bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithium clearance: modification by the loop of Henle in man.
Authors: Atherton J C , Doyle A , Gee A , Green R , Gingell S , Nicholls F , Pempkowiak L , Plange‐Rhule J
Published: December 2014

1. The contribution of Li+ reabsorption in the loop of Henle to lithium clearance (CLi) and the possible mechanism(s) involved were assessed in healthy volunteers. Four mechanisms were considered: (a) passive reabsorption in the thin ascending limb, (b) solvent drag in the thin descending limb, (c) the Na+, K+, 2Cl‐ transporter in the thick ascending limb and (d) paracellular movement in the thick ascending limb. 2. Since alterations in the corticomedullary osmolal concentration gradient produced by fluid restriction (500 ml day‐1) and subsequent water loading (15 ml kg‐1) did not affect either CLi (28.5 +/‐ 2.1 vs. 28.2 +/‐ 1.9 ml min‐1) or fractional lithium clearance (FELi; 23.5 +/‐ 2.0 vs. 23.0 +/‐ 1.9%), it is unlikely that substantial Li+ reabsorption occurs in the thin limbs by either passive movement or solvent drag. 3. Increasing plasma Li+ with unchanged plasma Na+ in salt‐replete volunteers was associated with only small reductions in CLi (32.8 +/‐ 1.3 ml min‐1, P less than 0.05) and FELi (27.3 +/‐ 1.8 vs. 25.3 +/‐ 2.0%, P less than 0.05). This suggests that substantial Li+ reabsorption on the Na+, K+, 2Cl‐ transporter does not occur. 4. Bumetanide increased FELi in salt‐depleted (LS) and salt‐replete (HS) volunteers and abolished the pre‐diuretic difference in FELi between salt intakes (LS, 16.6 +/‐ 1.5 vs. 38.7 +/‐ 2.3%, P less than 0.001; HS, 30.1 +/‐ 1.5 vs. 40.5 +/‐ 2.0%, P less than 0.001). Changes in CPO4 and CHCO3 were not detected. Acetazolamide produced comparable increases in FELi (LS, 16.6 +/‐ 1.5 vs. 38.7 +/‐ 2.2%, P less than 0.001; HS, 30.1 +/‐ 1.5 vs. 43.1 +/‐ 2.4%, P less than 0.01); and CPO4 and CHCO3 were increased. When tubular flow to the loop of Henle was increased by acetazolamide, the bumetanide‐induced increases in FELi were reduced (LS, 38.7 +/‐ 2.2 vs. 48.7 +/‐ 2.3%, P less than 0.001; HS, 43.1 +/‐ 2.4 vs. 48.1 +/‐ 2.6%, P less than 0.001). 5. These data are consistent with the view that (a) Li+ is reabsorbed by a bumetanide‐sensitive mechanism in the loop of Henle, (b) approximately 20 and 10% of the filtered load, respectively, is reabsorbed in the loop in salt‐depleted and salt‐replete volunteers, (c) flow‐dependent, voltage‐driven paracellular movement in the thick ascending limb is the likely mechanism and (d) this mechanism could account for the difference in Li+ reabsorption between low and high salt intakes.
Neurohumoral mechanisms and the role of arterial baroreceptors in the reno‐vascular response to haemorrhage in rabbits.
Authors: Courneya C A , Korner P I
Published: December 2014

1. Conscious rabbits, with implanted renal artery Doppler flow probes were bled at a constant rate (4 ml min‐1). We assessed the contribution of autonomic, hormonal and local factors to the renal vasoconstrictor response to 20% loss of blood volume (BV) and the role of the sinoaortic baroreceptors in the neurohumoral response. 2. With intact autonomic effectors, 20% BV loss was associated with a small fall in vascular conductance, which was completely unaffected by inhibition or blockade of the combined effects of the two major pressor hormones angiotensin II (AII) and arginine vasopressin (AVP). Combined blockade of the autonomic effects plus those of the two pressor hormones resulted in marked elevation of vascular conductance, considered to be due to the local effects of haemorrhage. This response provided the baseline for assessing the constrictor response in the intact animal which, during 20% BV loss, was entirely due to reflex activity through the sympatho‐adrenal system. 3. In contrast to the early phase of haemorrhage (less than 20% BV removal) both hormones played a role in the maintenance of mean arterial pressure immediately after haemorrhage and in the maintenance of renal vascular tone. This suggested that the contribution by hormones occurs only after more pronounced blood loss and hypotension. 4. In the presence of autonomic blockade with mecamylamine plus methscopolamine (plus a constant infusion of noradrenaline to maintain resting blood pressure) the renal vasoconstrictor response was similar to that of the intact animal. We have previously found that this regime is associated with greatly enhanced release of AVP and plasma renin activity. Sinoaortic denervation had no effect on this hormonally mediated vasoconstriction. 5. When the autonomic nervous system was intact but the effects of AII and AVP were blocked to prevent the accentuated hormonally mediated vasoconstriction, sinoaortic denervation completely abolished the normal autonomic renal constrictor response, which is thus largely under control of the arterial baroreceptors.
Postnatal development of lamb intestinal digestive enzymes is not regulated by diet.
Authors: Shirazi‐Beechey S P , Smith M W , Wang Y , James P S
Published: December 2014

1. Change in digestive enzyme activities determined biochemically in brush‐border membrane vesicles and cytochemically in isolated villi of lamb proximal intestine has been related to diet, intestinal structure and rumen development during the first 10 weeks of postnatal life. 2. Lactase activity halved, dipeptidylpeptidase IV activity doubled and aminopeptidase N and alkaline phosphatase activities remained constant during this period of development. Maintaining lambs on a milk replacer diet for 5 weeks after birth had no effect on this pattern of postnatal change in digestive enzyme activities. 3. Structural changes accompanying these selective effects on enzyme expression included a halving of villus height and a doubling of villus width. Villus surface area remained unaffected by these changes in height and width of villi. Crypt depth doubled during the first 10 weeks of postnatal life. Maintaining lambs on a milk replacer diet for 5 weeks did not affect this pattern of change in intestinal structure. 4. It appears from these results that postnatal decrease in lactase and increase in dipeptidylpeptidase IV activities are not regulated by factors such as diet, rumen development, or changes in intestinal structure. Attention is drawn to differences encountered between these results and a postnatal modification of glucose transport which clearly is dependent on diet.
Modulation of motor cortical excitability by electrical stimulation over the cerebellum in man.
Authors: Ugawa Y , Day B L , Rothwell J C , Thompson P D , Merton P A , Marsden C D
Published: December 2014

1. We have stimulated over the cerebellum of intact human subjects by applying single electrical stimuli through electrodes placed on the back of the head, approximately at the level of the inion. The intensity of stimulation used was below that required to produce direct EMG responses in pre‐activated muscles of the hand. 2. In ten subjects the effect of the stimulus over the cerebellum was to reduce the size of the EMG response in first dorsal interosseous muscle evoked by a magnetic stimulus to the cerebral cortex. In all subjects the onset of the period of suppression occurred when the test magnetic cortical shock followed the conditioning cerebellar shock by 5 ms. The duration of the suppression lasted from 3 to 7 ms. 3. The amount of suppression was related to the intensity of stimulation over the cerebellum. At 15% below the threshold for direct motor activation there was no effect; increasing suppression was evident at 10, 5 and 0% below motor threshold. 4. With a conditioning‐test interval of 5‐6 ms the suppression was the same whether the target muscle was relaxed or active. With longer conditioning‐test intervals (12 and 15 ms) the amount of suppression was greater in active than relaxed muscles. 5. The short‐latency suppression was greatest when the stimulating anode was ipsilateral to the target muscle and contralateral to the stimulated sensorimotor cortex. The later period of suppression was insensitive to the polarity of stimulation. When the stimulating electrodes were moved 2 cm caudally or cranially the short latency suppression disappeared whereas the longer latency suppression was still observed with the electrodes in the lower position. 6. Different results were obtained when the test EMG response was produced by an electrical (rather than magnetic) stimulus over the sensorimotor cortex. The short latency effect was no longer visible whereas the longer latency effect was the same as when testing with a magnetic cortical stimulus. 7. We suggest that a single electrical stimulus across the base of the skull (particularly with the anode over one cerebellar hemisphere) produces a short latency (5‐6 ms) disfacilitation of the contralateral motor cortex through activation of cerebellar structures. A later (12 and 15 ms), less specific suppression which is present when testing in active muscles is thought to be mediated by a different mechanism and probably produces its effect at the level of the spinal cord.
Development of anomalous rectification (Ih) and of a tetrodotoxin‐resistant sodium current in embryonic quail neurones.
Authors: Schlichter R , Bader C R , Bernheim L
Published: December 2014

1. The developmental expression of an inwardly rectifying current activated by membrane hyperpolarization (Ih) and of a tetrodotoxin (TTX)‐resistant Na+ current (INa(TR)) was studied using freshly dissociated ganglionic quail neurones of various embryonic ages. This work was carried out on parasympathetic (ciliary) and sensory (trigeminal and dorsal root) ganglion neurones with the whole‐cell configuration of the patch‐clamp technique. 2. In sensory and parasympathetic neurones, Ih was activated at potentials more negative than ‐60 mV and displayed strong inward rectification. No sign of time‐ or voltage‐dependent inactivation was apparent. Ih was carried by both Na+ and K+ ions and was selectively and reversibly blocked by extracellular Cs+. 3. During the development of sensory neurones, Ih was observed for the first time between embryonic day 10 (E10) and E11 and the percentage of neurones expressing the current increased subsequently, reaching a plateau level of about 80% at E14. In the parasympathetic neurones of the ciliary ganglion, Ih was already detected at E10 and the percentage of neurones possessing the current increased until E16, a stage at which all neurones were found to express Ih. 4. In the presence of TTX (1 microM), an inward Na+ current, INa(TR), was recorded in sensory neurones after E12. This current was activated at potentials more depolarized than ‐30 mV and its amplitude was maximal at +5 mV. INa(TR) showed time‐ and voltage‐dependent inactivation. Half‐maximal steady‐state inactivation was observed at ‐40 mV. 5. INa(TR) was observed for the first time after E12 in sensory neurones and the percentage of neurones with INa(TR) increased until E14. Thereafter, 80% of the neurones had the current. In contrast, INa(TR) was never observed in the parasympathetic neurones of the ciliary ganglion during embryonic development. 6. Our results with parasympathetic and sensory neurones suggest that the expression of INa(TR) is linked to the phenotype and not to the embryonic origin of a neurone.
Cytosolic free Ca2+ during operation of sodium‐calcium exchange in guinea‐pig heart cells.
Authors: Noma A , Shioya T , Paver L F , Twist V W , Powell T
Published: December 2014

1. Membrane current generated by the Na(+)‐Ca2+ exchange mechanism was recorded in single guinea‐pig ventricular myocytes using the whole‐cell voltage‐clamp technique and the intracellular free calcium concentration ([Ca2+]i) was monitored using the fluorescent probe Indo‐1, applied intracellularly through a perfused patch pipette. The reversal potential of the exchanger (ENa, Ca) was measured from records of the 2 mM‐Ni(2+)‐sensitive current and used in an attempt to clamp [Ca2+]i at a level determined by the ionic compositions of the external and pipette solutions. 2. Measurements of ENa, Ca indicated that [Ca2+]i was close to that in the pipette solution when the holding potential was set at the ENa, Ca expected for a 3Na+:1Ca2+ exchanger. The measured value of ENa, Ca was more positive than the theoretical value when the membrane potential was held positive to ENa, Ca and the opposite was true when the holding potential was more negative than the expected ENa, Ca. 3. As Indo‐1 diffused into the cell from the whole‐cell clamp electrode, the intensities of the fluorescent signals measured at 405 and 480 nm increased with time, with no obvious saturation over a 10‐45 min recording period. However, the ratio of these two signals reached a steady level within 5 min after rupture of the patch membrane, when the holding potential was set at the expected ENa, Ca of the exchanger. The intensity ratios measured using pipette solutions containing 600 and 803 nM [Ca2+] were almost equal to the ratios obtained extracellularly from internal solutions of identical compositions, but in experiments using pipette solutions having lower [Ca2+] the intensity ratios measured in myocytes were higher than those obtained extracellularly. 4. If the membrane was depolarized or hyperpolarized, the fluorescence ratio either increased or decreased, respectively. These changes in the fluorescence ratio were virtually blocked by the extracellular application of 2 mM‐Ni2+. 5. When the concentration of bis(O‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA) in the recording pipette was reduced from 30 to 1 mM, an increase in [Ca2+]i was observed during a depolarizing ramp pulse. The Ca2+ influx estimated by integrating the 2 mM‐Ni(2+)‐sensitive current during the pulse correlated with the increase in [Ca2+]i estimated from Indo‐1 using the extracellular calibration curve, but the values of the influx determined directly from Indo‐1 fluorescence were always larger than those calculated from the exchanger current.(ABSTRACT TRUNCATED AT 400 WORDS)
Hypoxic vasodilatation in isolated, perfused guinea‐pig heart: an analysis of the underlying mechanisms.
Authors: von Beckerath N , Cyrys S , Dischner A , Daut J
Published: December 2014

1. The mechanisms underlying hypoxic dilatation of coronary arteries were studied in isolated guinea‐pig hearts perfused with physiological salt solution at 37 degrees C. The hearts were perfused at a constant rate of 3‐10 ml min‐1; coronary perfusion pressure (CPP) and isovolumetric left ventricular pressure (LVP) were measured with piezoresistive transducers. 2. Addition of the K+ channel opener cromakalim (500 nM) to the perfusate caused a maximal vasodilatation in beating hearts, i.e. a decrease in CPP of about 50%. Switching from normal perfusate (partial pressure of O2 (PO2), 650‐700 mmHg) to hypoxic perfusate (PO2, 9‐10 mmHg) caused a similar vasodilatation. Both of these effects were prevented by 2 microM‐glibenclamide, a blocker of ATP‐sensitive potassium channels. Hypoxic vasodilatation was accompanied by a marked decrease in LVP, which was reduced by 56 +/‐ 22% (mean +/‐ S.D.) in the presence of glibenclamide. 3. In hearts arrested by increasing the K+ concentration of the perfusate to 15 mM, the addition of the adenosine‐uptake inhibitor dipyridamole evoked a maximal vasodilatation and this was inhibited by 76 +/‐ 7% in the presence of glibenclamide. 4. The adenosine antagonist 8‐phenyltheophylline (8‐PT; 5 microM) inhibited the vasodilatation induced by dipyridamole by 88 +/‐ 10%. In contrast, hypoxic vasodilatation was unaffected by 5 microM 8‐PT. This suggests that hypoxic dilatation of coronary arteries is not mediated by release of adenosine from cardiomyocytes. 5. In order to test whether release of endothelium‐derived relaxing factor (EDRF) contributed to hypoxic vasodilatation we blocked EDRF synthesis with N omega‐nitro‐L‐arginine (NNA). When applied at a perfusion rate of 10 ml min‐1 to arrested hearts, 10 microM‐NNA increased CPP by 35% and prolonged the delay between application of hypoxic solution and half‐maximal vasodilatation from 52 +/‐ 9 to 129 +/‐ 29 s. 6. Under control conditions the relation between perfusion rate and the CPP measured in the steady state was linear. In the presence of 10 microM‐NNA coronary resistance was increased more than twofold at low perfusion rates; at perfusion rates between 4 and 10 ml min‐1 coronary resistance decreased progressively. This change in the pressure‐flow relationship may be responsible for the alterations in the time course of hypoxic vasodilatation induced by NNA. 7. In order to test whether changes in energy metabolism in coronary smooth muscle cells were responsible for hypoxic vasodilatation we blocked glycolysis by replacing the glucose in the perfusate with deoxyglucose (DOG).(ABSTRACT TRUNCATED AT 400 WORDS)
Motor cortical representation of the diaphragm in man.
Authors: Maskill D , Murphy K , Mier A , Owen M , Guz A
Published: December 2014

1. Transcranial magnetic stimulation was performed using a figure‐of‐eight‐shaped coil over the right motor cortex with the aim of identifying those areas involved with activation of the diaphragm. 2. The response of the right and left hemi‐diaphragms was recorded using surface electrodes in either the 7th or 8th intercostal spaces 3 cm lateral to the anterior costal margin on either side. 3. The compound muscle action potentials recorded over the left diaphragm in response to transcranial magnetic stimulation were maximal when the centre of the figure‐of‐eight coil was placed approximately 3 cm to the right of the mid‐line and 2‐3 cm anterior to the auricular plane. 4. The amplitude of the response recorded from the diaphragm depended upon the angulation of the figure‐of‐eight coil and hence the direction of the stimulating current. 5. The response of the inspiratory muscles to magnetic stimulation of one side of the brain was predominantly contralateral but a small response was seen on the ipsilateral side. Ultrasonic techniques confirmed that the diaphragm was responding contralaterally and not ipsilaterally.
The effect of discrete stimulation of carotid body chemoreceptors on atrial natriuretic peptide in anaesthetized dogs.
Authors: al‐Obaidi M , Whitaker E M , Karim F
Published: December 2014

1. In seven chloralose‐anaesthetized and artificially ventilated beagles, the carotid sinus regions were vascularly isolated and perfused with either arterial or mixed (arterial and venous) blood (PO2 46.4 +/‐ 1.5 mmHg, mean +/‐ S.E.M.) to stimulate the chemoreceptors at constant flow and pressure. Cervical vagosympathetic trunks were ligated in all dogs, and gallamine triethiodide (2.0 mg kg‐1 h‐1, I.V.) was given in five dogs. Right atrial pressure was measured in all dogs, and left atrial pressure in four dogs. Mean aortic pressure was held constant (91.0 +/‐ 3.0 mmHg) by means of a reservoir connected to the animal via the common carotid and femoral arteries. Plasma atrial natriuretic peptide (ANP) was measured by radioimmunoassay and urinary sodium by flame photometry. 2. In seven dogs with mean carotid sinus pressure maintained at 96.0 +/‐ 4.3 mmHg, stimulation of the carotid chemoreceptors for 25 min produced significant increases in left atrial pressure of 41.2 +/‐ 3.3% (n = 4; P less than 0.005) from 5.4 +/‐ 0.6 cmH2O and of 30.9 +/‐ 4.5% (n = 7; P less than 0.002) in ANP from 31.6 +/‐ 2.1 pg ml‐1. However, chemoreceptor stimulation produced significant decreases in urine flow rate of 26.1 +/‐ 1.9% (n = 9; P less than 0.001) from 0.29 +/‐ 0.03 ml min‐1 (100 g kidney weight)‐1 and sodium excretion of 29.0 +/‐ 2.3% (P less than 0.001) from 8.5 +/‐ 1.7 mumol min‐1 (100 g kidney weight)‐1 but right atrial pressure and heart rate did not change significantly. In three of the dogs, beta‐adrenoceptor blockade by atenolol (2 mg kg‐1, I.V.) greatly reduced the effects of chemoreceptor stimulation on plasma levels of ANP. 3. The results show, for the first time, that discrete stimulation of the carotid chemoreceptors caused an increase in plasma ANP levels, probably due to the reflex increase in atrial pressure that results from an inhibition of the cardiac sympathetic nerves, and an increase in venous return from a reduction of peripheral vascular capacitance.
Membrane properties and synaptic responses of rat striatal neurones in vitro.
Authors: Jiang Z G , North R A
Published: December 2014

1. A tissue slice containing a section of striatum was cut obliquely from rat brain so as to preserve adjacent cortex and pallidum. Intracellular recordings were made from 368 neurones, using either conventional or tight‐seal configurations. 2. Two types of neurone were distinguished electrophysiologically. Principal cells (96%) had very negative resting potentials (‐89 mV) and a low input resistance at the resting membrane potential (39 M omega): membrane conductance (10 nS at ‐65 mV) increased within tens of milliseconds after the onset of hyperpolarization (99 nS at ‐120 mV). Secondary cells (4%) had less negative resting potentials (‐60 mV) and a higher input resistance (117 m omega at the resting potential): hyperpolarization caused an inward current to develop over hundreds of milliseconds that had the properties of H‐current. 3. Most principal cells were activated antidromically by electrical stimulation of the globus pallidus or internal capsule. Intracellular labelling with biocytin showed that principal cells had a medium sized soma (10‐18 microns), extensive dendritic trees densely studded with spines and, in some cases, a main axon which extended towards the globus pallidus. 4. Electrical stimulation of the corpus callosum or external capsule evoked a depolarizing postsynaptic potential. This synaptic potential was reversibly blocked by a combination of 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 10 microM) and DL‐2‐amino‐5‐phosphonovaleric acid (APV, 30 microM), but was unaffected by bicuculline (30 microM) and picrotoxin (100 microM). The underlying synaptic current had a fast component (time to peak about 4 ms), the amplitude of which was linearly related to membrane potential and which was blocked by CNQX; in CNQX the synaptic current had a slower component (time to peak about 10 ms) which showed voltage dependence typical of N‐methyl‐D‐aspartate (NMDA) receptors. Both currents reversed at ‐5 mV. 5. Focal electrical stimulation within the striatum (100‐300 microns from the site of intracellular recording) evoked a synaptic potential that was partially blocked (45‐95%) by CNQX and APV: the remaining synaptic potential was blocked by bicuculline (30 microM). The bicuculline‐sensitive synaptic current reversed at the chloride equilibrium potential. 6. The findings confirm that the majority of neostriatal neurones (principal cells, medium spiny neurones) project to the pallidum and receive synaptic inputs from cerebral cortex mediated by an excitatory amino acid acting through NMDA and non‐NMDA receptors. These cells also receive synaptic inputs from intrinsic striatal neurones mediated by GABA.(ABSTRACT TRUNCATED AT 400 WORDS)
Ca2+ and voltage inactivate Ca2+ channels in guinea‐pig ventricular myocytes through independent mechanisms.
Authors: Hadley R W , Lederer W J
Published: December 2014

1. L‐type Ca2+ currents and Ca2+ channel gating currents were studied in isolated guinea‐pig ventricular heart cells using the whole‐cell patch‐clamp technique, in order to investigate the mechanism of Ca(2+)‐dependent inactivation. The effect of altering the intracellular Ca2+ concentration ([Ca2+]i) on these currents was studied through photorelease of intracellular Ca2+ ions using the photolabile Ca2+ chelators DM‐nitrophen and nitr‐5. 2. We found that step increases in [Ca2+]i produced by photorelease could either increase or decrease the L‐type Ca2+ current. Specifically, Ca2+ photorelease from DM‐nitrophen almost exclusively caused inactivation of the Ca2+ current. In contrast, Ca2+ photorelease from nitr‐5 had a biphasic effect: a small, rapid inactivation of the Ca2+ current was followed by a slow potentiation. These two Ca(2+)‐dependent processes seemed to differ in their Ca2+ dependence, as small Ca2+ photoreleases elicited potentiation without a preceding inactivation, whereas larger photoreleases elicited both inactivation and potentiation. 3. The mechanism of the Ca(2+)‐dependent inactivation of Ca2+ channels was explored by comparing the effects of voltage and photoreleased Ca2+ on the Ca2+ current and the Ca2+ channel gating current. Voltage was found to reduce both the Ca2+ current and the gating current proportionally. However, Ca2+ photorelease from intracellular DM‐nitrophen inactivated the Ca2+ current without having any effect on the gating current. 4. The dephosphorylation hypothesis for Ca(2+)‐dependent inactivation was tested by applying isoprenaline to the cells before eliciting a maximal rise of [Ca2+]i (maximal flash intensity, zero external [Na+]i). Isoprenaline could completely prevent Ca(2+)‐dependent inactivation under these conditions, even when [Ca2+]i rose so high as to cause an irreversible contracture of the cell. 5. We concluded from these experiments that voltage and Ca2+ ions inactivate the L‐type Ca2+ channel through separate, independent mechanisms. In addition, we found that Ca(2+)‐dependent inactivation does not result in the immobilization of gating charge, and apparently closes the Ca2+ permeation pathway through a mechanism that does not involve the voltage‐sensing region of the channel. Furthermore, we found that Ca(2+)‐dependent inactivation is entirely sensitive to beta‐adrenergic stimulation. These facts suggest that either Ca(2+)‐dependent inactivation results from Ca(2+)‐dependent dephosphorylation of the Ca2+ channel, or that Ca(2+)‐dependent inactivation is modulated by protein kinase A.
Electrogenic uptake of sulphur‐containing analogues of glutamate and aspartate by Müller cells from the salamander retina.
Authors: Bouvier M , Miller B A , Szatkowski M , Attwell D
Published: December 2014

1. The effect of sulphur‐containing analogues of glutamate and aspartate on the membrane current of glial cells was studied by whole‐cell clamping Müller cells isolated from the salamander retina. 2. L‐Cysteic acid (CA), L‐cysteinesulphinic acid (CSA), L‐homocysteic acid (HCA), L‐homocysteinesulphinic acid (HCSA) and S‐sulpho‐L‐cysteine (SC) all evoked an inward membrane current that was large at negative potentials, and was smaller (but did not reverse) at more positive potentials up to +30 mV. 3. Removal of external sodium ions abolished the amino acid‐evoked currents. Whole‐cell clamping with pipettes containing no potassium led to a rapid suppression of the currents, that did not occur when potassium was included in the pipette. 4. The dependence of the currents on sulphur‐containing amino acid concentration obeyed first‐order Michaelis‐Menten kinetics. The current evoked by co‐application of L‐glutamate and a sulphur‐containing analogue was smaller than the sum of the currents produced by glutamate alone and by the sulphur analogue alone. 5. These data are consistent with the sulphur amino acid‐evoked current being caused by uptake on the electrogenic glutamate uptake carrier, which co‐transports an excess of Na+ ions into the cell, and counter‐transports one K+ ion out of the cell. 6. The apparent Km (Michaelis‐Menten constant) values for activation of uptake by CA (6 microM) and by CSA (60 microM) are low enough for uptake on the glutamate uptake carrier to be a plausible mechanism for terminating the postulated neurotransmitter action of these agents. However, the apparent Km values for uptake of HCA (2.95 mM), HCSA (1.65 mM) and SC (greater than 1 mM) are much higher than the EC50 (half‐maximal effective concentration) concentrations for these agents' activation of NMDA (N‐methyl‐D‐aspartate) channels. 7. Comparing the concentrations of sulphur amino acids needed to activate NMDA channels with their rate of uptake suggests that their potency for causing excitotoxic damage should follow the sequence HCA greater than SC greater than HCSA greater than Glu greater than CSA greater than Asp greater than CA.
Hemi‐gap‐junction channels in solitary horizontal cells of the catfish retina.
Authors: DeVries S H , Schwartz E A
Published: December 2014

1. Solitary horizontal cells were isolated from catfish retinas and their membrane current was recorded with a whole‐cell voltage clamp. Reducing the extracellular Ca2+ concentration produced a current that could be suppressed by dopamine. This Ca(2+)‐ and dopamine‐sensitive current is hereafter termed I gamma. The voltage dependence, cytoplasmic regulation, and permeability of the I gamma channel suggest that it is half of a gap‐junction channel. 2. I gamma was voltage and time dependent. In the steady state, the current‐voltage relation displayed outward rectification at voltages more depolarized than 0 mV and a negative resistance region at voltages more hyperpolarized than ‐15 mV. The reversal potential was 3.3 +/‐ 1.5 mV when NaCl was the predominant extracellular salt and potassium‐D‐aspartate was the predominant intracellular salt. 3. The size of I gamma depended on the extracellular Ca2+ concentration. I gamma was maximal at external Ca2+ concentrations below 10 microM, half‐maximal at 220 microM‐Ca2+, and reduced to less than 4% of its maximum amplitude at external Ca2+ concentrations above 1 mM. Increasing the extracellular Ca2+ concentration reduced the amplitude of I gamma without changing the shape of the current‐voltage relation or the kinetics of inactivation. Thus, rectification does not result from a voltage‐dependent block by extracellular Ca2+. 4. Patches of cell membrane were voltage clamped in both the cell‐attached and excised‐patch configurations. In the cell‐attached configuration, the addition of dopamine to the solution outside the patch pipette blocked the opening of channels within the membrane patch. Thus, dopamine closes I gamma channels by initiating an intracellular messenger cascade. In the excised‐patch configuration, a maximum conductance of 145 pS was measured while Cs+ and tetraethylammonium+ (TEA+) were the only monovalent cations on both sides of the membrane. 5. The ability of dopamine to suppress I gamma was blocked by introducing an inhibitor of the cyclic AMP‐dependent protein kinase, PKI5‐24, into the cytoplasm. Thus, the action of dopamine is mediated by a pathway that includes the activation of a cyclic AMP‐dependent kinase. 6. I gamma was suppressed by nitroprusside, an agent which activates guanylate cyclase and increases the intracellular cyclic GMP concentration. The effect of nitroprusside was not altered by the intracellular application of PKI5‐24. Thus, nitroprusside suppresses I gamma through a pathway that does not include the activation of a cyclic AMP‐dependent kinase.(ABSTRACT TRUNCATED AT 400 WORDS)
Slow and fast transient potassium currents in cultured rat hippocampal cells.
Authors: Ficker E , Heinemann U
Published: December 2014

1. Potassium currents have been recorded from rat hippocampal neurons in dissociated cultures prepared at E17‐E19. Currents were studied with the whole‐cell version of the patch clamp method. The kinetics and pharmacological properties of two transient outward currents have been characterized. 2. Most of the recordings have been done in cells which had been in culture 10‐18 days. Both a fast and a slow transient current could be elicited. A subtraction procedure was used to isolate the fast transient current. The fast transient current decayed monoexponentially with a time constant of about 10 ms. The slow transient current decayed with two time constants in the order of 500 ms and of 3.4 s. The reversal potential of the slow current shifted by 54 mV for a tenfold change in extracellular potassium concentration. 3. Studies on the removal of inactivation for the two currents revealed time constants of 29 and 107 ms for the fast and slow transient current, respectively. 4. The steady‐state inactivation properties of the fast transient current were determined by studying the current with a fixed depolarizing command of ‐10 mV and varying pre‐pulse amplitudes from a holding potential of ‐50 mV. The inactivation curve could be fitted with a Boltzmann equation. Half‐maximal inactivation occurred at ‐81 mV. The steady‐state activation properties of the fast transient current were determined by varying the depolarizing voltage commands following a fixed pre‐pulse to ‐110 mV. The threshold for activation was between ‐70 and ‐60 mV. Half‐maximal activation was reached at ‐19 mV. 5. The steady‐state inactivation properties of the slow transient current were determined by studying the current elicited by varying the hyperpolarizing voltage steps from a holding potential of 0 mV. The inactivation curve could be fitted with a Boltzmann equation. Half‐maximal inactivation was obtained at ‐61 mV. The steady‐state activation properties were determined in a manner similar to the fast current. The threshold for activation was between ‐40 and ‐30 mV. 6. The slow transient current was not inactivated immediately when the conditioning pre‐pulse was stopped. The rate of current decay increased with stimulus frequency. 7. Both transient currents were sensitive to 4‐aminopyridine (4‐AP). The fast transient current was blocked completely by 5 mM provided a pre‐pulse of 1 s to ‐110 mV was employed. The slow transient current was already depressed by 4‐AP applied in the 100 microM range but could never be blocked completely.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in discharge rate of fusimotor neurones provoked by fatiguing contractions of cat triceps surae muscles.
Authors: Ljubisavljević M , Jovanović K , Anastasijević R
Published: December 2014

1. Changes in discharge rate of thirty‐one fusimotor neurones to triceps surae muscles during long‐lasting, fatiguing contractions of these muscles were studied in decerebrate cats. Discharges of fusimotor neurones were recorded from the nerve filaments. Muscle contractions were elicited by electrical stimulation of either the muscle nerves (twenty‐one neurones) or the corresponding ventral roots (ten neurones), until the muscle tension fell to about 30% of its initial value. 2. Early and late changes could be recognized in fusimotor discharge rate during long‐lasting muscle contraction. The early changes obviously not related to muscle fatigue, consisted of an initial increase at the onset of muscle contraction and a subsequent decrease to or below the resting discharge level. The late change in discharge rate, supposedly related to muscle fatigue, was an increase developing gradually towards the end of muscle contraction, ranging at its peak from 2 to 15 impulses/s (mean value 5.5 impulses/s, n = 31) and outlasting the contraction for 20‐320 s. 3. When the contracting muscle was made ischaemic the late increase in fusimotor discharge rate started earlier and was maintained until the arterial clamp was removed. After severing the muscle nerves distal to the site of stimulation no changes, a slight sustained increase, or else a decrease in fusimotor discharge rate occurred during electrical stimulation of either muscle nerves or ventral roots. At its cessation the spontaneous firing rate was reassumed immediately. Stimulation of the distal stumps of the severed nerves elicited no changes in fusimotor discharge rate. 4. It is proposed that the late increase in fusimotor discharge rate may appear due to autogenetic excitation of fusimotor neurones by discharge from group III and IV muscle afferent fibres provoked and/or enhanced by metabolic products liberated in muscle tissue during the fatiguing contraction. The fusimotor firing was estimated to remain elevated to a level twice that of the spontaneous activity on average for approximately 120 s after the muscle contraction. Its functional role in muscle fatigue is discussed.
Electrophysiology of a slow (0.5‐4 Hz) intrinsic oscillation of cat thalamocortical neurones in vivo.
Authors: Dossi R C , Nuñez A , Steriade M
Published: December 2014

1. Electrophysiologically identified thalamocortical neurones have been intra‐ and extracellularly recorded in acutely prepared cats, under different anaesthetic conditions. 2. A slow (0.5‐4 Hz) membrane potential oscillation was observed in thalamocortical cells recorded in motor, sensory, associational and intralaminar thalamic nuclei. The oscillation consisted of rhythmic low‐threshold spikes alternating with after‐hyperpolarizations. 3. About 80% of the neurones with intact cortical connections were set into the slow oscillatory mode by bringing their membrane potential to between ‐68 and ‐90 mV. The oscillation did not depend upon the occurrence of fast action potentials and did not outlast the imposed hyperpolarization. 4. Anatomical or functional disconnection from related cortical areas resulted in a membrane potential hyperpolarization of about 9 mV and in the occurrence of spontaneous slow oscillations in virtually all recorded neurones. The intrinsic nature of the phenomenon was supported by the lack of rhythmic postsynaptic potentials as the cells were prevented from oscillating by outward current injection. 5. In contrast with other thalamic nuclei, the slow oscillation has not been observed in anterior thalamic neurones despite their having similar basic electrophysiological properties. 6. Barbiturate administration suppressed the slow oscillatory mode, an effect accompanied by a decrease in the membrane input resistance. 7. Multiunit recordings of spontaneously oscillating cells showed epochs characterized by phase‐related firing. This synchronous discharge was paralleled by a clear‐cut build‐up of field potentials in the frequency range of electroencephalogram slow or delta waves. 8. These results demonstrate that the majority of thalamocortical neurones are endowed with electrophysiological properties allowing them to oscillate at 0.5‐4 Hz, if they have a membrane potential more negative than ‐65 mV and a high input resistance. Such a condition is physiologically achieved in the deepest stages of electroencephalogram‐synchronized sleep, as a result of brain stem‐thalamic as well as cortico‐thalamic deafferentation. We postulate a thalamic contribution in the genesis of electroencephalogram delta waves during slow wave sleep, once independently oscillating thalamocortical cells become in phase.
Cyclic nucleotide‐dependent regulation of agonist‐induced calcium increases in mouse megakaryocytes.
Authors: Ikeda M , Kurokawa K , Maruyama Y
Published: December 2014

1. The regulatory effects of cyclic AMP and cyclic GMP on ADP‐ and thrombin‐induced increases in [Ca2+]i were studied in mouse bone marrow megakaryocytes. Changes in [Ca2+]i were continuously monitored in single Fura‐2‐loaded cells using microspectrofluorometry, and cyclic nucleotides were directly introduced into the single cells using the whole‐cell patch‐clamp technique. 2. ADP increased [Ca2+]i in a concentration‐dependent fashion, and its threshold concentration was in the order of 0.01 microM. A low dose of ADP (below 0.1 microM) induced a transient response of [Ca2+]i which recovered to original levels during the stimulation. A high dose of ADP (0.3‐10 microM) induced a biphasic response of [Ca2+]i with an initial peak and a plateau lasting until the end of the stimulation. Repeated stimulation with the same dose of ADP induced a reduced response, probably as a result of desensitization. 3. Thrombin increased [Ca2+]i in a concentration‐dependent manner. The time courses of the responses were different from those caused by ADP. Thrombin‐induced responses lacked the initial sharp peak observed in ADP‐induced responses, and caused a sustained response. 4. The ADP‐induced increase in [Ca2+]i was antagonized by the presence of prostaglandin E1 (PGE1, 100‐1000 nM), in the medium, and by direct injection of cyclic AMP (100‐500 microM) or cyclic GMP (500 microM) into the megakaryocyte. When 500 microM‐cyclic AMP was injected into the cells, the rise of [Ca2+]i induced by ADP was reduced by 85%. Effects of these antagonists were inhibited by treatment with a protein kinase inhibitor, H‐8. Thrombin‐induced increases in [Ca2+]i were reduced by direct injection of cyclic AMP or cyclic GMP. 5. ADP could induce an increase in [Ca2+]i in the absence of external Ca2+. The time course of the response was essentially similar to that observed in the normal condition (1 mM‐CaCl2), but the size of the response was reduced by 33%. Thus, 67% of the rise in [Ca2+]i induced by ADP could be accounted for by calcium mobilization from internal storage pools. The presence of NiCl2 (5 mM) duplicated the effects of external Ca2+ removal, suggesting the involvement of a Ca2+ influx pathway, which could be inhibited by Ni2+ in ADP stimulation. 6. Injection of cyclic AMP or cyclic GMP reduced ADP‐induced increases in [Ca2+]i under conditions of inhibited Ca2+ influx by NiCl2 (5 mM).(ABSTRACT TRUNCATED AT 400 WORDS)
The development of cortico‐motoneuronal projections investigated using magnetic brain stimulation in the infant macaque.
Authors: Flament D , Hall E J , Lemon R N
Published: December 2014

1. The effects of magnetic brain stimulation on electromyographic (EMG) activity recorded from arm and hand muscles have been investigated in five infant and six adult macaque monkeys under ketamine sedation. 2. In the adults, brief, short‐latency EMG responses could be readily evoked with magnetic stimuli of 40‐50% of the maximum stimulator output (1.5 T). 3. In a cross‐sectional study of five infant macaques, it was difficult to evoke EMG responses in young infants (less than 5 months old). Clear short‐latency responses were first evoked in an animal 5.75 months old. This change was accompanied by an increase in the probability of occurrence of the responses. 4. In a longitudinal study of two infant monkeys over a period ranging from 2.5 to 14.5 months of age we found that clear short‐latency responses were first evoked at 4 and at 5.5 months, respectively. In both animals there was a steady fall in response threshold which reached the adult range at 6.5 and 8 months, respectively. EMG responses in animals older than 8 months were indistinguishable from those in adults. 5. In the longitudinal study we also noted that the latency of EMG responses to magnetic brain stimulation declined with age. Since there were no comparable changes in the peripheral conduction time in these animals, we attribute this result to a decrease in central conduction time. 6. Parallel behavioural observations of the natural behaviour of the same animals within a colony indicated that mature precision movements of the fingers were not used until 5‐6 months of age. 7. In two adult monkeys, the latency of EMG responses evoked in the extensor digitorum and first dorsal interosseous muscles by direct stimulation of the corticospinal tract, via electrodes implanted in the medullary pyramids, was found to be 0.7‐1.7 ms shorter than that of responses evoked by magnetic stimuli. It is argued that at least the earliest component of these latter responses is conducted over the cortico‐motoneuronal pathway. 8. The mechanisms likely to contribute to the late appearance of EMG responses to brain stimulation are discussed. One of these is probably the establishment of mature cortico‐motoneuronal connections, which are not present at birth.
Background current in sino‐atrial node cells of the rabbit heart.
Authors: Hagiwara N , Irisawa H , Kasanuki H , Hosoda S
Published: December 2014

1. The Ca2+ current, K+ current, hyperpolarization‐activated current, Na(+)‐K+ pump current and the Na(+)‐Ca2+ exchange current were all blocked by appropriate blockers and the remaining time‐independent currents were investigated in single pacemaker cells of the rabbit sino‐atrial node using the whole‐cell patch clamp technique. 2. Exchanging the bathing solution from Tris‐hydroxymethyl‐aminomethane hydrochloride (Tris) Na+ free to 150 mM‐Na+ induced an inward current and the slope conductance of the current‐voltage relationship increased from 0.45 +/‐ 0.18 to 0.87 +/‐ 0.33 nS (n = 71) at ‐50 mV. The remaining conductance in Tris Na(+)‐free solution was essentially the same when Tris was substituted with tetraethylammonium (TEA) or N‐methyl‐D‐glucamine (NMG). The current density of the Na(+)‐dependent inward current obtained by subtracting the current in Tris Na(+)‐free from that in 150 mM‐Na+ solution was 0.73 +/‐ 0.21 pA/pF (n = 71) at ‐50 mV. We called this current the Na(+)‐dependent background current. 3. The membrane conductance was reduced by lowering the temperature of the external solution from 36 to 23 degrees C. In Tris Na(+)‐free solution, the temperature‐sensitive component was outward at all potentials, whereas it showed a reversal potential at around ‐20 mV in 150 mM‐Na+ solution. This reversal potential was interpreted as a sum of the Cs+ efflux and Na+ influx, by comparing the Na(+)‐dependent inward currents obtained at 36 degrees C and those at 23 degrees C. 4. Divalent cations (2 mM‐Ni2+, 1 mM‐Ba2+ or 2 mM‐Ca2+) reduced only the outward current in the Tris Na(+)‐free solution, while in the 150 mM‐Na+ solution, they reduced both the inward and outward components of the current which had a reversal potential of around ‐10 mV. 5. Amiloride depressed the membrane conductance in 150 mM‐Na+, Cs+ or Rb+ external solution, though only at negative membrane potentials, which suggests amiloride has a voltage‐dependent effect on the background current. 6. Removal of Cl‐ from the external solution or the addition of a Cl‐ channel blocker (4,4'‐dinitrostilbene‐2,2'‐disulphonic acid disodium salt, DNDS) failed to affect the membrane conductance. 7. When the monovalent cation‐dependent inward current was measured by subtracting the current in the Tris solution from those recorded in the various monovalent cation solutions, the current amplitude decreased in the order: Rb+ greater than K+ greater than Cs+ greater than Na+ greater than Li+, which suggests a poor cation selectivity of this current system.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of sympathetic activity and galanin on cardiac vagal action in anaesthetized cats.
Authors: Ulman L G , Potter E K , McCloskey D I
Published: December 2014

1. Stimulation of the right cardiac sympathetic nerve for 3 or 5 min at 16 Hz in the presence of effective beta‐adrenoceptor blockade evoked prolonged attenuation of subsequent cardiac vagal action in anaesthetized cats. Concurrent sympathetic and vagal stimulation, both at 16 Hz for the same period of time as sympathetic stimulation alone, reduced or abolished the inhibition of vagal action which followed when sympathetic stimulation was given alone. 2. A series of three successive intravenous injections of galanin all caused attenuation of vagally induced slowing of the heart, but the effect of each injection was less than that of the previous one. A fourth injection of galanin given after a 45 or 60 min rest period showed return of sensitivity. 3. Sympathetic stimulation at 16 Hz for 5 min was less efficient in causing attenuation of vagal slowing when applied following the administration of exogenous galanin. This is consistent with galanin being the mediator of vagal attenuation following sympathetic stimulation.