bluuebunny/crossref_metadata_2025 huggingface dataset:
Relaxation of ventricular cardiac muscle.
Authors: Brutsaert D L , de Clerck N M , Goethals M A , Housmans P R
Published: December 2014

1. The load bearing capacity during relaxation of ventricular cardiac muscle from various animal species was investigated. 2. The effect of load on the time course of relaxation was analysed either by comparing afterloaded contractions against various loads or by imposing abrupt alterations in load (load clamps). 3. In heart muscle from the mammalian species studied relaxation was sensitive to loading conditions, whereas in frog heart muscle relaxation was largely independent of the loading conditions. The mechanical properties of relaxation of cardiac muscle appear, therefore, governed by the interplay of a load‐controlled and an activation‐controlled decay mechanism, the relative importance of which differs with species. 4. Load‐dependence may be the mechanical expression of the ratio of the number of force generating sites at any time during contraction and relaxation to the load to be carried; this mechanism would predominate in mammalian animal species with a well developed calcium sequestering sarcoplasmic reticulum. Activation‐dependence would seem to predominate in animal species, such as frog, in which calcium sequestration appears to be the rate limiting step during relaxation.
Relaxation of mammalian single cardiac cells after pretreatment with the detergent Brij‐58.
Authors: Brutsaert D L , Claes V A , De Clerck N M
Published: December 2014

1. The influence of load and activation on relaxation of heart muscle has been studied. 2. Cardiac cells devoid of functioning sarcolemma were isolated from rat and cat ventricular myocardium. Pretreatment with the detergent Brij‐58 destroyed residual sarcoplasmic reticulum function. In order to analyse the mechanical properties of relaxation in these cells, a new miniature transducer was designed which could measure force by feedback sensing (resolution of 1 microgram). Contraction was induced by ionophoretically released calcium ions. Activation, sequestration of calcium and loading conditions could be controlled independently. 3. The time course of relaxation was shown to be governed by the amount of calcium released, and unlike intact preparations from rat or cat heart (but like those from frog), to be independent of load and of alterations in load. 4. We conclude that relaxation of the cardiac contractile system is determined basically by an activation‐dependent mechanism, which is masked by load dependence in intact muscle preparations with a well developed calcium sequestering membraneous system.
Crayfish stretch receptor: an investigation with voltage‐clamp and ion‐sensitive electrodes.
Authors: Brown H M , Ottoson D , Rydqvist B
Published: December 2014

1. The membrane characteristics of the slowly adapting stretch receptor from the crayfish, Astacus fluviatilis, were examined with electrophysiological techniques consisting of membrane potential recording, voltage clamp and ion‐sensitive microelectrodes. 2. The passive membrane current (Ip) following step changes of the membrane potential to levels above 0 mV required more than a minute to decay to a steady‐state level. 3. The stretch‐induced current (SIC, where SIC = Itotal‐‐Ipassive) was not fully developed until the Ip had decayed to a steady state. 4. With Ip at the steady state and the stretch‐induced current at the O‐current potential, a slow stretch‐induced inward current was isolated. The latter reaches a maximum after 1 sec of stretch and declines even more slowly after stretch. The I‐V relation of the slow current had a negative slope and reversed sign near the resting potential. It is suggested that this current is due to a Cl‐ conductance change. 5. The stretch‐induced current, consisting of a rapid transient phase and a steady component can be isolated from the slow stretch‐induced current at a holding potential corresponding to the resting potential. 6. The SIC‐Em relation is non‐linear and reverses sign at about +15 mV. 7. In a given cell, the reversal potential of the stretch‐induced potential change obtained with current clamp coincided with the 0‐current potential of the stretch‐induced current obtained by voltage clamp. The average value from twenty‐six cells was +13 +/‐ 6.5 mV; cell to cell variability seemed to be correlated with dendrite length. 8. Tris (mol. wt. 121) or arginine (mol. wt. 174) susbstituted for Na+ reduces but does not abolish the stretch‐induced current. 9. The permeability ratios of Tris:Na and arginine:Na were estimated from changes in the 0‐current potential as these cations replaced Na+ in the external medium. The PTris:PNa was somewhat higher (0.31) than the Parginine:PNa ratio (0.25). 10. Changes in the external Ca2+ concentration had no effect on the 0‐current potential in Na or Tris saline. However, reducing Ca2+ did augment the stretch‐induced current in either saline. A tenfold reduction of Ca2+ increased the conductance (at the 0‐current level) about twofold. 11. Intracellular K+ and Cl‐ activities were obtained with ion sensitive electrodes. The average values from six cells were aiK = 133 +/‐ 34 mM and aiCl = 15.2 +/‐ 1.8 mM S.D.). EK was about 20 mV more negative than Em and ECl was about 10 mV more positive than Em. 12. aik and resting Em undergo large changes in K+‐free solutions. After 60 min, ak was reduced eightfold and Em was reduced from ‐67 to ‐40 mV. Reduced Ca2+ in K+‐free augments the rate of these changes. Receptor potential amplitude was also reduced in K+‐free solution but could be restored upon polarizing the membrane to the pre‐existing resting level.
The intracellular sodium activity of cardiac Purkinje fibres during inhibition and re‐activation of the Na‐K pump.
Authors: Deitmer J W , Ellis D
Published: December 2014

1. The intracellular Na activity, aiNa, of sheep heart Purkinje fibres was continuously monitored using Na+‐sensitive glass micro‐electrodes. The effects of removal and restoration of external K, and of application and removal of various cardioactive steroids, were investigated. 2. The aiNa increased in K‐free solutions and rapidly recovered on addition of external K. The rate of this recovery depended on both the external K concentration, [K]o, and the aiNa. The rate of aiNa recovery was found to be half maximally activated at a [K]o of about 10 mM. If corrections are applied to allow for changes in the net passive Na influx at various [K]o, then this value is increased to approximately 12.5 mM. 3. At a given [K]o, there appeared to be a linear relationship between the rate of aiNa recovery and the level to which aiNa had increased in K‐free solution (over the range of aiNa from 7.5 to 31 mM). 4. Addition of the cardioactive steroids strophanthidin, acetylstrophanthidin, actodigin (AY 22,241) or dihydro‐ouabain produced rapid changes of aiNa. At low concentrations, these compounds sometimes produced a small decrease in aiNa, while at concentrations above 10(‐7) M they produced a dose‐dependent increase. 5. The effects on aiNa of both low and high concentrations of all these cardioactive steroids were readily reversible within 120 min. The time course of the aiNa recovery mainly depended on the concentration of the cardioactive steroid applied, and on the level to which aiNa had increased. 6. Upon addition of a cardioactive steroid (above 10(‐7) M, aiNa at first increased almost linearly with time. The rates of such an increase were measured during this period at various cardioactive steroid concentrations and used to produce dose‐response curves. The concentrations that produced a half‐maximum rate of aiNa increase were near to 10(‐6) M for strophanthidin and acetylstrophanthidin, but near to 10(‐5) M for actodigin and dihydro‐ouabain. 7. The mean maximum rate of aiNa increase produced by the addition of a high cardioactive steroid concentration was 0.49 +/‐ 0.17 mM/min (+/‐S.D., n = 21). This would indicate a net passive Na influx into the cells of approximately 2.8 p‐mole/cm2sec. 8. This maximum rate of aiNa increase could be achieved by the addition of 10(‐5) M‐strophanthidin or acetylstrophanthidin, but 10(‐4) to 10(‐3) M‐actodigin or dihydro‐ouabain was required to produce a similar rate of increase. 9. The addition of these high cardioactive steroid concentrations produced an initially rapid increase of aiNa. After 15‐30 min this aiNa increase slowed considerably. The aiNa appeared to reach a 'plateau' within 2‐4 hr at levels much below those predicted for a Na electrochemical equilibrium across the cell membrane.
Reciprocal inhibition during the tonic stretch reflex in the decerebrate cat.
Authors: Fu T C , Hultborn H , Larsson R , Lundberg A
Published: December 2014

1. The aim of this study was to investigate post‐synaptic reciprocal Ia inhibition during the stretch reflex; particularly the extent to which an increased Ia excitation of the Ia inhibitory interneurones will be counteracted by recurrent inhibition from motor axon collaterals. For this purpose we investigated depression of monosynaptic test reflexes antagonist flexors (reciprocal inhibition) during static stretch of quadriceps or triceps surae in unanaesthetized decerebrate cats. 3. With increasing stretch of the extensor muscle there was first a linear augmentation of reciprocal inhibition, but along with the stretch reflex in the extensor a plateau appeared in the inhibition of the flexors, although the extensor stretch reflex (judged by the e.m.g.) increased with further stretching. Within the range of stretching of triceps surae which gave increased stretch reflexes the plateau in the reciprocal inhibition was usually maintained, while during stretching of quadriceps a second phase of augmenting reciprocal inhibition often appeared. Stretch beyond the level which increased the stretch reflex activity gave augmenting reciprocal inhibition both in case of quadriceps and triceps surae. 3. Excitability measurements from central terminals of Ia afferents revealed that the increasing reciprocal inhibition during increasing stretch reflex activity in quadriceps was associated with a primary afferent depolarization in knee flexor Ia afferents; there was no corresponding effect in ankle flexor Ia afferents during stretch reflexes in triceps surae. 4. The primary afferent depolarization evoked in knee flexor Ia afferents by electrical nerve stimulation was then compared with the presynaptic inhibition of knee flexor monosynaptic test reflexes produced by the same stimuli. The results suggest that the second phase of increasing reciprocal inhibition in knee flexors is due to presynaptic inhibition and accordingly that the depth of post‐synaptic reciprocal inhibition remains constant at different degrees of stretch reflex activity in both knee and ankle extensors. 5. It is postulated that during increasing stretch reflex activity the increment in Ia excitation and recurrent inhibitio; on to the Ia inhibitory interneurones almost exactly balance each other. It is suggested that recurrent inhibition of Ia inhibitory interneurones may serve as a segmental autoregulatory mechanism to keep 'alpha‐gamma‐linked reciprocal inhibition' at a constant depth during different levels of agonist activity.
Ballistic contractions in fast or slow human muscles; discharge patterns of single motor units
Authors: Desmedt John E. , Godaux Emile
Published: December 2014

1. Single motor units were recorded from the masseter, soleus and first dorsal interosseous muscles of normal adult man. An analysis of discharge patterns was carried out either during slow ramp voluntary contractions, or during self‐initiated isolated ballistic voluntary contractions. The isometric myogram was simultaneously recorded.

2. Each motor unit was only recruited when the peak force of a brisk contraction exceeded a certain value and a ‘ballistic force threshold’ (in kg) was estimated for the unit from a large series of brisk contractions of different strengths. For each muscle, the ranking order for recruitment of different motor units recorded from one electrode position was virtually identical in slow ramp versus brisk ballistic contractions of different force (Kendall rank correlation coefficient = 0·91‐1·0). There was no evidence for any consistent selective activation of fast twitch motor units in ballistic contractions.

3. The ballistic force threshold is considerably reduced with respect to the slow ramp force threshold for the motor units of the soleus muscle. This drop is also marked for the units of the first interosseous and tibialis anterior muscles, whereas it is only small for the units of the masseter muscle. These data have been validated after consideration of the complicating factor related to the possible differential involvement of synergic muscles in ramp or ballistic contractions.

4. In the masseter and first interosseous muscles, the time to peak is about 80 msec in small ballistic voluntary contractions and it increases to about 150 msec in strong contractions. This effect appears related to repetitive discharges of single motor units when their force threshold is exceeded. By contrast, in the soleus muscle, the time to peak remains at about 150 msec both in small and in strong ballistic contractions and most soleus motor units fire only one spike in the ballistic burst.

5. Brisk ballistic contractions are graded in force by the recruitment of additional motor units according to their usual rank order. The importance of rate gradation through the repetitive firing of motor units varies in the different human muscles investigated, being quite significant in isometric brisk contractions of the masseter and first interosseous muscles but much less so in the soleus muscle in which little repetitive firing of single motor units was observed over the range of ballistic forces studied.
Tactile sensibility in the human hand: relative and absolute densities of four types of mechanoreceptive units in glabrous skin.
Authors: Johansson R S , Vallbo A B
Published: December 2014

1. Single unit impulses were recorded with percutaneously inserted tungsten needle electrodes from the median nerve in conscious human subjects. 2. A sample of 334 low threshold mechanoreceptive units innervating the glabrous skin area of the hand were studied. In accordance with earlier investigations, the units were separated into four groups on the basis of their adaptation and receptive field properties: RA, PC, SA I and SA II units. 3. The locations of the receptive fields of individual units were determined and the relative unit densities within various skin regions were calculated. The over‐all density was found to increase in the proximo‐distal direction. There was a slight increase from the palm to the main part of the finger and an abrupt increase from the main part of the finger to the finger tip. The relative densities in these three regions were 1, 1.6, 4.2. 4. The differences in over‐all density were essentially accounted for by the two types of units characterized by small and well defined receptive fields, the RA and SA I units, whereas the PC and SA II units were almost evenly distributed over the whole glabrous skin area. 5. The spatial distribution of densities supports the idea that the RA and SA I units account for spatial acuity in psychophysical tests. This capacity is known to increase in distal direction along the hand. 6. On the basis of histological data regarding the number of myelinated fibres in the median nerve, a model of the absolute unit density was proposed. It was estimated that the density of low threshold mechanoreceptive units at the finger tip is as high as 241 u./cm2, whereas in the palm it is only 58 u./cm2.
Noradrenaline as a possible mediator of the actions of angiotensin on fluid transport by rat rejunum in vivo
Authors: Levens N. R. , Munday K. A. , Parsons B. J. , Poat Judith A. , Stewart C. P.
Published: December 2014

1. Net fluid absorption and transmural potential difference were measured in the rat jejunum in vivo.

2. Increased rates of net fluid transport were observed following infusions of angiotensin or noradrenaline. There was a small, but significant, fall in transmural p.d. associated with noradrenaline but not with angiotensin infusions.

3. The α‐adrenergic antagonists phentolamine and dihydroergotamine abolished both the angiotensin and the noradrenaline stimulations of transport and the noradrenaline‐induced fall in p.d., whereas the β‐adrenergic antagonist propranolol did not significantly affect these responses.

4. Phentolamine did not alter the rise in p.d. following administration of the cholinergic agonist pilocarpine.

5. The protein synthesis inhibitor cycloheximide abolished both the angiotensin and the noradrenaline‐induced stimulation of fluid transport.

6. Neither angiotensin nor noradrenaline significantly altered jejunal cyclic AMP levels.

7. Bilateral nephrectomy had no apparent effect upon the increase in fluid transport following noradrenaline infusions.

8. The noradrenaline‐induced stimulation of transport was unaffected, and the fall in p.d. potentiated in rats pre‐treated with reserpine, but a marked inhibition of transport was observed following angiotensin infusions.

9. The results are consistent with the view that noradrenaline may mediate the actions of angiotensin upon intestinal fluid absorption in the rat.
A dual effect of formaldehyde on the inwardly rectifying potassium conductance in skeletal muscle.
Authors: Hutter O F , Williams T L
Published: December 2014

1. The inwardly rectifying potassium conductance of the membrane of frog sartorius muscle fibres is greatly reduced by treatment of muscles for 30 min with a solution containing formaldehyde (10 mM). 2. A transient increase in the conductance of the inward rectifier is observed early during formaldehyde action. 3. Analysis of the biphasic time course of the conductance changes, as determined under controlled voltage conditions, suggests that treatment with formaldehyde alters simultaneously, but in opposite ways, two factors that determine the conductance of the inward rectifier. 4. The linear component of the current‐voltage relation, which dominates the relation at strongly positive potentials, is not affected while the above changes occur. But on prolonged exposure to formaldehyde the leak conductance increases. 5. The effects of formaldehyde on the inward rectifier are reversible on prolonged superfusion with normal Ringer solution. 6. The slight inward rectification remaining after most of the extracellular K is replaced by Rb, is similarly reduced by treatment with formaldehyde. 7. The results are interpreted in terms of the chemical properties of formaldehyde and present views of the mechanisms of inward rectification.
Left ventricular inotropic responses to stimulation of carotid body chemoreceptors in anaesthetized dogs.
Authors: Hainsworth R , Karim F , Sofola O A
Published: December 2014

1. Dogs were anaesthetized with chloralose and artificially ventilated. The regions of both carotid bifurcations were vascularly isolated and perfused at constant pressure with arterial blood or with venous or hypoxic blood. 2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dtmax) with aortic pressure and heart rate held constant. 3. Stimulation of the chemoreceptors with venous blood from the inferior vena cava resulted in a decrease in dP/dtmax from 510 +/‐ 27 kPa.s‐1 to 418 +/‐ 21 kPa.s‐1 (mean +/‐ S.E.): a change of 17.9 +/‐ 1.0% 4. In experiments in which the oxygen tension of the blood perfusing the carotid chemoreceptors was decreased in steps between 10 and 3 kPa, by use of an oxygenator, graded responses of dP/dtmax were obtained at each step. 5. The inotropic responses to chemoreceptor stimulation were abolished by raising carotid pressure. 6. The inotropic responses were abolished either by crushing both carotid bodies or both ansae subclaviae, indicating that the reflex originates from the carotid bodies and that the efferent pathway is in the cardiac sympathetic nerves.
Central effect of taurine and its analogues on fever caused by intravenous leukocytic pyrogen in the rabbit.
Authors: Lipton J M , Ticknor C B
Published: December 2014

1. Taurine infused I.C.V. after I.V. injection of leukocytic pyrogen (LP) inhibited the initial rise in body temperature and prolonged fever when infusion was stopped. 2. Similar infusion of taurine also inhibited the hypertermic effect of I.C.V. PGE2 (0.5 microgram) but did not cause prolonged hyperthermia. 3. I.C.V. administration of the taurine analogues hypotaurine and beta‐alanine, compounds which have been shown previously to compete with taurine for facilitated transport in C.N.S. tissue, also inhibited the initial increase in body temperature and prolonged LP fever. 4. These results suggest that taurine prolongs LP fever by preferentially occupying a carrier system normally required for termination of the effects of endogenous pyrogens or related central mediators of fever. There was no evidence that taurine prolongs fever by blocking inactivation of central PGE2, a substance proposed previously to be a central mediator of fever.
Charge movement and membrane capacity in frog muscle.
Authors: Adrian R H , Peres A
Published: December 2014

1. The transient current required to impose a step charge of potential has a complex time course especially in the region of internal potential between ‐50 and ‐40 mV. 2. Examination of non‐linear transient current in this voltage range suggests two components of charge movement: (a) an initial more‐or‐less exponential movement, and (b) a slower component with a complex time course. 3. Measurements of membrane capacity support such a division and confirm the steeper voltage dependence of the slower charge movement. 4. Permanent depolarization to 40 mV appears to immobilize the slowly moving charge. Depolarization to ‐20 mV immobilizes both charge movements, and uncovers the presence of a third charge which seems to correspond to Charge 2 (cf. Adrian & Almers, 1976b; Adrian, Chandler & Rakowski, 1976).
Scaling factor relating conduction velocity and diameter for myelinated afferent nerve fibres in the cat hind limb.
Authors: Boyd I A , Kalu K U
Published: December 2014

1. Compound action potentials were recorded from certain muscle and cutaneous nerves in normal and chronically de‐efferentated hind limbs of cats during stimulation of the appropriate dorsal spinal roots, 2. The peaks for groups I, II and III in the compound action potential were correlated with the corresponding peaks in the fibre‐diameter histograms of the same de‐efferentated nerve after processing it for light microscopy. 3. The scaling factor (ratio of conduction velocity in m/sec to total diameter in micrometer) was not constant for all sizes of fibre nor did it increase progressively with fibre size. Evidence is presented that a logarithmic relation between conduction velocity and fibre diameter is not appropriate. 4. In muscle nerves the scaling factor for fibres fixed by glutaraldehyde perfusion and embedded in Epon was 5.7 for group I afferent fibres and 4.6 for myelinated fibres in both group II and group III. 5. In cutaneous nerves the scaling factor was 5.6 for large fibres (group I or Abeta) and 4.6 for small fibres (group III or Adelta). 6. The scaling factor for group I fibres is the same as was found previously for alpha‐efferent fibres, and that for groups II and III is the same as for gamma‐efferent fibres (Boyd & Davey, 1968). 7. The possibility that there is a clear discontinuity in scaling factor between fibres in groups I and alpha, and those in other functional groups, is discussed. 8. It is concluded that there must be some structural feature of alpha and group I fibres which differs from that of smaller myelinated fibres. It is likely that a difference in the relative thickness of the myelin sheath is involved and possibly also in the conductances responsible for generating the action potential.
The effects of calcium on outward membrane currents in the cardiac Purkinje fibre.
Authors: DiFrancesco D , McNaughton P A
Published: December 2014

1. Properties of outward membrane currents in Purkinje fibres from sheep's hearts have been studied with particular reference to the effects of external Ca. 2. Altering Cao is found to shift the potential‐dependence of channel neutralize negative charges at the external face of the membrane, but the different magnitudes of the effects of low Cao on the pace‐maker and plateau currents suggest that the affinities of Ca‐binding sites adjacent to each channel type are widely different. 3. Raising Cao causes a positive shift in the pace‐maker current reversal potential, EK2, which may reflect a small elevation in the K concentration (Kc) in the restricted cleft space immediately outside the membrane. Other possible causes of the shift in EK2 are also discussed. 4. Raising Cao has effects on the plateau and pace‐maker current rectifier relations, and on the time‐independent membrane current, which resemble those of a small increase in extracellular K concentration. 5. Possible mechanisms for an increase in Kc in elevated Cao are discussed. Positive shifts in EK2 can be observed even when the membrane current becomes more inward, so it seems unlikely that the increase in Kc results from an activation of K channels by Ca ions. It is possible that increases in Ca partially inhibit the Na:K exchange pump. 6. The maximum transient outward current elicited by strong depolarizing steps is not affected by moderate reductions in Cao. 7. Reducing Nao depresses the pace‐maker current rectifier relation with little shift in the activation curve. 8. We conclude that some of the effects of Cao on outward currents are due to shifts in the potential‐dependence of channel activation, while others result from a small increase in Kc. No evidence for a direct effect of Ca on K channels has been found in the present study.
Electrical properties associated with wide intercellular clefts in rabbit Purkinje fibres.
Authors: Colatsky T J , Tsien R W
Published: December 2014

1. Rabbit Purkinje fibres were studied using micro‐electrode recordings of electrical activity or a two‐micro‐electrode voltage clamp. Previous morphological work had suggested that these preparations offer structural advantages for the analysis of ionic permeability mechanisms. 2. Viable preparations could be obtained consistently by exposure to a K glutamate Tyrode solution during excision and recovery. In NaCl Tyrode solution, the action potential showed a large overshoot and fully developed plateau, but no pacemaker depolarization at negative potentials. 3. The passive electrical properties were consistent with morphological evidence for the accessibility of cleft membranes within the cell bundle. Electrotonic responses to intracellular current steps showed the behaviour expected for a simple leaky capacitative cable. Capacitative current transients under voltage clamp were changed very little by an eightfold reduction in the external solution conductivity. 4. Slow current changes attributable to K depletion were small compared to those found in other cardiac preparations. The amount of depletion was close to that predicted by a cleft model which assumed free K diffusion in 1 micron clefts. 5. Step depolarizations over the plateau range of potentials evoked a slow inward current which was resistant to tetrodotoxin but blocked by D600. 6. Strong depolarizations to potentials near 0 mV elicited a transient outward current and a slowly activating late outward current. Both components resembled currents found in sheep or calf Purkinje fibres. 7. These experiments support previous interpretations of slow plateau currents in terms of genuine permeability changes. The rabbit Purkinje fibre may allow various ionic channels to be studied with relatively little interference from radial non‐uniformities in membrane potential or ion concentration.
Pancreatic acinar cells: effects of microionophoretic polypeptide application on membrane potential and resistance
Authors: Petersen O. H. , Philpott H. G.
Published: December 2014

1. Acinar cell membrane potential and resistance were measured from superfused segments of mouse pancreas, in vitro, using intracellular glass micro‐electrodes. One or two extracellular micropipettes containing caerulein, bombesin nonapeptide (Bn) or acetylcholine (ACh) were placed near to the surface of the impaled acinus. The secretagogues were ejected rapidly from the micropipettes by ionophoresis.

2. Each secretagogue evoked a similar electrical response from the impaled acinar cell: membrane depolarization and a simultaneous reduction in input resistance. The duration of cell activation from caerulein ionophoresis was longer than that observed for ACh and Bn. The cell response to the peptide hormone applications could be repeated in the presence of atropine.

3. The minimum interval before the onset of cell depolarization after caerulein ionophoresis was determined. Values ranged between 500 and 1000 msec. The minimum latencies after Bn ionophoresis were 500‐1400 msec.

4. With two electrodes inserted into electrically coupled acinar cells, direct measurements of the caerulein and Bn null potentials were made. At high negative membrane potentials an enhanced depolarization was evoked by caerulein ionophoresis. At low negative membrane potentials the caerulein stimulation produced a diminished depolarization, and at membrane potentials less than — 10 mV acinar cell hyperpolarizations were observed. A similar series of responses was obtained in experiments where Bn ionophoresis was used. The caerulein and the Bn null potentials were always contained within — 10 to — 15 mV.

5. The results describe the almost identical electrical response of acinar cells to stimulation by ACh, caerulein and bombesin. All three secretagogues have similar null potentials and latencies of activation on acinar cells. The bombesin latency responses appear as short as those measured for caerulein and provide electro‐physiological evidence that Bn acts directly on acinar cells. The findings support the hypothesis that ACh, caerulein and Bn, though acting on different receptors, evoke the observed changes in electrical properties of acinar cell membranes, through a common pathway.
Electromechanical noise in atrial muscle cells of the carp: a possible ionic feed‐back mechanism.
Authors: Akselrod S , Landau E M , Lass Y
Published: December 2014

1. Spontaneous electrical fluctuations (+/‐ 0.2‐0.4 mV) were recorded in 'quiescent' atrial fibres of the carp. 2. The noise decreased in acetylcholine, small hyperpolarization and EGTA. 3. The noise increased (to +/‐ 1‐2 mV) and became more synchronous in K+‐free Ringer and in ouabain. 4. Large voltage fluctuations (+/‐ 1‐2 mV) were accompanied by a fine mechanical tremor, indicating intracellular [Ca2+] fluctuations. 5. Spectral analysis showed a clear resonant frequency at about 1 Hz, indicating that the noise cannot result from the random switching of independent ionic channels. 6. We propose that the intracellular [Ca2+] and the membrane K+‐conductance are involved in a feed‐back loop which can oscillate and produce the electromechanical noise. The frequency of oscillation is determined by the relatively slow diffusion of Ca2+ from the intracellular reservoir to the surface membrane.
Presynaptic action of curare.
Authors: Glavinović M I
Published: December 2014

1. As a result of a conditioning phrenic nerve stimulus, end‐plate currents (e.p.c.s) in a voltage clamped uncurarized cut diaphragm show a facilitation which reaches its maximum at 30‐40 msec and subsequently decays with a time constant from 150 to 200 msec. In curarized (cut or uncut) diaphragms, however, the conditioning stimulus causes a depression which reaches its maximal value at 10 msec and then decays slowly with a time constant of about 3 sec. This indicates that curare strongly interferes with the process of transmitter release. 2. The presynaptic action of curare is also evident if short tetanic trains are given. In uncurarized preparations e.p.c.s decay in size much more slowly than in curarized preparations, and usually show a transient facilitation. 3. These results can be explained in terms of a model where curare blocks presynaptic depolarizing action of ACh. As a result of this presumed curare action a small increase in Ca permeability and subsequent entry of Ca associated with depolarization are also blocked, and the facilitation resulting from that entry of Ca is abolished.
The excitation and depression of spinal neurones by ibotenic acid.
Authors: Curtis D R , Lodge D , McLennan H
Published: December 2014

1. The firing of spinal interneurones and Renshaw cells by microelectrophoretic (+/‐)‐ibotenate, which was approximately eight times more active as an excitant than L‐glutamate, was followed by prolonged depression of the sensitivity of the neurones to excitant amino acids and acetylcholine. 2. The depression, which lasted for 15‐‐30 min when ibotenate was ejected for 3‐‐6 min, was blocked by the GABA‐antagonist bicuculline methochloride, and was independent of prior firing since it occurred with subthreshold concentrations of ibotenate and when ibotenate firing had been blocked by DL‐alpha‐aminoadipate. 3. When administered electrophoretically for 5 min, muscimol, a potent GABA agonist, reduced neuronal excitability for prolonged periods and this effect was also prevented by bicuculline methochloride. 4. The depression of neuronal excitability produced by GABA, taurine, isoguvacine or 3‐aminopropane sulphonate, ejected for periods of 5‐‐6 min, recovered rapidly. 5. It is suggested that ibotenate is converted in vivo to muscimol or a related compound which has a prolonged, bicuculline‐sensitive depressant action on the excitability of neurones.
Intraventricular microinjections of a stable analogue of prostaglandin endoperoxide cause fever in rabbits.
Authors: Harrisberg C J , Laburn H , Mitchell D
Published: December 2014

1. Derivatives of arachidonic acid other than prostaglandin are pyrogenic, the likely candidates being the prostaglandin endoperoxides and/or the thromboxanes. 2. Intraventricular microinjections in rabbits of a stable analogue of prostaglandin endoperoxide resulted in dose‐dependent increases of rectal temperature. The pyrexia was delayed in onset; no significant change in body temperature occurred for at least an hour. 3. The pyrexia was unaltered by simultaneous injection of the potent prostaglandin synthetase inhibitor indomethacin. 4. We suggest that both prostaglandins and prostaglandin endoperoxides may be implicated in fever.
Functional characteristics of slowly adapting pulmonary stretch receptors in the turtle (Chrysemys picta).
Authors: Jones D R , Milsom W K
Published: December 2014

1. Single nerve fibre discharge has been recorded from slowly adapting pulmonary stretch receptors in single‐pithed turtles on artificial ventilation. 2. Receptor discharge during static and dynamic lung inflations showed that lung volume was the major stimulus of these receptors. The rate and degree of change in transpulmonary pressure were without direct effect. 3. The response of these receptors to static and dynamic lung inflation differed only quantitatively from those of bronchopulmonary stretch receptors in mammals. The lower discharge frequencies and sensitivities of the turtle receptors may arise from the low body temperature of these animals. 4. The sensitivity of turtle pulmonary receptors to CO2 was greater than that recorded for bronchopulmonary receptors of mammals although the effects of CO2 on receptor discharge were qualitatively similar. In several instances, receptor discharge was totally inhibited throughout the ventilatory cycle by inflation with 5‐‐10% CO2 in air.
Dependence of motoneurone properties on the length of immobilized muscle
Authors: Gallego R. , Kuno M. , Núñez R. , Snider W. D.
Published: December 2014

1. The soleus muscle of adult cats was fixed in a shortened or lengthened position for 2 weeks by immobilizing the leg with a plaster cast. To eliminate the effects of reflex activity arising from the muscle, the lumbosacral dorsal roots were sectioned on the side of leg immobilization.

2. The soleus muscle showed a significant decrease in weight after immobilization in a shortened position. Immobilization of the muscle in a lengthened position produced no significant changes in its weight.

3. Two weeks after transection of the throacic spinal cord, the soleus muscle showed a significant decrease in weight. This decrease was prevented by immobilization of the muscle in a lengthened position. Immobilization in a shortened position caused no further muscle atrophy in cord‐transected animals.

4. Soleus motoneurones showed a significant decrease in the duration of after‐hyperpolarization (a.h.p.) 2 weeks after immobilization of the muscle in a shortened position, whereas immobilization of the muscle in a lengthened position caused no significant changes in the duration of a.h.p.

5. A decrease in the duration of a.h.p. of soleus motoneurones induced by cord transection was significantly prevented by immobilization of the muscle in a lengthened position but not by immobilization in a shortened position.

6. In a variety of experimental conditions, the mean duration of a.h.p. of soleus motoneurones was significantly correlated with the soleus muscle: body wt. ratio.

7. It is concluded that certain motoneurone properties depend upon the condition of the innervated muscle and that the primary factor responsible for the trophic influence is metabolic change in the muscle rather than contractile activity itself.
Diuresis from left atrial receptors: effect of plasma on the secretion of the Malpighian tubules of Rhodnius prolixus.
Authors: Kappagoda C T , Knapp M F , Linden R J , Pearson M J , Whitaker E M
Published: December 2014

1. Stimulation of left atrial receptors by distension of a balloon in the lumen of the left atrium of anaesthetized dogs was shown to result in an increase in urine flow. Plasma samples obtained from these dogs during control periods and during periods of stimulation were applied to the Malpighian tubules of Rhodnius prolixus. 2. It was found that the tubules suspended in test plasma secreted at a significantly lower rate than those suspended in control plasma. 3. These differences were also evident in extracts of plasma prepared using the solvent n‐butanol. 4. Cutting or cooling the cervical vagi abolished these differences along with the increase in urine flow. It is argued that this preparation of the Malpighian tubule of Rhodnius prolixus could be used as a means of detecting the diuretic agent responsible for the increase in urine flow.
The effect of hypothalamic lesions on immuno‐reactive alpha‐melanocyte stimulating hormone secretion in the rat.
Authors: Penny R J , Tilders F J , Thody A J
Published: December 2014

We have examined the hypothesis that MSH secretion in the rat is under a tonic inhibitory control by the central nervous system. Electrothermic lesions were made in the medio‐basal hypothalamus (m.b.h.) which destroyed the hypothalamo‐hypophyseal connexions. Plasma and pituitary alpha‐MSH wwere measured using a sensitive and specific radioimmunoassay technique. Pituitary alpha‐MSH content decreased to 17% of control levels 24 hr after the lesion and returned to normal by 7 days. Plasma alpha‐MSH was maximally elevated 15 min after the lesion, and returned to normal by 2 hr. No further change over control levels was found for the remainder of the experiment (98 days). The similarity of the plasma alpha‐MSH response after m.b.h. lesions to that found previously after administration of long acting dopamine receptor blocking drugs suggests that these lesions may interrupt impulse flow in dopaminergic tubero hypophyseal neurones which are thought to be important in the inhibitory control of MSH secretion in the rat. From our present results it seems that the rat pituitary, unlike that of lower vertebrates, is able to re‐establish basal MSH secretion very quickly after disconnexion from central control.
Afferent sympathetic unmyelinated fibres with left ventricular endings in cats.
Authors: Casati R , Lombardi F , Malliani A
Published: December 2014

1. We recorded the electrical impulse activity of thirty‐three single afferent fibres with left ventricular endings from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocity ranged from 0.23 to 0.98 m/sec (group C). 2. The endings of each fibre were localized to the left ventricle by mechanical probing performed at the end of the experiment on the non‐beating heart. No fibre had multiple sensory fields. 3. The impulse activity (0.95 +/‐ 0.2 impulses/sec) was spontaneous but most often a fixed temporal correlation between impulses and ventricular dynamics was not detectable. It was increased during occlusion of the thoracic aorta, I.V. administration of isoprenaline or infusion of saline. It was unaffected by asphyxia, haemorrhage and I.V. administration of acetylcholine. It was decreased during occlusion of inferior vena cava. Therefore these ventricular receptors appeared to be mainly sensitive to mechanical events. 4. The fibres were excited during the occlusion of the left main coronary artery, after a latency of 14.5 +/‐ 1.3 sec. They were also excited during ventricular fibrillation, exhibiting the highest values of impulse activity (2.51 +/‐ 0.4 impulses/sec). The increase in impulse activity during ventricular fibrillation was sometimes immediate and extreme, with peak frequencies of about 50 impulses/sec. 5. These spontaneously active ventricular receptors with unmyelinated nerve fibres participate in the transmission of the continuous impulse activity which from the cardiovascular system reaches the spinal cord through the sympathetic nerves and which is likely to contribute to the neural control of circulation. Thus the unmyelinated cardiac sympathetic afferents should not be considered as purely nociceptive in function.
Studies of the development of brain barrier systems to lipid insoluble molecules in fetal sheep.
Authors: Dziegielewska K M , Evans C A , Malinowska D H , Møllgård K , Reynolds J M , Reynolds M L , Saunders N R
Published: December 2014

1. The development of the blood‐brain and blood‐c.s.f barriers to lipid insoluble substances of different molecular radii has been studied in fetal sheep, early (60 days) and late (125 days) in gestation, using labelled erythritol (C14), sucrose (3H or 14C), inulin (3H or 14C) and albumin (125I), or albumin and IgG detected by immunoassay. 2. Morphological studies of fetal brain and choroid plexus at the same gestational stages were carried out using thin section electron microscopy and the freeze fracture techniques. 3. Penetration of markers into c.s.f. was substantially greater at 60 days than at 125 days, but at both ages the steady‐state level achieved appeared to be related to molecular size. 4. A simple model describing penetration from blood into c.s.f. at 60 days is proposed. It involves the assumption that c.s.f. and brain extracellular fluid are effectively separate compartments; morphological and permeability data which supports this assumption is presented. The data for c.s.f. at 60 days are consistent with the suggestion that the markers penetrate into c.s.f. by diffusion and are not restricted by small pores in the interface between blood and c.s.f. 5. The reduction in penetration which occurred by 125 days for all markers except erythritol appears to be accounted for by an increase in the sink effect and a decrease in the effective surface area for exchange between blood and c.s.f. 6. Intercellular tight junctions of both cerebral endothelial cells and choroid plexus epithelial cells were well formed at 60 days gestation. There was no change in junctional characteristics previously thought to correlate with transepithelial permeability (tight junction depth and strand number) between the two ages studied, although there were marked changes in permeability. 7. Evidence is advanced in support of the hypothesis that in the fetus much of the penetration of lipid insoluble non‐polar substances across the blood‐c.s.f. barrier and perhaps across the blood‐brain barrier occurs via a transcellular route consisting of a system of tubulo‐cisternal endoplasmic reticulum. Penetration via the choroid plexus appears to be the dominant route for penetration from blood into c.s.f. in the 60 day fetus.
Post‐natal development of amiloride sensitive sodium transport in pig distal colon.
Authors: Cremaschi D , Ferguson D R , Hénin S , James P S , Meyer G , Smith M W
Published: December 2014

1. Both electrophysiological properties and unidirectional Na and Cl fluxes have been determined across distal colons taken from pigs during early post‐natal development. 2. The transmural potential difference (Vms) was 5 mV in the new‐born and 10 mV in the 4 day old colon. The short circuit current (Scc) showed a three to sixfold increase during the first 10 days of post‐natal life. The microvillar membrane potential (Vm) fell from about ‐45 mV in the new‐born to ‐40 mV in the 4 day old colon. 3. Amiloride had no effect on Vms, Scc or Vm, measured in the new‐born animal. It reduced Vms and Scc, caused a hyperpolarization of Vm and increased the microvillar membrane/basolateral membrane resistance ratio (Rm/Rs) in colons taken from older animals. 4. The Scc of distal colons taken from new‐born and 1 day old pigs was only half that predicted from unidirectional measurements of Na flux. This discrepancy, which could not be completely accounted for by net CL absorption, disappeared in the older animals. 5. Net transport of Na doubled during the first 24 h of post‐natal life. Part of this transport took place through an amiloride sensitive, non‐electrogenic, pathway. 6. It is suggested that Na uses mainly a non‐electrogenic pathway to cross the mucosa of the new‐born pig. This pathway is replaced by an electrogenic amiloride sensitive mechanism in older animals. Aldosterone is thought to initiate these changes in Na tranport.
Studies of the electrical excitability of aorta smooth muscle of rabbit
Authors: Mekata F.
Published: December 2014

1. Electrical records were made from the smooth muscle of rabbit aorta in normal solution and after excitation by noradrenaline, by the partitioned chamber method.

2. Noradrenaline (3 × 10−7 g/ml.) produced depolarization and periodic slow potentials, the amplitudes of which were decreased by depolarizing currents and increased by small hyperpolarizing currents. Application of strong hyperpolarizing current stopped production of the slow potentials.

3. After application of small amounts of noradrenaline, electrical stimulation produced slow potentials.

4. Membrane resistance at the top of the slow potential induced by noradrenaline (3 × 10−7 g/ml.) was decreased to a few percent of the stable potential level during application of noradrenaline.

5. The voltage—current relationship of smooth muscle cells in the aorta showed marked cathodal rectification both in standard solution and upon the application of noradrenaline.

6. High K (24 m
M) elicited periodic slow potentials, the electrical properties of which were very similar to those induced by noradrenaline. Phentolamine (5 × 10−5 g/ml.) and guanithidine (10−5 g/ml.), however, blocked the production of these slow potentials.

7. The conditions required for the production of slow potentials are discussed.

8. Evoked slow potentials by current flow during application of noradrenaline (3 × 10−7 g/ml.) was recorded at 5 mm from the stimulating partition. Thus it is concluded that the slow potential can be conducted.