bluuebunny/crossref_metadata_2025 huggingface dataset:
The two power limits conditioning step frequency in human running.
Authors: Cavagna G A , Willems P A , Franzetti P , Detrembleur C
Published: December 2014

1. At high running speeds, the step frequency becomes lower than the apparent natural frequency of the body's bouncing system. This is due to a relative increase of the vertical component of the muscular push and requires a greater power to maintain the motion of the centre of gravity, Wext. However, the reduction of the step frequency leads to a decrease of the power to accelerate the limbs relatively to the centre of gravity, Wint, and, possibly, of the total power Wtot = Wext + Wint. 2. In this study we measured Wext using a force platform, Wint by motion picture analysis, and calculated Wtot during human running at six given speeds (from 5 to 21 km h‐1) maintained with different step frequencies dictated by a metronome. The power was calculated by dividing the positive work done at each step by the duration of the step (step‐average power) and by the duration of the positive work phase (push‐average power). 3. Also in running, as in walking, a change of the step frequency at a given speed has opposite effects on Wext, which decreases with increasing step frequency, and Wint, which increases with frequency; in addition, a step frequency exists at which Wtot reaches a minimum. However, the frequency for a minimum of Wtot decreases with speed in running, whereas it increases with speed in walking. This is true for both the step‐average and the push‐average powers. 4. The frequency minimizing the step‐average power equals the freely chosen step frequency at about 13 km h‐1: it is higher at lower speeds and lower at higher speeds. The frequency minimizing the push‐average power approaches the freely chosen step frequency at high speeds (around 22 km h‐1 for our subjects). 5. It is concluded that the increase of the vertical push does reduce the step‐average power, but that a limit is set by the increase of the push‐average power. Between 13 and 22 km h‐1 the freely chosen step frequency is intermediate between a frequency minimizing the step‐average power, eventually limited by the maximum oxygen intake (aerobic power), and a frequency minimizing the push‐average power, set free by the muscle immediately during contraction (anaerobic power). The first need prevails at the lower speed, the second at the higher speed.
Differentiation of sympathetic neurones projecting in the hypogastric nerves in terms of their discharge patterns in cats.
Authors: Jänig W , Schmidt M , Schnitzler A , Wesselmann U
Published: December 2014

1. Sympathetic neurones that project in the hypogastric nerves (HGNs) were analysed for their discharge patterns in anaesthetized cats. The activity of these neurones was recorded from their axons. Afferents from the pelvic organs (urinary bladder, colon, anal canal), and arterial baro‐and chemoreceptors were stimulated. 150 postganglionic and nine preganglionic neurones were analysed. 2. The postganglionic neurones exhibited reflex patterns that were typical of visceral vasoconstrictor neurones and various types of motility‐regulating neurones. Most motility‐regulating neurones and all visceral vasoconstrictor neurones had ongoing activity. 3. Postganglionic motility‐regulating neurones were not influenced by stimulation of arterial baro‐and chemoreceptors, but showed distinctive reflexes on stimulation of afferents from pelvic organs. Three subgroups of motility‐regulating neurones were identified: type 1 neurones (34% of the sample of postganglionic neurones) were excited from the urinary bladder and inhibited or not influenced from the colon. Type 2 neurones (14%) exhibited a reflex pattern reciprocal to that of the type 1 neurones. Anal motility‐regulating neurones (8%) were only influenced from the anal canal. The most powerful reflexes in these types of motility‐regulating neurones were elicited by mechanical stimulation of the anal mucosa. 4. Postganglionic visceral vasoconstrictor neurones (16% of the sample) were under powerful inhibitory control from the arterial baroreceptors and weakly excited by stimulation of arterial chemoreceptors. Visceral stimuli had little or no effect on most of these neurones. Some visceral vasoconstrictor neurones exhibited some overlap in their functional properties with motility‐regulating neurones. 5. Twenty‐eight per cent of our sample of postganglionic neurones showed no reflexes to the afferent stimuli used. About half of these neurones had on‐going activity. 6. Nine preganglionic neurones with on‐going activity were identified. Most of these neurones behaved like visceral vasoconstrictor or motility‐regulating neurones. 7. This study shows that the majority of postganglionic neurones that project in the HGNs can be divided into the same functional types as the lumbar preganglionic neurones that project to the inferior mesenteric ganglion. The proportions of the different types of neurones are similar at pre‐ and postganglionic levels. Thus the centrally generated patterns of activity are most likely faithfully transmitted from the spinal cord to the target organs in the pelvic cavity in functionally separate pathways.
Reciprocal Ia inhibition between elbow flexors and extensors in the human.
Authors: Katz R , Penicaud A , Rossi A
Published: December 2014

1. Reciprocal inhibition between elbow flexor and extensor muscles (biceps and triceps brachii) has been investigated in nine healthy subjects. Two techniques were used to assess changes in motoneurone excitability after stimulation of antagonist muscle afferents: (1) monosynaptic reflexes elicited by a mechanical stimulation of the distal muscle tendon (tendon tap); (2) post‐stimulus time histograms (PSTH) of voluntarily activated motor units. 2. Electrical stimulation of the antagonist muscle nerve produced a short‐latency and short‐lasting inhibition of the flexor and extensor motoneurones. The amount of this inhibition was found to be similar in both motor nuclei. 3. The inhibition could be evoked with conditioning electrical stimuli as low as 0.7 x motor threshold (MT) or by very weak tendon taps applied to the antagonist tendon. In the former case the threshold of this inhibition was found to be consistently increased after raising the threshold of Ia afferent fibres by a long‐lasting muscle vibration. Since a contribution from cutaneous afferent fibres was ruled out, it is concluded that this inhibition was Ia in origin. 4. Post‐stimulus time histograms of voluntarily activated triceps and biceps motor units were made following electrical stimulation of homonymous and antagonist muscle afferents. This enabled an estimate of the central synaptic delay of the inhibitory process. An average central delay of 0.94 ms in excess of that of monosynaptic facilitation was found, thus suggesting that the inhibitory process could be mediated by only one interneurone. 5. A conditioning reflex discharge elicited in the antagonist muscle by a tendon tap depressed or suppressed this inhibition. This depression was maximal when the reflex discharge was elicited 10‐20 ms before the conditioning stimulus for the inhibition and never lasted more than 30 ms. It is argued that the only mechanism compatible with such a depression is the inhibitory activity of Renshaw cells acting on the pathway mediating reciprocal inhibition. 6. We conclude that group Ia afferent fibres from elbow extensor and flexor muscles project monosynaptically onto Ia inhibitory interneurones to mediate disynaptic reciprocal inhibition of antagonist motoneurones.
Inactivation characteristics reveal two calcium currents in adult bovine chromaffin cells.
Authors: Bossu J L , De Waard M , Feltz A
Published: December 2014

1. Two calcium currents were identified by differences in their inactivation characteristics in adult chromaffin cells maintained in short‐term primary culture (3‐5 days). Calcium currents were recorded by means of the whole‐cell configuration using an intracellular medium highly buffered for pH and pCa. 2. Calcium current evoked from a holding potential of ‐90 mV inactivated along two components: an initial transient with a time constant of 250 ms followed by a plateau. 3. Steady‐state inactivation followed two processes which developed at two distinct membrane potentials. One process was half‐inactivated at low voltages around ‐55 mV and affected mainly the initial transient component. The other process, which affected mainly the sustained component of the calcium current, was half‐inactivated at voltages around ‐10 mV. The proportions of these two processes varied greatly from cell to cell. 4. The dihydropyridine antagonists (nicardipine and nifedipine applied at 10(‐5) M) and the phenylalkylamine D600 (5 x 10(‐6) M) shifted the half‐inactivation value towards ‐55 mV, indicating the suppression of the sustained component. The snail toxin, omega‐conotoxin, had the opposite effect; it shifted the half‐activation value towards ‐10 mV. 5. The calcium channel agonist Bay K 8644 (10(‐5) M) either had no effect or induced only a slight increase of the response, as did its (‐)‐enantiomer (10(‐6) M). To interpret the present results, we suggest that the L‐component was maximally activated in our recording conditions. 6. In chromaffin cells, the calcium current recorded in whole‐cell conditions is composed of two components with properties close to those of N‐ and L‐type currents described in sympathetic neurons.
A slow calcium‐dependent chloride current in rhythmic hyperpolarization in neurones of the rabbit vesical pelvic ganglia.
Authors: Nishimura T , Akasu T , Tokimasa T
Published: December 2014

1. Voltage‐clamp recordings were made from neurones of vesical pelvic ganglia isolated from the rabbit urinary bladder. A rhythmic outward current, ISH, which corresponds to the spontaneous hyperpolarization, occurred at fairly constant intervals in fifty‐eight of eighty‐four neurones superfused with Krebs solution. The peak amplitude of the ISH was 0.5 +/‐ 0.2 nA (n = 48; mean +/‐ S.E.M.). 2. The ISH was eliminated in a Krebs solution containing nominally zero calcium and 12 mM‐magnesium. Lowering the temperature of the superfusing solution from 36 to 22 degrees C also inhibited the occurrence of the ISH. 3. Bath application of caffeine increased the frequency of ISH. In contrast, ryanodine and procaine reversibly blocked ISH. 4. In thirty‐four of fifty‐eight neurones, the ISH was composed of two current components, an initial fast ISH with duration of 1‐10 s and a slow ISH lasting 15‐60 s. In the remaining twenty‐four neurones, ISH showed only the fast component. 5. The fast ISH was associated with an increased membrane conductance and the slow ISH was associated with a decreased membrane conductance. The reversal potentials of the fast and the slow ISH were ‐88 +/‐ 7 mV (n = 4) and ‐30 +/‐ 6 mV (n = 4), respectively. 6. Tetraethylammonium (5 mM) and barium (1 mM) blocked the fast ISH but not the slow ISH. Intracellular caesium injected by ionophoresis through a Cs(+)‐filled microelectrode blocked the fast ISH, without affecting the slow ISH. Apamin and (+)‐tubocurarine selectively suppressed the fast component of the ISH. 7. Substitution of isethionate (67 mM) for chloride increased the amplitude of the slow ISH and shifted the reversal potential of the slow ISH to +1 +/‐ 8 mV (n = 5). A slow ISH with amplitude of 0.1‐1 nA and was still observed in a low‐sodium (26.2 mM) solution. The stilbene derivative, 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS), a chloride channel blocker, suppressed the slow ISH. 8. These results suggest that ISH is composed of two distinct calcium‐dependent currents, a fast ISH produced by activation of potassium conductance and a slow ISH produced by inactivation of chloride conductance. 9. The after‐hyperpolarization (AHP) following the action potential was also composed of apamin‐sensitive and insensitive spontaneous hyperpolarizing oscillations. The apamin‐insensitive component of IAHP was increased by lowering external chloride activity, while it was depressed by SITS.
Dopamine actions on calcium currents, potassium currents and hormone release in rat melanotrophs.
Authors: Stack J , Surprenant A
Published: December 2014

1. Intracellular and whole‐cell recordings were made from primary cultures of rat intermediate pituitary cells; beta‐endorphin secretion was also measured by radioimmunoassay. The effects of dopamine receptor activation on hormone secretion, calcium currents and resting potassium conductance were compared. 2. Spontaneous sodium‐dependent action potentials occurred in 82% of cells recorded with intracellular microelectrodes and 64% of cells recorded with whole‐cell patch electrodes; the same proportion of cells showed spontaneous calcium‐dependent depolarizations in the presence of tetrodotoxin. 3. Calcium currents recorded from holding potentials of ‐90 or ‐70 mV showed transient and sustained components, both of which activated at ‐40 mV and had similar current‐voltage relations. Bay K 8644 (1 microM) increased both components by about 130% while nifedipine (1‐10 microM) decreased them by a maximum of 30%. Nickel (500 microM) inhibited transient and sustained components by 68 and 50%; cadmium (100 microM) abolished the current. omega‐Conotoxin (1 microM) reversibly inhibited the transient component by 26%. 4. The dopamine D2 receptor agonist, quinpirole (0.1‐10 microM) inhibited transient and sustained components in all cells by a maximum of 40 and 25% respectively. Quinpirole did not alter the time course of the current. 5. Quinpirole (1‐100 nM) hyperpolarized 90% of cells from which intracellular recordings were made and 55% of cells recorded from with whole‐cell patch pipettes. Maximum hyperpolarization of 16 +/‐ 4 mV from a resting potential of ‐44 +/‐ 5 mV was observed with 100 nM‐quinpirole; concentration producing half‐maximal effect was 3 nM. The hyperpolarization resulted from an increase in potassium conductance. 6. Quinpirole (1‐100 nM) decreased basal beta‐endorphin secretion by 55% and abolished secretion stimulated by Bay K 8644 or isoprenaline; concentrations producing half‐maximal inhibitions were 5‐10 nM. Tetrodotoxin (1 microM), nifedipine (1 microM), nickel (500 microM) and cadmium (100 microM) did not alter basal or stimulated secretion although higher concentrations of cadmium did inhibit stimulated hormone release. 7. Pertussis toxin pre‐treatment prevented all actions of quinpirole. 8. Thus, concentrations of quinpirole that abolished stimulated hormone secretion did not alter calcium currents; conversely, concentrations of calcium channel blockers that partially or completely inhibited calcium currents did not alter basal or stimulated secretion. These results may indicate that calcium influx through the voltage‐dependent calcium channels measured in these experiments does not contribute significantly to hormone release from melanotrophs.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of cholecystokinin in ganglionic transmission in the guinea‐pig gall‐bladder.
Authors: Mawe G M
Published: December 2014

1. The effects of cholecystokinin (CCK) on intact guinea‐pig gall‐bladder ganglia were investigated with intracellular, single‐electrode current‐ and voltage‐clamp recording techniques. 2. Cholecystokinin octapeptide (CCK‐8; 0.01‐100 nM) increased the amplitude of the fast excitatory postsynaptic potential (EPSP) that was evoked by stimulation of interganglionic fibre tracts. In most cases, neurones that exhibited subthreshold EPSPs in normal Krebs solution fired action potentials in the presence of CCK‐8. In a low Ca2+/high Mg2+ solution, CCK‐8 caused a 3‐fold increase in the amplitude of fast EPSPs. 3. The amplitude of the evoked excitatory postsynaptic current (EPSC) was increased by CCK‐8 (0.01‐100 nM) in a concentration‐dependent manner. The effect was maximal at 1.0 nM. 4. Cholecystokinin octapeptide caused a 3‐fold increase in the quantal content of the EPSP in a low Ca2+/high Mg2+ solution, but had no effect on the quantal size. 5. The specific CCK‐A receptor antagonist, MK‐329 (formerly L‐364,718; 1.0 nM), reversibly blocked the facilitatory effect of CCK‐8 on ganglionic transmission. However, the specific CCK‐B receptor antagonist, L‐365,260 (10 nM), did not alter the presynaptic facilitatory effect of CCK‐8. 6. The response of gall‐bladder neurones to exogenously applied ACh was not modified by CCK‐8. 7. Application of CCK‐8, by superfusion (0.001‐100 nM) or by pressure microejection (100 microM), had no effect on the membrane potential, membrane conductance, action potential, or threshold of gall‐bladder neurones. 8. Immunohistochemistry was employed to determine whether the actions of CCK could be elicited by release of the peptide from nerve terminals within the ganglionated plexus of the gall‐bladder. Immunoreactivity for CCK was not detected in the ganglionated plexus of the gall‐bladder, but CCK immunoreactivity was plentiful in control preparations of intestinal myenteric and submucosal plexuses. 9. These results show that CCK has a presynaptic facilitatory effect on fast synaptic transmission in guinea‐pig gall‐bladder ganglia, and that this effect is mediated by presynaptic CCK‐A receptors. Furthermore, it appears that such an effect would normally occur in response to hormonal CCK, rather than CCK that is released from nerve terminals.
Double‐pulse calcium channel current facilitation in adult rat sympathetic neurones.
Authors: Ikeda S R
Published: December 2014

1. Double‐pulse facilitation of Ca2+ channel currents in enzymatically dispersed adult rat superior cervical ganglion neurones was investigated using the whole‐cell variant of the patch‐clamp technique. Voltage‐clamp recordings were performed at room temperature (21‐24 degrees C) in solutions designed to isolate Ca2+ channel currents. 2. Ba2+ currents, elicited by a 0 mV test pulse, were increased in amplitude when preceded by a 40 ms pulse to voltages greater than 0 mV. The magnitude of facilitation was dependent on pre‐pulse voltage and reached a maximum of 50% (i.e. 1.5 x the current amplitude elicited without a pre‐pulse) at a pre‐pulse voltage of +80 mV. Half‐maximal facilitation occurred at about +25 mV. A small decrease (‐6%) in test pulse amplitude was present at pre‐pulse voltages between ‐40 and 0 mV. The magnitude of facilitation was also dependent on test pulse voltage. Facilitation was greatest between test pulse voltages of ‐10 and 0 mV. 3. Facilitation slowly decreased during prolonged (1 h) dialysis of the neurone even though the Ba2+ current amplitude was well maintained. 4. Increasing the pre‐pulse duration over the range 0‐120 ms produced an exponential increase in facilitation with a time constant of 17.3 ms. Conversely, lengthening the interpulse duration over the range 5‐915 ms, while maintaining a constant pre‐pulse amplitude and duration, resulted in an exponential decrease in facilitation with a time constant of 197 ms. 5. At a test potential of 0 mV, the decay of the facilitated Ba2+ current component was fitted to a double exponential function with time constants of about 25 and 150 ms. The time constants had little pre‐pulse voltage dependence between +30 to +80 mV. 6. The initial rising phase of both the control and facilitated Ba2+ current were reasonably well described by a single exponential (tau rise) after a delay of 300 microseconds. The tau rise versus test pulse potential relationship was ‘bell shaped’ over the test pulse voltage of ‐20 to +30 mV reaching a maximum near ‐5 mV. tau rise was similar for control and facilitated currents except at potentials greater than +10 mV where the rise of the facilitated current was accelerated. 7. Control and facilitated activation curves, as derived from tail current amplitudes, were described by the sum of two Boltzmann functions. A facilitating pre‐pulse produced an increase in the proportion of the current contributed by the component activated at more hyperpolarized test potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Control of action potentials and Ca2+ influx by the Ca(2+)‐dependent chloride current in mouse pituitary cells.
Authors: Korn S J , Bolden A , Horn R
Published: December 2014

1. Perforated patch recording was used to examine the influence of the calcium‐dependent chloride current (iCl(Ca)) on Ca2+ action potentials in AtT‐20 pituitary cells. The calculated chloride equilibrium potential (ECl) was adjusted by changing either intracellular or extracellular [Cl‐]. Action potential duration varied as a function of ECl. When ECl was set at ‐21 mV, both spontaneous and evoked action potentials displayed a long plateau phase between ‐20 and ‐25 mV, which typically lasted for several seconds. Setting ECl to more negative potentials resulted in briefer action potentials; at an ECl of ‐52 mV, no plateau phase was evident. Spontaneous depolarization and action potential firing still occurred when ECl was negative to firing threshold, which indicates that the slow depolarizing wave that precedes the firing of spontaneous action potentials does not require activation of ICl(Ca). 2. In voltage clamp experiments the magnitude of ICl(Ca) diminished slowly during a prolonged depolarization, over a time course that coincided with action potential termination. 3. Niflumic acid (100 microM) blocked ICl(Ca) by 90% but had no effect on either K+ or Ca2+ currents. This concentration of niflumic acid eliminated the plateau phase, but did not prevent the firing, of Ca2+ action potentials. 4. Internal [Ca2+] was measured photometrically after loading cells with the Ca2+ indicator dye, Fura‐2. Under voltage clamp conditions, concentrations of niflumic acid (30‐100 microM) that blocked depolarization‐evoked ICl(Ca) had little or no effect on simultaneously recorded Ca2+ transients. Perforated patch recording from Fura‐loaded cells showed that action potentials were temporally associated with transient increases in intracellular [Ca2+]. Niflumic acid (30‐100 microM) disrupted the rhythmic firing of spontaneous action potentials and associated intracellular Ca2+ transients. 5. Fluorescent measurements of Ca2+ transients were also made in cells unperturbed by patch recording, and were used as a measure of action potential duration in the absence of experimental alteration of internal [Cl‐]. Spontaneous Ca2+ transients were of long duration (approximately 2 s), which suggests that intracellular [Cl‐] is relatively high (40‐50 mM) in these cells. The spontaneous Ca2+ transients were inhibited by niflumic acid. 6. Niflumic acid up to 100 microM, had neglible effects on either basal or stimulated (by 2 microM‐(+/‐)‐isoprenaline) hormone secretion, as shown by radioimmunoassay of adrenocortotrophic hormone release.(ABSTRACT TRUNCATED AT 400 WORDS)
Some reflex cardioinhibitory responses in the cat and their modulation by central inspiratory neuronal activity.
Authors: Daly M D
Published: December 2014

1. Cats were anaesthetized with a mixture of chloralose and urethane, and were artifically ventilated. 2. An open pneumothorax was provided by two large‐bore tubes which were sealed in the sixth intercostal space on each side. They were connected to a Fleisch pneumotachograph. Phasic changes in central inspiratory neuronal activity were measured quantitatively as changes in the volume of the pneumothorax during temporary interruption of artificial respiration, the volume of the lungs being held constant at their end‐expiratory level. In this way the activity of slowly adapting pulmonary stretch receptors was maintained constant. 3. Reflex cardioinhibitory responses were elicited by stimulation of (a) the carotid body chemoreceptors by intracarotid injections of cyanide; (b) the arterial baroreflex by controlled elevations of the blood pressure; (c) cardiac receptors by left atrial injections of veratridine; and (d) pulmonary C fibres (including J receptors) by right atrial injections of phenylbiguanide. 4. The effects of central inspiratory neuronal activity on pulse interval were assessed by comparing the values observed during the inspiratory and expiratory phases of the respiratory cycle in the control state and during stimulation of each cardiovascular receptor group. 5. The carotid chemoreceptor‐induced bradycardia measured during the expiratory phase of respiration was reduced during inspiration to a value of about 15% of control. The central inspiratory drive was less effective in altering the reflex responses from the arterial baroreceptors and cardiac receptors, the corresponding values being 42 and 51% respectively. 6. In contrast, the bradycardia evoked by pulmonary C fibre stimulation was not significantly affected by the central inspiratory drive. 7. The differential nature of the modulation by the central inspiratory drive occurred independently of the integrity of the sympathetic nerve supply to the heart indicating that the cardiac efferents involved were largely fibres in the vagus nerves. 8. The possible explanation of these results in terms of central mechanisms is discussed.
A voltage‐dependent potassium current in rabbit coronary artery smooth muscle cells.
Authors: Volk K A , Matsuda J J , Shibata E F
Published: December 2014

1. Voltage‐ and time‐dependent outward currents were recorded from relaxed enzymatically isolated smooth muscle cells from the rabbit left descending coronary artery using a single pipette voltage clamp technique. The calcium‐activated potassium current was blocked by inclusion of EGTA in the pipette solution and CdCl2 in the extracellular bath. 2. Outward currents were elicited with depolarizing voltage steps to potentials positive to ‐20 mV. Long (5 s) voltage steps revealed slow inactivation of the current with a time constant of nearly 3 s at +60 mV. Potassium was identified as the predominant charge carrier by reversal potential measurements in potassium substitution experiments. 3. The results of kinetic analyses compared favourably with the Hodgkin‐Huxley model for a delayed rectifier with some deviations. The sigmoid current onset was best fitted by raising the activation variable (n) to the second power. Deactivation tail currents were consistently found to be comprised of two exponential components. The kinetics of activation and deactivation were strongly voltage‐dependent from ‐80 to +60 mV. 4. Envelope of tails experiments showed that the scaled tail current amplitudes followed the kinetic behaviour of current activation. The contribution of each of the two exponential tail components was also measured in these experiments. They did not reveal kinetically separable currents, nor were they differentially altered by 4‐aminopyridine (4‐AP), tetraethylammonium (TEA), or elevated [K+]o. 5. The steady‐state voltage‐dependence curves for both activation and inactivation were well fitted by a Boltzmann distribution with V1/2 = ‐5.60 mV and k = ‐8.66 mV for n infinity act and V1/2 = ‐24.20 mV and k = 5.16 mV for n infinity act. Super‐imposition of the two curves revealed a ‘window’ of voltage where channels are available for activation without completely inactivating. 6. Neither of the commonly used potassium channel blockers, TEA or 4‐AP, were particularly effective blockers of IK, reducing current by only 50‐70% at an extracellular concentration of 10 mM. TEA block was mildly voltage‐dependent and was more effective in reducing current towards the end of a 500 ms depolarization. 4‐AP, on the other hand, demonstrated considerable voltage‐dependence and preferentially reduced early currents. 7. Outward currents recorded from guinea‐pig and human coronary artery myocytes under the same conditions as in the rabbit cell experiments displayed similar characteristics.(ABSTRACT TRUNCATED AT 400 WORDS)
Role of disulphide bonds in burst‐like activity of nicotinic acetylcholine receptor channels in rat sympathetic neurones.
Authors: Derkach V A , Kurenny D E , Melishchuk A I , Selyanko A A , Skok V I
Published: December 2014

1. The effects of reduction of disulphide bonds in nicotinic acetylcholine receptors (nicotinic AChRs) with dithiothreitol (DTT) were studied in rat superior cervical ganglion neurones using the patch‐clamp method in whole‐cell and cell‐attached recording modes. 2. Dithiothreitol (1 mM) markedly reduced the ACh‐induced membrane current, while the action of ACh remained reversible. Conversely, bromoacetylcholine (BrACh), if applied after the treatment with DTT, caused irreversible activation of nicotinic AChRs manifested in the appearance of a non‐declined steady‐state component in BrACh‐induced currents accompanied by increased membrane current fluctuations. The successive reoxidation of sulphydryl groups by potassium ferricyanide (1 mM‐ferricyanide) restored the response to ACh. Ferricyanide itself had a weaker inhibitory effect on the ACh‐induced current, compared to the effect of DTT. 3. As a result of the action of DTT (1 mM), the spectrum of BrACh‐induced current noise shifted to a higher frequency range. 4. The distributions of durations of the gaps (closed states) and the bursts (the states identified as open states after the shortest gaps were ignored) in single‐channel activity of native (non‐treated with DTT) nicotinic AChRs caused by ACh (30 microM) and BrACh (30 microM) were similar and both revealed four to five and two to three components for gap intervals and burst durations respectively. 5. Single‐channel behaviour of reduced nicotinic AChRs was similar for both ACh and BrACh as agonists, but significantly differed from that in the native one. The first difference was the marked increase in the frequency of the appearance of long closed states of the channel that was presumably due to enhanced receptor desensitization. The second difference was an almost complete disappearance of long bursts associated with disappearance of the fastest component in gap interval distribution. 6. Mean conductance of single nicotinic AChR channels decreased by approximately 20% in the reduced receptor compared with that in the native one, for both agonists. 7. The results suggest a critical role of disulphide bonds for the functioning of native neuronal nicotinic AChRs: the disruption of disulphide bonds leads to the loss of burst‐like kinetics of the nicotinic AChR ionic channel.
Blockage and permeation of divalent cations through the cyclic GMP‐activated channel from tiger salamander retinal rods.
Authors: Colamartino G , Menini A , Torre V
Published: December 2014

1. Blockage and permeation of divalent cations through channels activated by guanosine 3',5'‐cyclic monophosphate (cyclic GMP) were studied in membrane patches excised from retinal rods of the tiger salamander Ambystoma tigrinum by rapidly changing the ionic medium bathing the intracellular side of the excised membrane. 2. The Na+ current, observed when 110 mM‐NaCl was present on both sides of the membrane patch, was reduced by the addition of 1 mM of the chloride salts of Ca2+, Mg2+, Sr2+, Ba2+ or Mn2+ to the bathing medium. The sequence of blocking potency at +60 mV was Mg2+ greater than Mn2+ approximately Ba2+ greater than Ca2+ greater than Sr2+, while at ‐60 mV it was Ba2+ greater than Ca2+ greater than Sr2+ greater than Mn2+ approximately Mg2+. For all divalent cations the blocking effect depended, in a complex way, on the membrane potential. 3. The blocking effect of Ca2+ and Mg2+ increased when the concentration of cyclic GMP was reduced from 100 to 5 microM. At ‐60 mV 1 mM‐Ca2+ blocked about 34% of the Na+ current in the presence of 100 microM‐cyclic GMP, while in the presence of 5 microM‐cyclic GMP, 1 mM‐Ca2+ blocked about 56% of the Na+ current. 4. When, in the presence of 100 microM‐cyclic GMP, 110 mM‐NaCl at the intracellular side was replaced by equiosmolar amounts of chloride salts of divalent cations (73.3 mM) a small outward current carried by divalent cations could be observed at large positive membrane potentials. At +60 mV the ratio between the current carried by Na+, Sr2+, Ca2+, Ba2+, Mg2+ and Mn2+ was 83.3:1.4:1:0.58:0.33:0.25. 5. In agreement with previous observations the dependence of the Na+ current on the concentration of cyclic GMP shows a clear co‐operativity among cyclic GMP molecules.4+ cyclic GMP‐gated channel in excised patches is similar to but not identical to the selectivity sequence of divalent cations through the channel in intact rods.
Dependence of autogenic and heterogenic stretch reflexes on pre‐load activity in the human arm.
Authors: Smeets J B , Erkelens C J
Published: December 2014

1. Subjects held their right arm in a horizontal plane. The angle of the elbow was 90 deg. They exerted forces in several directions in the plane of the arm, varying independently the pre‐load torques about shoulder and elbow. We measured electromyographic (EMG) activity in several arm muscles in response to force perturbations which extended the shoulder, without changing the elbow angle. 2. The EMG activity in flexors of both shoulder and elbow showed reflex responses at short latency (approximately 25 ms). In all muscles the reflex activity increased with the pre‐load activity of that muscle. 3. The short‐latency reflex activity of m. brachialis, which was not stretched by the perturbations, was independent of the pre‐load activity of the muscles acting over the shoulder. 4. From these results we conclude that the force resulting from the short‐latency reflex, assessed from the EMGs, does not counteract the perturbations exactly. Having found that the short‐latency reflex is dependent on the pre‐load direction, we argue that this dependence makes the short‐latency reflex suitable for correcting fast movements for misjudgements of load. 5. At longer latencies (greater than 50 ms) the direction of the force resulting from the reflex, assessed from the EMGs, was almost independent of the direction of the pre‐load. In our experiment the force resulting from the long‐latency reflex counteracted the perturbations quite well.
Involvement of GABA systems in feedback regulation of glutamate‐and GABA‐mediated synaptic potentials in rat neostriatum.
Authors: Calabresi P , Mercuri N B , De Murtas M , Bernardi G
Published: December 2014

1. Neostriatal neurones were recorded intracellularly from a rat corticostriatal slice preparation. Depolarizing postsynaptic potentials (DPSPs) were evoked by either cortical or intrastriatal stimulation. 2. Kynurenic acid (600 microM), an antagonist of excitatory amino acids, reduced the cortically‐evoked DPSPs by 88% while the intrastriatally evoked potentials were reduced by 48%. Bicuculline (100 microM) produced only a slight inhibition of the cortically evoked DPSPs (12%), but clearly depressed intrastriatal potentials (52%). 3. The effects of (‐)‐baclofen, a gamma‐aminobutyric acid (GABA)B receptor agonist, were studied on the cortically evoked DPSPs. In all the tested neurones (‐)‐baclofen, added to the superfusion medium, caused a concentration‐dependent decrease of these potentials (half‐maximal effect (EC50) = 800 nM). This effect was not affected by bicuculline. (‐)‐Baclofen did not change the membrane potential, the input resistance, current‐evoked firing frequency, or postsynaptic responses to exogenously applied glutamate. 4. The effects of (‐)‐baclofen on the DPSPs were compared to those produced by application of GABA and muscimol. GABA and muscimol decreased the DPSPs and caused a membrane depolarization coupled with a decrease of the membrane resistance. Bicuculline (100 microM) blocked the GABA‐induced changes of the membrane potential and of the resistance, but not the decrease of the synaptic potentials. All the effects produced by muscimol were blocked by bicuculline. 5. Following intrastriatal stimulation a residual kynurenate‐insensitive potential persisted; this potential was blocked by bicuculline (100 microM). (‐)‐Baclofen produced a dose‐dependent decrease of this potential (EC50 = 800 nM). The postsynaptic responses to exogenously applied GABA were unchanged by (‐)‐baclofen. 6. The amplitude of kynurenate and bicuculline‐sensitive DPSPs were stable at a frequency of 0.1 Hz. At frequencies between 0.3 and 3 Hz both these potentials were attenuated with the second stimulus and after about five stimuli a steady state was reached. Membrane potential and input resistance were not affected by these frequencies of stimulation. 7. Application of the GABA uptake inhibitor nipecotic acid (100‐300 microM) clearly reduced the amplitude of both kynurenate‐and bicuculline‐sensitive DPSPs evoked at low frequencies of stimulation (0.01‐0.3 Hz), but had lower effects at higher stimulation rates (1‐3 Hz). Application of nipecotic acid increased the duration of membrane responses to exogenously applied GABA.(ABSTRACT TRUNCATED AT 400 WORDS)
Two inward currents and the transformation of low‐frequency oscillations of rat and cat thalamocortical cells.
Authors: Soltesz I , Lightowler S , Leresche N , Jassik‐Gerschenfeld D , Pollard C E , Crunelli V
Published: December 2014

1. The contribution of a slow, mixed Na(+)‐K+, inward rectifying current (Ih) and the T‐type Ca2+ current (IT) (that underlies low‐threshold Ca2+ potentials) to the low‐frequency oscillations observed in rat and cat thalamocortical (TC) cells in vitro was studied using current clamp and single‐electrode voltage clamp recordings. 2. From a holding potential of ‐50 mV, voltage steps negative to ‐60 mV showed the presence of a slow, non‐inactivating inward current, Ih. This current was unaffected by Ba2+ (1‐4 mM), tetrodotoxin (0.5‐1 microM) and TEA (20 mM, n = 6), reversibly blocked by Cs+ (1‐3 mM), and its reversal potential (‐33.0 +/‐ 1.2 mV) followed changes in the extracellular Na+ and K+, but not Cl‐, concentration. 3. Application of Cs+ (1‐3 mM) abolished the pacemaker oscillations (n = 9), while in six cells that did not show any oscillatory activity Cs+ first evoked the spindle‐like oscillations that, in the continuous presence of these ions, were then transformed into the pacemaker oscillations before all activities were finally blocked: all these effects were accompanied by a hyperpolarization and a progressive decrease and final blockade of Ih. Cs+ had no effect on the ‘N‐methyl‐D‐aspartate’ (NMDA) oscillations (n = 5) and Ba2+ (2 mM, n = 8) did not block the pacemaker, the spindle‐like and the ‘NMDA’ oscillations. 4. In ten cells that showed the pacemaker oscillations selective activation of beta‐adrenoceptors by 10‐50 microM‐noradrenaline (in the presence of alpha‐noradrenergic antagonists) or by 20 microM‐isoprenaline first transformed the pacemaker oscillations into the spindle‐like oscillations that, in the continuous activation of beta‐receptors, were finally abolished: all these effects were accompanied by a depolarization and a progressive increase of Ih. 5. In TC cells that showed the pacemaker oscillations application of 1‐octanol (50‐100 microM), an antagonist of T‐type Ca2+ currents, reversibly blocked this activity but concomitantly decreased (50%) the cell input resistance (n = 5). Application of Ni2+ (0.2‐0.5 mM, n = 13), another antagonist of IT reversibly blocked the pacemaker, the spindle‐like and the ‘NMDA’ oscillations. 7. In cells showing the pacemaker oscillations it was found that the current developing from the most hyperpolarized potential of an oscillation cycle was an inward relaxation whose time course differed from that of Ih evoked at the same potential.(ABSTRACT TRUNCATED AT 400 WORDS)
Lanthanum actions on excitatory amino acid‐gated currents and voltage‐gated calcium currents in rat dorsal horn neurons.
Authors: Reichling D B , MacDermott A B
Published: December 2014

1. The effects of lanthanum ions (La3+) on voltage‐gated calcium currents (VGCCs) and excitatory amino acid (EAA)‐evoked currents were characterized using cultured or acutely dissociated neurons from the dorsal horn of the rat spinal cord. 2. VGCCs evoked by depolarizing voltage steps were reversibly blocked by La3+ with an apparent log dissociation constant Kd of 163 nM. 3. La3+ antagonism of currents evoked by NMDA was less potent, with an EC50 (half‐maximal effective concentration) of 2 microM. The block of NMDA‐evoked currents was voltage independent and non‐competitive with respect to activation of the NMDA receptor. 4. La3+ had both enhancing and blocking actions on currents evoked by kainate or by quisqualate; concentrations of La3+ between 1 and 100 microM enhanced kainate‐ and quisqualate‐evoked currents, while the currents were blocked by concentrations of La3+ greater than 100 microM. Both the blocking and the enhancing actions of La3+ were independent of membrane potential. 5. An enhancing dose of La3+ shifted the dose‐response curve for kainate to lower concentrations of agonist without changing the maximum evoked current, and a similar leftward shift of the quisqualate dose‐response curve occurred at non‐saturating concentrations of quisqualate. This enhancement might occur either due to increased affinity of the receptor for ligand, or by increased concentration of ligand at the membrane surface; the latter effect could result from a reduction in the membrane surface charge. 6. The divalent cation Zn(2+)‐mimicked the effects of La3+ on excitatory amino acid‐evoked currents in dorsal horn neurons, but was less potent both as a blocker and as an enhancer. This suggests that La3+ and Zn2+ could act with different potencies at the same site or sites, and that La3+ may be a useful probe for the mechanisms of Zn2+ effects. 7. Since La3+ enhances kainate‐ and quisqualate‐evoked responses at the same concentrations at which it suppresses VGCCs (and NMDA‐gated currents), it can be a useful probe for separating VGCC activation from kainate‐ and quisqualate‐induced depolarizations in experiments where voltage clamp is impractical.
The postsynaptic dorsal column pathway mediates cutaneous nociceptive information to cerebellar climbing fibres in the cat.
Authors: Ekerot C F , Garwicz M , Schouenborg J
Published: December 2014

1. The location in the spinal cord of the pathway mediating cutaneous nociceptive C fibre input to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was investigated in pentobarbitone‐anaesthetized cats. Lesions of the spinal cord at the segmental level of C3 sparing the dorsal funiculi (DF preparation) or lesions of the ipsilateral and part of the contralateral dorsal funiculi were made. 2. In the DF preparation, the cutaneous input to climbing fibres projecting to the C3 zone was the same as in cats with an intact spinal cord. Also, the topography of tactile and nociceptive receptive fields and the distribution of A‐ and C fibre‐evoked climbing fibre field potentials was similar to that in cats with an intact spinal cord. 3. In cats with an initially intact spinal cord the cutaneous nociceptive C fibre input and the topographically well organized tactile input to the C3 climbing fibres disappeared following a lesion of the ipsilateral and part of the contralateral dorsal funiculi. Following this lesion the receptive fields of the climbing fibres became indistinct and only irregular responses were evoked on skin stimulation. 4. It is concluded that the cutaneous nociceptive C fibre input from the forelimb to climbing fibres projecting to the C3 zone is mediated by the ipsilateral dorsal funiculus. Since cutaneous C fibres terminate exclusively in the spinal cord close to their entrance zone the postsynaptic dorsal column pathway must be part of this spino‐olivocerebellar pathway.
Alpha 1‐adrenoceptors reduce background K+ current in rabbit ventricular myocytes.
Authors: Fedida D , Braun A P , Giles W R
Published: December 2014

1. Ventricular myocytes were isolated by enzymatic dispersion of adult rabbit hearts, and voltage clamped using the whole‐cell variation of the patch clamp technique. Experiments were carried out at either 35 degrees C or room temperature (21‐23 degrees C). 2. In the presence of 10(‐3) M‐4‐aminopyridine to block the transient outward K+ current, and 10(‐6) M‐propranolol to block beta‐adrenoceptors, the alpha 1‐adrenergic agonist methoxamine produced action potential prolongation, and a small depolarization of the diastolic membrane potential. Under voltage clamp conditions, methoxamine decreased the magnitude of the inward rectifier K+ current, IK1, in both the inward and outward directions. This effect was dose dependent (10(‐5)‐10(‐3) M) and fully reversible upon wash‐out of the agonist. 3. The neurotransmitter noradrenaline (10(‐6)‐2 x 10(‐5) M), in the presence of propranolol (10(‐6) M), also reduced IK1 in ventricular cells, and this effect was blocked by the specific alpha 1‐adrenoceptor antagonist prazosin. 4. The alpha 1‐adrenoceptor‐mediated decrease in IK1 in ventricular myocytes was not affected by pre‐incubation of the cells with 0.5 micrograms/ml pertussis toxin (8‐10 h, 30‐32 degrees C). This result suggests that in rabbit ventricular cells, the alpha 1‐modulation of IK1 occurs via a pertussis toxin‐insensitive guanine nucleotide‐binding regulatory protein. 5. These observations demonstrate that IK1 in ventricular myocytes can be modulated by cardiac alpha 1‐adrenoceptors. The resulting changes in action potential repolarization and diastolic membrane potential may have significant effects on cardiac performance.
Characterization of radial force and radial stiffness in Ca(2+)‐activated skinned fibres of the rabbit psoas muscle.
Authors: Brenner B , Yu L C
Published: December 2014

1. When chemically skinned muscle fibres are activated by Ca2+ at an ionic strength of 170 mM, the spacing between the filaments has been shown to decrease with increasing force, suggesting that the cross‐bridges can generate force not only in the axial but also in the radial direction. In the present study, radial force and radial stiffness of activated single skinned rabbit psoas fibres were studied by X‐ray diffraction. The responses of the lattice spacing to changes in osmotic pressure by application of dextran T500, which is equivalent to force applied in the radial direction, was examined. The radial force generated by the attached cross‐bridges was calculated, with the approximation that a negligible fraction of cross‐bridges was attached in the relaxed muscle at the same ionic strength of 170 mM. 2. The active radial force was found to be a slightly non‐linear function of lattice spacing, reaching zero at 34 nm. The radial force was compressive at lattice spacing greater than 34 nm and expansive at less than 34 nm. 3. The active axial force, on the other hand, was found to be much less affected by the application of dextran T500. Active axial force increased by 4% to a plateau at 4% dextran T500 and then decreased by 10% at 8% dextran T500. 4. While not under osmotic pressure, the radial force of the activated fibre was determined to be 400 pN (single thick filament)‐1. This is of the same order of magnitude as the axial force. The radial stiffness was also comparable to the axial stiffness at 7 pN (thick filament)‐1 (0.1 nm)‐1. 5. The radial elasticity of the fully activated fibre differs significantly from that of the fibre in rigor. The radial stiffness exhibited by fibres in rigor was approximately five times higher, at 30 pN (thick filament)‐1 (0.1 nm)‐1 and the point where the radial force reached zero was 38 nm. 6. In the activated state, the point at which radial force reaches zero is independent of the level of Ca2+ activation, i.e. independent of the number of cross‐bridges attached to actin in the force‐generating state. We suggest that the zero‐force point is equivalent to the equilibrium point of a spring and is an intrinsic property of the radial elasticity of the cross‐bridge. 7. It is concluded that activated and rigor cross‐bridges exhibit a spring‐like property in the radial direction.(ABSTRACT TRUNCATED AT 400 WORDS)