bluuebunny/crossref_metadata_2025 huggingface dataset:
The Hexose-Proton Cotransport System of Chlorella
Authors: Komor Ewald , Tanner Widmar
Published: May 2004

The proton concentration in the medium affects the maximal velocity of sugar uptake with a Km of 0.3 mM (high affinity uptake). By decreasing the proton concentration a decrease in high affinity sugar uptake is observed, in parallel the activity of a low affinity uptake system (Km of 50 mM) rises. Both systems add up to 100%. The existence of the carrier in two conformational states (protonated and unprotonated) has been proposed therefore, the protonated form with high affinity to 6-deoxyglucose, the unprotonated form with low affinity. A plot of extrapolated Vmax values at low substrate concentration versus proton concentration results in a Km for protons of 0.14 µM, i.e. half-maximal protonation of the carrier is achieved at pH 6.85. The stoichiometry of protons cotransported per 6-deoxyglucose is close to 1 at pH 6.0–6.5. At higher pH values the stoichiometry continuously decreases; at pH 8.0 only one proton is cotransported per four molecules of sugar. Whereas the translocation of the protonated carrier is strictly dependent on sugar this coupling is less strict for the unprotonated form. Therefore at alkaline pH a considerable net efflux of accumulated sugar can occur. The dependence of sugar accumulation on pH has been measured. The decrease in accumulation with higher pH values can quantitatively be explained by the decrease in the amount of protonated carrier. The properties of the unprotonated carrier resemble strikingly the properties of carrier at the inner side of the membrane. The inside pH of Chlorella was measured with the weak acid 5,5-dimethyl-2, 4-oxazolidinedion (DMO). At an outside pH of 6.5 the internal pH was found to be 7.2. To explain the extent of sugar accumulation it has to be assumed that the membrane potential also contributes to active sugar transport in this alga.
Muscle Compliance and the Longitudinal Transmission of Mechanical Impulses
Authors: Schoenberg Mark , Wells Jay B. , Podolsky Richard J.
Published: May 2004

The time required for a mechanical impulse to propagate from one end to the other was measured directly in frog sartorius muscles and in fiber bundles from the semitendinosus muscle. When the fibers were fully activated, the transmission velocity was 170 mm/ms. In resting fibers the transmission time was three to four times greater than in activated fibers. Control experiments indicated that the transmission time across the tendons was negligible. A muscle compliance of 55–80 Å per half sarcomere was estimated from these data. The "measurement time" of the method was calculated to be about 15 µs. This relatively short measurement time makes the method potentially useful for detecting changes in cross-bridge compliance.
Force-Generating Capacity and Contractile Protein Content of Arterial Smooth Muscle
Authors: Murphy R. A. , Herlihy Jeremiah T. , Megerman J.
Published: May 2004

After correction for extracellular space (40%) determined from electron micrographs, the maximum isometric force developed by strips prepared from the media of the hog carotid artery (2.2 x 106 dyn/cm2) can be extrapolated to give a value of 3.7 x 106 dyn/cm2 for the smooth muscle component of the strip. Three independent estimates of the myosin content of the smooth muscle cells were made based on (a) exhaustive extraction and purification with estimates of preparative losses, (b) the myosin catalyzed ATPase activity of media homogenates, and (c) quantitative densitometry of the peaks containing myosin, actin, and tropomyosin after disk electrophoresis of sodium dodecyl sulfate-treated media homogenates. The results were consistent and gave a myosin content of 5–10 mg/g media, or 8–17 mg/g cell. Method (c) gave myosin:actin:tropomyosin weight ratios of 1:3.2:0.8. Although measured force developed by the smooth muscle cell exceeds that of mammalian striated muscle, the myosin content in smooth muscle is about five times lower. The actin content of smooth muscle is relatively high. The actin and myosin contents are consistent with thick and thin filament ratios observed in electron micrographs of vascular smooth muscle.
Energy liberation and chemical change in frog skeletal muscle during single isometric tetanic contractions.
Authors: Homsher E , Rall J A , Wallner A , Ricchiuti N V
Published: May 2004

Recent data obtained from Rana temporaria sartorius muscles during an isometric tetanus indicate that the time-course of phosphocreatine (PC) splitting cannot account for the total energy (heat + work) liberation (Gilbert et al. 1971. J. Physiol. (Lond.) 218:)63). As this conclusion is important to an understanding of the chemical energetics of contraction, similar experments were performed on unpoisoned, oxygenated Rana pipiens sartorius muscles. The muscles were tetanized (isometrically) at 0 degrees C for 0.6, 1, or 5 s; metabolism was rapidly arrested by freezing the muscles with a specially designed hammer apparatus, and the frozen muscles were chemically analyzed. Comparable myothermal measurments were made on frogs from the same batch. Results of these experiments indicate: (a) The energy liberation parallels the PC and ATP breakdown with a proportionality constant of 10.7 kcal/mol; (b) comparably designed experiments with sartorius muscles of R. temporaria revealed that the ratio of energy liberation to PC splitting was significantly greater than that observed in R. pipiens sartorius muscles; (c) there is no systematic difference between experiments in which metabolism was arrested by the hammer apparatus and others using a conventional immersion technique.
Longitudinal impedance of single frog muscle fibers.
Authors: Mobley B A , Leung J , Eisenberg R S
Published: May 2004

The longitudinal impedance of single skeletal muscle fibers has been measured from1 to 10,000 Hz in an oil gap apparatus which forces current to flow longitudinally down the fiber. The impedance observed is purely resistive in some fibers from the semitendinosus muscle and in two fibers from the sartorius muscle. In other fibers from the semitendinosus muscle a small phase shift is observed. The mean value of the maximum phase shift observed from all fibers is 1.07 degrees. The artifacts associated with the apparatus and method are examined theoretically and it is shown that one of the likely artifacts could account for the small phase observed. It is concluded that the longitudinal impedance of skeletal muscle fibers is essentially resistive and that little, if any, longitudinal current crosses the membranes of the sarcoplasmic reticulum.
Olfactory receptor responses to sex pheromone components in the redbanded leafroller moth.
Authors: O'Connell R J
Published: May 2004

Electrical responses of single olfactory receptor neurons of the male redbanded leafroller moth were elicited by each of the principle components of the sex pheromone and six other behaviorally active compounds. Response frequencies to equal intensities of each of these compounds and changes in response frequency with increasing amounts of any one compound, varied from receptor to receptor. These differences in response characteristics appear to be due to factors intrinsic to the olfactory recptor neuron and not to factors external to it. The encoding of odor quality by these receptor neurons cannot be in the simple presence or absence of activity in any one of them. Rather, odor quality may be encoded by the pattern of activity which invariably arises across an ensemble of receptor neurons, each having its own distribution of sensitivities.
Membrane response to current pulses in spheroidal aggregates of embryonic heart cells.
Authors: Dehaan R L , Fozzard H A
Published: May 2004

Hearts from chick embryos aged 4,7, or 14 days were dissociated into their component cells, and the cells allowed to reassociate in the form of smooth-surfaced spheroidal aggregates on a gyratory shaker. Records from intracellular electrodes inserted into two widely spaced cells in a spontaneously beating aggregate indicated that the action potentials occurred virtually simultaneously. In aggregates made quiescent with tetrodotoxin, the voltage response to a current pulse injected in one cell could be noted by recording with a second microelectrode at various distance from the current source. The magnitude of the response was found not to vary with distance. It is concluded that the component cells in an aggregate are normally tightly coupled electrically; the cell boundaries do not constitute an appreciable resistive barrier. Such ag-regates behave as virtually isopential systems, with properties similar to those of single spherical cells, as modeled by Eisenberg and Engel (1970. J. Gen. Physiol. 55:736-757). Passive membrane time constant ranged from 11 to 31 ms, with a mean value of 17 ms; this value did not vary with aggregate size. Input resistance (V/I) varied inversely with aggregate size, as predicted, but with much scatter in the measured values. Specific membrane resistance was calculated as either 13,000 or 800 ohm-cm2 depending on whether input resistance was attributed to the total cell surface membrane area or to the outer surface of the sphere alone. No systematic difference in passive electrical properties of aggregates composed of 4-, 7-, and 14-day cells was seen. It is concluded that these aggregates may be suitable for voltage clamp analysis of their excitable membrane properties.
Threshold phenomena in chemoreception and taxis in slime mold Physarum polycephalum.
Authors: Ueda T , Terayama K , Kurihara K , Kobatake Y
Published: May 2004

The plasmodium of Physarum polycephalum reacts to various kinds of chemicals substances and moves towards or away from them. Threshold concentration of recognition of chemicals was examined in terms of membrane potential and of the averaged motive force of tactic movement by using a double-chamber method, i.e., a single plasmodium was placed between two compartments through a narrow ditch, and differences in membrane potential and in pressure between two compartments were measured. Results are summarized as follows: (a) By increasing the concentration of various substances in one compartment, the membrane potential started to change at a certain threshold concentration, C-th, for each chemical. Chemotactic movement of the plasmodium took place at the same threshold concentration. These results held both for attractants (glucose, galactose, phosphates, pyrophosphates, ATP, c-AMP, etc) and for repellents (various inorganic salts, sucrose, fructose, etc.). (b) The threshold concentration, Cth, for inorganic salts decreased remarkably with increase of the valences of cations, zeta, and was proportional to Z-6, I.E., THE Shultze-Hardy rule known in the field of colloid chemistry was found to be applicable. (c) The plasmodium distinguished the species of monovalent cations in the following order: H(Li(K(Na(Rb(Cs(NH-4 Plots of log Cth against the lyotropic number of anion fell on different straight lines for each monovalent cation species. (d) Plots of log Cth, against the reciprocal of the absolute tempe lines were almost the same and gave a value of 12 kcal/mol for the enthalpy change. These results suggest that the recognition of chemical substances appears as the result of a structural change of the membrane at the threshold point, and that the change in membrane structure is transmitted simultaneously to the motile system of the plasmodium.
Action of ouabain on sodium transport in toad urinary bladder, Evidence for two pathways for sodium entry.
Authors: Finn A L
Published: May 2004

The cardiac glycoside ouabain inhibits transepithelial sodium transport in the toad urinary bladder. It is shown that this drug reduces the rate coefficient for sodium exit at the serosal pump site. In addition, ouabain inhibits entry across the mucosal border whenever the electrochemical potential gradient for sodium is made less favorable. The data are interpreted as indicating the existence of two separate pathways for sodium entry, one of which is ouabain inhibitable.
A synthetic strand of cardiac muscle: its passive electrical properties.
Authors: Lieberman M , Sawanobori T , Kootsey J M , Johnson E A
Published: May 2004

The passive electrical properties of synthetic strands of cardiac muscle, grown in tissue culture, were studied using two intracellular microelectrodes: one to inject a rectangular pulse of current and the other to record the resultant displacement of membrane potential at various distances from the current source. In all preparations, the potential displacement, instead of approaching a steady value as would be expected for a cell with constant electrical properties, increased slowly with time throughout the current step. In such circumstances, the specific electrical constants for the membrane and cytoplasm must not be obtained by applying the usual methods, which are based on the analytical solution of the partial differential equation describing a one-dimensional cell with constant electrical properties. A satisfactory fit of the potential waveforms was, however, obtained with numerical solutions of a modified form of this equation in which the membrane resistance increased linearly with time. Best fits of the waveforms from 12 preparations gave the following values for the membrane resistance times unit length, membrane capacitance per unit length, and for the myoplasmic resistance: 1.22 plus or minus 0.13 x 10-5 omegacm, 0.224 plus or minus 0.023 uF with cm-minus 1, and 1.37 plus or minus 0.13 x 10-7 omegacm-minus 1, respectively. The value of membrane capacitance per unit length was close to that obtained from the time constant of the foot of the action potential and was in keeping with the generally satisfactory fit of the recorded waveforms with solutions of the cable equation in which the membrane impedance is that of a single capacitor and resistor in parallel. The area of membrane per unit length and the cross-sectional area of myoplasm at any given length of the preparation were determined from light and composite electron micrographs, and these were used to calculate the following values for the specific electrical membrane resistance, membrane capacitance, and the resistivity of the cytoplasm: 20.5 plus or minus 3.0 x 10-3 omegacm-2, l.54 plus or minus 0.24 uFWITHcm-minus 2, and 180 plus or minus 34 omegacm, respectively.
Activities of potassium and sodium ions in rabbit heart muscle.
Authors: Lee C O , Fozzard H A
Published: May 2004

Activities (a) of intracellular K and Na in rabbit ventricular papillary muslces were determined with cation-selectivve glass microelectrodes and concentrations (C) were estimated with flame photometry. The CK and aK of the muscles were 134.9 +/- 3.1 mM (mean value +/- SE) and 82.6 mM, respectively, at 25 degrees C. The corresponding CNa and aNa were 32.7 +/- 2.7 and 5.7, respectively. The apparent intracellular activity coefficients for K (gammaK) and Na (gammaNa) were 0.612 and 0.175, respectively. Similar results were obtained at 35 +/- 1 degree C. gammaK was substantially lower than the activity coefficient (0.745) of extracellular fluid (Tyrode's solution), which might be expected on the basis of a different intracellular ionic strength. gammaNa was much lower than that of extracellular fluid, and suggest that much of the Na was compartmentalized or sequestered. For external K concentrations greater than 5 mM, the resting membrane potentials agreed well with the potential differences calculated from the K activity gradients across the cell membrane as a potassium electrode. These results emphasize that potassium equilibrium potentials in heart muscle should be calculated by activities rather than concentrations.
Resolution of the potassium ion pump in muscle fibers using barium ions.
Authors: Sjodin R A , Ortiz O
Published: May 2004

When frog sartorius muscles recover from Na enrichment in the presence of external K, net K entry into the fibers occurs by both passive movement and active inward transport via a K pump. Under normal conditions, it has not been possible to experimentally distinguish these processes. Fractionation into the flux components must be accomplished from inferences concerning the K conductance or permeability during a period of rapid Na extrusion. The best estimates indicate that 60-80% of the K entry occurs via the K pump. In the presence of Ba ions, the membrane permeability to K is very much reduced. Under these conditions, Na-enriched muscles underwent a normal recovery in the presence of external K, and the amount of inward K movement due to the K pump rose to over 90% of the total K entry. The characteristics of the K pump studied by this means were: (a) essentially complete inhibition by 10(-4) M ouabain, (b) inhibition by [Na]omicron, (c) activation by [K]omicron according to a rectangular hyperbola in the absence of [Na]omicron, (d) linear activation by [Na]iota over a wide range in concentration, (e) zero or undetectably low pumping rate as [Na]iota leads to 0, (f) the number of Na ions actively transported per K ion actively transported is 1.4-1.7 normally and 1.1 in the presence of Ba.
Variation of muscle stiffness with force at increasing speeds of shortening.
Authors: Julian F J , Sollins M R
Published: May 2004

Single frog skeletal muscle fibers were attached to a servo motor and force transducer by knotting the tendons to pieces of wire at the fiver insertions. Small amplitude, high frequency sinusoidal length changes were then applied during tetani while fibers contracted both isometrically and isotonically at various constant velocities. The amlitude of the resulting force oscillation provides a relative measure of muscle stiffness. It is shown from an analysis of the transient force responses observed after sudden changes in muscle length applied both at full and reduced overlap and during the rising phase of short tetani that these responses can be explained on the basis of varying numbers of cross bridges attached at the time of the length step. Therefore, the stiffness measured by the high frequency legth oscillation method is taken to be directly proportional to the number of cross bridges attached to thin filament sittes. It is found that muscle stiffness measured in this way falls with increasing shortening velocity, but not as rapidly as the force. The results suggest that at the maximum velocity of shortening, when the external force is zero, muscle stiffness is still substantial. The findings are interpreted in terms of a specific model for muscle contraction in which the maximum velocity of shortening under zero external load arises when a force balance is attained between attached cross bridges somr interpretations of these results are also discussed.
Electrophysiological properties of the membrane and acetylcholine receptor in developing rat and chick myotubes.
Authors: Ritchie A K , Fambrough D M
Published: May 2004

Membrane properties of rat and chick myotubes in various stages of development were studied. Resting membrane potentials (Em) increased from -8 to -55 mV in both rat and chick as the myotubes developed from myoblasts to large multinucleated fibers. In the rat myotubes, this increase was not accompanied by significant changes in specific membrane resistivity or changes in Na+ and K+ ion distribution. Nor have we observed a significant electrogenic component to the resting Em of mature rat myotubues under normal circumstances. A progressive increase in the passive permeability of the membrane to K+ relative to Na+ ions has been observed which can account for the changes in Em with development. In contrast to the changes in the ionic selectivity of the membrane, we have found that the ionic selectivity of the ACh receptor of rat and chick myotubes remains constant during the same period of myotube development.
Light-sensitive swelling of isolated frog rod outer segments as an in vitro assay for visual transduction and dark adaptation.
Authors: Bownds D , Brodie A E
Published: May 2004

Frog rod outer segments swell slowly after being shaken from an excised retina into a modified Ringer's solution. The swelling has the following characteristics: (a) It is suppressed by illumination which bleaches only 500 rhodopsin molecules per outer segment per second. This is approximately the level required to saturate the in vivo receptor potential. (b) Light suppression is seen in NaCl but not in KCl solutions. (c) Dark swelling is labile and is enhanced by calf serum, low calcium concentrations, dithiothreitol, and cyclic nucleotide phosphodiesterase inhibitors. (d) Lowering the pH to 5.5 or removing magnesium reversibly reduces dark swelling to the same extent as illumination. (e) The amount of light required for maximal suppression of dark-swelling increases approximately 10-fold if the calcium concentrations is lowered by EGTA addition. (f) The effect of illumination is irreversibly abolished by antimycin and other inhibitors of mitochondrial electron transport. (g) A process analogous to dark adaptation in vivo can be observed: If 10-50% of the rhodopsin present is bleached and the outer segments are then kept dark, rapid dark swelling returns after a period of 15-45 min. This swelling is again sensitive to light. We tentatively ascribe the light suppression of swelling to the same decrease in sodium permeability which is observed on illuminating living receptor cells. The experiments suggest that outer segments retain their competence to perform both transduction and dark adaptation after their separation from the retina.
Models for coupling of salt and water transport; Proximal tubular reabsorption in Necturus kidney.
Authors: Sackin H , Boulpaep E L
Published: May 2004

Models for coupling of salt and water transport are developed with two important assumptions appropriate for leaky epithelia. (a) The tight junction is permeable to both sale and water. (b) Active Na transport into the lateral speces is assumed to occur uniformly along the length of the channel. The proposed models deal specifically with the intraepithelial mechanism of proximal tubular resbsorption in the Necturus kidney although they have implications for epithelial transport in the gallbladder and small intestine as well. The first model (continuous version) is similar to the standing gradient model devised by Diamond and Bossert but used different boundary conditions. In contrast to Diamond and Bossert's model, the predicted concentration profiles are relatively flat with no sizable gradients along the interspace. The second model (compartment version) expands Curran's model of epithelial salt and water transport by including additional compartments and considering both electrical and chemical driving forces for individual Na and Cl ions as well as hydraulic and osmotic driving forces for water. In both models, ion and water fluxes are investigated as a function of the transport parameters. The behavior of the models is consistent with previously suggested mechanisms for the control of net transport, particularly during saline diuresis. Under all conditions the predicted ratio of net solute to solvent flux, or emergent concentration, deviates from exact isotonicity (except when the basement membrane has an appreciable salt reflection coefficient). However, the degree of hypertonicity may be small enough to be experimentally indistinguishable from isotonic transport.
Sodium flux through the sodium channels of axon membrane fragments isolated from lobster nerves.
Authors: Barnola F V , Villegas R
Published: May 2004

The efflux of 22Na from vesicles formed by axolemma fragments isolated from lobster nerves was studied in the presence and in the absence of drugs having well-known action on the sodium channels. The vesicles were equilibrated 12-14 h at 4 degrees C with 22Na in lobster solution containing 1 mM ouabain. Afterwards the suspension was divided: one portion was used as control and the others were treated with veratrine (0.025-0.50 mg/ml), tetrodotoxin (1-2,000 nM) in the presence of veratrine, or tetrodotoxin alone. After 3 h at 20-22 degrees C, the suspensions were diluted into nonradioactive solutions and the 22Na efflux followed by a rapid filtration technique. The results revealed that veratrine increases the efflux rate and the additional application of tetrodotoxin abolishes it, e.g., 0.50 mg of veratrine/ml increases the rate, expressed in 10(-2) min(-1), from 0.59 +/- 0.04 (mean +/- SEM; n = 13) to 0.86 +/- 0.05 (n = 13), and the addition of 100 nM tetrodotoxin diminishes it to 0.48 +/- 0.07 (n = 4). This increase and diminution are statistically significant (P less than 0.005), but this is not the case between the control and the veratrine plus tetrodotoxin values (P greater than 0.05). 50% of the diminution is produced by 11.9 +/- 2.4 nM tetrodotoxin. Tetrodotoxin alone produces a slight diminution of the 22Na efflux. Batrachotoxin (0.50 muM) has an action similar to veratrine's. These findings are considered evidence of the presence of functioning sodium channels in the isolated axolemma fragments.
Role of intracellular calcium and sodium in light adaptation in the retina of the honey bee drone (Apis mellifera, L).
Authors: Bader C , Baumann F , Bertrand D
Published: May 2004

In the honey bee drone, the decrease in sensitivity to light of a retinula cell exposed to background illumination was found to be accurately reflected by the difference in amplitude between the initial transient depolarization and the lowest steady depolarization evoked by the background light. It is shown that both the decrease in sensitivity to light and the accompanying drop in potential from the transient to the plateau can be prevented by injecting EGTA intracellularly. A decrease in duration and amplitude of responses to short test flashes such as observed immediately after illumination was found to occur too when Ca or Na, but not K, Li, or Mg injected into dark-adapted retinula cells. Injection of EGTA into a retinula cell maintained a steady state of light adaptation, was found to cause an increase in amplitude and duration of the response to a short test flash, thus producing the effects of dark adaptation. It is suggested that, in the retina of the honey bee drone, an increase in intracellular calcium concentration plays a central role in light adaptation and that an increase in intracellular sodium concentration, resulting from the influx of sodium ions during the responses to light, could lead to this increase in intracellular free calcium.
Effects of Mg and Ca on the side dependencies of Na and K on ouabain binding to red blood cell ghosts and the control of Na transport by internal Mg.
Authors: Bodemann H H , Hoffman J F
Published: May 2004

The effect of alteration in the concentration of internal Mg on the rate of ouabain binding to reconstituted human red blood cell ghosts has been evaluated as well as the effect of Mgi on Na:Na compared to Na:K exchange. It was found that the dependence of the rate of ATP-promoted ouabain binding on the combined presence of Nai and Ko which occurs at high [Mg]i is lost when the concentration of Mgi is lowered. The sensitivity of the external surface for Ko is also changed since Ko can now inhibit the ouabain binding rate in the absence of Nai; on the other hand Nao at low [Mg]i can stimulate ouabain binding indicating that the relative affinity of the outside surface for Nao has either increased or that for Ko has decreased or both. Thus the effects of changes in [Mg]i result in a change in the side-dependent actions of Na and K and emphasize the possible difficulties of interpreting results obtained on systems lacking sidedness. Mgi was found to be required for Pi-promoted ouabain binding and that the inhibitory action of Nai increased as [Mg]i was increased. In addition, Ca was found to be most effective in inhibiting the rate of ATP-promoted ouabain binding when Na and K were present together than when either was present alone. Na:K exchange was found to be more sensitive to the concentration of Mgi than Na:Na exchange; at low [Mg]i Na:K exchange could be stimulated without changing the extent of Na:Na exchange. These results are consistent with the idea that conformational states of the pump complex are directly influenced by [Mg]i.
Ion transport studies and determination of the cell wall elastic modulus in the marine alga Halicystis parvula.
Authors: Graves J S , Gutknecht J
Published: May 2004

Using cultured cells of the marine alga, Halicystis parvula, we measured the concentrations of 11 inorganic ions in the vacuolar sap and the electrical potential difference (PD) between the vacuole and the external solution. In normal cells under steady-state conditions a comparison of the electrochemical equilibrium (Nernst) potential for each ion with the PD of -82 mV (inside negative) indicates that Na+ and K+ are actively transported out of the vacuole whereas all anions are pumped into the cell. Although the [K+] in the vacuole is only 9 mM, the cytoplasmic [K+] is about 420 mM, which suggests that the outwardly directed pump is at the tonoplast. Using large Halicystis cells we perfused the vacuole with an artificial seawater and conducted a short-circuit analysis of ion transport. The short-circuit current (SCC) of 299 peq - cm-2-s-1 is not significantly different from the net influx of Cl-. There is a small, but statistically significant net efflux of K+ (less than 1 pmol-cm-2.-1), while the influx and efflux of Na+ are not significantly different. Therefore, the SCC is a good measure of the activity of the Cl- pump. Finally, we measured the volumetric elastic modulus (epsilon) of the cell wall by measuring the change in cell volume when the internal hydrostatic pressure was altered. The value of epsilon at applied pressures between 0 and 0.4 atm is about 0.6 atm, which is at least 100-fold lower than the values of epsilon for all other algae which have been studied.
Calcium transport in intact human erthrocytes.
Authors: Plishker G , Gitelman H J
Published: May 2004

Intact human erythrocytes can be readily loaded with calcium by incubation in hypersomotic media at alkaline pH. Erythrocyte calcium content increases from 15-20 to 120-150 nmol/g hemoglobin after incubation for 2 h at 20 degree C in a 400 mosmol/kg, pH 7.8 solution containing 100 mM sodium chloride, 90 mM tetramethylammonium chloride, 1 mM potassium chloride, and 10 mM calcium chloride. Calcium uptake is a time-dependent process that is associated with an augmented efflux of potassium. The ATP content in these cells remains at more than 60% of normal and is not affected by calcium. Calcium uptake is influenced by the cationic composition of the external media. The response to potassium is diphasic. With increasing potassium concentrations, the net accumulation of calcium initially increases, becoming maximal at 1 mM potassium, then diminishes, falling below basal levels at concentrations above 3 mM potassium. Ouabain inhibits the stimulatory effect of low concentrations of potassium. The inhibitory effects of higher concentrations of potassium are ouabain insensitive and independent of the external calcium concentration. Sodium also inhibits calcium uptake but this inhibition can be modified by altering the external concentration of calcium. The effux of calcium from loaded erythrocytes is not significantly altered by changes in osmolality, medium ion composition, or ouabain. It is concluded that hypertonicity increases the net uptake of calcium by increasing the influx of calcium and that some part of the sodium potassium transport system is involved in this influx process.
Propagated spikes and secretion in a coelenterate glandular epithelium.
Authors: Mackie G O
Published: May 2004

The rete mirabile of Hippopodius (Cl. Hydrozoa, O. Siphonophora) is a sheet of giant endoderm cells penetrated by branches of the ventral radial canal. The cells appear to be highly polyploid. The rough ER is very richly developed and expanded ER cisternae containing amorphous material (presumably synthesized protein) are observed near the outer cell surface. The cells are electrically coupled, and are connected by gap junctions. The rete is electrically excitable and cell to cell conduction of action potentials at 10 cm/s is observed. The action potentials are all-or-none, positive-going events, showing amplitudes of about 70 mV and arising from a 44 mV resting potential. Slowly developing and decaying secondary depolarizations, capable of summing to the 20 mV level, are also observed. After passage of a train of impulses, the rete cells swell and secretion drops appear at the surface, these changes becoming apparent within a few seconds. In 15 mM Mn2+ the response fails to occur, and secondary depolarizations ("secretion potentials") are not seen. Spike propagation is not affected. In Na+-free solutions the spikes are reduced and propagation eventually fails. It is suggested that the spikes are sodium-dependent events which trigger a calcium-dependent secretory process. The composition and biological activity of the secretion are uncertain, but indirect evidence suggests a possible defensive or repellant role for the response.
The permeability of the sodium channel in Myxicola to the alkali cations.
Authors: Ebert G A , Goldman L
Published: May 2004

Relative permeabilities to the alkali cations were determined, from the reversal potential (VRev), for the Na channel of internally perfused voltage-clamped Myxicola giant axons. PLi/PNa and PK/PNa are 0.94 and 0.076, respectively. Rb and Cs are not measurably permeant. VRev vs. the internal Na activity was well described by the constant field equation over a 300-fold range of internal Na concentrations. In agreement with findings on squid axons, the PK/PNa was found to increase when the K content of the internal perfusate was reduced (equivalent per equivalent substitution with TMA). Internal Rb and Cs also decreased the PK/PNa. The order of effectiveness of internal K, Rb, and Cs in increasing the Na selectivity of the Na channel was Cs greater than Rb greater than or equal to K. External Li increases the PK/PNa but this may be due to the formation of LiF internally. It may be that substances do not have to traverse the channel in order to affect the selectivity filter. Evidence is presented which suggests that the selectivity of the Na channel may be higher for Na in intact as compared to perfused giant axons. It was concluded that the channel selectivity properities do not reflect only some fixed structural features of the channel, but the selectivity filter has a labile organization.
Analysis of the rhodopsin cycle in limulus ventral photoreceptors using the early receptor potential.
Authors: Lisman J E , Sheline Y
Published: May 2004

The early receptor potential (ERP) was recorded intracellularly from Limulus ventral photoreceptors. The ERP in cells dissected under red light was altered by exhaustive illumination. No recovery to the original wafeform was observed, even after 1 h in the dark. The ERP waveform could be further altered by chromatic adaptation or by changes in pH. The results indicate that at pH 7.8 there are two interconvertible pigment states with only slightly different lambdamax, whereas at pH 9.6 there are two interconvertible states with very different lambdamax. Under all conditions studied the ERPs were almost identical with those previously obtained in squid retinas. This strongly suggests that light converts Limulus rhodopsin to a stable photoequilibrium mixture of rhodopsin to a stable photoequilibrium mixture of rhodopsin and metarhodopsin and that, as in squid, the lambdamax of metarhodopsin depends on pH. This conversion at pH 7.8 is associated with a small (0.7 log unit) decrease in the maximum sensitivity of the late receptor potential. Thus the component of adaptation linked to changes in rhodopsin concentration is unimportant in comparison to the "neural" component.
Effect of verapamil and of extracellular Ca and Na on contraction frequency of cultured heart cells.
Authors: McCall D
Published: May 2004

Monolayer cultures of myocardial cells were prepared by trypsin dispersion of neonatal rat ventricles. The cells were cultured for 4-5 days by which time a synchronously contracting monolayer of some 1.0 x 10(6) cells per 6-cm diam petri dish had formed. The contraction frequency and Na influx of the cells were unaffected by tetrodotoxin (2 x 10(-5) mg/ml) but both were markedly reduced by the addition of verapamil (10(-9) M to 10(-5) M). The effect of verapamil on both parameters occurred very rapidly. Although unresponsive to change in [Ca]0 between 0.3 mM and 3.0 mM, the contraction frequency of the cells declined rapidly as the [Ca]0 was reduced below 0.3 mM. On the other hand the beating rate of the cells was linearly related to [Na]0 below 40 mM the cells ceased to contract. It is therefore apparent that both [Ca]0 and [Na]0 contribute to the maintenance of the contraction frequency of cultured myocardial cells, but the latter is by far the more important. There also appeared to be, under all conditions, a close relationship between verapamilsensitive Na influx and contraction frequency. For the greater part this relationship was linear although at higher Na influx values it appeared to show evidence of saturation.
Permeability of the sodium channel in Myxicola to organic cations.
Authors: Binstock L
Published: May 2004

The relative permeability of sodium channels to organic cations was determined in the Myxicola giant axon. Ionic currents under potential control were measured in seawater and in sodium-free solutions containing the organic cation. The measured reversal potential and the Goldman equation were used to obtain the relative permeabilities. The permeability sequence was found to be: sodium greater than hydroxylamine greater than hydrazine greater than ammonium greater than guanidine greater than formamidine greater than aminoguanidine greater than methylamine. Measurements were also made on sodium and several of the organic cations at different concentrations. The relative permeabilities of the ions were found to be independent of concentration. Qualitatively, the permeability sequence for the Myxicola giant axon was similar to that of the frog node of Ranvier.
Regulation by magnesium of intracellular calcium movement in skinned muscle fibers.
Authors: Stephenson E W , Podolsky R J
Published: May 2004

The effect of Mg on Ca movement between the sarcoplasmic reticulum (SR) and myofilament space (MFS) was studied in skinned muscle fibers by using isometric force as an indicator of MFS Ca. In Ca-loaded fibers at 20 degrees C, the large force spike induced by Ca in 1 mM Mg (5 mM ATP) was strongly inhibited in 3 mM Mg, and force development was extremely slow. After a brief Ca stimulus in 1 mM Mg, relaxation in Ca-free solution was significantly faster in 3 mM Mg. These changes were due to altered Ca movements, since the effect of 3 mM Mg on steady force in CaEGTA solutions was small. Changes in Mg alone induced force transients apparently due to altered Ca movement. In relaxed fibers, decreasing the Mg to 0.25 mM caused phasic force development. In contracting fibers in Ca solutions, increasing the Mg caused a large transient relaxation. The effects of increased Mg were antagonized by 0.5 mM Cd, an inhibitor of the SR Ca transport system. The results indicate that active Ca uptake by the SR in situ is stimulated by Mg, and that it can affect local MFS [Ca++] in the presence of a substantial Ca source. These results provide evidence that an increased rate of Ca uptake in 3 mM Mg could account for inhibition of the large force spike associated with Ca-induced Ca release in skinned fibers.
Calcium-activated conductance in skate electroreceptors: current clamp experiments.
Authors: Clusin W T , Bennett M V
Published: May 2004

When current clamped, skate electroreceptor epithelium produces large action potentials in response to stimuli that depolarize the lumenal faces of the receptor cells. With increasing stimulus strength these action potentials become prolonged. When the peak voltage exceeds about 140 mV the repolarizing phase is blocked until the end of the stimulus. Perfusion experiments show that the rising phase of the action potential results from an increase in calcium permeability in the lumenal membranes. Perfusion of the lumen with cobalt or with a zero calcium solution containing EGTA blocks the action potential. Perfusion of the lumen with a solution containing 10 mM Ca and 20 mM EGTA initially slows the repolarizing process at all voltages and lowers the potential at which it is blocked. With prolonged perfusion, repolarization is blocked at all voltages. When excitability is abolished by perfusion with cobalt, or with a zero calcium solution containing EGTA, no delayed rectification occurs. We suggest that repolarization during the action potential depends on an influx of calcium into the cytoplasm, and that the rate of repolarization depends on the magnitude of the inward calcium current. Increasingly large stimuli reduce the rate of repolarization by reducing the driving force for calcium, and then block repolarization by causing the lumenal membrane potential to exceed ECa. Changes in extracellular calcium affect repolarization in a manner consistent with the resulting change in ECa.
Properties of visual cells in the lateral eye of Limulus in situ: intracellular recordings.
Authors: Barlow R B , Kaplan E
Published: May 2004

Two types of potential fluctuations, large and small, recorded intracellularly from photoreceptors in the dark-adapted Limulus eye in situ underlie the dual properties of the impulse discharge of the optic nerve fibers. The small potential fluctuations (SPFs)--the well-known quantum bumps--were normally less than 20 mV in amplitude. The large potential fluctuations (LPFs) were up to 80 mV in amplitude. LPFs appear to be regenerative events triggered by SPFs that enable single photon absorptions in retinular cells to fire off nerve impulses in the eccentric cell. In the dark, SPFs and LPFs occur spontaneously. At low light intensities, LPFs are the major components of the receptor potential. At high intensities, LPFs are suppressed and SPFs become the major components. SPFs and LPFs together enable single photoreceptor cells to encode approximately a 9-log unit range of light intensity. Excising the eye from the animal or cutting off its blood supply generally abolishes LPFs and thereby reduces the range of light intensity coded in the optic nerve discharge.
THE INFLUENCE OF ELECTROLYTES ON THE STABILITY OF RED BLOOD CORPUSCLE SUSPENSIONS
Authors: Oliver Jean , Barnard Leonard
Published: May 2004

Two types of stability are observed in suspensions of red blood cells. In weak concentrations of electrolytes the stability depends on the electric charge of the cells and suspension is unstable below a certain critical P.D.

In strong concentrations of electrolyte, the stability bears no relation to the charge.
TEMPERATURE AND FORWARD MOVEMENT OF PARAMECIUM
Authors: Glaser Otto
Published: May 2004

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.
THE PHOTOTROPIC MECHANISM IN RANATRA
Authors: Crozier W. J. , Federighi H.
Published: May 2004

Definite proof is obtained that in the phototropic orientation of Ranatra the relative postures of the appendages, resulting in a bilateral difference of effective stroke in swimming, is the mechanism of orientation; the frequency of locomotor movements is the same on the two sides of the body.
THE EFFECT OF VALENCY OF CATIONS AND ANIONS ON NEGATIVELY AND POSITIVELY CHARGED RED BLOOD CELLS
Authors: Oliver Jean , Barnard Leonard
Published: May 2004

1. Under comparable conditions, valency effect may be demonstrated with a suspension of red blood cells and the cations and anions of salts.

2. The valency of the cation determines the degree of the effect on negatively charged cells, the valency of the anion, the effect on positively charged cells.

3. Anomalies in valency effects with different salts and red cell suspensions are in part due to variations in H ion concentration, depending on the degree of hydrolysis of the salt.
THE VISUAL DISCRIMINATION OF INTENSITY AND THE WEBER-FECHNER LAW
Authors: Hecht Selig
Published: May 2004

1. A study of the historical development of the Weber-Fechner law shows that it fails to describe intensity perception; first, because it is based on observations which do not record intensity discrimination accurately, and second, because it omits the essentially discontinuous nature of the recognition of intensity differences.

2. There is presented a series of data, assembled from various sources, which proves that in the visual discrimination of intensity the threshold difference ΔI bears no constant relation to the intensity I. The evidence shows unequivocally that as the intensity rises,

the ratio

See PDF for Equation

first decreases and then increases.

3. The data are then subjected to analysis in terms of a photochemical system already proposed for the visual activity of the rods and cones. It is found that for the retinal elements to discriminate between one intensity and the next perceptible one, the transition from one to the other must involve the decomposition of a constant amount of photosensitive material.

4. The magnitude of this unitary increment in the quantity of photochemical action is greater for the rods than for the cones. Therefore, below a certain critical illumination—the cone threshold—intensity discrimination is controlled by the rods alone, but above this point it is determined by the cones alone.

5. The unitary increments in retinal photochemical action may be interpreted as being recorded by each rod and cone; or as conditioning the variability of the retinal cells so that each increment involves a constant increase in the number of active elements; or as a combination of the two interpretations.

6. Comparison with critical data of such diverse nature as dark adaptation, absolute thresholds, and visual acuity shows that the analysis is consistent with well established facts of vision.
THE KINETICS OF STARVATION
Authors: Wetzel Norman C.
Published: May 2004

1. The relative weight loss of pigeons on starving rations may be represented by a simple modification of the law of autocatalysis.

2. An equation giving the actual weight of the animals during the 53 day period of the experiment is derived by means of the hypothesis that the process of inanition is governed by the simultaneous velocity relations between two independent, homogeneous systems, such that

MT = (A0 → 0) + (B0 → BC)

in which A is taken proportional to the amount of carbohydrate-fat reserves, and B proportional to the amount of reacting body protoplasm.

3. The course of starvation is governed by the rate of destruction of body protein, but it is modified by the amount and by the rate of destruction of reserve materials.

4. The processes of breaking down tissues are analogous to those by which tissues are synthesized.

5. The close agreement between observed and calculated values suggests that the original assumptions set forth in deriving the foregoing equations were valid.

6. Attention is called to the fact that the time of onset of beriberi in pigeons is coincident with the half period of starvation.