bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ELECTRICAL CONDUCTIVITY OF PURE PROTOPLASM
Authors: Brooks S. C.
Published: May 2004

The electrical conductivity of the plasmodium of the slime-mold Brefeldia maxima (Fr.) Rost., which constitutes practically pure protoplasm, was found to be approximately equivalent under normal conditions to that of a 0.00145 N NaCl solution, and about 2.8 times that of the liquid in contact with which it developed.

When bathed in 1 per cent sea water, the conductivity was much increased, becoming greater than that of the surrounding fluid.

These preliminary tests are in agreement with the supposition that the protoplasm is permeable to and in equilibrium with its environment in so far as electrolytes are concerned.
NOTE ON THE EXCITATION AND INHIBITION OF LUMINESCENCE IN BERŒ
Authors: Heymans C. , Moore A. R.
Published: May 2004

1. The ions of Ca and K condition general luminescence, and are therefore necessary to the conduction of the impulse.

2. In van't Hoff's solution from which Mg is omitted, Berœ shows hyperirritability with respect to luminescence. This is the result of the action of Ca and K ions unantagonized by Mg.

3. The luminescent material spread on filter paper does not show luminescence in sea water, NaCl, MgCl2, or saccharose solutions isotonic with sea water. In solutions of CaCl2, SrCl2, BaCl2, KCl, and K2SO4 the indicator paper glows with a bright luminescence.

4. In dark adapted Berœ, luminescence is inhibited by a certain quantity of light. This quantity has an average value of 57,285 meter-candle-minutes, which is twelve times the value given by Mnemiopsis.
THE EFFECT OF LIGHT ON THE PERMEABILITY OF PARAMECIUM
Authors: Packard Charles
Published: May 2004

1. The permeability of Paramecium to NH4OH is greater when the cells are exposed to light than it is when they are in darkness.

2. This change can be demonstrated in cells exposed to monochromatic red light, though it is small. It becomes greater as the wave lengths shorten, and is greatest in the near ultra-violet.

3. The permeability increases as the duration of exposure to light is prolonged.

4. These experiments demonstrate the necessity of controlling the illumination when using Paramecium in physiological tests.
THE KINETICS OF THE DECOMPOSITION OF PEROXIDE BY CATALASE
Authors: Northrop John H.
Published: May 2004

It has been shown that the experimental results obtained by Morgulis in a study of the decomposition of hydrogen peroxide by liver catalase at 20°C. and in the presence of an excess of a relatively high concentration of peroxide are quantitatively accounted for by the following mechanisms.

1. The rate of formation of oxygen is independent of the peroxide concentration provided this is greater than about 0.10 M.

2. The rate of decomposition of the peroxide is proportional at any time to the concentration of catalase present.

3. The catalase undergoes spontaneous monomolecular decomposition during the reaction. This inactivation is independent of the concentration of catalase and inversely proportional to the original concentration of peroxide up to 0.4 M. In very high concentrations of peroxide the inactivation rate increases.

4. The following equation can be derived from the above assumptions and has been found to fit the experiments accurately.

See PDF for Equation

in which x is the amount of oxygen liberated at the time t, A is the total amount of oxygen liberated (not the total amount available), and K is the inactivation constant of the enzyme.
THE LOCOMOTION OF LIMAX
Authors: Crozier W. J. , Federighi H.
Published: May 2004

In Limax the lifting of additional loads during vertical ascension does not alter the law of linear proportionality between speed and frequency of pedal waves, or that between speed and dimensions of the single waves; for equal velocities of progression these quantities are the same, regardless of the mass lifted. The pedal organ of the slug, although under the control of central impulses, is thus essentially an independent effector.
THE GROWTH OF DUCKWEEDS IN MINERAL NUTRIENT SOLUTIONS WITH AND WITHOUT ORGANIC EXTRACTS
Authors: Saeger Albert
Published: May 2004

1. Detmer's solution and a modified Knop's solution are unfavorable culture media for the growth of Spirodela polyrhiza.

2. When the modified Knop's solution was diluted to 10 times its volume, Spirodela polyrhiza and Lemna valdiviana grew and reproduced for periods of 26 months and 21 months, respectively.

3. Growth in the dilute Knop's solution, which alone can support the growth of Spirodela indefinitely, was considerably stimulated over a period of 23 days by adding to every liter the water-soluble material of 0.4 gm. autolyzed yeast, or the material of 2.5 gm. peat soluble in a 1 per cent solution of NaHCO3.

4. The nature of the stimulus or of the protection afforded by the organic material is as yet unknown.

5. The necessity of organic accessory foods (auximones) in the nutrition of green plants cannot be accepted as an established fact.
METABOLISM DURING EMBRYONIC AND METAMORPHIC DEVELOPMENT OF INSECTS
Authors: Fink David E.
Published: May 2004

1. For species of insects that deposit their eggs on foliage, as Leptinotarsa decemlineata, Crioceris asparagi, and Anasa tristis, the rates of metabolism as measured by the CO2 output or the oxygen intake indicate, during embryonic development, a short formative period, followed by a very active extended growth. Those species that deposit their eggs in the soil, as Cotinis nitida and Popillia japonica, show that the formative period is greatly extended and the growth period similarly lengthened.

2. It has been shown from metabolism experiments that intensive histolysis occurs during the prepupal period and becomes less intensive during pupal development.

3. Metabolism experiments show a greater amount of energy change during embryonic development as compared to the energy developed during metamorphosis. This is shown by the greater CO2 output and by the oxygen intake.

4. Low respiratory quotients, varying from 0.42 to 0.71, have been obtained during the embryonic and pupal development of insects, resembling similar low quotients obtained with hibernating forms.

5. Changes from a neutral to an acid reaction (pH 6.8 to 5.9) have been observed to take place in some species during prepupal and early pupal development. As metamorphosis is completed a converse change occurs (pH 5.9 to 6.8). Changes in pH from an acid to neutral reaction were also observed to take place in some species, as Cotinis nitida and Hylemyia cilicrura, during embryonic development.
TEMPERATURE CHARACTERISTIC FOR HEART RHYTHM OF THE SILKWORM
Authors: Crozier W. J. , Federighi H.
Published: May 2004

The critical thermal increment for the reaction controlling the frequency of the heart beat in mature silkworms is 12,200 calories. This determination agrees quantitatively with the increment deduced for other activities of arthropods in which the rate of central nervous discharge is believed to be the controlling element.
PULSATION OF THE CONTRACTILE VACUOLE OF PARAMECIUM AS AFFECTED BY TEMPERATURE
Authors: Cole William H.
Published: May 2004

1. The rate of pulsation of the anterior contractile vacuole of Paramecium caudatum under chloretone anesthesia has been determined over a range of temperatures from 9–31°C. It has been found that the rate is a logarithmic function of the temperature according to the Arrhenius equation. From 9–16° the temperature characteristic (µ) has the value 25,600; from 16–22° it is 18,900; and from 22–31° it becomes 8,600.

2. It is concluded that there are at least three underlying reactions responsible for pulsation, the rates of which vary. Which reaction becomes the limiting one depends upon the range of temperature considered.

3. It does not appear that oxidative processes alone determine the rate of pulsation, although they may be of fundamental importance.
A TEST FOR DIFFUSIBLE IONS
Authors: Northrop John H.
Published: May 2004

1. The distribution of pepsin between particles of gelatin or coagulated egg albumin and the outside solution has been found to be equal to the distribution of chloride or bromide ion under the same conditions. This is the case from pH 1 to 7, and in the presence of a variety of salts.

2. Pepsin is therefore probably a monovalent anion.

3. Under certain conditions the enzyme may be adsorbed on the surface of the protein particles. This reaction is irreversible and is markedly influenced by the presence of low concentrations of electrolytes.
THE PRODUCTION OF CARBON DIOXIDE BY NERVE
Authors: Parker G. H.
Published: May 2004

1. A modified Osterhout respiratory apparatus for the detection of CO2 from nerve is described.

2. The lateral-line nerve from the dogfish discharges CO2 at first with a gush for half an hour or so and then steadily at a lower rate for several hours.

3. Simple handling of the nerve does not increase the output of CO2; cutting it revives gush.

4. The CO2 produced by nerve is not escaping simply from a reservoir but is a true nervous metabolite.

5. The rate of discharge of CO2 from a quiescent nerve varied from 0.0071 to 0.0128 mg. per gram of nerve per minute and averaged 0.0095 mg.

6. Stimulated nerve showed an increased rate of CO2 production of 15.8 percent over that of quiescent nerve.

7. The results of these studies indicate that chemical change is a factor in nerve transmission.
THE EFFECTS OF LIGHT ON LUMINOUS BACTERIA
Authors: Harvey E. Newton
Published: May 2004

A conservative statement would therefore be that luminous bacteria show no changes in luminescence as a result of illumination by 625 foot candles for 1.5 minutes when examined 1/200 of a second after exposure, and none as the result of illumination by 15,000 foot candles for 6 minutes when examined ⅙ of a second after exposure.
THE RELATIVE IMPORTANCE OF pH AND CARBON DIOXIDE TENSION IN DETERMINING THE CESSATION OF CILIARY MOVEMENT IN ACIDIFIED SEA WATER
Authors: Haywood Charlotte
Published: May 2004

The length of time that cilia from the gills of Mylilus continue to beat in acidified sea water depends to some extent on the pH of the solution but to a greater extent on its carbon dioxide tension.
CRITICAL INCREMENT FOR OPERCULAR BREATHING RHYTHM OF THE GOLDFISH
Authors: Crozier W. J. , Stier T. B.
Published: May 2004

The temperature characteristic for opercular breathing rhythm in the quiescent goldfish is 16,500 calories. The reactions governing the frequency of breathing movements in vertebrates appear to be constituent links in the oxidative metabolism of the controlling cells.
THE KINETICS OF STARVATION
Authors: Wetzel Norman C.
Published: May 2004

1. The loss of weight in pigeons subjected to prolonged starvation on water alone may be accurately represented by an appropriate form of the law of autocatakinesis.

2. This function, within proper limitations, gives a definite indication as to the nature and character of the fundamental reactions involved. In addition, it provides quantitative measures of the relative progress and importance of these reactions.

3. Analytically, the process of starvation consists of two nearly symmetrical cycles, corresponding chemically to the destruction of the carbohydrate-fat reserves and to the decomposition of body protein.

4. A suitable transformation overcoming certain difficulties inherent in the general form of the law is discussed and applied to the data reported.
DIURNAL CHANGES IN THE ACIDITY OF BRYOPHYLLUM CALYCINUM
Authors: Gustafson Felix G.
Published: May 2004

1. It has been shown that there is a diurnal change in the H ion concentration in Bryophyllum calycinum corresponding approximately to the total acidity changes. The H ion concentration increases at night and decreases during the day.

2. Light is the main factor in causing the decrease in acidity, though it also occurs in the dark. but much more slowly.

3. External oxygen tension does not seem to influence the acidity of the plant, nor does it influence the decomposition of the extracted juice.
A SIMPLE MICRO VESSEL WITH ELECTRODE FOR DETERMINING THE HYDROGEN ION CONCENTRATION OF SMALL AMOUNTS OF FLUID
Authors: Bodine Joseph Hall , Fink David E.
Published: May 2004

A convenient and accurate method is described for the electrometric determination of the hydrogen ion concentration of small amounts of fluid (0.015 to 0.020 cc.). The suitability of such a method for work on insect blood and body fluids is particularly pointed out.
STUDIES ON LUMINOUS BACTERIA
Authors: Morrison Thomas F.
Published: May 2004

1. A method has been described whereby the intensity of the light of luminous bacteria may be measured in a quantitative manner.

2. It is pointed out that the temperature coefficients for light intensity do not follow the van't Hoff rule, but are higher and vary with each 10° temperature interval.

3. From a comparison with other data it is found that the process is not a simple one, but that the observed curve is the resultant of several reactions which proceed simultaneously.

4. The discrepancies in the temperature coefficients in the neighborhood of the "optimum temperature" may be due to a process of coagulation of the colloidal particles of the enzyme. This coagulation will tend to cause a deviation of the curve away from that normal for chemical reactions.
Delayed rectification in the transverse tubules: origin of the late after-potential in frog skeletal muscle.
Authors: Kirsch G E , Nichols R A , Nakajima S
Published: May 2004

Tetanic stimulation of skeletal muscle fibers elicits a train of spikes followed by a long-lasting depolarization called the late after-potential (LAP). We have conducted experiments to determine the origin of the LAP. Isolated single muscle fibers were treated with a high potassium solution (5 mM or 10 mM K) followed by a sudden reduction of potassium concentration to 2.5 mM. This procedure produced a slow repolarization (K repolarization), which reflects a diffusional outflow of potassium from inside the lumen of the transverse tubular system (T system). Tetanic stimulation was then applied to the same fiber and the LAP was recorded. The time courses of K repolarization and LAP decay were compared and found to be roughly the same. This approximate equality held under various conditions that changed the time courses of both events over a wide range. Both K repolarization and the LAP became slower as fiber radius increased. These results suggest that LAP decay and K repolarization represent the same process. Thus, we conclude that the LAP is caused by potassium accumulation in the T system. A consequence of this conclusion is that delayed rectification channels exist in the T system. A rough estimation suggests that the density of delayed rectification channels is less in the T system than in the surface membrane.
Lability of the prolonged depolarizing afterpotential in Balanus photoreceptors.
Authors: Lantz R C , Wong F , Mauro A
Published: May 2004

A large cell to cell variability of the prolonged depolarizing afterpotential (PDA) decay time constant (tau) has been measured in Balanus eberneus lateral ocelli. While 25% of the cells had PDA's of long duration, tau greater than 10 min. 45% of the cells tested showed either weak (tau less than 60 s) PDA or none at all. The variability was not reflected in the late receptor potential. All the cells showed normal light-coincident responses. The variability was not due to some alteration of the thermal stability of the pigment states, since after monochromatic adaptation the amplitude of the early receptor potential remained unchanged for at least 30 min. In addition, in some cells that initially showed PDAs of long duration, the decay time was either shortened or abolished after exposure to anoxia. Again, the late receptor potential and the stability of the pigments remained unaffected. These results indicate that the mechanisms which give rise to the PDA are not always tightly coupled to the direct chain of events that lead to the light-coincident response.
Inactivation of the sodium channel. II. Gating current experiments.
Authors: Armstrong C M , Bezanilla F
Published: May 2004

Gating current (Ig) has been studied in relation to inactivation of Na channels. No component of Ig has the time course of inactivation; apparently little or no charge movement is associated with this step. Inactivation nonetheless affects Ig by immobilizing about two-thirds of gating charge. Immobilization can be followed by measuring ON charge movement during a pulse and comparing it to OFF charge after the pulse. The OFF:ON ratio is near 1 for a pulse so short that no inactivation occurs, and the ratio drops to about one-third with a time course that parallels inactivation. Other correlations between inactivation and immobilization are that: (a) they have the same voltage dependence; (b) charge movement recovers with the time coures of recovery from inactivation. We interpret this to mean that the immobilized charge returns slowly to "off" position with the time course of recovery from inactivation, and that the small current generated is lost in base-line noise. At -150 mV recover is very rapid, and the immobilized charge forms a distinct slow component of current as it returns to off position. After destruction of inactivation by pronase, there is no immobilization of charge. A model is presented in which inactivation gains its voltage dependence by coupling to the activation gate.
A quantitative comparison of the effects of intracellular calcium injection and light adaptation on the photoresponse of Limulus ventral photoreceptors.
Authors: Fein A , Charlton J S
Published: May 2004

Calcium ions were iontophoretically injected into ventral photoreceptors of Limulus by passing current between two intracellular pipettes. Changes in sensitivity and photoresponse time course were measured for both light adaptation and Ca++ injection. We found for some photoreceptors that there was no significant difference in the photoresponse time course for desensitization produced by light adaptation or by Ca++ injection. In other photoreceptors, the time delay of photoresponse for Ca++ injection was slightly longer than for light adaptation. The variability of threshold response amplitude and time delay decreases when the photoreceptor is desensitized by either light adaptation or Ca++ injection. The peak amplitude versus log stimulus intensity relationships for controls, light adaptation, and Ca++ injection all could be described very closely by a single template curve shifted along the log intensity axis. A 40- to 50-fold change in sensitivity is associated with a 2-fold change in photoresponse time delay for both light adaptation and Ca++ injection.
Increased intracellular sodium mimics some but not all aspects of photoreceptor adaptation in the ventral eye of Limulus.
Authors: Fein A , Charlton J S
Published: May 2004

The effects of the intracellular iontophoretic injection of Na+ ions have been quantitatively compared with adaptation in ventral photoreceptors of Limulus. We find that: (a) both light adaptation and sodium injection are associated with a decrease in the variability of the threshold response amplitued; (b) both light adaptation and sodium injection are associated with a decrease in the absolute value of the temporal dispersion of the threshold response time delay; (c) the same template curve adequately fits the intensity response relationships measured under light adaptation and Na+ injection; (d) both light adaptation and Na+ injection produce a fourfold decrease in response time delay for a desensitization of 3 log units; (e) the time coures of light adaptation and dark adaptation is significantly faster than the onset of and recovery from desensitization produced by Na+ injection; (f) unlike local illumination, Na+ injection does not produce localized desensitization of the photoreceptor. These findings suggest that a rise in intracellular Na+ concentration makes at most only a minor contribution (probably less than 5%) to the total adaptation of these receptors in the intensity range we have examined (up to 3 log units above absolute threshold). However, changes in intracellular Na+ concentration may contribute to certain components of light and dark adaptation in these receptors.
Light-induced voltage noise in the photoreceptor of Drosophila melanogaster.
Authors: Wu C F , Pak W L
Published: May 2004

The Drosophila photoreceptor potential is thought to be composed of discrete unit potentials called bumps. The steady-state receptor potential and the accompanying voltage fluctuations were recorded intracellularly under steady illumination. The occurrence rate, effective amplitude, and duration of the bumps were deduced by assuming a shot noise model. Over a wide range of light intensity, the duration of bumps remained essentially constant (25-30 ms). Below the saturation intensity for the receptor potential, the bump rate was roughly proportional to the intensity, and the adjustment of bumps to smaller size at higher intensity was mainly responsible for the nonlinear behavior of the receptor potential. The reduction in size of bumps at increasing light intensity was found to be due mainly to the diminishing magnitude of the bump current, and not to some other secondary effects. The bump rate saturated at about 3 x 105-106 events/s.
Desensitization onset and recovery at the potassium-depolarized frog neuromuscular junction are voltage sensitive.
Authors: Scubon-Mulieri B , Parsons R L
Published: May 2004

The influence of voltage on the time-course of desensitization onset and recovery has been studied at the frog neuromuscular junction. The activation-desensitization sequence was determined from carbachol-induced end-plate currents in potassium-depolarized fibers voltage-clamped either to -40 mV or +40 mV. The time-course of both desensitization onset and recovery developed exponentially, with onset occurring more rapidly than recovery. Desensitization onset was voltage dependent, the onset time constant being 8.3 +/- 1.3 s (11 fibers) at -40 mV and 19.3 +/- 3.4 s (15 fibers) at +40 mV. Recovery from desensitization was also influenced by voltage. The extent of recovery after 2 min was 80.4 +/- 6.3% in those fibers voltage-clamped to -40 mV and 57.4 +/- 3.6% in those fibers voltage-clamped to +40 mV. The voltage dependence of desenistization onset and recovery did not result from a difference in ability to control voltage at these two levels of membrane potential. These results demonstrate that in the potassium-depolarized preparation the processes controlling both desensitization onset and recovery of sensitivity from the desensitivity from the desensitized state are influenced by membrane voltage.
Contractile activation phenomena in voltage-clamped barnacle muscle fiber.
Authors: Caputo C , Dipolo R
Published: May 2004

Tension development in voltage-clamped barnacle muscle fibers occurs with depolarizing pulses so small as not to activate the potassium and calcium conductance systems. Peak tension and the tension time integral appear to be graded by both amplitude and duration of the depolarizing pulses. Subthreshold depolarizing conditioning pulses shorter than 500 ms potentiate the response to a given test pulse. This effect diminishes and reverts when the duration of the conditioning pulse is increasingly prolonged. The relationship between fiber membrane potential and tension developed in response to depolarizing pulses is described by an S-shaped curve. The tension saturates at a membrane potential of about +10 mV (inside positive). For a given pulse duration the saturation value remains constant even when the fiber interior reaches a value of +230 mV, which is well above what may be estimated to be the equilibrium potential of calcium ions (Eca = +120). In the presence of 5 mM external procaine, the shape of the tension-potential curve changes; the maximum value tension besides being diminished is not sustained by falls when the potential approaches the estimated value for Eca. These results suggest that under physiological conditions the contractile activator is probably released from an internal store, and that the calcium entering the fiber as inward current does not play a direct major role in contractile activation.
Anion inhibitor-sensitive unidirectional sodium movements in the human erythrocyte.
Authors: Callahan T J , Goldstein D A
Published: May 2004

The increased unidirectional sodium influx found when human erythrocytes are suspended in isotonic salt solutions containing bicarbonate ions as a replacement for chloride ions was examined. The increased sodium movement appears to have the transport characteristics of anion movement. Inhibitors of anion transport such as furosemide, fluorodinitrobenzene (FDNB), and 4-acetamido-4'-isothiocyano-stilbene-2-2'-disulfonic acid (SITS) drastically inhibit these augmented sodium movements. An ion-pair mechanism appears to phenomenologically describe much of the data. A possible role for carbamino groups is considered. Such a model, however, required additional assumptions to explain the selectivity and the anion inhibitor effects.
Kinetics and stoichiometry of Na-dependent Li transport in human red blood cells.
Authors: Sarkadi B , Alifimoff J K , Gunn R B , Tosteson D C
Published: May 2004

This paper describes the kinetics and stoichiometry of a tightly coupled Na-Li exchange transport system in human red cells. The system is inhibited by phloretin and furosemide but not by ouabain. Li influx by this system increases and saturates with increasing concentrations of external Li and internal Na and is inhibited competitively by external Na. Comparable functions relate Li efflux and Na efflux to internal and external Li and Na concentrations. Analysis of these relations yields the following values for the ion concentrations required to half-maximally activate the transport system: internal Na and Li 9.0 and 0.5 mM, respectively, external Na and Li 25 and 1.5 mM, respectively. The system performs a 1:1 exchange of Na and Li moving in opposite directions across the red cell membrane. We found no evidence for a simultaneous transport of more than one Na and Li by the system. The maximum transport rate of Na-dependent Li transport varied between 0.1 and 0.37 mmol/(liter of cells X h) in the red cells of the five normal male subjects studied. No significant variations between individual subjects were observed for bicarbonate-stimulated Li transport and for the residual Li fluxes which occur in the absence of bicarbonate and in the presence of ouabain plus phloretin.
Intracellular characteristics and responses of taste bud and lingual cells of the mudpuppy.
Authors: West C H , Bernard R A
Published: May 2004

Intracellular recordings of membrane potentials of mudpuppy lingual cells were made with micropipette electrodes. Three types of cells were distinguished by their responses to chemical stimulation. Surface epithelial (SE) cells outside of taste buds responded with large membrane potential and resistance changes to a variety of stimuli representing the four taste qualities. Salts and acids evoked particularly large potential changes, and MgCl2, acids, and quinine greatly increased the membrane resistance. One type of taste bud cell (TB-1) was characterized by large depolarizations to K salts, and the other type of taste bud cell (TB-2) characteristically hyperpolarized to MgCl2, acid, and sugar solutions. Membrane resistance changes accompanying TB-1 and TB-2 cell responses were relatively small compared to those of SE cells. Electrotonic coupling was observed between pairs of SE and TB-2 cells but not for pairs of TB-1 cells nor cells of different types. After recording cell responses, dye-marking allowed verification of results in situ and histologically. From the identification of cells in section, it is hypothesized the TB-1 and TB-2 cells correspond to light and dark cells, respectively. Responses of TB-1 cells imply a taste receptive function; wheras TB 2-cell responses suggest secretory, supportive, and (or) receptive functions. Factors affecting cellular characteristics, non-taste bud cell responsiveness, response mechanisms, and function of electrotonic coupling are discussed in relation to taste reception.
Net charge and oxygen affinity of human hemoglobin are independent of hemoglobin concentration.
Authors: Gros G , Rollema H S , Jelkmann W , Gros H , Bauer C , Moll W
Published: May 2004

The dependence of net charge and oxygen affinity of human hemoglobin upon hemoglobin concentration was reinvestigated. In contrast to earlier reports from various laboratories, both functional properties of hemoglobin were found to be independent of hemoglobin concentration. Two findings indicate a concentration-independent net charge of carbonmonoxy hemoglobin at pH 6.6: (A) The pH value of a given carbonmonoty hemoglobin solution remains constant at 6.6 when the hemoglobin concentration is raised from 10 to 40 g/dl, indicating that there is no change in protonation of titratable groups of hemoglobin: (b) the net charge of carbonmonoxy hemoglobin as estimated from the Donnan distribution of 22Na+ shows no dependence on hemoglobin concentration in this concentration range. The oxygen affinity of human hemoglobin was determined from measurements of oxygen concentrations in equilibrated samples using a Lex-O2-Con apparatus (Lexington Instruments, Waltham, Mass.). P50 averaged 11.4 mm Hg at 37 degrees C, pH = 7.2, and ionic strength approximately 0.15. Neither P50 nor Hill's n showed any variation with hemoglobin concentrations increasing from 10 to 40 g/dl.
Analysis of sodium and potassium redistribution during sustained permeability increases at the innervated face of Electrophorus electroplaques.
Authors: Lester H A
Published: May 2004

Cholinergic agonists cause an increase in the membrane permeability of Na and K at the innervated face of Electrophorus electroplaques. Therefore, sustained exposure to agonist reduces Na and K concentration gradients. There gradients are monitored with voltage-clamp sequences and pharmacological treatments that selectively measure the Nernst potentials for individual ions. EK is normally near--90 mV but moves toward zero during bath application of agonist. Depolarizations by bath-applied agonist measure primarily this shift of EK, not short-circuiting of EK by the agonist-induced conductance. After a rapid jump of agonist concentration, there is a fast (millisecond) depolarization due to the conductance increase, followed by a much slower additional "creep" due to the shift in EK. Sodium replaces the lost intracellular potassium: ENa, normally very positive, also moves toward zero. The shifts in EK and ENa are normally reversible but become permanent after blockade of the Na-K pump. In the presence of agonist, the shifts can be driven further by passing current of the appropriate polarity. Similar ion redistribution occurs with other drugs, such as batrachotoxin and nystatin, which induce prolonged increases in Na permeability. The redistributions cause little net change in the reversal potential of the neurally evoked postsynaptic current.
Heterogeneity in dog red blood cells: sodium and potassium transport.
Authors: Castranova V , Hoffman J F
Published: May 2004

After incubation in isotonic KCl, dog red blood cells can be separated by centrifugation into subgroups which assume different cell volumes and possess different transport characteristics. Those red cells which swell in isotonic KCl exhibit a higher permeability to K and possess a greater volume dependence for transport of K than those red cells which shrink. A high Na permeability characterizes cells which shrink in isotonic KCl and these cells exhibit a larger volume-dependent Na flux than those red cells which swell. These two subgroups of red cells do not seem to represent two cell populations of different age. The results indicate that the population of normal cells is evidently heterogeneous in that the volume-dependent changes in Na and K permeability are distributed between differnt cell types rather than representing a single cell type which reciprocally changes its selectivity to Na and K.
The initiation of excitation and light adaptation in Limulus ventral photoreceptors.
Authors: Lisman J E , Strong J A
Published: May 2004

Two types of experiments indicate that light adaptation and excitation are initiated by the same, rather than different, populations of visual pigment. (a) The criterion action spectra of light adaptation and excitation are the same. (b) Increment-threshold curves were measured with a voltage-clamp technique under conditions of high and low concentration of plasma membrane rhodopsin (Rhpm). SD, the dark-adapted sensitivity, and 1/I2, the inverse of the background irradiance that desensitized by 0.3 log units, underwent the same fractional change when the rhodopsin concentration was changed. Both quantities appear to be linearly related to Rhpm. Reversible reductions in Rhpm were achieved by orange irradiation during a brief increase of extracellular pH from 7.8 to 10. This procedure would be unlikely to produce similar concentration changes in a hypothetical intracellular pigment because the concurrent change in intracellular pH, measured using the dye, phenol red, was only 0.45 pH units. It is thus unlikely that an intracellular pigment initiates light adaptation. On the assumption that light adaptation is mediated by a light-induced release of Ca++ from an intracellular store. the results reported here imply that an intracellular transmitter is needed to couple Rhpm to the intracellular store.
Synaptic inputs to the ganglion cells in the tiger salamander retina.
Authors: Wunk D F , Werblin F S
Published: May 2004

The postsynaptic potentials (PSPs) that form the ganglion cell light response were isolated by polarizing the cell membrane with extrinsic currents while stimulating at either the center or surround of the cell's receptive field. The time-course and receptive field properties of the PSPs were correlated with those of the bipolar and amacrine cells. The tiger salamander retina contains four main types of ganglion cell: "on" center, "off" center, "on-off", and a "hybrid" cell that responds transiently to center, but sustainedly, to surround illumination. The results lead to these inferences. The on-ganglion cell receives excitatory synpatic input from the on bipolars and that synapse is "silent" in the dark. The off-ganglion cell receives excitatory synaptic input from the off bipolars with this synapse tonically active in the dark. The on-off and hybrid ganglion cells receive a transient excitatory input with narrow receptive field, not simply correlated with the activity of any presynaptic cell. All cell types receive a broad field transient inhibitory input, which apparently originates in the transient amacrine cells. Thus, most, but not all, ganglion cell responses can be explained in terms of synaptic inputs from bipolar and amacrine cells, integrated at the ganglion cell membrane.
Calcium content and net fluxes in squid giant axons.
Authors: Requena J , Mullins L J , Brinley F J
Published: May 2004

Axons freshly dissected from living specimens of the tropical squid Dorytheutis plei have a calcium content of 68 mumol/kg of axoplasm. Fibers stimulated at 100 impulses/s in 100 mM Ca seawater increase their Ca content by 150 mumol/kg.min; axons placed in 3 Ca (choline) seawater increase their Ca content by 12 mumol/kg.min. Axons loaded with 0.2--1.5 mmol Ca/kg of axoplasm extruded Ca with a half time of 15--30 min when allowed to recover in 3 Ca (Na) seawater. The half time for recovery of loaded axons poisoned with carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and iodoacetic acid (IAA) is about the same as control axons. Axons placed in 40 mM Na choline seawater (to reduce chemical gradient for Na) or in 40 mM Na, 410 mM K seawater to reduce the electrochemical gradient for Na to near zero either fail to lose previously loaded Ca or gain further Ca.
Thyroid thermogenesis in adult rat hepatocytes in primary monolayer culture: direct action of thyroid hormone in vitro.
Authors: Ismail-Beigi F , Bissell D M , Edelman I S
Published: May 2004

We have studied the effect of 3,5,3'-triiodothyronine (T3) on the respiration of adult rat hepatocytes in primary monolayer culture prepared from hypothyroid rat liver. After addition of T3 to the culture medium at a concentration of 2 x 10(-7) M, oxygen consumption of the cultured cells increased detectably at 24 h and was maximal at 72--96 h, relative to control cultures (38.0 +/- 1.8 vs. 25.0 +/- 1.5 microliter/h.mg protein). The thyroid-responsive enzymes, Na+ + K+-activated adenosine triphosphatase (NaK-ATPase) and alpha-glycerophosphate dehydrogenase (GPD), each exhibited increased activity in response to T3, in parallel with the change in oxygen consumption, whereas the activity of Mg-dependent ATPase was unaffected. These responses to T3 were dose dependent over similar concentration ranges, the half-maximal response for each occurring at ca 8 x 10(-10) M. In thyroid-treated cells, the observed increase in respiration was almost completely (90%) inhibited after addition of ouabain (10(-3) M) to the culture medium. It was found also that a 4-h exposure of the cultured hepatocytes to T3 was sufficient to elicit a significant thermogenic response, measured at a time (48 h later) when T3 was no longer present in the medium. The response to T3 occurred in fully defined culture medium and was independent of the presence or absence of hypothyroid rat serum, corticosterone, or insulin, and cellular ATP was unaffected by T3 in concentrations up to 2 x 10(-7) M. The findings document that adult rat hepatocytes in primary monolayer culture respond directly to thyroid hormone; the increases in respiration and NaK-ATPase activity elicited by T3 were cotemporal and apparently coordinate.
Potassium modulation of taurine transport across the frog retinal pigment epithelium.
Authors: Miller S S , Steinberg R H
Published: May 2004

Net taurine transport across the frog retinal pigment epithelium-choroid was measured as a function of extracellular potassium concentration, [K+]o. The net rate of retina-to-choroid transport increased monotonically as [K+]o increased from 0.2 mM to 2 mM on the apical (neural retinal) side of the tissue. No further increase was observed when [k+]o was elevated to 5 mM. The [K+]o changes that modulate taurine transport approximate the light-induced [K+]o changes that occur in the extracellular space separating the photoreceptors and the apical membrane of the pigment epithelium. The taurine-potassium interaction was studied by using rubidium as a substitute for potassium and measuring active rubidium transport as a function of extracellular taurine concentration. An increase in apical taurine concentration, from 0.2 mM to 2 mM, produced a threefold increase in active rubidium transport, retina to choroid. Net taurine transport can also be altered by relatively large, 55 mM, changes in [Na+]o. Apical ouabain, 10(-4) M, inhibited active taurine, rubidium, and potassium transport; in the case of taurine, this inhibition is most likely due to a decrease in the sodium electrochemical gradient. In sum, these results suggest that the apical membrane contains a taurine, sodium co-transport mechanism whose rate is modulated, indirectly, through the sodium pump. This pump has previously been shown to be electrogenic and located on the apical membrane, and its rate is modulated, indirectly, by the taurine co-transport mechanism.
Ouabain binding and coupled sodium, potassium, and chloride transport in isolated transverse tubules of skeletal muscle.
Authors: Lau Y H , Caswell A H , Garcia M , Letellier L
Published: May 2004

The affinity and number of binding sites of [3H]ouabain to isolated transverse (T) tubules were determined in the absence and presence of deoxycholate. In both conditions the KD was approximately 53 nM while deoxycholate increased the number of binding sites from 3.5 to 37 pmol/mg protein. We concluded that the ouabain binding sites were located primarily on the inside of the isolated vesicle and that the vesicles were impermeable to ouabain. ATP induced a highly active Na+ accumulation by the T tubules which increased Na+ in the T tubular lumen by almost 200 nmol/mg protein. The accumulation had an initial fast phase lasting 2-3 min and a subsequent slow phase which continued for at least 40 min. The rate of the initial fast phase indicated a turnover number of 20 Na+/s. The Na+ accumulation was prevented by monensin but was unaffected by valinomycin. Ouabain did not influence Na+ uptake, but digitoxin inhibited it. At low K+ the accumulation of Na+ was reduced 3.7-fold below the value at 50 mM K+. 86Rb, employed as a tracer to detect K+, showed a first phase of K+ release while Na+ was accumulated. After 2-3 min, K+ was reaccumulated while Na+ continued to increase in the lumen. T tubules accumulated Cl- on addition of ATP. This suggested that ATP initiated an exchange of Na+ for K+ followed by uptake of Na+ and K+ accompanied by Cl-.
Calcium measurement in the periphery of an axon.
Authors: Mullins L J , Requena J
Published: May 2004

Aequorin was microinjected into squid giant axons, the axons were stimulated, and the change in light emission was followed. This response was compared with that found when the axon, in addition to being microinjected with aequorin, is also injected with the dye phenol red. Large concentrations of phenol red injected into axons result in a high probability that photons emitted by aequorin, when it reacts with Ca in the core of the axoplasm, will be absorbed before they escape from the axon; photons produced by the aequorin reaction at the periphery of the axoplasm are much less likely to be absorbed. This technique thus favors observing changes in Cai taking place in the periphery of the axon. Stimulation in 50 mM Ca seawater of an aequorin-phenol red-injected axon at 180 s-1 for 1 min produces a scarcely detectable change in Cai; the addition of 2 mM cyanide (CN) to the seawater produces an easily measureable increase in Cai, suggesting that mitochondrial buffering in the periphery is substantial. Making the pH of the axoplasm of a normal axon alkaline with 30 mM NH4+ -50 mM Ca seawater, reduces the resting glow of the axon but results in an even more rapid increase in Cai with stimulation. In a phenol red-injected axon, this treatment results in a measureable response to stimulation in the absence of CN.
Calcium distribution in Amoeba proteus.
Authors: Prusch R D , Hannafin J A
Published: May 2004

A preliminary investigation of the distribution of cellular calcium in Amoeba proteus was undertaken. Total cellular calcium under control conditions was found to be 4.59 mmol/kg of cells. When the external Ca++ concentration is increased from the control level of 0.03 to 20 mM, a net Ca++ influx results with a new steady-state cellular calcium level being achieved in integral of 3 h. At steady state the amount of calcium per unit weight of cells is higher than the amount of calcium per unit weight of external solution when the external concentration of Ca++ is below 10 mM. At external Ca++ concentrations above this level, total cellular calcium approaches the medium level of Ca++. Steady-state calcium exchange in Amoeba proteus was determined with 45Ca. There is an immediate and rapid exchange of integral of 0.84 mmol/kg of cells or 18% of the total cellular calcium with the labelled Ca++. Following this initial exchange, there was very little if any further exchange observed. Most of this exchanged calcium could be eliminated from the cell with 1 mM La+++, suggesting that the exchanged calcium is associated with the surface of the cell. Increase in either the external Ca++ concentration of pH raise the amount of exchangeable calcium associated with the cell. Calcium may be associated with the cell surface as a co-ion in the diffuse double layer or bound to fixed negative sites on the surface of the cell. If Ca++-binding sites do exist on the cell surface, there may be more than one type and they may have different dissociation constants. The cytoplasmic Ca++ ion activity is probably maintained at very low levels.
Cation selectivity of acetylcholine-activated ionic channel of frog endplate.
Authors: Watanabe S , Narahashi T
Published: May 2004

Ionic selectivity of the acetylcholine-activated ionic channel of frog endplate membranes to various organic cations has been studied. The ratio of test cation permeability (PX) to sodium permeability (PNa) was estimated by two methods, one based on the measurements in test cation solutions of the amplitude of transient depolarization induced by iontophoretic application of acetylcholine, and the other on the measurements of the reversal potential for the membrane current induced by iontophoretic application of acetylcholine under voltage-clamp conditions. The endplate channel is relatively nonselective to various test cations. The permeabilities relative to Na are ammonium (1.71), formamidine (1.49), methylamine (1.39), hydrazine (1.35), and Li (0.76), as measured from the reversal potential for acetylcholine currents, and guanidine (0.74), aminoguanidine (0.20), methylguanidine (0), and choline (0) as measured from the amplitude of acetylcholine potential. Methylguanidine and aminoguanidine block the endplate channel with the apparent dissociation constants of 0.5 and 15 mM, respectively. Based on these data, the dimensions of selectivity filter of acetylcholine-activated channel appear to be slightly larger than those of the sodium channel of frog nodes and smaller than those of the epithelial membrane of gallbladder of frogs and rabbits.
Influence of light and calcium on guanosine 5'-triphosphate in isolated frog rod outer segments.
Authors: Biernbaum M S , Bownds M D
Published: May 2004

Frog rod outer segments contain approximately 0.25 mol of GTP and 0.25 mol of ATP per mol of rhodopsin 3 min after their isolation from the retina. UTP and CTP are present at 10-fold and 100-fold lower levels, respectively. Concentrations of GTP and ATP decline in parallel over the next 4 min to reach relatively stable levels of 0.1 mol per mol of rhodopsin. Illumination reduces the concentration of endogenous GTP but not ATP. This light-induced decrease in GTP can be as large as 70% and has a half-time of 7 s. GTP is reduced to steady intermediate levels during extended illumination of intermediate intensity, but partially returns to its dark-adapted level after brief illumination. The magnitude of the decrease increases as a linear function of the logarithm of continuous light intensity at levels which bleach between 5 X 10(2) and 5 X 10(6) rhodopsin molecules/outer segment per second. This exceeds the range of intensities over which illumination causes decreases in the cyclic GMP content and permeability of isolated outer segments (Woodruff and Bownds. 1979. J. Gen. Physiol. 73:629-653). Thus, over 4 log units of light intensity, a sensitivity control mechanism functions to make extended illumination less effective in stimulating a GTP decrease. GTP levels in dark-adapted outer segments are sensitive to changes in calcium concentration in the suspending medium. If the external calcium concentration is reduced to 10(-8) M, GTP concentration is lowered to the same level caused by saturating illumination, and the GTP remaining is no longer light-sensitive. Lowering calcium concentration to intermediate levels between 10(-6) and 10(-8) M reduces GTP to stable intermediate levels, and the GTP remaining can be reduced by light. Restoration of millimolar calcium drives synthesis of GTP, but not of ATP, and GTP lability towards illumination is again observed. These calcium-induced changes in GTP are diminished by the addition of the divalent cation ionophore A23187. Lowering or raising magnesium levels does not influence the GTP concentration. These data raise the possibility that light activates either a calcium transport mechanism driven by the hydrolysis of GTP, or some other calcium-sensitive GTPase activity of unknown function. Known light-dependent reactions involving cyclic nucleotide transformations and rhodopsin phosphorylation appear to account for only a small fraction of the light-induced GTP decrease.