bluuebunny/crossref_metadata_2025_split huggingface dataset:
MAINTAINED ACTIVITY IN THE CAT'S RETINA IN LIGHT AND DARKNESS
Authors: Kuffler S. W. , Fitzhugh R. , Barlow H. B. 
Published: May 2004

Nervous activity has been recorded from the unopened eye of decerebrate cats. Recordings were made with metal electrodes or with small micropipettes from ganglion cells or nerve fibers.
Continuous maintained discharges were seen in all ganglion cells during steady illumination of their receptive fields, as well as in complete darkness. Possible artefacts, such as electrode pressure, abnormal circulation, anesthetic, and several other factors have been excluded as the source of the maintained discharge. Visual stimuli are therefore transmitted by modulating the ever present background activity.
Discharge frequencies were measured following changes of retinal illumination. No consistent patterns of frequency change were found. The maintained discharge frequency may be permanently increased or decreased, or may remain practically unchanged by altering the steady level of illumination. In addition, there were often transient frequency changes during the first 5 to 10 minutes after changing illumination, before a final steady rate was established.
A statistical analysis of the impulse intervals of the maintained discharge showed: (a) the intervals were distributed according to the gamma distribution (Pearson's type III), (b) the first serial correlation coefficient of the intervals was between –0.10 and –0.24, with a mean value of –0.17, which is significantly different from zero, (c) the higher order serial correlation coefficients were not significantly different from zero. Thus the firing probability at any time depends on the times of occurrence of the two preceding impulses only, and in such a way as to indicate that each impulse is followed by a transient depression of excitability that outlasts the following impulse.
The possible sites at which spontaneous or maintained activity may originate in the retina are discussed.
STEPS IN THE PRODUCTION OF MOTONEURON SPIKES
Authors: Fuortes M. G. F. , Frank K. , Becker Mary C. 
Published: May 2004

1. Spikes evoked in spinal motoneurons by antidromic stimulation normally present an inflection in their rising phase. A similar inflection is present in spikes evoked by direct stimulation with short pulses.
2. In either case the inflection becomes less prominent if the motoneuron membrane is depolarized and more prominent when it is hyperpolarized. Both antidromic and direct spikes may fall from the level of the inflection thus evoking a "small spike" only if sufficient hyperpolarization is applied. Similar events occur when antidromic or direct spikes are evoked in the aftermath of a preceding spike.
3. Spikes evoked by direct stimuli applied shortly after firing of a "small spike" may also become partially blocked at a critical stimulus interval. At shorter intervals, however, spike size again increases and no inflection can be detected in the rising phase.
4. When a weak direct stimulus evokes a small spike only, a stronger stimulus may evoke a full spike. Curves of the strength of the stimuli required for eliciting small or full spikes have been constructed in a number of conditions.
5. To explain the results it is assumed that threshold of the major portions of the soma membrane is higher than the threshold of the axon, the transition occurring over a finite area near the axon hillock. Following antidromic or direct stimulation, soma excitation is then initiated in the region of the axon hillock. Spread of activity towards the soma occurs at first slowly and with low safety factor. At this stage block may be easily evoked. Safety factor for propagation increases rapidly as the growing impulse involves larger and larger areas of the soma membrane so that, once the critical areas are excited, activation of the remaining portions of the soma membrane will suddenly occur.
STAPHYLOCOCCAL VIROLYSIN, A PHAGE-INDUCED LYSIN
Authors: Ralston D. J. , Lieberman Miriam , Baer B. , Krueger A. P. 
Published: May 2004

Virolysin is a lysin which appears in Staphylococcus aureus K1 cells infected with phage P14; together with phage, virolysin is released from phage-infected cells at the time of lysis. Autolysin is a lysin formed by uninfected cells of the K1 strain; autolysin is released from uninfected cells by autolysis.
They show the following similarities: Both agents act within the genus Micrococcus. They lyse cells only after the cell has been subjected to a damaging or "sensitizing" treatment, such as heat, bacteriophage, acetone, or ultraviolet irradiation. The course of lysis of heated cells by both lysins has been found to proceed in a similar manner. A constant percentage of cells is lysed, independent of the concentration of lysin; the residual cells remain resistant to either lysin. Lysis proceeds logarithmically with time, and the velocity constants K are proportional to the lysin concentration. K increases with increasing temperature.
Both lysins are unaffected by antiserum to the phage. They are inhibited alike by a number of chemicals, including known enzyme inhibitors. Both agents are destroyed by proteolytic enzymes and are precipitated by 40 per cent saturation with (NH4)2SO4. Both lysins are very thermolabile.
The two lysins differ with respect to their pH optimum, antigenic relationship and specificity for Micrococcus lysodeikticus.
These results suggest that (1) both lysins have many properties associated with enzymes, (2) the lysis of heated cells, which they produce, has some of the characteristics of a chemical reaction, (3) the lysin from the phage-infected cell is clearly different from the lysin of the uninfected cell.
THE PROPORTION OF MUTANTS IN BACTERIAL CULTURES
Authors: Northrop John H. , Kunitz M. 
Published: May 2004

The proportion of mutants in a growing culture of organisms will depend upon (a) the rate at which the wild cells produce them (with or without growth), (b) the back mutation rate, and (c) the growth rates of the wild and mutant cells. If the mutation rate without growth and the back mutation rate are neglected, the growth of a mutant is expressed by
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and the ratio of the mutant to wild by
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in which λ = mutation frequency rate constant, "mutation rate," A = growth rate constant of wild cells W, B = growth rate constant of mutant cells M. If the term [B – (1 – 2λ)A] is positive, the proportion of mutants increases continuously. If it is negative, the proportion of mutants reaches a constant value
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If mutation is assumed to occur without growth at the rate C, then the corresponding equations are (11), (12), and (14).
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If (B + C – A) is negative and t = ∞,
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If C &lt;&lt; A,
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ION AND WATER FLUXES IN THE ILEUM OF RATS
Authors: Curran Peter F. , Solomon A. K. 
Published: May 2004

Studies have been carried out on the movement of salt and water across the small intestine of the rat. Segments of the ileum of anesthetized rats have been perfused in vivo with unbuffered NaCl solutions or isotonic solutions of NaCl and mannitol. Kinetic analysis of movements of Na24 and Cl36 has permitted determination of the efflux and influx of Na and Cl. Net water absorption has been measured using hemoglobin as a reference substance.
Water was found to move freely in response to gradients of osmotic pressure. Net water flux from isotonic solutions with varying NaCl concentration was directly dependent on net solute flux. The amount of water absorbed was equivalent to the amount required to maintain the absorbed solute at isotonic concentration. These results have been interpreted as indicating that water movement is a passive process depending on gradients of water activity and on the rate of absorption of solute.
The effluxes of Na and Cl are linear functions of concentration in the lumen, but both ions are actively transported by the ileum according to the criterion of Ussing (Acta Physiol. Scand., 1949, 19, 43). The electrical potential difference between the lumen and plasma has been interpreted as a diffusion potential slightly modified by the excess of active Cl flux over active Na flux.
The physical properties of the epithelial membrane indicate that it is equivalent to a membrane having negatively charged uniform right circular pores of 36 Å radius occupying 0.001 per cent of the surface area.
The action of air ions on bacteria
Authors: Krueger A. P. , Smith R. F. , Go Ing Gan 
Published: May 2004

Techniques have been devised for studying quantitatively the effects of air ions on microorganisms suspended in small drops. In smog-contaminated atmospheres moderate concentrations of positive and negative air ions exerted a protective effect on staphylococci by delaying the drop in pH customarily observed and by diminishing the rate of evaporation. In clean air higher concentrations of positive and negative air ions accelerated the rate of death of staphylococci apparently by direct action on the cells and by increasing the rate of evaporation.
Air ion action in these experiments did not involve cell agglutination or direct radiation from the radioactive isotopes employed.
SIMULTANEOUS HYDROLYSES OF ESTERS AND PROTEINS AT SATURATION LEVELS
Authors: Castañeda-Agulló M. , Del Castillo Luz M. 
Published: May 2004

A direct titration method for the determination of proteolytic activity is discussed. This involves the potentiometric measurement of the volume of 0.08 N NaOH required to maintain a constant pH (8.0) during the time of the hydrolysis. It is a sensitive method which presents several advantages; viz., it measures simultaneously protease and esterase activity, it follows the hydrolysis very closely and from the first stages; the titration is continuous and on the same sample. This method determines a constant fraction of the groups titratable by formol titration. The ratio formol: direct titration is represented by a factor "f" which is presumed to be distinct for each protein-enzyme system.
Kinetic studies, using this method, revealed that the rates of hydrolysis of mixtures casein-gelatin on one hand, casein-BAEE or gelatin-BAEE on the other, are always larger than those of the corresponding isolated substrates. In many cases the resulting rates are equal or nearly equal to the sum of the individual rates, even though the mentioned rates have been determined within the saturation zones for every substrate.
The former observations are inconsistent with the theory of the formation of an intermediary enzyme-substrate compound, unless it is assumed that the enzyme has a specific active group for each substrate.
THE DISTRIBUTION OF INORGANIC PHOSPHATE IN AMPHIBIAN MUSCLE
Authors: Briner G. P. , Simon Shirley E. , Shaw F. H. 
Published: May 2004

The Na+, K+, and inorganic phosphate levels of the plasma and sartorius muscle of the toad Bufo marinus were determined.
Soaking in normal Ringer brought about the usual cation shifts, but did not alter the level of inorganic phosphate in the cell.
Increases in the external phosphate level brought about an increase in the internal phosphate, but the apparent phosphate space of muscle is somewhat smaller than the apparent Cl- space.
Phosphate spaces were compared with inulin spaces and were found to be significantly greater.
Alteration of the H+ concentration of the high phosphate Ringer did not alter the partition of phosphate across the cell membrane.
These results have been found to be consistent with the theory of a three compartment system for muscle, wherein the tissue is assumed to consist of an extracellular phase, and two intracellular phases. The inorganic phosphate of the cell is assumed to be adsorbed onto the "ordered phase," and increments in organic phosphate found on raising the external level are assumed to take place in the "free intracellular phase."
THE PROTEIN COATS OR "GHOSTS" OF COLIPHAGE T2
Authors: Lehman I. R. , Herriott Roger M. 
Published: May 2004

Assimilation of oxygen, inorganic phosphate, and ammonia nitrogen by normal T2 phage and T2 ghost-infected E. coli B was studied. The rate of oxygen and phosphorus uptake by ghost-infected bacteria is similar to that of normal and phage-infected cells. The R.Q. in glucose-salts medium remains approximately 1. Assimilation of ammonia nitrogen by ghost-infected bacteria is maintained at a rate approximately 80 per cent of normal.
The inorganic phosphate which is assimilated was found to be incorporated into TCA-soluble compounds which were rapidly released into the medium. Within 5 minutes after absorption of the ghosts there was a loss from the cell of TCA-soluble constituents including organic phosphorus and compounds which absorb at 260 mµ. No corresponding breakdown of nucleic acid present in the cell prior to infection could be detected. The incorporation of inorganic phosphate into organic linkages in the ghost-infected cell and its release into the medium were found to proceed at a rate approaching that of the incorporation of inorganic phosphorus into the nucleic acid of normal cells. The net increase in 260 mµ absorbing compounds appeared to be inhibited.
THE ACTION OF ALPHA CHYMOTRYPSIN UPON MIXTURES OF ESTERS AND PROTEINS AT ENZYME-SATURATING CONCENTRATIONS
Authors: Castañeda-Agulló M. , del Castillo Luz M. 
Published: May 2004

The behavior of α-chymotrypsin has been studied in the simultaneous presence of two different substrates, each present in the reaction mixture at its saturation level. Mixtures of two esters were hydrolyzed at rates intermediate between the rates of hydrolysis of each ester when present alone, suggesting, in this case, competitive hydrolysis. In contrast, the rates of hydrolysis in mixtures of casein with gelatin or of either protein with an ester were equal to the sum of the rates of hydrolysis of the separate substrates, indicating in these cases independent hydrolysis. The activity of the α-chymotrypsin preparation used could not be attributed to contamination with other enzymes. Studies of the effect of soy bean inhibitor on chymotrypsin indicate that the mechanism of inhibition with protein substrates differs from that when esters are used, providing further evidence that α-chymotrypsin reacts differently with esters and proteins.
These results indicate that if chymotrypsin forms specific complexes with its substrates, it must possess at least three distinct active sites. However there is independent chemical evidence that the proteolytic and esterolytic activities of this enzyme reside in the same active center. If this is true, the experimental observations reported here cannot be explained unless it is supposed that this enzyme does not form specific Michaelis complexes with its substrates.
THE THERMAL STABILITY OF RHODOPSIN AND OPSIN
Authors: Hubbard Ruth 
Published: May 2004

Rhodopsin, the red photosensitive pigment of rod vision, is composed of a specific cis isomer of retinene, neo-b (11-cis), joined as chromophore to a colorless protein, opsin. We have investigated the thermal denaturation of cattle rhodopsin and opsin in aqueous digitonin solution, and in isolated rod outer limbs. Both rhodopsin and opsin are more stable in rods than in solution. In solution as well as in rods, moreover, rhodopsin is considerably more stable than opsin. The chromophore therefore protects opsin against denaturation. This is true whether rhodopsin is extracted from dark-adapted retinas, or synthesized in vitro from neo-b retinene and opsin. Excess neo-b retinene does not protect rhodopsin against denaturation. The protection involves the specific relationship between the chromophore and opsin. Similar, though somewhat less, protection is afforded opsin by the stereoisomeric iso-a (9-cis) chromophore in isorhodopsin.
The Arrhenius activation energies (Ea) and entropies of activation (ΔS‡) are much greater for thermal denaturation of rhodopsin and isorhodopsin than of opsin. Furthermore, these values differ considerably for rhodopsins from different species —frog, squid, cattle—presumably due to species differences in the opsins.
Heat or light bleaches rhodopsin by different mechanisms, yielding different products. Light stereoisomerizes the retinene chromophore; heat denatures the opsin. Photochemical bleaching therefore yields all-trans retinene and native opsin; thermal bleaching, neo-b retinene and denatured opsin.
TUBULAR SECRETION OF CREATINE, TRIMETHYLAMINE OXIDE, AND OTHER ORGANIC BASES BY THE AGLOMERULAR KIDNEY OF LOPHIUS AMERICANUS
Authors: Forster Roy P. , Berglund Fredrik , Rennick Barbara R. 
Published: May 2004

Creatine and trimethylamine oxide (TMAO) are the chief nitrogenous constituents of normal Lophius urine, and both of these organic bases characteristically have high urine/plasma concentration ratios.
Competition studies involving various organic bases indicate that creatine and TMAO are excreted independently by separate transport mechanisms.
TMAO excretion is inhibited competitively by tetraethylammonium ion (TEA) and by cyanine dye No. 863—compounds previously shown to be transferred actively by an organic base-secreting mechanism of general occurrence among vertebrates.
TEA does not inhibit competitively the active tubular reabsorption of TMAO in Squalus with doses which markedly depress its tubular excretion in Lophius. Glycine, which inhibits creatine reabsorption in the dog, does not interfere competitively with its secretion in Lophius.
ION TRANSPORT IN NITELLOPSIS OBTUSA
Authors: MacRobbie Enid A. C. , Dainty J. 
Published: May 2004

The distribution and rates of exchange of the ions sodium, potassium, and chloride in single internodal cells of the ecorticate characean, Nitellopsis obtusa, have been studied.
In tracer experiments three kinetic compartments were found, the outermost "free space" of the cell, a compartment we have called "protoplasmic non-free space", and the cell sap.
The concentrations in the vacuole were 54 mM Na+, 113 mM K+, and 206 mM Cl-. The steady state fluxes across the vacuolar membrane were 0.4 pmole Na+/cm.2 sec., 0.25 pmole K+/cm.2 sec., and 0.5 pmole Cl-/cm.2 sec.
The protoplasmic Na/K ratio is equal to that in the vacuole but protoplasmic chloride is relatively much lower. Osmotic considerations suggest a layer 4 to 6 µ thick with sodium and potassium concentrations close to those in the vacuole. The fluxes between protoplasm and external solution were of the order of 8 pmoles Na+/cm.2 sec. and 4 pmoles K+/cm.2 sec.
We suggest that the protoplasm is separated from the cell wall by an outer protoplasmic membrane at which an outward sodium transport maintains the high K/Na ratio of the cell interior, and from the vacuole by the tonoplast at which an inward chloride transport maintains the high vacuolar chloride. The tonoplast appears to be the site of the principal diffusion resistance of the cell, but the outer protoplasmic membrane probably of the main part of the potential.
THE ENTRANCE OF WATER INTO BEEF AND DOG RED CELLS
Authors: Villegas Raimundo , Barton T. C. , Solomon A. K. 
Published: May 2004

The rate constants for diffusion of THO across the red cell membrane of beef and dog, and the rate of entrance of water into the erythrocytes of these species under an osmotic pressure gradient have been measured. For water entrance into the erythrocyte by diffusion the rate constants are 0.10 ± 0.02 msec.-1 (beef) and 0.14 ± 0.03 msec.-1 (dog); the permeability coefficients for water entrance under a pressure gradient of 1 osmol./cm3 are 0.28
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These values permit the calculation of an equivalent pore radius for the erythrocyte membrane of 4.1 A for beef and 7.4 A for dog. In the beef red cell the change in THO diffusion due to osmotically produced cell volume shifts has been studied. The resistance to THO diffusion increases as the cell volume increases. At the maximum volume, (1.06 times normal), THO diffusion is decreased to 0.84 times the normal rate. This change in diffusion is attributed to swelling of the cellular membrane.
THE ACTION OF ENZYMES ON RHODOPSIN
Authors: Radding Charles M. , Wald George 
Published: May 2004

The effects have been examined of chymotrypsin, pepsin, trypsin, and pancreatic lipase on cattle rhodopsin in digitonin solution.
The digestion of rhodopsin by chymotrypsin was measured by the hydrolysis of peptide bonds (formol titration), changes in pH, and bleaching. The digestion proceeds in two stages: an initial rapid hydrolysis which exposes about 30 amino groups per molecule, without bleaching; superimposed on a slower hydrolysis which exposes about 50 additional amino groups, with proportionate bleaching. The chymotryptic action begins at pH about 6.0 and increases logarithmically in rate to pH 9.2.
Trypsin and pepsin also bleach rhodopsin in solution. A preparation of pancreatic lipase bleached it slightly, but no more than could be explained by contamination with proteases.
In digitonin solution each rhodopsin molecule is associated in a micelle with about 200 molecules of digitonin; yet the latter do not appear to hinder enzyme action. It is suggested that the digitonin sheath is sufficiently fluid to be penetrated on collision with an enzyme molecule; and that once together the enzyme and substrate are held together by intermolecular attractive forces, and by the "cage effect" of bombardment by surrounding solvent molecules.
The two stages of chymotryptic digestion of rhodopsin may correspond to an initial rapid fragmentation, such as has been observed with many proteinases and substrates; superimposed upon a slower digestion of the fragments. Since the first phase involves no bleaching, this may mean that rhodopsin can be broken into considerably smaller fragments without loss of optical properties.
THE PHOTOSENSITIVE RETINAL PIGMENTS OF FISHES FROM RELATIVELY TURBID COASTAL WATERS
Authors: Munz Frederick W. 
Published: May 2004

Digitonin extracts have been prepared from the retinae of a dozen species of marine and euryhaline teleost fishes from turbid water habitats. Spectrophotometric analysis of the extracts shows that the photosensitive retinal pigments of these species have maximum absorption above 500 mµ. In nine species there are retinene1 pigments with λmax between 504 and 512 mµ. In the marine but euryhaline mullet, Mugil cephalus, there is a porphyropsin with λmax 520 mµ. A mixture of rhodopsin and porphyropsin in an extract of a marine puffer, Sphoeroides annulatus, was disclosed by partial bleaching with colored light. In addition, one other species has a 508 mµ pigment, of which the nature of the chromophore was not determined.
The habitats in which these fishes live are relatively turbid, with the water greenish or yellowish in color. The spectral transmission of such waters is probably maximal between 520 and 570 mµ. It is suggested that the fishes have become adapted to these conditions by small but significant shifts in spectral absorption of their retinal pigments. These pigments are decidedly more effective than rhodopsin in absorption of wavelengths above 500 mµ. This offers a possible interpretation of the confusing array of retinal pigments described from marine and euryhaline fishes.
A STUDY OF INOTROPIC MECHANISMS IN THE PAPILLARY MUSCLE PREPARATION
Authors: Abbott B. C. , Mommaerts W. F. H. M. 
Published: May 2004

The length-tension diagram, the force-velocity relation, the characteristics of the series elasticity, and the duration of the active state have been studied on the papillary muscle preparation of the cat heart, and on other examples of cardiac muscle.
Positive inotropic changes such as the staircase phenomenon and post-extrasystolic potentiation occur without lengthening, but frequently with shortening, of the duration of the active state. They are accompanied by an increased velocity of contraction, and may be caused either by an intensification of the active state or by an alteration of the force-velocity characteristics of the contractile component.
The changes in the force-velocity relation point to an adaptation of the velocity-efficiency relation in dependence on the frequency of contraction.