bluuebunny/crossref_metadata_2025_split huggingface dataset:
Protein fractions from mouse salivary glands affecting epithelial cells in organ culture
Authors: Banks Barbara E. C. , Walter S. J. 
Published: December 2014

1. Extracts of male mouse submaxillary gland have been fractionated on G 150 Sephadex and DEAE cellulose.2. A number of the protein fractions obtained appear to cause proliferation of epithelial cells in organ cultures of rat tissues.3. All fractions active in organ culture possess proteolytic enzyme activity.4. The proteolytic enzymes trypsin, pronase and collagenase produce epithelial disorganization in organ culture.5. The organ culture effect is reduced in the presence of proteolytic enzyme inhibitors and abolished by pretreatment of proteins with diisopropylfluorophosphonate.6. The presence of mitotic inhibitors does not reduce the organ culture effect.7. The effect is not associated with an increase in the DNA content of tissue explants.8. No evidence has been found for the existence, in mouse salivary glands, of a specific growth factor acting on epithelial cells.
An electrophysiological dissection of the hypothalamic regions which regulate the pre‐ovulatory secretion of luteinizing hormone in the rat
Authors: Dyer R. G. 
Published: December 2014

1. Extracellular action potentials were recorded from 299 single units in the preoptic and anterior hypothalamic areas of fifty‐two female rats anaesthetized with urethane. The units were categorized by their response to single biphasic pulses (ca. 1 mA; 1 msec duration) applied to the ventromedial/arcuate region of the hypothalamus.2. Experiments with five lactating rats demonstrated that the effective zone of stimulation was confined within the ventromedial/arcuate region. This observation was supported by further evidence obtained during unit recording sessions.3. Antidromic action potentials were recorded from 122 (41%) of the neurones monitored in preoptic and anterior hypothalamic areas. These Type A cells were characterized by their very slow discharge rate (median for spontaneously active units 1·2 spikes/sec) when contrasted with adjacent cells (median 3·9 spikes/sec). Orthodromic action potentials were not observed in thirty‐six Type A cells. The antidromically identified neurones had an average conduction rate of 0·32 m/sec. The absolute refractory period of the soma, computed by separation of the IS and SD components of the antidromic action potentials recorded from forty‐four neurones, ranged from < 3·0 to > 100 msec. With ten units it was not possible to obtain a soma dendritic (SD) wave by antidromic activation even though the initial segment (IS) wave was seen clearly and the orthodromic potentials consisted of both IS and SD waves.4. Type B cells (32% of population) were excited and/or inhibited by the ventromedial/arcuate stimulation but were not antidromically activated. This post‐stimulatory change in discharge rate lasted for up to 400 msec.5. Type C cells (27% of population) showed no change in spontaneous activity after stimulation of the ventromedial arcuate area. These neurones had discharge rates similar to Type B cells.6. The previously reported prooestrous increase in firing rate, recorded from neurones in the ventral part of the preoptic/anterior hypothalamic area was restricted to cell Types B and C.
Systemic arterial baroreceptors in ducks and the consequences of their denervation on some cardiovascular responses to diving
Authors: Jones D. R. 
Published: December 2014

1. In the duck systemic arterial baroreceptors which cause bradycardia in response to induced hypertension are located in the walls of the ascending aorta, innervated by the depressor nerves.2. The location of the baroreceptors was confirmed both histologically and by recording activity from the depressor nerve. Stimulation of the central cut end of a depressor nerve caused transient bradycardia and a fall in blood pressure which was maintained throughout the period of stimulation.3. Cardiovascular adjustments to submergence of 2 min duration were monitored in intact, sham‐operated and denervated ducks. The sham‐operated and denervated ducks were used in the experiments some 20–50 days post‐operation. The denervations were checked at post‐mortem.4. In the first series of experiments on young ducks mean arterial pressure during a 2 min dive fell by 30% in intact, 17·5% in sham‐operated, and 48% in denervated ducks. In all ducks heart rate was reduced by 84–85%.5. In a second series of experiments on older ducks sciatic artery blood flow was also recorded and mean arterial blood pressure fell by 9·2% in intact and by 53% in denervated animals, although there were no significant differences in heart rate during the 2 min dives. In normal animals sciatic vascular resistance increased after 2 min submergence by 7·86 ± 1·7 times, whereas in denervated ducks it increased by only 2·32 ± 0·5 times.6. The role of systemic arterial baroreceptors in generation of the cardiovascular responses to submergence in ducks is discussed in terms of the input supplied by the baroreceptors to the central nervous system.
The positive dynamic current and its inactivation properties in cardiac Purkinje fibres
Authors: Fozzard Harry A. , Hiraoka Masayasu 
Published: December 2014

1. The positive dynamic current in sheep cardiac Purkinje fibres was studied using ‘voltage clamp’ technique. The major portion of this current was carried by Cl− ions.2. A pre‐step in membrane potential changed the response of this current to a subsequent depolarization in a way that is similar to the Na inactivation process described by Hodgkin & Huxley (1952a, b).3. Recovery of this current after its activation could be described reasonably well by a single exponential process, and the time course of the recovery varied with membrane voltage.4. The relation of steady‐state inactivation of the current to membrane voltage showed a sigmoid shape, varying from 100% at membrane potential of −30 mV to 0% at −80 mV. The membrane potential at 50% inactivation was −53 mV.5. The Cl− current may play a role in the shape of the Purkinje fibre action potential, but exact definition depends on determining the voltage and time dependence of all the ionic currents that flow during the plateau.
Chemoreceptor properties of glomus tissue found in the carotid region of the cat
Authors: Matsuura S. 
Published: December 2014

1. ‘Miniglomera’ appearing as small masses of tissue with ample vascularization were found around the common carotid artery of the cat. Physiological, gross anatomical and electron microscopic studies were conducted on these tissues.2. The chemosensory function of each ‘miniglomus’ was evident from the behaviour of the afferent nerve fibres supplying the tissue: afferent responses became more active during asphyxia, when the blood flow through the tissue was reduced or blocked and when cyanide or ACh were applied. The afferent impulses became more infrequent during hyperventilation.3. Sensory frequency response curves constructed against percentage of inhaled O2 showed that the impulses of single units increased in frequency with lowering of O2 content of the inhaled gas.4. These miniglomera are innervated by afferent fibres emerging from the nodose ganglion; sometimes these fibres are contained in the aortic or common carotid baroreceptor nerves, but sometimes they emerge as independent nerves. None of the miniglomera are supplied by branches of the sinus nerve.5. The fine structure of the miniglomus is similar to that of the carotid body. The tissue contains two types of cells: glomus cells which contain dense cored granules, and sustentacular cells whose fine processes enclose the former. Membrane densifications occur where glomus cells lie adjacent to one another or where they are contacted by nerve terminals. Nerve fibres are common in the miniglomus but they contact glomus cells less frequently than in the carotid body.
Cyclic variation of potassium conductance in a burst‐generating neurone in Aplysia
Authors: Junge Douglas , Stephens Cathy L. 
Published: December 2014

1. The hyperpolarization between bursts in the R 15 cell of Aplysia is accompanied by an increase in membrane slope conductance.2. The post‐burst hyperpolarization can be observed with ouabain, lithium, or potassium‐free solution if artificial inward current is applied. The hyperpolarization can be observed with dinitrophenol or cooling to 10° C, with no injected current. Thus, the hyperpolarization apparently is not due to the cyclic activity of an electrogenic pump.3. A reversal potential for the post‐burst hyperpolarization can be demonstrated by passage of inward current during the inter‐burst period. The reversal of direction of the potential depends on recent occurrence of a burst.4. The reversal potential varies with external potassium concentration, but not with chloride or sodium.5. The post‐burst hyperpolarization is not blocked by external tetraethylammonium at a concentration which greatly prolongs the action potentials.6. During the onset of spike blockage by, and recovery from, calcium‐free+tetrodotoxin saline, the bursts of action potentials appear to be driven by endogenous waves of membrane potential.7. The hyperpolarizing phase of the waves in calcium‐free+tetrodotoxin medium is accompanied by an increased slope conductance.8. A reversal potential can be demonstrated for the hyperpolarization following a wave in calcium‐free+tetrodotoxin medium by applying inward current during the interwave period.9. The waves in calcium‐free+tetrodotoxin medium are blocked by ouabain but can be reinstated by artificial hyperpolarization.10. The post‐burst hyperpolarization and the post‐wave hyperpolarization appear to result from a periodic increase in membrane conductance, primarily to potassium ions.
Temperature dependence of the ionic current kinetics of Myxicola giant axons
Authors: Schauf C. L. 
Published: December 2014

1. The temperature dependence of the sodium and potassium conductances of Myxicola giant axons was studied in the range of 1–18° C.2. Analysis of voltage clamp records for step depolarizations of 20–150 mV yielded Q10's for ḡNa, ḡK, and g1 of 1·3–1·5. The steady‐state parameters m∞ (v), n∞ (v) were independent of temperature. The time constants had Q10's of: 2·64 ± 0·2 for τm; 2·56 ± 0·2 for τh; 3·02 ± 0·3 for τn.3. τh determined from the effects of prepulse duration rather than the decline in sodium current during a step depolarization had a Q10 of 2·47 ± 0·2.
Calcium inward currents in internally perfused giant axons
Authors: Meves H. , Vogel W. 
Published: December 2014

1. Voltage clamp experiments were carried out on squid axons perfused with an isotonic solution of 25 m
M‐CsF + sucrose and placed in a Na‐free solution of 100 m
M‐CaCl2 + sucrose.2. Depolarizing voltage steps produced inward currents of 4–6 μA/cm2 peak amplitude which decayed slightly during a 60 msec pulse; the inward current disappeared when the internal potential reached +50 to +60 mV and became outward for larger depolarizations.3. Tetrodotoxin completely blocked the inward current and part of the outward current. No inward currents were seen with 100 m
M‐MgCl2 + sucrose as the external solution. Substituting acetate for external Cl− did not abolish the tetrodotoxin‐sensitive outward currents.4. It is concluded that the inward current is carried by Ca and the tetrodotoxin‐sensitive outward current by Cs ions, both moving through the Na channel.5. The reversal potential of the tetrodotoxin‐sensitive current was in the average +54 mV. Raising the external Ca concentration or adding NaCl to the external solution increased the reversal potential; lowering the external Ca concentration or replacing the internal CsF by a Na salt decreased the reversal potential.6. From the reversal potentials of the tetrodotoxin‐sensitive current measured with varying external and internal solutions the relative permeabilities of the Na channel were calculated as PCa/PCs = 1/0·6, PCa/PNa = 1/10 to 1/7 and PCs/PNa = 1/22 to 1/9 by means of the constant field equation. The permeability ratios suggest that under these experimental conditions the Na channel is still primarily permeable to Na ions, although its selectivity is relatively small.7. The time course of the tetrodotoxin‐sensitive Ca inward current was different from the time course of the Na inward current. The Na current consisted of an initial peak followed by a more slowly decaying component, the Ca current showed only the slow component.8. The slowly inactivating tetrodotoxin‐sensitive Ca inward currents give rise to the long lasting action potentials which have first been observed by Tasaki and coworkers under similar conditions.
Sensory receptors in the sheep's foot
Authors: Evans M. H. 
Published: December 2014

1. Median and ulnar nerves of anaesthetized Soay sheep have been investigated in vivo.2. The compound action potentials of these nerves indicate that the most rapidly conducting fibres had mean velocities of 87 m/sec in the median nerve and 57 m/sec in the ulnar nerve. The mean conduction velocities of the axons responsible for the Group A γδ wave in the median nerve were 23–30 m/sec and those responsible for the Group A δ wave in the ulnar nerve conducted at 23–26 m/sec.3. Single myelinated afferents were isolated by microdissection of median and ulnar nerves in the metacarpal region, and action potentials were recorded from hair follicle units, cutaneous mechanoreceptors, deeply situated proprioceptors, and from units of unknown function which were spontaneously active.4. The hair follicle units fell into two categories: ‘diffuse’ units which innervated many hairs in an area of about 1–3 cm2 anywhere on the hairy skin above the hoof, and ‘localized’ units which innervated a few hairs within small areas of the skin adjacent to the hoof. The ‘diffuse’ units generally resembled the ordinary hair follicle units of other animals except that in the sheep the afferents had higher conduction velocities. The ‘localized’ units also had large myelinated axons, but their physiological properties differed in several aspects from the guard hair, tylotrich and carpal hair units which have been studied in other animals.
Activation of descending control of the spinocervical tract by impulses ascending the dorsal columns and relaying through the dorsal column nuclei
Authors: Brown A. G. , Martin H. F. 
Published: December 2014

1. Micro‐electrode recordings were made from axons of the spinocervical tract in unanaesthetized decerebrate cats.2. Orthodromic activation of the dorsal columns and dorsal column nuclei was used to condition responses evoked in spinocervical tract neurones from cutaneous nerves. Such conditioning produced inhibition of transmission through the tract. The inhibition had a time course of 200 msec or more with maximal action at 30–70 msec and was most effective against polysynaptic responses.3. After removal of the cerebellum or section of the cerebellar peduncles the degree of inhibition was reduced but inhibition could still be evoked by activation of the dorsal columns and dorsal column nuclei.4. Transection of the brain stem just rostral to the dorsal column nuclei removed the inhibitory effects although segmental inhibition was not affected.5. It is concluded that impulses ascending the dorsal columns and relaying through the dorsal column nuclei can lead to activation of descending control of the spinocervical tract. Parts of the pathways involved include the cerebellum and the brain stem. It is unlikely that the cells in the dorsal column nuclei which have descending axons are concerned with the control of transmission through the spinocervical tract.
Voltage clamp analysis of acetylcholine produced end‐plate current fluctuations at frog neuromuscular junction
Authors: Anderson C. R. , Stevens C. F. 
Published: December 2014

1. Acetylcholine produced end‐plate current (e.p.c.) noise is shown to be the results of statistical fluctuations in the ionic conductance of voltage clamped end‐plates of Rana pipiens.2. These e.p.c. fluctuations are characterized by their e.p.c. spectra which conform to a relation predicted from a simple model of end‐plate channel gating behaviour.3. The rate constant of channel closing α is determined from e.p.c. spectra and is found to depend on membrane potential V according to the relation α = BeAV (B = 0·17 msec−1±0·04
S.E., A = 0·0058 mV−1±0·0009
S.E. at 8° C) and to vary with temperature T with a Q10 = 2·77, at −70 mV. A and B in this expression both vary with T and therefore produce a membrane potential dependent Q10 for α.4. Nerve‐evoked e.p.c.s and spontaneous miniature e.p.c.s decay exponentially in time with a rate constant which depends exponentially on V. The magnitude and voltage dependence of this decay constant is exactly that found from e.p.c. spectra for the channel closing rate α.5. The conductance γ of a single open end‐plate channel has been estimated from e.p.c. spectra and is found not to be detectibly dependent on membrane potential, temperature and mean end‐plate current. γ = 0·32±0·0045 (
S.E.) × 10−10 mhos. Some variation in values for γ occurs from muscle to muscle.6. It is concluded that the relaxation kinetics of open ACh sensitive ionic channels is the rate limiting step in the decay of synaptic current and that this channel closing has a single time constant. The relaxation rate is independent of how it is estimated (ACh produced e.p.c. fluctuations, e.p.c., m.e.p.c.), and is consistent with the hypothesis that individual ionic channels open rapidly to a specific conductance which remains constant for an exponentially distributed duration.7. The voltage and temperature dependence of the channel closing rate constant agree with the predictions of a simple dipole‐conformation change model.
Release of noradrenaline from slices of cat spleen by pre‐treatment with calcium, strontium and barium
Authors: Garcia A. G. , Kirpekar S. M. 
Published: December 2014

1. Spleen slices pre‐incubated for different periods at 4° C in Krebs solution containing varying concentrations of calcium, up to 96 m
M, lost their endogenous noradrenaline stores when reincubated in normal Krebs solution at 37° C for 2 hr. Rate of loss of noradrenaline was roughly related to the calcium concentration of the pre‐incubation medium and the pre‐exposure time.2. Pre‐treatment with isotonic barium or strontium (96 m
M) Krebs solution also induced release of noradrenaline from spleen slices when re‐exposed to normal Krebs solution. Barium was more effective than either calcium or strontium.3. The enhanced release induced by calcium pre‐treatment occurred in the absence of calcium, with or without EGTA.4. Tissue calcium concentration of spleen slices was 0·68 m‐mole/kg. Pre‐treatment of slices with normal or 96 m
M calcium‐Krebs solution for 4 hr at 4° C increased the calcium concentration to 2·57 and 9·9 m‐mole/kg, respectively.5. Ouabain, which caused a dose‐dependent release of noradrenaline, did not modify the release induced by calcium pre‐treatment.6. Spleen slices prepared from cats anaesthetized with sodium pentobarbitone instead of ether were resistant to noradrenaline depletion by calcium pre‐treatment.7. Evoked release of [3H]noradrenaline by high potassium from calcium‐pre‐treated slices did not occur in the absence of external calcium, even though the calcium pre‐treatment enhanced the tissue concentration of this ion by nearly tenfold.8. Net uptake of noradrenaline in normal and in treated slices whose noradrenaline content was severely reduced by barium pre‐treatment or sodium withdrawal was comparable.9. Specific activity of released and endogenous [3H]noradrenaline increased as the tissue stores of noradrenaline were reduced.10. It is suggested that the spontaneous loss of tissue noradrenaline after pre‐treatment with high‐calcium solution was due to inhibition of sodium‐potassium‐activated ATPase by intracellular accumulation of calcium ions. Evidence is presented to suggest that vesicles depleted of their endogenous transmitter by pre‐treatment with calcium, strontium or barium, or by sodium withdrawal, are re‐used for the storage and release of exogenous noradrenaline.
Influence of previous mechanical events on the contractility of isolated cat papillary muscle
Authors: Jewell B. R. , Rovell J. M. 
Published: December 2014

1. The influence of previous mechanical events on myocardial contractility has been investigated in the cat papillary muscle preparation.2. When a muscle that had been producing a stable response under isometric conditions was allowed to shorten isotonically, its ability to do so increased in successive beats until it reached a steady level, which represented a potentiated state compared with that seen in the first isotonic beat and in the preceding stable isometric contractions.3. The increase in tension development in the first isometric beat after a period of isotonic beating was used as an index of the degree of potentiation. It was found to be well correlated with the changes in other parameters that could have been used for this purpose.4. The main determinants of the degree of potentiation produced by a period of isotonic beating were:(a) the amount by which the muscle shortened. This was inversely related to the force opposing shortening (i.e. the isotonic load);(b) the number of isotonic beats. There was some potentiation (about 10%) after a single isotonic beat, but the number of beats required for maximal potentiation (up to 25%) depended on the frequency of stimulation; about 8 beats were required at 24 min−1.5. An isotonic release during the rise of tension in an isometric response was even more effective in potentiating the next isometric beat than an afterloaded contraction against the same load. Isotonic releases at later times had a diminishing influence on tension development in the next isometric beat.6. In the absence of stimulation, the potentiated state produced by a period of isotonic beating decayed with a half‐time of about 50 sec. When the muscle was stimulated it disappeared sooner, and its rate of decay depended on the frequency of stimulation; at 24 min−1 about 8 beats were required to restore contractility to its previous steady level.7. The characteristics of the decay of the potentiated state were closely similar to those of the potentiated states that can be produced by various electrical interventions, and the possibility that all of these might have the same underlying mechanism is discussed.8. Attention is drawn to the practical implications of this phenomenon in the design of experiments in which the muscle contracts under changing mechanical conditions.
The temperature dependence of the movement of sodium ions associated with nerve impulses
Authors: Cohen L. B. , Landowne D. 
Published: December 2014

1. The movement of sodium ions across the membrane of the squid giant axon was measured by the use of radioactive tracers. Unidirectional fluxes were measured at rest and when the nerve was stimulated. The difference was considered the extra flux association with nerve impulses.2. The extra influx in intact axons at room temperature was 5·5 p‐mole/cm2. impulse. At 6° C the extra influx was 6·5 p‐mole/cm2. impulse giving a Q10 of 1/1·2.3. In perfused axons a Q10 of 1/1·6 was obtained for the extra sodium influx in bracketed experiments on individual axons.4. The Q10 of the extra sodium efflux associated with nerve impulses was found to be 1/1·2 in intact axons.5. Hodgkin & Huxley had predicted a much larger temperature dependence for the extra fluxes. If this difference between prediction and experiment does not result from some experimental error, then the class of models for the ion fluxes suggested by Hodgkin & Huxley may be inapplicable.