bluuebunny/crossref_metadata_2025 huggingface dataset:
Sympathetic nervous system activity during skin cooling in humans: relationship to stimulus intensity and pain sensation.
Authors: Kregel K C , Seals D R , Callister R
Published: December 2014

1. Our aim was to determine the relationship between efferent sympathetic nervous system activity to skeletal muscle (MSNA) and both the dynamics of the stimulus and pain sensation during localized skin cooling in humans. MSNA in the lower leg (peroneal microneurography), heart rate, arterial blood pressure, hand skin and muscle temperatures and perceptions of pain were recorded in ten healthy subjects before, during and after immersion (3 min) of a hand in water of different temperatures ranging from non‐noxious to extremely noxious (28, 21, 14, 7 and 0 degrees C). 2. Immersion produced an abrupt, water temperature‐dependent fall in hand skin temperature (initial 30 s) followed by a more gradual decline. In contrast, the fall in hand muscle temperature was almost linear during immersion. Throughout immersions at the 28, 21, and 14 degrees C water temperatures and during the initial phase of the 7 degrees C level, sensations ranged from not painful to somewhat painful; however, the latter phase of the 7 degrees C immersion and the entire 0 degrees C level were perceived as intensely painful. 3. During the initial 15‐30 s of immersion at the 21‐7 degrees C water temperatures, MSNA decreased from control levels in all subjects (47‐58% on average, P < 0.05), whereas mean arterial blood pressure did not change. MSNA then returned to and remained at control levels throughout the 28‐14 degrees C immersions, although arterial pressure, primarily systolic, rose slightly. 4. After some delay, MSNA increased during immersion at both the 7 degrees C (P < 0.05 at 90 s) and 0 degrees C (P < 0.05 at 60 s) levels in a progressive, water temperature‐dependent manner, achieving peak values of approximately 200 and 300% of control, respectively, by 2.0‐2.5 min. These elevations in MSNA were associated with parallel increases in arterial pressure. 5. Heart rate rose during the onset of immersion at all water temperatures (P < 0.05), but fell rapidly to control levels after 60‐90 s. The increases were small (approximately 5 beats/min) and similar at the 28‐7 degrees C levels, but were twice as great at the coldest water temperature.(ABSTRACT TRUNCATED AT 400 WORDS)
Tectal and tegmental excitation in dorsal neck motoneurones of the cat.
Authors: Alstermark B , Pinter M J , Sasaki S
Published: December 2014

1. Intracellular recordings were made from 116 splenius (SPL) and 103 biventer cervicis and complexus (BCC) alpha‐motoneurones in nineteen cats anaesthetized with alpha‐chloralose. 2. Electrical stimulation in the contralateral tectum evoked disynaptic excitatory postsynaptic potentials (EPSPs) in the motoneurones when a train of stimuli was applied in the ventral layers throughout the superior colliculus. In the rostral half of the superior colliculus, these EPSPs were due to stimulation of ascending collaterals of tectofugal neurones. EPSPs of a presumed trisynaptic linkage could only be evoked from the dorsal and intermediate tectal layers in the caudal half of the superior colliculus. It is concluded that the tectofugal neurones which evoked the disynaptic EPSPs are mainly located in the caudal half of the superior colliculus. 3. Disynaptic EPSPs were evoked in the motoneurones by a train of stimuli in the contralateral fields of Forel and Zona incerta, which were due to stimulation of ascending collaterals from the tectofugal neurones. 4. Spatial facilitation experiments revealed that tectal disynaptic EPSPs in the neck motoneurones were mediated via reticulospinal neurones with convergent input from cortico‐reticular neurones. 5. A train of stimuli in the ipsilateral tectum evoked EPSPs with latencies compatible with a trisynaptic linkage, while disynaptic EPSPs at low threshold could be elicited from the underlying tegmentum. Similar disynaptic EPSPs could be evoked from the ipsilateral fields of Forel. It is suggested that some of the disynaptic tegmental EPSPs in SPL and BCC motoneurones can be mediated via a tegmento‐reticulospinal pathway which originates in the cuneiform nucleus.
The effect of inspiratory muscle fatigue on breathing pattern and ventilatory response to CO2.
Authors: Mador M J , Tobin M J
Published: December 2014

1. The effects of inducing inspiratory muscle fatigue on the subsequent breathing pattern were examined during resting unstimulated breathing and during CO2 rebreathing. In addition, we examined whether induction of inspiratory muscle fatigue alters CO2 responsiveness. 2. Global inspiratory muscle fatigue and diaphragmatic fatigue were achieved by having subjects breathe against an inspiratory resistive load while generating a predetermined fraction of either their maximal mouth pressure or maximal transdiaphragmatic pressure until they were unable to generate the target pressure. 3. Induction of inspiratory muscle fatigue had no effect on the subsequent breathing pattern during either unstimulated breathing or during CO2 rebreathing. 4. Following induction of inspiratory muscle fatigue, the slope of the ventilatory response to CO2 was significantly decreased from 18.8 +/‐ 3.3 during control to 13.8 +/‐ 2.1 l min‐1 (% end‐tidal CO2 concentration)‐1 with fatigue (P < 0.02).
Re‐evaluation of calcium currents in pre‐ and postsynaptic neurones of the chick ciliary ganglion.
Authors: Yawo H , Momiyama A
Published: December 2014

1. Presynaptic nerve terminals of ciliary ganglia of the chick embryo were identified by the accumulation of dextran‐tetramethylrhodamine applied to the cut end of the oculomotor nerve. Ca2+ currents were then recorded from the identified nerve terminals. 2. Whole‐cell recordings were carried out simultaneously from a presynaptic terminal and its postsynaptic cell. The generation of presynaptic Ca2+ currents induced a postsynaptic response with a short delay. Electrical coupling was present in eight of fifteen pairs. The coupling ratio did not exceed 5%. 3. High‐threshold Ba2+ currents were observed in presynaptic terminals without any evidence for the presence of low‐threshold Ca2+ channels. The Ba2+ current was completely blocked by 50 microM Cd2+. 4. The presynaptic Ca2+ current induced by a long depolarizing pulse showed inactivation, but this inactivation was diminished when Ca2+ was replaced with Ba2+. 5. The presynaptic Ba2+ current was insensitive to dihydropyridines (DHPs). omega‐Conotoxin GVIA (omega CgTX) suppressed a large fraction of the Ba2+ current irreversibly. About 10% of the Ba2+ current was resistant to both DHPs and omega CgTX. 6. The omega CgTX‐sensitive component was not sensitive to changes in the holding potential between ‐120 and ‐50 mV. The omega CgTX‐resistant component tended to be inactivated at depolarized holding potentials. 7. In some perisynaptic Schwann cells, small Ca2+ currents were observed. These Ca2+ currents increased monotonically with depolarization. 8. Only high‐threshold Ca2+ channel currents were observed in postsynaptic ciliary cells. Exposure to 50 microM Cd2+ completely abolished the Ca2+ current. 9. About 25% of the Ba2+ currents were blocked by nifedipine (10 microM) in ciliary cells. The nifedipine‐resistant component was partly blocked by omega CdTX (10 microM) leaving a small component (about 20%) which was resistant to both nifedipine and omega CgTX. 10. In ciliary cells, the fraction of Ba2+ currents blocked by omega CgTX was not affected by the presence or absence of nifedipine. Similarly, nifedipine blocked the Ba2+ currents to the same extent whether omega CgTX was present or not. The Ba2+ currents potentiated by Bay K 8644 were eliminated by nifedipine. 11. It is concluded that the presynaptic terminal of chick ciliary ganglion did not possess DHP‐sensitive Ca2+ channels in contrast with the postsynaptic cell. Two subpopulations of presynaptic Ca2+ channels were distinguishable by their sensitivity to omega CgTX and membrane potential.
The role of the motor cortex in the control of vigour of locomotor movements in the cat.
Authors: Beloozerova I N , Sirota M G
Published: December 2014

1. The impulse activity of single neurones in the motor cortex (MC) was recorded extracellularly using movable varnish‐insulated tungsten microelectrodes in four adult freely moving cats. The cats walked inside the experimental box with various loadings in the swing or stance phases of the step cycle. The mean discharge rate (mR) and the depth of frequency modulation (dM) in each neurone were estimated over 10‐100 steps. 2. The activity of thirty‐one cells (including eighteen pyramidal tract neurones (PTNs)) was recorded during uphill walking on a 10 deg inclined floor. The mR in 68%, and the dM in 77% of neurones changed by less than 20% during uphill locomotion compared to walking on a level surface. 3. The activity of the same neurones was also recorded during downhill walking, also on a 10 deg inclined plane. The mR in 69% and the dM in 78% of neurones changed by less than 20% during downhill locomotion compared with walking on a level surface. 4. The activity of twenty‐three (the left hemisphere) cells (sixteen PTNs) during walking with the floor swaying to the right (R) and to the left (L) was compared to activity during locomotion on a stable surface. The mR in 83% and the dM in 83% of cells in R‐steps, and in 82 and 77% of cells, respectively, in L‐steps changed by less than 20%. 5. The activity of thirty‐seven cells was studied during locomotion at various speeds. The mR in 68% and the dM in 38% of cells changed by less than 20% during fast and slow locomotion compared to middle‐speed locomotion. The dM in 46% of neurones increased with the transfer from slow to fast walking. 6. The activity of thirty‐one MC cells was recorded during locomotion with loads of 85 g attached to the distal part of each elbow. The mR in 52% and the dM in 48% of neurones changed by more than 20%. 7. The activity of twenty‐eight cells (six PTNs) was studied in steps when an animal turned. The swing of the limb contralateral to the recorded MC was shorter (condition 1) in turning steps in one direction, and was longer (condition 2) in turning steps in the opposite direction. The mR in 50% and the dM in 50% of cells in condition 1 and in 52% and 59%, respectively, of cells in condition 2 changed by more than 20%.(ABSTRACT TRUNCATED AT 400 WORDS)
Alterations in contractile properties and Ca2+ transients by beta‐and muscarinic receptor stimulation in ferret myocardium.
Authors: Hongo K , Tanaka E , Kurihara S
Published: December 2014

1. To clarify the mechanism which regulates the time course of twitch tension when beta‐ and muscarinic receptors are stimulated, intracellular Ca2+ transients, Ca2+ sensitivity of the contractile element and the cross‐bridge cycling rate (CCR) were measured in ferret ventricular muscles. 2. Isoprenaline (Iso; 0.1 microM) increased peaks of Ca2+ transients measured with aequorin and tension, and abbreviated the time courses of both signals. Addition of acetylcholine (ACh; 0.01‐1 microM) to the Iso‐treated preparation dose dependently decreased the peaks of both signals and restored the time course of Ca2+ transients. However, the time course of tension was not recovered by the addition of ACh, and the relaxation time in particular, was further shortened by ACh. Carbachol (1 microM) applied to the Iso‐treated preparation yielded similar results. 3. [Ca2+]i and tension at a quasi‐steady level of tetanic contraction, which was produced by ryanodine (5 microM) and repetitive stimulation, were measured and Ca2+ sensitivity of the contractile element was estimated. Iso (0.1 microM) decreased the Ca2+ sensitivity and the addition of ACh (1 microM) completely recovered it to the control level. 4. In order to measure CCR, the perturbation analysis method was applied to steady‐state tension of tetanic contraction. The CCR was not altered even when the tetanic tension level was decreased to 50% by decreasing [Ca2+]o. Iso (0.1 microM) slightly decreased the tetanic tension level and increased the CCR from 2.73 to 3.25 Hz. The effect of Iso was observed when the Iso‐decreased tension was recovered by an increase in [Ca2+]i. The addition of ACh (1 microM) recovered the CCR which was increased by Iso, to the control level. Atropine (10 microM) blocked the effect of ACh, and carbachol (1 microM) restored the CCR increased by Iso to the control level. 5. The time course of Ca2+ transients, Ca2+ sensitivity and CCR were antagonistically regulated by beta‐ and muscarinic receptor stimulation, but the time course of tension did not parallel the changes in these parameters. Therefore, these results suggest that the time course of tension, particularly the relaxation time, is not determined by the time course of Ca2+ transients, Ca2+ sensitivity and the CCR, and that other factors might be involved in the regulation of the time course of tension when beta‐ and muscarinic receptors are stimulated.
Phase‐dependent dynamic responses of respiratory motor activities following perturbation of the cycle in the cat.
Authors: Oku Y , Dick T E , Cherniack N S
Published: December 2014

1. Electroneurographical (ENG) activities of a phrenic nerve, a thyroarytenoid (TA) branch of a recurrent laryngeal nerve, and a triangularis sterni (TS) branch of an internal intercostal nerve were recorded in decerebrate, vagotomized and paralysed cats. A superior laryngeal nerve (SLN) was stimulated electrically. Our objective was to evaluate transient changes in motor activity following a brief perturbation of the respiratory cycle by SLN stimulation. 2. Each motor nerve recorded represents a separate phase of the respiratory cycle. We measured the duration of phrenic ENG activity for inspiratory phase duration (TI) and similarly the duration of TA and TS ENG activity for the duration of stages I and II of expiration, respectively. Changes in the duration of the total respiratory cycle (TTOT) were also measured. Therefore, the changes in TTOT were accounted for directly by changes in each phase of the respiratory cycle. 3. Perturbation during the inspiratory phase inhibited phrenic activity either reversibly or irreversibly (premature termination of inspiration) depending on the strength and timing of the stimulus. Reversible inhibition of inspiration was associated with a transient activation (< 100 ms) of the TA nerve followed by a reactivation of the phrenic nerve, but the duration of the subsequent stages I and II of expiration remained the same. Thus, the prolongation of TTOT was completely accounted for by the lengthening of TI. 4. Premature termination of inspiration was followed by either a shortening (the first half of inspiration) or a lengthening (the second half of inspiration) of the duration of stage I expiration and consistently by a shortening of the duration of stage II expiration. The magnitude of these changes in the durations of stages I and II of expiration was phase dependent. Changes in the duration of all three phases of motor activity contributed to the changes in TTOT. 5. Perturbation during stage I expiration prolonged this stage but did not affect the duration of the succeeding stage (stage II expiration). The increase in the duration of stage I expiration appeared constant and not dependent on the time when the perturbation was delivered in stage I expiration. Thus, the change in TTOT was less phase dependent during stage I expiration than during inspiration and stage II expiration and was accounted for by changes in the duration of TA activity alone. 6. Perturbation during stage II expiration inhibited TS activity and evoked TA activity transiently.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibition of cardiac vagal action by galanin but not neuropeptide Y in the brush‐tailed possum Trichosurus vulpecula.
Authors: Courtice G P , Potter E K , McCloskey D I
Published: December 2014

1. Stimulation of the right cardiac sympathetic nerve for 2 min at 16 Hz in the presence of either beta‐ or alpha‐ and beta‐adrenoceptor blockade evoked attenuation of cardiac vagal action in eight possums: 31.3 +/‐ 10.3% maximum inhibition of cardiac vagal action on prolonging pulse interval, with a time to half‐recovery of 4.9 +/‐ 1.1 min. 2. Intravenous injection of galanin (2‐3.5 nmol kg‐1) evoked similar inhibition of cardiac vagal action: 41.3 +/‐ 4.1% maximum inhibition of cardiac vagal action on pulse interval, with a time to half‐recovery of 13.4 +/‐ 2.3 min. 3. Intravenous injection of neuropeptide Y (NPY) at greater molar doses (6.5‐10 nmol kg‐1) caused no inhibition of cardiac vagal action. 4. The galanin injections caused a powerful pressor response: 57.1 +/‐ 4.9 mmHg increase in systolic blood pressure. NPY caused a smaller pressor response, despite administration of higher molar doses: 36.7 +/‐ 3.0 mmHg increase in systolic blood pressure. 5. In the possum, galanin but not NPY can mimic the effects of cardiac sympathetic nerve stimulation on vagal action. Galanin also causes large pressor effects.
Calcium currents in aged rat dorsal root ganglion neurones.
Authors: Kostyuk P , Pronchuk N , Savchenko A , Verkhratsky A
Published: December 2014

1. The whole‐cell voltage clamp technique was used to record calcium currents in the somatic membrane of rat cultured dorsal root ganglion neurones. 2. Neurones were enzymatically isolated from animals of three age groups (neonatal, 2‐7 days; adult, 7 months; and old, 30 months) and maintained in primary culture 3‐14 days. 3. The neurones isolated from neonatal and old rats showed two distinct types of Ca2+ currents, a low‐threshold transient current and a high‐threshold sustained current, whereas neurones from old rats showed only a high‐threshold calcium current. 4. The density of the high‐threshold calcium current was 28.4 +/‐ 6.3 pA/pF (mean +/‐ S.E.M., n = 54) in neonatal, 39.1 +/‐ 7.2 pA/pF (n = 62) in adult and 11.0 +/‐ 4.6 pA/pF (n = 64) in old dorsal root ganglion neurones. 5. We found no difference in elementary high‐threshold Ca2+ current characteristics in neurones from different age groups. The single‐channel conductance was (with 60 mM Ca2+ in the recording pipette) 16.0 +/‐ 2.7 pS (mean +/‐ S.E.M., n = 9) in neonatal, 16.2 +/‐ 1.7 pS (n = 11) in adult and 16.4 +/‐ 1.2 pS (n = 12) in old neurones. 6. Current‐voltage relations and kinetics of high‐threshold calcium currents showed no detectable age‐dependent difference. 7. The run‐down of high‐threshold calcium currents in dorsal root ganglion neurones from old rats was practically insensitive to intracellular administration of cyclic AMP and ATP. The same intervention caused a significant deceleration of Ca2+ current run‐down in the majority of neonatal and in some adult cells. 8. We suggest that the disappearance of the low‐threshold calcium current and reduction of high‐threshold calcium current with ageing is due to a depression of calcium channel expression during late ontogenesis. The decrease of sensitivity of high‐threshold calcium channels to phosphorylation by cyclic AMP‐dependent protein kinase in aged neurones could also be a reason for altered turnover between silent and functional pools of calcium channels, which may underlie the age‐dependent decline in the density of high‐threshold calcium channels.
Calcium accumulation by organelles within Myxicola axoplasm.
Authors: al‐Baldawi N F , Moore J E , Abercrombie R F
Published: December 2014

1. 45Ca2+ accumulation into inulin‐inaccessible compartments within cytoplasm from the giant axon of Myxicola infundibulum was measured as a function of free calcium, pH, and time. Accumulation reached a maximum after 1 h and remained stable for at least 3 h. 2. At 0.5, 5, and 50 microM [Ca2+], in the presence of 1 mM ATP or 5 mM succinate, steady‐state calcium uptake had a bell‐shaped dependence on pH with a maximum near pH 7. Uptake was abolished by the proton uncoupling reagent carbonyl cyanide p‐trifluoromethoxy‐phenylhydrazone (FCCP, 4 micrograms ml‐1). 3. Uptake of the membrane permeant cation, [14C]‐tetraphenylphosphonium (TPP+), also had a bell‐shaped dependence on pH with a maximum pH approximately 7, suggesting a pH dependence of the electrical potential of a membrane enclosed cytoplasmic compartment. Cyanide (2 mM) inhibited TPP+ uptake. 4. Inositol 1,4,5‐trisphosphate (IP3, 10 microM), reduced steady‐state calcium accumulation by 20‐22% at 0.5 microM free calcium, pH 7 (P < 0.01, n = 16) and at 5 microM free calcium, pH 8 (P < 0.0005, n = 35). No effects of IP3 were found at other pH or calcium concentrations. 5. Neither guanosine 5'‐triphosphate (GTP) nor inositol 1,3,4,5‐tetrakisphosphate (IP4) had an effect on calcium uptake (5 microM [Ca2+], pH 8). 6. At 0.5 microM free calcium; vanadate (10 microM) inhibited 20‐30%, of the 45Ca2+ accumulation, thapsigargin (33 nM) inhibited 20‐30%, and cyanide (2 mM) plus oligomycin B (2 micrograms ml‐1), or valinomycin (1 microM), inhibited 70‐80%. The fraction of uptake sensitive to thapsigargin fell as the free calcium increased; however, the sensitivity of uptake to cyanide plus oligomycin B was approximately 80% for 0.5, 5.0, and 50 microM [Ca2+]. 7. Thapsigargin had no additional inhibiting effect in the presence of cyanide plus oligomycin B. IP3 had no effect in the presence of cyanide plus oligomycin B or other mitochondrial inhibitors. 8. Results suggest the presence of both mitochondrial (70‐80%) and non‐mitochondrial (20‐30%) calcium pools in this system (at 0.5‐5.0 microM Ca2+). The apparent non‐mitochondrial uptake (sensitive to thapsigargin, or IP3) is not detectable in the presence of mitochondrial inhibitors. We interpret these results as evidence of functional communication between mitochondrial and non‐mitochondrial calcium stores.
Depolarization of group II muscle afferents by stimuli applied in the locus coeruleus and raphe nuclei of the cat.
Authors: Riddell J S , Jankowska E , Eide E
Published: December 2014

1. Electrical stimuli applied in the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei produce a profound depression of transmission in reflex pathways from group II muscle afferents. The present experiments were performed to determine whether presynaptic inhibitory mechanisms contribute to these effects. 2. Changes in the excitability of afferent terminals to electrical stimuli have been used as an indication of primary afferent depolarization (PAD) produced by conditioning stimuli applied within the LC/SC and raphe nuclei and, for comparison, in the nucleus ruber. Group II afferents originating from ankle flexor muscles and terminating in the midlumbar segments were used for testing. 3. Clear changes in excitability were observed in fourteen of nineteen group II fibres in which the effects of conditioning stimuli applied in the LC/SC were tested and in twelve of seventeen fibres in which the effects of stimuli applied within the raphe nuclei were tested. By comparison, only one of the twelve fibres tested with conditioning stimuli applied to the nucleus ruber was found to be influenced. These effects matched those of the same conditioning stimuli on field potentials evoked by group II afferents at the location at which the terminals of group II fibres were stimulated. 4. Stimuli applied in the LC/SC and in the raphe nuclei both produced a mean decrease in threshold stimulus current of 19%. These effects are comparable to those produced by the most effective volleys in peripheral afferent which, in the same fibres, produced a mean decrease in threshold stimulus current of 24%. 5. In all cases (twelve) in which the effects of stimuli applied in the LC/SC and raphe nuclei were tested on the same group II fibre, either both or neither were found to be effective. This strengthens previous indications that some populations of neurones might be activated by stimuli applied in each of these regions of the brain. 6. In contrast to group II afferents, group Ia afferents investigated in the same experiments were only exceptionally affected. Of seven fibres tested with stimuli applied in the LC/SC, six with stimuli applied in the raphe nuclei and seven with stimuli applied in the nucleus ruber, only one fibre showed any clear change in threshold and this was a single fibre which was similarly affected by stimuli in all three sites. 7. It is concluded that presynaptic inhibitory mechanisms contribute to the depression of transmission in spinal reflex pathways from group II muscle afferents produced by stimulation in the LC/SC and raphe nuclei.
Photo‐released intracellular Ca2+ rapidly blocks Ba2+ current in Lymnaea neurons.
Authors: Johnson B D , Byerly L
Published: December 2014

1. The effect of intracellular Ca2+ on Ba2+ current flowing through voltage‐dependent Ca2+ channels was studied using the whole‐cell patch‐clamp technique on isolated neurons from the snail Lymnaea stagnalis. Intracellular Ca2+ was increased by flash photolysis of the caged Ca2+ compound DM‐nitrophen and measured with the optical indicator fluo‐3. 2. After the highest intensity flashes, peak Ba2+ current was blocked by 42% with a time constant of 5 ms. The onset of the block followed a similar time course whether channels were activated or closed. The Ba2+ current surviving after the flash had the same voltage dependence of activation and rate of inactivation as did the total Ba2+ current before the flash. 3. Recovery of the Ba2+ current from block was nearly complete and occurred with a time constant of 16 s. Multiple episodes of photolysis‐induced block could be studied in the same cell when 7‐10 min were allowed between flashes. In some cells, recovery from block was accompanied by a transient enhancement of the current above the pre‐block magnitude. 4. Neurons greatly reduced the ability of photolysis to increase Ca2+, both by unloading the DM‐nitrophen before flashes were applied and by rapidly buffering the photolytically released Ca2+. Maximal flashes on extracellular droplets of the DM‐Ca2+ solution created a Ca2+ jump from 110 nM to 40 microM. In contrast, the same flashes on DM‐Ca(2+)‐loaded neurons resulted in a Ca2+ transient starting from a baseline of 36 nM to a peak of 130 nM. This intracellular Ca2+ transient decayed with three time constants (120 ms, 2 s and 13 s). 5. Endogenous buffer(s) binds Ca2+ rapidly. When intracellular Ca2+ was monitored within 2 ms of the flash, no rapid Ca2+ spike due to binding of photo‐released Ca2+ could be detected. Addition of dibromo‐BAPTA to the intracellular solution reduced the block by one third, which is consistent with the measured reduction of intracellular Ca2+. This indicates that the endogenous buffer can bind Ca2+ as rapidly as dibromo‐BAPTA and as fast as Ca2+ is released by photolysis. 6. The Ca2+ dependence of the block, obtained by varying flash intensity, indicates some saturation by 130 nM. A simple two‐state model of the block consistent with both the time course of block and recovery and the concentration dependence gave a dissociation constant of approximately 50 nM and forward rate constant of 7 x 10(8) M‐1 s‐1.(ABSTRACT TRUNCATED AT 400 WORDS)
Temperature dependence of the light response in rat rods.
Authors: Robinson D W , Ratto G M , Lagnado L , McNaughton P A
Published: December 2014

1. The effects of temperature on the light responses of rat rods have been investigated over the range 17‐40 degrees C. 2. The amplitude of the light‐sensitive current increased with temperature with a mean temperature coefficient (Q10) of 2.47. 3. The amplitude of the Na(+)‐Ca2+, K+ exchange current decreased with temperature when expressed as a fraction of the light‐sensitive current, showing that the light‐sensitive channel becomes less permeable to calcium as the temperature is raised. The time constant of relaxation of the exchange current was little affected by temperature. 4. The flash intensity required to give a half‐saturating response increased with temperature with a mean Q10 of 1.68. 5. The responses to single photoisomerizations were determined from amplitude histograms of the responses to dim‐flash trains. The amplitude of the response to a single photoisomerization decreased with temperature when expressed as a fraction of the light‐sensitive current, but the change was not sufficient to account for the overall decrease in sensitivity. 6. The fraction of dim flashes that produced a photoisomerization decreased with temperature. This decrease in photon capture efficiency together with the decrease in the relative size of the single photon event fully accounts for the observed change in sensitivity. 7. The speed of the falling phase of the dim‐flash response was accelerated more by warming than the rising phase, and it was therefore not possible to superimpose light responses at different temperatures by a simple change in time scale.
Whole‐cell currents in isolated resting Necturus gastric oxynticopeptic cells.
Authors: Supplisson S , Loo D D , Sachs G
Published: December 2014

1. Necturus gastric mucosa secretes Cl‐ actively across the gastric glands which are composed almost entirely of acid‐ and enzyme‐secreting oxynticopeptic cells. Single channel studies on Necturus oxynticopeptic cells have shown that the basolateral membrane possesses multiple K(+)‐selective channels but no observable Cl‐ channels while the apical membrane has Cl‐ channels but no observable K+ channels. To relate these channel properties to the conductance of the whole cell we have investigated the macroscopic membrane currents with conventional whole‐cell patch‐clamp techniques. 2. When bathed in amphibian Ringer solution, gastric oxynticopeptic cells had a membrane resistance of 47.8 +/‐ 2.8 M omega and a membrane capacitance of 75.5 +/‐ 2.7 pF (n = 82). This gave a specific membrane resistance of 3260 +/‐ 160 omega cm2 (n = 82). Reversal potentials of the oxynticopeptic cells were ‐13.8 +/‐ 1.2 mV (n = 45) for an intracellular Cl‐ concentration ([Cl‐]i) of 42 mM and were significantly more negative ‐24.4 +/‐ 3.1 mV (n = 31, P < 0.001) for [Cl‐]i = 22 mM. 3. In the absence of ATP in the pipette solution, there was an 80% reduction of the whole‐cell current with a typical half‐time (t1/2) of 5 min. The run‐down was not observed when the pipette solution contained 4 mM ATP. 4. A slow and voltage‐independent inhibition of 80% of the whole‐cell currents occurred after addition of NPPB (35 microM). Ba2+ (10 mM) produced a reversible inhibition of 20% of the total current. Together, 35 microM NPPB and 10 mM Ba2+ eliminated 95% of the whole‐cell currents. These data suggest that in the resting oxynticopeptic cells Cl‐ carried the major fraction of the current while K+ ions carried only a small fraction. 5. Total replacement of Cl‐ in the pipette and bath solution by gluconate‐ increased the membrane resistance to 751 +/‐ 104 M omega (n = 53) and shifted the reversal potential to ‐38.1 +/‐ 2.8 mV (n = 53). 6. Increasing the bath K+ concentration from 6 to 91 mM activated a current which had a high selectivity for K+ over choline+, Li+, Na+, Rb+ and Cs+ and was independent of Cl‐. The activation of this K+ current (IK*) by high external K+ was not seen with ATP‐free pipette solution. 7. Ba2+ or Cs+ had a voltage‐dependent blocking effect of this inward K+ current. Ouabain (1 mM) or SCH 28080 (200 microM), specific inhibitors of the Na+,K(+)‐ATPase and H+,K(+)‐ATPase, had no effect.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in motor unit synchronization following central nervous lesions in man.
Authors: Farmer S F , Swash M , Ingram D A , Stephens J A
Published: December 2014

1. Single motor unit spike trains have been recorded during voluntary isometric contraction of the affected intrinsic hand muscles of patients with unilateral central nervous lesions. These have been compared with similar recordings made from the patients' unaffected hand muscles and with recordings made from the hand muscles of healthy subjects. 2. Cross‐correlation analysis was performed between the times of occurrence of the motor unit spike trains. The time course of central cross‐correlogram peaks constructed for normal subjects and stroke patients was used to infer properties of the underlying common EPSPs and the impulse‐generating properties of the motoneurones. The results of this analysis were compared between the two groups. In addition, the size and time course of cross‐correlogram peaks obtained from the patients were related both to the patients' clinical state and to their hand and fine finger function. 3. Central nervous lesions were found to result in either a narrowing or broadening of the time course of motor unit synchronization. These changes were attributed either to an increase in the size of common EPSPs with respect to synaptic noise, or to the effects of presynaptic synchronization of motoneurone inputs. 4. Longitudinal studies of motor unit discharges in the year following the stroke demonstrated, in some patients, differences in the level of motor unit synchronization. These paralleled improvements in the patients' fine motor control. Pooled data from patients with varying deficits of fine motor control confirmed that loss or reduction of motor unit synchronization was associated with a corresponding slowing in the performance of rapidly alternating finger movements. 5. The results of the present study suggest that the branched common presynaptic inputs that generate motor unit synchronization are either of corticospinal tract origin or are intimately dependent on its function. Differences in the strength and time course of motor unit synchronization are demonstrated that may reflect the altered behaviour of presynaptic inputs to motoneurones following central nervous damage in man.
Force relaxation, labile heat and parvalbumin content of skeletal muscle fibres of Xenopus laevis.
Authors: Lännergren J , Elzinga G , Stienen G J
Published: December 2014

1. Measurements were made of stable (hb) and labile (ha) maintenance heat rate, slowing of relaxation as a function of tetanus duration, and parvalbumin (PA) content in intact single muscle fibres of types 1 and 2 from Xenopus laevis. The majority of experiments were performed at 20 degrees C. In addition, total and myofibrillar ATPase activity was measured in skinned Xenopus fibres, also of types 1 and 2; these studies were performed at 4 degrees C. 2. In agreement with a previous study hb was significantly higher in type 1 (175 +/‐ 13 mW (g wet wt)‐1; n = 8) than in type 2 fibres (88 +/‐ 9 mW (g wet wt)‐1; n = 7). The value of ha was 236 +/‐ 22 and 117 +/‐ 16 mW (g wet wt)‐1, respectively (mean +/‐ S.E.M.). ha decayed with a time constant of 0.27 +/‐ 0.02 (n = 8) and 0.33 +/‐ 0.02 s (n = 7). 3. The early relaxation rate of tetanic force, extrapolated to the onset of stimulation (yo + yb; where yo is ‘extra’ rate of relaxation and yb steady rate) was 85.6 +/‐ 4.2 s‐1 for type 1 fibres (n = 8) and 62.7 +/‐ 7.3 s‐1 for type 2 fibres (n = 7). Relaxation rate at the end of a 1.8 s tetanus (yb) was 29.4 +/‐ 1.6 and 33.3 +/‐ 1.5 s‐1, respectively; thus, there was more slowing with tetanus duration in type 1 fibres. The time constant for slowing of relaxation with tetanus duration was similar to that for decay of ha. 4. Parvalbumin concentration, [PA], was 0.45 +/‐ 0.04 mM in type 1 (n = 7) and 0.22 +/‐ 0.04 mM (n = 7) in type 2 fibres. 5. For individual fibres positive correlations were found between the ‘extra’ rate of relaxation (yo), labile heat (ha) and [PA]. Significantly more labile heat was liberated than can be accounted for by the enthalpy change of Ca2+ binding to PA. 6. For five fibres (type 1) studied both at 20 and 10 degrees C, the magnitude of slowing of relaxation, expressed as yo/(yo + yb), was 0.58 +/‐ 0.03 at 20 degrees C and 0.65 +/‐ 0.03 at 10 degrees C. 7. Both slowing of relaxation and labile heat were depressed in the second of two closely spaced tetani in type 1 fibres. Repriming of both effects followed similar, biphasic time courses and required more than 10 min for completion at 20 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)
Retinal origins of the temperature effect on absolute visual sensitivity in frogs.
Authors: Aho A C , Donner K , Reuter T
Published: December 2014

1. The absolute sensitivity of vision was studied as a function of temperature in two species of frog (Rana temporaria, 9‐21 degrees C, and Rana pipiens, 13‐28 degrees C). 2. Log behavioural threshold (measured as the lowest light intensity by which frogs trying to escape from a dark box were able to direct their jumping) rose near‐linearly with warming with a regression coefficient of 1.26 +/‐ 0.03 log units per 10 degrees C (Q10 = 18). Threshold retinal illumination corresponded to 0.011 photoisomerizations per rod per second (Rh* s‐1) at 16.5 degrees C. 3. The effect of dim backgrounds on jumping thresholds suggested ‘dark lights’ of 0.011 Rh* s‐1 at 16.5 degrees C and 0.080 Rh* s‐1 at 23.5 degrees C, corresponding to Q10 = 17. 4. Response thresholds of retinal ganglion cells were extracellularly recorded in the isolated eyecup of R. temporaria. The thresholds of the most sensitive cells when stimulated with large‐field steps of light were similar to the behavioural threshold and changed with temperature in a similar manner. 5. The decrease in ganglion cell 'step’ sensitivity with warming consisted of a decrease in summation time (by a factor of 2‐3 between 10 and 20 degrees C) and an increase in the threshold number of photoisomerizations (a decrease in ‘flash’ sensitivity, by a factor of 2‐5 over the same interval). No effect of temperature changes on spatial summation was found. 6. Frequency‐of‐response functions of ganglion cells indicated an 11‐fold increase in noise‐equivalent dark light between 10 and 20 degrees C (mean values in four cells 0.009 vs. 0.10 Rh* s‐1). 7. The temperature dependence of ganglion cell flash sensitivity could be strongly decreased with dim background illumination. 8. It is concluded that the desensitization of dark‐adapted vision with rising temperature is a retinal effect composed of shortened summation time and lowered flash sensitivity (increased numbers of photons required for a threshold response) in ganglion cells. The desensitization bears no simple relation to the apparent retinal noise increase.
Changes in myoplasmic pH and calcium concentration during exposure to lactate in isolated rat ventricular myocytes.
Authors: Cairns S P , Westerblad H , Allen D G
Published: December 2014

1. We investigated the mechanisms involved in the rise of myoplasmic calcium concentration ([Ca2+]i) when isolated rat ventricular myocytes were exposed to lactate. The intracellular pH (pHi) and [Ca2+]i were measured using the fluorescent indicators 2',7'‐bis(carboxyethyl)‐5(6)‐carboxyfluorescein (BCECF) and fura‐2, respectively. Cell shortening was used as a measure of contractile performance. 2. Exposure to 20 mM lactate at the normal extracellular pH (pHo 7.4) for 10 min caused the pHi to fall rapidly by 0.24 pH units and cell shortening was reduced. Thereafter, pHi partially recovered by 0.16 pH units, which was paralleled by a recovery of shortening. 3. Exposure to lactate at a reduced extracellular pH (pHo 6.4) induced a very large acidosis of 0.70 pH units and cell shortening was abolished. During maintained exposure to lactate the pHi remained constant and cell shortening did not recover. 4. Application of Na(+)‐H+ exchanger inhibitors, amiloride or ethylisopropyl‐amiloride (EIPA), abolished the recovery of pHi and shortening during maintained exposure to lactate at pHo 7.4 and caused an additional acidosis during maintained application of lactate at pHo 6.4. 5. Application of lactate at both the normal and reduced pHo resulted in a rapid, followed by a slower, rise in [Ca2+]i. The diastolic and systolic [Ca2+]i and the amplitude of the systolic rise in the [Ca2+]i (the Ca2+ transient) all increased in both the rapid and the slow phase. 6. When lactate was applied at pHo 7.4, in the presence of EIPA, the initial rise of [Ca2+]i still occurred but the slower increase was abolished. This suggests an involvement of the Na(+)‐H+ exchanger in the slower rise of [Ca2+]i. 7. In conclusion, the Na(+)‐H+ exchanger is an important regulator of pHi during a lactate‐induced intracellular acidosis. The rise of [Ca2+]i involves at least two mechanisms: (i) a rapid component which may represent reduced myoplasmic Ca2+ buffering, impaired Ca2+ removal by the sarcoplasmic reticulum or a direct inhibitory effect of protons on the Na(+)‐Ca2+ exchanger; (ii) a slower component linked to stimulation of Na(+)‐H+ exchanger which causes an increased [Na+]i and stimulates the Na(+)‐Ca2+ exchanger, resulting in an enhanced Ca2+ influx.
Ca2+ channel modulating effects of heparin in mammalian cardiac myocytes.
Authors: Lacinova L , Cleemann L , Morad M
Published: December 2014

1. The effect of heparin on L‐type Ca2+ channels in rabbit, rat and guinea‐pig cardiac myocytes was studied using the whole‐cell patch clamp method. 2. Sodium salts of heparin uniformly suppressed the Ca2+ current, ICa, independent of their molecular weight, in the rat and guinea‐pig ventricular and rabbit atrial myocytes. The suppression of ICa by heparin was dose dependent and reached its maximum, about 30%, around 10 microM. Heparin did not alter the voltage‐dependence or the steady‐state inactivation properties of ICa. These effects were specific to heparin as another polysaccharide, dextran, failed to have any effect on ICa. 3. The suppressive effect of heparin was not diminished when [Ca2+]o was increased to 10 mM, or when Ba2+ was the charge carrier through the Ca2+ channel. 4. Spectrophotometric assays showed that heparin‐induced changes in [Ca2+]o generally were too small to alter ICa significantly. 5. In myocytes buffered with 0.1 mM EGTA, the suppressive effect of heparin was more prominent on the inactivating than on the maintained component of ICa. 6. When extracellular Na+ was replaced by Cs+, the heparin suppressive effect was accompanied by a 10 mV shift of both the voltage dependence of activation and the steady‐state inactivation parameters toward more negative potentials. 7. When both Mg2+ and Na+ were omitted from the bathing solutions, the suppressive effect of heparin was significantly enhanced such that almost 80% of the current was blocked. 8. In Cs(+)‐based solutions 10 mM [Mg2+]o suppressed ICa by about 70% and heparin partially relieved this block. Heparin, however, did not counteract the Mg(2+)‐induced suppression of ICa in Na(+)‐based solution. 9. Extracellularly applied heparin did not alter the isoprenaline‐induced enhancement of ICa or interfere with the blocking effect of phorbol esters on ICa. 10. Heparin thus appears to interfere with the permeation of Ca2+ through the channel by a mechanism regulating the Ca(2+)‐induced inactivation of the Ca2+ channel. Na+ and Mg2+ appear to alter the kinetics and the magnitude of the suppressive effect of heparin on the Ca2+ channel, suggesting an interaction of these cations with either the Ca2+ or the heparin‐binding sites of the channel.
Separate measures of ATP utilization and recovery in human skeletal muscle.
Authors: Blei M L , Conley K E , Kushmerick M J
Published: December 2014

1. The chemical changes during contractile activity were separated from recovery metabolism in the forearm flexor musculature in normal human subjects using 31P nuclear magnetic resonance (NMR) spectroscopy. Percutaneous, supramaximal twitch stimulation of the median and ulnar nerves was used in combination with temporary ischaemia of the forearm to characterize the summed ATPase activity. The recovery following restoration of blood flow provided a measure of oxidative ATP synthesis activity. These processes were measured based on the dynamics of creatine phosphate (PCr) content. 2. Muscle oxygen stores were depleted using ischaemia without stimulation as indicated by PCr breakdown after 250 +/‐ 33 s (mean +/‐ S.D.; n = 5), which provided a measure of the basal metabolic rate (0.008 +/‐ 0.002 mM s‐1, n = 5). 3. The PCr breakdown rate during twitch stimulation of the oxygen‐depleted muscle was constant at 1 Hz at 0.15 +/‐ 0.03 mM PCr per second or per twitch (n = 8). A constant cost per twitch was found from 0.5 to 2 Hz stimulation (depletion of PCr per twitch = 0.15 mM per twitch). 4. No net anaerobic recovery of PCr was found during a 2 min post‐stimulation ischaemia. 5. Upon restoration of blood flow, PCr recovery followed an exponential time course with a time constant of 63 +/‐ 14 s (n = 8). From these recovery rates, the capacity for oxidative phosphorylation was estimated to be 0.4 mM s‐1. 6. This experimental approach defines a non‐invasive and quantitative measure of human muscle ATPase rate and ATP synthetase rate.
Synaptic inhibition in primary and secondary chronic epileptic foci induced by intrahippocampal tetanus toxin in the rat.
Authors: Empson R M , Jefferys J G
Published: December 2014

1. Injecting twelve mouse minimum lethal doses of tetanus toxin into one hippocampus of a rat leads to the development of chronic epileptic foci in both hippocampi. These generate intermittent epileptic discharges for 6‐8 weeks. Here we compare GABAergic inhibition, 10‐18 days after injection, in slices prepared from the injected and contralateral hippocampi (respectively the primary and the secondary or ‘mirror’ foci), using both neurochemical and electrophysiological methods. 2. Epileptic activity was recorded from slices of both hippocampi from all tetanus toxin‐injected rats. Evoked epileptic discharges were similar on the two sides, but spontaneous epileptic discharges were more common contralaterally. 3. Ca(2+)‐dependent, K(+)‐stimulated (synaptic) release of radiolabelled GABA was depressed in slices from the injected hippocampus, compared with vehicle‐injected controls. In contrast, slices from the contralateral hippocampus had normal levels of Ca(2+)‐dependent, K(+)‐stimulated GABA release, even though adjacent slices were epileptogenic. 4. Intracellular recordings revealed that both fast and slow stimulus‐evoked inhibitory postsynaptic potentials (IPSPs) were abolished in CA3 pyramidal cells in the primary focus. In the secondary focus, however, fast IPSPs were seen in seven of twenty‐five cells, and slow IPSPs were seen in all cells if the stimulus was strong enough. 5. Monosynaptic IPSPs were isolated pharmacologically by blocking glutamatergic excitatory postsynaptic potentials (EPSPs) with 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and D(‐)‐2‐amino‐5‐phosphopentanoic acid (AP‐5). No monosynaptic IPSPs were uncovered in cells from the primary focus at any stimulus strength. Monosynaptic IPSPs were evoked in all cells from both the secondary focus and control slices. The estimated conductances of monosynaptic fast IPSPs were similar in cells from the secondary focus and from the controls, although the former required twice the stimulus strength. 6. Slow IPSPs were found in the secondary focus and in controls, but not in the primary focus. They were sensitive to 3‐amino‐2‐(4‐chlorophenyl)‐2‐hydroxy‐propylsulphonic acid (2‐OH saclofen). The estimated conductances of slow IPSPs evoked by weak stimuli in the secondary focus were much smaller than in the controls. However, stimuli that could trigger epileptic discharges in the secondary focus, evoked 2‐OH saclofen‐sensitive slow IPSPs with estimated conductances approaching the controls. This marked increase in the slow IPSP did not occur when EPSPs, and epileptic bursts, were blocked with CNQX and AP‐5, suggesting that a strong barrage of excitation is needed to generate full‐sized slow IPSPs in the secondary focus.(ABSTRACT TRUNCATED AT 400 WORDS)