bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of membrane depolarization in the contractile response of the rabbit basilar artery to 5‐hydroxytryptamine.
Authors: Garland C J
Published: December 2014

1. 5‐Hydroxytryptamine (5‐HT, 10(‐9)‐10(‐4) M) depolarized and contracted smooth muscle cells (resting potential: ‐69.1 +/‐ 0.9 mV, n = 112) in isolated cylindrical segments of the rabbit basilar artery. 2. Simultaneous measurement of membrane potential and wall tension (n = 43, thirteen vessels) showed that the onset of 5‐HT‐induced depolarization coincided with the onset of smooth muscle contraction in the majority of cells studied. In addition, the onset of relaxation which followed the wash‐out of 5‐HT always preceded the onset of membrane repolarization by 52 +/‐ 8 s (n = 14). 3. In 30% of smooth muscle cells exposed to concentrations of 5‐HT greater than 10(‐6) M, fast rhythmic depolarizations (amplitude 10‐20 mV) were superimposed on the developing depolarization. Rhythmic membrane depolarization was always followed by rhythmic smooth muscle contraction, which peaked 2‐4 s after the peak of the fast depolarization. 4. Muscle contraction, but not depolarization, produced with concentrations of 5‐HT greater than 10(‐7) M, was significantly increased by the removal of intimal‐endothelial cells. 5. Smooth muscle depolarization recorded in the presence of increased extracellular K+ (greater than 5.2 mM) preceded the onset of smooth muscle contraction. For a similar change in membrane potential produced with either increased extracellular K+ or 5‐HT, the corresponding increase in arterial wall tension was always greater with 5‐HT. 6. The depolarization and contraction induced by 5‐HT was markedly reduced or abolished if extracellular Na+ was totally replaced, isosmotically, with either sucrose or Tris at pH 7.4. Normal‐sized contraction, but not depolarization, was recorded with 5‐HT in Na+‐free Tris solution at pH 8. 7. These observations suggest that 5‐HT‐stimulated contraction in cerebrovascular smooth muscle is largely a result of mechanisms other than depolarization of the smooth muscle cell membrane which it produces. However, high concentrations of 5‐HT (greater than 10(‐6) M) can stimulate additional depolarization, which has a faster time course and rhythmic nature. Discrete depolarizations of this type are responsible for initiating additional, phasic smooth muscle contractions.
The effects of chemical fixation on the permeability of frog mesenteric capillaries.
Authors: Clough G , Michel C C
Published: December 2014

1. We have investigated the effects on microvascular permeability of two chemical fixatives, glutaraldehyde/formaldehyde mixture and osmium tetroxide, both of which are used widely in electron microscopy. 2. The permeability of single perfused frog mesenteric capillaries was assessed using the technique of Michel (1980) to estimate the hydraulic conductance (Lp) of the vessel walls and the effective osmotic pressure (sigma delta pi) which could be exerted across them by the neutral macromolecule, Ficoll 70. 3. In each experiment, Lp and sigma delta pi were estimated in the same capillary before and after chemical fixation with either an aldehyde mixture (n = 6) or 1% osmium tetroxide (n = 6). In the absence of serum proteins in the perfusate, the values of Lp recorded prior to fixation were high. The effect of both fixatives was to reduce Lp. With aldehydes the mean value (+/‐ S.E.M.) of Lp fell from 22.1 (+/‐ 6.3) x 10(‐3) to 5.7 (+/‐ 2.0) x 10(‐3) microns s‐1 cmH2O‐1. With osmium tetroxide the mean Lp fell from 29.1 (+/‐ 8.5) x 10(‐3) to 8.6 (+/‐ 3.6) x 10(‐3) microns s‐1 cmH2O‐1. 4. The perfusates contained the neutral macromolecule, Ficoll 70, at a concentration of 60 mg ml‐1 which exerted an osmotic pressure of 35 cmH2O in a membrane osmometer. In the absence of plasma proteins in the perfusate, sigma delta pi was only a fraction of this perfusate oncotic pressure prior to fixation. After aldehyde treatment there was a small but insignificant decrease in sigma delta pi. Osmium tetroxide, however, increased sigma delta pi from a mean (+/‐ S.E.M.) of 6.3 (+/‐ 1.6) cmH2O before fixation to 16.4 (+/‐ 2.8) cmH2O after fixation, P less than 0.01 using a paired t test. 5. In three experiments, the reflection coefficient of the capillary wall to NaCl sigma NaCl, was measured using the technique of Curry, Mason & Michel (1976) before and after osmium fixation. Fixation raised sigma NaCl from a mean value (+/‐ S.E.M.) of 0.009 (+/‐ 0.001) to one of 0.017 (+/‐ 0.004). Although these changes may be interpreted as an increase in the contribution to the total Lp of the capillary wall of channels which are available only to water, the changes are too small for such a mechanism to account for the increase in reflection coefficient to Ficoll 70. 6. The reduction in Lp following chemical fixation could represent an increase in the hydraulic resistance of either the capillary wall itself, or in the tissues surrounding the vessel.(ABSTRACT TRUNCATED AT 400 WORDS)
Cardiovascular responses evoked from the fastigial region of the cerebellum in anaesthetized and decerebrate rabbits.
Authors: Bradley D J , Paton J F , Spyer K M
Published: December 2014

1. The rostral and caudal regions of the fastigial nucleus (f.n.) in both anaesthetized and decerebrate rabbits have been stimulated electrically while monitoring phrenic nerve activity, heart rate, blood pressure and blood flow to the kidney and hindlimb in addition to recording renal sympathetic nerve activity. 2. Stimulation of the rostral region of the f.n. in the anaesthetized and decerebrate rabbit produced a silencing of phrenic nerve discharge, either no change in heart rate or a vagally mediated bradycardia and a pressor response associated with vasoconstriction in both renal and femoral beds which resulted from an increase in sympathetic vasomotor tone. 3. Stimulation of the caudal region of the f.n. in the anaesthetized rabbit evoked apnoea and a bradycardia which was partially attenuated by vagal blockade. Also, a depressor response was obtained with no change in renal vascular resistance, a transient inhibition of renal sympathetic nerve discharge and a vasodilation in the hindlimb resulting from the withdrawal of sympathetic vasoconstrictor tone. In contrast, electrical stimulation of the same site in the unanaesthetized decerebrate rabbit evoked an increase in central inspiratory drive, a tachycardia and a pressor response with vasoconstriction in both vascular beds. The cardiac and vascular responses were abolished after sympathetic blockade. 4. Administration of a small dose of anaesthetic to the decerebrate preparation did not affect the direction of the cardiovascular or central respiratory responses evoked from the rostral f.n. but reversed the pattern of response elicited from the caudal f.n. to that seen in the intact anaesthetized rabbit. 5. The results of the present study suggest the existence of two separate regions associated with the f.n. which can influence the cardiovascular system in the rabbit. Furthermore, it would seem that the cardiovascular responses evoked from the vicinity of the caudal and rostral poles of the f.n. are mediated by two distinct pathways which might suggest two separate functional roles for the cerebellum in cardiovascular control in the rabbit.
Separate mechanisms inside and outside the blood—brain barrier inducing metabolic changes in febrile rabbits
Authors: Morimoto Akio , Murakami Naotoshi , Myogin Takahito , Takada Mitsuaki , Teshirogi Shyuichi , Watanabe Tatsuo
Published: December 2014

1. We investigated the acute phase response induced by either intravenous (I.V.) or intracerebroventricular injections of bacterial endotoxin or endogenous pyrogen. These caused either monophasic or biphasic fever, and the response includes changes in plasma concentration of iron, zinc, copper, fibrinogen and in circulating leucocyte count.

2. The I.V. injection of a small dose of endotoxin or endogenous pyrogen produced a monophasic fever, while a large dose produced a biphasic fever. The ventricular injection of endogenous pyrogen produced a fever similar to the second phase of the biphasic fever.

3. The I.V. injection of a small dose of endotoxin or endogenous pyrogen produced a low plasma zinc 8 h after injection, while the ventricular injection of endogenous pyrogen produced a low plasma zinc 24 h after injection. The I.V. injection of a large dose of endotoxin or endogenous pyrogen induced a low plasma zinc 8 and 24 h after injection, suggesting that the hypozincaemia induced by the large dose was mediated by both peripheral and central action of endogenous pyrogen with different time courses.

4. The I.V. injection of the small dose did not affect the level of the plasma copper concentration but the I.V. injection of the large dose and the ventricular injection increased it 24 h after injection. It is considered that the plasma copper concentration is mainly controlled by the central action of endogenous pyrogen.

5. The changes in the plasma iron and fibrinogen concentration and the circulating white blood cell count induced by the different doses and by the different routes showed very similar patterns, indicating that these are simultaneously controlled by both peripheral and central actions of endogenous pyrogen.

6. The present results show that there are two separate mechanisms involved in the acute phase response, one inside and one outside the blood—brain barrier. From the consideration that endogenous pyrogen released from the phagocytic leucocytes induces fever and acute phase response by its action on both the peripheral target organs and the central nervous system, it is suggested that endogenous pyrogen acts both centrally and peripherally, in the same manner as other hormonal agents such as corticosteroids.
Effects of stimulation of nasal and superior laryngeal inputs on the hindlimb vasculature of anaesthetized cats.
Authors: Jordan D , Paton J F , Wood L M
Published: December 2014

1. In chloralose‐anaesthetized artificially ventilated cats, either stimulation of the nasal mucosae with water or electrical stimulation of the superior laryngeal nerve (s.l.n.) resulted in apnoea, as measured from the phrenic nerve activity, and a rise in perfusion pressure of a hindlimb perfused at constant flow. In the absence of changes in venous pressure this vascular response would indicate vasoconstriction in the hindlimb. There was, however, no significant change in either heart rate or arterial blood pressure. 2. Simultaneous stimulation of the nasal mucosae and s.l.n. also resulted in apnoea but with a larger hindlimb vasoconstriction than was obtained with stimulation of only one input. This increased vasoconstriction was not significantly different from the one which in theory could be obtained by summing the two individual responses from stimulation of the nasal mucosae or s.l.n. 3. In cats anaesthetized with chloralose‐urethane, stimulation of the nasal mucosae or s.l.n. also evoked an apnoea and hindlimb vasoconstriction. However, in these animals this was accompanied by a bradycardia and small fall in arterial blood pressure. 4. The present results show that whilst stimulation of two parts of the upper respiratory tract evokes qualitatively similar responses in the hindlimb vasculature, simultaneous activation of the two stimuli does not appear to result in facilitation of this hindlimb vasoconstrictor response, simply an addition of those obtained on separate stimulation. The bradycardia evoked in response to upper airway stimulation is dependent on the anaesthetic used and in the present experiments could only be obtained in animals anaesthetized with choralose‐urethane.
Tonic contraction of canine gastric muscle during long‐lasting calcium removal and its dependence on magnesium.
Authors: Filipponi K , Golenhofen K , Hofstetter V , Hohnsbein J , Lammel E , Lukanow J
Published: December 2014

1. Tonic contractions induced by acetylcholine (ACh) in canine gastric fundus preparations were shown to persist during long‐lasting exposure to Ca2+‐free solution containing EGTA (1 mmol/l). These EGTA‐resistant contractions amounted to up to more than 50% of maximal ACh‐control responses in physiological salt solution. They could be evoked repeatedly for more than 20 h without reduction in size, each contraction lasting as long as ACh was present. 2. During prolonged exposure to Ca2+‐free solution at normal Mg2+ concentration ([Mg2+]O = 1.2 mmol/l), the preparations exhibited a slowly developing contracture (elevation of the baseline of contraction), which was particularly pronounced in strips taken from the circular layer of the muscular wall (44% of control ACh‐maximum after 4 h in Ca2+‐free solution). Contracture could be suppressed either by increasing [Mg2+]O to 6‐10 mmol/l or by depolarizing the cell membrane (replacement of external Na+ by K+). However, contracture also developed if, at physiological [Na+]O and [K+]O, [Mg2+]O was further increased to 50 mmol/l. 3. The combined effects of [Mg2+]O and membrane potential suggest that contracture is caused by a gain of Mg2+ by the cells. This conclusion is based on the assumption that (a) the cytoplasmic Mg2+ concentration is determined by the transmembrane electrochemical gradient acting on Mg2+, the magnesium permeability of the cell membrane (PMg) and an active extrusion mechanism, and that (b) Ca2+ removal leads to an increase of PMg which is (partly) prevented by an appropriate increase of [Mg2+]O. 4. 45Ca efflux experiments, performed at [Mg2+]O = 10 mmol/l to avoid interference of ACh responses with contracture, showed that the cellular 45Ca content decreased from some 200 mumol/kg wet wt. to less than 10 mumol/kg wet wt. within 10‐20 h in Ca2+‐free solution. Activations by ACh did not produce any detectable increase in 45Ca efflux. 5. The calcium ionophore A23187 (10(‐5) mol/l), applied in order to increase the calcium permeability of the cell membrane, did not reduce the EGTA‐resistant contractions. 6. Experimental procedures conducted to replace calcium within intracellular stores by strontium or barium did not affect the EGTA‐resistant ACh response. However, prior uptake of manganese by the cells had an amplifying effect. 7. Caffeine (30 mmol/l) failed to produce contraction in Ca2+‐free solution, whereas ACh evoked contractile responses, both in the presence of and after application of caffeine.(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic basis of membrane potential in developing ectoderm of the Xenopus blastula.
Authors: Baud C
Published: December 2014

1. The membrane potential and permeabilities of blastomeres isolated from the ectoderm of stage 6‐10 Xenopus blastulae have been investigated. The increase in membrane potential between stages 6 and 9, reported previously in intact embryos, is not clearly apparent in isolated cells. However, marked differences were observed between early and late stages. 2. The membrane specific resistance was high at all stages (100‐300 k omega cm2) and increased from stage 6 to stage 9. This specific resistance is much higher than previous estimates of the permeability of newly formed membrane after fertilization and very different from values reported for differentiated cells. 3. The membrane Na‐K pump activity has been measured at all stages by applying ouabain to the cells (10(‐4) to 10(‐3) M). The pump rate per unit surface area, calculated as the ratio of the ouabain‐sensitive part of the resting potential to the specific resistance, decreased from stage 7 (about 0.19 microA/microF) to stage 9 (about 0.04 microA/microF). 4. The ouabain‐insensitive part of the resting potential increased from stage 6 to 9. At all stages, the blastomeres were permeable primarily to K+; blastomeres at stage 9 were more sensitive to change of external K+ than at stage 7, suggesting an increase in K+ selectivity. 5. The membrane potential was very sensitive to external pH at all stages. External protons appeared to block the permeability to K+. At low pH, it was possible to demonstrate some permeability of early blastomeres to Na+. 6. At variable times after impalement, cells underwent an increase in K+ permeability of 5‐ to 10‐fold. This seems to be due to ion leak from the intracellular electrode. 7. This dual membrane state was observed at all stages and it may explain some of the earlier reports of high K+ permeability.
Salt appetite in the pigeon in response to pharmacological treatments.
Authors: Epstein A N , Massi M
Published: December 2014

1. In response to furosemide‐induced sodium depletion pigeons showed a robust salt appetite. Following the 1st depletion they started to ingest 3% NaCl after a latency of 373 +/‐ 69 s and in 24 h they took 21.16 +/‐ 3.07 ml of this solution (vs. a daily mean intake of 1‐2 ml prior to the depletion). 2. The appetite was selective as shown by the fact that when, after depletion, 0.34 M‐CaCl2 was offered (which is equiosmotic to 3% NaCl) pigeons took just a trivial amount of it. 3. Analysis of sodium losses following the natriuretic treatment revealed that pigeons respond to sodium depletion with an excessive overconsumption of NaCl solution. In the 2 h after access to salt they took about 3 times the amount of sodium lost. 4. Repeated sodium depletions sharply reduced the latency to the ingestion of salt and produced larger intakes. However, the overall amount of salt taken in 24 h after the later depletions was very similar and statistically indistinguishable from that taken following the 1st depletion. 5. Subchronic deoxycorticosterone acetate treatment (2 mg pigeon‐1 day‐1 I.M.) increased daily 3% NaCl intake, but large variability was observed in the response. 4 mg pigeon‐1 day‐1 evoked a reliable 3% NaCl intake which was particularly marked from the 5th day of the treatment. 6. Pulse intracerebroventricular (I.C.V.) injection of purified hog renin evoked water intake within about 1 min of injection, followed (about 6 h later) by increased salt intake. In the 24 h after renin injection pigeons took 16.58 +/‐ 2.89 ml of 3% NaCl. On the 2nd day following injection salt intake was still higher than in controls. 7. In conclusion, our results show that pigeons respond to sodium depletion with a robust salt appetite. Moreover, salt appetite can be evoked by deoxycorticosterone acetate as well as by renin. These findings suggest that in the pigeon salt appetite may be an endocrine‐induced behaviour controlled by mineralocorticoids and by the renin‐angiotensin system.
Acetylcholine regulation of nicotinic receptor channels through a putative G protein in chick myotubes.
Authors: Eusebi F , Grassi F , Molinaro M , Zani B M
Published: December 2014

1. Single‐channel currents induced by acetylcholine (ACh) were recorded from unstriated and non‐innervated embryonic chick myotubes using the cell‐attached patch‐clamp technique. 2. ACh applied to the non‐patched membrane decreased both channel opening probability and conductance. These ACh‐induced effects occurred also when the non‐patched membrane was exposed to nominally Ca2+‐free extracellular medium, but were absent when it was treated with curare. 3. ACh‐induced membrane current recorded under whole‐cell patch‐clamp conditions decreased in amplitude and time course when myotubes were intracellularly loaded with guanosine‐5'‐O‐(3‐thiotriphosphate) GTP gamma S), but not with guanosine‐5'‐O‐(2‐thiodiphosphate) (GDP beta S) or cyclic adenosine‐5'‐monophosphate (cyclic AMP). Internal perfusion of GTP gamma S affected the ACh‐induced openings in a similar manner to the non‐patch ACh application. 4. These results suggest that ACh, in addition to its direct effect, acts indirectly on the nicotinic receptor channels by delivering an intracellular messenger and through the activation of a putative G protein.
Two calcium‐activated potassium conductances in a subpopulation of coeliac neurones of guinea‐pig and rabbit.
Authors: Cassell J F , McLachlan E M
Published: December 2014

1. Some of the sympathetic neurones in coeliac ganglia isolated from young guinea‐pigs and rabbits were found to generate action potentials followed by after‐hyperpolarizations with durations of 3‐8 s, much longer than those (congruent to 300‐500 ms) observed in the majority of other mammalian sympathetic neurones. 2. This type of ganglion cell discharged only once at the onset of a depolarizing step unless a very high intensity current was applied. Passive and voltage‐dependent membrane conductances studied in detail in guinea‐pig ganglia differed from those in the two other classes of sympathetic ganglion cell described previously (Cassell, Clark & McLachlan, 1986). 3. By using a single microelectrode to voltage clamp the soma, it was possible to demonstrate that both fast and slow components of the tail current following initiation of an uncontrolled 'action current' in neurones with long after‐hyperpolarizations (l.a.h.) were carried by K+ ions, as was the fast tail current (time constant, tau congruent to 130 ms) present in other coeliac neurones. 4. The amplitude of both components of the tail current in l.a.h. neurones was markedly reduced by the replacement of Ca2+ by Mn2+, Co2+ or Ba2+ ions. These manoeuvres had similar effects on the fast tail current in other coeliac neurones. 5. Both time course and amplitude of the fast tail current were increased when Ca2+ concentration was raised, or when several 'action currents' were initiated, whereas only the amplitude of the slow tail current was affected. 6. The time course of the slow tail current could be described by the sum of two exponentials with tau on = 285 ms and tau off = 1.3 s at 35 degrees C occurring after a delay of 60 ms. This current had a Q10 of about 4 between 35 and 25 degrees C. In contrast, the Q10 of the fast component was about 2. 7. Morphine (10(‐6) M) and vasoactive intestinal polypeptide (10(‐6) M) had no effect on the outward tail current in l.a.h. neurones, but 5‐hydroxytryptamine (10(‐6) M) was found to abolish the slow component without affecting the fast component. 8. The slow tail current was activated in the subthreshold range of membrane potentials, and its properties could account for the firing characteristics of this subpopulation of sympathetic neurones. 9. The two calcium‐activated potassium conductances that are responsible for the prolonged after‐hyperpolarization resemble those in a subpopulation of nodose ganglion cells with unmyelinated axons (Fowler, Greene & Weinreich, 1985).(ABSTRACT TRUNCATED AT 400 WORDS)
Long‐term potentiation involves enhanced synaptic excitation relative to synaptic inhibition in guinea‐pig hippocampus.
Authors: Abraham W C , Gustafsson B , Wigström H
Published: December 2014

1. Tetanization of hippocampal pyramidal cell afferents travelling in stratum radiatum of area CA1 induces both long‐term potentiation (l.t.p.) of extracellularly recorded excitatory postsynaptic potentials (e.p.s.p.s), and an increase in the number of cells firing, as measured by the extracellular population spike, for a given sized field e.p.s.p. The mechanism of this latter change, known as e.p.s.p.‐spike (E‐S) potentiation, was investigated in the guinea‐pig hippocampal slice preparation. 2. Plots of the E‐S relation before and after tetanization were constructed from measures taken over a series of stimulus strengths. Tetanization of afferents in stratum radiatum decreased the spike threshold by 24%, while the gamma‐aminobutyric acid antagonist picrotoxin (PTX) decreased spike threshold by 72%. Sequential administration of PTX and tetanization, in either order, resulted in no more change in the E‐S threshold than did PTX application alone. 3. Extracellular synaptic potentials, matched for initial slope before and after tetanization by adjusting the stimulus strength, showed an increased peak amplitude and increased peak latency following tetanization. PTX produced similar but larger percentage changes. Tetanization in the presence of PTX, however, did not alter the field potential wave shape. 4. Intracellular postsynaptic potentials (p.s.p.s) were also matched for initial slope before and after tetanization. Tetanization induced p.s.p. shape changes similar to those observed extracellularly, i.e. in the direction of less inhibition. Such changes did not occur in the presence of PTX. 5. Inhibitory p.s.p.s (i.p.s.p.s) were studied in depolarized pyramidal cells with microelectrodes filled with QX‐314. Tetanization of afferents in stratum radiatum produced i.p.s.p. increases in eight of nineteen cells. These increases were generally attributable to an increased activity in the recurrent inhibitory pathway. Tetanization of the alveus failed to produce any lasting increases in the i.p.s.p. amplitude. 6. Tetanization of afferents in stratum radiatum decreased the ratio of the intracellular i.p.s.p. to field e.p.s.p. over stimulus strengths below population spike threshold. Above population spike threshold, the ratio tended towards its pretetanization level. 7. The results indicate that E‐S potentiation results from an increase in the level of depolarization reached by a synaptic potential of given initial slope. These findings support the hypothesis that tetanization induces greater l.t.p. of excitatory inputs onto pyramidal cells than of inputs onto feed‐forward inhibitory interneurones.
Contribution of two types of calcium currents to the pacemaker potentials of rabbit sino‐atrial node cells.
Authors: Hagiwara N , Irisawa H , Kameyama M
Published: December 2014

1. Two types of calcium currents, the transient type and long‐lasting type, were examined by both whole‐cell and cell‐attached patch‐clamp modes in single isolated sino‐atrial node cells of the rabbit. 2. In the whole‐cell clamp mode, in response to a depolarizing pulse to ‐40 mV from a holding potential of ‐80 mV, a transient type calcium current with an amplitude of 2.1 +/‐ 0.7 pA/pF (mean +/‐ S.D.; n = 15) was recorded. The threshold potential was approximately ‐50 mV. 3. Nickel (40 microM) and tetramethrin (0.1 microM) blocked the transient type calcium current without appreciable effects on the long‐lasting type. Nifedipine and D600 blocked the long‐lasting type, but did not affect the transient type. Cadmium (20 microM) and cobalt (2 mM) inhibited both types of calcium currents equally. 4. Both types of calcium currents showed an increased amplitude with increasing extracellular calcium concentration. The values of the Michaelis constant, Km, were 0.95 mM for the transient type and 3.92 mM for the long‐lasting type, indicating that these types represent two different classes of channels. 5. In the cell‐attached patch‐clamp mode, the single‐channel conductance of the transient type calcium current was 8.5 pS, by using 100 mM‐BaCl2 in the pipette, whereas that of the long‐lasting type was 16.0 pS, under the same conditions. Each of these values was similar to those found in other cells, respectively. 6. In the whole‐cell clamp mode, the transient type current began to inactivate at ‐70 mV and was fully inactivated at ‐40 mV. The steady‐state inactivation curve of the transient type current was approximately 50 mV negative to that of the long‐lasting type. The overlap of the membrane potential between the activation and inactivation curves was small. The time constant of the inactivation shortened from 20 to 5 ms as the potential became progressively positive over the range from ‐80 to +30 mV. 7. Isoprenaline (1 microM) increased the amplitude of the long‐lasting type Ca2+ current, but was not effective on the transient type, suggesting that the long‐lasting type calcium current may be responsible for the positive chronotropic effect of isoprenaline. 8. While recording spontaneous electrical activity of the cell, application of 40 microM‐nickel induced bradycardia and this effect was enhanced when the membrane was constantly hyperpolarized.(ABSTRACT TRUNCATED AT 400 WORDS)
Shift of activity from slow to fast muscle during voluntary lengthening contractions of the triceps surae muscles in humans.
Authors: Nardone A , Schieppati M
Published: December 2014

1. Raw or rectified and integrated electromyograms (integrated EMGs) of the leg muscles were recorded during (a) isotonic ramp shortening or lengthening contractions consisting of foot plantar flexions against a constant load, or dorsal flexions accomplished by braking the load and yielding to it, respectively, and (b) isometric increasing or decreasing plantar torques accomplished by graded contractions or relaxations of the triceps muscles. 2. During plantar flexions or increasing torques, the EMG of soleus, gastrocnemius lateralis, medialis, and peroneus increased in parallel. During decreasing torques, motor unit derecruitment took place gradually and simultaneously. The tibialis anterior was silent. During dorsal flexions, one of two characteristic patterns was observed in different subjects: (a) soleus was abruptly derecruited at the beginning of the task, while gastrocnemius lateralis (or medialis) exhibited a large recruitment lasting throughout the lengthening contraction; (b) soleus remained active during the task, showing large motor unit potentials, while the gastrocnemius lateralis recruitment was of a lesser extent than in (a). Peroneus derecruitment was gradual and tibialis anterior activity was absent in both cases. 3. The EMG patterns observed during plantar flexions or in increasing and decreasing torques, and the two patterns observed during shortening or lengthening contractions, were closely reproduced during sinusoidal oscillations of the foot or in isometric contractions and relaxations. 4. When recruitment of the gastrocnemius lateralis was present during dorsal flexion, the slope of its integrated EMG envelope was steeper, the higher the velocity of lengthening contraction. The most rapid and the slowest tasks, however, did not require its activation. Gastrocnemius lateralis integrated EMGs of an amplitude similar to those occurring during lengthening contractions were observed only during ballistic plantar flexions. 5. The two patterns of triceps activation occurring during lengthening contraction could be traced to different mechanical characteristics of the soleus muscles, the gastrocnemius lateralis being activated preferentially in subjects with long soleus half‐relaxation times, and the soleus in subjects with short soleus half‐relaxation times. 6. The soleus and gastrocnemius lateralis H reflexes were tested during shortening and lengthening contractions.(ABSTRACT TRUNCATED AT 400 WORDS)
Maximum velocity of shortening related to myosin isoform composition in frog skeletal muscle fibres.
Authors: Edman K A , Reggiani C , Schiaffino S , te Kronnie G
Published: December 2014

1. The velocity of unloaded shortening (V0), the myofibrillar ATPase activity and the immunoreactivity to two monoclonal antibodies (A1 and A2) that were raised against the myosin heavy chains were studied in single fibres of the anterior tibialis muscle of Rana temporaria. V0 was recorded for the fibre as a whole using the slack‐test method. Myofibrillar ATPase activity was determined by means of a quantitative histochemical technique. 2. A highly significant, direct relationship was found to exist between V0 and the myofibrillar ATPase activity recorded in the same single fibres. Both V0 and the myofibrillar ATPase activity changed in proportion to the cross‐sectional area of the fibres. 3. Muscle fibres that had first been characterized with respect to V0 and myofibrillar ATPase activity were exposed to monoclonal antibodies A1 and A2. Thin fibres, having relatively low V0 and low myofibrillar ATPase activity, reacted preferentially with A1. Thick fibres, on the other hand, exhibiting relatively high V0 and high myofibrillar ATPase activity, were preferentially stained by A2. A third category of fibres reacted with both A1 and A2. The results support the view that the variability in shortening velocity and myofibrillar ATPase activity that exists among twitch fibres in frog skeletal muscle is based on differences in myosin heavy‐chain composition. 4. Attempts were made to elucidate further the previous observation (Edman, Reggiani & te Kronnie, 1985) that the velocity of unloaded shortening (V0) differs along the length of individual muscle fibres. To this end discrete segments (0.5‐0.7 mm in length) of intact fibres were delineated by opaque markers of hair that were placed on the fibre surface. The change in length between two adjacent markers (one segment) was recorded photo‐electrically while the fibre was released to shorten against a very small load between 2.2 and 2.0 micron sarcomere lengths. In the majority of fibres (eight out of eleven preparations), V0 and myofibrillar ATPase activity exhibited similar patterns of variation along the fibre. Pooled data from thirty‐three segments of twelve fibres showed a positive correlation between V0 and myofibrillar ATPase activity (P less than 0.05). 5. The possibility was explored that the myosin isoform composition might vary along the length of an individual muscle fibre. For this purpose bundles of fibres were cross‐sectioned at 0.5‐1 mm intervals along their entire length and the reactivity to monoclonal antibody A2 was tested at each location.(ABSTRACT TRUNCATED AT 400 WORDS)
Gastric electromyographic activity in the milk‐fed lamb.
Authors: Reid A M , Titchen D A
Published: December 2014

1. Electromyographic (EMG) activity of the reticulum, reticulo‐omasal orifice (ROO) and abomasum was recorded from conscious lambs. 2. In fasted lambs diphasic reticular EMG bursts occurred at intervals of 60 +/‐ 13 s. In association with the second phase of the reticular EMG burst there was consistently a period of inactivity of the EMG of the ROO of 2.4‐11.0 s (5.5 +/‐ 2.0 s, mean +/‐ S.D.). This period of quiescence ended with the onset of a burst of EMG activity of the ROO of 4.1 +/‐ 0.8 s termed here a long burst of activity. Preceding the following reticular EMG burst there were further long bursts of EMG activity of the ROO at intervals of 11.1 +/‐ 1.3 s or intermixing or replacement of long burst activity with short bursts which were of duration 1.1 +/‐ 0.3 s and which occurred at intervals of 2.4 +/‐ 0.5 s. 3. When the lambs were shown milk and at times when they could be expected to anticipate milk being provided, a period of inactivity of the EMG of the ROO developed for up to 60 s. In association with this there was commonly an increase in the frequency of reticular EMG bursts which at times became monophasic. 4. With the start of sucking there was quiescence of the EMG of the ROO which persisted throughout periods of sucking for up to 90 s. Simultaneously with the disappearance of activity of the ROO there was a monophasic burst of the reticular EMG, which was followed by either quiescence or disorganized low voltage activity. Inactivity of the EMG of the ROO still developed when lambs sucked milk after administration (I.V.) of atropine, phentolamine or propranolol, but not after hexamethonium. 5. In lambs observed over a period 30‐60 min after feeding the diphasic reticular bursts occurred every 85 +/‐ 24 s and the duration of the period of inactivity of the EMG of the ROO associated with each reticular burst (3.7 +/‐ 1.2 s) was significantly less (P less than 0.001) than in fasted lambs. Short bursts of EMG activity of the ROO occurred more frequently than in fasted lambs. 6. In fasted lambs bursts of EMG activity of the body of the abomasum occurred at frequencies of 6‐12 min‐1 and those of the antrum and pylorus at ca. 6 min‐1 but episodes of such activity were intermittent.(ABSTRACT TRUNCATED AT 400 WORDS)
Visual resolution of macaque retinal ganglion cells.
Authors: Crook J M , Lange-Malecki B , Lee B B , Valberg A
Published: December 2014

1. The visual resolving ability of different types of macaque retinal ganglion cells was estimated at different retinal eccentricities, by measuring the amplitude of modulated responses to black‐white gratings of spatial frequencies near the resolution limit for each cell. 2. The resolving ability of tonic, spectrally opponent ganglion cells was usually similar to that of phasic, non‐opponent ganglion cells at similar eccentricities, except that at eccentricities greater than 10 deg some tonic ganglion cells with remarkably high resolution (up to ca. 15 cycles/deg) were found. Our cell sample was limited within the central 2 deg of the visual field, however. 3. Only a small proportion of phasic ganglion cells showed an increase of mean firing level to gratings near the resolution limit. The maintained firing of tonic ganglion cells was higher than that of phasic ganglion cells. 4. With red‐black or green‐black gratings, the resolution of phasic ganglion cells was unaffected. For red or green on‐centre ganglion cells, a marked deterioration of resolving ability occurred when the grating was of a colour to which a cell responded poorly (green‐black gratings for red on‐centre cells, and red‐black gratings for green on‐centre cells). A slight improvement in resolving ability occurred when the grating was of an excitatory colour. 5. For a sub‐sample of cells, we compared resolution limit with centre size as determined from area‐threshold curves. For both phasic and tonic ganglion cells, resolution limit (the period length just resolved) was about half the centre diameter, as is the case for cat ganglion cells. This implies that the centre sizes of phasic and tonic monkey ganglion cells are similar at most eccentricities. 6. We attempt to relate these results to primate retinal anatomy and visual resolution, determined behaviourally.
Effect of peripherally administered atriopeptin III on water intake in rats.
Authors: Kaufman S , Monckton E A
Published: December 2014

1. Extracellular fluid deficits of 33% were produced in male Long‐Evans rats by peritoneal dialysis. The conscious, unrestrained animals were then infused I.V. for 30 min with atriopeptin III at doses of 0.01, 0.1, 0.5 and 1.0 micrograms/min. At 5 min into the infusion, the rats were offered water and subsequent intakes were monitored. Since atrial natriuretic peptide (ANP) causes hypotension, one group of control animals was given an injection of diazoxide sufficient to match this fall in blood pressure. 2. A similar group of rats was prepared for measurement of plasma ANP achieved by infusion. 3. Relative to the saline‐infused controls, atriopeptin III did not reduce water intake. Indeed, intake was increased at the highest dose of 1.0 micrograms/min. 4. Relative to the diazoxide controls, water intake was influenced by atriopeptin III in a dose‐dependent manner, the greatest attenuation being observed at infusions of 0.1 microgram/min. 5. Infusion of atriopeptin III at 0.1 microgram/min caused plasma ANP levels to rise from 252 +/‐ 21 to 532 +/‐ 136 pg/ml (n = 9, P less than 0.05) at 15 min. The lowest dose (0.01 microgram/min) caused no detectable increase in plasma levels. 6. It is concluded that, in groups of hypovolaemic rats matched for blood pressure, atriopeptin III caused a dose‐related reduction in water intake.
Acetylcholine release by bradykinin, inositol 1,4,5‐trisphosphate and phorbol dibutyrate in rodent neuroblastoma cells.
Authors: Higashida H
Published: December 2014

1. The action of bradykinin (BK), inositol 1,4,5‐trisphosphate (InsP3), and phorbol dibutyrate (PDBu) on the release of acetylcholine (ACh) was studied electrophysiologically on short‐distance (less than 20 micron) synapses formed between cultured NG108‐15 mouse neuroblastoma x rat glioma hybrid cells and rat muscle cells. Action potentials in NG108‐15 cells did not usually evoke an excitatory junction potential (EJP) in the muscle cell in this system. 2. Ionophoretic application of BK onto the somatic surface of an NG108‐15 cell produced an increase in frequency of miniature end‐plate potentials (MEPPs) for 40‐50s in the paired myotube. Some MEPPs were evoked during BK‐induced hyperpolarization (10‐20 s) of the hybrid cell soma. A few MEPPs were also elicited during BK‐induced depolarization. 3. Ionophoretic injection of Ca2+ into an NG108‐15 cell soma generated MEPPs for a very brief period (less than 3 s), coincident with somatic hyperpolarization. No increase was observed during a subsequent somatic depolarization induced by a larger current of Ca2+. 4. Ionophoretic injection of InsP3 into the cytoplasm of an NG108‐15 cell soma transiently evoked MEPPs during the InsP3‐induced hyperpolarizing phase. A large InsP3 injection caused sustained generation of MEPPs for 2‐4 min, associated with InsP3‐evoked depolarization. 5. Within 3‐5 min after exposure of NG108‐15‐myotube pairs to 1 microM‐PDBu, the MEPP frequency increased by 2‐5 times and reached a plateau after 8 min. The increase continued after wash‐out of the drug. The PDBu‐induced increase of MEPPs was still observed when the membrane potential of the NG108‐15 cell was clamped at ‐30 mV. 6. The data suggest that the BK‐induced facilitation results from the action of two intracellular second messengers: an InsP3‐dependent release of Ca2+ from the intracellular storage sites and protein phosphorylation by diacyclglycerol (DAG)‐activated protein kinase C.
Effects of tetraethylammonium ions on frequency‐dependent vasopressin release from the rat neurohypophysis.
Authors: Hobbach H P , Hurth S , Jost D , Racké K
Published: December 2014

1. Isolated rat neurohypophyses were fixed by their stalks to a platinum wire electrode and superfused with oxygenated Krebs‐HEPES solution. Vasopressin release into the medium was determined by radioimmunoassay. Vasopressin secretion was increased by electrical stimulation at different frequencies (3‐30 Hz) and different train lengths (75‐900 pulses). The effects of tetraethylammonium (TEA) ions and of enhanced calcium were tested. 2. Electrical stimulation at 7.5 or 15 Hz evoked a markedly larger release of vasopressin than stimulation at 3 Hz. During continuous stimulation at 7.5 and 15 Hz the evoked vasopressin release per pulse declined rapidly, but with similar time constants for both frequencies indicating that the fatigue of the release process was strongly time dependent. The kinetic analysis showed also that the initial release per pulse was identical for 7.5 and 15 Hz stimulation. Nevertheless, with increasing duration, stimulation at 7.5 Hz became less efficient (in terms of release per total stimulus) than stimulation at 15 Hz and this was due to the time‐dependent fatigue. 3. TEA (10 mM) increased the release of vasopressin evoked by 3 Hz stimulation much more than that evoked by 15 Hz stimulation resulting in an equieffective activation of release by both stimuli. On the other hand, elevation of the extracellular calcium from 1.2 to 3 mM did not alter the different efficiency of stimuli of 3 and 15 Hz. In the presence of TEA the time‐dependent fatigue of the release during continuous stimulation was prevented, but an additional, slower component of the fatigue became apparent which was release or impulse dependent. 4. As prolongation of the action potential by TEA facilitates preferentially the hormone release evoked by low (ineffective) frequencies, it is suggested that a frequency‐dependent broadening of action potentials which reportedly occurs on neurosecretory neurones may play an important role in the frequency‐dependent facilitation of hormone release from the rat neurohypophysis.
Dependence of acetylcholine receptor channel kinetics on agonist concentration in cultured mouse muscle fibres.
Authors: Jackson M B
Published: December 2014

1. The patch‐clamp technique was used to study channel gating kinetics of the acetylcholine receptor. The agonist carbachol was used at concentrations varying from 0.10 to 20 microM. 2. Data in which many channels were often open at the same time were analysed with the aid of mathematical expressions that relate the stochastic behaviour of a many‐channel system to the kinetic parameters of a single channel. These methods provide consistent estimates of parameters. This consistency suggests that there is no correlation between the kinetics of channel closure and the density of channels in a patch of membrane. 3. Closed times were well fitted by a sum of two exponentials. Addition of a third exponential component never significantly improved the quality of the fit. 4. A sum of two exponentials usually provided the best fit to open times. The ratio of the fractions of slowly closing and rapidly closing channels increased linearly with agonist concentration, in a manner consistent with the opening of singly and doubly liganded receptor channels. 5. Analysis of closed‐time densities at various times after seal formation was used to follow the time course of desensitization. No changes in the kinetics of closure were detected during desensitization. 6. At 0.10 microM‐carbachol the frequency at which openings were observed was only slightly more than the background frequency of spontaneous opening. At 20 microM‐carbachol, immediately after seal formation and before the onset of desensitization, the frequency of opening was approximately 300 times higher. 7. The frequency of appearance of brief‐duration openings increased linearly with carbachol concentration and saturated at approximately 5 microM. The frequency of appearance of long‐duration openings increased as the square of the agonist concentration, with only a slight hint of saturation. 8. The results presented here are discussed within the framework of a two‐binding‐site model for the allosteric activation of the acetylcholine receptor. Estimates are made of all of the equilibrium constants and many of the rate constants of the relevant reaction scheme. The two ligand binding sites are found to be very different in terms of their dissociation constants and their influence on the channel gating transitions. These results have implications for the energetics of receptor activation and for the utilization of binding energy by the receptor.
Tension responses of frog skeletal muscle fibres to rapid shortening and lengthening steps.
Authors: Bressler B H , Dusik L A , Menard M R
Published: December 2014

1. A study has been carried out of the tension responses of single fibres from frog semitendinosus muscle at 4 degrees C which occur in response to rapid lengthening and shortening steps throughout the isometric tetanus. 2. Instantaneous stiffness values were calculated as the ratio of the tension change to the length change. 3. Stiffness was seen to increase more rapidly than the tension during the initial development of force and was constant during the tetanus plateau. During the relaxation phase of tension, stiffness declined more slowly than the force up to the shoulder; thereafter both declined rapidly and with a nearly similar time course. 4. Throughout the initial rise of force, the period of maximum force development and the early phase of relaxation, a rapid stretch produced a significantly greater tension change than a rapid release. The fibres appeared 'stiffer' during a stretch. 5. The experimental results are shown to be consistent with the suggestion that cross‐bridges may detach during a small rapid shortening step but remain attached during a similar lengthening step.