bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of phorbol ester on cholecystokinin octapeptide‐evoked exocrine pancreatic secretion in the rat.
Authors: Francis L P , Camello P J , Singh J , Salido G M , Madrid J A
Published: December 2014

1. A comparative study was made of the effect of the phorbol ester, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) on cholecystokinin octapeptide‐evoked exocrine pancreatic secretion in the anaesthetized rat and isolated permeabilized pancreatic acinar cells. 2. Cholecystokinin octapeptide (CCK8; 0.10‐6.40 nmol (kg body weight)‐1) induced dose‐dependent increases in pancreatic juice flow, total protein output and amylase release in the anaesthetized rat. 3. Administration of TPA (10(‐8) mol (kg body weight)‐1) in combination with CCK8 resulted in marked attenuation of the CCK8‐evoked secretory response. 4. Simultaneous injection of polymyxin B (10(‐8) mol (kg body weight)‐1), an inhibitor of protein kinase C, with TPA and CCK8 reversed the inhibitory effect of the phorbol ester on CCK8‐induced pancreatic juice flow, total protein output and amylase release. 5. In permeabilized rat pancreatic acini CCK8 (10(‐13)‐10(‐9) M) elicited dose‐dependent increases in [3H]leucine‐labelled protein secretion (3H‐labelled protein release). Combining TPA (10(‐8) M) with CCK8 resulted in an inhibition of the CCK8‐induced 3H‐labelled protein release especially at lower concentrations of CCK8. At higher concentrations of CCK8, TPA was unable to inhibit the CCK8‐evoked 3H‐labelled protein release. Again, polymyxin B reversed the TPA‐induced inhibition of CCK8‐evoked 3H‐labelled protein output. 6. The results indicate that protein kinase C activation may play an important physiological role in modulating the CCK8‐evoked secretory response in rat pancreas in vivo and in vitro.
Changes in sodium channels during neural differentiation in the isolated blastomere of the ascidian embryo.
Authors: Okamura Y , Shidara M
Published: December 2014

1. The current density and the kinetics of voltage‐sensitive sodium channels during neural differentiation were examined in the isolated, cleavage‐arrested blastomere of ascidian embryos which contains presumptive neural regions. The macroscopic sodium current were measured with the two‐microelectrode voltage‐clamp technique and the single sodium channel currents were recorded with the patch‐clamp technique under the cell‐attached configuration. 2. The entire time course of sodium channel development could be divided into three phases from the current density and channel gating properties. 3. In the first phase, from fertilization to about 40 h, the density of the sodium channel current was from 8 to 50 microA cm‐2. The channel gating properties were similar to those of the sodium channel in the egg cell except for a negative shift in the voltage dependence of the peak inward current, the steady‐state inactivation, and the decay time constant. The sodium channels in this phase were classified as ‘type‐I’ channels. 4. In the second phase (40‐60 h after fertilization), the density of the sodium channel current increased from 20 to 800 microA cm‐2. The curves of the I‐V relationship and of the steady‐state inactivation shifted in the positive direction by 5‐10 mV. 5. At 45‐55 h, when the rate of increase in the sodium current was greatest, as much as 40 microA cm‐2 h‐1, the decay time course of the sodium current became slowest. The time for the current to decline from the peak to the one‐tenth of the peak (t 1/10) increased to about five times that in the first phase. After 55 h t 1/10 gradually decreased. 6. In this phase, steady‐state inactivation curves showed two inflexion points at different levels of membrane potential and were fitted with a sum of two Boltzmann distribution curves with distinct parameters. The relative contribution of the component with its voltage dependence shifted in the positive direction tended to decrease with development. 7. On examining single‐channel recordings, two types of sodium channel were identified in this phase. One type (type‐II) showed frequent repetitions of open‐to‐shut states throughout a voltage step. The ensemble current of the type‐II channel showed a slow decay, suggesting that this type of channel may underlie the markedly slow decay of the macroscopic current in this phase. The second type (type‐III) had more late openings than the type‐I channel but fewer than the type‐II channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of stretch‐activated ion channels in Xenopus oocytes.
Authors: Yang X C , Sachs F
Published: December 2014

1. The gating and permeation properties of endogenous stretch‐activated (SA) ion channels in Xenopus oocytes have been studied using the patch‐clamp single channel recording technique. 2. As estimated from the probability of being open (Po), SA channels were equally sensitive to suction or pressure. The Po was also weakly sensitive to voltage, increasing with depolarization. Channel activation did not require Ca2+. 3. Kinetic analysis of single‐channel records indicated that there are three closed states and one open state. Among three closed‐time distributions, the longest was the most sensitive to both pipette pressure and membrane voltage. The open time was independent of both pressure and voltage under a wide variety of ionic conditions, but was sensitive to the species of extracellular ion as follows: Na+ greater than Cs+ greater than K+ greater than Rb+ greater than Li+. The open time had a monotonic mole fraction relationship in mixtures of Li+ and K+. 4. The SA channels were cation‐selective inward rectifiers. The selectivity for permeation, based on slope conductance, was: K+ greater than NH4+ greater than Cs+ greater than Rb+ greater than Na+ greater than Li+ greater than Ca2+. 5. Tetraethylammonium (TEA+) was impermeable but was not a channel blocker. 6.Open‐channel current amplitude saturated with increasing extracellular K+, and was a monotonic function of the mole fraction of Li+ and K+ in mixtures of the two ions. 7. The channel has at least two separate ion binding sites: an intra‐channel site suggested by the permeation data, and an allosteric site suggested by the voltage‐independent effects of permeant ions on open time. A symmetric two‐barrier, one‐site model can quantitatively describe the permeation data. A kinetic model is proposed to quantify the gating kinetics and the effect of ion binding at the allosteric site.
M‐current noise and putative M‐channels in cultured rat sympathetic ganglion cells.
Authors: Owen D G , Marsh S J , Brown D A
Published: December 2014

1. Whole‐cell recordings of M‐currents and single‐channel recordings have been made in cultured rat sympathetic ganglion (SCG) neurones using the patch clamp technique. 2. Muscarine caused a reduction in macroscopic M‐current relaxations, induced by voltage steps, and a concomitant reduction in whole‐cell current noise. Power spectra of the muscarine‐sensitive component of current noise were fitted with two Lorentzian components corresponding, on average, to 162 and 15 ms. The longer time constant was very similar to that of deactivation tail currents measured at the same potential. 3. The single‐channel conductance at ‐30 mV was estimated from power density spectra and whole‐cell current‐variance relationships to be 1‐2 pS. 4. Putative single M‐channels, activated by depolarization, were identified in cell‐attached and outside‐out patches from cultured SCG neurones. In particular, the ensemble average of a small amplitude channel (estimated to be ca4 pS in physiological [K+]) in a cell‐attached patch, exhibited a similar time dependence to whole‐cell M‐current.
Convergence of Ia fibres from synergistic and antagonistic muscles onto interneurones inhibitory to soleus in humans.
Authors: Schieppati M , Romanò C , Gritti I
Published: December 2014

1. The possibility that Ia afferent fibres from the gastrocnemius medialis (GM) and from the tibialis anterior (TA) muscle could converge on to a single interneuronal pool inhibitory to the soleus motoneurones was investigated. 2. The soleus H reflex, evoked by tibial nerve stimulation in the popliteal fossa, was conditioned by separate or combined stimulation of the nerves to the GM or TA muscles. Stimulus intensity was below the motor threshold (MTh), and the conditioning‐test intervals were such as to evoke short‐latency inhibition of the soleus H reflex. Care was taken to avoid current spread and artifacts connected with the closeness in time and space of the conditioning and test stimuli. 3. Separate stimulation of both GM and TA nerves was able to induce significant inhibitory effects on the H reflex amplitude at stimulus strengths larger than 0.75 x MTh, on the average. Combined stimulation of the two nerves was able to reduce the H reflex at lower stimulus strengths, at which either nerve was ineffective alone. 4. Conditioning stimulus strengths close to the MTh reduced the H reflex to approximately 80% of the control value, both on single and combined stimulation, i.e. saturation of the inhibitory effect was found. 5. By extrapolating the regression line through the normalized data from all subjects, it was assumed that the smallest stimulus strength necessary to drive the inhibitory interneurones to threshold was, on the average, 0.5 and 0.6 x MTh, on combined and separate nerve stimulation, respectively. 6. Tonic voluntary activation of the soleus abolished the inhibitory effects of both separate and combined stimulations. This was tested on the H reflex, on the rectified and averaged EMG, and on the peristimulus histogram of single motor unit discharge. 7. The findings strongly suggest the existence of spatial summation of the effects from GM and TA muscle at the level of a single interneuronal pool. Most probably, the responsible afferent fibres are group I spindle afferents, and the interneurones those mediating the reciprocal inhibition. The data do not support the notion of parallel pathways, exclusive to each nerve.
Perceived pitch of vibrotactile stimuli: effects of vibration amplitude, and implications for vibration frequency coding.
Authors: Morley J W , Rowe M J
Published: December 2014

1. The effect of changes in amplitude on the perceived pitch of cutaneous vibratory stimuli was studied in psychophysical experiments designed to test whether the coding of information about the frequency of the vibration might be based on the ratio of recruitment of the PC (Pacinian corpuscle‐associated) and RA (rapidly adapting) classes of tactile sensory fibres. The study was based on previous data which show that at certain vibration frequencies (e.g. 150 Hz) the ratio of recruitment of the PC and RA classes should vary as a function of vibration amplitude. 2. Sinusoidal vibration at either 30 Hz or 150 Hz, and at an amplitude 10 dB above subjective detection thresholds was delivered in a 1 s train to the distal phalangeal pad of the index finger in eight human subjects. This standard vibration was followed after 0.5 s by a 1 s comparison train of vibration which (unknown to the subject) was at the same frequency as the standard but at a range of amplitudes from 2 to 50 dB above the detection threshold. A two‐alternative forced‐choice procedure was used in which the subject had to indicate whether the comparison stimulus was higher or lower in pitch (frequency) than the standard. 3. Marked differences were seen from subject to subject in the effect of amplitude on perceived pitch at both 30 Hz and 150 Hz. At 150 Hz, five out of the eight subjects reported an increase in pitch as the amplitude of the comparison vibration increased, one experienced no change, and only two experienced the fall in perceived pitch that is predicted if the proposed ratio code contributes to vibrotactile pitch judgements. At 30 Hz similar intersubject variability was seen in the pitch‐amplitude functions. 4. The results do not support the hypothesis that a ratio code contributes to vibrotactile pitch perception. We conclude that temporal patterning of impulse activity remains the major candidate code for pitch perception, at least over a substantial part of the vibrotactile frequency bandwidth.
Interval dependence of force and twitch duration in rat heart explained by Ca2+ pump inactivation in sarcoplasmic reticulum.
Authors: Schouten V J
Published: December 2014

1. The influence of the interstimulus interval on twitch duration was analysed in isolated heart muscle of the rat. When the muscle was in the steady state at interstimulus intervals at 5 s a test interval was interposed and varied. Duration of twitch and action potential, sarcomere length and peak force of the test beats were measured. 2. Twitch force and duration increased when the test interval was increased from 0.4 to 10 s. This effect was abolished by inhibitors of sarcoplasmic reticulum function (ryanodine, caffeine, Sr2+). Hence, the interval dependence is controlled by the sarcoplasmic reticulum. 3. Post‐extrasystolic potentiation, variation of [Ca2+]o and [Na+]o and blocking of iCa with nifedipine and Mn2+ led to large variations in force, reflecting variations in the amount of Ca2+ released from the sarcoplasmic reticulum. The effect on twitch duration was small, indicating that twitch duration was rather insensitive to the amount of released Ca2+, and not controlled by iCa and Na(+)‐Ca2+ exchange. 4. Action potential duration was much shorter than twitch duration and, depending on the intervention, changes were in the same or in opposite direction. Hence, the action potential did not determine twitch duration. 5. Small variations in sarcomere length amongst test contractions were observed, but these variations could not account for the effects of the test interval. 6. It is proposed that the Ca2+ pump in the sarcoplasmic reticulum is activated during each contraction and inactivates slowly. Thus, after a short interval the pump is still activated and rapidly sequesters much of the released Ca2+ leading to a small twitch and rapid relaxation. This mechanism ensures proper relaxation and diastolic filling of the ventricle. The biochemical basis and implications of the hypothesis are discussed.
4‐Aminopyridine causes a voltage‐dependent block of the transient outward K+ current in rat melanotrophs.
Authors: Kehl S J
Published: December 2014

1. Whole‐cell voltage‐clamp recordings were made from acutely dissociated melanotrophs obtained from adult rats. 2. In the presence of external Na+ and Ca2+ channel blockers and 20 mM‐tetraethylammonium (TEA) depolarizations to ‐40 mV or more evoked a fast‐activating fast‐inactivating outward K+ current (IK(f)). Double‐pulse experiments showed that steady‐state half‐inactivation occurred near ‐37 mV; half‐maximal activation of IK(f) occurred at ‐15 mV. Recovery from inactivation in most cells fitted a single exponential with a time constant of 40‐50 ms. 3. When applied either internally or externally, 1‐2.5 mM‐4‐aminopyridine (4‐AP) substantially reduced IK(f) but the degree of block was affected by the intensity, duration and frequency of depolarizing commands. 4. Analysis of the steady‐state voltage dependence of the block by 4‐AP showed that half‐maximal blocking occurred at approximately ‐31 mV. This implied that 4‐AP binds to the resting state of the IK(f) channel. 5. Studies of the time dependence for the blocking or unblocking of IK(f) showed that both processes were exponential with mean time constants of 1942 ms (at ‐70 mV) and 726 ms (at 20 mV), respectively. Recovery from inactivation was apparently unaffected by 4‐AP. 6. A four‐state sequential model in which 4‐AP reversibly binds to the resting state of the channel replicates the frequency dependence of the 4‐AP blockade.
Mechanism of action of substance P in guinea‐pig ileum longitudinal smooth muscle: a re‐evaluation.
Authors: Hall J M , Morton I K
Published: December 2014

1. A proposed mechanism of contractile action of substance P in guinea‐pig ileum longitudinal smooth muscle involving a decrease in membrane K+ permeability (PK) has been re‐examined. 2. Potentiation of responses to substance P by the K+ channel blocker tetraethylammonium (TEA) was originally proposed as evidence for a mechanism of action of substance P involving a decrease in PK. Potentiation was confirmed; however this was found not to be specific to substance P since a similar potentiation of responses was seen with agonists not thought to act via a decrease in PK. 3. Antagonism of contractile responses to substance P by noradrenaline was similarly confirmed. However, this antagonism was found to represent a non‐specific functional interaction through the inhibitory actions of beta‐adrenoceptors rather than the proposed specific interaction with an increase in PK by noradrenaline which is normally alpha 1‐adrenoceptor mediated. 4. Experiments were made measuring 86Rb efflux, in depolarized guinea‐pig ileum longitudinal smooth muscle, to estimate PK. These studies confirmed a reported decrease in PK with TEA, but failed to detect the previously reported decrease with substance P. 5. These results, although not disproving a suggested mechanism of direct contractile action of substance P in guinea‐pig ileum longitudinal smooth muscle involving a decrease in PK, do throw doubt on either the evidence, or its interpretation, as proposed by the original authors in support of such a mechanism.
Mechanisms underlying presynaptic inhibition through alpha 2‐adrenoceptors in guinea‐pig submucosal neurones.
Authors: Shen K Z , Surprenant A
Published: December 2014

1. Intracellular recordings were made from submucosal neurones of the guinea‐pig ileum. The actions of noradrenaline, somatostatin and [Met5]enkephalin on nicotinic synaptic potentials (EPSPs) were studied. 2. In one series of experiments, agonists were applied by superfusion; noradrenaline (0.1‐20 microM) decreased EPSP amplitude by 95‐100% in all neurones. Similar application of somatostatin (1‐100 nM) inhibited EPSPs in about half the neurones by a maximum of 40%. [Met5]enkephalin (0.1‐10 microM) did not alter EPSPs. Idazoxan and yohimbine competitively antagonized the action of noradrenaline with dissociation equilibrium constants of 20 and 30 nM respectively. 3. In another series of experiments, noradrenaline and somatostatin were applied locally from a pipette so that they reached presynaptic terminals but not the cell bodies or axons of the presynaptic cell: noradrenaline inhibited EPSPs by 90% in all neurones but somatostatin had no effect. When applied locally to the cell bodies giving rise to the presynaptic fibres, both agonists inhibited EPSPs in half the neurones by 40%. 4. When noradrenaline was applied locally to presynaptic terminals, the latency to onset of noradrenaline to inhibit EPSPs was 45‐160 ms; cadmium applied similarly depressed EPSPs in 5‐50 ms. 5. Pertussis toxin pre‐treatment only partially blocked presynaptic inhibition caused by noradrenaline but abolished the reduction of EPSP amplitude by somatostatin. 6. It is concluded that noradrenaline and somatostatin reduce the amplitude of the fast EPSP because they hyperpolarize cell bodies and prevent action potential initiation. Noradrenaline, but not somatostatin, has an additional action to inhibit acetylcholine release by acting at nerve terminal receptors. 7. The presynaptic inhibitory action of noradrenaline results from activation of alpha 2‐adrenoceptors at nerve terminals but the mechanism(s) by which these presynaptic receptors act cannot be explained adequately by either activation of a potassium conductance and/or inhibition of a calcium conductance.
Responses of bone and joint blood vessels in cats and rabbits to electrical stimulation of nerves supplying the knee.
Authors: Ferrell W R , Khoshbaten A , Angerson W J
Published: December 2014

1. Experiments were performed to assess the extent to which knee joint blood flow in cats and rabbits is affected by electrical stimulation of the nerve supply to the knee. 2. Absolute changes in blood flow were measured using the radiolabelled microsphere (approximately 15 microns) technique whilst relative changes in blood flow were assessed using laser Doppler flowmetry. 3. Despite deep general anaesthesia, sympathetic nerve fibres innervating cat knee joint blood vessels showed marked ‘tone’. 4. Blood flow to the joint capsule (synovium and overlying fibrous and areolar tissues) was substantially reduced (by approximately 90% in the cat and approximately 45% in the rabbit) during electrical stimulation of the articular nerve supply. 5. The percentage change in the laser Doppler flowmeter signal did not differ significantly from the percentage change in blood flow measured by microsphere technique. 6. Blood vessels in the cancellous bone of the distal femur (condyles) and proximal tibia (plateau) appear to be innervated by vasoconstrictor fibres which reach their effectors via the articular nerves. However, the cortical bone and red marrow of the diaphysis of the femur do not receive such innervation. 7. The potency of the vasoconstrictor influences acting on joint blood vessels could be of relevance in the pathogenesis of inflammatory joint diseases.
Intracellular mechanisms for alpha 1‐adrenergic regulation of the transient outward current in rabbit atrial myocytes.
Authors: Braun A P , Fedida D , Clark R B , Giles W R
Published: December 2014

1. The intracellular mechanism(s) underlying the decrease of a transient outward K+ current (It) induced by alpha 1‐adrenergic agonists was studied in isolated adult rabbit atrial myocytes using whole‐cell voltage clamp and cell‐attached patch clamp techniques. Experiments were carried out at 22‐23 degrees C. 2. Application of the specific alpha 1‐adrenergic agonist, methoxamine, produced a decrease in It which was irreversible after the non‐hydrolysable GTP analogues, GTP gamma S and Gpp(NH)p, had been introduced into cells via the recording micropipette. 3. Pre‐treatment of cells with 0.1‐0.15 microgram/ml pertussis toxin (PT) for 8‐9 h at 30‐34 degrees C did not prevent the alpha 1‐induced decrease in It. Yet, this protocol, as measured by the PT‐catalysed incorporation of [32P]ADP‐ribose in membrane‐associated 40 and 41 kDa proteins, effectively caused the ADP‐ribosylation of approximately 70% of the PT‐sensitive GTP‐binding proteins (i.e. Gi) in these treated cells. After taking into account the proportion of non‐viable cells (20‐30%), the effectiveness of this treatment probably approaches 100% in the viable myocytes from which electrophysiological recordings were made. 4. Cell‐attached patch recordings showed that bath application of methoxamine altered the single‐channel events underlying It by decreasing their opening probability. Averaged currents from ensemble single‐channel openings recorded in the presence of 0.2 mM‐methoxamine outside the patch reproduced the features of alpha 1‐adrenergic modulation of the macroscopic It observed during whole‐cell voltage clamp measurements. This observation provides evidence for the involvement of a diffusible intracellular second messenger in the alpha 1‐adrenergic modulation of It. 5. The protein kinase C (PKC) activators, 4 beta‐phorbol 12‐myristate 13‐acetate (PMA) and 1‐oleoyl‐2‐acetylglycerol (OAG) increased It, when included in the bath perfusate, whereas the inactive analogues, 4 alpha‐phorbol and 4 alpha‐phorbol 12,13‐didecanoate, had no effect on It. 6. Exposure of cells to the PKC inhibitors, staurosporine and H‐7, either by bath superfusion or intracellularly, via the recording micropipette, did not block the decrease in It produced by methoxamine. 7. Prolonged stimulation of atrial myocytes for 7‐9 h at 22 degrees C with 500 nM‐PMA produced a ‘down‐regulation’ of endogenous PKC activity, as well as a physical loss of the immunoreactive enzyme, as measured by an in vitro assay, and an anti‐PKC monoclonal antibody, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of pH changes on human and ferret detrusor muscle function.
Authors: Liston T G , Palfrey E L , Raimbach S J , Fry C H
Published: December 2014

1. The effects of altering extracellular pH on the electrically evoked contractions of ferret and human bladder (detrusor) smooth muscle have been investigated. pH was varied by changing superfusate PCO2 or NaHCO3 concentration. Acidosis increased force when superfusate PCO2 was raised but decreased force when the NaHCO3 concentration was reduced. 2. Intracellular pH (pHi) in isolated ferret detrusor cells was measured separately by epifluorescence microscopy. Extracellular pH changes caused by altering superfusate PCO2 were accompanied by similar changes of pHi, whereas variation of the NaHCO3 concentration had smaller effects on pHi. 3. It was proposed that intracellular acidosis increased contraction but extracellular acidosis depressed contraction. 4. Other interventions, such as addition and removal of NH4Cl, Cl‐ replacement, and NaHCO3 replacement with HEPES, changed pHi and had predictable effects on force. It was possible to describe unique relationships between tension and either intracellular or extracellular pH regardless of the means whereby pH changes were brought about. 5. Resting tension was reduced whether brought about by either intracellular or extracellular acidosis. K+ contractures were similarly affected by acidosis. Ferret preparations showed low levels of spontaneous activity, which was reduced by acidosis and enhanced by alkalosis.
Sources of adenosine released during neuromuscular transmission in the rat.
Authors: Smith D O
Published: December 2014

1. The levels of adenine nucleotides and adenosine which accumulate in the neuromuscular junction during nerve stimulation of the rat extensor digitorum longus (EDL) muscle were assayed biochemically. The sources were also determined by the use of different inhibitors. 2. ATP and total adenine nucleotide release increased as stimulation frequency increased, consistent with previous evidence indicating ATP release from presynaptic sources. 3. Adenosine levels also increased during nerve stimulation. However, accumulation decreased by 46‐58% when muscle activation was blocked by the addition of d‐tubocurarine (dTC). Adenosine levels also decreased by 40‐59% when adenine nucleotide hydrolysis to adenosine was blocked by the addition of 1 mM‐alpha,beta‐methyladenosine 5'‐diphosphate. Thus, approximately half of the extracellular adenosine is released from activated muscle while the other half is derived from adenine nucleotide hydrolysis. 4. Similar quantities of adenine nucleotide and acetylcholine (ACh) accumulated during nerve stimulation. With adenine nucleotide and ACh hydrolysis blocked by alpha,beta‐methyladenosine 5'‐diphosphate and eserine, respectively, the calculated amounts of adenine nucleotide and ACh released were 1.2 x 10(‐16) and 1.5 x 10(‐16) mol (stimulus impulse)‐1 endplate‐1. 5. AH5183 (vesamicol), which blocks ACh release, reduced extracellular ACh and adenine nucleotide accumulation by 40 and 45%, respectively. It did not affect adenosine release from the activated muscle. 6. Theophylline (100 microM), which blocks adenosine receptors, caused ATP accumulation to increase by 38%; extracellular levels of adenosine derived from adenine nucleotide hydrolysis also increased by 17%. These results are consistent with the presence of adenosine‐mediated inhibition of adenine nucleotide release. 7. It is concluded that adenine nucleotides (presumably in the form of ATP) and ACh are released jointly, and that ATP is hydrolysed fairly rapidly to adenosine. Adenosine resulting from ATP hydrolysis accounts for about half of the extracellular adenosine accumulating during nerve stimulation, while the other half is released directly by the underlying muscle.
Correlation between the discharges of motor units recorded from the same and from different finger muscles in man.
Authors: Bremner F D , Baker J R , Stephens J A
Published: December 2014

1. Cross‐correlation analysis of the discharges of individual motor units recorded from various different finger muscles has been performed during weak, isometric, voluntary contractions in man. 2. The dominant feature in 88% of the cross‐correlograms studied was a narrow, central peak, the area of which significantly exceeded that expected for independent processes (P less than 0.001). The highest bin counts in these central peaks were mostly within 5 ms of time zero in the histograms, and the base of these peaks extended between 5 and 31 ms (modal value = 13 ms with 90% of the values lying between 8 and 18 ms). The width and displacement of the central cross‐correlogram peaks were similar irrespective of whether the contributory spike trains were recorded from motor units active in the same finger muscle or recorded from motor units in different, co‐activated finger muscles. 3. The time course of the central peaks in this study was found to be consistent with the hypothesis that it is generated by the joint occurrence of EPSPs evoked in motoneurones by branches of common stem presynaptic fibres using the theoretical model developed by Kirkwood (Kirkwood & Sears, 1978). The model parameters providing the best fit with our experimental data imply that synaptic contacts on motoneurones made by these common inputs lie on average peripherally in the dendritic tree and generate small (less than 300 microV) EPSPs superimposed on a high level of background synaptic noise. 4. Minima (troughs) were found either side of the central peak in 27% of the cross‐correlograms studied, and their appearance was invariably associated with a large central peak. These secondary features could not be modelled with the same operator parameters that describe the central peaks. Their presence was particularly noticed in association with very regular discharges from the output motoneurones. 5. Smaller and broader secondary peaks symmetrically displaced 30‐55 ms either side of the large, narrow central peak were observed in 7% of the cross‐correlograms studied. We suggest that these secondary features which were found at lags shorter than the interspike interval of the contributory motor unit spike trains reflect the autocorrelation functions of the spike trains of common input fibres. On this basis the observed displacement of these secondary peaks from the primary feature in the cross‐correlogram indicate firing rates for common input fibres in the range 18‐33 impulses s‐1. 6. In a small number of cases (1.4%) the cross‐correlogram was flat and indistinguishable from the results of cross‐correlating independent spike train data.
Variation in the degree of synchronization exhibited by motor units lying in different finger muscles in man.
Authors: Bremner F D , Baker J R , Stephens J A
Published: December 2014

1. Cross‐correlation analysis was performed on the discharges of motor units recorded from the same or from different finger muscles during weak, voluntary isometric contractions in man. 2. In 88% of cases such cross‐correlograms contained a narrow central peak indicating synchronization between the firing of the contributory motor units. Expressed in terms of the synchronization index, b (peak area/total number of reference plus response spikes) the amount of synchronization found in these different recordings ranged from b = 0.0057 to b = 0.1436 (n = 1230). The duration of the synchronization (measured across the base of the peak) ranged from 5 to 31 ms (mode = 13 ms). 3. For each pair of motor units examined the amount of synchronization between their firing varied from minute to minute of a long recording. In around half the cases studied this variation appeared to correspond to variation in the firing rates of the two motor units whereas in the other half of cases tested no relationship was found between the firing rates and the amount of synchronization. 4. Some motor unit pairings consistently showed more synchronization than other motor unit pairings within the same muscle. A frequency histogram of the synchrony measurements from all of the motor unit pairings tested in that muscle showed a unimodal and continuous distribution. 5. Some subjects consistently showed two or three times more motor unit synchronization than others in equivalent recordings. This rank order of motor unit synchronization in different subjects was found to be the same in all muscle pairings tested. 6. A similar distribution in the amount of motor unit synchronization found in different muscle pairings was found in all subjects tested. In the first place the firing of motor units which act on widely separated fingers was less synchronized than the firing of motor units acting on adjacent fingers. Secondly, motor units acting on the lateral fingers (thumb, index) showed less synchronization in their discharges than motor units acting on medial fingers (ring, little). Finally the firing of motor units in the finger flexor muscles were less synchronized than the firing of motor units in either the finger abductor or the finger extensor muscles. 7. The synchronization of motor unit activity in different muscles indicates the presence of a widespread projection pattern for the branches of some last‐order input fibres to finger muscle motoneurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Characteristics of sympathetic preganglionic neurones in the lumbar spinal cord of the cat.
Authors: Gilbey M P , Stein R D
Published: December 2014

1. In anaesthetized cats extracellular recordings have been made from antidromically identified sympathetic preganglionic neurones, located in the 2nd and 3rd lumbar segments, with axons projecting into the left lumbar sympathetic chain beyond the L4 ganglion. Sympathetic preganglionic neurones have been characterized with respect to: axonal conduction velocities, firing patterns in relation to ECG and phrenic nerve activity, responses to noxious stimuli applied to the ipsilateral hindlimb and ionophoretically applied 5‐HT. 2. Two hundred and ninety‐seven sympathetic preganglionic neurones were studied. Their axonal conduction velocities (0.5‐13.9 m/s) were in the B and C fibre range. Sixty‐eight had on‐going activity and the remainder were quiescent. Of the 229 quiescent sympathetic preganglionic neurons, 111 were activated by the ionophoretic application of glutamate. 3. Of the 100 sympathetic preganglionic neurones analysed for an ECG‐related pattern of discharge, forty‐nine had no, and fifty‐one had an ECG‐related pattern of discharge. Both sympathetic preganglionic neurones with on‐going activity and glutamate activated cells exhibited ECG‐related patterns of discharge. 4. Only six of fifty sympathetic preganglionic neurones had a respiratory‐related activity pattern. Three had maximal discharge during expiration and three during inspiration. 5. Forty‐one sympathetic preganglionic neurones were examined for their response to noxious stimulation of the ipsilateral hindlimb. Ten had their activity decreased (seven glutamate‐activated, three with on‐going activity), seven had their activity increased (four glutamate‐activated and three with on‐going activity) and twenty‐four were unaffected. These results demonstrate that both sympathetic preganglionic neurones with on‐going activity and glutamate‐activated neurones can be influenced by noxious input. Ten sympathetic preganglionic neurones had properties consistent with them having a skin vasoconstrictor function and three with muscle vasoconstrictor function. 6. Ionophoretic application of 5‐HT in the vicinity of fifty‐one sympathetic preganglionic neurones caused increases in the discharge of 53%, decreases in the firing of 12% and did not affect the discharge of 35%. 7. Sympathetic preganglionic neurones which had excitatory responses to 5‐HT showed only decreased discharge or no response to noxious stimulation of the ipsilateral hindlimb. Conversely, sympathetic preganglionic neurones which had discharge decreased by 5‐HT had primarily excitatory responses to noxious inputs. 8. It is concluded that lumbar sympathetic preganglionic neurones consist of a heterogeneous population with respect to their physiological properties and their responses to ionophoretically applied 5‐HT: both may be related to function.
Regulation of Ca2+ current in frog ventricular cardiomyocytes by 5'‐guanylylimidodiphosphate and acetylcholine.
Authors: Parsons T D , Lagrutta A , White R E , Hartzell H C
Published: December 2014

1. Calcium currents (ICa) were measured in frog ventricular myocytes using the whole‐cell patch clamp technique and a perfused pipette. The effect of internal perfusion with the hydrolysis‐resistant GTP analogue, GppNHp (5'guanylylimidodiphosphate), on basal ICa and ICa stimulated with forskolin or isoprenaline was examined to gain insight into the role of G proteins in ICa regulation. 2. Without added guanine nucleotides, isoprenaline stimulated ICa approximately 14‐fold with an EC50 of 0.09 microM. Forskolin stimulated ICa approximately 10‐fold with an EC50 of 0.30 microM. 3. Internal 30 microM‐GppNHp produced an approximately 80% decrease in ICa elevated by 0.3 microM‐isoprenaline or 3 microM‐forskolin. The inhibition of isoprenaline stimulation was due to a decrease in the maximal stimulation from approximately 14‐fold to approximately 14‐fold without a significant change in the EC50. In contrast, the reduction in forskolin stimulation was due to a 22‐fold increase in the EC50 to 11.4 microM, with little change in maximal stimulation. 4. The inhibition of stimulated ICa by GppNHp is likely to be mediated by a G protein, because the effects of GppNHp are irreversible, and are blocked by excess GTP. ICa is affected similarly by GppNHp and by ACh. This suggests that GppNHp activates the same G protein that is normally activated by ACh, but activation by GppNHp occurs in the absence of agonist occupation of the muscarinic receptor. 5. The increase in the EC50 for forskolin produced by internal GppNHp was reversed by exposure to isoprenaline, which itself did not affect ICa amplitude. On average, exposure to isoprenaline in the presence of GppNHp caused an irreversible 81‐fold decrease in the EC50 for forskolin to 0.14 microM. Stimulation of ICa by forskolin after internal GppNHp and exposure to isoprenaline was completely blocked by the protein kinase A inhibitor PKI(5‐22). 6. These effects do not involve the phospholipase C system, because they are not mimicked by phorbol esters or internal inositol 1,4,5‐trisphosphate (IP3) and are not blocked by bromophenacyl bromide or neomycin. 7. Direct effects of G proteins on ICa were not evident, because internal perfusion with PKI(5‐22) completely inhibited isoprenaline‐ or forskolin‐stimulated increases in ICa, and neither ACh nor internal GppNHp (30‐500 microM) affected basal ICa or ICa elevated by internally perfused cyclic AMP. 8. These results suggest that the predominant site of action of the inhibitory G protein activated by either GppNHp or ACh is adenylyl cyclase. Furthermore, the internally perfused frog cardiomyocytes may provide a useful approach for probing the detailed interactions of G proteins, forskolin, and adenylyl cyclase in an intact cell.
Effect of heat acclimation on diurnal changes in body temperature and locomotor activity in rats.
Authors: Shido O , Sakurada S , Nagasaka T
Published: December 2014

1. The present study was performed to examine the effects of heat exposure hours hours at a fixed time once a day on diurnal variations of deep body temperature, heat balance and locomotor activity in rats. 2. The heat‐exposed group (HE) was subjected to an ambient temperature of 33.5 degrees C for about 5 h in the last half of the dark phase daily for at least 10 consecutive days, while the control rats were constantly kept at 24 degrees C. 3. After the completion of the heat exposure schedule, hypothalamic temperature (Thy), heat loss, heat production and locomotor activity of HE rats significantly decreased for 3‐4 h during the period of previous heat exposure time and formed a characteristic trough in the dark phase, which was never observed in the control rats or in the HE rats before the start of the heat exposure schedule. 4. The troughs of Thy, heat loss and heat production in the dark phase were persistent for at least 2 days after the end of the heat exposure schedule. The reductions of locomotor activity in this period were, however, observed only on the first day after stopping the heat exposure schedule. 5. These results suggest that the time memory for heat exposure was formed in heat‐acclimated rats and was persistent for at least 2 days after the removal of heat exposure. It is also concluded that the reduction in metabolic heat production contributed to the fall of Thy during the period of heat exposure.
Calcium influx in resting conditions in a preparation of peptidergic nerve terminals isolated from the rat neurohypophysis.
Authors: Toescu E C
Published: December 2014

1. Calcium accumulation in a preparation of nerve terminals isolated from the rat neurohypophysis was measured both in rapid (10‐60 s) and long‐term (up to 60 min) uptake experiments, by use of 45Ca2+ as radiotracer and ion‐exchange chromatography as separation method. Unless otherwise stated all experiments have been performed in the absence from the incubation media of secretagogues or depolarizing agents. 2. The uptake of 45Ca2+ in nerve terminals was linear up to 30‐45 s, with an apparent initial rate of uptake of 0.98 nmol Ca2+ (mg protein)‐1 min‐1. 3. The level of 45Ca2+ accumulation was sensitive to manipulations of electrochemical gradient for Na+ across the plasma membrane. Alterations of extracellular concentrations of Na+ affected secretory activity to a larger extent than manipulations of internal Na+. These effects were not qualitatively dependent on the nature of the replacement for Na+. 4. Removal of extracellular Na+ induced a significant increase of both the level of 45Ca2+ accumulation and of the apparent initial rate of uptake. The concentration for half‐maximal stimulatory effect was 40 mM‐Na+. 5. The analysis of the stimulatory effect of high extracellular K+ on the 45Ca2+ accumulation reveals at least two components: a depolarization and an intrinsic K+ effect. 6. Sodium channel inhibitors (TTX, 1.25 microM) decreased significantly the level of 45Ca2+ accumulation, an effect which was evident from the first minute of exposure to the drug. 7. A specific L‐type Ca2+ channel blocker (nicardipine) inhibited 45Ca2+ uptake, in a dose‐dependent manner. Simultaneous addition of both TTX and nicardipine (20 microM) decreases the 45Ca2+ uptake up to 50%. 8. In conclusion, the uptake of Ca2+ in isolated peptidergic nerve terminals, incubated in resting conditions, is mediated by at least three pathways: a TTX‐sensitive and a nicardipine (dihydropyrine)‐sensitive pathway and through a Na(+)‐Ca2+ exchange‐dependent mechanism. The principal route of Ca2+ entry appears to be through TTX‐sensitive channels.
Neurally evoked potentiation of tonic contractions in the guinea‐pig vas deferens involves adenosine receptors.
Authors: Tsunoo A , Kurokawa M , Takahashi K
Published: December 2014

1. In the pelvic plexus‐vas deferens preparation of the guinea‐pig, conditioning stimulation of the pelvic nerves depressed the phasic component of biphasic contractions evoked by test stimulation of the hypogastric nerves, but potentiated the tonic component. 2. Similarly, in the deganglionated vas deferens preparation, conditioning stimulation applied directly to postganglionic nerves issuing from the pelvic nerve side of the pelvic plexus depressed the phasic component of biphasic contractions evoked by test stimulation of the nerves issuing from the plexus on the side of the hypogastric nerve, but potentiated the tonic component. 3. In the deganglionated preparation in the presence of alpha,beta‐methylene adenosine 5'‐triphosphate (alpha,beta‐mATP) by which the phasic component was removed, test contractions were markedly reduced by phentolamine and prazosin, and potentiated in a manner dependent on the magnitude of conditioning stimulation. 4. In the deganglionated preparations that were persistently exposed to alpha,beta‐mATP (5‐10 microM), attempts were made to identify the substance(s) mediating the potentiation of the prazosin‐sensitive contractions and their sites of action. 5. Noradrenaline and neuropeptide Y depressed the test contractions. 6. ATP, adenosine 5'‐diphosphate, adenosine 5'‐monophosphate and adenosine potentiated the contractions. Inosine and adenine were without effect. The effect of ATP was antagonized by 8‐phenyltheophylline. N6‐Cyclohexyladenosine (CHA) potentiated the contractions in a dose‐dependent and 8‐phenyltheophylline‐sensitive manner. 7. The conditioning stimulation‐induced potentiation of test contractions was antagonized by 8‐phenyltheophylline, but was further increased by dipyridamole. 8. Methoxamine‐evoked contractions were potentiated by conditioning stimulation of the nerves in a manner antagonized by 8‐phenyltheophylline, and also by CHA. 9. Adenosine and CHA inhibited in an 8‐phenyltheophylline‐sensitive manner field stimulation‐induced release of 3H‐activity from deganglionated vas deferens preloaded with [3H]noradrenaline. 10. In the deganglionated preparation that was not exposed to alpha, beta‐mATP, ATP‐evoked contractions were potentiated by conditioning stimulation and by CHA. 11. It is indicated that conditioning stimulation and adenosine exert opposite actions on phasic and on tonic contractions in spite of the results showing that each of them postjunctionally potentiates the responses to both ATP and noradrenaline. 12. These results suggest that conditioning stimulation releases adenosine and that adenosine potentiates tonic contractions by increasing the responsiveness of the muscle to noradrenaline through the postjunctional adenosine receptors.
Inositol tetrakisphosphate liberates stored Ca2+ in Xenopus oocytes and facilitates responses to inositol trisphosphate.
Authors: Parker I , Ivorra I
Published: December 2014

1. The actions of the putative second messenger inositol 1,3,4,5‐tetrakisphosphate (Ins(1,3,4,5)P4) were studied by injecting it into voltage‐clamped oocytes while recording Ca(2+)‐dependent chloride membrane currents and, in some experiments, fluorescence signals from Ca2+ indicators. 2. Ins(1,3,4,5)P4 evoked a rise in intracellular Ca2+ and associated chloride current in oocytes bathed in normal or Ca(2+)‐free Ringer solutions. The fluorescence Ca2+ signal showed a prolonged rise with superimposed oscillations, whereas the current reflected only the oscillatory component. 3. Injections of inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) evoked currents showing an initial transient, followed by oscillations. Ins(1,3,4,5)P4 evoked similar oscillations, but the transient component was usually small or absent. Ins(1,3,4,5)P4 was about 20‐fold less potent than Ins(1,4,5)P3, as measured by comparing doses required to elicit currents with the same integral. The most sensitive oocytes responded to about 1 fmol Ins(1,3,4,5)P4 and 0.1 fmol Ins(1,4,5)P3. 4. Injections of Ins(2,4,5)P4 evoked oscillatory currents, with a potency about three times greater than Ins(1,4,5)P3. Ins(1,3,4)P4 was ineffective in some oocytes even at doses of several picomoles, but in other oocytes evoked small transient and oscillatory currents with a potency 100 times or more less than Ins(1,3,4,5)P4. 5. Injections of Ins(1,3,4,5)P4 made into the animal hemisphere of the oocyte evoked larger currents than injections into the vegetal hemisphere. 6. Photo‐release of Ins(1,4,5)P3 from caged Ins(1,4,5)P4 loaded into the oocyte was used to examine interactions between Ins(1,4,5)P3 and Ins(1,3,4,5)P4. Injection of low (ca 1 fmol) doses of Ins(1,3,4,5)P4 shortly before a light flash greatly facilitated currents evoked by photo‐release of near‐threshold amounts of Ins(1,4,5)P3. This facilitation was unaffected by removal of extracellular Ca2+ and arose because Ins(1,3,4,5)P4 reduced the threshold amount of Ins(1,4,5)P3 required to evoke a response. 7. Larger amounts (several femtomoles) of Ins(1,3,4,5)P4 depressed responses evoked by photo‐release of Ins(1,4,5)P3. This may arise because Ca2+ liberated by Ins(1,3,4,5)P4 inhibits the ability of Ins(1,4,5)P3 to release further Ca2+. 8. We conclude that Ins(1,3,4,5)P4 liberates intracellular Ca2+ in the oocyte in a manner similar to that of Ins(1,4,5)P3, and suggest that a physiological role for Ins(1,3,4,5)P4 may be to facilitate responses to Ins(1,4,5)P3.