THE PHOTOTROPIC EXCITATION OF LIMAX

The photic orientation of Limax creeping geotropically upon a vertical plate is such that the phototropic vector determining the angular deflection β from the vertical path is proportional to log I. This is proved by the fact that with horizontal illumination tan β is directly proportional to log I; with non-horizontal light rays from a small source the ratio See PDF for Equation is directly proportional to log I (where A = the angle between light rays and the path of orientation), the vector diagram of the field of excitation being in this case not a right-angled triangle.     

THE COUPLED REDOX POTENTIAL OF THE LACTATE-ENZYME-PYRUVATE SYSTEM

1. The term "coupled redox potential" is defined. 2. The system lactic ion See PDF for Equation pyruvic ion + 2H⁺ + 2e is shown to be reversible (when the enzyme is lactic acid dehydrogenase) and its coupled redox potential between pH 5.2 and 7.2 at 32°C. is: See PDF for Equation 3. The free energy of the reaction: lactic ion (1m) → pyruvic ion (1m) = -ΔF = –14,572. 4. The standard free energy of formation (ΔF ₂₉₈) of pyruvic acid (l) is estimated at –108,127. This is merely an approximation as some necessary data are lacking. 5. The importance of coupled redox potentials as a factor in the regulation of the equilibrium of metabolites is indicated.     

THE VIOLOGEN INDICATORS

The tabulation gives the normal potentials of the various indicators at 30°C.; referred to the normal hydrogen electrode, the accuracy is estimated to be ±0.002 volt. Normal potentials of the viologens at 30°C.: Methyl viologen –0.446 volts Ethyl viologen –0.449 volts Betaine viologen –0.444 volts Benzyl viologen –0.359 volts Supposing some solution brings about a coloration of one of these indicators to the extent of A per cent of the maximum color, the oxidation-reduction potential of this solution is E = E_o – 0.06 log See PDF for Equation where E_o is the normal potential according to the above tabulation. This normal potential is independent of pH.     

INFLUENCE OF LIGHT OF VERY LOW INTENSITY ON PHOTOTROPIC REACTIONS OF ANIMALS

1. The negative phototropism of certain land isopods was investigated over a large range of intensities, especially low ones. The responses were determined quantitatively by measuring the angle through which an animal turned away from a line perpendicular to the rays of light. 2. In the absence of light the undirected movements set up by obscure stimuli were such as to compensate each other statistically, the average path being a movement in the direction in which the animal was headed. 3. Over a large range of intensities (0.0026 m.c. up) the average turning is maximal, about 55° (Oniscus). This maximal response is due to an anatomical peculiarity, in that the carapace cuts off the light on the eye after the animal has turned 50–60°. This peculiarity probably accounts for specific differences among land isopods. Any light, therefore, which is strong enough to turn an animal through this maximal angle in a radial distance of 10 cm. will give results whose mean will be maximal. 4. Below 0.0026 m.c. the amount of angular deflection becomes less and less, in proportion to the logarithm of the intensity, until at 0.00003 m.c. the movements are the same as in darkness. 5. This proportionality between amount of turning and the logarithm of the intensity indicates the photochemical nature of phototropism on the basis of Hecht''s work with Mya. As a result, Loeb''s theory of phototropism may then be stated in the mathematical form See PDF for Equation in which I ₁ and I ₂ are the two intensities, E ₁ and E ₂, their respective effects, and R, the muscular action set up by the difference in photochemical effect on the two sides.     

ON THE EXCITATION OF TISSUE BY MEANS OF CONDENSER DISCHARGES

Equations are derived for the capacity-voltage relations for stimulation of tissue by condenser discharges, using the hypothesis that the local excitatory process p grows under the influence of an applied potential V according to the equation, See PDF for Equation where K and k are constants. It is further assumed that the local excitatory process becomes adequate when it attains a value h ± α V where h and α are constants and V is the applied potential at the particular instant that the adequate value is attained. The equations so obtained are applied to the data of several authors on several types of tissue and the agreements obtained are sufficiently good. It is shown in one case that the direct current equation and the condenser discharge equation each derived from the above bases are consistent when applied to data from the same preparation.     

THE KINETICS OF PENETRATION : I. EQUATIONS FOR THE ENTRANCE OF ELECTROLYTES

When the only solute present is a weak acid, HA, which penetrates as molecules only into a living cell according to a curve of the first order and eventually reaches a true equilibrium we may regard the rate of increase of molecules inside as See PDF for Equation where P_M is the permeability of the protoplasm to molecules, M_o, denotes the external and M_i the internal concentration of molecules, A_i denotes the internal concentration of the anion A^- and See PDF for Equation (It is assumed that the activity coefficients equal 1.) Putting P_MF_M = V_M, the apparent velocity constant of the process, we have See PDF for Equation where e denotes the concentration at equilibrium. Then See PDF for Equation where t is time. The corresponding equation when ions alone enter is See PDF for Equation. where K is the dissociation constant of HA, P_A is the permeability of the protoplasm to the ion pair H⁺ + A^-, and A_ie denotes the internal concentration of A_i at equilibrium. Putting P_AKF_M = V_A, the apparent velocity constant of the process, we have See PDF for Equation and See PDF for Equation When both ions and molecules of HA enter together we have See PDF for Equation where S_i = M_i + A_i and S_ie is the value of S_i at equilibrium. Then See PDF for Equation V_M, V_A, and V_MA depend on F_M and hence on the internal pH value but are independent of the external pH value except as it affects the internal pH value. When the ion pair Na⁺ + A^- penetrates and Na_i = BA_i, we have See PDF for Equation and See PDF for Equation where P _NaA is the permeability of the protoplasm to the ion pair Na⁺ + A^-, Na_o and Na_i are the external and internal concentrations of Na⁺, See PDF for Equation, and V _Na is the apparent velocity constant of the process. Equations are also given for the penetration of: (1) molecules of HA and the ion pair Na⁺ + A^-, (2) the ion pairs H⁺ + A^- and Na⁺ + A^-, (3) molecules of HA and the ion pairs Na⁺ + A^- and H⁺ + A^-. (4) The penetration of molecules of HA together with those of a weak base ZOH. (5) Exchange of ions of the same sign. When a weak electrolyte HA is the only solute present we cannot decide whether molecules alone or molecules and ions enter by comparing the velocity constants at different pH values, since in both cases they will behave alike, remaining constant if F_M is constant and falling off with increase of external pH value if F_M falls off. But if a salt (e.g., NaA) is the only substance penetrating the velocity constant will increase with increase of external pH value: if molecules of HA and the ions of a salt NaA. penetrate together the velocity constant may increase or decrease while the internal pH value rises. The initial rate See PDF for Equation (i.e., the rate when M_i = 0 and A_i = 0) falls off with increase of external pH value if HA alone is present and penetrates as molecules or as ions (or in both forms). But if a salt (e.g., NaA) penetrates the initial rate may in some cases decrease and then increase as the external pH value increases. At equilibrium the value of M_i equals that of M_o (no matter whether molecules alone penetrate, or ions alone, or both together). If the total external concentration (S_o = M_o + A_o) be kept constant a decrease in the external pH value will increase the value of M_o and make a corresponding increase in the rate of entrance and in the value at equilibrium no matter whether molecules alone penetrate, or ions alone, or both together. What is here said of weak acids holds with suitable modifications for weak bases and for amphoteric electrolytes and may also be applied to strong electrolytes.     

STUDIES IN THE PHYSICAL CHEMISTRY OF THE PROTEINS : VI. THE ACTIVITY COEFFICIENTS OF THE IONS IN CERTAIN OXYHEMOGLOBIN SOLUTIONS.

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 See PDF for Equation in which µ is the ionic strength, and S ₀ is the solubility in the absence of salt. 3. The values of S ₀ 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 ELECTRIC RESISTANCE AND CAPACITY OF BLOOD FOR FREQUENCIES BETWEEN 800 AND 4? MILLION CYCLES

1. The variation of the experimental values (R (ω)), (C (ω)) of the resistance and capacity of blood for increasing frequencies is approximately represented by the equation: See PDF for Equation in which R _o and C _o are the resistance and capacity of the blood at low frequency and See PDF for Equation is the resistance of the blood at infinite frequency. Formulæ (1) and (2) are derived by considering the blood as equivalent to the system shown in the diagram (a) of Fig. 1. 2. By the application of formula (1) to our experimental data the value of R(∞) can be extrapolated with high accuracy. R(∞) represents the resistance) which would have been obtained at low frequency, if the membranes around the corpuscles could have been removed. 3. The specific resistance of the corpuscle interior can be calculated by equation (5), using experimental values for R(∞), for the volume concentration of the blood and for the specific resistance of the serum. 4. The specific resistance of the interior of the red corpuscle of the calf is found to be 3.5 ± 10 per cent times the specific resistance of the serum.     

The proportion of mutants in bacterial cultures

The proportion of mutants in a growing culture of organisms will depend upon (a) the rate at which the wild cells produce them (with or without growth), (b) the back mutation rate, and (c) the growth rates of the wild and mutant cells. If the mutation rate without growth and the back mutation rate are neglected, the growth of a mutant is expressed by See PDF for Equation and the ratio of the mutant to wild by See PDF for Equation in which λ = mutation frequency rate constant, "mutation rate," A = growth rate constant of wild cells W, B = growth rate constant of mutant cells M. If the term [B – (1 – 2λ)A] is positive, the proportion of mutants increases continuously. If it is negative, the proportion of mutants reaches a constant value See PDF for Equation If mutation is assumed to occur without growth at the rate C, then the corresponding equations are (11), (12), and (14). See PDF for Equation If (B + C – A) is negative and t = ∞, See PDF for Equation If C << A, See PDF for Equation     

THE KINETICS OF OSMOTIC SWELLING IN LIVING CELLS

The rate of swelling of unfertilized sea urchin eggs in hypotonic sea water was investigated. Analysis of curves leads to the following conclusions. 1. The rate of swelling follows the equation, See PDF for Equation where V _eq., V ₀, and V_t stand for volume at equilibrium, at first instant, and at time t, respectively, the other symbols having their usual significance. This equation is found to hold over a wide range of temperatures and osmotic pressures. This relation is the one expected in a diffusion process. 2. The rate of swelling is found to have a high temperature coefficient (Q ₁₀ = 2 to 3, or µ = 13,000 to 19,000). This deviation from the usual effect of temperature on diffusion processes is thought to be associated with changes in cell permeability to water. The possible influence of changes in viscosity is discussed. 3. The lower the osmotic pressure of the solution, the longer it takes for swelling of the cell. Thus at 15° in 80 per cent sea water, the velocity constant has a value of 0.072, in 20 per cent sea water, of 0.006.     

TEMPERATURE AND FORWARD MOVEMENT OF PARAMECIUM

1. The rate of forward movement in Paramecium as affected by changes in temperature can be described accurately in terms of the Arrhenius equation. See PDF for Equation 2. For the range from 6–15°, µ = 16,000; from 16–40°, µ = 8,000. These values fall within the limits characteristic for chemical processes. 3. On the principle of velocity control by the slowest rate, it is assumed that in Paramecium at temperatures above normal, control passes from one underlying reaction to another. 4. The views expressed by Rice, the recent results of Crozier, and certain µ values given by Arrhenius all suggest that µ = 16,000 may represent an oxidation, and µ = 8,000 either a modified oxidation or an hydrolysis. 5. For the system of controls, the catenary series O → A → E with the lower µ value attached to the precursor reaction is adequate. We may also assume a cyclical system analogous to Meyerhof''s conception of carbohydrate metabolism in muscle. In this case it is necessary to assign µ = 16,000 to the oxidation of A and E and µ = 8,000 to the synthesis E → O. This model also accounts for the fact that the data might be interpreted as involving, apparently, a depletion of A at the higher temperature.     

Transient Phases of the Isometric Tetanus in Frog's Striated Muscle

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant α. α a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation See PDF for Equation for temperatures between 1 and 20°C and for sarcomere lengths 2.0–2.8 µm. The energy of activation, E, does not vary significantly with s; E = 13.9 ± 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 µm) is about three times greater than A(2.8 µm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r₀ in a twitch to r_∞ for large D. The rate constant for decrease of r with D increases with s and with T. r₀ and r_∞ obey the Arrhenius equation and decrease with increasing s.     

TEMPERATURE AND CRITICAL ILLUMINATION FOR REACTION TO FLICKERING LIGHT : IV. ANAX NYMPHS

At fixed flash frequency (_F = 20, _F = 55) and with constant light time fraction (50 per cent) in the flash cycle, the critical illumination I for response of Anax nymphs to visual flicker falls continuously as the temperature rises. The temperature characteristic µ for the measure of excitability (1/I) increases continuously with elevation of temperature. The form of the F - log I curve does not change except at quite high temperature (35.8°), and then only slightly (near F = 55); F_max. is not altered. The very unusual form of the 1/I curve as a function of temperature is quantitatively accounted for if two processes, with respectively µ = 19,200 and µ = 3,400, contribute independently and simultaneously to the control of the speed of the reaction governing the excitability; the velocities of these two processes are equal at 15.9°.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : XI. ON FLICKER WITH SUBDIVIDED FIELDS

In Vol. 27, No. 5, May 20, 1944, page 403, in the eighth line from the bottom of the page, the comma after "intensity" should be a semicolon. On page 413, in the second formula from the bottom of the page, for See PDF for Equation read See PDF for Equation On the same page, formula 2 should read See PDF for Equation On page 414, line 3, at the end of the line add "or" to read "of the level of I or of F." On page 422, in the first line below the figure legend, for "illuminate" read "illuminated." On page 430, line 22, for "lighteb dars" read "lighted bars."     

THE VISUAL INTENSITY DISCRIMINATION OF THE HONEY BEE

1. Bees respond by a characteristic reflex to a movement in their visual field. By confining the field to a series of parallel stripes of different brightness it is possible to determine at any brightness of one of the two stripe systems the brightness of the second at which the bee will first respond to a displacement of the field. Thus intensity discrimination can be determined. 2. The discriminating power of the bee''s eye varies with illumination in much the same way that it does for the human eye. The discrimination is poor at low illumination; as the intensity of illumination increases the discrimination increases and seems to reach a constant level at high illuminations. 3. The probable error of See PDF for Equation decreases with increasing I exactly in the same way as does See PDF for Equation itself. The logarithm of the probable error of ΔI is a rectilinear function of log I for all but the very lowest intensities. Such relationships show that the measurements exhibit an internal self-consistency which is beyond accident. 4. A comparison of the efficiency of the bee''s eye with that of the human eye shows that the range over which the human eye can perceive and discriminate different brightnesses is very much greater than for the bee''s eye. When the discrimination power of the human eye has reached almost a constant maximal level the bee''s discrimination is still very poor, and at an illumination where as well the discrimination power of the human eye and the bee''s eye are at their best, the intensity discrimination of the bee is twenty times worse than in the human eye.     

Resveratrol Attenuates the Na+-Dependent Intracellular Ca2+ Overload by Inhibiting H2O2-Induced Increase in Late Sodium Current in Ventricular Myocytes

Background/Aims

Resveratrol has been demonstrated to be protective in the cardiovascular system. The aim of this study was to assess the effects of resveratrol on hydrogen peroxide (H₂O₂)-induced increase in late sodium current (I _Na.L) which augmented the reverse Na⁺-Ca²⁺ exchanger current (I _NCX), and the diastolic intracellular Ca²⁺ concentration in ventricular myocytes.

Methods

I _Na.L, I _NCX, L-type Ca²⁺ current (I _Ca.L) and intracellular Ca²⁺ properties were determined using whole-cell patch-clamp techniques and dual-excitation fluorescence photomultiplier system (IonOptix), respectively, in rabbit ventricular myocytes.

Results

Resveratrol (10, 20, 40 and 80 µM) decreased I _Na.L in myocytes both in the absence and presence of H₂O₂ (300 µM) in a concentration dependent manner. Ranolazine (3–9 µM) and tetrodotoxin (TTX, 4 µM), I _Na.L inhibitors, decreased I _Na.L in cardiomyocytes in the presence of 300 µM H₂O₂. H₂O₂ (300 µM) increased the reverse I _NCX and this increase was significantly attenuated by either 20 µM resveratrol or 4 µM ranolazine or 4 µM TTX. In addition, 10 µM resveratrol and 2 µM TTX significantly depressed the increase by 150 µM H₂O₂ of the diastolic intracellular Ca²⁺ fura-2 fluorescence intensity (FFI), fura-fluorescence intensity change (△FFI), maximal velocity of intracellular Ca²⁺ transient rise and decay. As expected, 2 µM TTX had no effect on I _Ca.L.

Conclusion

Resveratrol protects the cardiomyocytes by inhibiting the H₂O₂-induced augmentation of I _Na.L.and may contribute to the reduction of ischemia-induced lethal arrhythmias.     

ON THE EQUILIBRATION OF GEOTROPIC AND PHOTOTROPIC EXCITATIONS IN THE RAT

The intensity of light required to just counterbalance geotropic orientation of young rats, with eyelids unopened, is so related to the angle of inclination (α) of the creeping plane that the ratio log I/log sin α is constant. This relationship, and the statistical variability of I as measured at each value of α, may be deduced from the known phototropic and the geotropic conduct as studied separately, and affords proof that in the compounding of the two kinds of excitation the rat is behaving as a machine.     

ORIENTATION BY OPPOSED BEAMS OF LIGHT

Computations of the effective angular inclination (H) of the photoreceptive surfaces of the two sides, based upon measurements of orientation angles under the action of beams of light directly opposed or crossing at right angles, show that with larvae of Calliphora and of Lucillia H declines as the total illumination decreases (i.e., as the angle of orientation away from the more intense light increases). H is greater with the two lights opposed at 180°; this may be due to the difference in refraction. For the more sharply pointed larvae of Lucillia, H is less than half as great as in Calliphora.     

The rhodopsin system of the squid

Squid rhodopsin (λ_max 493 mµ)—like vertebrate rhodopsins—contains a retinene chromophore linked to a protein, opsin. Light transforms rhodopsin to lumi- and metarhodopsin. However, whereas vertebrate metarhodopsin at physiological temperatures decomposes into retinene and opsin, squid metarhodopsin is stable. Light also converts squid metarhodopsin to rhodopsin. Rhodopsin is therefore regenerated from metarhodopsin in the light. Irradiation of rhodopsin or metarhodopsin produces a steady state by promoting the reactions, See PDF for Equation Squid rhodopsin contains neo-b (11-cis) retinene; metarhodopsin all-trans retinene. The interconversion of rhodopsin and metarhodopsin involves only the stereoisomerization of their chromophores. Squid metarhodopsin is a pH indicator, red (λ_max 500 mµ) near neutrality, yellow (λ_max 380 mµ) in alkaline solution. The two forms—acid and alkaline metarhodopsin—are interconverted according to the equation, Alkaline metarhodopsin + H⁺ acid metarhodopsin, with pK 7.7. In both forms, retinene is attached to opsin at the same site as in rhodopsin. However, metarhodopsin decomposes more readily than rhodopsin into retinene and opsin. The opsins apparently fit the shape of the neo-b chromophore. When light isomerizes the chromophore to the all-trans configuration, squid opsin accepts the all-trans chromophore, while vertebrate opsins do not and hence release all-trans retinene. Light triggers vision by affecting directly the shape of the retinene chromophore. This changes its relationship with opsin, so initiating a train of chemical reactions.