bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of heparin on excitation‐contraction coupling in skeletal muscle toad and rat.
Authors: Lamb G D , Posterino G S , Stephenson D G
Published: December 2014

1. Intracellularly applied heparin was found to cause a novel, use‐dependent block of excitation‐contraction (E‐C) coupling in skinned skeletal muscle fibres of the toad. After one to four depolarizations in the presence of 100 micrograms ml‐1 heparin, no further depolarization‐induced responses could be elicited, even though addition of caffeine or lowering [Mg2+] could still induce massive Ca2+ release. This effect could not be reversed by extensive wash‐out of the heparin (> 15 min). 2. Heparin (100 micrograms ml‐1) did not abolish subsequent depolarization‐induced responses if applied while the voltage sensors were in either their resting or inactivated states, that is (a) while a fibre remained fully polarized, (b) when a fibre was already chronically depolarized or (c) after a fibre had been depolarized in the presence of D600 (gallopamil) and then repolarized. 3. When a toad fibre was depolarized in heparin, with the associated Ca2+ release blocked by the presence of 10 mM intracellular Mg2+, subsequent E‐C coupling was abolished. Heparin did not interrupt E‐C coupling when Ca2+ release was triggered in the absence of any depolarization, by either caffeine or low [Mg2+]. Thus, the opening of the Ca2+ release channels was neither necessary nor sufficient for heparin to abolish E‐C coupling. 4. Heparin had direct effects on the contractile apparatus in toad fibres, increasing the Ca2+ sensitivity and decreasing the maximum Ca(2+)‐activated force. These effects could only be partly reversed by extensive wash‐out of heparin. 5. At 100 micrograms ml‐1, both low molecular weight heparin and pentosanpolysulphate, another highly sulphated polysaccharide, were less effective than heparin in blocking the depolarization‐induced response and in changing the properties of the contractile apparatus, and these effects could be substantially reversed by wash‐out. Two other polyanions, de‐N‐sulphated heparin (100 micrograms ml‐1), which lacked N‐sulphate groups, and polyglutamate (500 micrograms ml‐1), had no measurable effect on either E‐C coupling or the contractile apparatus. 6. In skinned fibres of the extensor digitorum longus muscle of the rat, 100 micrograms ml‐1 heparin had little or no effect on E‐C coupling and on the Ca2+ sensitivity of the contractile apparatus, but caused a larger reduction of the maximum Ca(2+)‐activated force than in skinned fibres of the toad. 7. These results indicate that heparin blocks E‐C coupling in toad muscle if, and only if, it is present when the voltage sensors are activated by depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
Spatial relations of flicker signals in the two rod pathways in man.
Authors: Sharpe L T , Hofmeister J , Fach C C , Stockman A
Published: December 2014

1. Flicker signals originating from the human rod photoreceptors seem to have access to two retinal pathways: one slow and sensitive, the other fast and insensitive. The phase lag between signals in the two pathways grows monotonically with frequency, reaching 180 deg near 15 Hz. 2. At 15 Hz, destructive interference between the slow and the fast signals can cause two related phenomena: (i) a suprathreshold intensity region‐‐the perceptual null‐‐within which the perception of flicker vanishes, and (ii) a double branching of the 15 Hz rod‐detected flicker threshold versus intensity (TVI) curve. 3. Here we investigate the effect of changing target size on these phenomena in normal human observers. We find that the double‐branched flicker TVI curve and the perceptual null are found for all targets larger than 2 deg in diameter. For smaller diameter targets, however, neither the lower branch of the double‐branched flicker TVI curve nor the null are found. 4. While this might suggest that the slow rod signals are selectively disadvantaged by the use of small targets, phase measurements relative to a cone standard reveal that the slow signals are always present. For targets < or = 2 deg in diameter, however, they remain below detection threshold because of destructive interference with the fast rod signals. Thus, for small targets, the perceptual null is not absent, but has merged with (and therefore obliterated) the lower branch of the double‐branched flicker TVI function. 5. This situation could arise if decreasing the target size causes a parallel reduction in the sensitivities of both pathways, rather than a selective reduction in the sensitivity of either one. Our findings are therefore consistent with a model in which the large‐scale spatial organization of the two rod pathways is roughly similar.
Pulsatile secretion of oxytocin during parturition in the pig: temporal relationship with fetal expulsion.
Authors: Gilbert C L , Goode J A , McGrath T J
Published: December 2014

1. To assess changes in oxytocin release as they occur in relation to the rapid progress of events at fetal expulsion, continuous automated blood withdrawals (3 ml min‐1) from an indwelling jugular catheter and intramammary pressure recordings were obtained from nine primiparous pigs (190‐220 kg). Data were acquired over 16 h of normal parturition, during which thirty‐five piglets were born. 2. Oxytocin secretion during parturition, when measured by radioimmunoassay (RIA) in blood collected and pooled every minute, showed a baseline secretion (19.8‐88.37 pg ml‐1) that was raised relative to preterm values. Analysis of individual secretion profiles revealed significant fluctuations or peaks of concentration superimposed on this baseline, with a slow periodicity of 4‐12 min. These substantial peaks in secretion were not temporally related to fetal expulsion or visible abdominal contractions. 3. A small (13%) but significant increase in plasma oxytocin was also seen when assay data from the minutes coinciding with a birth were meaned and compared with the following minutes. This rise did not persist into further minutes. 4. Intramammary pressure recordings revealed a highly repeatable and characteristic phenomenon in that fetal expulsion was followed after 33.74 +/‐ 1.31 s (mean +/‐ S.E.M. time from emergence of fetus to peak pressure rise) in thirty‐three of thirty‐five instances by a distinctive and rapid bolus release of oxytocin. These ‘postpartum oxytocin pulses’ could be closely mimicked by injections of exogenous oxytocin (0.03‐1.0 ng kg‐1; lag time from jugular injection to peak pressure rise, 20.44 +/‐ 0.99 s). The timing of this event coincided with the small postpartum pulse measurable by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)
Magnetic stimulation of ferret papillary muscle.
Authors: Weidmann S
Published: December 2014

1. Ferret papillary muscles were magnetically stimulated by the discharge of a capacitor through an inductance. 2. An induced current density of 39 mA cm‐2 averaged over 280 microseconds (= 11 microC cm‐2) corresponded to threshold. 3. A short galvanic current pulse was found to have a comparable charge threshold. 4. The time‐varying magnetic field or the magnetically induced electrical field did not result in excitation unless current was allowed to flow. 5. Threshold conditions could be reached by adding subthreshold magnetically induced current to subthreshold galvanic current. A suprathreshold galvanic current could be prevented from exciting by simultaneously applying induced current of opposite direction. 6. It is concluded that outward current through the membrane capacity is the stimulus, independent of the origin of the current.
Contractile properties and temperature sensitivity of the extraocular muscles, the levator and superior rectus, of the rabbit.
Authors: Frueh B R , Hayes A , Lynch G S , Williams D A
Published: December 2014

1. Contractile and fatigue‐resistance characteristics, temperature sensitivity (10‐37 degrees C) of contraction, and histochemical fibre types were determined for two of the extraocular muscles, the superior rectus and levator palpebrae superioris (levator), of the rabbit. 2. The levator displayed similar contractile characteristics (time to peak, half‐relaxation time of twitch response, and twitch‐tetanus force ratio) to mammalian fast‐twitch limb muscle at room temperature (20 degrees C). However, normalized twitch and tetanic force levels were significantly less than those found in limb muscle. The superior rectus displayed the characteristics of even faster contraction than the levator at 20 degrees C, but generated lower maximum force levels than the levator. 3. The twitch response of the superior rectus showed a biphasic relaxation phase. This response was not due to non‐twitch (tonic) fibres present in the superior rectus as it was unaffected by propranolol application during muscle stimulation. 4. The superior rectus and levator displayed significantly less fatigue in the tetanic force response than fast‐twitch limb muscles did in response to a fatiguing electrical stimulation protocol. The levator was significantly more fatigue resistant than the superior rectus. 5. The force responses of both extraocular muscles displayed a similar dependence on temperature (10‐37 degrees C) to limb skeletal muscles. 6. The superior rectus and levator exhibited a high proportion of fast‐twitch muscle fibres (type II) as shown by myosin ATPase staining. Succinate dehydrogenase activity indicated that these muscles showed a high oxidative capacity, with a staining intensity typical of type I or type II A fibres of limb muscles. 7. The results emphasize the morphological and functional complexity of mammalian extraocular muscles. The combination of very fast contractile properties with high oxidative capacity make these muscles well suited to their role in eye/eyelid movement.
Outwardly rectifying chloride current in rabbit osteoclasts is activated by hyposmotic stimulation.
Authors: Kelly M E , Dixon S J , Sims S M
Published: December 2014

1. We characterized chloride currents in freshly isolated rabbit osteoclasts using whole‐cell and single channel patch‐clamp recording configurations. Depolarization activated an outwardly rectifying current in 40‐50% of cells, distinct from the inwardly rectifying K+ current we have previously reported in osteoclasts. 2. The outwardly rectifying current persisted under conditions where all K+ currents were blocked. Furthermore, the outward current was reversibly inhibited by Cl‐ transport blockers 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS); 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS); 4,4'‐dinitrostilbene‐2,2'‐disulphonic acid (DNDS); and niflumic acid. The blocked current had a reversal potential close to the predicted chloride equilibrium potential and was dependent on the chloride concentration gradient. 3. In those osteoclasts in which outwardly rectifying current was not initially apparent, exposure to hyposmotic extracellular solution resulted in its reversible activation. The induced current was due to Cl‐, based on its reversal close to the chloride equilibrium potential and sensitivity to blockade by Cl‐ channel inhibitors. The hyposmotically induced current could be activated in Ca(2+)‐free solutions containing 0.2 mM EGTA. 4. When studied in the current‐clamp configuration, hyposmotic stimulation caused depolarization from ‐76 +/‐ 5 to ‐5 +/‐ 6 mV (mean +/‐ S.D., n = 7). 5. Unitary Cl‐ currents were recorded in the cell‐attached patch configuration at positive potentials. Single channels had a slope conductance of 19 +/‐ 3 pS (n = 5). Reduction of the external [Cl‐] shifted the current‐voltage relationship in the positive direction, supporting the conclusion that these were Cl‐ currents. Like the whole‐cell currents, single channel Cl‐ currents were activated by exposure of cells to hyposmotic bathing solution. 6. We conclude that rabbit osteoclasts express an outwardly rectifying Cl‐ current that can be activated by osmotic stress. Cl‐ channels may play a role in cell volume regulation and may also provide conductive pathways for dissipating the potential difference that arises from electrogenic proton transport during bone resorption.
K+ and Cl‐ transport mechanisms in bovine pigment epithelium that could modulate subretinal space volume and composition.
Authors: Bialek S , Miller S S
Published: December 2014

1. Conventional and ion‐selective double‐barrelled microelectrodes were used in an in vitro bovine retinal pigment epithelium (RPE)‐choroid preparation to measure the changes in membrane voltage, resistance and intracellular K+ and Cl‐ activities produced by small, physiological changes in extracellular potassium ([K+]o). 2. In the intact eye, light‐induced changes in [K+]o occur in the extracellular (or subretinal) space that separates the neural retina and the RPE apical membrane. These [K+]o changes can be approximated in vitro by decreasing apical bath [K+]o from 5 to 2 mM. 3. This in vitro change in [K+]o simultaneously decreased intracellular Cl‐ and K+ activities (aCli and aKi) by 25 +/‐ 6 mM (n = 8) and 19 +/‐ 7 mM (n = 4) (mean +/‐ S.D.), respectively. In control Ringer solution (5 mM [K+]o) aCli and aKi were 65 +/‐ 10 mM (n = 28) and 65 +/‐ 8 mM (n = 6), respectively. 4. The [K+]o‐induced decreases in aCli and aKi were both significantly inhibited, either by blocking the apical membrane K+ conductance with Ba2+ or the basolateral membrane Cl‐ conductance with DIDS (4,4'‐diisothiocyano‐stilbene‐2,2'‐disulphonic acid). 5. Transepithelial current pulses were used to determine the relative basolateral membrane Cl‐ conductance, TClBAS, was approximately 0.6 (n = 3), and the relative apical membrane K+ conductance, TKAP, was approximately 0.7 (n = 2). Step changes in basal bath [K+]o were used to estimate the relative basolateral membrane K+ conductance, TKBAS, was approximately 0.34 (n = 3). 6. These data show that the apical membrane K+ conductance and the basolateral membrane Cl‐ conductance are electrically coupled. In vivo, this coupling could have significant functional importance by modulating the relative hydration of the subretinal space, regulating RPE cell volume, and buffering the chemical composition of the subretinal space.
Interneurones in pathways from group II muscle afferents in sacral segments of the feline spinal cord.
Authors: Jankowska E , Riddell J S
Published: December 2014

1. Properties of dorsal horn interneurones that process information from group II muscle afferents in the sacral segments of the spinal cord have been investigated in the cat using both intracellular and extracellular recording. 2. The interneurones were excited by group II muscle afferents and cutaneous afferents but not by group I muscle afferents. They were most effectively excited by group II afferents of the posterior biceps, semitendinosus, triceps surae and quadriceps muscle nerves and by cutaneous afferents running in the cutaneous femoris, pudendal and sural nerves. The earliest synaptic actions were evoked monosynaptically and were very tightly locked to the stimuli. 3. EPSPs evoked monosynaptically by group II muscle afferents and cutaneous afferents of the most effective nerves were often cut short by disynaptic IPSPs. As a consequence of this negative feedback the EPSPs gave rise to single or double spike potentials and only a minority of interneurones responded with repetitive discharges. However, the neurones that did respond repetitively did so at a very high frequency of discharges (0.8‐1.2 ms intervals between the first 2‐3 spikes). 4. Sacral dorsal horn group II interneurones do not appear to act directly upon motoneurones because: (i) these interneurones are located outside the area within which last order interneurones have previously been found and (ii) the latencies of PSPs evoked in motoneurones by stimulation of the posterior biceps and semitendinosus, cutaneous femoris and pudendal nerves (i.e. the main nerves providing input to sacral interneurones) are compatible with a tri‐ but not with a disynaptic coupling. Spatial facilitation of EPSPs and IPSPs following synchronous stimulation of group II and cutaneous afferents of these nerves shows, however, that sacral interneurones may induce excitation or inhibition of motoneurones via other interneurones. 5. Comparison of the properties of group II interneurones in the sacral segments with those of previously studied group II interneurones in the midlumbar segments leads to the conclusion that these two populations of neurones are specialized for the processing of information from different muscles and skin areas. In addition, equivalents of only one of the two subpopulations of midlumbar interneurones have been found at the level of the pudendal nucleus: neurones with input from group II but not from group I muscle afferents. Neurones integrating information from group I and II muscle afferents and in direct contact with motoneurones thus seem to be scarce in the sacral segments.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium‐activated potassium channels in goldfish hair cells.
Authors: Sugihara I
Published: December 2014

1. Characteristics of Ca(2+)‐activated K+ channels in the basolateral membrane of hair cells isolated from the caudal part of the goldfish saccular macula were studied mainly with the inside‐out mode of the patch clamp method. 2. Several types of Ca(2+)‐activated K+ channels differing in unitary conductance were identified. The conductances (n = 156) ranged from 130 to 320 pS (when measured in symmetrical 125 mM KCl) and could be roughly separated into four groups, centred on values of 150, 200, 250 and 300 pS. The pharmacological profile, assessed by, for example, tetraethylammonium blockade, and the relatively large conductance indicated that these channels can be classified as large‐conductance Ca(2+)‐activated K+ channels (BK channels). The relative permeability of these channels to different ion species was in the order K+ (1.0) > Rb+ (0.8) > NH4+ (0.14) > Na+, Cs+ (< 0.05). 3. Curves relating open state probability to [Ca2+]i, for membrane potentials between ‐50 and +50 mV, were similar to those observed for BK channels of rat muscle. However, the maximum open state probability (100‐1000 microM [Ca2+]i and 50 mV membrane potential) was 0.4‐0.9, and always less than 1. 4. These channels had a short arithmetic mean open time ranging from 0.08 to 1.2 ms (0.08‐0.5 ms in 88% of cases) and an arithmetic mean shut time ranging from 0.24 to 1.2 ms (10 microM [Ca2+]i and 50 mV membrane potential). The shut intervals were more sensitive to changes in [Ca2+]i and membrane potential than were the open intervals. 5. The distribution of individual open and shut intervals was fitted with the sum of exponential functions. Except for the slowest shut component, which only accounted for less than 1% of shut events, all other components had time constants shorter than 1 ms. As a result of these short open and shut intervals, the current trace had a flickery pattern rather than a burst‐interburst pattern. 6. There was a rough correlation between unitary conductance and mean open time, i.e. channels with a large unitary conductance had a longer mean open time. 7. The sensitivity to [Ca2+]i of the Ca(2+)‐activated K+ channel in goldfish hair cells was one to two orders of magnitude lower than that of BK channels in rat muscle. Channels with a longer mean open time had a higher Ca2+ sensitivity. 8. The stability of the single Ca(2+)‐activated K+ channel kinetics was studied by measuring the ‘moving’ mean duration of open and shut intervals.(ABSTRACT TRUNCATED AT 400 WORDS)
Inactivation of outward Na(+)‐Ca2+ exchange current in guinea‐pig ventricular myocytes.
Authors: Matsuoka S , Hilgemann D W
Published: December 2014

1. Outward Na(+)‐Ca2+ exchange currents were measured in freshly dissociated guinea‐pig myocytes to probe in intact cells the functional status of exchanger inactivation reactions, described previously in giant excised cardiac membranes patches. 2. When the cytoplasmic (pipette) solution contained 40 mM Na+ and 0.1 microM free Ca2+ (50 mM EGTA), the outward exchange current activated by extracellular Ca2+ decayed with time (time constant, 13.1 +/‐ 2.6 s; n = 6), and an inward current transient was observed upon removal of extracellular Ca2+. Both the current decay and the subsequent inward current transient were remarkably diminished with a saturating (100 mM) pipette Na+ concentration. 3. With 100 mM cytoplasmic Na+ and 140 mM extracellular Na+, a significant fraction of the exchanger population is predicted to be in an inactive state. Intracellular application of 2 mg ml‐1 chymotrypsin and 5 microM sodium tetradecylsulphate, both of which decrease Na(+)‐dependent inactivation in giant membrane patches, increased the outward exchange current by about 160‐170%, suggesting that about 60‐70% of exchangers might be inactivated. 4. With 100 mM cytoplasmic Na+ and no extracellular Na+ (replaced with 140 mM Li+), application of extracellular Ca+ was predicted to reorient exchanger binding sites from the extracellular side to the cytoplasmic side and thereby favour inactivation. During such protocols, the outward exchange current decayed by 60‐80% when activated by extracellular Ca2+. The current decayed similarly when extracellular Ca2+ and Na+ were applied together, whereby current magnitudes were about 3‐fold smaller. 5. The decay of outward exchange current usually followed a biexponential time course (5.8 +/‐ 3.5 and 27.3 +/‐ 16.3 s, means +/‐ S.D., n = 11). Intracellular application of 0.5‐2 mg ml‐1 trypsin attenuated the fast component more than the slow component, suggesting that the fast component reflects an inactivation process. 6. Current‐voltage (I‐V) relations of the outward exchange current became less steep during the inactivation protocols, but this flattening could not be correlated with inactivation. 7. Replacement of extracellular Li+ with N‐methyl‐D‐glucamine (NMG), tetraethylammonium (TEA), sucrose or Cs+ resulted in a flattening of I‐V relations and a decrease of the outward exchange current amplitude by approximately 3‐fold, but the kinetics and extent of inactivation were not remarkably changed. Thus, the mechanism of inactivation appears to be independent of the mechanism(s) of activation by extracellular monovalent cations.(ABSTRACT TRUNCATED AT 400 WORDS)
Dynamics of circus movement re‐entry across canine Purkinje fibre‐muscle junctions.
Authors: Gilmour R F , Watanabe M
Published: December 2014

1. To determine the cellular electrophysiological mechanisms for unidirectional conduction block and re‐entrant excitation, single cycles of circus movement re‐entry were induced in canine Purkinje fibre‐papillary muscle preparations containing two Purkinje fibre‐muscle junctions (PMJs). The preparations were mounted in a partitioned tissue bath that permitted independent superfusion of each PMJ. The pre‐existing dispersion of refractoriness between PMJs was accentuated by superfusing PMJ1 with normal Tyrode solution or Tyrode solution containing 6‐8 mM KCl and superfusing PMJ2 with Tyrode solution containing 0.5 mM heptanol and 4‐10 mM KCl. 2. Premature stimuli delivered to the Purkinje fibre induced unidirectional anterograde conduction block at PMJ2. Conduction proceeded from Purkinje cells to papillary muscle at PMJ1 and from papillary muscle retrogradely across the previously blocked PMJ2. 3. The difference in refractory periods between the two PMJs defined a range of premature coupling intervals within which re‐entry was inducible. Conduction block at the PMJ occurred in papillary muscle at short coupling intervals and in the Purkinje fibre at longer intervals. 4. Once initiated, re‐entry could be reset or annihilated by properly timed subthreshold current pulses delivered to cells at the PMJ. 5. To define better the mechanisms for conduction block and re‐entry, an analytical model was developed using non‐linear regression analysis to derive equations from the experimental results. Varying parameters within the constraints of the model reproduced the key features of the rate‐dependent conduction block observed experimentally. Critical elements of the model included the induction of significant activation delays at short diastolic intervals and a reduction in the rate of action potential duration restitution after exposure to heptanol. 6. These results help to establish the conditions necessary for induction of one‐dimensional circus movement re‐entry and to define the roles of non‐linearities of activation delay and excitability in the dynamics of conduction block at the PMJ.
Endogenous variations and sodium intake‐dependent components of diurnal sodium excretion patterns in dogs.
Authors: Boemke W , Palm U , Corea M , Seeliger E , Reinhardt H W
Published: December 2014

1. Automated, sequential, 20 min urine collections were made to provide a record of diurnal variations of urinary sodium excretion (UNaV) in seven dogs, in which the same daily intake of sodium, potassium and water was administered, at first orally (between 08.30 and 08.50 h) on day 1 and then by i.v. infusion at a constant rate on days 2 and 3. This basic protocol was employed for two different levels of sodium intake: normal (NSI; 2.5 mmol (kg body wt)‐1 (24 h)‐1) and high (HSI; 14.5 mmol (kg body wt)‐1 (24 h)‐1). 2. The aims were: firstly, to establish the diurnal pattern of UNaV under these circumstances; secondly, to find out whether the quantity of sodium administered influences this diurnal pattern; and thirdly, to distinguish endogenous fluctuations from intake‐dependent components in the UNaV excretion patterns. 3. On day 1 (oral intake) all dogs exhibited a similar excretion pattern, which peaked between 13.00 and 15.00 h on both diets and then diminished again over the remainder of the 24 h period. 4. On days 2 and 3 (infusion) UNaV fluctuated within a considerable range. 5. On HSI, the maximal UNaV rates on day 1 were about double those observed on infusion days. On HSI, UNaV during infusion days seems to consist of a constant basal component of about 5‐6 mumol (kg body wt)‐1 min‐1 upon which a fluctuating component is superimposed. The basal component may be a reactive homeostatic response to the high sodium intake, whereas the superimposed fluctuating component may reflect endogenous variations.(ABSTRACT TRUNCATED AT 250 WORDS)
Attenuation of fever and release of cytokines after repeated injections of lipopolysaccharide in guinea‐pigs.
Authors: Roth J , McClellan J L , Kluger M J , Zeisberger E
Published: December 2014

1. The effects of repeated injections of bacterial lipopolysaccharide (LPS) at 3 day intervals on abdominal temperature and systemic release of tumour necrosis factor alpha (TNF)‐like and interleukin‐6 (IL‐6)‐like activity were measured in guinea‐pigs. 2. After the third injection of LPS the fever response was significantly attenuated. 3. TNF‐like activity (peak 1 h after LPS injection) and IL‐6‐like activity (peak 3 h after LPS injection) in plasma changed correspondingly, both being significantly reduced after the third and subsequent injections of LPS. 4. The increase of IL‐6‐like activity in plasma after LPS injection correlated to the febrile change in body temperature. This correlation remained manifest throughout the whole time course of the development of endotoxin tolerance. 5. The reduced production of TNF‐like activity after repeated injections of LPS correlated to the attenuation of the fever index, the integration of the thermal response after LPS application. 6. The results support the hypothesis that one component of the development of endotoxin tolerance is reduced production and release of cytokines in response to repeated injections of the same amount of LPS.
Ventilatory acclimatization to chronic hypoxia: relationship to noradrenaline metabolism in the rat solitary complex.
Authors: Schmitt P , Soulier V , Péquignot J M , Pujol J F , Denavit-Saubié M
Published: December 2014

1. The relationship between ventilatory acclimatization to chronic hypoxia (10% O2‐90% N2) and noradrenaline metabolism was examined in two regions located immediately caudal and rostral to the obex within the rat solitary complex. 2. Three experimental protocols were established. In protocol 1, the percentage changes in respiratory tidal volume, frequency and minute ventilation elicited by 4, 7, 10 and 14 days of hypoxia were assessed by flow plethysmography in awake rats, and then the content of tyrosine hydroxylase was measured in the solitary complex. In protocol 2, the time course response of tyrosine hydroxylase protein level was determined after 3, 7, 14 and 22 days of hypoxia by using a quantitative immunoblotting method for the protein assay. In protocol 3, the turnover of noradrenaline was estimated in the solitary complex after 14 days of hypoxia. 3. A progressive increase in ventilation was observed to reach a maximum (+105 +/‐ 15%, mean +/‐ S.E.M.) above normoxic control after 10 days of hypoxia, at which time it stabilized. Furthermore, tyrosine hydroxylase protein increased progressively and reached a maximal level at 14 days of hypoxia (+36 +/‐ 4%, mean +/‐ S.E.M.). Return to the basal level of tyrosine hydroxylase was observed after 22 days of hypoxia. 4. Tyrosine hydroxylase content (+36 +/‐ 4%) and noradrenaline turnover (+394 +/‐ 3%) increased exclusively in the caudal part of the solitary complex. 5. The ventilatory acclimatization to chronic hypoxia preceded the increase in tyrosine hydroxylase and these two parameters were significantly correlated. 6. These data suggest that ventilatory acclimatization to chronic hypoxia is associated with topical modifications of the brainstem catecholamine metabolism.
The influence of indomethacin on the ventilatory response to CO2 in newborn anaesthetized piglets.
Authors: Wolsink J G , Berkenbosch A , DeGoede J , Olievier C N
Published: December 2014

1. Indomethacin, a cyclo‐oxygenase inhibitor, decreases baseline values of cerebral blood flow, attenuates the cerebrovascular sensitivity to CO2 and stimulates ventilation in newborn piglets. 2. In twelve newborn anaesthetized piglets we investigated the influence of indomethacin on the ventilatory response to CO2 using the dynamic end‐tidal forcing technique by applying square‐wave changes in end‐tidal CO2 tension of 1.5‐2.0 kPa at constant end‐tidal PO2 of 15 kPa. 3. Each response, measured on a breath‐to‐breath basis, is separated into a fast peripheral and a slow central component with each component characterized by a CO2 sensitivity, a time constant, a time delay and an apnoeic threshold. 4. The results showed that indomethacin increases the central CO2 sensitivity from 232 +/‐ 38 to 292 +/‐ 43 ml min‐1 kPa‐1 (mean +/‐ S.E.M.). Neither the peripheral CO2 sensitivity nor the apnoeic threshold changed. 5. The central on‐transient and off‐transient time constants increased from 50.0 +/‐ 7.4 and 81.0 +/‐ 9.6 s, respectively, to 69.1 +/‐ 9.8 and 139.9 +/‐ 13.4 s after indomethacin. 6. Using a physiological model we argue that the respiratory effects of indomethacin are due to effects on cerebral blood flow.
Post‐hyperventilation apnoea in conscious humans.
Authors: Meah M S , Gardner W N
Published: December 2014

1. In nine normal subjects, analysis was performed of the number, length and location of apnoeic pauses during 20 min of recovery following voluntary overbreathing (VHV). Four different rates of recovery of end‐tidal PCO2 (PET,CO2), studied in randomized order, were induced by overbreathing to 15 or 25 mmHg, each for 3 or 6 min. Subjects breathed mildly hyperoxic gas mixtures (inspired PO2 approximately 250 mmHg) to and fro into an open circuit via a mouthpiece and pneumotachograph. 2. Apnoeic pauses rarely occurred immediately after the end of VHV but gradually increased in number and length. When averaged across all subjects and protocols, the largest pauses occurred 2.0 +/‐ 0.3 min (S.D.; range 1.6‐2.4 min) after the end of VHV. Based on a definition of apnoea as expiratory time greater than 6 s, apnoeas occurred between mean times of 0.8 and 5.6 min after the end of VHV, the end of this period being associated with a mean PET,CO2 value of 36.4 mmHg, which was below the initial mean resting value of 39.8 mmHg. 3. Within this apnoeic period, 80% of experiments produced apnoeas of less than 10 s duration, 61% of between 10 and 20 s duration and 42% of between 20 and 30 s duration. Only one out of nine subjects consistently failed to show apnoeas. 4. The range of lengths of individual apnoeas and the number per minute were independent of the length and level of VHV and were not significantly different between the four protocols. 5. The number and length of apnoeas did not change in repeated runs in each subject. We were not able to confirm previous reports that apnoeas occurred more frequently in subjects familiar with the experiment. 6. These results reconciled previous studies showing either apnoea or hyperpnoea following voluntary overbreathing in conscious humans. They showed an initial period of heightened breathing lasting about a minute with few apnoeas, consistent with ‘after‐discharge’. Beyond that, apnoeas occurred as an ‘all‐or‐nothing’ phenomenon as long as PET,CO2 was on average less than 3.4 mmHg below resting PET,CO2. The occurrence and length of apnoeas was consistent in individual subjects with no evidence of a learning effect.
Interactions among calcium compartments in C6 rat glioma cells: involvement of potassium channels.
Authors: Manor D , Moran N , Segal M
Published: December 2014

1. Variations in intracellular free Ca2+ concentration ([Ca2+]i) induced by alteration of the extracellular concentrations of Ca2+ ([Ca2+]o) and K+ ([K+]o) were imaged in single fluo‐3‐loaded C6 glioma cells. In addition, the effect of membrane potential on [Ca2+]i was investigated in fura‐2‐loaded, voltage‐clamped cells. 2. Step alterations of [Ca2+]o from 0 to 10 nM were followed by proportional variations in [Ca2+]i, with a maximum 7‐fold increase and an apparent half‐maximum at [Ca2+]o of 1.5 mM. 3. The time to half‐maximum change (t1/2) of [Ca2+]o‐associated [Ca2+]i variations ranged between 10 and 50 s, and was inversely related to the amplitude of [Ca2+]o steps. 4. Transient, serotonin‐induced [Ca2+]i elevations, used as a measure of Ca2+ availability in inositol 1,4,5‐trisphosphate‐sensitive stores, were diminished within 10 min in 0 mM [Ca2+]o, but were unaffected by [Ca2+]o changes in the 1‐5 mM range. 5. Restoration of normal [Ca2+]i following its elevation by serotonin was delayed by removal of external Na+ or Cl‐ and was enhanced by warming the medium to 37 degrees C. These conditions did not affect [Ca2+]o‐associated [Ca2+]i variations. 6. [Ca2+]o‐associated [Ca2+]i variations were depressed by La3+ and Ba2+, while blockers of voltage‐activated Ca2+ channels were ineffective. 7. Elevated [K+]o depressed the basal level of [Ca2+]i, and in high concentrations (70‐140 mM) also diminished the response to serotonin. 8. Depolarizing the membrane potential of voltage‐clamped cells reversibly reduced [Ca2+]i. These membrane‐potential associated [Ca2+]i variations were blocked by La3+, Ba2+ and TEA, all of which also depolarized membrane resting potential. 9. Apamin (at 1‐10 microM), a blocker of [Ca2+]i‐activated K+ channel, totally and reversibly prevented [Ca2+]o‐associated [Ca2+]i variations. 10. These studies indicate that C6 cells are responsive to variations in [Ca2+]o, and that a K+ channel is a possible path through which Ca2+ penetrates into the cell.
Activation of ATP‐sensitive potassium currents in guinea‐pig gall‐bladder smooth muscle by the neuropeptide CGRP.
Authors: Zhang L , Bonev A D , Nelson M T , Mawe G M
Published: December 2014

1. The actions of a neuroactive peptide, calcitonin gene‐related peptide (CGRP), and the ATP‐sensitive potassium (K+ATP) channel activator lemakalim on guinea‐pig gall‐bladder smooth muscle cells were investigated using intracellular recording from intact preparations and whole‐cell patch clamp recording from acutely dissociated myocytes. 2. CGRP and lemakalim caused a glibenclamide‐sensitive hyperpolarization of the plasma membrane of intact cells with an associated suppression of spontaneous action potentials. 3. In isolated smooth muscle cells, CGRP (10 nM) and lemakalim (10 microM) activated currents that were glibenclamide sensitive, voltage independent and potassium selective. 4. External TEA+ at 1.0 and 10.0 mM inhibited glibenclamide‐sensitive, CGRP‐activated currents by 3.8 and 66.5%, respectively. 5. Increases in the intracellular ATP concentration from 0.1 to 5.0 mM reduced the glibenclamide‐sensitive potassium current in the presence of CGRP (10 nM) or lemakalim (10 microM) by > 60%. The increase in the intracellular ATP also reduced the steady‐state glibenclamide‐sensitive current by > 80%. 6. These findings indicate that CGRP activates K+ATP channels to hyperpolarize the membrane of gall‐bladder smooth muscle cells. This hyperpolarization may be an important mechanism underlying the relaxant effects of CGRP on the gall‐bladder.
Photoreleased inositol 1,4,5‐trisphosphate‐induced response in single smooth muscle cells of rat portal vein.
Authors: Loirand G , Grégoire G , Pacaud P
Published: December 2014

1. The Ca2+ release in response to inositol 1,4,5‐trisphosphate (InsP3) was studied in single patch‐clamped smooth muscle cells of rat portal vein. InsP3 was photochemically produced from a caged InsP3 precursor included in the pipette solution. Changes in internal Ca2+ concentration ([Ca2+]i) were monitored by measuring Ca(2+)‐activated K+ current. 2. Photoreleased InsP3 evoked a transient K+ current which was abolished when 10 mM EGTA or 5 mg ml‐1 heparin was included in the pipette. The amplitude and time course of the K+ current responses depended on the light‐flash intensity. The amplitude increased, and the latency and the time to peak decreased, with increasing flash intensity, suggesting that the amount of released Ca2+ varied as a function of the amount of InsP3 photoreleased. 3. The K+ current response to photolysis of caged InsP3 was abolished in the presence of 10 mM caffeine; conversely, caffeine was inefficient at inducing at K+ current when applied immediately after a light flash of maximal intensity. 4. The time course of the recovery of the K+ response evoked by a light flash of supramaximal intensity was similar to that obtained for the 10 mM caffeine‐induced K+ current. The response recovered to 50% of control with an interval (t1/2) of about 10 s between pulses. The time course of the recovery of submaximal response to photoreleased InsP3 was considerably slower (t1/2 = 1 min), and did not correspond to that obtained for a response of similar amplitude evoked by 2 mM caffeine. 5. Responses to photoreleased InsP3 obtained after the cells were bathed for 3 min in Ca(2+)‐free solution were compared with those obtained in 2 mM Ca2+ solution. Responses to light flashes of submaximal intensity were proportionally more inhibited than those evoked by supramaximal stimulations. 6. In portal vein smooth muscle cells, the InsP3‐sensitive Ca2+ store seems also to be sensitive to caffeine. Our results suggest that the InsP3‐induced Ca2+ release was modulated by regulatory mechanisms.
Functional expression of A‐currents in embryonic chick sympathetic neurones during development in situ and in vitro.
Authors: Raucher S , Dryer S E
Published: December 2014

1. The functional expression of transient voltage‐activated K+ currents (IA) was examined using whole‐cell recording techniques in embryonic chick sympathetic ganglion neurones that developed in situ and under various growth conditions in vitro. 2. The density of IA increased dramatically during development in sympathetic neurones isolated acutely between embryonic days 7 and 20 (E7‐E20). The time course of IA inactivation became significantly faster between E7 and E13. With these protocols, neuronal differentiation and development occurred entirely in situ. 3. Sympathetic neurones isolated at E9 and maintained in vitro for 4 days did not express a normal IA compared to neurones isolated acutely at E13. Those neurones that were in physical contact with other neurones expressed normal densities of IA, but the resulting inactivation kinetics were abnormally slow. Sympathetic neurones that were cultured on the membrane fragments of lysed neurones expressed normal densities of IA even when they failed to make visible connections with other viable neurones, but the resulting inactivation kinetics were abnormally slow. Those cultured neurones that were not in physical contact with other cells or their membranes had markedly reduced densities of IA with abnormally slow inactivation kinetics. 4. Application of 5‐100 ng ml‐12.5 S nerve growth factor by itself did not promote normal A density of kinetics in E9 sympathetic neurones cultured for 4 days. 5. Sympathetic neurones that developed in vitro in physical contact with ventral spinal cord explants, cardiac myocytes or aortic smooth muscle cells expressed normal densities of IA, but the inactivation kinetics were abnormally slow. Cell culture media conditioned by these tissues failed to promote normal IA expression. Sympathetic neurones cultured as explants or maintained under depolarizing conditions did not express a normal IA. 6. Embryonic chick sympathetic neurones exhibit developmental changes in the density and kinetics of IA that can be regulated independently by extrinsic environmental factors including interactions with insoluble components of the plasma membranes of some cells.
Exercise‐induced changes in plasma potassium and the ventilatory threshold in man.
Authors: McLoughlin P , Popham P , Linton R A , Bruce R C , Band D M
Published: December 2014

1. It has been reported that, during incremental exercise testing, the patterns of change in ventilation (VE) and arterial K+ (Ka+) are similar, suggesting that changing Ka+ may lead to the phenomenon of the ventilatory threshold through its action on the peripheral chemoreceptors. 2. Expiratory ventilation, oxygen consumption, CO2 production (VE, VO2, VCO2), arterialized venous PCO2 (Pav, CO2; see Methods), pH (pHav), K+ (Kav+) and lactate were measured during incremental exercise tests undertaken by six normal male subjects under control conditions and during lactic acidosis following severe exercise (experimental trial). 3. A ventilatory threshold, associated with a period of isocapnic buffering, was observed under both control and experimental conditions. During the control trial, plots of Kav+ against VO2 showed an inflexion close to the ventilatory threshold. Throughout the experimental trial Kav+ rose linearly relative to VO2. In both control and experimental trials Kav+ concentrations were similar at the ventilatory threshold. 4. These results suggest that the pattern of change of Ka+ cannot account for the phenomenon of the ventilatory threshold. The possibility that the peripheral chemoreceptor response is non‐linear above a critical value of Ka+ requires further investigation.
Differential beta‐adrenergic regulation and phenotypic modulation of voltage‐gated calcium currents in rat aortic myocytes.
Authors: Neveu D , Quignard J F , Fernandez A , Richard S , Nargeot J
Published: December 2014

1. We studied the beta‐adrenergic regulation of voltage‐gated Ca2+ channel currents using the whole‐cell patch‐clamp technique (18‐22 degrees C) in freshly isolated and in cultured (1‐20 days) rat aortic vascular smooth muscle cells (VSMCs). These currents include a transient low‐voltage‐activated (LVA) current and two L‐type‐related high‐voltage‐activated currents (HVA1 and HVA2, respectively). 2. At 10 microM, the beta‐adrenergic agonist, isoprenaline, increased the HVA2 current (65 +/‐ 30%, n = 10) but had no effect on LVA and HVA1 currents. This potentiation was dose dependent in the range 0.01‐10 microM, developed with a slow time course and was mimicked by elevating intracellular cyclic AMP using the permeant analogue dibutyryl cyclic AMP (100 microM). 3. In the well‐differentiated freshly isolated myocytes, only the HVA1 current was recorded. In cultured cells, a predominant frequency of occurrence of LVA and HVA1 currents was observed in modulated and differentiated myocytes, respectively. The occurrence of the HVA2 current was stable during culture but this current disappeared when the cells were confluent. It was retrieved when the confluent cells were dispersed and subcultured. 4. In conclusion, we present evidence for a differential beta‐adrenergic regulation of three types of Ca2+ channel current in adult rat aortic VSMCs. The differential expression of these currents, associated with marked changes in cell phenotypes in vitro, suggests that they serve distinct physiological functions.
GABA receptor mediation of median preoptic nucleus‐evoked inhibition of supraoptic neurosecretory neurones in rat.
Authors: Nissen R , Renaud L P
Published: December 2014

1. This study evaluated the influence of focal electrical and chemical microstimulation in the median preoptic nucleus (MnPO) on the excitability of putative vasopressin and oxytocin neurones recorded in the supraoptic nucleus of urethane‐ or pentobarbitone‐anaesthetized rats. 2. In vasopressin neurones, single 1 Hz stimulation reduced the excitability of 120/139 cells. Trains of repetitive 5‐30 Hz stimulation, or microinfusion of glutamate into the MnPO, similarly induced a cessation in spontaneous phasic or continuous firing in 17/18 and 17/20 vasopressin neurones, respectively. In 20/21 cells, locally applied bicuculline (100 microM) attenuated MnPO‐evoked depressant responses whereas strychnine (100 microM) and timolol (20 microM) were without effect on 5/5 vasopressin neurones. In three cells, bicuculline applications were associated with marked increases in MnPO‐evoked excitations. 3. In oxytocin neurones, single‐pulse (1 Hz) electrical stimulation in MnPO evoked an increase in the excitability in 51/59 cells. However, in 6/7 oxytocin cells tested, glutamate microinfusions into MnPO induced prolonged suppression in firing. During trains of stimuli (5‐30 Hz), 26/44 cells displayed an initial increase in firing associated with the first few impulses but this was then replaced by suppression of activity; another ten cells displayed excitation alone, and eight cells demonstrated only suppression. The depressant responses evoked during trains of MnPO stimulation were blocked by 100 microM bicuculline (6/6 cells tested) whereas strychnine was ineffective (2/2 cells tested). 4. These results suggest that the MnPO provides a mainly depressant influence on supraoptic vasopressin and oxytocin neurones, perhaps through the activation of postsynaptic GABAA receptors.