bluuebunny/crossref_metadata_2025 huggingface dataset:
State‐dependent radial elasticity of attached cross‐bridges in single skinned fibres of rabbit psoas muscle.
Authors: Xu S , Brenner B , Yu L C
Published: December 2014

1. In a single skinned fibre of rabbit psoas muscle, upon attachment of cross bridges to actin in the presence of ADP or pyrophosphate (PPi), the separation between the contractile filaments, as determined by equatorial X‐ray diffraction, is found to decrease, suggesting that force is generated in the radial direction. 2. The single muscle fibres were subjected to compression by 0‐8% of dextran T500. The changes in lattice spacings by dextran compression were compared with changes induced by cross‐bridge attachment to actin. Based on this comparison, the magnitude and the direction of the radial force generated by the attached cross‐bridges were estimated. The radial cross‐bridge force varied with filament separation, and the magnitude of the radial cross‐bridge force reached as high as the maximal axial force produced during isometric contraction. 3. One key parameter of the radial elasticity, i.e. the equilibrium spacing where the radial force is zero, was found to depend on the ligand bound to the myosin head. In the presence of ADP, the equilibrium spacing was 36 nm. In the presence of MgPPi the equilibrium spacing shifted to 35 nm and Ca2+ had little effect on the equilibrium spacing. 4. The equilibrium spacing was independent of the fraction of cross‐bridges attached to actin. The fraction of cross‐bridges attached in rigor was modulated from 100% to close to 0% by adding up to 10 mM of ATP gamma S in the rigor solution. The lattice spacing remained at 38 nm, the equilibrium spacing for nucleotide‐free cross‐bridges at mu = 170 mM. 5. Radial force generated by cross‐bridges in rigor at large lattice spacings (38 nm < or = d10 < or = 46 nm) appeared to vary linearly with lattice spacing. 6. The titration of ATP gamma S to fibres in rigor provided a correlation between the radial stiffness of the nucleotide‐free cross‐bridges and the equatorial intensities. The relation between the equatorial intensity ratio I11/I10 and radial stiffness appeared to be approximately linear. 7. The fibres under different conditions showed a wide range of radial stiffness, which was not proportional to the apparent axial stiffness of the fibre. If the apparent axial stiffness is a measure of the fraction of cross‐bridges bound to actin, it follows that the radial elastic constant is state dependent; or vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)
The relation between stimulus and response in olfactory receptor cells of the tiger salamander.
Authors: Firestein S , Picco C , Menini A
Published: December 2014

1. Olfactory receptor cells were isolated from the adult tiger salamander Ambystoma tigrinum and the current in response to odorant stimuli was measured with the whole‐cell voltage‐clamp technique while odorants at known concentrations were rapidly applied for controlled exposure times. 2. Three odorants, cineole, isoamyl acetate and acetophenone, were first applied at 5 x 10(‐4) M. Out of forty‐nine cells tested, 53% responded to one odorant only, 22% to two odorants and 25% to all three odorants. 3. The amplitude of the current in response to a given odorant concentration was found to be dependent on the duration of the odorant stimulus and reached a saturating peak value at 1.2 s of stimulus duration. 4. The current measured at the peak of the response for odorant steps of 1.2 s as a function of odorant concentration was well described by the Hill equation for the three odorants with Hill coefficients higher than 1 and K1/2 (odorant concentration needed to activate half the maximal current) ranging from 3 x 10(‐6) to 9 x 10(‐5) M. 5. It is concluded that olfactory receptor cells are broadly tuned and have a low apparent affinity for odorants, integrate stimulus information over time, and have a narrow dynamic range.
Modulation of EPSP shape and efficacy by intrinsic membrane conductances in rat neocortical pyramidal neurons in vitro.
Authors: Nicoll A , Larkman A , Blakemore C
Published: December 2014

1. Intracellular recordings were made from pyramidal neurons in layers II/III and V of rat visual cortical slices. Distal and proximal excitatory postsynaptic potentials (EPSPs) were evoked using extracellular bipolar electrodes placed on the slice horizontal to each cell, near the apical and basal dendrites respectively. Experiments were conducted in the presence of 2‐amino‐5‐phosphonopentanoate, picrotoxin and, in most cases, 2‐hydroxy‐saclofen. 2. For layer II/III pyramidal neurons, voltage undershoots following distal and proximal EPSPs (n = 7 pairs) and injected somatic pulses were rarely apparent. In layer V pyramidal neurons substantial voltage undershoots were recorded following distal and proximal EPSPs (n = 27 pairs) and injected somatic pulses, with undershoot being greatest for apical inputs (P = 0.001). The greater undershoots following apical EPSPs were also apparent in semilogarithmic plots of voltage decay where the slope of decay for apical EPSPs was quicker than the voltage decay following pulses of current injected at the soma. There was no significant difference in the shapes of distal and proximal EPSPs in layer II/III or layer V pyramidal cells under control conditions. 3. Pharmacological agents were used to reduce voltage undershoots. The most successful of these was alinidine, a putative blocker of the slow inward rectifier (IH) conductance. In the presence of bath‐applied 100 microM alinidine, undershoots were significantly reduced and it became possible to distinguish the relative origins of EPSPs on the basis of their shape. Distally generated EPSPs (n = 14) had rise times and half‐widths that were 2.8 and 1.5 times longer respectively than those evoked proximally (n = 10; P = 0.001 for both parameters). 4. These results confirm previous theoretical simulations of somatic recordings in passive model neurons where distal EPSPs display slower rise times and longer half‐widths than proximal EPSPs. The present results suggest that, at least in pyramidal neurons of layer V, distal synaptic inputs can be specifically modulated by intrinsic membrane conductances.
Differential sympathetic reactions during cerebral ischaemia in cats: the role of desynchronized nerve discharge.
Authors: Kocsis B , Fedina L , Gyimesi‐Pelczer K , Ladocsi T , Pasztor E
Published: December 2014

1. Sympathetic nerve discharge (SND) of three postganglionic nerves with different functions and anatomical locations was simultaneously recorded at rest and during severe cerebral ischaemia (Cushing reaction). The three nerves, controlling the heart (inferior cardiac nerve), visceral (renal nerve) and skeletal muscle circulation (vertebral nerve), were selected with the assumption that their activity pattern will represent the differential central autonomic command to the major players of the circulatory response to cerebral ischaemia. 2. Changes in the power density spectra of the nerve signals, and in the pairwise coherence functions, elicited by the cerebral ischaemia, were evaluated separately for the rhythmic (R‐SND, i.e. between 0 and 6 Hz) and high‐frequency (HF‐SND, i.e. between 12 and 100 Hz) components of the nerve signals. 3. The sympathetic nerve response to cerebral ischaemia developed in two phases. Phase 1 was a massive R‐SND reaction and phase 2 was characterized by SND desynchronization and by the emergence of HF‐SND. The power of HF‐SND occupied a wide band between 12 and 80 Hz with maximum between 20 and 30 Hz. All three nerves were involved in the Cushing response but the magnitude and character of the reactions were specific for each nerve. In the cardiac nerve, the power of the rhythmic component of the discharge increased almost twice the control and remained dominant during the whole reaction, strongly modulating HF‐SND during the second phase. In the vasomotor nerves, R‐SND was suppressed during phase 2 and HF‐SND occupied 65% of the total power of the signal. Near equal R‐ to HF‐SND proportions, however, were reached on different activity levels in renal and vertebral nerves. Whereas total renal SND did not change, the power of the vertebral SND increased more than twice. In addition, desynchronization in the vertebral SND was preceded by a massive R‐SND reaction during phase 1, which was missing in the renal nerve. 4. For all possible nerve pairs, R‐SND was highly coherent before the reaction and remained so during intracranial pressure elevation, regardless of the direction and magnitude of the changes in absolute and/or relative power of this component in different nerves. On the other hand, HF‐SND never correlated between any of the nerve pairs indicating that this component in each nerve originated from specific sources of regional sympathetic activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Transducer properties of the rapidly adapting stretch receptor neurone in the crayfish (Pacifastacus leniusculus).
Authors: Rydqvist B , Purali N
Published: December 2014

1. The transducer properties of the rapidly adapting stretch receptor neurone of the crayfish (Pacifastacus leniusculus) were studied using a two‐microelectrode voltage clamp technique. 2. The impulse response to ramp‐and‐hold extensions of the receptor muscle typically consisted of a high frequency burst followed by cessation of impulses within a relatively short time depending on the amplitude of extension. The type of adaptation was consistent with earlier studies. The stimulus‐response relationship for the impulse frequency was non‐linear and had a slope in a log‐log plot of 2.9. 3. When impulse generation was blocked by tetrodotoxin (TTX), (block of Na+ channels) the receptor potential was extension dependent and similar to that found in the slowly adapting receptor. For small extensions there was an initial peak followed by a fall to a steady potential level. For large extensions the potential response during the ramp phase consisted of a peak followed by a constant potential level lasting to the end of the ramp. When the extension changed to the hold phase the potential fell towards a steady state. The relation between extension and amplitude of receptor potential was non‐linear and saturated at ‐40 to ‐30 mV (extensions > 15% of zero length, lo). 4. When potassium channels were blocked by TEA (50 mM) and 4‐aminopyridine (4‐AP, 5 mM) (and Na+ channels blocked by TTX) the shape of the generator potential become less complex with an increased amplitude for large extensions. 5. When the receptor neurone was voltage clamped at the resting potential, extension of the receptor muscle produced an inwardly directed receptor current, the stretch‐induced current (SIC). The response consisted of a fast transient phase which decayed towards a steady state. The SIC peak amplitude was dependent on extension in a sigmoidal fashion and saturated at 190 nA (extensions > 25% of lo). The slope of the steepest part of the stimulus‐response relation (between 10 and 20% extension) was 4.7 +/‐ 0.25 (mean +/‐ S.E.M.) in a log‐log plot. 6. The peak amplitude of the SIC increased with increasing extension speed (ramp steepness), the relation between the slope of the ramp and current amplitude being a first order (hyperbolic) function. The amplitude of the receptor current was voltage dependent and had a reversal potential of +16.2 +/‐ 1.8 mV (mean +/‐ S.E.M., 32 cells). From the reversal potential the permeability ratio, PNa/PK, of the transducer permeability system was calculated to be 1.5. The I‐V curve of SIC was non‐linear.(ABSTRACT TRUNCATED AT 400 WORDS)
Baroreceptor reflex‐linked changes in catechol metabolism in the rat rostral ventrolateral medulla.
Authors: Rentero N , Kitahama K , Quintin L
Published: December 2014

1. Using in vivo voltammetry, this study relates catecholamine metabolism within the rat rostral ventrolateral medulla to the level of mean arterial pressure (MAP) under halothane anaesthesia. 2. A vasopressor region was circumscribed with electrical stimulations in an area located 1000‐1700 microns rostral to the obex. A catechol signal was then ascertained within this area. The recording site was surrounded with phenyl‐N‐methyl‐ethanolamine transferase immuno‐positive cell bodies. 3. Three levels of decrease of arterial pressure were induced with nitroprusside infusion: ‐15, ‐35 and ‐55 mmHg (n = 5 in each group) from baseline for 30 min. This led to increases in the catechol signal which were inversely related to the degree of hypotension (P < 10(‐4) vs. saline for the 35 and 55 mmHg groups, P < 0.05 for the 35 mmHg group as compared to the 15 and 55 mmHg groups following recovery from hypotension). 4. Following sino‐aortic deafferentation, nitroprusside‐induced hypotension (‐35 mmHg) did not lead to any change in the catechol signal in the rostral ventrolateral medulla (n = 5). Furthermore, controlled hypotension induced in intact rats did not evoke any change in the catechol signal recorded in a dopaminergic area of the midbrain, the ventral tegmental area (A10 area; n = 5). 5. An infusion of phenylephrine increased MAP by 35 mmHg from a baseline pressure of 105 mmHg for 30 min and evoked a non‐significant decrease in the catechol signal (n = 5). In another group of rats a lower baseline pressure (80 mmHg) was stabilized (n = 5) with a higher concentration of halothane. An identical increment in pressure was then produced by a phenylephrine infusion and led to a significant reduction in the catechol signal (P < 0.05 vs. saline under similar conditions; n = 5). 6. The new findings of this study are that the level of activity of the metabolism of catecholamine in the rostral ventrolateral medulla (i) is continuously related to the level of arterial pressure, (ii) functions close to its resting level under baseline conditions and is primarily engaged during hypotension and (iii) is baroreflex linked. 7. Given the lack of direct evidence for a link between unit activity and catechol metabolism, these changes in catechol activity, recorded continuously in vivo next to adrenergic cell bodies, may represent the biochemical‐specific counterpart of changes in the level of electrical unitary activity of presumed adrenergic cardiovascular medullospinal sympathoexcitatory neurons. Therefore, it provides evidence that adrenaline‐synthesizing neurons in the rostral ventrolateral medulla respond to baroreceptor inputs.
Effects of ryanodine on the properties of Ca2+ release from the sarcoplasmic reticulum in skinned skeletal muscle fibres of the frog.
Authors: Oyamada H , Iino M , Endo M
Published: December 2014

1. We studied the effects of ryanodine on the functions of the sarcoplasmic reticulum (SR) in skinned muscle fibres from Xenopus laevis. 2. Ryanodine treatment decreased the Ca2+ uptake capacity of the SR in a fixed Ca2+ loading condition. The extent of the decrease in the SR Ca2+ uptake capacity was closely correlated with the activity of the Ca(2+)‐induced Ca2+ release (CICR) during the ryanodine treatment. This suggests, in agreement with the previous biochemical results, that ryanodine acts on the CICR channels when they are open. 3. The rate of Ca2+ leakage from the SR increased after ryanodine treatment. However, the leakage rate constants were independent of the degree of the loss of SR Ca2+ uptake capacity by the ryanodine treatment. This is inconsistent with the notion that the SR is a single uniform compartment and that the decline in the SR Ca2+ uptake capacity is a result of the increase in the Ca2+ leakage. 4. Partial recovery of the Ca2+ uptake capacity of the ryanodine‐treated SR was observed when Ca2+ loading was carried out in the presence of 10 mM procaine. This indicates that procaine partially blocks the open‐locked channels. 5. After Ca2+ loading in the presence of procaine, removal of procaine induced a rapid release of Ca2+ from the SR through the open‐locked channels. This rapid release was dependent both on the adenine nucleotide concentration and on the Ca2+ concentration. Thus, the ‘open‐locked’ CICR channels are still regulated by Ca2+ and adenine nucleotides.
Changes in global cerebral blood flow in humans: effect on regional cerebral blood flow during a neural activation task.
Authors: Ramsay S C , Murphy K , Shea S A , Friston K J , Lammertsma A A , Clark J C , Adams L , Guz A , Frackowiak R S
Published: December 2014

1. The primary objective of this study was to examine in man, how induced changes in global cerebral blood flow (gCBF) affected a regional cerebral blood flow (rCBF) increase resulting from a neural activation task (opening of eyes). A secondary objective was to quantify how such induced changes in gCBF were distributed between representative regions of either predominantly grey matter or white matter. 2. Positron emission tomography with intravenous infusion of H2(15)O, was used to measure gCBF in six normal males. Concomitant measures of rCBF were obtained in three different regions of interest (ROI): a representative area of predominantly grey matter, a representative area of predominantly white matter and an area of visual cortex. 3. Cerebral blood flow was altered by establishing steady‐state changes in PCO2 at a near constant ventilation of approximately 30 l min‐1. The mean PET,CO2 (+/‐ S.D.) levels (mmHg) that resulted were: low, 21.8 +/‐ 1.8; normal, 39.8 +/‐ 1.0, and high, 54.8 +/‐ 1.2. The normal and high levels were obtained by adding appropriate amounts of CO2 to the inspirate. The corresponding mean gCBF levels across all six subjects with eyes closed were: low, 24.2 +/‐ 4.6; normal, 37.2 +/‐ 3.9 and high, 66.8 +/‐ 7.6 ml min‐1 dl‐1. 4. Blood flow in grey matter (insular cortex) and white matter (centrum semiovale) at normal levels of PCO2 averaged 56.8 +/‐ 10.1 and 20.3 +/‐ 3.4 ml min dl‐1 respectively. As PCO2 rose, the increase in rCBF to grey matter was approximately three times greater than that to white matter. 5. An activation state of eyes open in a brightly lit room was compared to a baseline state of eyes closed in a darkened room at the three levels of PCO2 (and hence at three levels of gCBF). Over the whole gCBF range a significant (P = 0.028) effect of increasing rCBF in the visual cortex ROI was found in response to opening the eyes; the effect of this activation on rCBF was not significantly dependent (P = 0.34) on the PCO2 (and hence gCBF) level. The effect of the activation on the rCBF was apparently ‘additive’ to the rise of rCBF associated with PCO2‐related gCBF increase. 6. The results confirm the need to normalize for changes in gCBF during studies of rCBF in response to an activation protocol. They also provide support for the use of an ‘additive’ model to achieve such normalization provided that other cortical areas behave in a similar manner to that of the visual cortex.
Ca2+ and Sr2+ entry induced Ca2+ release from the intracellular Ca2+ store in smooth muscle cells of rat portal vein.
Authors: Grégoire G , Loirand G , Pacaud P
Published: December 2014

1. Changes in cytosolic free Ca2+ concentration ([Ca2+]i) induced by membrane depolarizations were investigated using indo‐1 microspectrofluorimetry in single patch‐clamped smooth muscle cells of rat portal vein at room temperature (20‐21 degrees C) and in the presence of 2 mM Ca2+. 2. During a 1 s depolarization from ‐50 to ‐30 mV [Ca2+]i rose, but, although the Ca2+ current was terminated by repolarization to ‐50 mV, [Ca2+]i continued to increase in a regenerative manner. The delay between the end of the voltage step and the peak of the [Ca2+]i rise was reduced by increasing the depolarization. 3. When a second identical depolarization was rapidly applied (8‐13s) after the first one, it induced an identical Ca2+ current but a smaller increase in [Ca2+]i which started to decay upon repolarization. 4. A low concentration of caffeine (0.05 mM), applied to cells showing a small depolarization‐induced [Ca2+]i transient which reached a peak at the end of the voltage step, produced an increase in amplitude and in duration of the [Ca2+]i rise without changing the amplitude of the depolarization‐induced Ca2+ current. 5. The depolarization‐induced [Ca2+]i rise was shortened and reduced in amplitude after noradrenaline‐ (NA 10 microM) or caffeine‐ (5 mM) induced release of Ca2+ store and when the patch pipette solution contained ryanodine (100 microM). Under these conditions, the depolarization‐induced [Ca2+]i transient was maximal at the end of the voltage step and declined immediately when the membrane was repolarized at ‐50 mV. 6. Experiments were done by replacing extracellular Ca2+ by Sr2+. Depolarization‐induced Sr2+ entry through voltage‐dependent Ca2+ channels could evoke an increase in indo‐1 fluorescence which occurred after the termination of the voltage step. This delayed component of fluorescence increase displayed properties similar to those of the regenerative [Ca2+]i rise recorded in the Ca(2+)‐containing solution. 7. The inefficiency of the second of two successive depolarizations to produce the delayed component of [Ca2+]i rise was not due to the emptiness of the intracellular Ca2+ store since, under these conditions, caffeine was still able to induce a Ca2+ release. 8. It is concluded that depolarization‐evoked Ca2+ or Sr2+ entry through voltage‐dependent Ca2+ channels induced the release of Ca2+ from an intracellular store, which could occur in a regenerative manner, independent of the termination of the triggering current.
Sodium current‐induced calcium signals in isolated guinea‐pig ventricular myocytes.
Authors: Lipp P , Niggli E
Published: December 2014

1. Na+ current (INa)‐induced Ca2+ transients were studied in ventricular myocytes isolated from adult guinea‐pig hearts. The fluorescent Ca2+ indicator fluo‐3 or a mixture of fluo‐3 and fura‐red were used in conjunction with confocal microscopy to follow the intracellular Ca2+ concentration while membrane currents were measured simultaneously with the whole‐cell configuration of the patch‐clamp technique. 2. Ca2+ release from the sarcoplasmic reticulum (SR) could be triggered either by Ca2+ current (ICa) or Na+ current (INa). Analysis of INa‐induced Ca2+ signals at higher temporal resolution revealed a faster upstroke of these transients when compared with those triggered by ICa. 3. In the presence of 20 microM ryanodine to block SR Ca2+ release ICa elicited a verapamil‐sensitive Ca2+ transient with a slow upstroke. INa also induced a residual Ca2+ transient that was insensitive to 10 microM verapamil and characterized by a rapid upstroke. 4. The existence of a residual Ca2+ transient in the absence of SR Ca2+ release and L‐type ICa indicates that INa is indeed able to evoke an increase in [Ca2+]i without uncontrolled activation of Ca2+ channels. 5. Substitution of extracellular Na+ by Li+ suppressed INa‐induced Ca2+ transients, suggesting that the Ca2+ release and the residual Ca2+ transient can only be elicited by influx of Na+ and not by Li+. This result supports the notion that both the residual Ca2+ transient as well as the INa‐induced Ca2+ release are mediated by the Na(+)‐Ca2+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
Chemical activation of caudal medullary expiratory neurones alters the pattern of breathing in the cat.
Authors: Bongianni F , Corda M , Fontana G A , Pantaleo T
Published: December 2014

1. The purpose of this work was to ascertain whether the activation of caudal expiratory neurones located in the caudal part of the ventral respiratory group (VRG) may affect the pattern of breathing via medullary axon collaterals. 2. We used microinjections of DL‐homocysteic acid (DLH) to activate this population of neurones in pentobarbitone‐anaesthetized, vagotomized, paralysed and artificially ventilated cats. Both phrenic and abdominal nerve activities were monitored; extracellular recordings from medullary and upper cervical cord respiratory neurones were performed. 3. DLH (160 mM) microinjected (10‐30 nl for a total of 1.6‐4.8 nmol) into the caudal VRG, into sites where expiratory activity was encountered, provoked an intense and sustained activation of the expiratory motor output associated with a corresponding period of silence in phrenic nerve activity. During the progressive decline of the activation of abdominal motoneurones, rhythmic inspiratory activity resumed, displaying a decrease in frequency and a marked reduction or the complete suppression of postinspiratory activity as its most consistent features. 4. Medullary and upper cervical cord inspiratory neurones exhibited inhibitory responses consistent with those observed in phrenic nerve activity, while expiratory neurones in the caudal VRG on the side contralateral to the injection showed excitation patterns similar to those of abdominal motoneurones. On the other hand, in correspondence to expiratory motor output activation, expiratory neurones of the Bötzinger complex displayed tonic discharges whose intensity was markedly lower than the peak level of control breaths. 5. Bilateral lignocaine blockades of neural transmission at C2‐C3 affecting the expiratory and, to a varying extent, the inspiratory bulbospinal pathways as well as spinal cord transections at C2‐C3 or C1‐C2, did not suppress the inhibitory effect on inspiratory neurones of either the ipsi‐ or contralateral VRG in response to DLH microinjections into the caudal VRG. 6. The results show that neurones within the column of caudal VRG expiratory neurones promote inhibitory effects on phrenic nerve activity and resetting of the respiratory rhythm. We suggest that these effects are mediated by medullary bulbospinal expiratory neurones, which may, therefore, have a function in the control of breathing through medullary axon collaterals.
Effect of exercise intensity on potassium balance in muscle and blood of man.
Authors: Vøllestad N K , Hallén J , Sejersted O M
Published: December 2014

1. The rise of plasma [K+] during high intensity exercise is due to an initially rapid loss of K+ from the exercising muscle to the circulation. The K+ loss is primarily governed by the balance between K+ efflux rate from the muscle cells and the reuptake rate. It has been assumed that the reuptake rate is proportional to [K+] in the femoral vein ([K+]fv) during short‐lasting uphill running, but this may not hold true for other types and durations of exercise. 2. In four subjects, initial rates of increase and decay of [K+]fv at start and end of bicycle exercise were quantified by means of K(+)‐sensitive electrodes inserted into the femoral vein. Responses to exercise intensities between 90 and 440 W were examined. Both the initial rate of rise and the rate of decay of [K+]fv were linearly related to power. 3. In six subjects, exercising at 60, 85 and 110% of maximal oxygen uptake, blood was obtained from the femoral artery and vein. The veno‐arterial concentration difference for K+ across the exercising leg decayed with half‐times of about 3 min at all exercise levels and became not significantly different from zero at low powers. This fits with a good match between K+ efflux and reuptake rates at the cellular level. 4. Arterial plasma [K+] ([K+]a) rose faster with increasing exercise intensity, reaching peak values of 5.7 +/‐ 0.1, 6.0 +/‐ 0.2 and 8.0 +/‐ 0.2 mmol l‐1. [K+]a fell again over the subsequent 5 min at the lowest intensity in spite of significant loss of muscle K+. Hence, released K+ was redistributed to other compartments outside the vascular bed. 5. While K+ loss increased linearly with increasing power, [K+]a showed a curvilinear relationship. Thus redistribution of K+ is less efficient at high intensities. [K+]a correlated better with relative work load than with absolute work load. 6. Reuptake of K+ after the end of the high intensity bout of exercise caused [K+]a to fall with a half‐time of 31 s. The rate of K+ reuptake in the exercising muscle was not proportional to [K+]a or [K+]fv. However, at the level of the muscle cell, the rate of K+ reuptake was probably inversely related to intracellular [K+].
Contrasting actions of cocaine, local anaesthetic and tetrodotoxin on discharge properties of rat aortic baroreceptors.
Authors: Andresen M C , Brodwick M , Yang M
Published: December 2014

1. Effects of cocaine, lignocaine, benzocaine and tetrodotoxin (TTX) on the simultaneously measured pressure‐ and diameter‐discharge frequency relations of single fibre baroreceptors were compared in rat in vitro aortic arch‐aortic nerve preparations. 2. Between 1 and 10 microM, cocaine produced selective increases in the pressure threshold shifting the pressure‐response curve without altering the gain or threshold frequency. At near‐blocking concentrations, gain was depressed as well. Cocaine experiments were done in nitroprusside (NP, 1 microM). Neither NP or NP with cocaine altered diameter (P > 0.36). 3. Lignocaine (at > 10 microM) and benzocaine (at > 100 microM) shifted pressure‐response curves to higher pressures and generally depressed discharge by increasing pressure threshold and decreasing maximum discharge frequency (P < 0.05). Gain decreased and threshold frequency increased at higher concentrations. Diameter was unaffected by lignocaine or benzocaine (P > 0.14). 4. TTX increased thresholds and discharge frequencies at threshold but did not shift pressure‐discharge curve locations. This produced superimposable discharge curves with changes occurring as losses of discharge points in the threshold region. Diameter was unaffected by TTX (P > 0.80). 5. The contrasting patterns of effects between TTX and local anaesthetics suggest that blockade of TTX‐sensitive sodium channels alone may not be responsible for the effects of cocaine, lignocaine and benzocaine.
Cardiovascular and respiratory effects of stimulation of cell bodies of the parabrachial nuclei in the anaesthetized rat.
Authors: Lara J P , Parkes M J , Silva-Carvhalo L , Izzo P , Dawid‐Milner M S , Spyer K M
Published: December 2014

1. In order to assess the importance of the parabrachial nuclei in modulating cardiorespiratory activity, electric current or microinjections of glutamate were used to stimulate discrete regions of the parabrachial nuclei in anaesthetized rats. 2. Stimulation of cell bodies in the medial region of the parabrachial nuclei and in the Kölliker‐Fuse nuclei, caused an expiratory facilitatory response. This consisted mainly of a decrease in respiratory rate as measured by observing phrenic nerve activity. 3. Stimulation of cell bodies in the lateral region of the parabrachial nuclei caused an inspiratory facilitatory response. This consisted mainly of an increase in respiratory rate. 4. At the majority of sites (16 out of 20) where changes in respiratory rate were elicited by glutamate injection or electrical stimulation an increase in blood pressure was observed. The coexistence of increases in blood pressure and heart rate indicates the presence of inhibition of the heart rate component of the baroreflex and/or an increase in cardiac sympathetic drive. 5. The expiratory facilitatory response was not evoked reflexly by the rise in blood pressure since it was still present after administration of guanethidine, which abolished the rise in blood pressure. 6. The interactions between the parabrachial nuclei and the medullary respiratory complex in eliciting these changes are discussed.
Endogenous H+ modulation of NMDA receptor‐mediated EPSCs revealed by carbonic anhydrase inhibition in rat hippocampus.
Authors: Gottfried J A , Chesler M
Published: December 2014

1. The occurrence of extracellular alkaline transients during excitatory synaptic transmission suggests that the NMDA receptor H(+)‐modulatory site may have a physiological role. Here we amplify these pH shifts using benzolamide (a carbonic anhydrase inhibitor) and describe concomitant effects on EPSCs in whole‐cell clamped CA1 neurones in rat hippocampal slices. 2. In CO2‐HCO3(‐)‐buffered media, benzolamide increased the time to 50% decay (t50) of the EPSCs by 78 +/‐ 14% (P < 0.01, n = 10). This occurred simultaneously with amplification of the extracellular alkaline shift (154 +/‐ 14%). 3. In CO2‐HCO3(‐)‐buffered media containing DL‐2‐amino‐5‐phosphonovalerate (APV), the EPSC t50 was unaltered by benzolamide, while the extracellular alkaline shifts were increased (111 +/‐ 23%, n = 8). 4. In Hepes‐buffered media, neither the EPSC t50 nor the extracellular alkaline shift was altered by benzolamide (n = 9). 5. These data demonstrate that NMDA receptor activity is dependent on the buffering kinetics of the brain extracellular space. The results suggest that endogenous pH shifts can modulate NMDA receptor function in a physiologically relevant time frame.
K(+)‐aggravated myotonia: destabilization of the inactivated state of the human muscle Na+ channel by the V1589M mutation.
Authors: Mitrovié N , George A L , Heine R , Wagner S , Pika U , Hartlaub U , Zhou M , Lerche H , Fahlke C , Lehmann‐Horn F
Published: December 2014

1. Wild type (WT) and V1589M channels were expressed in human embryonic kidney (HEK293) cells for the study of the pathophysiology of the V1589M muscle Na+ channel mutation leading to K(+)‐aggravated myotonia. 2. In comparison to WT, whole‐cell recordings with V1589M channels showed an increased Na+ steady‐state to peak current ratio (Iss/Ipeak) (3.15 +/‐ 0.70 vs. 0.87 +/‐ 0.10%, at ‐15 mV) and a significantly faster recovery from inactivation. The recovery time constants, tau r1 and tau r2, were decreased from 1.28 +/‐ 0.12 to 0.92 +/‐ 0.08 ms and from 4.74 +/‐ 0.94 to 2.66 +/‐ 0.51 ms for the WT and mutant channels, respectively. 3. Single‐channel recordings with mutant channels showed higher probability of short isolated late openings (0.40 +/‐ 0.09 vs. 0.06 +/‐ 0.02, at ‐30 mV) and bursts of late openings (0.011 +/‐ 0.003 vs. 0.003 +/‐ 0.001, at ‐30 mV) compared to WT. 4. These results suggest that the mutation increases the probabilities for channel transitions from the inactivated to the closed and the opened states. 5. Increased extracellular concentrations of K+ had no effects on either V1589M or WT currents in HEK293 cells. The aggravation of myotonia seen in patients during increased serum K+ may arise from the associated membrane depolarization which favours the occurrence of late openings in the mutant channel.
Synaptic potentiation of dual‐component excitatory postsynaptic currents in the rat hippocampus.
Authors: Clark K A , Collingridge G L
Published: December 2014

1. Whole‐cell patch‐clamp recording has been used to study tetanus‐induced synaptic potentiation of dual‐component excitatory postsynaptic currents (EPSCs) in the CA1 region of rat hippocampal slices, following blockade of GABAA and GABAB receptor‐mediated synaptic inhibition. 2. At a holding potential of ‐60 mV, the initial slope of the EPSC (between 10 and 60% of maximum amplitude) provided an accurate measurement of the AMPA receptor‐mediated component, and the amplitude of the EPSC at a latency of 100 ms provided the best estimate of the size of the NMDA receptor‐mediated component. 3. Neurons were voltage clamped for at least 45 min prior to delivery of a tetanus (test intensity, 100 Hz, 1 s). Measurements at 10 and 30 min following the tetanus were used as indications of short‐term potentiation (STP) and long‐term potentiation (LTP), respectively. One set of neurons were voltage clamped at ‐60 mV throughout. These neurons could be subdivided into two populations on the basis of whether or not there was LTP (n = 9), or only STP (n = 6), of the AMPA receptor‐mediated component. A second set of neurons were voltage clamped at ‐60 mV for 30 min and then at ‐50 mV for 15 min before, during and for 30 min following tetanization. In these experiments there was STP but not LTP (n = 8). 4. In all neurons (n = 23), the time course of the potentiation of the NMDA receptor‐mediated component paralleled that of the AMPA receptor‐mediated component. In addition, potentiation of the NMDA and AMPA receptor‐mediated components were of a similar magnitude. 5. These data demonstrate that it is possible to induce LTP by high frequency stimulation after 45 min of whole‐cell recording. Under these conditions, there is a parallel potentiation of the AMPA and NMDA receptor‐mediated components of dual‐component EPSCs. This constitutes the first evidence, from studies of dual‐component synaptic responses, which is consistent with a presynaptic locus of expression of tetanus‐induced STP and LTP in the hippocampus.
Ca2+ influx during agonist and Ins(2,4,5)P3‐evoked Ca2+ oscillations in HeLa epithelial cells.
Authors: Thorn P
Published: December 2014

1. Histamine‐stimulated [Ca2+]i oscillations were studied in > 162 HeLa cells using the techniques of Ca2+ imaging, patch clamp and single‐cell indo‐1 fluorescence. 2. [Ca2+]i oscillations in HeLa cells were acutely dependent on extracellular Ca2+ and were also blocked by the extracellular addition of Cd2+ (100 microM). The Mn2+ quench technique, using fura‐2 fluorescence, demonstrated that agonist‐stimulated Ca2+ oscillations were associated with an increase in plasma membrane Mn2+ permeability. However, no cyclic fluctuations in Mn2+ influx were resolved over the period of [Ca2+]i spiking. 3. In whole‐cell patch clamped cells an imposed potential of +80 mV was shown to block the thapsigargin‐induced Ca2+ influx. Histamine and Ins(2,4,5)P3‐induced [Ca2+]i oscillations were tested for the phase dependence on extracellular Ca2+ by rapidly switching the membrane potential to +80 mV, reversibly blocking Ca2+ influx. Ca2+ spikes were abolished by steps to +80 mV made at the point of spike initiation but not by steps made after development of the rapid rising phase of the spike. Steps of membrane potential to +80 mV, for increasing periods of time during the interspike period, increased the latency to the next [Ca2+]i spike by up to a maximum of approximately 150% of the control interspike interval. 4. It is concluded that the extracellular Ca2+ dependence of the histamine‐induced [Ca2+]i oscillations is due to a crucial role of Ca2+ influx during spike initiation and an additional important role in setting the interspike interval. The results obtained can be interpreted in terms of a constant stimulated Ca2+ influx during [Ca2+]i spiking.
The electrophysiological properties of rat primary afferent neurones with carbonic anhydrase activity.
Authors: Prabhakar E , Lawson S N
Published: December 2014

1. Intracellular recordings of action potentials (APs) and after‐hyperpolarizations (AHPs) were made from the L3, L4 and L5 dorsal root ganglia (DRGs) of 6‐ to 8‐week‐old anaesthetized female Wistar rats in vitro at 36.5 +/‐ 1 degree C. Neurones were classified by their conduction velocities (CVs) as A alpha/beta (> 12 m s‐1), A delta (1.3‐12 m s‐1) or C fibre neurones (< 1.3 m s‐1). 2. Following the recording, fluorescent dye was injected intracellularly. Sections of injected neurones were tested for carbonic anhydrase (CA) activity histochemically. Reaction product intensity and cell size were measured. Control experiments showed that intracellular dye, time in vitro, axotomy and electrical stimulation did not affect proportions of CA‐positive neurones or their size distributions. 3. Approximately 28‐30% of DRG neurones were CA positive. Their sizes were approximately normally distributed and covered the entire size range of DRG neurones with no correlation between size and CA intensity. A greater proportion of A alpha/beta cells (62%) than of A delta (32%) or C cells (38%) were CA positive, but CA intensity was not correlated with CV. 4. In A neurones mean AP duration was significantly shorter in CA‐positive cells; for CA‐positive and CA‐negative cells, respectively, these values were 1.6 and 2.8 ms for A delta cells; 1.1 and 1.7 ms for A alpha/beta cells; and were 1.2 and 2.3 ms for all A cells. CA intensity was negatively correlated with AP duration at base in all these groups. 5. Again in A neurones, the mean AHP durations were significantly shorter in the CA‐positive cells; the mean AHP durations to 80% recovery for positive and negative cells were 8.8 and 36 ms, respectively, for A alpha/beta cells and were 8.6 and 26 ms, respectively, for all A cells. CA intensity was negatively correlated with AHP duration in A alpha/beta cells and all A cells together. 6. A fibre cells with the longer AP and AHP durations were all CA negative, while cells with the shorter durations included both CA‐positive and CA‐negative cells. 7. CA‐positive and CA‐negative A fibre neurones therefore have different electrophysiological characteristics. It is suggested that CA‐negative A fibre neurones may have slower somatic firing rates and different sensory functions from the CA‐positive neurones.
Action potential propagation and propagation block by GABA in rat posterior pituitary nerve terminals.
Authors: Jackson M B , Zhang S J
Published: December 2014

1. A theoretical model was developed to investigate action potential propagation in posterior pituitary nerve terminals. This model was then used to evaluate the efficacy of depolarizing and shunting GABA responses on action potential propagation. 2. Experimental data obtained from the posterior pituitary with patch clamp techniques were used to derive empirical expressions for the voltage and time dependence of the nerve terminal Na+ and K+ channels. The essential structure employed here was based on anatomical and cable data from the posterior pituitary, and consisted of a long cylindrical axon (diameter, 0.5 mm) with a large spherical swelling (diameter, 4‐21 mm) in the middle. 3. In the absence of an inhibitory conductance, simulated action potentials propagated with high fidelity through the nerve terminal. Swellings could block propagation, but only when sizes exceeded those observed in the posterior pituitary. Adding axonal branches reduced the critical size only slightly. These results suggested that action potentials invade the entire posterior pituitary nerve terminal in the absence of inhibition or depression. 4. The addition of inhibitory conductance to a swelling caused simulated action potentials to fail at the swelling. Depolarizing inhibitory conductances were 1.6 times more effective than shunting inhibitory conductances in blocking propagation. 5. Inhibitory conductances within the range of experimentally observed magnitudes and localized to swellings in the observed range of sizes were too weak to block simulated action potentials. However, twofold enhancement of GABA responses by neurosteroid resulted in currents strong enough to block propagation in realistic swelling sizes. 6. GABA could block simulated propagation without neurosteroid enhancement provided that GABA was present throughout a region in the order of a few hundred micrometres. For this widespread inhibition depolarizing conductance was 2.2 times more effective than shunting conductance. 7. These results imply two modes of propagation block, one resulting from highly localized release of inhibitory transmitter under conditions potentiating GABA responses, and the other resulting from widespread release of GABA in the absence of receptor potentiation. 8. The Na+ channels of the posterior pituitary nerve terminal have a unique voltage dependence that allows small depolarizations to inactivate without causing activation. The voltage dependence of this Na+ channel may serve as a specialized adaptation that facilitates in allowing small depolarizing conductances to block action potential propagation.
Synaptic and membrane mechanisms underlying synchronized oscillations in the ferret lateral geniculate nucleus in vitro.
Authors: Bal T , von Krosigk M , McCormick D A
Published: December 2014

1. The cellular basis for generation of spindle waves and a slower synchronized oscillation resembling absence seizures was investigated with extracellular and intracellular recording techniques in slices of ferret dorsal lateral geniculate nucleus (LGNd) maintained in vitro. 2. Intracellular recording from LGNd relay cells in vitro revealed that spindle waves occurred once every 3‐30 s and were associated with barrages of inhibitory postsynaptic potentials (IPSPs) occurring at a frequency of 6‐10 Hz. These IPSPs resulted in the generation of rebound low threshold Ca2+ spikes at 2‐4 Hz, owing to the intrinsic propensity of LGNd relay cells to generate oscillatory burst firing in this frequency range. These rebound bursts of action potentials were highly synchronized with local multiunit and single unit activity. 3. The spindle wave‐associated IPSPs in LGNd relay cells exhibited a mean reversal potential of ‐86 mV. This reversal potential was shifted to more depolarized membrane potentials with the intracellular injection of Cl‐ through the use of KCl‐filled microelectrodes. Simultaneous recording from the perigeniculate nucleus (PGN) and LGNd revealed the IPSPs to be synchronous with the occurrence of burst firing in the PGN. Excitation of PGN neurons with local electrical stimulation after pharmacological block of excitatory amino acid transmission resulted in bicuculline‐sensitive IPSPs in relay neurons similar in amplitude and time course to those occurring during spindle waves. 4. Application of (‐)‐bicuculline methiodide resulted in the abolition of spindle wave‐associated IPSPs or in the slowing of the rate of rise, an increase in amplitude and a prolongation of these IPSPs; this resulted in a synchronized 2‐4 Hz oscillation, in which each relay cell strongly burst on nearly every cycle, thus forming a paroxysmal event. Bath application of the GABAB receptor antagonist 2‐OH‐saclofen blocked these slowed oscillations, indicating that they are mediated by the activation of GABAB receptors. In contrast, pharmacological antagonism of GABAB receptors did not block the generation of normal spindle waves. 5. These and other results indicate that spindle waves are generated in the ferret LGNd in vitro as a network phenomenon occurring through an interaction between the relay cells of the LGNd and the GABAergic neurons of the PGN. We propose that burst firing in PGN cells hyperpolarizes relay neurons through activation of GABAA receptors. These IPSPs result in rebound burst firing in LGNd cells, which then excite PGN neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Heterogeneity of neuronal nicotinic acetylcholine receptors in thin slices of rat medial habenula.
Authors: Connolly J G , Gibb A J , Colquhoun D
Published: December 2014

1. Neuronal nicotinic acetylcholine receptors in slices of rat medial habenula were studied using patch clamp recording techniques. 2. Whole cell current responses to cytisine could be blocked by hexamethonium, as expected for nicotinic receptors. The whole cell current‐voltage relations were linear at negative membrane potentials, but showed strong inward rectification when chloride currents were minimized. 3. When 1 mM Ca2+ (0 mM Mg2+) was present in the external recording solution, the single channel conductances elicited by acetylcholine or nicotine in twenty patches were in the range 39‐58 pS, with a mean of 47 pS. There appeared to be at least two groups of conductances. 4. In the open point amplitude distributions of three patches, the most common amplitude corresponded to 41 pS (81% of the area). In another four patches the most common amplitude corresponded to a mean conductance of 51 pS (83% of the area). Direct transitions between open levels were rare. 5. Channel closed times were not significantly different for the two conductance groups. However, for the four patches with predominantly 51 pS openings, the means of the distributions of open times longer than two filter rise times averaged 5.8 ms. Those patches with predominantly 41 pS openings averaged 14 ms. Also, for patches with predominantly 51 pS openings the overall mean burst length was 5.8 ms, whereas for patches with predominantly 41 pS openings it was 16.1 ms. 6. These observations suggest that 51 and 41 pS openings result from the activity of at least two, but possibly more, different receptor subtypes. We conclude that nicotinic receptors in the rat ventral medial habenula are heterogeneous.