bluuebunny/crossref_metadata_2025_split huggingface dataset:
An ATPase dependent, radiosensitive acidic microclimate essential for intestinal folate absorption
Authors: Kesavan V. , Noronha J. M. 
Published: December 2014

1. 5‐Methyltetrahydrofolic acid transport was studied across everted sacs of rat jejunal segments from control and whole body X‐irradiated (700 rad) rats at 10−5
M concentrations (at which optimum transport occurs) at various pHs.2. The folate transport from mucosal to serosal compartment was inhibited by about 55% in irradiated rat at the pH of the intestinal chyme (6·5). Extraneous ATP in the incubation system could restore the defective transport of the irradiated intestine.3. The maximum folate transport which occurred at pH 4·0 was not adversely affected by whole body irradiation. An acidic, pH dependent, passive uptake of 5‐methyltetrahydrofolic acid was observed.4. The normal absorption barrier of the small bowel was not disrupted by the acidification process as practically no uptake was observed with irradiated segments pretreated at pH 4·0 except in the presence of ATP.5. Leucine and serine transport at a zero concentration gradient indicated active transport mechanisms which were not affected by acidification. Their uptake was additively increased in the presence of glucose and ATP, further indicating that the normal physiology of the intestines was not affected by the acidification process.6. An intestinal mucosal cell surface ATPase was observed which was Mg2+ dependent. It could hydrolyse solution phase ATP and thus generate the protons necessary for the acidification of a microenvironment where passive uptake of the neutral folate species could occur.7. The ATPase activity was inhibited about 90% by 50 m
M‐Na azide at pH 6·5. Below this concentration folate transport was also inhibited.8. Na azide did not inhibit folate transport at pH 4·0, suggesting that its inhibition of folate uptake at pH 6·5 is related to its inhibitory effect on ATPase, rather than on folate transport per se. ATPase activity was therefore essential for folate transport at the pH of the intestinal chyme.
Renal bicarbonate reabsorption in the new‐born dog
Authors: Kleinman Leonard I. 
Published: December 2014

1. Renal bicarbonate reabsorption was measured in thirty new‐born dogs 2‐27 days of age. Plasma bicarbonate was varied in the puppies by exchanging their blood with blood containing high levels of bicarbonate and low levels of chloride.2. The exchange transfusion resulted in increases of plasma pH, PCO2 and bicarbonate in the puppies without changing plasma sodium and potassium or glomerular filtration rate (g.f.r.) and body weight.3. There was no tubular reabsorption maximum (Tm) for bicarbonate and reabsorption values as high as 50 μequiv/ml. g.f.r. could be attained. No animals excreted bicarbonate at plasma levels below 25 m
M and some animals had plasma bicarbonate threshold values in excess of 40 m
M.4. Bicarbonate reabsorption increased as arterial PCO2 rose (r = 0·62) but this was due to the rise of filtered bicarbonate since (a) there was no correlation between arterial PCO2 and bicarbonate reabsorption when factored by filtered bicarbonate and (b) lowering arterial PCO2 by mechanical hyperventilation did not reduce bicarbonate reabsorption corrected for filtered load.5. Inhibition of renal carbonic anhydrase by acetazolamide (50 mg/kg) resulted in an inhibition of bicarbonate reabsorption of only 4·5 μequiv/ml. g.f.r. (less than 20% of the total). Even with renal carbonic anhydrase inhibited, there was no bicarbonate Tm and bicarbonate reabsorption values as high as 40 μequiv/ml. g.f.r. could be attained.6. There was good correlation (r = 0·82) between inhibition of sodium and bicarbonate reabsorption during renal carbonic anhydrase inhibition. However, with carbonic anhydrase inhibited, there was no correlation between arterial PCO2 and bicarbonate reabsorption.7. These results demonstrate that tubular bicarbonate reabsorption mechanisms in the new‐born dog are as efficient as those reported for the adult as long as body fluid and plasma sodium and potassium levels are carefully maintained.8. The results are also consistent with a bicarbonate reabsorptive mechanism explained either by direct ionic bicarbonate reabsorption or by hydrogen ion secretion with diffusion of carbonic acid.
The force—velocity relation of isolated twitch and slow muscle fibres of Xenopus laevis
Authors: Lännergren J. 
Published: December 2014

1. A study has been made of the relation between force and speed of shortening, or lengthening, in isolated twitch and slow muscle fibres, dissected from the iliofibularis muscle of Xenopus laevis. Both after‐loaded and quick‐release contractions were studied. Twitch fibres were stimulated electrically to give tetanic contractions (5‐20 °C); slow fibres were activated by a rapid change to solutions with high K concentration (30‐75 m
M; experiments at 21‐24 °C).2. The velocity of slow fibres was constant during shortening over 10% length change in after‐loaded contractions, except at forces exceeding about 0·8 of isometric tension, P0. In quick‐release experiments, shortening velocity was found to depend not only on the relative load, P/P0, but also on the instant when the release was made. With increasing time after onset of contraction the initial rate of shortening decreased; also, a progressive fall in speed during shortening became more marked.3. The fall in initial shortening speed with time of release from the onset of a contracture was more pronounced at high [K]o than at low.4. The relation between the relative force, P/P0, and shortening velocity, V, in after‐loaded contractions (75 m
M‐K) and quick‐release contractions (45 m
M‐K, early releases) in slow fibres could be represented by a hyperbola with the constants a = 0·10P0, b = 0·11 lengths/sec; extrapolated Vmax. was 1·10 lengths/sec.5. Isometric tension and maximum shortening velocity in slow fibres were very nearly constant between 32 and 75 m
M‐K. a/P0, however, was clearly reduced at 32 m
M‐K, representing a more curved P-V relation.6. Force—velocity data for twitch fibres (quick‐release contractions, 20 °C) were reasonably well fitted by a hyperbola (a = 0·38P0, b = 1·97 lengths/sec, Vmax. = 5·20 lengths/sec), but a systematic deviation was observed for forces exceeding 0·6P0.7. a/P0 for twitch fibres was found to be independent of temperature in the range 5‐20 °C. Q10 for b was 2·24 (10‐20 °C), and 2·86 (5‐10 °C).8. Vmax. for twitch fibres was calculated to be 6·34 lengths/sec at 22·5 °C, the average temperature in the slow fibre experiments. The maximum shortening velocity in twitch fibres is thus 6 times higher than in slow fibres.9. When loads in the range 1·1‐1·4P0 were quickly applied to an actively contracting slow fibre, lengthening of the fibre occurred in two phases, an initial rapid phase, followed by a phase of extremely slow lengthening. In corresponding experiments on twitch fibres lengthening was rapid at first and then gradually became slower.10. Factors affecting the shape of the force—velocity curve are discussed. Calculations based on A. F. Huxley's (1957) model for muscle contraction indicated that cross‐bridge turnover rate is about 15 times lower in slow than in twitch fibres.
Identification of different sodium compartments from smooth muscle cells, fibroblasts and endothelial cells, in arteries and tissue culture
Authors: Garay R. P. , Moura Anne Marie , Osborne-Pellegrin Mary J. , Papadimitriou A. , Worcei M. 
Published: December 2014

1. The 22Na efflux curve from the rat tail artery, at 35 °C, can be analysed as the sum of three distinct components, from 0 to 90 min of washout. After an initial diffusional component the two late exponential components Be−kBt and Ce−kCt have the following values: B = 3·03 ± 0·15 m‐mole/kg wet wt. and C = 0·56 ± 0·04; kB = 0·145 ± 0·005 min−1 and kC = 0·015 ± 0·007.2. In order to identify the cellular origin of the different compartments we compared the 22Na efflux curve from the rat tail artery with the curves obtained from whole rabbit aortal strips, rabbit aortal medial or adventitial strips; and primary cultures from rabbit aorta medial smooth muscle cells, cultures of a non‐fusing muscle cell line (BC3H1), fibroblasts and endothelial cells.3. It is possible to identify under these experimental conditions the cellular compartments from which the different exponential components of the efflux from the whole arteries originate. Fibroblasts and endothelial cultures, as well as adventitial strips exchange 22Na slowly with exponential constants resembling kC. Their efflux rate constants are: fibroblast cultures 0·010 ± 0·002 min−1, endothelial cells 0·015 ± 0·003 min−1 and adventitia 0·019 ± 0·007 min−1. Smooth muscle cells are exclusively responsible for the intermediate component Be−kBt, but they present also a slow component, indistinguishible from the slow exponential component from the other types of cells in the artery. The rate constants for muscle cells are: rabbit aortic media kB 0·25 ± 0·09 min−1 and kC = 0·013 ± 0·004 min−1; medial cultures kB = 0·202 ± 0·005 min−1 and kC1 = 0·020 ± 0·003 min−1; and BC3H1 cell culture kB = 0·205 ± 0·083 min−1 and kC = 0·016 ± 0·003 min−1.4. The efflux from compartment B of smooth muscle cells is inhibited by ouabain and in the absence of extracellular K+. The efflux from compartment C is inhibited only by ouabain but not by the suppression of extracellular K+.5. We propose a distribution of Na+ in smooth muscle cells in two intracellular compartments: (1) Na+ freely dissolved in the sarcoplasm, exchanging with the kinetics of compartment B and (2) a second cellular compartment which could be contained in the sarcoplasmic reticulum exchanging with the kinetics of compartment C.6. On the basis of the previous model of Na+ distribution, considering our values, and without any correction, the estimated sarcoplasmic concentration of Na+ is 9·6 m
M, compatible with the direct measurements obtained in skeletal and heart muscle. The Na+ concentration in the sarcoplasmic reticulum would be 4‐10 times higher than in the cytoplasm. In order to increase the accuracy of our calculations it would be necessary to account for the interdiffusion and back diffusion of Na+ between compartments. It is not possible to attain this goal at the present time.
Pancreatic acinar cells: the effect of carbon dioxide, ammonium chloride and acetylcholine on intercellular communication
Authors: Iwatsuki N. , Petersen O. H. 
Published: December 2014

1. Segments of mouse pancreatic or exorbital lacrimal gland were superfused with saline solutions. Under visual control two micro‐electrodes were inserted into neighbouring cells within the same acinus or into neighbouring acini. Cell to cell electrical coupling was assessed by injecting rectangular current pulses through one electrode and measuring the electrotonic potential change in the same cell (V1) and in the neighbouring cell (V2). Acetylcholine (ACh) was added locally to impaled acini by micro‐ionophoresis from an extracellular micropipette.2. Exposure of the tissues to a Krebs solution equilibrated with 100% CO2 caused a rapid increase in the size of electrotonic potential changes in the current injection cell and disappearance of the electrotonic potential changes in a neighbouring acinus or cell. This electrical uncoupling of previously coupled cells was rapidly reversible upon return to a solution equilibrated with 95% O2 and 5% CO2.3. Reduction of electrical intercellular coupling was also obtained using smaller CO2 concentrations (50, 20 or 10%). In these cases the effects developed more slowly and were less dramatic. Reducing the extracellular HCO3 concentration enhanced the uncoupling effect of 10 or 20% CO2. However, weak uncoupling effects were still observed using 10 or 20% CO2 in combination with a high bicarbonate concentration maintaining a constant extracellular pH (7·4).4. Reductions in extracellular pH (down to 5·5) achieved by varying combinations of Tris base and Tris HCl had no effect on electrical coupling. Brief periods of anoxia (100% N2) also had no effect.5. Exposure to 20% CO2 markedly enhanced the uncoupling effect of a brief ionophoretic pulse of ACh.6. Exposure of the tissue to 10 m
M‐NH4Cl, a procedure expected to increase the intracellular pH, counteracted the uncoupling effect of ACh. During sustained uncoupling caused by a sustained ACh stimulation a brief period of exposure to NH4Cl caused an immediate and fully reversible recoupling.7. It is concluded that variations in intracellular pH have marked effects on the electrical coupling between neighbouring cells in the pancreatic and lacrimal acinar tissue.
Intracellular citrate or externally applied tetraethylammonium ions produce calcium‐dependent action potentials in an insect motoneurone cell body
Authors: Pitman Robert M. 
Published: December 2014

1. Electrophysiological observations have been made upon the cell body of an identified motoneurone of the cockroach, Periplaneta americana. Normal responses were compared with those observed after intracellular injection of citrate anions or when the preparation was bathed in solutions containing tetraethylammonium ions (TEA+).2. Normally when depolarized, the motoneurone soma gave a series of damped oscillations; the amplitude of these responses increased with increase in the applied current.3. After citrate ions had been injected into the neurone soma, all‐or‐none action potentials were evoked by depolarization; such responses appeared about 5‐10 min after the onset of citrate injection. Injection of EGTA produced similar effects. Citrate and EGTA probably produce their effect through a reduction in the intracellular free calcium concentration.4. When preparations were bathed in saline solution containing 50 m
M‐TEA+, soma depolarization produced prolonged all‐or‐none action potentials (up to approximately 100 msec duration).5. The action potentials produced by citrate injection or externally applied TEA+ appeared to have a similar ionic mechanism; they were not depressed by sodium‐free solutions or by tetrodotoxin (4 × 10−6
M) but were reversibly blocked in saline solution containing 40 m
M‐manganous chloride.6. The overshoot amplitude of action potentials recorded after injection of citrate anions or in solutions containing TEA+ showed a 22·5 mV change for a ten‐fold change in the external calcium concentration.7. Both intracellular citrate and external TEA+ caused a significant increase in the input resistance and membrane time constant of the motoneurone.8. It is concluded that action potentials generated under various experimental conditions in the soma of this insect motoneurone map have differing ionic mechanisms.
Synapse formation in intact innervated cutaneous‐pectoris muscles of the frog following denervation of the opposite muscle
Authors: Rotshenker Shlomo 
Published: December 2014

1. Denervation of one cutaneous‐pectoris muscle of the frog induces the formation of new synapses in the intact innervated muscle on the opposite side. After crushing the motor nerve to the left muscle the incidence of polyneuronal innervation in the right intact muscle increased from an average normal value of 16% to an average value of 27% (Rotshenker & McMahan, 1976).2. The formation of the new synapses in the intact muscle is independent of the presence of denervated muscle fibres or degenerating axons peripheral to the site of axotomy. After removing the left cutaneous‐pectoris muscle, the proportion of polyneuronally innervated muscle fibres in the right intact muscle increased to an average value of 34%.3. The number of new synapses formed in one muscle is dependent upon the type of the lesion to the motor nerve to the opposite muscle; 40% of the muscle fibres on the right side were found to be polyneuronally innervated after transecting the motor nerve on the opposite side, as compared to 27% after crushing it.4. The delay with which new synapses are formed on the unoperated side is dependent upon the distance from the spinal cord of the axotomy. New synapses were detected 4‐8 weeks after cutting the opposite nerve close to the muscle. Placing the site of axotomy close to the spinal cord shortened the delay and new synapses were detected as early as 9 days after the operation.5. The stimulus for the formation of new synapses by an intact nerve is ineffective if the injured nerve on the contralateral side originates from distant segments of the spinal cord. The pattern of innervation in cutaneous‐pectoris muscles was not altered following denervation of distant muscles in the hind limb.6. These results suggest that the signal for sprouting and synapse formation may arise in the damaged nerve cells, central to the site of axotomy, and then be communicated transneuronally within the spinal cord to the intact motoneurones on the opposite side.
Calcium carrying system in the giant muscle fibre of the barnacle species, Balanus nubilus
Authors: Beirao P. S. , Lakshminarayanaiah N. 
Published: December 2014

1. Single barnacle muscle fibres from Balanus nubilus were internally perfused with an isotonic solution containing 180 m
M‐tetraethylammonium acetate and the effects of Ca concentration in the external solution on the voltage‐clamp currents, especially the initial inward current, were examined.2. Muscle fibre in external solution containing no added Ca (concentration of Ca < 10−5
M) gave a current—voltage curve that showed a small inward current followed by a small outward current. An identical curve was obtained when the chloride in the external solution was replaced by acetate.3. The peak inward current increased with increase in Ca concentration in the external solution; but the increase in peak current for equal increments of Ca concentration was reduced and attained saturation conforming to an adsorption regime which can be described by the Langmuir equation.4. A double reciprocal plot of peak inward current due to Ca as a function of Ca concentration gave values of 20.7 m
M and 200% (the current due to 20 m
M‐Ca normalized to 100%) for the dissociation constant and the maximum current respectively. These values were found to depend on the concentration of Mg used in the external solutions.5. The peak inward Ca currents measured at two Ca concentrations as a function of pH were unaffected in the pH range 6.5‐8.8; however when the pH was reduced below 6.5, the currents were depressed.
Amylase secretion in the rabbit parotid gland when stimulating the sympathetic nerves during parasympathetic activity
Authors: Gjörstrup Per 
Published: December 2014

1. In anaesthetized rabbits amylase secretion from the parotid gland was investigated. Secretion was evoked by sympathetic nerve stimulation, either alone or superimposed on a parasympathetic background secretion, imitating the resting secretion present in the waking animal.2. Sympathetic nerve stimulation at frequencies below 1 Hz was alone subthreshold for fluid secretion, but could greatly increase the amounts of amylase present in fluid secretion produced by parasympathetic nerve stimulation. The amylase output due to sympathetic nerve stimulation alone at 10 Hz did not exceed that seen in response to a stimulation at 1 Hz superimposed on parasympathetic activity.3. The amylase output in response to superimposed sympathetic stimulation was not influenced by the rate of fluid secretion, which was altered by stimulating the parasympathetic nerves at different frequencies.4. Sympathetically‐evoked amylase secretion was abolished after β1‐block. The amylase secretion remaining on parasympathetic activation was sparse.5. It is concluded that secretion of amylase in response to sympathetic nerve stimulation requires the presence of a parasympathetic fluid secretion to be washed along the glandular ducts. Parasympathetic activity may also augment the sympathetic effect on amylase secretion.
Light responses of ganglion cells in the retina of the turtle
Authors: Bowling D. B. 
Published: December 2014

1. Recordings were made from single axons of 218 ganglion cells in the optic nerve of the turtle, Pseudemys scripta elegans. Responses to light stimuli were used to classify 182 of the cells into four functional groups.2. Movement‐sensitive cells (113 units) responded best to moving stimuli independent of the stimulus colour or direction of motion. Their receptive fields were organized into antagonistic centres and surrounds with the same spectral sensitivity. Based on their patterns of response they were of three types: ON‐centre, OFF‐centre, and ON—OFF.3. Directionally selective cells (sixty‐five units) responded best to stimuli that moved in one preferred direction and not to stimuli that moved in the opposite direction. Their receptive fields had antagonistic centres and surrounds with the same spectral sensitivity. An area of silent inhibition could be shown on one side of the receptive fields. The preferred directions appeared to fall into three groups separated by about 120 degrees. Response patterns were of two types; OFF‐centre and ON—OFF.4. Sensitizable colour cells (two units) had centre‐surround organization with red‐green opponent responses from both the centre and the surround (double opponent cells). In addition, the sensitivity to either of the opponent colours was effectively turned on or off by a steady background of the other opponent colour.5. Orientation cells (two units) responded best to moving bars of specific orientations in the visual field. Their receptive fields consisted of adjacent mutually antagonistic areas with linear boundaries.6. Under photopic conditions all of the ganglion cells were most sensitive to light near 630 nm wave‐length, the spectral maximum of the red‐sensitive single cones in the turtle retina. About 75% of the cells had a secondary spectral peak near 560 nm, the spectral maximum of the green‐sensitive single cones. Three cells had unusually broad sensitivity extending into the blue portion of the spectrum. Over half of the cells received additional input from rods as evidenced by a shift in spectral sensitivity and increases in latencies and receptive field sizes with dark‐adaptation.7. Measurements of the absolute sensitivity of the ganglion cells showed that a threshold response required absorption of several hundred photons in the red‐sensitive cones of the receptive field centre. After 10 min dark adaptation the rods required absorption of about 20 photons.