bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of effect of peptide length and sulphation on acid secretory potency of gastrin in the cat in vivo and in vitro.
Authors: Hirst B H , Holland J , Marr A P , Parsons M E , Sanders D J
Published: December 2014

The gastric‐acid secretory potency of gastrin peptides was investigated in vivo, in conscious cats prepared with gastric fistula, and in vitro, with kitten isolated gastric mucosae. The influence of peptide length on potency was investigated by comparing synthetic human gastrin heptadecapeptide, non‐sulphate (shG17ns) with a synthetic gastrin butyloxycarbonyl hexapeptide (G6ns), and the influence of sulphation by comparison of G6ns with its sister sulphated peptide (G6s). When exogenous doses were compared, shG17ns was the most potent peptide (mean exogenous dose for half‐maximal stimulation (EDe50) : 0.33 nmol kg‐1 h‐1), and was 15.8 times more potent than G6ns (EDe50:5.14 nmol kg‐1 h‐1). This potency ratio was reduced to 9.4 when circulating immunoreactive concentrations of the two peptides were compared (mean circulating concentration for half‐maximal stimulation (EDc50) : shG17ns, 201 pM; G6ns, 1890 pM). The greater potency ratio when exogenous doses were compared was due to the greater metabolic clearance rate (m.c.r.) of the shorter gastrin (m.c.r.: shG17ns, 37 ml kg‐1 min‐1; G6ns, 121 ml kg‐1 min‐1). In vitro, shG17ns (mean concentration for half‐maximal stimulation (EC50) : 1.99 nM) was 2.8 times more potent than G6ns (EC50: 5.57 nM). Sulphation of the hexapeptide increased its potency 3.6‐fold when exogenous doses were compared (EDe50 G6s: 1.42 nmol kg‐1 h‐1). The greater potency of the sulphated peptide appeared to be due to its lower m.c.r. (20 ml kg‐1 min‐1), and was eliminated when circulating concentrations were compared; potency ratio G6ns: G6s, 1.1. We conclude that the increased potency of short gastrin peptides observed upon sulphation is likely to be due to increased resistance to metabolic clearance. Part of the increased potency observed with increasing peptide length can also be explained by increased resistance to clearance, but the small potency difference in vitro may reflect greater affinity for gastrin receptors.
Long‐term potentiation of transmitter release induced by repetitive presynaptic activities in bull‐frog sympathetic ganglia.
Authors: Koyano K , Kuba K , Minota S
Published: December 2014

Long‐lasting potentiation of transmitter release induced by repetitive presynaptic activities in bull‐frog sympathetic ganglia was studied by recording intracellularly fast excitatory post‐synaptic potentials (fast e.p.s.p.s.). Following a brief period of post‐tetanic potentiation or depression (less than 10 min), the amplitude of the fast e.p.s.p. was potentiated for a period between several tens of minutes and more than 2 h in response to tetanic stimulation of the preganglionic nerve in twenty‐one out of twenty‐eight cells. Quantal analysis revealed that this long‐term potentiation of the fast e.p.s.p. (l.t.p.) was accompanied by an increase in quantal content m (in nine out of twenty‐one cells), quantal size (four cells) or both (eight cells). The increased quantal content (presynaptic l.t.p.) declined exponentially (ten cells) or decayed gradually to a certain enhanced level which lasted several hours. In contrast, the increased quantal size grew with a relatively long latency (10‐25 min) and remained relatively constant for at least 2 h. The magnitude of presynaptic l.t.p. increased with increased duration of the presynaptic tetanus (33 Hz) from 2 to 5 s. No l.t.p. was elicited by a 1‐s tetanus, whereas the time course appears to be independent of the tetanus duration and the magnitude of l.t.p. There was a positive correlation between the magnitude of presynaptic l.t.p. and the pre‐tetanic quantal content up to m = 3, but the former deviated from linear regression when the value of the latter exceeded 3. No l.t.p. occurred when quantal content was less than 0.5. A tetanus (33 Hz, 10 s) applied in Ca2+‐free solution elicited no presynaptic l.t.p., while the same tetanus in normal Ringer solution produced a large presynaptic l.t.p. Presynaptic l.t.p. was enhanced in magnitude at low temperature (8‐10 degrees C). These results demonstrate the existence of a use‐dependent, long‐term potentiation of transmitter release in bull‐frog sympathetic ganglia. Several possible mechanisms are discussed in terms of Ca2+‐buffering mechanisms of the presynaptic nerve terminals.
Effects of angiotensin or carbachol on sodium intake and excretion in adrenalectomized or deoxycorticosterone‐treated rats.
Authors: Fitzsimons J T , Fuller L M
Published: December 2014

In adrenalectomized, deoxycorticosterone‐treated and normal rats, injection of angiotensin II through a cannula implanted in the preoptic region caused increased intakes of hypertonic NaCl and water when both fluids were available, whereas injection of carbachol through the same cannula only caused increased water intake. Carbachol depressed NaCl intake of adrenalectomized rats that were allowed access to hypertonic NaCl after being deprived of it for 24 h. Angiotensin‐stimulated rats were more likely to go into positive sodium balance than controls, whereas carbachol‐stimulated animals were more likely to go into negative balance. After angiotensin, adrenalectomized or deoxycorticosterone‐treated rats drank a larger proportion of their total fluid intake as hypertonic NaCl than did normal rats. Angiotensin caused significant increases in sodium excretion in normal, isotonic saline‐loaded and deoxycorticosterone‐treated rats, but not in adrenalectomized rats, although angiotensin caused increased intakes of NaCl in all groups. On the other hand, carbachol caused a significant increase in sodium excretion at 1 h in all groups despite the absence of an increase in NaCl intake. After angiotensin, only normal rats showed a significant kaliuresis at 1 h, whereas all carbachol‐injected rats showed increased potassium excretion. Therefore, angiotensin is a primary stimulus to increased sodium appetite, normally acting in conjunction with other stimuli which enhance its effect, whereas carbachol is a central inhibitor of sodium appetite.
Analysis of the antipyretic action of alpha‐melanocyte‐stimulating hormone in rabbits.
Authors: Clark W G , Holdeman M , Lipton J M
Published: December 2014

alpha‐Melanocyte‐stimulating hormone (alpha‐MSH) or paracetamol was injected into a lateral cerebral ventricle (I.C.V.) of rabbits with elevations in rectal temperature induced by sodium arachidonate (I.C.V.), prostaglandin E2 (I.C.V.) or leucocytic pyrogen (I.V.). alpha‐MSH (200 ng) was more effective than paracetamol (0.5 mg) in reducing fever caused by leucocytic pyrogen, but it did not alter hyperthermia induced by sodium arachidonate. In contrast, paracetamol reduced hyperthermic responses to arachidonate by about 70%. Neither alpha‐MSH nor paracetamol affected hyperthermic responses to prostaglandin E2. The doses of alpha‐MSH and paracetamol used in these experiments did not interfere with thermoregulation in a cold environment (10 degrees C). We conclude (1) that alpha‐MSH and paracetamol differ in their central mechanism of antipyresis or (2) that inhibition of arachidonic acid metabolism by paracetamol is not requisite for its antipyretic effect, in which case central release of alpha‐MSH may mediate the antipyretic effect of paracetamol.
Membrane currents and their modification by acetylcholine in isolated single atrial cells of the guinea‐pig.
Authors: Iijima T , Irisawa H , Kameyama M
Published: December 2014

The ionic currents in isolated single atrial cells of the guinea‐pig heart were analysed by the patch‐clamp technique applied to whole‐cell recordings and the effects of acetylcholine (ACh) on the membrane potential and currents were studied. Resting and action potentials of single isolated cells were normal. Upstroke velocity was sensitive to tetrodotoxin. Action potential duration was slightly shorter than in multicellular preparations. Voltage‐clamp experiments demonstrated the presence of a Ca2+ current (iCa), and inward rectifying and outward rectifying K+ currents. The Ca2+ current was abolished by 2 mM‐Co2+ or 10(‐6) M‐D600, and the K+ currents were greatly reduced by intracellular application of Cs+ using the patch electrode and simultaneously superfusing the cell with 5 mM‐Cs+ Tyrode solution. Acetylcholine shortened the action potential duration in a dose‐dependent manner. The threshold dose of ACh was about 10(‐9) M and the maximal effect was obtained with 10(‐6) M. The resting membrane potential was hyperpolarized by 1‐3 mV. ACh (10(‐8)‐10(‐6) M) increased the K+ currents both on depolarization and on hyperpolarization in a dose‐dependent manner in the presence of 10(‐6) M‐D600. The ACh‐induced K+ outward current revealed a progressive deactivation ('relaxation'), with a time constant of 111 +/‐ 16 ms at around 0 mV. When the K+ outward currents were minimized with Cs+, the reduction of iCa by 10(‐8) M‐ACh was insignificant, and became 17 +/‐ 2.5, 26 +/‐ 3.5 and 26 +/‐ 5% of the control value in 10(‐7), 10(‐6) and 10(‐5) M‐ACh, respectively. The inactivation time course of iCa recorded from the Cs+‐loaded cells was not affected by 10(‐7) M‐ACh. These results suggest that ACh activates predominantly a K+ conductance in the guinea‐pig atrium. The superimposition of a relaxing K+ outward current on iCa may lead to over‐estimation of the decrease in iCa.
Efferent modulation of hair cell tuning in the cochlea of the turtle.
Authors: Art J J , Crawford A C , Fettiplace R , Fuchs P A
Published: December 2014

Intracellular recordings were made from turtle cochlear hair cells in order to study the changes in their tuning properties resulting from electrical stimulation of the efferent axons. Efferent stimulation caused a reduction in the amplitude of the receptor potential at the hair cell's most sensitive or characteristic frequency, an increased amplitude at frequencies more than an octave below the characteristic frequency, and no change at very high frequencies. These differential effects resulted in a broadening of each cell's tuning curve, which, during maximal efferent stimulation degenerated from a sharply tuned resonance to a critically damped low‐pass filter. Efferent alterations in tuning were also inferred from the oscillations in membrane potential produced by acoustic clicks or extrinsic currents. The quality factor (Q) of tuning, derived from the decay of the oscillations, was progressively reduced with synaptic hyperpolarizations up to about 5 mV in amplitude. A consequence of efferent action was that the wave forms of transient pressure changes were more faithfully encoded as changes in hair cell membrane potential. Hyperpolarization of a hair cell by steady current injection resulted in a lowering of its characteristic frequency and quality factor, and an increase in steady‐state resistance. By comparison, for a given reduction in quality factor, efferent stimulation was associated with a smaller change in characteristic frequency. This difference is expected if the resonance is also damped by the shunting action of the synaptic conductance. Perfusion with perilymphs containing 0.5‐15 mM of the potassium channel blocker, tetraethylammonium bromide (TEA) reduced the hair cell's frequency selectivity, whether assayed acoustically or with extrinsic currents. Lower TEA concentrations abolished the efferent inhibitory post‐synaptic potential with only a minor change in tuning. TEA produced other effects different from efferent stimulation including (i) a lowering of the characteristic frequency, and (ii) a highly asymmetric receptor potential. These observations suggest that the efferents do not simply block membrane conductances associated with tuning. We conclude that the efferent modification of the shape of the tuning curve may be a composite result of the synaptic conductance and the hyperpolarization of the hair cell membrane.
A calcium‐dependent reversible permeability increase in microvessels in frog brain, induced by serotonin.
Authors: Olesen S P
Published: December 2014

The effect of serotonin on brain microvascular permeability was studied by measurement of changes in the electrical resistance of the venular vascular wall, induced by this substance. Intravenous administration of serotonin decreased the electrical resistance in a dose‐dependent manner with Kd congruent to 8.2 microM. The maximal decrease in electrical resistance was about 33%. The electrical resistance fell within seconds following the application and returned to the control value after 1‐5 min. Serotonin applied to the outside of the brain vessels had no effect on electrical resistance. Pre‐treatment with the 5‐HT2 receptor antagonist Ketanserin blocked the serotonin response completely. The serotonin response was strongly inhibited by pre‐treatment with the calcium‐entry blocker verapamil (Isoptin). The findings demonstrate that serotonin reversibly increases blood‐brain barrier permeability. The effect is mediated via 5‐HT2 receptors located at the luminal surface of the cerebrovascular endothelium and is dependent on mobilization of extracellular Ca2+.
Movements of cross‐bridges during and after slow length changes in active frog skeletal muscle.
Authors: Matsubara I , Yagi N
Published: December 2014

The cross‐bridge movements underlying the tension responses of active muscle to slow length changes were studied by a time‐resolved X‐ray diffraction method. During an isometric tetanus at 2 degrees C, the meridional reflexion at 1/14.3 nm‐1 was 55% more intense than in the resting state, suggesting that the myosin heads maintain the 14.3 nm periodicity of the thick filament. When active muscle was stretched by 7% at a constant speed of 0.03‐0.70 muscle lengths s‐1, the intensity of the meridional reflexion decreased progressively as the tension increased continuously during the stretch. This suggests that the myosin heads spread out along the thick filament. During stress relaxation after a stretch, the intensity returned gradually toward the active isometric level, suggesting a rearrangement of the myosin heads. The meridional intensity changed in a similar manner when active muscle was released by 7% at the same speeds; it decreased progressively during the release and returned gradually to the isometric level after completion of the release. The intensity decrease during a release was smaller than that during a stretch, provided the speed was low (0.03‐0.09 muscle lengths s‐1). It was concluded that the tension responses to slow length changes are due to shifts of the myosin heads along the thick filament, and that the elastic element responsible for tension production is located in the myosin molecules.
Changes in capillary distribution in rat fast muscles following nerve crush and reinnervation.
Authors: Large J , Tyler K R
Published: December 2014

The recovery of muscle weight and contraction tension was measured in rat anterior tibialis muscle following unilateral crushing of the lateral popliteal nerve. Muscle twitch and tetanic tensions and muscle weight had recovered to control values within 6‐8 weeks after the nerve was crushed. Capillary supply to each of the four types of muscle fibre present in the intact muscle, and within the groups of adjacent fibres of similar histochemical reaction for succinate dehydrogenase and myofibrillar actomyosin ATPase found in the reinnervated muscle, was computed by the method of Gray & Renkin (1978). Capillary area density (capillaries/mm2) within the grouped regions of the reinnervated muscle was not significantly different from the supply to the same fibre type in intact contralateral muscles. Capillary/fibre ratio for the more glycolytic fibre types (alpha W, alpha?) was lower than in intact muscle, while the values for both alpha R and beta R oxidative fibres agreed closely with control values. It seems that selective growth and loss of capillaries occurs during reinnervation, adjusting capillary supply to meet the changed metabolic demands of the individual fibres following regrouping.
Central stimulation of breathing movements in fetal lambs by prostaglandin synthetase inhibitors.
Authors: Koos B J
Published: December 2014

In unanaesthetized fetal lambs at 125‐135 days gestation in utero central acidosis caused by perfusion of the cerebral ventricular system with a solution containing less than 1 mM‐HCO3‐ (cerebrospinal fluid (c.s.f.) pH 6.98) or intravenous infusion of ammonium chloride (c.s.f. pH 7.1) produced an increase in the depth and frequency of episodic breathing but no change in electrocortical activity, heart rate or arterial pressure. Administration of prostaglandin synthetase inhibitors, sodium meclofenamate (0.8‐10 mg/kg I.V. or 0.6‐2.6 mg/kg intracerebrally) or acetylsalicylic acid (6.7 mg/kg I.V.) caused prolonged episodes of fetal breathing during low and high voltage electrocortical activity, with a large increase in breath amplitude. Blood gas values, heart rate, blood pressure, electrocortical activity and eye movements were not altered. In fetuses whose brain stems had been sectioned in the upper pons or the inferior colliculus, sodium meclofenamate induced prolonged deep breathing. Intravenous prostaglandin E2 abolished the continuous breathing induced by meclofenamate, but not breathing movements enhanced by hypercapnia or hypoxia. It is concluded that the central chemoreceptors respond to acidosis in near‐term lamb fetuses qualitatively as in adult animals. Secondly, the results suggest that prostaglandin E2 and the inhibitors of prostaglandin synthesis also act centrally in the lower pons or medulla to modulate fetal breathing.
Characteristics of the vagally driven non‐adrenergic, non‐cholinergic inhibitory innervation of ferret gastric corpus.
Authors: Andrews P L , Lawes I N
Published: December 2014

This paper reports a quantitative in vivo study on the vagal activation of the intramural non‐adrenergic, non‐cholinergic inhibitory nerves in the ferret gastric corpus. The nature of the inhibitory neurotransmitter was also investigated. In the atropinized, guanethidine‐treated, urethane‐anaesthetized ferret, electrical stimulation (10 s at 20 V, 1‐20 Hz, 0.5 ms pulses) of the cervical vagi produced a prompt fall in intracorpus pressure that was related to the stimulus frequency. The maximal response was achieved at 10 Hz. The time taken for the intracorpus pressure to return to pre‐stimulus levels after a 10 s period of stimulation was related to the stimulus frequency; at 10 Hz the pressure took approximately 11 min to recover. In contrast to studies in the cat (Martinson & Muren, 1963), there was no detectable difference in the electrical threshold for activation of the vagal excitatory and vagal inhibitory fibres. The nature of the vagal non‐adrenergic, non‐cholinergic inhibitory neurotransmitter was investigated using a variety of antagonists and agonists. Adenosine triphosphate (ATP), adenosine, alpha beta‐methylene ATP and beta gamma‐methylene ATP all contracted the corpus in the presence of vagotomy, atropine, guanethidine and indomethacin. The vagally induced fall in corpus pressure was not blocked by high doses of alpha beta‐methylene ATP. A variety of peptides were investigated for their effects on corpus pressure in the presence of atropine, guanethidine and vagotomy. Bombesin, pentagastrin, substance P, cholecystokinin octapeptide (CCK‐8) and bradykinin all produced an increase in intracorpus pressure. Neurotensin and vasoactive intestinal polypeptide (VIP) both decreased intracorpus pressure, and of the two VIP most closely mimicked the response to vagal activation of the non‐cholinergic, non‐adrenergic inhibitory neurones. The results provide support for the involvement of a peptide (possibly VIP) rather than a purine in the vagally driven decrease in intracorpus pressure in the ferret.
Electroretinograms evoked by sinusoidal excitation of human cones.
Authors: Abraham F A , Alpern M , Kirk D B
Published: December 2014

The amplitude and phase of the fundamental Fourier component of the human electroretinogram (e.r.g.) were recorded with a synchronous detection method under conditions in which each of the three species of cones can be assumed most sensitive in turn. Weber‐Fechner behaviour is well established at, or more distal in the retina than, the source of these voltages. Results over the frequency range 7‐50 Hz exclude a diffusion model of human flicker perception. The e.r.g. phase vs. frequency plot found with a 'red' test differs from that obtained with a 'green'. The shapes of the e.r.g. field sensitivity action spectra agree with those of the subject's IIj(mu) (j = 3, 4 and 5) mechanisms of Stiles and with in situ measurements of the absorbance spectra of human cone pigments. Threshold phase with each test was independent of background wave‐length but, consistent with the results in 3, the phase of the response to the 'red' test (25 Hz) differed significantly from that to the 'green'. If these differences resulted from the absorption of test photons of different colours at different points along the outer segment (independent of cone spectral sensitivity), they would be as clear on dichromats as on trichromats. Results on a protanope are inconsistent with this prediction. We infer that differences in phase are due to the different kinetics of different cone mechanisms and that the e.r.g.s studied here are evoked by exciting only the most sensitive cone mechanism, even though dark‐adaptation studies prove that at e.r.g. threshold the test is well above psychophysical threshold for all three cone species. If the inference in 5 is correct, studies of sensitivity across the retina suggest that the spatial distribution of long‐, middle‐ and short‐wave‐sensitive cones in the human retina differ remarkably.
The role of cyclic nucleotides in modulation of the membrane potential of the Schwann cell of squid giant nerve fibre.
Authors: Evans P D , Reale V , Villegas J
Published: December 2014

The role of cyclic nucleotides in mediating the effects of nicotine cholinergic receptors has been investigated in Schwann cells of the giant nerve fibre of the squid. Elevation of cyclic AMP levels in this preparation by means of the phosphodiesterase inhibitor, theophylline, by the diterpene adenylate cyclase activator, forskolin, and by cyclic nucleotide analogues mimics the action of activating the nicotinic cholinergic receptors in producing a long‐lasting hyperpolarization of the membrane potential of the Schwann cell. Theophylline and forskolin also potentiate the effects of carbachol and of neural stimulation on the Schwann cell. The results suggest that the nicotinic receptor of the squid Schwann cell is likely to mediate its effects via a mechanism that activates adenylate cyclase. The results are discussed in terms of the role of cyclic AMP in the complex multistep interaction between the giant axon of the squid and its surrounding Schwann‐cell layer.
Activity dependence of action potential duration in rat supraoptic neurosecretory neurones recorded in vitro.
Authors: Bourque C W , Renaud L P
Published: December 2014

Action potential durations, measured at one‐third peak amplitude, were examined during intracellular recordings in 134 supraoptic nucleus neurones maintained in vitro in perfused hypothalamic explants. Spike durations ranged between 1.2 and 3.9 ms and were dependent on firing frequency. Shortest measurements (1.74 +/‐ 0.03 ms; mean +/‐ S.E. of mean) were obtained during relative quiescence, i.e. less than or equal to 0.5 Hz. A gradual increase in firing frequency through continuous injection of depolarizing current prolonged spike duration, with maximum levels (2.68 +/‐ 0.05 ms) achieved at 20 Hz. When interspike interval variability was eliminated and firing was more precisely regulated by brief 15‐20 ms intracellular current pulses given at pre‐determined frequencies, a proportional relationship between increasing spike duration and firing frequency was retained but the change in spike duration at frequencies between 2 and 10 Hz was less pronounced. Once action potentials had achieved the long duration configuration, their return to the shorter duration took place gradually during any succeeding silent interval with a time constant of 4.9 s. Action potential broadening occurred progressively and was most pronounced at the onset of spontaneous or current‐induced bursts. In thirty‐six phasically active neurones, spike broadening at the onset of a burst was concurrent with the presence of 5‐10 consecutive short (less than or equal to 100 ms) interspike intervals; thereafter, despite a greater than 50% reduction in firing frequency, action potential durations remained prolonged throughout the burst. In all of nineteen cells tested, frequency‐dependent changes in spike duration were reversibly decreased or blocked by Cd2+, Co2+ and Mn2+, or when CaCl2 was exchanged for equimolar amounts of EGTA in the perfusion medium. These observations indicate that a Ca2+ conductance contributes to frequency‐ and firing‐pattern‐dependent changes in spike duration in rat supraoptic nucleus neurones.
The mechanical properties of ciliary bundles of turtle cochlear hair cells.
Authors: Crawford A C , Fettiplace R
Published: December 2014

The mechanical behaviour of the ciliary bundles of hair cells in the turtle cochlea was examined by deflecting them with flexible glass fibres of known compliance during simultaneous intracellular recording of the cell's membrane potential. Bundle motion was monitored through the attached fibre partially occluding a light beam incident on a photodiode array. The change in photocurrent was assumed to be proportional to bundle displacement. For deflexions of 1‐100 nm towards the kinocilium, the stiffness of the ciliary bundles was estimated as about 6 X 10(‐4) N/m, with the fibre attached to the top of the bundle. When the fibre was placed at different positions up the bundle, the stiffness decreased approximately as the inverse square of the distance from the ciliary base. This suggests that the bundles rotate about an axis close to the apical pole of the cell and have a rotational stiffness of about 2 X 10(‐14) N. m/rad. Step displacements of the fixed end of the flexible fibre caused the hair cell's membrane potential to execute damped oscillations; the frequency of the oscillations in different cells ranged from 20 to 320 Hz. Displacements towards the kinocilium always produced membrane depolarization. The amplitude of the initial oscillation increased with displacements up to 100 nm and then saturated. For small displacements of a few nanometres, the hair cell's mechanoelectrical sensitivity was estimated as about 0.2 mV/nm. Force steps delivered by the flexible fibre caused the bundle position to undergo damped oscillations in synchrony with the receptor potential. The mechanical oscillations could be abolished with large depolarizing currents that attenuated the receptor potential. When placed against a bundle, a fibre's spontaneous motion increased and became quasi‐sinusoidal with an amplitude several times that expected from the compliance of the system. It is suggested that the hair bundle drives the fibre. We conclude that turtle cochlear hair cells contain an active force generating mechanism.
Inactivation of calcium channels in mammalian heart cells: joint dependence on membrane potential and intracellular calcium.
Authors: Lee K S , Marban E , Tsien R W
Published: December 2014

Ca channel currents were recorded in Cs‐loaded calf cardiac Purkinje fibres and Cs‐dialysed myocytes from guinea‐pig ventricle to evaluate the dependence of Ca channel inactivation on membrane depolarization and intracellular free Ca concentration ([Ca]i). The decay of Ca channel current during a maintained depolarization was slowed when external Ca was replaced by Sr or Ba. The decay reflected a genuine inactivation of Ca channel conductance, as assessed by the decreased amplitude of inward tail currents following progressively longer depolarizing pulses in ventricular cells. Increasing depolarization slowed inward current inactivation in the presence of extracellular Ca concentration ([Ca]o), but speeded inactivation in the presence of extracellular Ba concentration ([Ba]o), suggesting the participation of fundamentally different mechanisms. Ca channel currents were recorded in Ca‐free external solutions to study 'voltage‐dependent inactivation'. Inactivation of outward Ca channel current due to Cs efflux was seen with external Ba or in the absence of any permeant divalent cation. With Ca as the charge carrier, increasing [Ca]o speeded the rate of inactivation as expected for [Ca]i‐dependent inactivation. The relationship between inactivation and the intracellular Ca transient was assessed by double‐pulse experiments. Conditioning pulses that produced maximal inward Ca current and contractile tension left behind more inactivation than either stronger or weaker depolarizations. The agreement between maximal inward current and maximal inactivation remained close when their voltage dependence was shifted along the voltage axis by elevation of [Ca]o. We conclude that inactivation of cardiac Ca channels is both [Ca]i dependent and voltage dependent. The [Ca]i‐dependent process may serve as a negative feed‐back mechanism for regulating Ca entry into heart cells; the voltage‐dependent mechanism may prevent a secondary rise in Ca channel current when intracellular Ca falls during maintained depolarization of cardiac cells.
C‐fibre excitation and tonic descending inhibition of dorsal horn neurones in adult rats treated at birth with capsaicin.
Authors: Cervero F , Plenderleith M B
Published: December 2014

Single unit electrical activity has been recorded from dorsal horn neurones in the lumbar cord of rats anaesthetized with sodium pentobarbitone. Three groups of animals were used: normal adult rats, adult rats that had been treated at birth with capsaicin (50 mg kg‐1 s.c.) and adult rats that had been injected at birth with the drug vehicle only. Rats treated at birth with capsaicin showed a substantial reduction in the number of afferent C fibres as indicated by the virtual absence of C waves in the compound action potentials evoked in the sural nerve by antidromic stimulation of the L4‐L6 dorsal roots. No significant differences were found in any of the parameters measured between the vehicle treated and the untreated animals. Therefore, rats from these two groups are referred to as control animals. All dorsal horn neurones studied were driven by electrical stimulation of the A fibres in the ipsilateral sural nerve and had cutaneous receptive fields in the ipsilateral hind limb. Two groups of neurone were distinguished: those receiving an input from A fibres only (A only) and those neurones that could also be driven by sural C fibres (A + C). In the control group, 56% of the neurones were A only and 44% were A + C. In capsaicin‐treated rats these proportions were significantly different: 78% and 22% respectively. No differences were found in receptive field sizes of A‐only neurones between those recorded in control rats and those from capsaicin‐treated animals. However, a large and significant increase in receptive field size of A + C neurones was observed in capsaicin‐treated rats compared to their counterparts in normal animals. In control rats 80% of the A + C neurones showed tonic descending inhibition of their C‐fibre‐evoked responses as assessed by reversible spinalization. In capsaicin‐treated rats this proportion fell to 47% of the A + C neurones. The magnitude of the tonic descending inhibition was also reduced in the fewer A + C neurones of capsaicin‐treated rats that were subjected to it. Only 4% of A + C neurones with tonic descending inhibition in capsaicin‐treated rats were powerfully inhibited compared to 26% in control animals. The mean number of spikes evoked by C‐fibre stimulation of the sural nerve in A + C neurones of control and of capsaicin‐treated rats was not significantly different between these two groups of animals in the intact and in the spinalized states.(ABSTRACT TRUNCATED AT 400 WORDS)
Sympathetic modulation of cold‐receptive neurones in the trigeminal system of the rat.
Authors: Davies S N
Published: December 2014

The effects of cervical sympathetic electrical stimulation on the activity of cold‐receptive neurones in the trigeminal system of the rat have been studied. Sympathetic stimulation caused excitation and/or suppression of cold‐receptive cells in the trigeminal nucleus caudalis. The responses were complex but within any one cell low‐frequency stimulation (below 5 Hz) usually (81% of cells) caused excitation, while high‐frequency stimulation (above 10 Hz) caused excitation and suppression. The temperature of the cutaneous receptive fields was 'clamped' with a thermode. Measurements of surface and intradermal temperatures suggested that the temperature fall caused by sympathetic stimulation was not sufficient to account for the increased firing rate observed. The suppression was blocked by a low dose of phentolamine; it was mimicked by carotid occlusion and may be a consequence of vasoconstriction. The excitation was resistant to beta‐blockade; it was best mimicked by the alpha‐agonist phenylephrine. Similar frequency‐dependent excitations and suppressions, and responses to pharmacological agonists, were obtained in recordings from cold‐receptive primary afferent neurones in the trigeminal ganglion. The excitation may be a complex secondary effect, or there may be a direct alpha‐receptor‐mediated excitation of cold‐receptive primary afferent fibres by the sympathetic system.
Neural control of electrical gastric activity in response to inflation of the antrum in the rabbit.
Authors: Deloof S , Rousseau J P
Published: December 2014

The respective roles of the extrinsic innervation (vagal and splanchnic) and of the myenteric plexus in the control of gastric motility were investigated in rabbits by quantifying the effect of cutting the extrinsic nerves on the electrical response of the antrum and pylorus to inflation of the antrum. In intact animals the frequency of bursts during distension was significantly increased above the frequency during the 30 min preceding inflations. The interval from the end of step inflation to the first burst recorded after inflation was significantly longer than the mean interval between bursts in the 30 min preceding inflation, whereas no such difference was observed following ramp inflation. Both atropine and hexamethonium abolished the responses to distension. The basal rhythm of bursts recorded on the antrum and pylorus was markedly reduced during the first 3 days after vagotomy: the mean values of the frequency in response to distension were significantly less than those in intact animals, whereas the first interval after inflation was significantly increased. Thereafter no such differences were encountered. The only change after section of the splanchnic nerves was a significant reduction in the first interval after inflation, resulting in rapid restoration of the initial rhythm at the end of inflation. In vagotomized animals with cut splanchnic nerves, the basal electrical activity of the antrum was not affected but the responses to step inflations were much greater; the frequency of bursts during distension and the first interval after inflation were both significantly increased. Section of the vagal afferent fibres changed neither the frequency of the basal rhythm nor the responses to distension. These results indicate that the tonic excitatory effect mediated by vagal efferents on the basal rhythm of the antrum is of central origin and independent of visceral inputs. Local mechanisms within the peripheral plexus of neurones could be responsible for the enhanced responses to step inflations, which would normally be adjusted by the central mechanisms through the extrinsic innervation. Possible effects of changes in the sensitivity of the post‐ganglionic neurones are discussed.
Noradrenaline and adenosine triphosphate as co‐transmitters of neurogenic vasoconstriction in rabbit mesenteric artery.
Authors: von Kügelgen I , Starke K
Published: December 2014

The largest rami caecales of the ileocolic artery, which is a branch of the mesenteric artery, were perfused at a constant rate of flow. Either vasoconstriction (as an increase in perfusion pressure) or the release of previously incorporated [3H]‐noradrenaline was measured. Noradrenaline and ATP, but not carbachol, serotonin, adenosine, Arg‐vasopressin and neuropeptide Y, caused marked vasoconstriction. When the sympathetic vasoconstrictor axons in the arterial wall were stimulated by electrical field pulses (either 5 pulses at 10 Hz or 100 pulses at 5 Hz; 0.3 ms pulse width, 200 mA current strength), the ensuing vasoconstriction was at best slightly reduced by phentolamine, prazosin and phenoxybenzamine. The response to 100 pulses, 5 Hz was even enhanced by phentolamine and yohimbine. All antagonists except yohimbine blocked the effect of exogenous noradrenaline. Prazosin did not change the effect of exogenous ATP. alpha,beta‐Methylene‐ATP (3‐15 mumol/l) elicited transient vasoconstriction. Subsequently, responses to ATP as well as to electrical stimulation were reduced and recovered slowly. The response to noradrenaline was not changed. That part of the electrically induced vasoconstriction that remained after alpha,beta‐methylene‐ATP was almost abolished by phentolamine or prazosin. Pre‐treatment of the animals with reserpine decreased but did not prevent the electrically evoked contraction of their arteries. The reserpine‐resistant response was not changed by prazosin but was abolished by alpha,beta‐methylene‐ATP. The vasoconstriction elicited by electrical pulses was not affected by atropine or methysergide but was entirely blocked by tetrodotoxin, guanethidine or exposure to 6‐hydroxydopamine. In arteries pre‐incubated with [3H]‐noradrenaline, electrical stimulation (100 pulses at 5 Hz) increased the outflow of tritium. The evoked overflow was blocked by tetrodotoxin, not changed by alpha,beta‐methylene‐ATP (9 mumol/l) or prazosin, and enhanced by phentolamine, phenoxybenzamine and yohimbine. We conclude that, in the branch of the mesenteric artery examined, both noradrenaline and ATP or a closely related compound transmit information from sympathetic neurones to smooth muscle. An alpha‐adrenoceptor antagonist can reduce neurogenic vasoconstriction by blockade of post‐junctional alpha‐(probably alpha 1) receptors, reserpine by selective depletion of noradrenaline, and alpha,beta‐methylene‐ATP by desensitization of the post‐junctional ATP (probably P2) receptor mechanism. Noradrenaline and ATP appear to be released from the same neurone. In addition, prejunctional alpha 2‐adrenergic autoinhibition of transmitter release operates in the artery. alp
Tightness of the blood‐brain barrier and evidence for brain interstitial fluid flow in the cuttlefish, Sepia officinalis.
Authors: Abbott N J , Bundgaard M , Cserr H F
Published: December 2014

Cephalopod molluscs have complex brains and behaviour, yet little is known about the permeability of their blood‐brain interface. The accompanying paper characterized the fluid compartments of the brain and presented evidence for restricted permeability of the blood‐brain interface to albumin. The present paper investigates the permeability of the interface to small non‐electrolytes. [14C]Polyethylene glycol (PEG, mol. wt. 4000), and [51Cr]EDTA (mol. wt. 342) were injected intravenously or intramuscularly, and their penetration into brain and muscle studied up to 48 h. Tracers equilibrated with muscle interstitial fluid (ISF) at relatively short times, but in brain ISF reached only 0.5‐0.65 X their plasma concentration. This is qualitative evidence for the presence in brain of a barrier to these molecules and an efficient drainage mechanism for ISF. Quantitative treatment of the uptake data allows calculation of the permeability X surface area product (PS) and the permeability coefficient (P). For the brain PS and P are in the range 1‐3 X 10(‐4) ml g‐1 min‐1 and 1‐3 X 10(‐8) cm s‐1 respectively, (PEG), and 3 X 10(‐4) ml g‐1 min‐1 and 3‐4 X 10(‐8) cm s‐1 respectively (Cr‐EDTA). The P values are close to those reported for mammalian brain. Assuming that the lack of equilibration in brain is due to ISF flow, the rate of flow can be calculated. Values for vertical and optic lobe are approximately 0.2 microliter g‐1 min‐1, again close to those reported for mammalian brain. It is concluded that the tightness of the Sepia blood‐brain barrier approaches that of mammals, and a flowing ISF system is present. An association between a tight barrier and higher central nervous system integrative function is suggested. The significance of these findings for the evolution of control of the brain microenvironment is discussed.
Evidence for the ordered release of rubidium ions occluded within the Na,K‐ATPase of mammalian kidney.
Authors: Glynn I M , Howland J L , Richards D E
Published: December 2014

When Na,K‐ATPase containing occluded rubidium ions is exposed to orthophosphate, in the presence of magnesium ions, there is a rapid release of half or all of the occluded ions. This behaviour is observed irrespective of whether the occluded‐rubidium form of the enzyme is generated by putting the unphosphorylated enzyme in a sodium‐free medium containing rubidium ions, or by allowing rubidium ions to catalyse the hydrolysis of phosphoenzyme made by adding ATP to enzyme suspended in a medium containing sodium and magnesium ions. The release of occluded rubidium ions by orthophosphate requires the presence of magnesium, presumably because phosphorylation is necessary. Whether the addition of orthophosphate causes the rapid release of all or of half of the occluded rubidium depends on whether free rubidium (or potassium, thallium or (probably) caesium ions) are present in the medium at the time the orthophosphate is added. In the absence of free ions of these species, all of the occluded rubidium is released. In their presence (in adequate concentration), only half of the occluded rubidium is released. The relative effectiveness of the different potassium congeners in preventing the rapid release of 50% of the occluded rubidium when orthophosphate is added is: thallium greater than rubidium greater than potassium greater than caesium. Lithium and sodium are ineffective even at high concentrations, and sodium ions strongly antagonize the effect of free rubidium ions. In a sodium‐free, Tris medium, the concentration of free rubidium ions necessary for a half‐maximal effect is about 30 microM. In a medium containing 250 microM‐free rubidium, the concentration of sodium necessary to reduce the effect of free rubidium by 50% is about 500 microM. These figures are compatible with the hypothesis that the free rubidium or other ions act at the potassium‐loading sites at the extracellular face of the pump. By starting with enzyme occluding unlabelled rubidium, and using 86Rb‐labelled free rubidium, it is possible to show that the free ions that prevent the rapid release of half of the occluded ions themselves become occluded. These experiments are significant in two ways. First, they provide direct evidence for the existence of a second route for the release of occluded rubidium (and therefore presumably of occluded potassium) ions. Secondly, they seem to require that the release of occluded ions by this route occurs in an ordered fashion.
Differential effects of carbon dioxide and pH on central chemoreceptors in the rat in vitro.
Authors: Harada Y , Kuno M , Wang Y Z
Published: December 2014

The brain stem, cervical cord and attached phrenic nerve were excised from neonatal rats and superfused in vitro. Respiratory activity was recorded from the phrenic nerve following transection of all the cranial nerves and dorsal roots. The frequency of spontaneous periodic activity recorded from the phrenic nerve was 6‐14/min during superfusion with a saline solution equilibrated with 5% CO2 in O2 at 25 degrees C (pH 7.3). The magnitude of respiration was estimated from the peak value of phrenic activity integrated for each 0.1 s period. When the pH of the superfusion fluid was altered by changing the HCO3‐concentration at constant PCO2, respiratory activity increased in low pH and decreased in high pH. These changes were maintained as long as a given pH was held. Respiratory changes observed under these conditions were characterized by alterations in both respiratory frequency and magnitude. When the CO2 level of the superfusion fluid was altered, maintaining constant pH by modified HCO3‐concentrations, respiratory activity increased at high PCO2 and decreased at low PCO2. These changes were transient and lasted only for a few minutes after exposure to a new level of PCO2. Respiratory changes observed under these conditions were characterized by alterations in magnitude but not in frequency. At constant PCO2 an increase in the HCO3‐concentration occasionally enhanced the magnitude of respiration before respiratory activity was depressed by the increased pH. This suggests that HCO3‐ may act independently as a stimulus to the central chemoreceptor. It is concluded that the mammalian central chemoreceptor for respiratory control is responsive independently to H+ and CO2 and that H+ and CO2 exert differential effects on the respiratory centre in terms of frequency and magnitude. It is suggested that frequency modulation and magnitude (tidal volume) modulation for respiratory control are triggered at different regions in the respiratory centre and/or rely on different mechanisms.
Neurones in the brain stem of the cat excited by vagal afferent fibres from the heart and lungs.
Authors: Bennett J A , Goodchild C S , Kidd C , McWilliam P N
Published: December 2014

Extracellular recordings were made from 164 neurones in the nucleus tractus solitarius and dorsal motor vagal nucleus of the chloralose‐anaesthetized cat. 139 neurones were excited synaptically and 25 non‐synaptically by electrical stimulation of cardiac and pulmonary vagal branches. Synaptically excited neurones fall into two populations, one activated solely by myelinated afferent fibres and a second activated solely by non‐myelinated afferent fibres. 94 neurones were synaptically excited by afferent fibres in a single vagal branch while 45 were excited by stimulation of two or three branches. Neurones responding to volleys in myelinated afferent fibres were located in both medial and lateral regions of the nucleus tractus solitarius whilst those excited by non‐myelinated afferent fibres were restricted to the medial region. Consistent differences in the locations of neurones excited by stimulation of either cardiac or pulmonary or by single or several branches could not be distinguished.
Influence of loop diuretics and anions on passive potassium influx into human red cells.
Authors: Chipperfield A R
Published: December 2014

Passive K influx into human red cells was measured with and without Cl ions, Na ions and loop diuretics. Ouabain and loop diuretics appear to inhibit specifically and respectively the Na pump and (Na+K) 'co‐transport'. Inhibitors of other pathways, e.g. 4,4'‐diisothiocyantostilbene‐2,2'‐disulphonic acid or amiloride did not inhibit passive K influx. Loop diuretics inhibited with high apparent affinity in Na‐containing media and with low apparent affinity in Na‐free media where there was a substantial Cl‐dependent component. The Cl concentration dependence was measured using six anion substitutions for Cl. With NO3, acetate and gluconate, the curves were sigmoidal and not fully saturable at 150 mM‐Cl; with iodide and thiocyanate, the curves were convex; with sulphate, there was saturation at 120 mM‐Cl. The half‐maximal K influx as a function of [Na]0 was 40 mM for the Cl‐dependent flux component and 12 mM for the diuretic‐sensitive flux.