bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of tension and stiffness due to reduced pH in mammalian fast‐ and slow‐twitch skinned skeletal muscle fibres.
Authors: Metzger J M , Moss R L
Published: December 2014

1. The pH dependence of the Ca2+ sensitivities of isometric tension and stiffness was investigated at 10 and 15 degrees C in skinned single fibres from rat and rabbit fast‐ and slow‐twitch skeletal muscles. Stiffness was determined by recording the tension responses to sinusoidal length changes (3.3 kHz); peak‐to‐peak amplitude of the length change was monitored by laser diffraction and averaged approximately 1.3 nm (half‐sarcomere)‐1. We have assumed that stiffness provides a measure of the number of cross‐bridge attachments to actin. 2. At maximal Ca2+ activation, stiffness was depressed by 22 +/‐ 2% (mean +/‐ S.E.M.) in fast‐twitch fibres but was unchanged in slow‐twitch fibres when pH was lowered from 7.00 to 6.20. As reported previously, maximum tension was depressed by 20‐45% at low pH, with the effect being greater in fast‐twitch compared to slow‐twitch fibres. 3. In fast‐twitch fibres at 10 and 15 degrees C the Ca2+ concentrations for half‐maximal activation of tension and stiffness were increased at low pH. In slow‐twitch fibres, similar effects were observed at 15 degrees C, but at 10 degrees C there were no changes in the Ca2+ sensitivities of tension and stiffness when pH was lowered. 4. Linear relationships between relative tension and relative stiffness were obtained at all temperatures, with slopes of 1.04 +/‐ 0.01 at pH 7.00 and 0.76 +/‐ 0.01 at pH 6.20 in fast‐ and slow‐twitch fibres, indicating that force per cross‐bridge attachment is similarly reduced at low pH in both types of fibres. 5. In both fast‐ and slow‐twitch fibres, rigor tension (no added ATP or creatine phosphate; pCa 9.0) was depressed by 35 +/‐ 7% and stiffness by 12 +/‐ 4% when pH was reduced from 7.00 to 6.20. Since cross‐bridge cycling is inhibited in rigor the effect of low pH to depress rigor tension suggests that pH directly modulates the strength of the bond formed between actin and myosin. 6. The effect of low pH to reduce the apparent number of cross‐bridge attachments during maximal Ca2+ activation in fast‐ but not slow‐twitch fibres could account for the greater H(+)‐induced depression of maximum force in fast‐twitch fibres. In both fibre types, the decrease in the number of cross‐bridge attachments at submaximal concentrations of Ca2+ may in part account for the loss in Ca2+ sensitivity of tension at low pH, due perhaps to a reduction in co‐operative activation of the thin filament by bound cross‐bridges.
The somatosensory intercollicular nucleus of the cat's mesencephalon.
Authors: Blomqvist A , Danielsson I , Norrsell U
Published: December 2014

1. Unitary, neural activity was sampled with tungsten electrodes in the mesencephalic, intercollicular region of cats anaesthetized with chloralose. The units' stereotaxic co‐ordinates were noted and they were tested for activation by adequate tactile, visual and acoustic stimuli as well as electrical nerve stimulation. The units' geometrical gradations were afterwards translated into morphological terms by means of unbiased, cytoarchitectonic identifications of those structures which had been penetrated by the electrodes. 2. The primary objectives were the conventional, somatosensory units, which had reliable, low‐threshold, tactile receptive fields and could not be activated by the two other types of adequate stimulation. There were 139 such units from a total sample of 495. 3. These somatosensory units were found to occupy many of the region's structures, notably the intercollicular nucleus (INC), the nucleus of the brachium of the inferior colliculus, the stratum griseum intermedium and the stratum griseum profundum of the superior colliculus. INC was the only structure which had an exclusively somatosensory input. 4. The units of INC had tactile receptive fields varying between one and several hundred square centimetres. Convergence of afferent input from outside these fields could sometimes be demonstrated by nerve stimulation. The latencies of activation from the contralateral sciatic nerve were, on average, shorter for units of INC than for the somatosensory units of the other intercollicular structures, and INC units could also follow higher stimulation frequencies. 5. The findings support the assumption that INC may constitute a distinct mesencephalic centre for somatosensory function.
In‐series compliance of gastrocnemius muscle in cat step cycle: do spindles signal origin‐to‐insertion length?
Authors: Elek J , Prochazka A , Hulliger M , Vincent S
Published: December 2014

1. It has been claimed that stretch in the non‐contractile (extramysial) portion of muscles is substantial, and may produce large discrepancies between the origin‐to‐insertion muscle length and the internal length variations 'seen' by muscle spindle endings. 2. In eight pentobarbitone‐anaesthetized cats, we estimated stretch in the extramysial portion of medial gastrocnemius (MG) muscle with a method similar to the spindle null technique. 3. Length variations of MG previously monitored in a normal step cycle were reproduced with a computer‐controlled length servo. The responses of test MG spindle endings were monitored in dorsal root filaments. Distributed stimulation of ventral root filaments, rate‐modulated by the step‐cycle EMG envelope, served to reproduce step‐cycle forces. The filaments were selected so as to have no fusimotor action on the test spindle. 4. Spindle responses in active cycles were compared with those in passive cycles (stretch, but no distributed stimulation). In some cases concomitant tonic fusimotor stimulation was used to maintain spindle responsiveness throughout the cycle, both in active and passive trials. Generally, small discrepancies in spindle firing were seen. The passive trials were now repeated, with iterative adjustments of the length function, until the response matched the spindle firing profile in the active trial. The spindle 'saw' the same internal length change in the final passive trial as in the active trial. Any difference between the corresponding length profiles was attributed to extramysial displacement. 5. Extramysial displacement estimated in this was was maximal at short mean muscle lengths, reaching about 0.5 mm in a typical step cycle (force rising from 0 to 10 N). At longer mean muscle lengths where muscle force rose from say 2 to 12 N in the cycle, extramysial displacement was in the range 0.2‐0.4 mm. 6. Except at very short lengths, the displacement was probably mainly tendinous. On this assumption, our results suggested that the stiffness of the MG tendinous compartment was force related, and about double that of cat soleus muscle at any given force. Calculations indicated that though the stretch was small, the MG tendon would store and release enough strain energy per cycle to contribute significantly to the E3 phase of the step cycle. The discrepancies in spindle firing were generally quite subtle, so we reject the claim that extramysial stretch poses a serious difficulty for inferences about fusimotion from chronic spindle afferent recordings.
Private inhibitory systems for the X and Y pathways in the dorsal lateral geniculate nucleus of the cat.
Authors: Lindström S , Wróbel A
Published: December 2014

1. Inhibitory connections of X‐ and Y‐type principal cells in the cat's dorsal lateral geniculate nucleus were studied with intracellular recording techniques in barbiturate‐anaesthetized animals. Cells were identified as principal cells by antidromic activation from the visual cortex and as X or Y types by their responses to visual stimulation. 2. Graded electrical stimulation was used to obtain selective activation of X and Y ganglion cell axons. The optic nerves were stimulated through ring electrodes behind the eye bulbs and the evoked nerve volley was monitored by an optic tract electrode. The nerve volley consisted of two well‐segregated components, an early, low‐threshold Y component and a late, high‐threshold X component. 3. All principal cells received monosynaptic excitation and disynaptic feed‐forward inhibition from optic nerve fibres. The excitatory and inhibitory postsynaptic potentials were evoked by Y axons in Y cells and by X axons in X cells. Thus, the feed‐forward inhibitory pathway to principal cells is type selective. 4. Recurrent inhibition was evoked in all cells by antidromic activation of principal cell axons in the visual cortex. The recurrent inhibitory potentials had significantly shorter latencies in Y than in X cells but with considerable overlap between the two samples. This overlap presumably reflects a similar overlap in antidromic conduction times for X and Y principal cell axons. 5. Recurrent inhibitory potentials evoked in the orthodromic direction by optic nerve stimulation originated from Y axons in Y principal cells and from X axons in X cells as would be expected for a type‐selective recurrent inhibitory pathway. 6. It is concluded that X and Y principal cells in the dorsal lateral geniculate nucleus have similar but functionally separate inhibitory circuits.
Intracellular recording from neurones of the guinea‐pig gall‐bladder.
Authors: Mawe G M
Published: December 2014

1. Intracellular recordings were made from neurones of the guinea‐pig gall‐bladder in vitro. Intracellular injection of horseradish peroxidase revealed a simple structure, consisting of a soma and a single process, but no discernible dendritic arborization. 2. The resting membrane potential was ‐50.5 +/‐ 0.4 mV and the input resistance was 80 M omega. 3. Gall‐bladder neurones spiked only once at the onset of depolarizing current pulses. Action potentials were blocked by tetrodotoxin, but a Ca2(+)‐dependent spike could be elicited in the presence of tetrodotoxin and tetraethylammonium. 4. Action potential after‐hyperpolarizations had a duration of 172 +/‐ 3.7 ms and reversed at a membrane potential of ‐93 mV; this reversal potential was linearly related to the logarithm of the external potassium concentration. The initial phase of the after‐hyperpolarization was inhibited by tetraethylammonium (1‐10 mM) and was not affected by 3,4‐diaminopyridine. The late phase of the after‐hyperpolarization was blocked by apamin (10 nM) or curare (500 microM). Both the early and late phases of the after‐hyperpolarization were inhibited when the preparation was perfused with a calcium‐free, high‐magnesium solution. The calcium‐free, high‐magnesium solution had no effect on the membrane potential or input resistance of these cells. 5. Fast excitatory synaptic responses and antidromic responses were elicited in gall‐bladder neurones by focal stimulation of fibre tracts. High‐frequency fibre tract stimulation often resulted in prolonged, calcium‐dependent, depolarizations that were associated with a decrease in input resistance. 6. 5‐Hydroxytryptamine and substance P caused depolarizations that were associated with a decrease in input resistance. Bethanechol caused hyperpolarizations that were associated with a decrease in input resistance and which were blocked by atropine.
Changes in arterial K+ and ventilation during exercise in normal subjects and subjects with McArdle's syndrome.
Authors: Paterson D J , Friedland J S , Bascom D A , Clement I D , Cunningham D A , Painter R , Robbins P A
Published: December 2014

1. We have examined the relationship between ventilation (VE), lactate (La) and arterial plasma K+ concentrations [( K+]a) during incremental exercise in six normal subjects and in four subjects with McArdle's syndrome (myophosphorylase deficiency) who do not become acidotic during exercise. 2. In normal subjects, [K+]a rose to ca 7 mM at the point of exhaustion. The time courses of the increases in VE, La and [K+]a were all similar during the exercise period. La reached its peak concentration during the recovery from exercise when both VE and [K+]a were returning to resting levels. 3. McArdle's subjects, like normal subjects, had a non‐linear ventilatory response during incremental exercise. Their [K+]a was closely related to VE throughout exercise and recovery. 4. The arterial pH of McArdle's subjects, rather than remaining constant, actually rose from the onset of exercise. 5. For a given level of exercise, the levels of VE and [K+]a were greater in the McArdle's subjects than in normal subjects. 6. These findings are consistent with the idea that hyperkalaemia may contribute significantly to the drive to breathe, especially during heavy exercise.
Regional changes in ventricular excitability during load manipulation of the in situ pig heart.
Authors: Dean J W , Lab M J
Published: December 2014

1. The effect of load manipulation on myocardial excitability was studied in the anaesthetized, in situ pig heart. 2. A 33% increase in systolic left ventricular pressure achieved by aortic clamping reduced the mean effective refractory period by 11 ms (7.6%, P less than 0.01); whereas a 15% reduction in ventricular pressure achieved by intravenous infusion of sodium nitroprusside increased the mean effective refractory period by 4 ms (3.2%, P less than 0.05). 3. Changes in action potential duration, measured to 70% repolarization, roughly paralleled those of the effective refractory period. 4. The changes in effective refractory period were inhomogeneous, with a greater change occurring at the apex compared to the base in response to an increase in load, i.e. there was an increase in regional dispersion of refractoriness across the left ventricle. 5. Since inhomogeneity of repolarization and refractoriness is known to be potentially arrhythmogenic, these findings suggest that mechanical factors may contribute directly to the arrhythmias commonly seen clinically in high load states such as congestive cardiac failure and may also have consequences for the treatment of such arrhythmias.
Potassium currents in hair cells isolated from the cochlea of the chick.
Authors: Fuchs P A , Evans M G
Published: December 2014

1. Potassium currents were characterized in tall hair cells of the chick's cochlea. Outward potassium currents were found to flow through two distinct classes of channels. 2. Individual hair cells were isolated from 200 microns long segments of the apical half of the chick's cochlea. Whole‐cell voltage‐clamp and current‐clamp recordings were made from these cells. 3. Voltage responses to injected current ranged from high‐frequency (100‐250 Hz) oscillations in some cells, to slowly repetitive Ca2+ action potentials or slow oscillations (5‐20 Hz) in others. 4. Ionic currents recorded in voltage clamp also varied in different hair cells. Cells with high‐frequency voltage oscillations had rapidly activating Ca2(+)‐dependent outward K+ current, IK(Ca). Cells that generated action potentials had slow delayed rectifier outward K+ current, IK, and inward rectifier current, IIR. All hair cells had inward Ca2+ current. 5. IK(Ca) activated positive to ‐45 mV. Tail currents reversed at the K+ equilibrium potential. This current was eliminated in Ca2(+)‐free solutions, or when exposed to 10 mM‐TEA. This outward current was fully activated within 1‐3 ms at 0 mV. The whole‐cell current was noisy and ensemble variance analysis suggested a single‐channel conductance of 63 pS near 0 mV. 6. IK activated positive to ‐50 mV. Tail currents reversed at the K+ equilibrium potential. This current was not eliminated in Ca2(+)‐free solutions, and was relatively resistant to external TEA. IK activated slowly, reaching peak values in 10‐20 ms at 0 mV. This current showed little variance and the average single‐channel conductance based on macroscopic noise near 0 mV was 8 pS. 7. External tetraethylammonium (TEA) or Ca2(+)‐free saline eliminated the high‐frequency voltage oscillations seen in many basal cells. In contrast TEA had little effect on slow action potentials (or low‐frequency oscillations) seen in cells with IK. 8. IK(Ca) was prominent in hair cells originating 1.0‐2.0 mm from the cochlear apex. IK and IIR dominated the membrane conductance of tall hair cells originating within 0.5 mm of the cochlear apex. 9. The frequency of voltage oscillation in apical cells was temperature‐dependent, nearly doubling for each 10 degrees C rise in temperature. 10. IIR activated at membrane potentials negative to ‐75 mV. The average time constant of activation at ‐100 mV was 2 ms. Tail currents reversed at the K+ equilibrium potential and did not depend on the external Na+ concentration. IIR was blocked by 5 mM‐Cs+ or 100 microM‐Ba2+ in the external saline.
Stretch‐activated channels in single early distal tubule cells of the frog.
Authors: Hurst A M , Hunter M
Published: December 2014

1. Single stretch‐activated channels have been studied in cell‐attached and excised patches from single early distal tubule (diluting segment) cells of Rana temporaria. 2. The channels can be reversibly activated, in both cell‐attached and excised patches, by the application of negative pressure to the pipette causing mechanical stretching of the cell membrane. In cell‐attached patches, application of 14.8 cmH2O negative pressure to the patch pipette increased reversibly the open probably from 0.11 to 0.87. 3. The channel conductance in the cell‐attached configuration with standard Ringer solution in the pipette is 21.3 pS. 4. The channel is non‐specific. In excised inside‐out patches ion substitution experiments show that the channel does not discriminate between sodium and potassium ions, nor does it appear to select for cations over anions. 5. The channel is voltage sensitive such that depolarizing the cell opens the channel. The open probability at the resting membrane potential, 0.89, was reduced to 0.26 at a hyperpolarizing potential of 100 mV (holding pressure of ‐20.1 cmH2O or ‐206 Pa). 6. The sensitivity of the channel to mechanical stretching suggests that the channel may be involved in cell volume regulation.
Adrenal responses to corticotrophin‐releasing factor in conscious hypophysectomized calves.
Authors: Jones C T , Edwards A V
Published: December 2014

1. Adrenal responses to intra‐aortic infusions of pure synthetic ovine corticotrophin‐releasing factor (CRF) have been investigated in functionally hypophysectomized calves previously fitted with an adrenal clamp. 2. CRF caused an increase in the output of cortisol from the adrenal gland, which was dose related over the range 4‐8 pmol min‐1 and maximal at the higher of these doses; this response was observed at a dose below that which produced any change in adrenal vascular resistance. Cortisol output was also found to be related linearly to the rate at which CRF was estimated to be presented to the gland during these infusions. 3. The infusions of CRF also provoked the release of small, but readily detectable, amounts of adrenocorticotrophin‐like peptides (ACTH) from the gland. This was mainly in the form of ACTH1‐39 with some pro‐opiomelanocortin (POMC) also being released. 4. Comparison of the adrenal steroidogenic response to exogenous CRF with that to synthetic ACTH1‐24 showed that CRF was the more potent; in each case cortisol output was related linearly to the presentation rate of the peptide. 5. It is concluded that the adrenal cortex in the calf is capable of releasing cortisol in response to exogenous CRF at low concentrations and is even more sensitive to CRF than it is to exogenous ACTH over the dose range that was employed.
Alterations in cat knee joint blood flow induced by electrical stimulation of articular afferents and efferents.
Authors: Khoshbaten A , Ferrell W R
Published: December 2014

1. Experiments were performed in cats anaesthetized with pentobarbitone. Laser Doppler flowmetry was used to assess the responses of knee joint blood vessels to nerve stimulation under control conditions and in the presence of different adrenoceptor antagonists in order to establish the nature of neurotransmitters released from articular nerve fibres. 2. The posterior articular nerve (PAN) supplying the knee was stimulated at different intensities, and frequency‐response curves were obtained. In fourteen animals electrical stimulation of PAN produced an initial vasoconstriction during stimulation which in eight of these was followed by a prolonged dilatation on cessation of stimulation. The constrictor response was increased as a function of frequency but was little altered with increasing intensity beyond a threshold level. 3. The constrictor response to electrical stimulation of PAN was markedly reduced by the alpha‐adrenergic antagonist phentolamine (10(‐5) M, the alpha 1‐blocker prazosin (10(‐5) M), and guanethidine (10(‐5) M) which inhibits the release of noradrenaline, ATP, and neuropeptide Y from sympathetic nerve endings. 4. The constrictor response to PAN stimulation was unaffected by the alpha 2‐blocker rauwolscine and the P2‐purinoceptor desensitizer alpha,beta‐methylene ATP. 5. The dilator response was due to activation of afferent fibres as it could also be produced by direct electrical stimulation of the L7 dorsal roots. 6. The dilator response to stimulation of PAN or the L7 dorsal root was reduced by prior intra‐articular injection of 100 micrograms of the substance P antagonist D‐Pro4‐D‐Trp7,9,10‐SP4‐11. 7. These results suggest that the vasoconstrictor response to electrical stimulation of PAN is most likely to be mediated via noradrenaline acting mainly upon alpha 1‐adrenoceptors. As the dilator response to articular nerve stimulation is reduced by a substance P antagonist, the mediator inducing this response may be substance P or a related neurokinin.
5‐Hydroxytryptamine responses in neonate rat motoneurones in vitro.
Authors: Wang M Y , Dun N J
Published: December 2014

1. Current and voltage recordings were made from antidromically identified motoneurones (MNs) in transverse thoracolumbar spinal cord slices of neonatal rats. 2. Applied by superfusion (10‐100 microM) or pressure ejection, 5‐hydroxytryptamine (5‐HT) elicited a slow depolarization (or inward current) in 81% and a hyperpolarization (or outward current) in 9% of responsive MNs; the responses persisted in a low‐Ca2+, high‐Mg2+ or tetrodotoxin (TTX)‐containing solution. 3. 5‐HT induced the occurrence in some MNs of excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs), which were reversibly eliminated by TTX, low‐Ca2+, high‐Mg2+ solution or by the 5‐HT2 receptor antagonists ketanserin and spiperone. Also, kynurenic acid and strychnine abolished, respectively, the 5‐HT‐induced EPSPs and IPSPs. 4. The 5‐HT depolarization was associated with increased membrane resistance, was reduced by hyperpolarization and nullified near ‐100 mV. The extrapolated reversal potential was shifted to a positive direction in elevated [K+]o. 5. The depolarizing response was mimicked by the 5‐HT2 receptor agonist (+2‐)‐1(2,5‐dimethyoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride (DOI) and blocked by 5‐HT antagonists methysergide and cyproheptadine and by 5‐HT2 antagonists ketanserin and spiperone; methiothepin and MDL 72222 were without effect. 6. The 5‐HT hyperpolarization was associated with decreased membrane resistance. The 5‐HT1A agonist 8‐hydroxy‐2‐(di‐N‐propylamino) tetralin hydrobromide (8‐OH‐DPAT) mimicked the hyperpolarizing response. 7. Single or repetitive (10‐30 Hz) electrical stimuli elicited in about 30% of MNs, in addition to a fast EPSP, a slow EPSP with electrophysiological characteristics similar to that of 5‐HT induced depolarization. Methysergide and spiperone abolished the slow EPSPs evoked in some of these MNs. 8. It is suggested that 5‐HT, acting on 5‐HT2 and 5‐HT1A receptors, depolarizes and hyperpolarizes the MNs by decreasing and increasing K+ conductance. Additionally, 5‐HT activates, via 5‐HT2 receptors, excitatory and inhibitory interneurones, thereby indirectly affecting the activity of MNs. More importantly, 5‐HT released from intraspinal nerves appears to be the mediator of a slow EPSP in a population of MNs.
Blockage of synaptic release by brief hyperpolarizing pulses in the neuromuscular junction of the crayfish.
Authors: Arechiga H , Cannone A , Parnas H , Parnas I
Published: December 2014

1. Synaptic currents were evoked at the neuromuscular junction of the deep extensor abdominal muscle of the crayfish by direct depolarization of motor nerve endings. 2. Quantal content and time course of neurotransmitter release were determined from delay histograms of unitary release events recorded with a macropatch clamp technique. 3. Synaptic facilitation was elicited by pairing depolarizing pulses at intervals ranging from 10 to 200 ms. At 14 degrees C the duration of facilitation was about 50 ms. Reducing activity of the Nao(+)‐Cai2+ exchange by lowering [Na+]o by 50% resulted in prolonged facilitation, which lasted approximately 150 ms. 4. Normalized synaptic delay histograms at normal [Na+]o and 50% [Na+]o were the same for the first and the facilitated second response, indicating that activity of the Na(+)‐Ca2+ exchange does not determine the time course of release. 5. The application of a hyperpolarizing post‐pulse after the first depolarizing stimulus reduced release and altered its time course to a similar extent both in normal and in 50% [Na+]o. However, it did not affect the level and the time course of release of the facilitated response. 6. A hyperpolarizing post‐pulse given after the first and second pulses of a pair reduced release to the same extent for the two depolarizing pulses. 7. These results indicate that whereas manipulations thought to increase [Ca2+]i (i.e. reducing activity of the Nao(+)‐Cai2+ exchange or facilitation) affect the quantal content, they do not influence the time course of release. However, changes of membrane potential do affect the quantal content, and more importantly the time course of release, thus suggesting a contributory role of membrane potential in the control of synaptic release.
Time course of the membrane current underlying sensory transduction in salamander olfactory receptor neurones.
Authors: Firestein S , Shepherd G M , Werblin F S
Published: December 2014

1. Odour elicited currents in freshly isolated olfactory receptor neurones were analysed using the whole‐cell patch‐clamp technique. Brief pulses (35‐50 ms) and steps (100 ms‐5 s) of odour solution were delivered by pressure ejection from a nearby micropipette. 2. Pulses of odour solution directed at the cell induced an inward depolarizing current of 50‐750 pA leading to the generation of action potentials. The I‐V relation for this current was linear over the range ‐60‐(+)20 mV and showed a reversal potential of +5 mV. The magnitude of the current increased with stimulus strength, for a given pulse duration, over approximately one decade of concentration change. 3. Pulses of odour solution focally delivered to the cilia elicited a large response, but those directed toward the soma did not. Conversely pulses of K+ solution at the cilia failed to evoke any response while those directed at the dendrite and soma elicited an inward clamp current. This provides direct evidence that odour sensitivity is localized mainly to the cilia and possibly the distal dendrite. 4. The odour elicited current activated with a long latency of 150‐600 ms after the odour solution arrived at the cell. This latency, as well as the time‐to‐peak and the rise half‐time, were relatively independent of stimulus concentration, changing less than 25% over the entire concentration range of stimulus sensitivity. These observations are consistent with the participation of a second messenger system in olfactory transduction. 5. For brief stimulus pulses less than 100 ms, the stimulus diffused away before the odour response current reached its peak value, so that the peak and decay of the odour response occurred in the absence of significant odour stimulus. The time course of the current decay was fitted by a single exponential with a time constant that was concentration dependent, varying from 0.8 to 1.3 s. 6. For longer steps of stimulus presentation, up to 1 s, the magnitude of the response current became a function of the duration of the pulse as well as the stimulus concentration, indicating that the transduction process involved an integrating step. This is consistent with the idea that the odour elicited current is the result of the summation of many smaller unitary events. From responses to weak stimulation an integration period of 700‐1000 ms was calculated. 7. During prolonged steps of maintained stimulus presentation (greater than 5 s) the odour elicited current was transient.(ABSTRACT TRUNCATED AT 400 WORDS)
Na+ currents through low‐voltage‐activated Ca2+ channels of chick sensory neurones: block by external Ca2+ and Mg2+.
Authors: Lux H D , Carbone E , Zucker H
Published: December 2014

1. Whole‐cell currents through low‐voltage‐activated (LVA) Ca2+ channels carried by monovalent cations were studied in chick dorsal root ganglion (DRG) cells. 2. With 120 mM [Na+] on both sides of the membrane and [Ca2+]o less than or equal to 100 microM, the currents reversed at 0 mV. Their half‐times of activation and inactivation were strictly voltage‐dependent and decreased to near‐constant values of 0.6‐0.85 and 40 ms, respectively, at positive membrane potentials. The longer activation times were observed with [Ca2+]o greater than or equal to 50 microM. 3. The selectivity of the Ca2+ channel for monovalent ions with reference to internal Na+ was evaluated from the reversal potential. The Li+ and Na+ permeabilities were similar. The permeability ratios of K+ and Rb+ were 0.45, and 0.33 for Cs+. 4. Micromolar increases in [Ca2+]o produced small voltage shifts of half‐times of activation (less than or equal to +3 mV at 10 microM and +10 mV at 500 microM), but strongly depressed the Na+ current. The Ca2(+)‐induced block of Na+ current satisfied a 1:1 stoichiometry with an apparent KD of 1.8 microM at ‐20 mV. The block was, however, relieved with more positive and negative potentials, with KDs of 55 and 8.5 microM at +90 and ‐110 mV, respectively. 5. Relaxation time constants of block and unblock of Na+ currents through the LVA Ca2+ channel were measured on step changes to and from membrane potentials at which pronounced Ca2(+)‐induced block occurred. 6. At ‐20 mV, the time constants of block decreased with micromolar increase in [Ca2+]o in line with a blocking rate coefficient of 1.9 x 10(8) M‐1 s‐1, but settled to values of 0.18 ms at [Ca2+]o beyond 50 microM. The Na+ currents were unblocked with time constant (tau u) of around 0.25 ms at strongly positive and negative membrane potentials at 22 degrees C. 7. Tau u failed to show any obvious dependence on [Ca2+]o up to the millimolar range. This finding contradicts suggestions that removal of the block occurs in a [Ca2+]o‐dependent manner as a result of an increased probability of Ca2+ ion mobilization by repulsive forces with increased Ca2+ occupation of the channel. 8. The time course of unblock of Na+ currents was strongly temperature‐dependent showing a Q10 of 2.5 for tau u. 9. The voltage dependence of the Na+ current block by Ca2+ ions is best accounted for by a single, centrally located Ca2+ binding site.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses to excitatory amino acids of Purkinje cells' and neurones of the deep nuclei in cerebellar slice cultures.
Authors: Audinat E , Knöpfel T , Gähwiler B H
Published: December 2014

1. The actions of the endogenous excitatory amino acids (EAAS) glutamate (Glu), aspartate (Asp) and homocysteate (HCA) on Purkinje cells and neurones of the deep nuclei in cerebellar slice cultures were investigated using intracellular recordings in the single‐electrode voltage‐clamp mode and the whole‐cell configuration of the patch‐clamp technique. 2. Purkinje cells and neurones of deep cerebellar nuclei were identified according to their localization in the living cultures, their morphology as revealed by intracellular injections of Lucifer Yellow and their immunoreactivity to antibodies to the 28 kDa Ca2(+)‐binding protein. 3. When Purkinje cells were voltage‐clamped near their resting membrane potential in a TTX‐containing salt solution, Glu, Asp and HCA induced inward currents which were abolished by 6‐cyano‐7‐nitroxaline‐2,3‐dione (CNQX), a selective antagonist of the non‐N‐methyl‐D‐aspartate (NMDA) subtype of EAA receptors. The selective antagonist of NMDA receptors, D‐(‐)‐2‐amino‐5‐phosphonovaleric acid (D‐APV), was ineffective in blocking the responses induced by these three amino acids. NMDA, even at high concentrations and in magnesium‐free bathing solution, had no detectable effect on membrane properties of Purkinje cells grown in culture during 11‐34 days. 4. In magnesium‐containing saline, the amplitude of the responses induced by Glu, Asp and HCA was a linear function of the membrane potential. 5. In contrast, neurones of the deep cerebellar nuclei were responsive to NMDA and the inward currents induced by Glu, Asp and HCA were partially blocked both by CNQX and by D‐APV. 6. In magnesium‐containing saline, the amplitude of the currents induced by NMDA as well as by the three endogenous EAAs decreased at hyperpolarizing holding potentials whereas the current‐voltage relation of the responses induced by quisqualate (QA) was strictly linear. 7. It is concluded that Purkinje cells in cerebellar slice cultures do not express NMDA receptors and that excitation of these neurones by the endogenous amino acids Glu, Asp and HCA is mediated exclusively through the activation of non‐NMDA receptors. In the same preparation, neurones of the deep cerebellar nuclei possess NMDA and non‐NMDA receptors which can be both activated by the three endogenous excitatory amino acids.
Amino acid‐mediated EPSPs at primary afferent synapses with substantia gelatinosa neurones in the rat spinal cord.
Authors: Yoshimura M , Jessell T
Published: December 2014

1. Fast excitatory postsynaptic potentials (EPSPs) evoked by stimulation of A delta and C fibres were examined by intracellular recording from substantia gelatinosa (SG) neurones in a transverse slice preparation of adult rat spinal cord. 2. Single low‐intensity stimuli applied to the dorsal root activated A delta fibres and evoked monosynaptic EPSPs in 70% of SG neurones. In 5% of SG neurones, increasing the intensity and duration of stimulation evoked solely C fibre‐mediated EPSPs. About 20% of neurones received both A delta and C fibre input from primary afferents. 3. Low concentrations of tetrodotoxin (TTX, approximately 50 nM) blocked EPSPs evoked by stimulation of A delta fibres without affecting those evoked by C fibre stimulation. Higher concentrations of TTX (500 nM) also blocked C fibre‐evoked responses. 4. EPSPs evoked by A delta and C fibre stimulation reversed in polarity at membrane potentials near 0 mV, similar to the reversal potential of spontaneous EPSPs and of the potential change evoked by exogenous glutamate. 5. A delta and C fibre‐evoked EPSPs were depressed by kynurenate and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX); C fibre‐evoked EPSPs appeared to be less sensitive. 6. In the presence of TTX, only 50% of SG neurones were depolarized by L‐glutamate. However, neurones which exhibited no direct response to L‐glutamate received afferent‐evoked EPSPs which were sensitive to CNQX. In sensitive neurones, the depolarization evoked by L‐glutamate was depressed by only approximately 15% in the presence of CNQX, whereas afferent‐evoked EPSPs recorded from the same neurone were almost completely suppressed. Combined application of DL‐2‐amino‐5‐phosphonovaleric acid (APV) and CNQX depressed the response to L‐glutamate by only approximately 25%. 7. These findings suggest that A delta and C fibres use L‐glutamate or a related amino acid as a transmitter at synapses with substantia gelatinosa neurones. The postsynaptic actions of this transmitter are mediated predominantly by non N‐methyl‐D‐aspartic acid (NMDA) receptors. The failure of CNQX and APV to completely block the L‐glutamate‐evoked depolarization of substantia gelatinosa neurones raises the possibility that exogenously applied L‐glutamate activates a non‐NMDA receptor distinct from that which mediates the actions of the synaptically released afferent transmitter.
The response induced by intracellular cyclic AMP in isolated olfactory receptor cells of the newt.
Authors: Kurahashi T
Published: December 2014

1. Responses induced by intracellular cyclic nucleotides were analysed in isolated olfactory receptor cells of the newt under a voltage‐clamp condition by using the patch pipette in a whole‐cell recording configuration. Cyclic nucleotides were applied by diffusion from the patch pipette. 2. Introduction of either cyclic AMP or cyclic GMP caused a transient inward current in cells held at ‐50 mV. The response amplitude was dose‐dependent with the Hill coefficient of 3 and half‐saturating concentration of 300 microM (concentration in the pipette) for both cyclic AMP and cyclic GMP. Cyclic CMP was less effective than those two nucleotides. 3. The response to intracellular cyclic AMP was seen in all cilia‐bearing cells, but not in cells which lost the cilia during dissociation. The response latency was shorter when cyclic AMP was introduced into the ciliated terminal swelling (ca 0.2 s) rather than into the cell body (ca 1.4 s). These results suggest that the sensitivity to intracellular cyclic AMP is confined to the cilia. 4. The cyclic AMP‐induced current was transient (half decay time, ca 2.3s) despite the fact that cyclic AMP was continuously loaded from the patch pipette. The response time course was controlled by Ca2+; the reduction of external Ca2+ concentration (replaced with Mg2+) or loading the cell with 50 mM‐EGTA prolonged the cyclic AMP‐induced responses. The Ca2(+)‐induced suppression was reversible. 5. The reversal potential of the cyclic AMP‐induced transient current was ‐4.8 +/‐ 3.8 mV, and that of the current re‐induced by Ca2+ removal was 1.5 +/‐ 2.1 mV, suggesting that both currents flowed through the same ionic channel. The channel permeates all alkali metal ions with the permeability ratios of PLi:PNa:PK:PRb:PCs = 0.93:1:0.93:0.91:0.72, but not Cl‐ or choline ions. 6. These results demonstrate that the cyclic AMP‐induced response and the odorant‐induced response of the isolated olfactory cell have nearly identical characteristics. The present study supports the notion that cyclic AMP is the internal messenger mediating olfactory transduction.
The magnitude, time course and spatial distribution of current induced in salamander rods by cyclic guanine nucleotides.
Authors: Cameron D A , Pugh E N
Published: December 2014

1. Cyclic GMP was introduced into isolated salamander rods through a tight‐seal electrode attached to the inner segment while the outer segment was held in a suction electrode; nucleotide‐induced membrane current was recorded by both electrodes. After 3‐15s of nucleotide exposure the cells were stimulated with intense, brief flashes, which suppressed 90‐95% of the induced membrane current. 2. The magnitude of the induced light‐sensitive current depended little on the pipette cyclic GMP concentration in the range 10‐20 nM: the mean whole‐cell current magnitude was 1256 +/‐ 160 pA (mean +/‐ 2 S.E.M., n = 41). 3. Experiments and analyses addressed hypotheses about the nature of the magnitude limitation on the induced current. It was shown that the spatial distribution of nucleotide, the residual series resistance of the whole‐cell electrode, and the diminution of the ion gradients driving the induced current did not limit the current magnitude by more than 20%. 4. In contrast, the hypothesis that outer segment internal longitudinal resistance severely limits the magnitude of the cyclic GMP‐induced current was supported by experiments in which various lengths of the outer segment were drawn into the suction electrode. These showed that the ratio of nucleotide‐induced light‐sensitive current collected by the suction electrode to that collected by a whole‐cell electrode decreased steeply as a function of outer segment length excluded from the suction electrode, having an apparent space constant of 5‐7 microns. 5. A cable model of the rod was developed and used to analyse the magnitude of the nucleotide‐induced currents. The data are consistent with an outer segment longitudinal resistance of 1‐4 M omega microns‐1, and a maximum (space‐clamped) light‐sensitive current density of 313 pA microns‐1, equivalent to a total induced current of 7200 pA (23 microns outer segment). 6. A diffusion model was developed and combined with the non‐linear cable model to provide an account for the time course of the induced membrane currents. The results are consistent with an effective longitudinal diffusion coefficient of cyclic GMP in the outer segment of 3‐10 microns2 s‐1, and Hill coefficient of 2‐3 for the cyclic GMP gating of the light‐sensitive conductance. 7. 8‐Bromo‐cyclic GMP also caused the light‐sensitive membrane current to increase to about the same magnitude as did cyclic GMP.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of external pH changes on responses to excitatory amino acids in mouse hippocampal neurones.
Authors: Vyklický L , Vlachová V , Krůsek J
Published: December 2014

1. The whole‐cell and outside‐out configurations of the patch‐clamp technique were used to record responses to excitatory amino acids in mouse hippocampal neurones in cell culture at different pH. The amino acids kainate, quisqualate, N‐methyl‐D‐aspartate (NMDA) and L‐glutamate were applied by a rapid perfusion system. 2. In the whole‐cell recording mode the responses to NMDA or to low concentrations of glutamate, recorded in the absence of Mg2+ and with glycine in the extracellular superfusion solution, were antagonized by acidic pH and potentiated by an alkaline extracellular solution. Decrease in pH from 7.3 to 6.0 reduced NMDA responses to 33 +/‐ 2% and an increase in pH from 7.3 to 8.0 potentiated it to 141 +/‐ 6%. The responses to quisqualate and kainate were only slightly changed by altering the pH from 7.3 to 6.3 or 8.3. 3. The equilibrium dissociation constant (Kd) for H+ antagonism of responses to NMDA, estimated from the fit of a single‐binding‐site adsorption isotherm, was calculated to be 0.25 +/‐ 0.06 microM, corresponding to pH 6.6 +/‐ 0.1. The H+ attenuation of NMDA current was voltage independent at membrane potentials ‐60 to +30 mV. 4. H+ antagonism of responses to NMDA was reduced when the NMDA concentration was lowered. In the pH range 6.3‐8.3 the H(+)‐induced reduction did not vary with the concentration of glycine or Mg2+. The sensitivity of NMDA current to Zn2+ was unchanged in the pH range 6.3 +/‐ 8.0. These results suggest that H+ ions do not directly interfere with the binding of NMDA to its agonist recognition site or with the binding of glycine, Mg2+ and Zn2+ to the specific allosteric sites on the NMDA receptor‐channel complex. 5. In outside‐out patches held at ‐60 mV, unitary NMDA‐activated currents were recorded at pH 7.3 and 6.3. The mean NMDA single‐channel conductance (gamma) obtained for the largest and most frequent openings were: gamma 7.3 = 52.5 +/‐ 0.8 pS and gamma 6.3 = 51.8 +/‐ 0.9 pS. The duration of the mean channel open time, tau o, decreased from 4.75 +/‐ 0.25 ms in the control at pH 7.3 to 3.59 +/‐ 0.21 ms at pH 6.3. The mean burst duration, tau b, was reduced from 8.51 +/‐ 0.78 ms at control pH 7.3 to 5.1 +/‐ 0.34 ms at pH 6.3. The frequency of NMDA channel bursts was reduced by 31%.(ABSTRACT TRUNCATED AT 400 WORDS)
Localization and responses of neurones in the parieto‐insular vestibular cortex of awake monkeys (Macaca fascicularis).
Authors: Grüsser O J , Pause M , Schreiter U
Published: December 2014

1. In four Java monkeys (Macaca fascicularis) 152 vestibular neurones were recorded in the parietal cortex located in the upper bank of the lateral sulcus near the posterior end of the insula. We called this region parieto‐insular vestibular cortex (PIVC). PIVC extends about 6‐8 mm in the anterior‐posterior direction from the posterior part of the insula into the retroinsular region (stereotaxic co‐ordinates: anterior 4‐12 mm, lateral 16‐19 mm and vertical 3‐6 mm). 2. About two‐thirds of the neurones recorded from this region responded to vestibular stimuli; the non‐vestibular neurones responded predominantly to somatosensory stimulation of the neck and shoulder region. The PIVC area is a polysensory field, since almost all vestibular neurones were also activated by somatosensory and visual stimuli. Large‐field optokinetic stimulation was the most effective visual stimulus. 3. With vestibular stimuli, responses to angular acceleration were dominant; steady tilt in darkness rarely led to any change in neuronal spontaneous activity. Of sixty‐four neurones tested by rotation in more than one plane, fifty‐four responded to excitation of semicircular canal receptors aroused by rotation in more than one of the three experimental planes (roll, yaw, pitch). Compared with vestibular brain stem units PIVC neurones discharged with a higher variability. 4. In the responses to horizontal rotation of the animal 38% type I, 53% type II and 9% type III units were recorded (classification according to Duensing & Schaefer, 1958). The gain measured with horizontal sinewave rotation was lower by a factor of about 4 in PIVC neurones as compared with the responses of vestibular neurones in the brain stem or thalamus (VPL). The phase response characteristics and the gain increase with increasing sinewave stimulus frequency, however, were in the same range as observed in neurones of the afferent vestibular system. 5. When the vestibular responses to sinusoidal rotation were tested in all three experimental planes (yaw, roll, pitch), the response strength as expressed by the amplitude of the peristimulus time histograms (PSTHs) differed for the three rotational planes. For different units the relative sensitivity to rotation in each of the three planes also differed. We concluded from this observation that different PIVC units had different optimum sensitivity planes for rotation with respect to the head co‐ordinates, whereby all possible planes are represented.
Magnesium transport in ferret red cells.
Authors: Flatman P W , Smith L M
Published: December 2014

1. Mg2+ efflux from ferret red cells into a nominally Mg2(+)‐free medium is 41 +/‐ 2 mumol (l cell)‐1 h‐1. The properties of Mg2+ transport can be measured in these cells without the need for Mg2+ loading. 2. Amiloride, quinidine, imipramine and external divalent cations partially inhibit Mg2+ efflux. Maximal inhibition by these agents is about 60‐70% suggesting that at least two Mg2+ transport pathways exist. 3. As external Na+ is replaced by choline or N‐methyl‐D‐glucamine Mg2+ efflux is first stimulated, reaching a peak when external [Na+] ([Na+]o) is about 10 mM, and then inhibited. Mg2+ transport reverses direction so net Mg2+ uptake occurs when [Na+]o is reduced below 1 mM. 4. Mg2+ efflux is stimulated when 0.1 mM‐EDTA is added to the medium only when [Na+]o is low. 5. Reduction of cell ATP content to about 20 mumol (l cell)‐1 by treating cells with 2‐deoxyglucose stimulates Mg2+ efflux measured over the 2 h period following depletion. 6. Substantial Mg2+ influx can be observed in ferret red cells when they are incubated in media containing 10 mM‐Mg2+. Influx is stimulated by reducing [Na+]o to 10 mM. Further reduction of [Na+]o to below 1 mM reduces Mg2+ uptake. A component of uptake is inhibited by external Co2+. 7. Na(+)‐Mg2+ antiport may account for a substantial component of Mg2+ transport in ferret red cells. The direction of transport can be reversed by sufficiently lowering [Na+]o or by increasing external [Mg2+]. Analysis of the conditions at which transport reverses direction suggests transport with a stoichiometry of 1 Na+:1 Mg2+. Antiport with this stoichiometry would also explain maintenance of the physiological level of intracellular ionized Mg2+ in these cells.