bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterogenic components of a fast electrical potential in Drosophila compound eye and their relation to visual pigment photoconversion.
Authors: Stephenson R S , Pak W L
Published: May 2004

The electroretinogram of the dipteran compound eye in response to an intense flash contains an early, diphasic potential that has been termed the M potential. Both phases of the M potential arise from the photostimulation of metarhodopsin. The early, corneal-negative component, the M1, can be recorded intracellularly in the photoreceptors and has properties similar to the classical early receptor potential (ERP). The M1 is resistant to cold, anaesthesia, and anoxia and has no detectable latency. It depends on flash intensity and metarhodopsin fraction in the manner predicted for a closed, two-state pigment system, and its saturation is shown to correspond to the establishment of a photoequilibrium in the visual pigment. On the other hand, the dominant, corneal-positive component, the M2, does not behave like an ERP. It arises, not in the photoreceptors, but deeper in the retina at the level of the lamina, and resembles the on-transient of the electroretinogram in its reversal depth and sensitivity to cooling or CO2. The on-transient, which is present over a much wider range of stimulus intensity than the M potential, has been shown to arise from neurons in the lamina ganglionaris. Visual mutants in which the on-transient is absent or late are also defective in the M2. It is proposed that the M2 and the on-transient arise from the same or similar groups of second-order neurons, and that the M2 is a fast laminar response to the depolarizing M1 in the photoreceptors, just as the on-transient is a fast laminar response to the depolarizing late receptor potential. Unlike the M1, the M2 is not generally proportional to the amount of metarhodopsin photoconverted, and the M2 amplitude is influenced by factors, such as a steady depolarization of the photoreceptor, which do not affect the M1.
Intracellular pH changes induced by calcium influx during electrical activity in molluscan neurons.
Authors: Ahmed Z , Connor J A
Published: May 2004

Simultaneous measurements of electrical activity and light absorbance have been made on nerve cell bodies from Archidoris monteryensis injected with indicator dyes. pH indicators, phenol red and bromocresol purple, and arsenazo III, which under normal conditions is primarily a calcium indicator have been employed. Voltage clamp pulses which induced calcium influx caused an absorbance decrease of the pH dyes indicating an internal acidification. The onset of the pH drop lagged the onset of Ca2+ influx by 200-400 ms, and pH continued to decrease for several seconds after pulse termination which shut off Ca2+ influx. Trains of action potentials also produced an internal pH decrease. Recovery of the pH change required periods greater than 10 min. The magnitude of the pH change was largely unaffected by external pH in the range 6.8-8.4. The voltage dependence of the internal p/ change was similar to the voltage dependence of calcium influx determined by arsenazo III, and removal of calcium from the bathing saline eliminated the pH signal. In neurons injected with EGTA (1-5 mM), the activity-induced internal Ca2+ changes were reduced or eliminated, but the internal pH drop was increased severalfold in magnitude. After the injection of EGTA, voltage clamp pulses produced a decrease in arsenazo III absorbance instead of the normal increase. Under these conditions the dye was responding primarily to changes in internal pH. Injection of H+ caused a rise in internal free calcium. The pH buffering capacity of the neurons was measured using three different techniques: H+ injection, depressing intrinsic pH changes with a pH buffer, and a method employing the EGTA-calcium reaction. The first two methods gave similar measurements: 4-9 meq/unit pH per liter for pleural ganglion cells and 13-26 meq/unit pH per liter for pedal ganglion cells. The EGTA method gave significantly higher values (20-60 meq/unit pH per liter) and showed no difference between pleural and pedal neurons.
Sodium channels in presynaptic nerve terminals. Regulation by neurotoxins.
Authors: Krueger B K , Blaustein M P , Ratzlaff R W
Published: May 2004

Regulation of Na+ channels by neurotoxins has been studied in pinched-off nerve endings (synaptosomes) from rat brain. Activation of Na+ channels by the steroid batrachotoxin and by the alkaloid veratridine resulted in an increase in the rate of influx of 22Na into the synaptosomes. In the presence of 145 mM Na+, these agents also depolarized the synaptosomes, as indicated by increased fluorescence in the presence of a voltage-sensitive oxacarbocyanine dye [diO-C5(3)]. Polypeptide neurotoxins from the scorpion Leiurus quinquestriatus and from the sea anemone Anthopleura xanthogrammica potentiated the stimulatory effects of batrachotoxin and veratridine on the influx of 22Na into synaptosomes. Saxitoxin and tetrodotoxin blocked the stimulatory effects of batrachotoxin and veratridine, both in the presence and absence of the polypeptide toxins, but did not affect control 22Na influx or resting membrane potential. A three-state model for Na+ channel operation can account for the effects of these neurotoxins on Na+ channels as determined both by Na+ flux measurements in vitro and by electrophysiological experiments in intact nerve and muscle.
Volume regulation by Amphiuma red blood cells. The membrane potential and its implications regarding the nature of the ion-flux pathways.
Authors: Cala P M
Published: May 2004

After osmotic perturbation, the red blood cells of Amphiuma exhibited a volume-regulatory response that returned cell volume back to or toward control values. After osmotic swelling, cell-volume regulation (regulatory volume decrease; RVD) resulted from net cellular loss of K, Cl, and osmotically obliged H2O. In contrast, the volume-regulatory response to osmotic shrinkage (regulatory volume increase; RVI) was characterized by net cellular uptake of Na, Cl, and H2O. The net K and Na fluxes characteristic of RVD and RVI are increased by 1-2 orders of magnitude above those observed in studies of volume-static control cells. The cell membrane potential of volume-regulating and volume-static cells was measured by impalement with glass microelectrodes. The information gained from the electrical and ion-flux studies led to the conclusion that the ion fluxes responsible for cell-volume regulation proceed via electrically silent pathways. Furthermore, it was observed that Na fluxes during RVI were profoundly sensitive to medium [HCO3] and that during RVI the medium becomes more acid, whereas alkaline shifts in the suspension medium accompany RVD. The experimental observations are explained by a model featuring obligatorily coupled alkali metal-H and Cl-HCO3 exchangers. The anion- and cation-exchange pathways are separate and distinct yet functionally coupled via the net flux of H. As a result of the operation of such pathways, net alkali metal, Cl, and H2O fluxes proceed in the same direction, whereas H and HCO3 fluxes are cyclic. Data also are presented that suggest that the ion-flux pathways responsible for cell-volume regulation are not activated by changes in cell volume per se but by some event associated with osmotic perturbation, such as changes in intracellular pH.
Light-induced pigment granule migration in the retinular cells of Drosophila melanogaster. Comparison of wild type with ERG-defective mutants.
Authors: Lo M V , Pak W L
Published: May 2004

The dependence of pigment granule migration (PGM) upon the receptor potential was examined using several strains of electroretinogram (ERG)-defective mutants of Drosophila melanogaster. The mutants that have a defective lamina component but a normal receptor component of the ERG (no on-transient A [nonA] and tan) exhibited normal pigment granule migration. The mutants that have very small or no receptor potentials (certain no receptor potential A [norpA] alleles), on the other hand, exhibited no PGM. In the case of the temperature-sensitive norpA mutant, norpAH52, normal PGM was present at 17 degrees but not at 32 degrees C or above, corresponding to its electrophysiological phenotype. In the transient receptor potential (trp) mutant, whose receptor potential decays to the baseline within a few seconds during a sustained light stimulus, the pigment granules initially moved close to the rhabdomere when light was turned on but moved away after about 5 s during a sustained light stimulus. All these results lend strong support to the notion that PGM is initiated by a light-evoked depolarization of the receptor membrane, i.e., the receptor potential. However, under certain experimental conditions, the receptor potentials failed to induce PGM in the trp mutant. The depolarization of the receptor, thus, appears to be closely associated with PGM but is not a sufficient condition for PGM.
Modification of sodium and potassium channel gating kinetics by ether and halothane.
Authors: Bean B P , Shrager P , Goldstein D A
Published: May 2004

The effect of ether and halothane on the kinetics of sodium and potassium currents were investigated in the crayfish giant axon. Both general anesthetics produced a reversible, dose-dependent speeding up of sodium current inactivation at all membrane potentials, with no change in the phase of the currents. Double-pulse inactivation experiments with ether also showed faster inactivation, but the rate of recovery from inactivation at negative potentials was not affected. Ether shifted the midpoint of the steady-state fast inactivation curve in the hyperpolarizing direction and made the curve steeper. The activation of potassium currents was faster with ether present, with no change in the voltage dependence of steady-state potassium currents. Ether and halothane are known to perturb the structure of lipid bilayer membranes; the alterations in sodium and potassium channel gating kinetics are consistent with the hypothesis that the rates of the gating processes of the channels can be affected by the state of the lipids surrounding the channels, but a direct effect of ether and halothane on the protein part of the channels cannot be ruled out. Ether did not affect the capacitance of the axon membrane.
Ion transport mediated by the valinomycin analogue cyclo(L-Lac-L-Val-D-Pro-D-Val)3 in lipid bilayer membranes.
Authors: Latorre R , Donovan J J , Koroshetz W , Tosteson D C , Gisin B F
Published: May 2004

Cyclo(L-Lac-L-Val-D-Pro-D-Val)3 (PV-Lac) a structural analogue of the ion-carrier valinomycin, increases the cation permeability of lipid bilayer membranes by forming a 1:1 ion-carrier complex. The selectively sequence for PV-Lac is identical to that of valinomycin; i.e., Rb+ greater than K+ greater than Cs+ greater than or equal to NH+4 greater than Na+ greater than Li+. The steady-state zero-voltage conductance, G(0), is a saturating function of KCl concentration. A similar behavior was found for Rb+, Cs+, and NH+4. However, the ion concentration at which G(0) reaches a plateau strongly depends on membrane composition. The current-voltage curves present saturating characteristics, except at low ion concentrations of Rb+, K+, or Cs+. The ion concentration at which the saturating characteristics appear depends on membrane composition. These and other results presented in this paper agree with a model that assumes complexation between carrier and ion at the membrane-water interface. Current relaxation after voltage-jump studies were also performed for PV-Lac. Both the time constant and the amplitude of the current after a voltage jump strongly depend on ion concentration and membrane composition. These results, together with the stationary conductance data, were used to evaluate the rate constants of the PV-Lac-mediated K+ transport. In glycerolmonooleate they are: association rate constant, 2 x 10(6) M-1 s-1; dissociation rate constant, 4 x 10(5) s-1; translocation rate constant for complex, 5 x 10(4) s-1; and the rate of translocation of the free carrier (ks), 55 s-1. ks is much smaller for PV-Lac than for valinomycin and thus limits the efficiency with which the carrier is able to translocate cations across the membrane.
Regulation of the sodium permeability of the luminal border of toad bladder by intracellular sodium and calcium: role of sodium-calcium exchange in the basolateral membrane.
Authors: Chase H S , Al-Awqati Q
Published: May 2004

Sodium movement across the luminal membrane of the toad bladder is the rate-limiting step for active transepithelial transport. Recent studies suggest that changes in intracellular sodium regulate the Na permeability of the luminal border, either directly or indirectly via increases in cell calcium induced by the high intracellular sodium. To test these proposals, we measured Na movement across the luminal membrane (th Na influx) and found that it is reduced when intracellular Na is increased by ouabain or by removal of external potassium. Removal of serosal sodium also reduced the influx, suggesting that the Na gradient across the serosal border rather than the cell Na concentration is the critical factor. Because in tissues such as muscle and nerve a steep transmembrane sodium gradient is necessary to maintain low cytosolic calcium, it is possible that a reduction in the sodium gradient in the toad bladder reduces luminal permeability by increasing the cell calcium activity. We found that the inhibition of the influx by ouabain or low serosal Na was prevented, in part, by removal of serosal calcium. To test for the existence of a sodium-calcium exchanger, we studied calcium transport in isolated basolateral membrane vesicles and found that calcium uptake was proportional to the outward directed sodium gradient. Uptake was not the result of a sodium diffusion potential. Calcium efflux from preloaded vesicles was accelerated by an inward directed sodium gradient. Preliminary kinetic analysis showed that the sodium gradient changes the Vmax but not the Km of calcium transport. These results suggest that the effect of intracellular sodium on the luminal sodium permeability is due to changes in intracellular calcium.
Taste transduction mechanism: similar effects of various modifications of gustatory receptors on neural responses to chemical and electrical stimulation in the frog.
Authors: Kashiwayanagi M , Yoshii K , Kobatake Y , Kurihara K
Published: May 2004

Responses in the frog glossopharyngeal nerve induced by electrical stimulation of the tongue were compared with those induced by chemical stimuli under various conditions. (a) Anodal stimulation induced much larger responses than cathodal stimulation, and anodal stimulation of the tongue adapted to 5 mM MgCl2 produced much larger responses than stimulation with the tongue adapted to 10 mM NaCl at equal current intensities, as chemical stimulation with MgCl2 produced much larger responses than stimulation with NaCl at equal concentration. (b) The enhansive and suppressive effects of 8-anilino-1-naphthalenesulfonate, NiCl2, and uranyl acetate on the responses to anodal current were similar to those on the responses to chemical stimulation. (c) Anodal stimulation of the tongue adapted to 50 mM CaCl2 resulted in a large response, whereas application of 1 M CaCl2 to the tongue adapted to 50 mM CaCl2 produced only a small response. This, together with theoretical considerations, suggested that the accumulation of salts on the tongue surface is not the cause of the generation of the response to anodal current. (d) Cathodal current suppressed the responses induced by 1 mM CaCl2, 0.3 M ethanol, and distilled water. (e) The addition of EGTA or Ca-channel blockers (CdCl2 and verapamil) to the perfusing solution of the lingual artery reversibly suppressed both the responses to chemical stimulus (NaCl) and to anodal current with 10 mM NaCl. (f) We assume from the results obtained that electrical current from the microvillus membrane of a taste cell to the synaptic area supplied by anodal stimulation or induced by chemical stimulation activates the voltage-dependent Ca channel at the synaptic area.
Nonlinear summation of contractions in cat muscles. II. Later facilitation and stiffness changes.
Authors: Parmiggiani F , Stein R B
Published: May 2004

The force produced by cat muscles over time with two stimuli separated by a short interval is approximately three times that produced by a twitch of cat muscles. This facilitation of force production by a second stimulus involves both increases in magnitude and duration of the contraction. Increased magnitude is relatively more important in the fast-twitch plantaris muscle, whereas increased duration is more important in the slow-twitch soleus muscle. The facilitation decays in an approximately exponential manner with the interval between stimuli, having a time constant between one and two times the twitch contraction time in different muscles. If a third stimulus is added, the greatest facilitation is seen at intervals longer than the twitch contraction time. The drug Dantrolene, which specifically reduces Ca++ release from the sarcoplasmic reticulum, eliminates the delayed peak in facilitation with three stimuli. Associated with the increases in force with one or more stimuli are increases in muscle stiffness, which can be measured with small, brief stretches and releases that do not alter the time-course of contraction. The stiffness of soleus muscle reaches a peak after the peak in force. The increasing stiffness of the muscle can considerably facilitate transmission of force generated internally, in addition to any facilitation arising from Ca++-release mechanisms.
Block of endplate channels by permeant cations in frog skeletal muscle.
Authors: Adams D J , Nonner W , Dwyer T M , Hille B
Published: May 2004

Motor endplates of frog semitendinosus muscles were studied under voltage clamp. Current fluctuations induced by iontophoretic application of acetylcholine were analyzed to give the elementary conductance, gamma , and mean open time, tau , of endplate channels. Total replacement of the external Na+ ion by several other metal ions and by many permeant organic cations changed both gamma and tau . Except with NH4+ ions, the gamma values with foreign test ions were all smaller than expected from the independence relation and their previously measured permeability ratios. The more hydrophobic ions gave the smallest gamma values. Foreign permeant cations also depress gamma when mixed with Na+ ions. These effects could be interpreted in terms of binding of ions to a saturable site within the endplate channel as they pass through. The site for organic ions would have a hydrophobic component. Similar evidence is given for a metal ion binding site on the cytoplasmic end of the channel accessible to internal ions. Most foreign cations also shortened tau when applied externally. The changes of gating did not seem to be correlated with changes in gamma . Thus there is no evidence for control of tau by ions bound within the pore.
Calcium-dependent potassium current in barnacle photoreceptor.
Authors: Bolsover S R
Published: May 2004

When barnacle lateral eye photoreceptors are depolarized to membrane potentials of 0 to +50 mV in the dark, the plot of outward current through the cell membrane against time has two distinct maxima. The first maximum occurs 5-10 ms after the depolarization began. The current then decays to a minimum at approximately 500 ms after the onset of depolarization, and then increases to a second maximum 4-6 s after the depolarization began. If depolarization is maintained, the current again decays to reach a steady value approximately 1 min after depolarization began. The increase in current to the maximum at 4-6s from the minimum at approximately 500 ms is termed the "late current." It is maximum for depolarizations to around +25 mV and is reduced in amplitude at more positive potentials. It is not observed when the membrane is depolarized to potentials more positive than +60 mV. The late current is inhibited by external cobaltous ion and external tetraethylammonium ion, and shows a requirement for external calcium ion. When the calcium-sequestering agent EGTA is injected, the late current is abolished. Illumination of a cell under voltage clamp reduces the amplitude of the late current recorded subsequently in the dark. On the basis of the voltage dependence and pharmacology of the late current, it is proposed that the current is a calcium-dependent potassium current.
A three-barrier model for the hemocyanin channel.
Authors: Cecchi X , Alvarez O , Latorre R
Published: May 2004

Keyhole limpet hemocyanin forms ion-conducting channels in planar lipid bilayer membranes. Ionic current through the open hemocyanin channel presents the following characteristics: (a) it is carried mainly by cations; (b) it is a nonlinear function of membrane potential; (c) channel conductance is a saturating function of ion activity; (d) it shows ionic competition. A model for the open hemocyanin channel is developed from absolute reaction rate theory. The model calls for three energy barriers in the channel. Two energy barriers represent the entrance and exit of the ion into and out of the channel. The third barrier separates two energy minima that represent two binding sites. Furthermore, only one ion is allowed inside the channel at a given time. This model is able to recreate all the hemocyanin characteristics found experimentally in negatively charged and neutral membranes.
Chemical energetics of slow- and fast-twitch muscles of the mouse.
Authors: Crow M T , Kushmerick M J
Published: May 2004

The energy utilization associated with contraction was measured in isolated slow- and fast-twitch muscles of the mouse at 20 degrees C. The extent of this utilization was estimated from either the extent of high-energy phosphate splitting occurring during contraction (the initial chemical change, delta approximately P init) or from the extent of recovery resynthesis calculated from the observed oxygen consumption and lactate production occurring during the recovery period (recovery chemical resynthesis, delta approximately P rec). For short tetani, the cost to maintain isometric tension in the fast-twitch extensor digitorum longus (EDL) was approximately threefold greater than that in the slow-twitch soleus. With prolonged stimulation, however, the energy cost in the EDL diminished so that after 12 s of stimulation, the energy cost in the EDL was only 50% greater than that of the soleus. For both the slow-twitch soleus and the fast-twitch EDL and for all tetanus durations (up to 15 s), the extent of the initial chemical change was identical with the amount of recovery chemical resynthesis, showing that a biochemical energy balance existed in these muscles.
Titration of transport and modifier sites in the red cell anion transport system.
Authors: Wieth J O , Bjerrum P J
Published: May 2004

This work demonstrates the existence of titratable transport and modifier sites in the anion transport system of human red cells. Effects of alkaline extracellular pH on chloride exchange were studied up to pH 13 at 0 degrees C. The studies revealed two sets of reversible titratable groups. One set, having a pK of or approximately 11, appeared to be identical with the inhibitory halide-binding modifier site. Deprotonation of this site stimulated anion transport. The apparent dissociation constants of chloride and iodide at this modifier site were 0.3 and 0.06 M, respectively, and it was confirmed that the organic sulfonate NAP-taurine inhibits anion transport reversibly by a high-affinity interaction with halide-binding modifier sites at the extracellular side of the membrane. Other groups, with apparent pK of or approximately 12 at chloride concentrations above 0.1 M, were named as "transport sites" because transport function depended totally on their protonation. The apparent pK decreased when extracellular halide concentrations was lowered below 0.1 M. It was dependent of the intracellular chloride concentration, and was equally sensitive to extracellular pH of 13, was fully reversible. Hydroxyl ions were not transported to an appreciable extent by the anion exchange system. The pK values of both sets of groups make it likely that they are both arginyl residues, functioning as anion recognition sites similar to the role of functionally essential arginyl residues observed with numerous enzymes.
Effects of solvent and solute drag on transmembrane diffusion.
Authors: Van Bruggen J T , Chalmers B , Muller M
Published: May 2004

The present study compares and quantitates both solvent drag and solute drag forces in a system with both heteropore and homopore membranes. It is shown that tracer solute permeability can be increased if solution flow or driver solute flux is in the direction of tracer diffusion. Either force can decrease tracer permeability if the force can decrease tracer permeability if the force is opposite to the direction of tracer diffusion. The two forces can be additive or one force may reduce the effect of the other force. In the particular system quantitated, solute drag is shown to be some 300 times more effective than solvent drag on a mole-to-mole basis. The use of a number of solute pairs on other homopore and heteropore membranes confirms the finding that the two drag forces can be analyzed or manipulated in a variety of systems.
Candidate codes in the gustatory system of caterpillars.
Authors: Dethier V G , Crnjar R M
Published: May 2004

Larvae of tobacco hornworms offer unique opportunities to relate the electrophysiological output of identified chemosensory neurons to specific behavioral responses. Larvae can discriminate among three preferred plants with only eight functioning gustatory receptors. They can be induced to prefer any one of the plants, and these preferences can be reversed. All eight neurons respond to each plant sap. Two fire too infrequently to permit detailed analysis. Analyses of the remaining six show that all electrophysiological responses consist of phasic and tonic components. Only the "salt best" cell fires during the phasic period. Temporal analysis of the spike train during this period shows that tomato and tobacco could be distinguished from Jerusalem cherry but not from each other by a rate code. Measurements of behavioral response times together with the nonspecificity of this with respect of food plants, unacceptable plants, and sodium chloride eliminate a phasic period rate code as a probable mechanism for complex discrimination. Events occurring in the tonic period, when all cells are firing, suggest a major role for this period. Analyses of variance in the interval frequencies of the large and medium spikes suggest that a variance code could allow discrimination among the three plants as long as both cells were firing at the same time. Evidence has been found for temporal patterning in the tonic response of the "salt best" cell to Jerusalem cherry but is absent elsewhere. The most likely basis for coding the difference between each of the three plants is across-fiber patterning in which the relative rates of firing and the variances of all the sensory neurons in the tonic phase are critical.
Calcium accumulation by the sarcoplasmic reticulum in two populations of chemically skinned human muscle fibers. Effects of calcium and cyclic AMP.
Authors: Salviati G , Sorenson M M , Eastwood A B
Published: May 2004

In previous efforts to characterize sarcoplasmic reticulum function in human muscles, it has not been possible to distinguish the relative contributions of fast-twitch and slow-twitch fibers. In this study, we have used light scattering and 45Ca to monitor Ca accumulation by the sarcoplasmic reticulum of isolated, chemically skinned human muscle fibers in the presence and absence of oxalate. Oxalate (5 mM) increased the capacity for Ca accumulation by a factor of 35 and made it possible to assess both rate of Ca uptake and relative sarcoplasmic reticulum volume in individual fibers. At a fixed ionized Ca concentration, the rate and maximal capacity (an index of sarcoplasmic reticulum volume) both varied over a wide range, but fibers fell into two distinct groups (fast and slow). Between the two groups, there was a 2- to 2.5-fold difference in oxalate-supported Ca uptake rates, but no difference in average sarcoplasmic reticulum volumes. Intrinsic differences in sarcoplasmic reticulum function (Vmax, K0.5, and n) were sought to account for the distinction between fast and slow groups. In both groups, rate of Ca accumulation increased sigmoidally as [Ca++] was increased from 0.1 to 1 microM. Apparent affinities for Ca++ (K0.5) were similar in the two groups, but slow fibers had a lower Vmax and larger n values. Slow fibers also differed from fast fibers in responding with enhanced Ca uptake upon addition of cyclic AMP (10(-6) M, alone or with protein kinase). Acceleration by cyclic AMP was adequate to account for adrenaline-induced increases in relaxation rates previously observed in human muscles containing mixtures in fast-twitch and slow-twitch fibers.
Influx of calcium, strontium, and barium in presynaptic nerve endings.
Authors: Nachshen D A , Blaustein M P
Published: May 2004

Depolarization-induced (potassium-stimulated) influx of 45Ca, 85Sr, and 133Ba was measured in synaptosomes prepared from rat brain. There are two phases of divalent cation entry, "fast" and "slow;" each phase is mediated by channels with distinctive characteristics. The fast channels inactivate (within 1 s) and are blocked by low concentrations (less than 1 micro M) of La. The slow channels do not inactivate (within 10 s), and are blocked by high concentrations (greater than 50 micro M) of La. Divalent cation influx through both channels saturates with increasing concentrations of permeant divalent cation; in addition, each permeant divalent cation species competitively blocks the influx of other permeant species. These results are consistent with the presence of "binding sites" for divalent cations in the fast and slow channels. The Ca:Sr:Ba permeability ratio, determined by measuring the influx of all three species in triple-label experiments, was 6:3:2 for the fast channel and 6:3:1 for the slow channel. A simple model for ion selectivity, based on the presence of a binding site in the channel, could account well for slow and, to some extent, for fast, channel selectivity data.
IS LIVING PROTOPLASM PERMEABLE TO IONS?
Authors: Osterhout W. J. V.
Published: May 2004

The experiments indicate that under normal conditions little or no H2S enters the cell sap of Valonia macrophysa except as undissociated molecules.
ON THE ACCUMULATION OF DYE IN NITELLA
Authors: Irwin Marian
Published: May 2004

Living cells of Nitella were placed in different concentrations of brilliant cresyl blue solutions at pH 6.9. It was found that the greater the concentration of the external dye solution, the greater was the speed of accumulation of the dye in the cell sap and higher was the concentration of dye found in the sap at equilibrium.

Analysis of the time curves showed that the process may be regarded as a reversible pseudounimolecular reaction.

When the concentration in the sap is plotted as ordinates and the concentration in the outside solution as abscissae the curve is convex toward the abscissae. There is reason to believe that secondary changes involving injury take place as the dye accumulates and that if these changes did not occur the curve would be concave toward the abscissae.

The process may be explained as a chemical combination of the dye with a constituent of the cell. This harmonizes with the fact that the temperature coefficient is high (about 4.9). Various other possible explanations are discussed.
THE EXCRETION OF CARBON DIOXIDE BY FROG NERVE
Authors: Parker G. H.
Published: May 2004

1. Quiescent sciatic nerve of the frog discharges CO2 at the average rate of 0.00876 mg. CO2 per gram of nerve per minute.

2. Sciatic nerve steeped one minute in boiling water discharges CO2 at first at a low rate and after an hour and a half not at all.

3. Degenerated sciatic nerve discharges CO2 at a slightly higher rate than normal living nerve does.

4. Connective tissue from the frog discharges CO2 at an average rate of 0.0097 mg. per gram of tissue per minute.

5. Assuming that a nerve is composed of from one-half to one-quarter connective tissue the CO2 output from its strictly nervous components is estimated to be at a rate of 0.008 mg. CO2 per gram of nerve per minute.

6. Stimulated sciatic nerve increases the rate of its CO2 output over quiescent nerve by about 14 per cent. When this number is corrected for strictly nervous tissue the rate is about 16 per cent.

7. The increased rate of CO2 production noted on stimulation in normal sciatic nerves was not observed when they were boiled, blocked, or degenerated. It was also not observed with stimulated strands of connective tissue.
CONTRIBUTION TO THE THEORY OF PERMEABILITY OF MEMBRANES FOR ELECTROLYTES
Authors: Michaelis L.
Published: May 2004

From experiments on such membranes as apple skin, parchment paper membrane, and a membrane of completely dry collodion, results have been obtained which could be interpreted by the assumption that these membranes are less permeable for anions than for cations. In parchment paper there is only a relative diminution of the mobility of the anions, in the apple skin and in the dry collodion membrane there is practically no permeability for anions at all. The theory is developed which explains how the decrease or complete lack of mobility of anions influences the electromotive effects of the membrane and the diffusibility of electrolytes across a membrane. The results of the theory are compared with the experimental results.

In membranes impermeable for anions the permeability for cations gives the same order of cations as for the mobilities in a free aqueous solution. But the differences of the mobilities are enormously magnified, e.g. the mobilities of H• and Li•, which are in the proportion of about 1:10 in aqueous solution, are in proportion of about 1:900 in the collodion membrane. The general cause for the retardation of ionic mobility within the membrane may be supposed to be the increased friction of the water envelope dragged along by the ion in the capillary canals of the membrane. The difference of the effect on the cations and on the anions may be attributed to the electric charge of the walls of the canals.
STUDIES ON THE FORMATION AND IONIZATION OF THE COMPOUNDS OF CASEIN WITH ALKALI
Authors: Greenberg David M. , Schmidt Carl L. A.
Published: May 2004

1. Data from the results of transference experiments on solutions of the alkaline earth caseinates are given.

2. The data support the idea that part of the alkaline earth element is held by the casein in the form of complex ions.

3. Grounds are given for believing that the complex anions have a definite composition.
A STUDY OF THE CIRCULATION, BLOOD PRESSURE, AND RESPIRATION OF SHARKS
Authors: Lyon E. P.
Published: May 2004

The average branchial blood pressure in sand sharks was 32 mm. of mercury. The highest recorded in a resting animal was 43 mm. The average dorsal or systemic pressure was 23.3 mm.; highest 30 mm. The ratio of branchial to systemic pressure is about 3 to 2.

The pressure in both systems keeps up well under trauma; but under experimental conditions, with or without manipulation of viscera, slowly falls after several hours.

It rises with muscular effort, and a long rise usually follows stoppage of struggling. It rises when sodium carbonate is injected. The adrenalin curve resembles that in a mammal. Spontaneous rises and falls not attributable to the heart occur. Light in some animals increases blood pressure. It is suspected that these fishes have a vasomotor apparatus.

The heart rate except after trauma is practically always the same as the respiration rate, and there is some reason for believing that the heart rate is determined by the respiration rate. When not in step with respiration, the heart is slower and often in a simple ratio with respiration.

The heart is inhibited by all sorts of stimuli applied practically anywhere (except to the liver?). This effect is abolished by atropin.

Respiration is faster in small animals and averages 24 per minute. Respiration slowly decreases in strength with little change in rate. Usually respiration ceases long before the heart stops.
THE ANALYSIS OF THE GROWTH OF THE NORMAL WHITE MOUSE INTO ITS CONSTITUENT PROCESSES
Authors: Robertson T. Brailsford
Published: May 2004

1. The several growth-cycles which are distinguishable in the growth of an animal or plant are mutually independent in that they do not share a common catalyser.

2. The growth of the white mouse has been shown to consist of three autocatalytic processes and one "linear process" of weight-accretion. The parameters of these processes have been evaluated for one strain and generation of mice.

3. The first and most extensive autocatalytic process is asymmetrical, being defined by an equation of the type:

See PDF for Equation

The second and third cycles, which are more rapid and do not begin to affect the growth of the animal until a later stage of development, are symmetrical, being defined by equations of the type:

See PDF for Equation

4. The amplitude of the first autocatalytic growth-cycle in the mouse is almost the same in males and females, but the moment of maximum growth-velocity in the female anticipates that in the male, the velocity constant is smaller in the female, and the asymmetry estimated by the magnitude of the constant B, is greater in the female than in the male.

5. The amplitude of the second cycle is almost the same in males and females, but data are as yet lacking which would enable us to ascertain whether the velocity-constant and moments of maximum growth-velocity in this cycle differ in the two sexes or not.

6. The amplitude of the third cycle is much less in the female than in the male, and this difference of amplitude almost wholly accounts for the difference of adult weight in the two sexes. The velocity-constant of the third cycle is, however, greater in the female than in the male. Maximum growth velocity due to this cycle is attained at very nearly the same age in both sexes.

7. The origin of asymmetry in autocatalytic growth-processes is discussed. It is pointed out that asymmetry might originate in a progressive diminution of the velocity-constant. If this is the origin of the asymmetry of the first growth-cycle in the mouse, then it is shown that the velocity constant of autocatalysis in this cycle must be very nearly proportional to the nucleo-cytoplasmic ratio, as estimated by the chemical method of Le Breton and Schaeffer.

8. It is pointed out that no reliable measure of senescent loss of weight is available at present. It is shown that removal or decay of those conditions which initially maintain the separability of the growth-cycles which collectively constitute the growth of the white mouse would necessarily result in loss of weight.
THE REACTIONS OF CERIANTHUS TO LIGHT
Authors: Moore Mary Mitchell
Published: May 2004

1. When Cerianthus membranaceus is illuminated upon one side, the animal turns its anterior portion toward the source of light. The number of degrees through which the animal turns is proportional to the logarithm of the intensity of the light.

2. A light intensity of between 250 m.c. and 15,000 m.c. is necessary to cause retraction of the animal.

3. The part of the spectrum which is most effective in causing heliotropic bending of Cerianthus lies between µµ 510 and µµ 570.
THE INFLUENCE OF THE BACKWARD REACTION IN THE PEPTIC HYDROLYSIS OF ALBUMIN
Authors: Morrell Clarence A. , Borsook Henry , Wasteneys Hardolph
Published: May 2004

1. No destruction of pepsin by heat is demonstrable at pH 1.6 until a temperature of 40°C. is exceeded.

2. The influence of the backward reaction in peptic hydrolysis is shown in the diminishing rate at which increasing concentrations of protein are hydrolyzed.

3. The backward reaction causes the optimum for the hydrolysis of higher concentrations of protein to be attained at a lower temperature than with more dilute solutions.

4. The proteose and peptone associated with commercial pepsin retard hydrolysis in the same sense as the products due to the action of the enzyme.
STUDIES IN THE PHYSICAL CHEMISTRY OF THE PROTEINS
Authors: Cohn Edwin J. , Prentiss Adela M.
Published: May 2004

1. The solvent action of a neutral salt upon a protein, oxyhemoglobin, has been found identical to the solvent action of a neutral salt upon a bi-bivalent or uni-quadrivalent compound.

2. The solubility of oxyhemoglobin in phosphate solutions of varying ionic strength has been defined by the equation: log

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in which µ is the ionic strength, and S0 is the solubility in the absence of salt.

3. The values of S0 have been calculated to be 12.2, 11.2, and 13.1 gm. per liter respectively at pH 6.4, 6.6, and 6.8.

4. The relatively great solubility of oxyhemoglobin in water has been ascribed to the strong affinity constants for acid and base of certain groups in oxyhemoglobin.

5. The small change in the solubility of oxyhemoglobin effected by neutral salts suggests that but few such groups are dissociated in oxyhemoglobin in the state in which it crystallizes near its isoelectric point.

6. Certain of the other properties of oxyhemoglobin, such as its low viscosity, are considered in the light of its molecular weight and its valence type.
THE ORIENTATION OF ANIMALS BY OPPOSED BEAMS OF LIGHT
Authors: Crozier W. J.
Published: May 2004

When orientation is attained under the influence of beams of parallel light opposed at 180° the deflection θ from a path at right angles to the beams is given by tan

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where I1 and I2 are the photic intensities and H is the average angle between the photoreceptive surfaces. This expression is independent of the units in which I is measured, and holds whether the primary photosensory effect is proportional to I or to log I. When photokinetic side-to-side motions of the head occur, H decreases with increasing total acting light intensity, but increases if higher total light intensity restricts the amplitude of random movements; in each case, H is very nearly proportional to log I1I2.

For beams of light at 90°,

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The application of these equations to some particular instances is discussed, and it is shown why certain simpler empirical formulæ previously found by others yield fair concordance with the experimental data. The result is thus in complete accord with the tropism theory, since the equations are based simply on the assumption that when orientation is attained photic excitation is the same on the two sides.
THE RELATION OF THE AGE OF THE FEMALE TO CROSSING OVER IN THE THIRD CHROMOSOME OF DROSOPHILA MELANOGASTER
Authors: Bridges Calvin B.
Published: May 2004

The four methods of examining the relation of amount of multiple crossing over to age of mothers agree in showing that the "internode length" or average distance required for double crossing over has changed in a characteristic fashion, giving an M-shaped curve. These changes have not been independent of changes in total recombination but concomitant with them. However, the changes in recombination percentages were far greater than could be accounted for by change in internode length, and the larger factor must be assumed to be changes in the coefficients of crossing over. The amounts of these changes are greatest for the mid-sections of the chromosome and least for the distal sections. The changes in the two limbs are of like amount for equal distances from the center of symmetry in the distribution of simple and multiple crossing over.
EPIDEMIC ENCEPHALITIS AND SIMPLE HERPES
Authors: Flexner Simon
Published: May 2004

The purpose of this paper is to explain the state of our knowledge of the etiology of epidemic encephalitis, and especially to draw a line of demarcation between the established virus of simple herpes and the hypothetical virus of epidemic encephalitis. It had already been shown that the experimental observations on rabbits do no suffice to prove the identity of the herpes with the encephalitis virus. The discussion of the subject in this paper shows that identity cannot be postulated on the basis of the performed guinea pig experiments. Attention has been drawn to the significant fact that there is lack of harmony in the positive results of those investigators who believe that the incitants of epidemic encephalitis have been discovered. An attempt has been made to attribute some of the discrepancies reported by these investigators either to accidental and contaminating microbic agents, or to the uncovering of virulent agents preexisting in a latent state in the animals employed for inoculation, the existence of which was not previously known or suspected. Since past experience leads us to believe in a single incitant for widespread epidemic diseases, it is probable that, when certainly discovered, the microbe of epidemic encephalitis will prove to be simple and not multiple. The direct corollary to this point of view is that up to the present, the etiology of epidemic encephalitis has not been determined.
Cotransport of lithium and potassium in human red cells.
Authors: Canessa M , Bize I , Adragna N , Tosteson D
Published: May 2004

This paper reports the presence of human red cells of an additional ouabain-insensitive transport pathway for lithium ions, the Li-K cotransport. Several kinds of observations support this conclusion. Cells loaded to contain only K, Na, or Li do not exhibit furosemide-sensitive efflux. Simultaneous presence of K and Li on the same side of the membrane mutually stimulates furosemide-sensitive Li and K fluxes from that side. Cells loaded with both Na and Li exhibit no furosemide-sensitive Li efflux. Thus, Li can apparently replace Na but not K on the outward Na-K cotransport system in human red cells. Furthermore, Lio, like Ko, inhibits outward Na-K cotransport. Additional proof for coupled Li-K cotransport is provided by the observation that an outwardly directed K electrochemical potential gradient can drive net outwardly directed K electrochemical potential gradient can drive net outward Li movement against its gradient. There are several differences between Li-K cotransport and Li-Na countertransport. The cotransport system has an apparent affinity for Li that is about one-half that for Na and 30 times lower than the counter-transport system. Furosemide and chloride replacement inhibit cotransport but do not affect countertransport. The PCMBS loading procedure irreversibly inhibits countertransport but not cotransport. Furthermore, the two systems can apparently function at maximal rates simultaneously. Present evidence, than, indicates that the two pathways can be separated operationally as two different systems.