bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reconstruction of the action potential of ventricular myocardial fibres
Authors: Beeler G. W. , Reuter H. 
Published: December 2014

1. A mathematical model of membrane action potentials of mammalian ventricular myocardial fibres is described. The reconstruction model is based as closely as possible on ionic currents which have been measured by the voltage‐clamp method.2. Four individual components of ionic current were formulated mathematically in terms of Hodgkin—Huxley type equations. The model incorporates two voltage‐ and time‐dependent inward currents, the excitatory inward sodium current, iNa, and a secondary or slow inward current, is, primarily carried by calcium ions. A time‐independent outward potassium current, iK1, exhibiting inward‐going rectification, and a voltage‐ and time‐dependent outward current, ix1, primarily carried by potassium ions, are further elements of the model.3. The iNa is primarily responsible for the rapid upstroke of the action potential, while the other current components determine the configuration of the plateau of the action potential and the re‐polarization phase. The relative importance of inactivation of is and of activation of ix1 for termination of the plateau is evaluated by the model.4. Experimental phenomena like slow recovery of the sodium system from inactivation, frequency dependence of the action potential duration, all‐or‐nothing re‐polarization, membrane oscillations are adequately described by the model.5. Possible inadequacies and shortcomings of the model are discussed.
Inhibition of human motoneurones, probably of Renshaw origin, elicited by an orthodromic motor discharge
Authors: Bussel B. , Pierrot-Deseilligny E. 
Published: December 2014

1. The pattern of variations of a test H‐reflex after a conditioning H‐reflex was investigated in human subjects by an experimental design in which both reflexes involved the same soleus motoneurones. This was made possible by using a method based upon a collision in the motor axons between the orthodromic conditioning reflex volley and the antidromic volley elicited by a test stimulus supramaximal for the motor axons.2. The variations of the test reflex amplitude seen when increasing the conditioning reflex discharge were studied. This was made possible by facilitating the conditioning reflex without changing the strength of the afferent volley. This facilitation was obtained through a soleus stretch elicited by a stimulation of the plantar nerves.3. The amplitude of the test reflex depended only on the size of the conditioning reflex discharge.4. As long as the conditioning reflex was of low amplitude, all the motoneurones responsible for the conditioning response could be activated by the test volley, even though these motoneurones were undergoing after‐hyperpolarization. This indicates that, in man, the after‐hyperpolarization of the most excitable motoneurones can be completely overcome by a large Ia afferent volley.5. Increasing the conditioning reflex beyond a specific value resulted in an absolute decrease in the number of motoneurones involved in the test reflex. The amount of this decrease was related only to the amplitude of the conditioning reflex.6. This inhibition decreased progressively as the time interval separating the test stimulus from the conditioning stimulus increased. The time course of this inhibition was studied with conditioning reflexes of different amplitudes. The duration of the inhibition increased with the size of the conditioning reflex.7. These results strongly suggest that Renshaw cells excited by the conditioning reflex are responsible for this inhibition. The results are in agreement with observations made in animals on recurrent inhibition.
Rod‐cone interaction in light adaptation
Authors: Latch M. , Lennie P. 
Published: December 2014

1. The increment‐threshold for a small test spot in the peripheral visual field was measured against backgrounds that were red or blue.2. When the background was a large uniform field, threshold over most of the scotopic range depended exactly upon the background's effect upon rods. This confirms Flamant & Stiles (1948). But when the background was small, threshold was elevated more by a long wave‐length than a short wave‐length background equated for its effect on rods.3. The influence of cones was explored in a further experiment. The scotopic increment‐threshold was established for a short wave‐length test spot on a large, short wave‐length background. Then a steady red circular patch, conspicuous to cones, but below the increment‐threshold for rod vision, was added to the background. When it was small, but not when it was large, this patch substantially raised the threshold for the test.4. When a similar experiment was made using, instead of a red patch, a short wave‐length one that was conspicuous in rod vision, threshold varied similarly with patch size. These results support the notion that the influence of small backgrounds arises in some size‐selective mechanism that is indifferent to the receptor system in which visual signals originate. Two corollaries of this hypothesis were tested in further experiments.5. A small patch was chosen so as to lift scotopic threshold substantially above its level on a uniform field. This threshold elevation persisted for minutes after extinction of the patch, but only when the patch was small. A large patch made bright enough to elevate threshold by as much as the small one gave rise to no corresponding after‐effect.6. Increment‐thresholds for a small red test spot, detected through cones, followed the same course whether a large uniform background was long‐ or short wave‐length. When the background was small, threshold upon the short wave‐length one began to rise for much lower levels of background illumination, suggesting the influence of rods. This was confirmed by repeating the experiment after a strong bleach when the cones, but not rods, had fully recovered their sensitivity. Increment‐thresholds upon small backgrounds of long or short wave‐lengths then followed the same course.
Suppression of rat stomach histidine decarboxylase activity by histamine: H2‐receptor‐mediated feed‐back
Authors: Håkanson R. , Larsson L.-I. , Liedberg G. , Rehfeld J. F. , Sundler F. 
Published: December 2014

1. Gastrin activates rat stomach histidine decarboxylase. Exogenous histamine suppressed the basal enzyme activity in unoperated, in nephrectomized, in vagally denervated and in antrectomized rats, and counteracted the pentagastrin‐induced enzyme activation in unoperated rats.2. Kinetic analysis of enzyme‐catalysed histidine decarboxylation in extracts from untreated vagotomized and from histamine‐treated vagotomized rats showed that the histamine‐induced suppression of histidine decarboxylase activity probably reflects a reduced enzyme concentration. Moreover, the enzyme half‐life in vagotomized rats after treatment with histamine was shorter than the half‐life observed after inhibition of enzyme synthesis. These observations suggest that administration of histamine not only inhibits enzyme synthesis but also causes an accelerated rate of elimination of histidine decarboxylase.3. Intravenous infusion of histamine caused marked displacement of the pentagastrin dose—response curve, in a manner suggesting a reduced sensitivity to pentagastrin.4. After H2‐receptor blockade, but not after H1‐receptor blockade, histamine was less effective in suppressing the enzyme activity. Furthermore, H2‐receptor blockade augmented the pentagastrin‐induced enzyme activation.5. The results suggest that histamine (via H2‐receptors) reduces the sensitivity of the histamine‐storing cells to gastrin and that H2‐receptor blockade induces the opposite effects.6. We propose that the histamine‐storing cells in the rat stomach are endowed with H2‐receptors and that exogenous histamine is capable of acting directly on the histamine cells. This may reflect a physiological control mechanism whereby mobilized endogenous histamine modifies its own synthesis and release.
Close relation between TEA responses and Ca‐dependent membrane phenomena of four identified leech neurones
Authors: Kleinhaus Anna L. , Prichard James W. 
Published: December 2014

1. Tetraethylammonium chloride (TEA) was applied to four kinds of identified neurones in leech segmental ganglia, namely, the sensory cells responding to touch (T), pressure (P) and noxious (N) stimuli and the Retzius cell (R).2. TEA prolonged the action potentials of these cells to characteristically different degrees, in the order R > N > P > T, regardless of exposure time. This result was the same whether TEA was presented to the whole ganglion via the bathing fluid or injected iontophoretically into the soma of the cell under study.3. TEA in Na‐free solution caused the behaviour of the N cell membrane to be dominated by a Ca‐dependent, Mn‐blockable event identical in every respect except smaller size to the previously described behaviour of the R cell under the same conditions. The P cell displayed a still smaller event of the same kind, but none was detectable in the T cell.4. In the absence of both TEA and Na, when Ca was the only extra‐cellular cation available to carry current, active membrane responses to depolarization were present in the R cell (previous study) and the N cell; such responses were minimal in the P cell and absent from the T cell.5. Differences among the four cells in density of a divalent cation conductance mechanism are the simplest explanation for these observations, though a more complex explanation based on multiple, pharmacologically distinct K conductances is not excluded by our data.
Mechanism of milk secretion: milk composition in relation to potential difference across the mammary epithelium
Authors: Peaker M. 
Published: December 2014

1. In conscious lactating goats a significant correlation was found between blood—milk potential difference (p.d.) and milk [lactose] such that in goats with a lower milk [lactose], milk was more negative with respect to blood.2. When mannose was substituted for glucose in the substrate mixture of isolated perfused goat mammary glands, milk yield and milk [lactose] fell while milk [Na] and [K] increased; in parallel experiments the blood—milk p.d. changed such that milk became more negative with respect to blood. These changes were reversed following the addition of glucose.3. When milk was made hypertonic by the addition of hyperosmotic sucrose or lactose solutions, water entered milk osmotically and milk became electrically less negative or even positive with respect to blood in goats, cows and guinea‐pigs.4. No effect on p.d. was apparent following the addition of isosmotic sucrose to milk in goats.5. When milk was held in the teat of goats by a pneumatic cuff around the base of the teat, no effect on p.d. was apparent when hyperosmotic sucrose was introduced into this teat pouch.6. It is suggested that waterflow‐induced potentials (the streaming potential and the transport number effect) can be induced across the mammary epithelium.7. In goats exogenous oxytocin lowered milk [lactose] and blood—milk p.d. became less negative with respect to blood.8. In non‐lactating and mastitic glands of goats the blood—milk p.d. was within 0·5‐2·5 mV of zero.9. The effects of oxytocin, and the low p.d. in non‐lactating and mastitic glands, are compatible with the view that in such circumstances there is a paracellular pathway across the mammary epithelium which partially short‐circuits the two sides.10. It is suggested that, with water being drawn osmotically into milk to dilute newly formed lactose, waterflow‐induced potentials may be responsible for establishing the normal p.d. across the apical membrane of the secretary cell, thereby keeping milk [K] and [Na] lower than in intracellular fluid.
Dorsal horn cells that respond to stimulation of distant dorsal roots (cat)
Authors: Devor M. , Merrill E. G. , Wall P. D. 
Published: December 2014

Experiments were carried out to find if there were post‐synaptic effects produced by impulses in the long ranging primary afferents, which had been shown by Wall & Werman (1976) to extend from upper lumbar dorsal roots to the sacral segments. Dorsal rootlets were stimulated in decerebrate low‐spinal adult cats.1. The dorsal root potential and ventral root reflex were recorded on S1 root filaments, in response to stimulation of dorsal rootlets extending from L1 to S1. With increasing distance between stimulating and recording segments, these potentials became smaller and more delayed. In two animals, there was no response at S1 to stimulation of L1 and L2 dorsal roots.2. In all animals, stimulation of L3 or L4 dorsal roots produced cell responses in dorsal horn segments L7 or S1. The density of such cells was variable, from animal to animal. Responding cells were mainly concentrated laterally in the dorsal horn.3. The latency and response variability of L7‐S1, dorsal horn cells to L3‐L4 stimulation was consistent with at least some of them being fired monosynaptically.4. Cells that respond to stimulation of one distant rootlet respond to many closer rootlets as well.5. The receptive fields of L7‐S1 dorsal horn cells, responsive to stimulation of L3‐L4 rootlets, were typical of those generally found in the L7‐S1 segments, and were at some distance from the L4 dermatome. Only twenty cells had receptive fields which extended into the dermatome of the rootlets stimulated.6. It was established that some L4 cells respond to S1 dorsal root stimulation, just as the main study had shown that S1 responds to L4.7. It is concluded that substantial numbers of dorsal horn cells, including cells with many types of cutaneous receptive field, respond to two classes of synaptic in‐put: one effective in firing the cell upon natural cutaneous stimulation, and one relatively ineffective, capable of driving the cell only when stimulated electrically and thus carrying a synchronous volley from a number of highly convergent axons. The contribution of this secondary afferent channel to normal and pathological cord physiology has now to be determined.
Effect of changing the composition of the bathing solution upon the isometric tension—pCa relationship in bundles of crustacean myofibrils
Authors: Ashley C. C. , Moisescu D. G. 
Published: December 2014

1. The relative isometric tension—pCa relationship has been determined for isolated bundles of barnacle myofibrils under a variety of ionic conditions using [Ca2+]‐buffered solutions which also contained an ATP regenerating system (creatine phosphate and creatine kinase).2. The results are in better agreement with the ‘consecutive’ scheme of reaction rather than with the ‘independent’ alternative (Ashley & Moisescu, 1972) for the co‐operative action of two Ca2+ ions in the process of tension activation in crustacean skeletal muscle.3. Variations in the pH of the activating solutions did have a marked effect on the relative tension—Ca curve, although no effect was observed on the absolute maximum value for isometric tension. A shift in pH by 0·5 u. in the range 6·6‐7·6 shifted the Ca2+—activation curve by 0·5 log u. towards lower free Ca2+ concentrations.4. Changes in the free Mg2+ concentration of the activating solutions in the millimolar range produced a pronounced shift of the relative tension—pCa curve along the pCa axis. Increasing [Mg2+] from 1 to 5 m
M shifted the curve by about 0·7 log u. to higher free Ca2+ concentrations, without significantly modifying its steepness.5. Changes in the MgATP concentration of the activating solutions in the range of 1‐13 m
M had no significant effect on the relative tension—pCa relationship.6. Varying the K+ concentration in the activating solutions was also observed to have a marked effect upon the tension—pCa relationship in barnacle. An increase in the K+ concentration from 90 to 170 m
M shifted the curve by some 0·6 log u. towards higher free Ca2+ concentrations.7. Cooling the standard activating solutions from room temperature to +4° C made no apparent difference to the relative tension—pCa relationship, but decreased significantly the absolute tension responses.8. The results presented show that tonicity by itself has a marked effect upon the absolute steady‐state tension levels in isolated bundles of myofibrils.9. Maximum isometric tension in this preparation was not simply related to ionic strength, or to the monovalent cation concentration, but it depended, as well, upon the anionic composition of the activating solution. In addition, a change in ionic strength of 25 m
M over the range of 245‐270 m
M did not appear to modify the relative tension—pCa relationship.10. The effect of the physiologically occurring cations H+, K+, Mg2+ upon the relative isometric tension—pCa relationship can be accounted for on the basis of a model of competitive inhibition between these cations and Ca2+ for the functional unit for tension. This inhibitory effect appears to involve at least one H+, one Mg2+ and two K+ per each Ca2+ ion participating in the activation process of the functional unit for tension.
Excitation—contraction coupling in the smooth muscle cells of the rabbit main pulmonary artery
Authors: Casteels R. , Kitamura K. , Kuriyama H. , Suzuki H. 
Published: December 2014

1. Increasing the external K concentration depolarizes the smooth muscle cells of the main pulmonary artery, and this depolarization reaches a maximal slope of 58 mV for a tenfold change of [K]o. The threshold depolarization for inducing contraction is at 4 mV and the maximal contraction is reached at a [K]o of 58 m
M.2. Noradrenaline concentrations between 2 × 10−8
M and 10−7
M induce tension without depolarizing the cells, but at higher concentrations noradrenaline not only elicits a large tension response but also depolarizes the cells in a dose‐dependent way.3. The effect of noradrenaline on the pulmonary artery is appreciably modified by substituting sucrose for NaCl: the cells are slightly hyperpolarized and the tension response is very much reduced.4. By studying the tension response to noradrenaline in other experimental conditions which cause a small hyperpolarization of the cells, such as 5 m
M‐[Ca]o, 2.9 m
M‐[K]o or a small depolarization, such as 11·9 m
M‐[K]o, it was found that a slight modification of the membrane potential can exert an important effect on the noradrenaline response.5. A simultaneous decrease of [Ca]o and [Na]o reduces the tension response to all noradrenaline concentrations. It was found that a reduction of [Na]o exerts a more depressing effect than a reduction of [Ca]o. In interpreting these results we have to take into account changes of the membrane potential, of availability of Ca, and some competition between external Ca and Na.6. A study of the effect of different concentrations of noradrenaline in Krebs solutions and Ca‐free solution has shown that concentrations up to 2·5 × 10−7
M elicit contraction by increasing the Ca influx, while higher concentrations also induce a release of cellular Ca.7. Caffeine depolarizes the cells and reduces the membrane resistance. It modifies the K, Cl and Ca fluxes in the same way as noradrenaline, but it suppresses the mechanical response induced by noradrenaline.
The relationship between histamine secretion and 45calcium‐uptake by mast cells
Authors: Foreman J. C. , Hallett M. B. , Mongar J. L. 
Published: December 2014

1. Unstimulated mast cells from the peritoneal cavity of the rat take up 45Ca: the initial phase of rapid uptake being complete after 1 min incubation of the cells with the isotope. Stimulation of the mast cells with an antigen‐antibody reaction, dextran or concanavalin A induces an increase in the uptake of 45Ca which is accompanied by a release of granular material: this increase in 45Ca uptake is also complete in 1 min. The majority of the stimulated 45Ca uptake cannot be explained in terms of binding of Ca to released granular material, or to an enlargement in either the extracellular compartment or the cell surface area.2. The magnitude of the increase in 45Ca uptake caused by stimulating the mast cells increases when the degree of histamine secretion increases.3. The increased 45Ca uptake induced by stimulation of the mast cells and the degree of histamine secretion are both dependent on extracellular H ion concentration. Changes of pH cause similar changes in 45Ca uptake and secretion with maxima at pH 7.5.4. Two thirds of the 45Ca uptake induced by an antigen‐antibody reaction or by the Ca ionophore A 23187 is unaffected by inhibiting glycolysis and oxidative phosphorylation. Histamine secretion on the other hand is practically abolished by this metabolic inhibition. Thus, 45Ca uptake proceeds in the absence of the discharge of granules.5. Dibutyryl cyclic AMP or theophylline inhibit both the increase in 45Ca uptake and the histamine secretion caused by stimulating mast cells with an antigen‐antibody reaction. Cyclic AMP, cyclic GMP and dibutyryl cyclic GMP have no effect on uptake or secretion.6. The Ca ionophore, A 23187, induces uptake of 45Ca and histamine secretion, neither effect being inhibited by either dibutyryl cyclic AMP or theophylline.7. Phosphatidyl serine increases both 45Ca uptake and the histamine release induced by an antigen‐antibody reaction, dextran or concanavalin A.
The interaction of monovalent cations with the sodium pump of low‐potassium goat erythrocytes
Authors: Cavieres J. D. , Ellory J. C. 
Published: December 2014

1. The activation by Na ions and the effect of the anti‐L antibody on the sodium pump of low‐potassium type (LK) erythrocytes, have been studied by measuring ouabain‐sensitive ATPase activity of red cell membranes of LK goats. The experimental data were first corrected for incomplete occupation of the external K sites of the pump, using a saturation function obtained from influx experiments.2. Double‐reciprocal plots of the corrected rates against Na concentration at various fixed K concentrations, yield a pattern of competitive K inhibition when it is assumed that three equivalent sodium sites take part in the internal activation of LK‐(Na+K)‐ATPase. The dissociation constant of Na at each site (Km) lies between 10 and 20 m
M and that of K as competitive inhibitor (Ki), between 1.5 and 4.5 m
M.3. The maximal rate of hydrolysis of LK goat (Na + K)‐ATPase is not different from those usually obtained with the high‐potassium type (HK) red cell enzyme. Then, the low pumping rate of LK erythrocytes in physiological conditions is only reflecting the poor Na affinity, both absolute and relative, at the internal Na sites of their sodium pumps.4. The stimulation of the ouabain‐sensitive ATPase activity by sensitization of the membranes with anti‐L serum, is mediated by a threefold reduction of the Km/Ki ratio at each site. Km decreases by a factor of 10, but there is also a smaller diminution of Ki. The maximal rate of hydrolysis, however, is unchanged by the anti‐L treatment. The least‐squares fitting of the pooled data by the rate equation, converges better with less than three and more than two equivalent sodium sites.5. The affinity sequence at two external K sites of the LK goat erythrocyte sodium pump, determined in the presence of 100 m
M external Na, is Rb > K > Cs. It is obtained from the concentration dependence in influx experiments, and is the same as reported for human red cells.6. Cubic‐root Dixon plots of the corrected ouabain‐sensitive ATPase activity against the concentration of K and its congeners, show the sequence Tl > K > Rb > Na > Cs for the affinities at the internal cation sites of the LK sodium pump. Anti‐L treatment decreases the relative magnitude of Na and Cs selectivities, it being not certain whether a Rb—Na transition then occurs.7. The results are discussed in terms of possible mechanisms whereby the sodium pump of LK and HK red cells may adjust the properties of their cation sites upon translocation of monovalent cations.