bluuebunny/crossref_metadata_2025 huggingface dataset:
Motor units in a skeletal muscle of neonatal rat: mechanical properties and weak neuromuscular transmission.
Authors: Jones S P , Ridge R M
Published: December 2014

1. Isometric twitch and tetanic tensions were recorded from whole muscles and single motor units in isolated fourth deep lumbrical muscles from neonatal rats (most at 3‐5 days old) and from older rats of various ages. 2. Whole‐muscle time to peak contraction reduced from about 120 ms at birth to about 20‐25 ms at 20 days and older. 3. The number of motor units in the muscle was constant with age (eleven on average) and there was no significant branching of motor axons below the common peroneal nerve branching point in the thigh. 4. In the 3‐5 days age range, mean twitch:tetanus ratio for whole muscles was 0.299 and for single units was 0.177. As a consequence, mean motor unit size (as a percentage of whole‐muscle tension) was greater for tetani (29.7%) than for twitches (19.9%). This was not the case in muscles from animals 22 days or older. Evidence is given that the cause of this is low junctional efficacy in some neuromuscular junctions in neonatal muscle. Intracellular recordings supported this view. 5. The relationships of motor‐unit size to the contraction time, to the ratio of contraction time:half‐relaxation time, and to fatigue index are given. There was no indication of clear segregation of motor units into more than one population, but it is concluded that small motor units are more likely to contain a higher proportion of slowly contracting, fatigue‐resistant fibres than large units. 6. The level of overlap by axons in the lateral plantar nerve onto muscle fibres in a single sural nerve motor unit was greater in tetani than in twitches. The results indicate that the distribution of weak and strong inputs was not random, but that there was a tendency for one strong input to accompany a number of weak inputs (on average about two) on each muscle fibre. 7. Intracellular recording indicates that about 12% of fibres at 3‐5 days may be electrically coupled.
Potentiation of gamma‐aminobutyric‐acid‐activated chloride conductance by a steroid anaesthetic in cultured rat spinal neurones.
Authors: Barker J L , Harrison N L , Lange G D , Owen D G
Published: December 2014

1. Intracellular recordings from cultured rat spinal cord neurones demonstrated that Cl(‐)‐dependent responses to GABA (gamma‐aminobutyric acid) (but not glycine) were increased in amplitude and duration by the steroid anaesthetic alphaxalone (3 alpha‐hydroxy‐5 alpha‐pregnane‐11,20‐dione) at submicromolar concentrations that produced little or no effect on passive electrical properties. The non‐anaesthetic 3 beta‐hydroxy analogue was without effect on GABA‐evoked responses. 2. Under voltage clamp, membrane currents evoked by GABA were potentiated by alphaxalone without change in the reversal potential for the GABA‐evoked response. Fluctuation analysis of GABA‐evoked currents suggested that the mean open‐time of GABA‐activated channels was prolonged from 30 to 74 ms in the presence of the anaesthetic. 3. Higher concentrations of alphaxalone, similar to those reported during surgical anaesthesia, increased membrane conductance in the absence of exogenously applied GABA. Under voltage clamp, current responses to alphaxalone reversed at the same potential as did responses to GABA, suggesting that they result from increased Cl‐ conductance. 4. Alphaxalone responses were reduced by the GABA antagonist bicuculline. Fluctuation analysis of current responses to the anaesthetic suggest that they result from the activation of ion channels of long (100 ms) open‐time and elementary conductance indistinguishable from that of channels activated by GABA (20 pS). Taken together, these findings indicate that the steroid anaesthetic is able to directly activate Cl‐ conductance normally activated by GABA in spinal neurones. 5. The actions of the steroid at GABA‐receptor‐Cl(‐)‐channel complexes are similar to those produced by the anaesthetic barbiturates (e.g. pentobarbitone), although obtained at 50‐100‐fold lower concentrations. These effects on the inhibitory Cl(‐)‐conductance mechanism may be partly responsible for the depressant actions of alphaxalone on the mammalian central nervous system.
Comparison of the after‐effects of impulse conduction on threshold at nodes of Ranvier along single frog sciatic axons.
Authors: Carley L R , Raymond S A
Published: December 2014

1. Single axons were teased from the distal end of whole frog sciatic nerve and impulses were recorded with a suction electrode. The whole nerve trunk was stimulated using a gross electrode that was slowly moved for several centimetres along the length of the nerve. The threshold for initiation of an action potential showed periodic minima which were interpreted as the location of nodes of Ranvier. 2. Internodal distances were uniform along individual fibres but differed among fibres having matching conduction velocities, suggesting that other individuating characteristics are also important in determining the spacing of nodes. 3. A standard protocol was used to measure the activity dependence of threshold. Nodes along any given fibre were found to be alike in the dependence of threshold on impulse activity. Both the superexcitable phase and the depressed phase of the after‐effects of impulse activity were similar for successive nodes. This suggests that the activity dependence of an unbranched length of axon can be well characterized by looking at any one of its nodes. 4. Comparison of nodes from different axons showed large variations in activity dependence. Depressibility, denoting the relative tendency of an axon to show depression, was quantified either as the initial rate of rise in threshold (percentage increase/min) following the onset of repetitive stimulation or as the total rise in threshold (percentage increase) after 5 min of exposure to a standardized rate of repetitive stimulation. By either measure depressibility differed among axons more than it differed among nodes from a single axon. 5. Superexcitability following single impulses was measured in the absence of depression. Axons exhibiting a larger decrease in threshold during the superexcitable phase also tended to show larger depressions relative to other axons when stimulated at a given rate. 6. There was little correlation between conduction velocity and the magnitude of either the depressed phase or the superexcitable phase within the population of fibres studied. This suggests that axon diameter alone (as indicated by conduction velocity) cannot be responsible for the wide variations in the amplitude of the depressed phase or the superexcitable phase. 7. The results suggest that some process exists to constrain the nodes along a fibre to have a uniform activity dependence.
Neurotransmitter‐induced currents in retinal bipolar cells of the axolotl, Ambystoma mexicanum.
Authors: Attwell D , Mobbs P , Tessier-Lavigne M , Wilson M
Published: December 2014

1. Whole‐cell patch clamping was used to study the membrane properties of isolated bipolar cells and the currents evoked in them by putative retinal neurotransmitters. 2. Isolated bipolar cells show an approximately ohmic response to voltage steps over most of the physiological response range, with an average input resistance of 1.3 G omega and resting potential of ‐35 mV. These values are underestimates because of the shunting effect of the seal between the patch electrode and the cell membrane. Depolarization beyond ‐30 mV produces rapid activation (10‐100 ms) of an outward current (carried largely by potassium ions), which then inactivates slowly (0.5‐2 s). 3. Of five candidates for the photoreceptor transmitter, four (aspartate, N‐acetylhistidine, cadaverine, putrescine) had no effect on bipolar cells. The fifth substance, L‐glutamate, opened ionic channels with a mean reversal potential of ‐12 mV in some cells (presumed hyperpolarizing bipolar cells), and closed channels with a mean reversal potential of ‐13 mV in other cells (presumed depolarizing bipolar cells). 4. The conductance increase induced by glutamate in presumed hyperpolarizing bipolar cells was associated with an increase in membrane current noise. Noise analysis suggested a single‐channel conductance for the glutamate‐gated channel of 5.4 pS. The power spectrum of the noise increase required the sum of two Lorentzian curves to fit it, suggesting that the channel can exist in three states. 5. The conductance decrease induced by glutamate in presumed depolarizing bipolar cells was associated with a decrease in membrane current noise that could be described as the sum of two Lorentzian spectra, and which suggested a single‐channel conductance of 11 pS. The noise decrease implies that the channels closed by glutamate are not all open in the absence of the transmitter. 6. GABA (gamma‐aminobutyric acid) and glycine, transmitters believed to mediate lateral inhibition in the retina, open chloride channels in isolated bipolar cells, and increase the membrane current noise. Noise analysis suggested that the channels gated by GABA and glycine have conductances of 4.4 and 7.5 pS respectively. The noise spectra required the sum of two Lorentzian curves to fit them. 7. By whole‐cell patch clamping cells in retinal slices, the synaptic transmitter released by photoreceptors was shown to close channels with an extrapolated reversal potential around ‐3 mV in depolarizing bipolar cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Appearance of adenosine in venous blood from the contracting gracilis muscle and its role in vasodilatation in the dog.
Authors: Ballard H J , Cotterrell D , Karim F
Published: December 2014

1. In dogs anaesthetized with sodium pentobarbitone and artificially ventilated, the gracilis muscles were vascularly isolated and perfused at a constant flow rate of 51.2 +/‐ 9.8 ml min‐1 100 g‐1 muscle tissue (183 +/‐ 17.8% of resting blood flow; mean +/‐ S.E.; n = 13). 2. Electrical stimulation of the cut peripheral end of the obturator nerve (6 V, 4 Hz) resulted in muscle contraction (658 +/‐ 118 g 100 g‐1 force after 5 min), and an immediate decrease in arterial perfusion pressure from 179 +/‐ 15.7 mmHg to 87 +/‐ 10.0 mmHg (51.4 +/‐ 4.5% decrease in vascular resistance after 2 min of contraction). Venous oxygen tension decreased from 69.2 +/‐ 5.1 mmHg to 18.5 +/‐ 1.4 mmHg (n = 6). These values did not significantly alter during the remaining period of stimulation (10‐20 min). 3. The concentration of adenosine in arterial plasma did not change significantly during muscle contraction (137 +/‐ 23 nM; n = 10). However, the adenosine concentrations in venous plasma showed a significant (P less than 0.01) increase from a control value of 164 +/‐ 55 nM to 455 +/‐ 77 nM (n = 9) after 5 min of muscle contraction and remained high during the rest of the 20 min contraction. In six of the dogs adenosine concentrations were determined after 1 and 3 min of contraction and showed a smaller but statistically significant (P less than 0.05) rise in venous concentration. 4. During infusion of adenosine into the artery to give plasma concentrations between 0.3 microM and 1 mM, 72.6 +/‐ 2.1% (n = 29) of the infused adenosine was taken up by the tissues before it reached the vein. Comparison of vasodilatation and venous adenosine concentrations during adenosine infusion and muscle contractions showed that the released adenosine could contribute about 15% to the total vasodilatation after 1 min and about 40% between 5 and 20 min of contractions. Released adenosine could contribute about 80% to the vasodilatation that remained 5 min after the withdrawal of stimulation. Arterial perfusion pressure took 22 min to return to control, whereas adenosine release had fallen to zero within 10 min. 5. These data suggest that the released adenosine could contribute to exercise hyperaemia, but is unlikely to be the main factor, particularly in the initial stage.
Effects of sodium‐potassium pump inhibition and low sodium on membrane potential in cultured embryonic chick heart cells.
Authors: Jacob R , Lieberman M , Murphy E , Piwnica-Worms D
Published: December 2014

1. When the Na+‐K+ pump of cultured embryonic chick heart cells was inhibited by addition of ouabain with or without removal of external K+, the membrane potential rapidly depolarized to ‐40 mV and the Na+ content approximately doubled within 3 min. 2. After this, exposure to an [Na+]o of 27 mM caused a fall in Na+ content, a gain in Ca2+ content and a hyperpolarization. The hyperpolarization was approximately 25 mV in a [K+]o of 0 or 5.4 mM after 3 min of pump inhibition. After approximately 10 min of pump inhibition, the same hyperpolarization was observed in a [K+]o of 5.4 mM but in K+‐free solution the hyperpolarization increased to approximately 44 mV. 3. Varying [K+]o during the 10 min period of Na+‐K+ pump inhibition showed that the increase in hyperpolarization was associated with the period of exposure to K+‐free solution rather than the [K+]o at the time of lowering [Na+]o. 4. Changes in Na+ and Ca2+ content induced by exposure to an [Na+]o of 27 mM in K+‐free solution were similar at 3 and 10 min. This and the above observations suggest that the increased hyperpolarization was due to an increased membrane resistance. 5. 10 mM‐Cs+ reduced the low‐[Na+]o hyperpolarization by 26% but did not significantly affect the movements of Na+ and Ca2+. 1 mM‐La3+ reduced the low‐[Na+]o hyperpolarization by 15%: it also totally blocked the rise in Ca2+ content and partially blocked the fall in Na+ content. 1 mM‐Ba2+ reduced the low‐[Na+]o hyperpolarization by 20%. 6. Raising [Ca2+]o from 2.7 to 13.5 mM produced similar but smaller hyperpolarizations (approximately 6 mV after 3 min pump inhibition). High [Ca2+]o caused a rise in Ca2+ content but no significant drop in Na+ content. The hyperpolarization in high [Ca2+]o was insensitive to verapamil (20 microM) and 10 mM‐Cs+. 7. We conclude from the disparities between the magnitudes of the hyperpolarizations and the changes in ion contents that Na+‐Ca2+ exchange cannot be unequivocally identified as electrogenic solely from the low‐[Na+]o hyperpolarizations.
Comparison of effects of acetylcholine on calcium and potassium currents in frog atrium and ventricle.
Authors: Hartzell H C , Simmons M A
Published: December 2014

1. Ca2+ and K+ currents were measured in single atrial and ventricular myocytes from frog heart with the whole‐cell patch‐clamp technique. 2. K+ currents were blocked with intra‐ and extracellular Cs+ and the fast Na+ current was blocked with tetrodotoxin (TTX). The Ca2+ current (ICa) was evoked by a depolarizing pulse from ‐80 to 0 mV. ICa was larger in ventricular (3.4 +/‐ 2.5 microA/cm2) than atrial (1.6 +/‐ 2.5 microA/cm2) myocytes. 3. Acetylcholine (ACh) had no effect on basal ICa when K+ currents were blocked with Cs+ or Ba2+. Isoprenaline increased ICa and ACh reduced the isoprenaline‐stimulated current to basal levels. 4. In contrast, when K+ currents were not blocked, ACh reduced the net inward current and increased the outward current at the end of the depolarizing pulse. The outward current was studied in the presence of Cd2+ to block ICa. The steady‐state current‐voltage relationship inwardly rectified and reversed near the K+ reversal potential (EK). The magnitude of the steady‐state ACh‐activated K+ current at 0 mV was 1.0 +/‐ 0.7 microA/cm2 in ventricular cells and 3.67 +/‐ 1.7 microA/cm2 in atrial cells. 5. With depolarization, the outward current increased instantaneously and then decreased to a new steady level. The first phase of the decay occurred with a time constant similar to that of the activation of ICa. The Cd2+‐sensitive current (corresponding to ICa) was obtained by subtracting currents in the presence and absence of Cd2+. The Cd2+‐sensitive current was not affected by ACh. 6. The apparent effect of ACh on basal ICa can be explained quantitatively by activation of a time‐dependent K+ current by ACh that contaminates ICa.
Inhibition of secretory granule discharge during exocytosis in sea urchin eggs by polymer solutions.
Authors: Whitaker M , Zimmerberg J
Published: December 2014

1. We have investigated the effects of the osmotic pressure exerted by polymer solutions on exocytosis in sea urchin eggs. 2. Exocytosis is prevented by including a variety of polymers of different chemical composition and molecular weight in the sea water surrounding the eggs. Inhibition is complete at a polymer osmolality of 250 mosmol/kg. 3. The increase in membrane capacitance which occurs during exocytosis and which corresponds to the fusion of secretory granules with the plasma membrane is not substantially altered by inhibitory concentrations of polymer. 4. In the absence of the ions present in sea water, these polymers inhibit exocytosis at an osmolality of 950 mosmol/kg. 5. Calcium, magnesium and sodium ions reduce the polymer osmolality required to prevent exocytosis. 6. A comparison of the effects of monovalent and divalent ions indicates that the divalent ions bind to and stabilize the secretory granule contents. 7. These results demonstrate that polymers prevent exocytosis by preventing dispersal of the granule contents once fusion of the secretory granule with the plasma‐lemma has occurred. The ions present in sea water do not promote dispersal, rather, they hinder it. The contribution of ionic fluxes to granule swelling during exocytosis is discussed.
Stimulus selectivity and functional organization in the lateral suprasylvian visual cortex of the cat.
Authors: Blakemore C , Zumbroich T J
Published: December 2014

1. We have examined the responses of cells in the postero‐medial and postero‐lateral lateral suprasylvian areas (p.m.l.s./p.l.l.s.) in the medial and lateral banks of the middle suprasylvian sulcus of the anaesthetized, paralysed cat. 2. Visual responses were assessed qualitatively (for projected spot and bar stimuli) and quantitatively (for drifting, high‐contrast gratings of optimum spatial and temporal frequencies, but varying in orientation and direction of drift). There was excellent agreement between qualitative and quantitative estimates of preferred direction of motion. 3. Comparison of responses to motion in the preferred direction and the opposite direction confirmed that the percentage of units with strong directional preference is higher in this region of cortex than in other cortical and subcortical visual structures so far investigated. 4. Cells were comparatively well 'tuned' for the direction of motion of a grating: on average the half‐width at half‐amplitude for the variation in response around the principal preferred direction was 23.2 deg for p.m.l.s. and 25.3 deg for p.l.l.s., thus falling within the range found for complex cells in area 17. In this and other aspects of their direction selectivity, neurones in p.m.l.s. and p.l.l.s. were very similar to each other. 5. Quantitative analysis of the direction‐response functions revealed them frequently to be more complex than previously described. For many cells there were subsidiary response peaks in addition to the main peak at the principal preferred direction. Often there was an accessory peak 180 deg from the optimum direction (i.e. directional preference was incomplete), but there was also a clear tendency for responses to be specifically elevated for directions orthogonal to the principal direction. 6. Tests with stationary, contrast‐modulated gratings of the optimum spatial frequency, but differing in orientation, revealed that neurones responsive to such stimuli (though limited to about half the population) were orientation selective, their preferred orientations for stationary and drifting gratings being very similar. 7. The functional architecture of the lateral suprasylvian cortex was studied by means of single and multiple penetrations at different angles to the cortical surface: in most penetrations in p.m.l.s. the preferred directions of cells tended to shift progressively in small steps across the cortex, at a maximum rate of about 360 deg mm‐1. However, there were occasional 180 deg differences between neighbouring recording sites or between cells recorded at different depths within a single radial column.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in presynaptic inhibition of Ia fibres at the onset of voluntary contraction in man.
Authors: Hultborn H , Meunier S , Pierrot‐Deseilligny E , Shindo M
Published: December 2014

1. Two independent methods were used, in man, to assess changes in presynaptic inhibition of I a terminals at the onset of selective voluntary contractions: (1) measurement of the amount of heteronymous monosynaptic I a facilitation (from the quadriceps muscle to soleus motoneurones) to provide an assessment of the amount of ongoing presynaptic inhibition exerted on the I a fibres responsible for the facilitation; (2) measurement of the inhibition of H reflexes 40‐60 ms after a short vibration to the tibialis anterior tendon to estimate the excitability of the interneurones mediating presynaptic inhibition from tibialis anterior I a afferents to the I a afferents of the test H reflex (soleus or quadriceps). 2. At the onset of an isolated voluntary plantar flexion of the foot (gastrocnemius‐soleus contraction) the heteronymous facilitation from quadriceps to soleus was increased, reflecting a decreased presynaptic inhibition of the quadriceps I a terminals on soleus motoneurones. Vibratory inhibition of the soleus H reflex was decreased, reflecting an inhibition of transmission of presynaptic inhibition to homonymous soleus I a afferent terminals. 3. At the onset of the same gastrocnemius‐soleus contraction there was, on the contrary, an increased vibratory inhibition of the quadriceps H reflex indicating a facilitation of transmission of presynaptic inhibition to homonymous quadriceps I a afferent terminals. 4. At the onset of an isolated voluntary knee extension (quadriceps contraction) the opposite pattern was seen: the heteronymous facilitation from quadriceps to soleus was decreased and the vibratory inhibition of a soleus H reflex was increased, whereas the vibratory inhibition of the quadriceps H reflex was decreased. 5. These results indicate that presynaptic inhibition of I a afferent terminals on motoneurones of contracting muscles is decreased, permitting I a activity to contribute to excitation of voluntarily activated motoneurones. On the contrary, presynaptic inhibition of I a fibres to motoneurones of muscles not involved in the contraction is increased. It is argued that the former must be supraspinal in origin. 6. It is concluded that the control of presynaptic inhibition of I a fibres at the onset of movement may be organized so as to aid in achieving selectivity of muscle activation, i.e. so as to increase motor contrast.
Electrophysiological responses to dopamine of rat hypophysial cells in lactotroph‐enriched primary cultures.
Authors: Israel J M , Kirk C , Vincent J D
Published: December 2014

1. Cells from 14‐day‐old and lactating female rat pituitary glands were dissociated, separated and enriched on a continuous gradient of bovine serum albumin at unit gravity. They were maintained for at least 6 days in culture before perifusion and electrophysiological experiments were performed. 2. Immunofluorescent staining of the resulting gradient fractions (numbered F2 to F9) from both groups of animals indicated that the majority of lactotrophs were located in the light fractions (F3‐F4). However, a second population of lactotrophs was observed in the heavy fractions (F7‐F9) isolated from lactating females. 3. Basal secretion rates of prolactin were in the order of 2‐40 ng 2 min‐1 10(6) cells‐1 and were inhibited by dopamine in a dose‐dependent manner. 4. According to their electrophysiological properties, cells from 14‐day‐old females (first group) were categorized as follows: (1) inexcitable cells, which displayed a low resting potential of about ‐35 mV (39% of cells tested, n = 118); and (2) excitable cells, which displayed either triggered or spontaneous action potentials and resting membrane potentials higher than ‐50 mV (61% of cells tested, n = 185). 5. In the light fraction from lactating females (second group), the majority of the cells were excitable (70%) and showed high resting membrane potentials (‐50 to ‐55 mV) and 15% of these cells displayed spontaneous action potentials. 6. Heavy fractions (third group) contained a high percentage of non‐spontaneous but excitable cells (80% of the cells tested, n = 65). These cells were able to elicit action potentials after the cessation of hyperpolarizing current pulses ('off' potentials). 7. Action potentials were insensitive to the sodium channel blocker, tetrodotoxin (TTX; 5 x 10(‐6) M) but were reversibly blocked by calcium channel blockers such as cobalt, manganese and cadmium (10 mM). 8. In excitable cells from the three groups, dopamine (10(‐7) M) induced a hyperpolarizing response due to an increase of the membrane conductance. During this response, action potentials were inhibited. It was shown that this was not a direct effect of dopamine. The reversal potential of the dopamine‐induced response in these cells was found to be at ‐100 mV. This value was shifted to more positive potentials (‐50 mV) when high‐potassium medium was used (56 mM). 9. In non‐excitable cells (first group), dopamine (10(‐7) M) induced a hyperpolarizing response due to a decrease of the membrane conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of splanchnic nerve section on the sensitivity of the adrenal cortex to adrenocorticotrophin in the calf.
Authors: Edwards A V , Jones C T
Published: December 2014

1. Adrenal cortical responses to adrenocorticotrophin (ACTH) in conscious 2‐6‐week‐old calves, in which both splanchnic nerves had been cut at least 7 days previously, were compared with those of normal calves of the same age in order to discover whether splanchnic nerve section affects the sensitivity of the adrenal cortex to the trophin. 2. In one series of experiments an increase in the release of endogenous ACTH was elicited by an i.v. infusion of noradrenaline (333 ng min‐1 kg‐1 for 10 min) and in another the concentration of ACTH in the plasma was artificially increased by infusing synthetic ACTH1‐24 intravenously at either 5 or 10 ng min‐1 kg‐1 for 10 min. 3. In all groups mean plasma ACTH was linearly related to mean plasma cortisol and the sensitivity of the adrenal steroidogenic response to ACTH was found to be substantially reduced 7 or more days after section of both splanchnic nerves.
Hormone release from isolated nerve endings of the rat neurohypophysis.
Authors: Cazalis M , Dayanithi G , Nordmann J J
Published: December 2014

1. Isolated neurosecretory nerve endings were prepared from rat neurohypophyses. The amount of vasopressin (AVP) and oxytocin released was measured by radioimmunoassay. 2. The amount of hormone release under resting conditions was not affected by external calcium (Ca2+o). Secretion decreased by ca. 50% when external sodium (Na+o) was replaced by choline or sucrose. 3. Ouabain did not modify the basal AVP release. 4. The Na+ ionophore monensin increased the release of AVP only in the presence of Na+o. This increase was maintained during prolonged exposure to the ionophore and occurred in the presence of Ca2+o only. 5. In the presence of Ca2+o, the amount of evoked hormone release was dependent on the external K+ concentration. Half‐maximal activation was achieved with ca. 40 mM‐K+. The K+‐induced secretion was potentiated in Na+‐free solution. 6. Prolonged 100 mM‐K+‐induced depolarization in the presence of Ca2+o gave rise to a large increase in hormone secretion which decreased with time (t1/2 = 2.5 min). The release could be reactivated after permeabilization of the nerve terminals in the presence of micromolar concentrations of Ca2+. 7. A stepwise paradigm in which Ko+ is incrementally increased to 25, 50, 75 and then 100 mM released more AVP than a prolonged exposure to 100 mM‐K+. 8. Veratridine increased the amount of AVP released. This effect was considerably reduced in the absence of Nao+ and abolished in the presence of D600. 9. The depolarization‐induced AVP release was blocked by different Ca2+‐antagonists. Their effectiveness was nitrendipine = nicardipine greater than Cd2+ greater than Gd3+ greater than Co2+ = Mn2+. 10. The dihydropyridine Bay K 8644 potentiated both the basal and the K+‐evoked AVP release. Its maximal effect was obtained with 25‐50 mM‐Ko+. 11. In conclusion, the isolated neurohypophysial terminals which have both Na+ and Ca2+ channels and release AVP and oxytocin upon depolarization might be an excellent system to study further the mechanisms leading to secretion of neurohormones.
Fever induced in rabbits by intraventricular injection of rabbit and human serum albumin.
Authors: Morimoto A , Murakami N , Nakamori T , Watanabe T
Published: December 2014

1. Intraventricular injection of rabbit and human serum albumin, and rabbit endogenous pyrogen produced dose‐dependent fevers in rabbits. The pyrogenicity of albumin was less than one‐twentieth of the pyrogenicity of endogenous pyrogen. 2. Fevers induced by ventricular albumin were significantly suppressed by intraventricular injection of indomethacin which is a cyclooxygenase inhibitor. In contrast, subcutaneous injection had no effect. 3. Ventricular endogenous pyrogen induced several of the acute phase responses, i.e. decreases in the plasma concentration of iron and zinc, and increases in both the plasma concentration of copper and the white blood cell count. Albumin induced none of these responses. 4. It is concluded that fever induced by ventricular albumin is processed by prostaglandins synthesized within the central nervous system. However, ventricular albumin does not activate the central mechanism to induce acute phase responses.
Perchlorate and the relationship between charge movement and contractile activation in frog skeletal muscle fibres.
Authors: Csernoch L , Kovács L , Szücs G
Published: December 2014

1. The effects of perchlorate ions (1‐8 mM) on intramembrane charge movement, myoplasmic Antipyrylazo III Ca2+ transients and contractile activation were examined in voltage‐clamped cut skeletal muscle fibres of the frog. 2. Perchlorate shifted both the voltage dependence of charge movement and the rheobase of the strength‐duration relation for contraction threshold towards more negative membrane potentials. 3. Both charge movements and myoplasmic Ca2+ transients were much slower at the new rheobase in the presence of perchlorate than in the control solution but there was no change in the threshold amount of charge or in the calculated peak binding of Ca2+ to troponin C. 4. The peak release rate had a steeper voltage dependence than the non‐linear charge, but a lower concentration (2 mM) of perchlorate shifted both voltage dependences equally without altering the maxima in the amount of charge and in the rate of Ca2+ release. 5. The voltage dependence of the difference between total charge and charge at the threshold of Ca2+ transients agreed well with the voltage dependence of the rate of Ca2+ release in both the presence and absence of perchlorate. 6. It is concluded that the effect of perchlorate on contractile activation can be accounted for by its action on the intramembrane charge movement responsible for contraction, without significant effects on subsequent Ca2+ release from the sarcoplasmic reticulum or on Ca2+ binding to regulatory sites of troponin C.
Intracellular recordings from myenteric neurones in the human colon.
Authors: Brookes S J , Ewart W R , Wingate D L
Published: December 2014

1. Intracellular recordings were made from cells in the myenteric plexus of the human colon in freshly dissected tissue obtained from patients undergoing surgery for the removal of carcinomas or diverticular bowel. 2. Twenty‐seven cells from ten preparations were classified as neurones and had overshooting action potentials, an average resting potential of ‐54 +/‐ 9 mV, an average input impedance of 1.05 +/‐ 0.59 x 10(8) omega and a variety of synaptic inputs. 3. Twenty‐three (out of twenty‐five neurones tested) received nicotinic fast excitatory synaptic inputs (fast e.p.s.p.s) that were blocked reversibly by hexamethonium and mimicked by acetylcholine. These nerve cells bore a close resemblance to S cells that have been characterized in the guinea‐pig small‐bowel myenteric plexus. 4. One cell had a long after‐hyperpolarization following its impulses and was similar to AH cells in the guinea‐pig small bowel. 5. Three neurones received inhibitory synaptic inputs, up to 15 mV in amplitude, lasting up to 10 s, associated with a decrease in input impedance and with a reversal potential between ‐80 and ‐90 mV. 6. Slow excitatory synaptic potentials were only detected in the single AH cell. The slow e.p.s.p. was associated with a depolarization of up to 12 mV, an increase in excitability and an increase in the input impedance of the neurone. 7. The proportion of S and AH cells differ considerably from that reported in the guinea‐pig small‐bowel preparation. Possible causes of the differences are discussed.
Somatostatin increases an inwardly rectifying potassium conductance in guinea‐pig submucous plexus neurones.
Authors: Mihara S , North R A , Surprenant A
Published: December 2014

1. Intracellular recordings were made from neurones in the submucous plexus of the guinea‐pig caecum and ileum. 2. Somatostatin hyperpolarized more than 90% of the neurones. The lowest effective concentration was 300 pM and the maximum hyperpolarization (about 30‐35 mV) was caused by 30 nM. Under voltage clamp at ‐60 mV, somatostatin caused outward currents which reached a maximum of 350‐700 pA. 3. The hyperpolarization or outward current reversed polarity at a membrane potential (about ‐90 mV in control solutions) which changed according to the logarithm of the external potassium concentration. 4. The somatostatin current showed inward rectification; when the inward rectification of the resting membrane was prevented by extracellular caesium or rubidium, the inward rectification of the somatostatin current also disappeared. 5. A potassium conductance with the same properties was increased by alpha 2‐adrenoceptor agonists and by delta‐opioid receptor agonists; however, the effects of somatostatin were unaffected by antagonists at alpha 2‐ or delta‐receptors. The somatostatin analogue, cyclo‐aminoheptanoyl‐Phe‐D‐Trp‐Lys‐(benzyl)Thr, also did not antagonize the actions of somatostatin. 6. The hyperpolarization (or outward current) was unaffected by forskolin, cholera toxin, sodium fluoride, phorbol esters or intracellular application of adenosine 5'‐O‐(3‐thiotriphosphate) (ATP‐gamma‐S). However, when the recording electrode contained guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S) the hyperpolarizations reversed only partially when somatostatin application was discontinued, and repeated applications caused the membrane potential to approach and remain close to the potassium equilibrium potential. 7. It is concluded that somatostatin increases the conductance of a set of inwardly rectifying potassium channels in submucous plexus neurones. The coupling between somatostatin receptor and ion channel involves a guanosine 5'‐triphosphate‐binding protein, but is not likely to result from changes in intracellular levels of cyclic adenosine 3',5'‐monophosphate.
Monosynaptic excitation of thoracic motoneurones by inspiratory neurones of the nucleus tractus solitarius in the cat.
Authors: Duffin J , Lipski J
Published: December 2014

1. The connection between inspiratory neurones in the ventrolateral nucleus tractus solitarius (n.t.s.) and intercostal motoneurones was examined. 2. Descending axonal projections to contralateral T3‐T5 spinal segments were found for 110 of 142 (77%) ventrolateral n.t.s. neurones examined. 3. Antidromic mapping was used to locate the axons of thirty‐nine ventrolateral n.t.s. neurones in T4, and evidence for axon collaterals was found for thirty‐two of forty‐seven (68%) neurones examined. Axon collaterals were found in both T3 and T4 for four of nine neurones examined and in T3, T4 and T5 for two of three neurones examined. 4. Cross‐correlation histograms were calculated for sixty‐five ventrolateral n.t.s. neurones with the contralateral intercostal nerves. Peaks in the cross‐correlograms were assessed for significance by calculating k, the ratio of the peak bin count to the mean bin count. Significant peaks (k ratios 1.07‐1.24, mean 1.15) were found for twenty‐eight (39%) cross‐correlograms. Twelve of thirty‐three (36%) were for the whole external intercostal nerve, ten of twenty‐seven (37%) were for the whole internal intercostal nerve and six of eleven (54%) were for external intercostal nerve filaments. 5. Six of the cross‐correlogram peaks were less than or equal to 1.2 ms in width at a level half‐way between the peak and the mean bin count. The rest ranged from 2.0 to 4.6 ms (mean 3.0 ms). 6. Intracellular recordings from either internal or external intercostal motoneurones were made and averages of the intracellular potentials were computed using ventrolateral n.t.s. neurone spikes as triggers. 7. Thirty‐two spike‐triggered averages were computed for pairings between nineteen ventrolateral n.t.s. neurones and thirty‐two intercostal motoneurones (twenty‐five internal, seven external). Fast‐rising, short‐lasting depolarizations indicative of a monosynaptic e.p.s.p. were found for five ventrolateral n.t.s. neurones. 8. The characteristics of the cross‐correlogram peaks were considered with respect to the e.p.s.p. shapes and it was concluded that the intercostal motoneurones receive a significant monosynaptic excitation from ventrolateral n.t.s. neurones.
Voltage‐dependent intracellular pH in Helix aspersa neurones.
Authors: Meech R W , Thomas R C
Published: December 2014

1. The intracellular pH (pHi) of large nerve cells from the mollusc, Helix aspersa, was measured with pH‐sensitive micro‐electrodes. Cells were held under voltage clamp and the effect on pHi of different holding potentials was determined. 2. Depolarization of the cell from the resting potential (about ‐50 mV) to ‐10 mV produced a fall in pHi that could be reduced by bathing the cell in nominally Ca2+‐free saline. 3. At positive holding potentials pHi increased to a steady level that depended upon the electrochemical gradient for H+ across the cell membrane; it shifted by about 1 unit when the external pH was increased from 7 to 8 (or when the membrane potential increased by 58 mV, Thomas & Meech, 1982). 4. The depolarization‐induced increase in H+ permeability was insensitive to SITS (4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid, 20 microM), which blocks pHi regulation at the resting potential in these cells (Thomas, 1976). When pHi was displaced from a steady level by ionophoretic injection of HCl, there was a rapid recovery at depolarized potentials even in the presence of SITS. The H+ pathway appeared to be little affected by prolonged periods at positive membrane potentials. 5. The depolarization‐induced H+ efflux was insensitive to the metabolic inhibitor CCmP (carbonyl cyanide‐m‐chlorophenylhydrazone, 20 microM) and persisted in cells bathed in pH‐buffered n‐methyl glucamine‐gluconate. It was also insensitive to DCCD (N, N'‐dicyclohexylcarbodiimide, 10‐100 microM) and oligomycin (2‐10 micrograms/ml). 6. The H+ pathway could be fully blocked by 1 mM‐ZnCl2, 1 mM‐LaCl3, 1 mM‐CuCl2, 2 mM‐CdCl2 or 10 mM‐CoCl2. Other divalent ions such as BaCl2 (10 mM) produced a block at membrane potentials near 0 mV but the block was released at more positive potentials. Low levels of LaCl3 (0.1 mM), the organic Ca2+ channel antagonist D600 (100 mg/ml) and high levels of the K+ channel blocker TEA (50 mM) all had similar effects to Ba2+. 7. The K+ channel blocker 4‐aminopyridine (10 mM), which blocks H+ currents in perfused Lymnaea neurones (Byerly, Meech & Moody, 1984), has a complex action.(ABSTRACT TRUNCATED AT 400 WORDS)
Ryanodine releases calcium from sarcoplasmic reticulum in calcium‐tolerant rat cardiac myocytes.
Authors: Hansford R G , Lakatta E G
Published: December 2014

1. The hypothesis tested in this study is that ryanodine depletes sarcoplasmic reticulum (s.r.) Ca2+ loading in suspensions of single adult rat cardiac myocytes by effecting Ca2+ release into the myoplasm resulting in an increase in myoplasmic free [Ca2+] ([Ca2+]i). The latter was monitored by the fluorescent dye, quin2. 2. The competency of the technique to detect s.r. Ca2+ release was tested by using caffeine to induce Ca2+ release. The addition of 5‐10 mM‐caffeine to myocytes loaded with quin2 and incubated in a medium containing 1 mM‐Ca2+ gives a large, transient increase in fluorescence, which is interpreted as indicating an increase in [Ca2+]i. If the chelating agent EGTA is added to the cell suspension 1‐5 min prior to the caffeine, to a concentration sufficient to decrease extracellular Ca2+ to 0.1‐0.15 microM, then caffeine again gives a large, transient increase in fluorescence, indicative of the fact that sarcolemmal Ca2+ transport is not necessary for this response. The ionophore ionomycin also raises [Ca2+]i in a transient manner when added after EGTA. The addition of caffeine prior to ionomycin largely diminishes the response to the latter; however, addition of ionomycin prior to caffeine totally abolishes its effect to increase [Ca2+]i. This is taken to indicate that the intracellular store which is releasable by caffeine‐‐and which presumably reflects the s.r.‐‐is also releasable by ionomycin: ionomycin, however, also gives access to another, minor intracellular pool. 3. The plant alkaloid, ryanodine, at concentrations of 10(‐8) to 10(‐6) M, consistently causes a slow and prolonged increase in [Ca2+]i when added to cell suspensions incubated with 1 mM‐extracellular Ca2+. Under conditions precluding net entry of Ca2+ into the cell, viz. 0.1 microM‐extracellular Ca2+, ryanodine causes a more limited, partially reversible, increase in [Ca2+]i. 4. When added prior to EGTA, ryanodine attenuates, or prevents, the subsequent response to caffeine: efficacy depends upon the time of pre‐incubation (1‐10 min) and the concentration of ryanodine (10(‐8) to 10(‐6) M). When the response to caffeine is largely prevented by ryanodine, the response to ionomycin is also severely attenuated, i.e. there is no evidence that ryanodine causes sequestration of Ca2+ within an ionomycin‐sensitive pool.(ABSTRACT TRUNCATED AT 400 WORDS)
The extensibility of Aplysia nerve and the determination of true axon length.
Authors: Koike H
Published: December 2014

1. Characteristics of Aplysia nerves in response to extension were examined in comparison with nerves of the cat, frog and lobster. 2. Only the Aplysia nerve was easily elongated up to about 5 times its resting or relaxing length without impairing propagation of the action potential along the axon in the nerve. 3. The conduction velocity along the elongated nerve increased linearly in proportion to the nerve length in the range from the relaxing length to about 1.2‐1.5 times extension (the first phase). However, upon further extension it stayed constant regardless of the nerve length (the second phase). 4. In the relaxed nerve bundle the course of the axons was zigzagging and the axon membrane had numerous foldings or wrinklings. 5. The true length of the zigzagging axon was measured by analysing the length of intra‐axonal diffusion following intracellular injection of radioactive acetylcholine ([3H]ACh) whose diffusion kinetics in the axoplasm have been studied in detail (Koike & Nagata, 1979). The length of the axon coincided with the nerve length at which the first phase shifted to the second phase. 6. Cat and frog nerves shrank after dissecting out from the body. When extended, they showed the first phase from the shortened length to their original length in the body. These nerves lacked the second phase. The lobster nerve did not shrink and lacked both phases. 7. Thus the zigzagging course of the axon is suggested to be responsible for the first phase during which the axon length did not change but took a straight course upon nerve extension. 8. On the other hand, the second phase appears to be caused by actual extension of the axon itself and could be explained by reduction of the wrinklings of the membrane.
Electromyographic responses of a nasal muscle to stimulation of the nasal vestibule in the cat.
Authors: Davies A M , Eccles R
Published: December 2014

1. The effects of nasal stimulation using an air jet or balloon on the electromyographic (e.m.g.) activity of a nasal muscle, the levator labii superioris alaeque nasi component of the quadratus labii superioris muscle, were studied in the anaesthetized cat. 2. Respiratory related nasal e.m.g. activity was recorded and this normally consisted of two components, one coinciding with the onset of inspiratory airflow and a larger component which commenced at the onset of expiratory airflow and often persisted until the onset of the following inspiratory airflow. 3. An air jet (room air, 1‐8 l/min, temperature 24 degrees C) applied to the nasal vestibule by means of a small nozzle caused an increase in the amplitude of the ipsilateral spontaneous nasal e.m.g. activity. 4. The increase in nasal e.m.g. activity caused by the nasal air jet was unaffected by warming the airflow from 30 to 40 degrees C. 5. A sustained increase in nasal e.m.g. activity was caused by application of pressure to the walls of the nasal vestibule by means of a small balloon. 6. Section of the ethmoidal and infra‐orbital branches of the trigeminal nerve abolished the increase in nasal e.m.g. amplitude caused by nasal stimulation with the air jet, whilst section of the facial nerve abolished the spontaneous respiratory nasal e.m.g. activity. 7. The results indicate that there are sensory receptors in the nasal vestibule which respond to nasal positive pressure and cause a reflex increase in nasal e.m.g. activity.
An investigation of sodium‐calcium exchange in the smooth muscle of guinea‐pig ureter.
Authors: Aickin C C , Brading A F , Walmsley D
Published: December 2014

1. After application of ouabain (10(‐4) M), the intracellular Na+ activity (alpha iNa) of smooth muscle cells in the guinea‐pig ureter stabilizes at a relatively low level which can be rapidly lowered by reduction of external Na+ (Na+o) or elevation of Ca2+o. Both these procedures also elicit a transient contracture. These observations have previously been interpreted as evidence for Na+‐Ca2+ exchange. The presence of such an exchange mechanism has now been further investigated by measurements of alpha iNa, tension, ion analysis and 22Na efflux. 2. Ion analysis demonstrated that tissues were able to maintain a high cellular K+ content in the presence of ouabain, but slowly lost K+ and gained Na+ if K+o was also removed, as expected for an infinite outward gradient for K+ and a fully inhibited Na+ pump. 3. Tissues were only able to maintain a low cellular Na+ and high cellular K+ in the presence of ouabain if Ca2+ was present in the bathing solution. Reduction of Ca2+o to very low levels also caused a continual slow rise in alpha iNa in the presence of ouabain, provided that the prolonged depolarization caused by these low levels was prevented by elevation of Mg2+o. Alteration of the membrane potential by changing K+o at constant Na+o showed that alpha iNa decreased by about 1.2 mM for a 10 mV depolarization, within the range from ‐70 to ‐30 mV. 4. A small Ca2+o‐activated 22Na efflux was observed in ouabain‐treated tissues in the absence of Na+o. 40 mM‐Ca2+ was not more effective at activating this efflux than was 2.5 mM‐Ca2+, while 40 mM‐Mg2+ was ineffective. Restoration of the normal Na+o caused a large increase in the rate of 22Na loss. 5. Application of Mn2+ in the presence of ouabain caused a slow rise in alpha iNa and a small decline in resting tension. The fall in alpha iNa on reduction of Na+o was slowed by the presence of Mn2+ (mean half‐time increased from 1.7 to 5.0 min) and the concomitant contracture was almost abolished. These results are consistent with a Mn2+‐induced inhibition of Na+‐Ca2+ exchange. However, the fall in alpha iNa induced by elevation of Ca2+o was unaffected by the presence of Mn2+ and the attendant contracture was, if anything, enhanced. 6. Observation of changes in alpha iNa and tension at various Mn2+ and Ca2+ concentrations demonstrated a competitive interaction between the two divalent cations.(ABSTRACT TRUNCATED AT 400 WORDS)