions of the ventrolateral cerebellum produced little change in respiratory neural activities except when these stimulations were within the infracerebellar nucleus. Stimulations in this nucleus caused pronounced increases in expiratory activities of spinal nerves. Neither inspiratory activities of spinal nerves nor inspiratory or expiratory activities of the recurrent laryngeal nerve were altered. Studies in animals having intact or sectioned vagi yielded similar results. 6. Bilateral lesions of neurons in the infracerebellar nucleus by injections of kainic acid in animals having intact or sectioned vagi caused an irreversible loss of expiratory activities of spinal nerves with neither inspiratory spinal activities nor inspiratory and expiratory laryngeal activities being altered. Similar findings were obtained following unilateral ablation of the infracerebellar nucleus in vagotomized cats. However, in cats with intact vagi, unilateral ablation of the infracerebellar nucleus produced only transient changes in either inspiratory or expiratory neural activities.(ABSTRACT TRUNCATED AT 400 WORDS)
Regional heterogeneity of endothelium‐dependent vasodilatation in the rabbit kidney.
Authors: Cairns H S , Rogerson M E , Westwick J , Neild G H
Published: December 2014

1. Regional heterogeneity of endothelial function exists but its role in the local regulation of vascular tone is uncertain. This heterogeneity may be very important in the control of the glomerular filtration rate (GFR) in which the differential tone in the afferent and efferent arterioles is crucial. 2. When an endothelium‐independent vasodilator, prostacyclin (PGI2) or nitroprusside, was infused into anaesthetized rabbits there were dose‐dependent falls in both mean arterial pressure (MAP) and GFR; PGI2 (0.4 nmol kg‐1 min‐1) altered MAP and GFR by ‐18.5 +/‐ 3.6% (mean +/‐ S.E.M.) and ‐37.7 +/‐ 13.3% respectively and nitroprusside (30 nmol kg‐1 min‐1) by ‐29.7 +/‐ 3.1% and ‐67.0 +/‐ 2.4%. In contrast infusion of an endothelium‐dependent vasodilator, acetylcholine (ACh) or substance P, produced dose‐dependent decreases in MAP but dose‐dependent increases in GFR; ACh (10 nmol kg‐1 min‐1) ‐15.1 +/‐ 2.0% and +43.8 +/‐ 16.5% and substance P (30 nmol kg‐1 min‐1) ‐18.7 +/‐ 1.9% and +45.3 +/‐ 23.1% respectively. The effects of endothelium‐dependent and independent vasodilators on GFR was significantly different (p less than 0.005). 3. Simultaneous administration of indomethacin, Methylene Blue or NG‐monomethyl‐L‐arginine (L‐NMMA), inhibitors of cyclo‐oxygenase and endothelium‐derived relaxing factor (EDRF) respectively, attenuated or reversed the effect of ACh (10 nmol kg‐1 min‐1) on MAP and GFR. 4. These data suggest that endothelium‐dependent vasodilatation in the kidney has a heterogeneous effect on the renal microvasculature, exerting a preferential effect on afferent glomerular arterioles and thereby preserving GFR despite the fall in MAP.(ABSTRACT TRUNCATED AT 250 WORDS)
Inactivation kinetics of calcium current of acutely dissociated CA1 pyramidal cells of the mature guinea‐pig hippocampus.
Authors: Kay A R
Published: December 2014

1. The process of inactivation of the Ca2+ current of acutely dissociated pyramidal cells from the CA1 subfield of mature guinea‐pig hippocampus was characterized. The decline of the current after rapid activation could be approximated well by the sum of two exponentials (time constants approximately 200 ms and 2 s) and a constant offset. 2. The time constants of inactivation exhibited a voltage dependence consistent with a voltage‐dependent mechanism. However, under conditions which normally counteract Ca(2+)‐dependent inactivation (viz. intracellular bis(O‐aminophenoxy)‐ethane‐N,N,N',N'‐tetraacetic acid (BAPTA) and external Ba2+) all three showed a U‐shaped inactivation curve, characteristic of Ca(2+)‐dependent inactivation. 3. The rate of inactivation was found to increase with current at a given voltage; however, increasing external divalent ion concentrations did not accelerate inactivation. 4. Calcium imaging experiments, using the Ca(2+)‐sensitive probe, Fura‐2, were performed to estimate the accumulation of Ca2+ in the presence of 10 mM‐intracellular BAPTA. Under these conditions voltage steps which induced maximal Ca2+ currents lead to free Ca2+ concentrations of less than 500 nM in the bulk of the cytoplasm. 5. Elevation of the intracellular free Ca2+ concentration to above 1 microM suppressed all the components of the Ca2+ current. However, even at a concentration of 3 microM‐Ca2+ the U‐shaped inactivation curve persisted. 6. Substitution of Ca2+ for Ba2+ led to an acceleration of inactivation through an increase in the proportion of the fast process of inactivation and an acceleration of both the fast and slow rates of inactivation. 7. During the slow decline of Ca2+ current ('run‐down') the proportion of all three components remained approximately constant and there was little change in the rate of inactivation. 8. On the basis of the results I suggest that inactivation results fro a dual process of voltage‐ and Ca(2+)‐dependent inactivation. Ca(2+)‐dependent inactivation seems to result from the accumulation of Ca2+ close to the channel mouth. 9. The macroscopic properties of the Ca2+ channel are consistent with the existence of one channel type in the CA1 pyramidal cells.
Multiple effects of tetraethylammonium on N‐methyl‐D‐aspartate receptor‐channels in mouse brain neurons in cell culture.
Authors: Wright J M , Kline P A , Nowak L M
Published: December 2014

1. The mechanisms of tetraethylammonium (TEA) antagonism of N‐methyl‐D‐aspartate (NMDA) responses were investigated in cultured mouse cortical neurons by analysing single‐channel and whole‐cell currents from patch clamp recordings. TEA (1‐5 mM) decreased whole‐cell NMDA responses. Kainate and quisqualate receptor‐mediated responses were unaffected at these TEA concentrations. 2. In whole‐cell recordings, increasing the NMDA concentration while keeping the TEA concentration constant resulted in greater inhibition by TEA. Thus, TEA‐mediated inhibition of NMDA responses was not due to competitive antagonism, and the greater inhibition by a single dose of TEA as NMDA concentration was elevated indicated some form of non‐competitive inhibition. In single‐channel recordings, two inhibitory effects were seen in 1‐5 mM‐extracellular TEA: single‐channel conductance (gamma) was decreased, and the frequency of channel events was decreased. These effects were not accompanied by any change in average channel open time. 3. Single‐channel current‐voltage (I‐V) curves obtained in 2, 5, 10 and 30 mM‐TEA indicated the decrease in NMDA channel conductance was voltage dependent with larger reduction occurring as patches were hyperpolarized. The data were well fitted by the Woodhull model with the dissociation constant (KD) showing an e‐fold increase in inhibition for a 43‐45 mV change in membrane potential. The 0 mV KD was 45 mM‐TEA decreasing to about 11 mM at ‐60 mV. The TEA block site appeared to sense approximately 60% of the transmembrane potential field (delta = 0.6) for extracellular application of TEA. 4. The decrease in channel opening frequency seen in TEA was concentration dependent and generally more sensitive to extracellular TEA than the channel block effect. There was a 50% reduction in the number of NMDA channel openings observed in 5 mM‐TEA. Increasing either NMDA or glycine concentrations in constant TEA concentration caused an additional decrease in the frequency of NMDA channel opening. In contrast to extracellular TEA, intracellular TEA had no noticeable effect on open‐state probability. 5. NMDA single‐channel currents were observed at positive potentials after completely replacing pipette Cs+ by 140 mM‐TEA‐Cl indicating TEA could serve as a current carrier through NMDA channels. Single channel I‐V curves obtained with pipettes containing 70 or 140 nM‐TEA in place of equivalent amounts of Cs+ were fitted by the Goldman‐Hodgkin‐Katz (GHK) equation over the range of ‐80 to +70 mV assuming a permeability of 0.45 compared with a Cs+ permeability of 1.0.(ABSTRACT TRUNCATED AT 400 WORDS)
Noradrenaline receptors participate in the regulation of GABAergic inhibition in area CA1 of the rat hippocampus.
Authors: Andreasen M , Lambert J D
Published: December 2014

1. Standard intracellular recordings from CA1 pyramidal neurones in in vitro hippocampal slices have been used to investigate the effects of excitatory amino acid antagonists and adrenergic agents on evoked synaptic potentials. 2. Ortho‐ and antidromic stimulation were conducted with remotely placed electrodes in order to minimize the possibility of stimulating the interneurones directly. In addition to the excitatory postsynaptic potential (EPSP), orthodromic stimulation evoked an inhibitory sequence consisting of a fast and slow inhibitory postsynaptic potential (IPSP). The slow‐IPSP was blocked by intracellular injection of QX 314. Antidromic stimulation evoked a relatively pure fast‐IPSP. 3. In seven neurones the differential effects of glutamatergic receptor blockers on the fast‐IPSP were investigated. The N‐methyl‐D‐aspartate (NMDA) receptor blocker, DL‐2‐amino‐5‐phosphonovaleric acid (APV) was added after the full effect of the non‐NMDA receptor blocker, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) had been achieved. In three neurones, APV had no additional blocking effect, while in the remaining four neurones, both the ortho‐ and antidromically evoked IPSPs were reduced by 20‐50%. This suggests that NMDA receptors participate in the activation of some GABAergic interneurones, which was further confirmed by showing that the IPSP was enhanced by Mg(2+)‐free medium. 4. In the presence of CNQX (10 microM) and APV (50 microM) together, the ortho‐ and antidromically evoked fast‐IPSPs were greatly reduced. A small ‘residual’ IPSP remained which was best studied by depolarizing the neurone to around ‐50 mV. With maximum stimulation, this amounted to 26.3 +/‐ 15.4% (mean +/‐ S.E.M., n = 15) of the control IPSP evoked by orthodromic stimulation and 41 +/‐ 14.6% of the control IPSP evoked by antidromic stimulation. The following statements apply equally to the ortho‐ and antidromically activated residual IPSPs. 5. The residual IPSP was completely blocked by low concentrations of bicuculline, indicating that it is mediated by GABAA receptors. When compared with a control IPSP of similar amplitude, the residual IPSP was found to have a faster rise time and time‐to‐peak, but a similar decay time. 6. Neither the muscarinic cholinergic antagonist, atropine nor the presynaptic glutamate agonist, L‐2‐amino‐4‐phosphonobutyric acid (L‐APB) had any effect on the residual IPSP. 7. The residual IPSP was completely blocked by the adrenergic beta‐receptor antagonist, L‐propranolol (50‐100 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
Increase in Ib inhibition by antagonistic voluntary contraction in man.
Authors: Yanagawa S , Shindo M , Nakagawa S
Published: December 2014

1. Ib inhibition from gastrocnemius medialis (GM) muscle to soleus (Sol) muscle was studied at rest and at the onset of phasic voluntary contraction of antagonistic pretibial muscles in seventeen normal subjects. 2. In twelve out of seventeen subjects there was inhibition of Sol H reflex by GM conditioning stimulation at rest with a latency of 1.5‐3.0 ms and a threshold of 0.85‐1.00 times the motor threshold (MT). The amount of inhibition at 0.95‐1.05 x MT, which was calculated by subtracting the size of the conditioned reflex from that of the unconditioned one, ranged from 0.8 to 5.6% of the maximal M‐response or 2.9‐18.3% of control H reflex. This inhibition was ascribed to Ib inhibition, taking into account its latency and threshold. 3. On weak pretibial contraction the inhibition either increased in amount or newly appeared in all the subjects. When the strength of voluntary contraction was graded from 1 to 20% of the maximum, the increment in the amount of inhibition decreased or almost disappeared at strengths of more than several per cent. These facts imply that at least some of the Ib interneurones are facilitated to fire by descending commands alone without peripheral Ib impulses. Contralateral ankle dorsiflexion did not modify the inhibition. 4. Soleus muscle H reflex was not modulated at all by cutaneous stimulation instead of GM stimulation at rest, nor was it affected by cutaneous stimulation on ipsilateral antagonistic contraction. 5. It is concluded that activity in the Ib inhibitory pathway is facilitated at the onset of antagonistic voluntary contraction. This suggests that control of the Ib inhibitory pathway may be utilized in ordinary voluntary movement, and is presumably beneficial for smooth execution of movement.
Parathyroid hormone selectively inhibits L‐type calcium channels in single vascular smooth muscle cells of the rat.
Authors: Wang R , Karpinski E , Pang P K
Published: December 2014

1. The active synthetic N‐terminal fragment of bovine parathyroid hormone, bPTH‐(1‐34) at a concentration of 1 microM, decreased the peak amplitude of the long‐lasting (L‐type) calcium channel current by 37% (n = 14, P less than 0.01) in rat tail artery smooth muscle cells. By contrast, this fragment of parathyroid hormone (PTH) (1 microM) had no effect on the transient (T‐type) calcium channel current in the same cell preparation. 2. The inhibitory effect of bPTH‐(1‐34) on L‐channel currents was reversible and could be antagonized by the L‐channel agonist, Bay K 8644. In contrast, bPTH‐(1‐34) inhibited Bay K 8644‐induced amplification of L‐channel currents. 3. The inhibitory effect of bPTH‐(1‐34) on L‐Channel currents was dose dependent with a threshold concentration of less than 10(‐7), and voltage dependent with increased inhibition at more positive holding potentials. However, this effect of bPTH‐(1‐34) was not dependent on different pulse lengths or interpulse intervals. 4. The kinetics of deactivation of L‐channel currents were not changed although the instantaneous amplitude of the L‐channel tail current was reduced by bPTH‐(1‐34). 5. Application of bPTH‐(1‐34) antagonists (10(‐6) M‐bPTH‐(3‐34) and 10(‐5) M‐bPTH‐(7‐34] did not result in any significant change in the magnitude of L‐channel currents (n = 15 and n = 7, respectively). 6. Pre‐incubation of cells with bPTH‐(3‐34) for more than 15 min abolished the inhibitory effect of bPTH‐(1‐34) on L‐channel currents. 7. The present study provides direct evidence to demonstrate the PTH, an endogenous circulating hormone, is a selective inhibitor of L‐channel currents in vascular smooth muscle cells.
Changes in excitability and accommodation of human motor axons following brief periods of ischaemia.
Authors: Bostock H , Baker M , Grafe P , Reid G
Published: December 2014

1. The mechanism of post‐ischaemic ectopic impulse generation in nerve is not known, and previous measurements of excitability changes in human motor axons have appeared to conflict. We have used automatic threshold tracking and different stimulus‐response combinations to follow the effects on excitability of brief (5‐10 min) periods of ischaemia, too short to induce motor fasciculations. Excitability changes have been compared at different sites in axons innervating hand, arm and foot muscles. 2. Threshold was determined as the percutaneous stimulus current required to excite a single motor unit, or to evoke a constant multiunit response, after rectifying and integrating the electromyogram (EMG). Three different waveforms of stimulus current were compared: short (less than or equal to 2 ms) pulses, long (100‐200 ms) pulses to measure rheobase, and 100 ms current ramps. We also measured accommodation by recording the effects of subthreshold depolarizing currents on excitability. 3. Ischaemic and post‐ischaemic excitability changes were greatest in the proximal parts of the longest motor axons, and greater if the sphygmomanometer cuff was inflated over, rather than proximal to, the stimulating site. 4. Using integrated EMG responses from abductor digiti minimi, the ulnar nerve stimulated above the elbow became rapidly much less excitable after ischaemia when tested with short pulses, but more excitable when tested with current ramps. The rheobase rose briefly, but then fell, often below resting level, always staying below the pulse and ramp thresholds. 5. The latency of the response to a rheobasic stimulus altered in parallel with the threshold to short current pulses, and increased dramatically after ischaemia. This latency increase was associated with a prolonged phase of ‘negative accommodation’, i.e. the continued increase in excitability to a maintained subthreshold depolarizing current. 6. Changes in excitability and accommodation similar to those occurring after ischaemia were recorded following high frequency trains of stimuli. They were attributed primarily to hyperpolarization by the electrogenic sodium pump, since comparable changes could be induced by passing a steady hyperpolarizing current through the stimulating electrode. 7. Threshold and latency recordings from single motor units during and after ischaemia resembled in most respects the multiunit responses, but single unit rheobase did not show a post‐ischaemic fall below the resting level. Repetitive firing contributed to the low multiunit thresholds recorded with long current pulses during the post‐ischaemic period. 8. We conclude that human motor nerves become simultaneously both more and less excitable than normal after 10 min of ischaemia, depending on the choice of stimulus and response.(ABSTRACT TRUNCATED AT 400 WORDS)
Attenuation of exercise vasodilatation by adenosine deaminase in anaesthetized dogs.
Authors: Goonewardene I P , Karim F
Published: December 2014

1. In dogs anaesthetized with sodium pentobarbitone and artificially ventilated, the gracilis muscles were vascularly isolated and perfused at a constant flow of 28.4 +/‐ 4.6 ml min‐1 (100 g muscle tissue)‐1 (99.8 +/‐ 4.5% of maximum free flow, means +/‐ standard error of the mean (S.E.M.), n = 9). 2. Three to five minutes of electrical stimulation of the cut peripheral end of the obturator nerve (4 Hz, 6 V, 0.2 ms) resulted in muscle contraction (0.61 +/‐ 0.14 kg (100 g)‐1 during solvent infusion and 0.56 +/‐ 0.10 kg (100 g)‐1 during intra‐arterial adenosine deaminase infusion (50 U min‐1) and an immediate decrease in arterial perfusion pressure from 184.5 +/‐ 8.1 mmHg to 148.2 +/‐ 5.7 mmHg (18.7 +/‐ 3.4% decrease) during solvent infusion, and from 193.5 +/‐ 7.16 to 142.0 +/‐ 10.2 mmHg (25.4 +/‐ 6.1% decrease) during adenosine deaminase infusion 10 s after the commencement of muscle stimulation. After about 5 min of muscle contractions, the arterial perfusion pressure decreased to 120.8 +/‐ 7.8 mmHg (32.9 +/‐ 5.8% decrease) during solvent infusion, and to 152.8 +/‐ 11.2 mmHg (20.9 +/‐ 5.3% decrease) during adenosine deaminase infusion (i.e. 37.9 +/‐ 6.2% attenuation of the fall in arterial perfusion pressure). The time taken for 90% recovery of the arterial perfusion pressure was 72.1 +/‐ 10.9 s during solvent infusion, and 51.5 +/‐ 9.3 s during adenosine deaminase infusion (P less than 0.05). 3. Adenosine (2 x 10(‐3) mol l‐1) infusion in the resting muscle during solvent infusion (final concentration in arterial blood 1.3 x 10(‐4) +/‐ 6.0 x 10(‐5) mol l‐1) resulted in a 34.8 +/‐ 7.2% fall in arterial perfusion pressure but a fall of only 7.2 +/‐ 1.8% during adenosine deaminase infusion (50 U min‐1; P less than 0.05; n = 5) indicating that adenosine deaminase infused at 50 U min‐1 was more than adequate to metabolize endogenous adenosine produced during muscle contractions. 4. These data suggest that adenosine contributes about 40% to the sustained‐exercise vasodilatation under constant high‐flow conditions and also in post‐exercise vasodilatation, but does not contribute to the initiation of exercise vasodilatation.
Sodium‐dependent magnesium uptake by ferret red cells.
Authors: Flatman P W , Smith L M
Published: December 2014

1. Magnesium uptake can be measured in ferret red cells incubated in media containing more than 1 mM‐magnesium. Uptake is substantially increased if the sodium concentration in the medium is reduced. 2. Magnesium uptake is half‐maximally activated by 0.37 mM‐external magnesium when the external sodium concentration is 5 mM. Increasing the external sodium concentration increases the magnesium concentration needed to activate the system. 3. Magnesium uptake is increased by reducing the external sodium concentration. Uptake is half‐maximum at sodium concentrations of 17, 22 and 62 nM when the external magnesium concentrations are 2, 5 and 10 mM respectively. 4. Replacement of external sodium with choline does not affect the membrane potential of ferret red cells over a 45 min period. 5. Magnesium uptake from media containing 5 mM‐sodium is inhibited by amiloride, quinidine and imipramine. It is not affected by ouabain or bumetanide. Vanadate stimulates magnesium uptake but has no effect on magnesium efflux. 6. When cell ATP content is reduced to 19 mumol (1 cell)‐1 by incubating cells for 3 h with 2‐deoxyglucose, magnesium uptake falls by 50% in the presence of 5 mM‐sodium and is completely abolished in the presence of 145 mM‐sodium. Some of the inhibition may be due to the increase in intracellular ionized magnesium concentration ([Mg2+]i) from 0.7 to 1.0 mM which occurs under these conditions. 7. Magnesium uptake can be driven against a substantial electrochemical gradient if the external sodium concentration is reduced sufficiently. 8. These findings are discussed in terms of several possible models for magnesium transport. It is concluded that the majority of magnesium uptake observed in low‐sodium media is via sodium‐magnesium antiport. A small portion of uptake is through a parallel leak pathway. It is believed that the antiport is responsible for maintaining [Mg2+]i below electrochemical equilibrium in these cells at physiological external sodium concentration. Thus in ferret red cells the direction of magnesium transport can be reversed by reversing the sodium gradient.
Endogenous adenosine modulates stimulation‐induced depression at the frog neuromuscular junction.
Authors: Meriney S D , Grinnell A D
Published: December 2014

1. Endogenous adenosine, which is produced by enzymatic degradation of ATP released from synaptic vesicles, has been shown to be a potent inhibitor of acetylcholine release from motor nerve terminals. It has been proposed that this auto‐inhibition mechanism might contribute significantly to tetanic stimulation‐induced depression. 2. Levels of facilitation and depression during a 20 Hz stimulus train differ greatly in different terminals, but are strongly and non‐linearly correlated with the terminal's release characteristics (the amount of transmitter released per unit terminal length, or ‘release efficacy’). There is a weaker, approximately linear, correlation between depression and release efficacy at 2 Hz stimulation. 3. The effects of both endogenous and exogenously applied adenosine are also highly variable for different nerve terminals. We have shown that much of this variability can be attributed to the release efficacy of each terminal in the case of endogenous effects, and to the size of the nerve terminal in the case of exogenously applied adenosine receptor agonists. 4. When nerve terminals are pooled according to their individual release characteristics, endogenous adenosine can be shown to contribute significantly to stimulation‐induced depression of release primarily in terminals that release enough transmitter to generate significant levels of adenosine, but do not release so much transmitter that depletion of releasable quanta is severe.
Effects of neuropeptide‐Y on renal function and its interaction with sympathetic stimulation in conscious dogs.
Authors: Persson P B , Ehmke H , Nafz B , Lang R , Hackenthal E , Nobiling R , Dietrich M S , Kirchheim H R
Published: December 2014

1. The effects of neuropeptide‐Y (NPY) on renal function were investigated in conscious foxhounds. 2. Dose‐response curves (n = 7) were obtained for NPY by measuring renal blood flow (RBF), glomerular filtration rate (GFR), urine excretion (VU), sodium excretion (VNa), potassium excretion (VK) and plasma renin activity (PRA) at different infusion rates. All variables decreased with increasing infusion rates except for PRA, which surprisingly did not change during the different infusion rates. 3. The influence of the non‐constrictor dose of NPY at control pressure, and after servo‐controlling renal arterial pressure at 80 mmHg, was determined for these parameters (n = 6). 4. This was repeated during a reflex sympathetic activation via carotid sinus hypotension, in order to quantify a possible interaction between the sympathetic transmitter and co‐transmitter (n = 6). 5. The subthreshold NPY dose raised plasma NPY‐like immunoreactivity (NPY‐LI IR) significantly (renal venous plasma: 54 +/‐ 13 vs. 405 +/‐ 117 pg ml‐1; P less than 0.05) and enhanced the pressure‐dependent (80 mmHg) antidiuresis (0.48 +/‐ 0.06 vs. 0.24 +/‐ 0.02 ml min‐1; P less than 0.05), antinatriuresis (46 +/‐ 11 vs. 25 +/‐ 3 mumol min‐1; P less than 0.05), antikaliuresis (19 +/‐ 4 vs. 9 +/‐ 0.7 mumol min‐1; P less than 0.05) and pressure‐dependent renin release (0.95 +/‐ 0.27 vs. 3.0 +/‐ 1.1 ng angiotensin I ml‐1 h‐1; P less than 0.05). These effects are consistent with a non‐uniform vasoconstrictor action of NPY in the renal vascular bed (see accompanying papers). 6. The effects of NPY plus sympathetic activation were less than the sum of the two individual effects, which may rely on a presynaptic mechanism.
A role for endothelin in the maintenance of post‐ischaemic renal failure in the rat.
Authors: López‐Farré A , Gómez‐Garre D , Bernabeu F , López‐Novoa J M
Published: December 2014

1. Endothelin (ET) has been shown to reduce glomerular filtration rate (GFR) and renal blood flow (RBF) and may therefore be a possible mediator of the reduction of GFR and RBF observed in post‐ischaemic acute renal failure. 2. We infused a specific ET antibody, i.v., for 1 h before and 1 h after a 60 min period of renal ischemia by clamping the renal artery, and observed the changes in renal function (acute clearance and long‐term metabolic cage studies) compared with rats infused with non‐immune rabbit serum. 3. In acute and long‐term studies, better renal function, as judged by GFR and RBF was observed in rats treated with the ET antibody. Furthermore, ischaemic rats showed higher levels of plasma immunoreactive ET (7.02 +/‐ 1.17 pg ET (ml plasma)‐1; mean +/‐ S.E.M.) than normal rats where it was undetected. 4. We previously reported that glomeruli and renal platelet‐activating factor (PAF) production were increased after renal ischaemia. So, we studied the possible relationship between ET and glomeruli or renal PAF production in post‐ischaemic acute renal failure. 5. Glomeruli from ischaemic rats produced greater amounts of PAF than glomeruli from normal or anti‐ET antibody‐treated ischaemic rats. In addition, total renal PAF production was higher in ischaemic‐untreated than in non‐ischaemic or anti‐ET‐treated rats. Glomeruli incubated with 10(‐7) M‐endothelin produced much more PAF than those incubated in control conditions (138.4 +/‐ 10.5 vs. 80.2 +/‐ 9.4 pg PAF (mg protein)‐1; means +/‐ S.E.M.; n = 10). 6. In conclusion, the present study suggests that endothelin plays a role in the persistent renal vasoconstriction that characterizes post‐ischaemic acute renal failure. In addition, the observed increase in glomerular PAF production after renal ischaemia may be due to the action of endothelin.
Volume status influences atrial peptide‐induced water conductivity changes in leopard frog mesenteric capillaries.
Authors: Meyer D J , Huxley V H , McKay M K
Published: December 2014

1. Three sets of North American leopard frogs (Rana pipiens) were housed on damp sand (DS, n = 19), in fresh water (FW, n = 19), or with free access to both damp sand and fresh water (FA, n = 23) for a period of 5‐6 days. At the end of this period pithed frogs were prepared for measurement of capillary hydraulic conductivity and samples of whole‐blood, lymph and body cavity fluid were collected for measurement of haematocrit and protein content. 2. To measure hydraulic conductivity (Lp), individual capillaries of the mesenteries of the three groups were cannulated and perfused with a minimum of two, and a maximum of three, frog Ringer solutions. The first solution, common to all experiments, contained dialysed bovine serum albumin (BSA) at a concentration of 10 mg ml‐1. The second and third solutions also contained either 10 nM‐atrial peptide (AP) or 1 microM‐sodium nitroprusside (SNP). Lp was determined from measurements of fluid filtration rate at a minimum of two different capillary pressures (Michel, Mason, Curry, Tooke & Hunter, 1974). 3. In vessels from damp sand‐stored frogs (DS), the paired Lp in the presence of 10 nM‐atrial peptide (Lp, AP) was 3.2 +/‐ 0.4‐fold higher than Lp, BSA (n = 25). By contrast, in the FW group, Lp, AP did not differ significantly from Lp, BSA (Lp, AP‐FW/Lp, BSA = 1.3 +/‐ 0.2; n = 23). In frogs given free access to water and dry terrain the response to atrial peptide was similar to that observed in the DS group (Lp, AP‐FA/Lp, BSA = 3.6 +/‐ 07; n = 23). Thus, storage in fresh water appears to have inhibited the acute Lp response to atrial peptide observed in vessels from the FA or DS animals. 4. Atrial peptide and sodium nitroprusside elevate intracellular cyclic GMP levels by membrane receptor‐dependent and ‐independent processes, respectively. No difference was observed in the Lp response to 1 microM‐perfusate sodium nitroprusside (Lp, SNP) in DS (n = 7), FW (n = 8) or FA (n = 30) frogs (Lp, SNP/Lp, BSA ratios were 3.5 +/‐ 1.5‐, 2.7 +/‐ 0.8‐ and 2.6 +/‐ 0.5‐fold, respectively). Thus, the Lp response to sodium nitroprusside was not affected by storage conditions. 5. The mean haematocrit of skin blood samples from the DS groups was 26.5 +/‐ 1.0% (+/‐ S.E.M.) compared to 19.1 +/‐ 1.2% from the FW groups.(ABSTRACT TRUNCATED AT 400 WORDS)
Histamine H3‐receptor activation augments voltage‐dependent Ca2+ current via GTP hydrolysis in rabbit saphenous artery.
Authors: Oike M , Kitamura K , Kuriyama H
Published: December 2014

1. Actions of histamine on the voltage‐dependent Ba2+(Ca2+) currents (IBa, ICa) were investigated using the whole‐cell patch‐clamp technique on dispersed smooth muscle cells from the rabbit saphenous artery. 2. Histamine (half‐maximal dose, EC50 = 530 nM) augmented the IBa evoked by a brief depolarizing pulse (100 ms duration; to +10 mV from a holding potential of ‐80 mV) in a concentration‐dependent manner. The maximum augmentation was obtained with 30 microM‐histamine (1.29 times control). This augmentation of IBa was inhibited by the H3‐antagonist, thioperamide (Ki = 30 nM, slope of the Schild plot = 1.0), but not by H1‐ or H2‐antagonists (mepyramine or diphenhydramine, or cimetidine, respectively). 3. An H3‐agonist, R alpha‐methylhistamine (EC50 = 93 nM), also augmented IBa in a concentration‐dependent manner at a holding potential of ‐80 mV and the maximum augmentation (1.25 times control) was obtained with 10 microM. This augmentation was also inhibited by thioperamide, but not by the above H1‐ and H2‐ antagonists. 4. Intracellularly applied 500 microM‐guanosine 5'‐triphosphate (GTP) enhanced, but 1 mM‐guanosine 5'‐O‐(2‐thiodiphosphate) (GDP beta S) abolished, the histamine‐induced augmentation of IBa. When one of the non‐hydrolysable GTP analogues, guanosine 5'‐O‐(3‐thiotriphosphate) (GTP gamma S; greater than 5 microM), guanylyl‐imidodiphosphate (GMP‐PNP; 200 microM) or guanylyl (beta, gamma‐methylene)‐diphosphonate (GMP‐PCP; 1 mM) was intracellularly applied, the IBa amplitude evoked without the application of histamine was not affected, but the excitatory effect of histamine on IBa was reversed to an inhibition. Pre‐treatment with pertussis toxin (PTX: 300 ng/ml and 3 micrograms/ml) did not modify the histamine‐induced responses in the absence or presence of GTP gamma S. 5. 4 beta‐Phorbol 12,13‐dibutylate (PDBu) increased the amplitude of IBa. However, this action of PDBu was not enhanced by the application of GTP (500 microM) in the pipette, but additional application of histamine further increased the amplitude of IBa. Pre‐treatment with a potent non‐selective protein kinase inhibitor, 1‐(5‐isoquinolinesulphonyl)‐2‐methylpiperazine dihydrochloride (H‐7; 100 microM), did not modify the histamine‐induced current augmentation or inhibition observed in the presence or absence of intracellular GTP gamma S.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes of intracellular pH due to repetitive stimulation of single fibres from mouse skeletal muscle.
Authors: Westerblad H , Allen D G
Published: December 2014

1. The performance of skeletal muscle during repetitive stimulation may be limited by the development of an intracellular acidosis due to lactic acid accumulation. To study this, we have measured the intracellular pH (pHi) with the fluorescent indicator BCECF (2',7'‐bis(carboxyethyl)‐5(6)‐ carboxyfluorescein) during fatigue produced by repeated, short tetani in intact, single fibres isolated from the mouse flexor brevis muscle. 2. The pHi at rest was 7.33 +/‐ 0.02 (mean +/‐ S.E.M., n = 29, 22 degrees C). During fatiguing stimulation pHi initially went alkaline by about 0.03 units (maximum alkalinization after about ten tetani). Thereafter pHi declined slowly and at the end of fatiguing stimulation (tetanic tension reduced to 30% of the original; 0.3Po), pHi was only 0.063 +/‐ 0.011 units (n = 14) more acid than in control. 3. We considered three possible causes of acidosis being so small in fatigue: (i) a high oxidative capacity so that fatigue occurs without marked production of lactic acid; (ii) an effective transport of H+ or H+ equivalents out of the fibres; a high intracellular buffer power. 4. The oxidative metabolism was inhibited by 2 mM‐cyanide in three fibres. After being exposed to cyanide for 5 min without stimulation, the tetanic tension was reduced to about 0.9 Po and pHi was alkaline by about 0.1 units. The fibres fatigued faster in cyanide and the pHi decline in fatigue was more than twice as large as that under control conditions. 5. Inhibition of Na(+)‐H+ exchange with amiloride resulted in a slow acidification of rested fibres; resting pHi was not affected by either inhibition of HCO3(‐)‐Cl‐ exchange with DIDS (4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid) or inhibition of the lactate transporter with cinnamate. 6. Fibres fatigued in cinnamate displayed a markedly larger acidification (approximately 0.4 pH units) and tension fell more rapidly than under control conditions; inhibition of Na(+)‐H+ and HCO3(‐)‐Cl‐ exchange did not have any significant effect on fatigue. 7. The intracellular buffer power, assessed by exposing fibres to the weak base trimethylamine, was about 15 mM (pH unit)‐1 in a HEPES‐buffered solution (non‐CO2 or intrinsic buffer power) and about 33 mM (pH unit)‐1 in a bicarbonate‐buffered solution. Somewhat higher values of the intrinsic buffer power was obtained from changes of the partial pressure of CO2 (PCO2) of the bath solution. Application of lactate or butyrate frequently gave an infinite buffer power, which indicates that powerful pH‐regulating mechanisms operate in these cases.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of inhibitory neurotransmission in the isolated corpus cavernosum from rabbit and man.
Authors: Holmquist F , Hedlund H , Andersson K E
Published: December 2014

1. NG‐nitro‐L‐arginine (L‐NOARG, 10(‐4) M), an inhibitor of nitric oxide (NO) synthesis, had no contractile effect on isolated preparations of rabbit and human corpus cavernosum at baseline tension, but increased tension in preparations contracted by noradrenaline (rabbit 10(‐5) M, man 3 x 10(‐7)‐3 x 10(‐6) M) or K+ (rabbit 60 mM). 2. Electrical field stimulation (supramaximal voltage, 0.8 ms pulses, 5 s train duration, 0.5‐35 Hz) of rabbit and human corpus cavernosum preparations contracted by noradrenaline (rabbit 10(‐5) M, man 3 x 10(‐6) M) or endothelin‐1 (rabbit 10(‐8) M) produced relaxations that were sensitive to tetrodotoxin (10(‐6) M), and dependent on the frequency and number of pulses delivered. L‐NOARG (10(‐6)‐10(‐4) M), but not NG‐nitro‐D‐arginine (D‐NOARG, 10(‐6)‐10(‐4) M), inhibited electrically induced relaxations in a concentration‐dependent manner, and at 10(‐4) M the relaxations were virtually abolished. L‐Arginine (10(‐3) M), but not D‐arginine (10(‐3) M), partly reversed the inhibitory effect of L‐NOARG (10(‐4) M). In rabbit corpus cavernosum preparations, as with Methylene Blue (3 x 10(‐5) M), an inhibitor of the soluble guanylate cyclase, and haemoglobin (10(‐5) M), sequestering NO in the extracellular space, significantly reduced electrically evoked relaxations. Scopolamine (10(‐6) M) had little or no effect on relaxations induced by electrical field stimulation. 3. Preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(‐5) M, man 3 x 10(‐6) M) were relaxed by carbachol (10(‐9)‐10(‐4) M) in a concentration‐dependent manner. Scopolamine (10(‐6) M) and L‐NOARG (10(‐4) M) abolished, and Methylene Blue (3 x 10(‐5) M) and haemoglobin (10(‐5) M) greatly reduced, the carbachol‐induced relaxation, while D‐NOARG (10(‐4) M) had no significant effect. 4. In rabbit corpus cavernosum preparations contracted by noradrenaline (10(‐5) M), L‐NOARG (10(‐4) M) had no significant effect on relaxations induced by vasoactive intestinal polypeptide (10(‐6) M). 5. SIN‐1 (3‐morpholino‐sydnonimin hydrochloride, 10(‐8)‐3 x 10(‐4) M), which spontaneously liberates NO, relaxed preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(‐5) M, man 3 x 10(‐6) M) or endothelin‐1 (rabbit 10(‐8) M, man 3 x 10(‐9) M) in a concentration‐dependent way.(ABSTRACT TRUNCATED AT 400 WORDS)
Elevated muscle glycogen and anaerobic energy production during exhaustive exercise in man.
Authors: Bangsbo J , Graham T E , Kiens B , Saltin B
Published: December 2014

1. The effect of elevated muscle glycogen on anaerobic energy production, and glycogenolytic and glycolytic rates was examined in man by using the one‐legged knee extension model, which enables evaluation of metabolism in a well‐defined muscle group. 2. Six subjects performed very intense exercise to exhaustion (EX1) with one leg with normal glycogen (control) and one with a very high concentration (HG). With each leg, the exhaustive exercise was repeated after 1 h of recovery (EX2). Prior to and immediately after each exercise bout, a muscle biopsy was taken from m. vastus lateralis of the active leg for determination of glycogen, lactate, creatine phosphate (CP) and nucleotide concentrations. Measurements of leg blood flow and femoral arterial‐venous differences for oxygen content, lactate, glucose, free fatty acids and potassium were performed before and regularly during the exhaustive exercises. 3. Muscle glycogen concentration prior to EX1 was 87.0 and 176.8 mmol (kg wet wt)‐1 for the control and HG leg, respectively, and the decreases during exercise were 26.3 (control) and 25.6 (HG) mmol (kg wet wt)‐1. The net glycogen utilization rate was not related to pre‐exercise muscle glycogen concentration. Muscle lactate concentration at the end of EX1 was 18.8 (control) and 16.1 (HG) mmol (kg wet wt)‐1, and the net lactate production (including lactate release) was 26.5 (control) and 23.6 (HG) mmol (kg wet wt)‐1. Rate of lactate production was unrelated to initial muscle glycogen level. Time to exhaustion for EX1 was the same for the control leg (2.82 min) and HG leg (2.92 min). 4. Muscle glycogen concentration before EX2 was 14 mmol (kg wet wt)‐1 lower than prior to EX1. During EX2 the muscle glycogen decline of 19.6 mmol (kg wet wt)‐1 for the control leg was less than for the HG leg (26.2 mmol (kg wet wt)‐1). The muscle lactate concentrations at the end of EX2 were about 7‐8 mmol (kg wet wt)‐1 lower compared to EX1, and the net lactate production was reduced by 40%. The exercise time during EX2 was 0.35 min shorter for the control leg, while no difference was observed for the HG leg. 5. Total reduction in ATP and CP was similar during the four exercise bouts, while a higher accumulation of inosine monophosphate (IMP) occurred during EX2 for the control leg (0.72 mmol (kg wet wt)‐1) compared to the HG leg (0.20 mmol (kg wet wt)‐1).(ABSTRACT TRUNCATED AT 400 WORDS)