bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Various Ions on Resting and Spike Potentials of Barnacle Muscle Fibers
Authors: Hagiwara Susumu , Chichibu Shiko , Naka Ken-ichi
Published: May 2004

Effects of monovalent cations and some anions on the electrical properties of the barnacle muscle fiber membrane were studied when the intra- or extracellular concentrations of those ions were altered by longitudinal intra-cellular injection. The resting potential of the normal fiber decreases linearly with increase of logarithm of [K+]out and the decrement for a tenfold increase in [K+]out is 58 mv when the product, [K+]out ·[Cl-]out, is kept constant. It also decreases with decreasing [K+]in but is always less than expected theoretically. The deviation becomes larger as [K+]in increases and the resting potential finally starts to decrease with increasing [K+]in for [K+]in > 250 mM. When the internal K+ concentration is decreased the overshoot of the spike potential increases and the time course of the spike potential becomes more prolonged. In substituting for the internal K+, Na+ and sucrose affect the resting and spike potentials similarly. Some organic cations (guanidine, choline, tris, and TMA) behave like sucrose while some other organic cations (TEA, TPA, and TBA) have a specific effect and prolong the spike potential if they are applied intracellularly or extracellularly. In all cases the active membrane potential increases linearly with the logarithm of [Ca++]out/[K+]in and the increment is about 29 mv for tenfold increase in this ratio. The fiber membrane is permeable to Cl- and other smaller anions (Br- and I-) but not to acetate- and larger anions (citrate-, sulfate-, and methanesulfonate-).
Discrimination between Alkali Metal Cations by Yeast
Authors: Armstrong W. McD. , Rothstein A.
Published: May 2004

Extracellular pH markedly influences the ability of yeast cells to discriminate between K+ and Na+, with K+ favored to a greater degree at low pH. Studies of the kinetics of uptake of individual alkali metal cations by fermenting yeast indicate three zones relative to pH. Between pH 6 and 8, H+ has no effect. Below pH 4, H+ competitively inhibits the transport of each cation. Between pH 4 and 6, H+ acts kinetically as a predominantly non-competitive inhibitor. Both effects can be reversed by increasing the concentrations of cations. However, the concentrations required to reverse the competitive effect are considerably lower than those required to reverse the apparently non-competitive effect. It is suggested that H+ and the alkali metal cations can combine with two sites, a transport or carrier site, and a second, non-transporting site that influences the maximal rate of transport. Because the non-competitive inhibitory effect of H+ is considerably greater on the other cations than on K+, the discrimination in favor of K+ is increased severalfold at low pH, beyond that predicted on the basis of the relative affinities for the transport site.
The Efflux of Substances from Frog Ventricles to Sucrose and to Ringer's Solutions
Authors: Van Der Kloot William G. , Dane Benjamin
Published: May 2004

The frog ventricle in sucrose solution contracts for several hours at 25°C, and for as long as 24 hours at 5°G. The possibility that a fraction of the extracellular fluid remains outside of the excitable membrane was examined by measuring the efflux of tracers. The half-time for the efflux to sucrose solution at 25°C of C14 sucrose is about 1 minute, for Na24 is 6.5 minutes, and for Cl86 is 4 minutes. There is no evidence for the retention of an extracellular Na fraction. The Q10 for Na and Cl efflux is about 1.3. The half-time for K42 efflux is about 180 minutes; the Q10 is 1.7. The efflux rates of Na24, Cl36 and K42 to sucrose and to Ringer's solutions are quite similar. Ca45 efflux is only one-fifth as fast to sucrose solution as to Ringer's; the retention of Ca++ may be important for maintaining excitability in sucrose solution. P32 efflux is five times faster to sucrose solution than to Ringer's solution, and there is a similar increase in the rate of inosine loss to sucrose solution. The Q10 for efflux to sucrose solution is 2.2 for P32O4 and 2.4 for inosine. We suggest that energy metabolism is abnormal in ventricles in sucrose solution and that low temperature prolongs excitability by slowing the metabolic change.
Ion Transport in Isolated Rabbit Ileum
Authors: Schultz Stanley G. , Zalusky Ralph , Gass Arthur E.
Published: May 2004

Unidirectional Cl fluxes across in vitro segments of rabbit ileum have been determined both in the absence and in the presence of an electrochemical potential gradient. The results indicate that Cl transport in this preparation can be attributed to purely passive forces uninfluenced by solvent drag or exchange diffusion. Furthermore, on the basis of this and previous studies, it has been demonstrated that the sum of the partial ionic conductances of Na and Cl accounts for at least 90 per cent of the total tissue conductance.
Diffusion of Weak Acids across the Toad Bladder
Authors: Rosen Herman , Leaf Alexander , Schwartz William B.
Published: May 2004

Studies have been carried out, using the toad bladder, to determine the influence of pH on the permeability coefficients (Ktrans) of the non-ionic species of (a) a series of aliphatic acids ranging from propionic to octanoic and (b) the aromatic acids, benzoic and acetylsalicylic. The data demonstrate that as the acidity of the mucosal bathing solution is increased by changing pH from 6 to 4, the fluxes of propionic, butyric, and acetylsalicylic acids increase in direct proportion to the increase in the calculated non-ionic concentration; the permeability coefficients, therefore, remain constant. However, the fluxes of the six, seven, and eight carbon aliphatic acids and benzoic acid rise only slightly despite an almost tenfold increase in non-ionic concentration, the Ktrans falling from approximately 20,000 x 10-7 cm sec.-1 at pH 6 to approximately 2500 x 10-1 cm sec.-1 at pH 4. It has been tentatively proposed that the common characteristic of the compounds exhibiting this anomalous behavior is their non-polarity and high degree of lipid solubility. Possible explanations for the differences observed between the more lipid-soluble and less lipid-soluble compounds have been considered.
The Effect of Adaptation on the Taste Threshold Observed with a Semiautomatic Gustometer
Authors: Von Békésy Georg
Published: May 2004

A special "gustometer" has been built, which permits continuous measurement of the threshold of taste sensations. Taste sensations show strong adaptation even at the threshold level. The adaptation was much the same for the four primary tastes, but there were large individual differences. Of theoretical interest is the finding that adaptation to a taste can occur even with subliminal stimuli.
Intracellular Electrical Potentials in Frog Skin
Authors: Cereijido Marcelino , Curran Peter F.
Published: May 2004

The influence of changes in ionic composition of the bathing solutions on intracellular electrical potentials in frog skin has been examined. When the skin bathed in SO4 Ringer's solution is penetrated with a microelectrode two approximately equal potential jumps were frequently observed and most experiments were carried out with the electrode located between these steps. Substitution of Cl for SO4 in the bathing solutions caused a decrease in PD across both the "outer" and "inner" barriers. When the skin was short-circuited an average intracellular potential of -18 mv was found with both Cl and SO4 Ringer's. With the skin in SO4 Ringer's, decrease in Na concentration of the outside solution caused a decrease in PD between the microelectrode and the outside solution which was approximately the same as the decrease in total skin PD. With SO4 Ringer's, an increase in K concentration in the inside solution caused a marked decrease in total skin PD. However, only 50 per cent of this change occurred at the inner barrier, between the microelectrode and the inside solution. The remainder of the change occurred at the outer barrier. This observation does not appear to be consistent with the model of the skin proposed by Koefoed-Johnson and Ussing (Acta Physiol. Scand., 1958, 42, 298).
The Effect of Mucosal and Serosal Solution Cations on Bioelectric Properties of the Isolated Toad Bladder
Authors: Gatzy John T. , Clarkson T. W.
Published: May 2004

The spontaneous transtissue potential and the DC conductance of the isolated toad bladder were measured when the tissue was exposed to sulfate Ringer's solutions of modified ionic composition. Na+ was replaced to varying extents by (C2H5)3NH+, (C2H5)4N+, Li+, Cs+, K+, or Rb+. Reversible and irreversible changes were observed. The reversible changes were consistent with equations derived from the Nernst-Planck diffusion equation, and gave the following functional description of the bladder: (a) the potential measurements were compatible with two membranes in series; (b) the mucosal surface was more permeable to Na+ than to other monovalent cations; (c) the serosal surface was permeable to both K+ and Na+ but preferentially to K+; (d) the rate of Na+ diffusion across the mucosal membrane appeared to approach a maximum but two alternative interpretations are discussed; (e) the conductance data were consistent with the assumption of a constant concentration gradient for the penetrating ions within the membrane (Henderson's assumption) provided suitable hypotheses are made concerning the Na+ distribution between the membrane surfaces and the bulk phases of the adjacent solutions; (f) the conductance and spontaneous potential data suggested that the mucosal membranes of a small fraction of the epithelial cells were more permeable than the mucosal membranes of the majority of these cells. The irreversible changes were almost entirely associated with cation substitution in the serosal solution. However, Li+ produced an irreversible fall in voltage when added to either side of the tissue.
Sodium Extrusion and Potassium Uptake in Guinea Pig Kidney Cortex Slices
Authors: Whittembury Guillermo
Published: May 2004

Slices from the cortex corticis of the guinea pig kidney were immersed in a chilled solution without K and then reimmersed in warmer solutions. The Na and K concentrations and the membrane potential Vm were then studied as a function of the Na and K concentrations of the reimmersion fluid. It was found that Na is extruded from the cells against a large electrochemical potential gradient. Q10 for net Na outflux was ∼2.5. At bath K concentrations larger than 8 mM the behavior of K was largely passive. At the outset of reimmersion (Vm > EK) K influx seemed secondary to Na extrusion. Na extrusion would promote K entrance, being limited and requiring the presence of K in the bathing fluid. At bath K concentrations below 8 mM, K influx was up an electrochemical potential gradient. Thus a parallel active K uptake is apparent. Q10 for net K influx was ∼2.0. Dinitrophenol inhibited net Na outflux and net K influx, Q10 became <1.1 for both fluxes. The ratio between these fluxes varied. Thus at the outset of reimmersion the net Na outflux to net K influx ratio was >1. After 8 minutes it was <1.
The Time Course of the Loss and Recovery of Contracture Ability in Frog Striated Muscle Following Exposure to Ca-Free Solutions
Authors: Milligan J. V.
Published: May 2004

Using area under the contracture curve to quantitate contractures, the diffusion coefficient of calcium ions within the frog toe muscle during washout in a calcium-free solution and subsequent recovery after reintroduction of calcium to the bathing solution was calculated to be about 2 x 10-6 cm2/sec. The diffusion coefficient measured during washout was found to be independent of temperature or initial calcium ion concentration. During recovery it was found to decrease if the temperature was lowered. This was likely due to the repolarization occurring after the depolarizing effect of the calcium-free solution. The relation between contracture area and [Ca]o was found to be useful over a wider range than that between maximum tension and [Ca]o. The normalized contracture areas were larger at lower calcium concentrations if the contractures were produced with cold potassium solutions or if NO3 replaced Cl in the bathing solutions. Decreasing the potassium concentration of the contracture solution to 50 mM from 115 mM did not change the relation between [Ca]o and the normalized area. If the K concentration of the bathing solution was increased, the areas were decreased at lower concentrations of Ca.
Influence of Glucose on the Transmembrane Action Potential of Anoxic Papillary Muscle
Authors: MacLeod Don P. , Daniel E. E.
Published: May 2004

The response of the cat papillary muscle to anoxia has been found to alter depending on the glucose concentration in the medium. At a glucose concentration of 5 mM anoxia caused a marked reduction in force of contraction and action potential duration within 20 minutes. At a glucose concentration of 50 mM anoxia induced similar changes in the force of contraction but little or no change in action potential duration. Elevation of glucose concentration during an anoxic interval reversed the anoxia-induced changes in action potential but had little effect on force of contraction. This effect of glucose could be partially duplicated by xylose and 2-deoxyglucose and in addition, 2-deoxyglucose has been found to prevent the effect of subsequently added glucose. These sugars appear to be transported by a system responsible for glucose transport but are not metabolized to any extent. It would appear therefore that transport of glucose is in some way related to transport of potassium as increased potassium permeability is thought by many to be responsible for anoxia-induced changes in action potential duration.
Differential Spectral Sensitivity in the Optic Tectum and Eye of the Turtle
Authors: Granda Allen M. , Stirling Charles E.
Published: May 2004

Light flashes of calibrated wavelength and intensity were presented to the turtle eye and electrical responses were simultaneously recorded from the cornea and the optic tectum. Spectral sensitivity curves derived from criterion-response levels showed a characteristic red-sensitive process at both sites. At high criterion levels the two curves were quite similar. At low criterion-response levels the tectum showed an enhanced blue-green process not evident in the peripheral record. The sensitivity to blue-green may correspond to previously observed behavior.
Electrical and Mechanical Responses in Deep Abdominal Extensor Muscles of Crayfish and Lobster
Authors: Abbott Bernard C. , Parnas I.
Published: May 2004

Electrical and mechanical studies have been made of the deep abdominal extensor muscles, medial (DEAM) and lateral (DEAL), of crayfish and lobster. The medial muscle responds to direct (intracellular) and indirect stimulation with a transient membrane depolarization which exhibits the properties of a propagated non-decremental action potential but does not overshoot the zero level. The amplitude is about 30 mv in crayfish and 50 mv in lobster. It is followed by a fast all-or-none twitch whose duration at 20°C is 30 to 50 msec. and whose developed tension is 500 gm/cm2 or about half the tetanic value. Membrane potential is K+-dependent and immersion in high K+ induces a brief transient tension rise as in other twitch-type muscles. The action potential and twitch are normal even if all external Na+ is replaced with sucrose but vary with external Ca++, the action potential increasing 8 to 10 mv for a twofold increase in Ca++. The lateral muscle (DEAL) is much slower and responds to intracellular stimulation only with an electrotonic or a local response. Mechanical responses and relaxation speeds are slow with minimal duration of contraction of 0.5 to 2 seconds. Immersion in high K solutions induces large maintained tensions. Sarcomere length in the fast DEAM is uniform and about 2 µ at rest, but in the DEAL speed is less and sarcomere length is greater averaging about 4.5 µ but with a mixed population of fibers.
Isotope Flows and Flux Ratios in Biological Membranes
Authors: Kedem Ora , Essig Alvin
Published: May 2004

Precise evaluation of permeability of biological tissues is often prevented by imprecise knowledge of operative forces. This problem has been approached by analysis of fluxes of isotopic species applied to opposite surfaces of a membrane. A simple and rather general flux ratio equation has been derived which may permit evaluation of membrane permeability, even without knowledge of forces, or of the nature of active transport processes. Permeability as thus defined should be insensitive to coupled flows, either of other species or of metabolism. In appropriate circumstances application of the equation may permit evaluation of the contributions of the various processes to the transport of the examined species. Composite series membranes would be expected to obey the unmodified general equation. Heterogeneous parallel pathways would alter the relation in a predictable manner. The effect of isotope interaction is specifically incorporated. The formulation is applied to consideration of energetics of active transport.
Separation of Adenosine Triphosphatase of HK and LK Sheep Red Cell Membranes by Density Gradient Centrifugation
Authors: Tosteson D. C. , Cook P. , Blount R.
Published: May 2004

Membrane fragments from high potassium (HK) and low potassium (LK) sheep red cells were separated by density gradient centrifugation. Three preparations were studied: (1) HK membranes sonicated for 20 minutes, (2) HK membranes sonicated for 3 minutes, and (3) LK membranes sonicated for 3 minutes. The adenosine triphosphatase (ATPase) activity in the maximally disrupted preparation (1) was not sensitive to Na + K and was recovered in relatively small but heavy (specific gravity 1.19) fragments which made up no more than 8 per cent of the total membrane. Both Na + K-sensitive (S) and Na + K-insensitive (I) ATPase activity were found in the more gently broken up preparations (2) and (3) but the ratio of S- to I-ATPase was much greater in HK than in LK membrane fragments. S-ATPase activity in preparation (2) was about 50 per cent that observed in HK membranes prior to sonication. S-ATPase activity was recovered from the density gradient in relatively large but light (specific gravity 1.10) fragments. As was the case with the maximally disrupted preparation (1), I-ATPase activity in both preparations (2) and (3) was recovered in small but heavy (specific gravity > 1.20) fragments. The possibility that sensitivity of sheep red cell membrane ATPase to Na + K depends on the association between units containing the enzyme(s) and large, light, phospholipid-containing components is discussed.
The Location of Muscle Calcium with Respect to the Myofibrils
Authors: Winegrad Saul
Published: May 2004

Autoradiographs have been prepared from frog toe muscles soaked in Ca45 and fixed with an osmium-oxalate solution. A majority of the grains over the A bands were over the myofibrils. The grain density over the I bands was greatest over the space between the myofibrils. The significance of this distribution is discussed in the light of previous information about the longitudinal distribution of Ca45 in skeletal muscle.
Sodium, Potassium, and Chloride Concentrations in the Schwann Cell and Axon of the Squid Nerve Fiber
Authors: Villegas Jorge , Villegas Leopoldo , Villegas Raimundo
Published: May 2004

Sodium, potassium, and chloride concentrations were determined in the sheath cells and axoplasm of the nerve fiber of the squid Sepioteuthis sepioidea. The sheaths were obtained by slitting the nerve fiber, the extracellular electrolytes were washed out in isotonic sucrose solution, and the concentrations in the cells were determined after different soaking times in the sucrose solution. Values for the Schwann cell were calculated by extrapolation to zero time from the plots of the logarithms of the concentrations in the cells as a function of soaking time in sucrose solution. The Schwann cells made up 84 per cent of the sheath's total cellular volume. The Schwann cell concentrations in millimols per liter, are: 312 (404-241) for sodium, 220 (308-157) for potassium, and 167 (208-138) for chloride. The concentrations in the axoplasm (mean ± SE), in millimols per liter are: 52 ± 10 for sodium, 335 ± 25 for potassium, and 135 ± 14 for chloride. The possibility that some fraction of the Schwann cell electrolytes, especially of sodium, is bound, cannot be discarded.
Cation Transport in Escherichia coli
Authors: Epstein Wolfgang , Schultz Stanley G.
Published: May 2004

Measurement of cellular K and Na concentrations in growing Escherichia coli indicates that the osmololity of the medium is a major determinant of the cell K concentration. In contrast, the cell Na concentration is independent of the medium osmolality and is largely dependent on the Na concentration of the medium. Sudden changes in the osmolality of the medium lead to rapid changes in K content. Washing the cells with solutions of lower osmolality results in a very rapid loss of K, which is greater in more dilute and in cold solutions. A sudden increase in the osmolality of the growth medium produces a rapid uptake of K by a mechanism whose rate is a saturable function of the K concentration of the medium and which appears to involve an exchange of K for cellular H.
Analysis of Spike Electrogenesis and Depolarizing K Inactivation in Electroplaques of Electrophorus electricus, L
Authors: Nakamura Yutaka , Nakajima Shigehiro , Grundfest Harry
Published: May 2004

Voltage clamp analyses, combined with pharmacological tools demonstrate the independence of reactive Na and K channels in electrically excitable membrane of eel electroplaques. Spike electrogenesis is due to Na activation and is eliminated by tetrodotoxin or mussel poison, or by substituting choline, K, Cs, or Rb for Na in the medium. The K channels remain reactive, but K activation is always absent, the electroplaques responding only with K inactivation. This is indicated by an increased resistance when the membrane is depolarized by more than about 30 mv. The resting resistance (1 to 5 ohm cm2) is dependent upon the ionic conditions, but when K inactivation occurs the resistance becomes about 10 ohm cm2 in all conditions. K inactivation does not change the EMF significantly. The transition from low to high resistance may give rise to a negative-slope voltage current characteristic, and to regenerative inactivation responses under current clamp. The further demonstration that pharmacological K inactivation (by Cs or Rb) leaves Na activation and spike electrogenesis unaffected emphasizes the independence of the reactive processes and suggests different chemical compositions for the membrane structures through which they operate.
The Spread of Excitation in the Embryonic Chick Heart
Authors: Lieberman Melvyn , Paes de Carvalho Antonio
Published: May 2004

The spread of excitation in embryonic chick hearts, ranging in age from 7 to 20 days, was studied with both intracellular and extracellular electrodes. Evidence that the delay in ventricular excitation could be attributed to the cells of the entire atrioventricular (AV) ring was obtained, in part, from sagittal sections of the heart. In the intact preparation, uniform propagation occurred throughout the atrial roof at an apparent conduction velocity of 0.4 to 0.5 meter/sec. Delay of impulse propagation was localized in a very narrow band of tissue which extended across the AV ring. The apparent conduction velocity of this tissue was between 0.003 and 0.005 meter/sec. Both normal and retrograde propagation revealed the spread of conduction across the AV ring to be decremental in nature. This finding was supported by high frequency stimulation experiments which gave rise to AV block localized in the cells of the AV ring. Cardiac rhythmicity and AV transmission were responsive to acetylcholine and norepinephrine in much the same manner as in the adult mammalian heart. The present findings are in support of the hypothesis that the embryonic AV ring is the functional counterpart of the adult AV node.
Muscle Volume Changes
Authors: Baskin R.J. , Paolini P.J.
Published: May 2004

Measurements have been made of the volume changes accompanying single isometric and isotonic twitches of frog sartorius muscle. The volume change consists of a rapid increase, a subsequent decrease, and a return to the initial volume; the order of magnitude of increase and decrease is 10-5 cc/g of muscle. This volume change is length-dependent: the initial increase becomes more pronounced as the initial length of the muscle is decreased, while the volume decrease is greatest at reference length and is diminished for longer and shorter initial lengths. Muscle volume changes are also dependent upon temperature and amount of shortening: the return phase is prolonged as the temperature is lowered; and, in an isotonic twitch, a volume increase accompanying muscle shortening is superimposed upon the volume change described for an isometric twitch. These "shortening volume changes" may correspond to the volume decrease observed in frog muscle under a passive stretch. If the active state is prolonged by the use of a frog Ringer solution in which iodide ions have been substituted for chloride ions, the time course of the volume decrease is likewise prolonged; this suggests a relationship between the volume decrease and the active state of the muscle.
Interpretation of Tracer Washout Curves from a Population of Muscle Fibers
Authors: Zierler Kenneth L.
Published: May 2004

Consideration is given to the role of a population of muscle fibers of distributed diameters in the observed washout of a tracer, with particular reference to radioisotopic K and muscle fibers. It is concluded that if washout of tracer from a single fiber is described as first order, then washout of tracer from a population of fibers is apt to appear as first order.
Effects of Dinitrophenol and Oligomycin on the Coupling between Anaerobic Metabolism and Anaerobic Sodium Transport by the Isolated Turtle Bladder
Authors: Bricker Neal S. , Klahr Saulo
Published: May 2004

Dinitrophenol (1 x 10-5 M) has been found to inhibit anaerobic sodium transport by the isolated urinary bladder of the fresh water turtle. Concurrently, anaerobic glycolysis was stimulated markedly. However, tissue ATP levels diminished only modestly, remaining at approximately 75% of values observed under anaerobic conditions without DNP. The utilization of glucose (from endogenous glycogen) corresponded closely to that predicted from the molar quantities of lactate formed. Thus the glycolytic pathway was completed in the presence of DNP and if ATP were synthesized normally during glycolysis, synthesis should have been increased. On the other hand, the decrease in Na transport should have decreased ATP utilization. Oligomycin did not block sodium transport either aerobically or anaerobically, but ATP concentrations did decrease. When anaerobic glycolysis was blocked by iodoacetate, pyruvate did not sustain sodium transport thus suggesting that no electron acceptors were available in the system. Two explanations are entertained for the anaerobic effect of DNP: (a) Stimulation by DNP of plasma membrane as well as mitochondrial ATPase activity; (b) inhibition of a high energy intermediate derived from glycolytic ATP or from glycolysis per se. The arguments relevant to each possibility are presented in the text. Although definitive resolution is not possible, we believe that the data favor the hypothesis that there was a high energy intermediate in the anaerobic system and that this intermediate, rather than ATP, served as the immediate source of energy for the sodium pump.
The Steady-State Transport of Oxygen through Hemoglobin Solutions
Authors: Keller K. H. , Friedlander S. K.
Published: May 2004

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated.
Studies on the in Vitro Interaction of Electrical Stimulation and Ca++ Movement in Sarcoplasmic Reticulum
Authors: Lee Kwang S. , Ladinsky Herbert , Choi Sin J. , Kasuya Y.
Published: May 2004

Sarcoplasmic reticulum fragments (S.R.F.) were isolated from skeletal and heart muscles. These fragments were found to take up Ca++ very actively from media. When monophasic square waves were passed through the S.R.F. suspension, the Ca++ uptake by S.R.F. was decreased. When the suspension was stimulated electrically after the Ca++ was taken up by S.R.F., the initiation and the cessation of the stimulation were followed by the release and re-uptake of Ca++ by S.R.F., respectively. The degree of inhibition of the Ca++ uptake as well as of the Ca++ release by electrical stimulation was dependent on the voltage and the frequency of stimulation. The presence of inorganic phosphate or oxalate modified the influence of electrical stimulation on the release and the uptake of Ca++ by S.R.F. Attempts were made to observe the release of Ca++ by electrical stimulation from unfractionated sarcoplasmic reticulum remaining in myofibers, and the interaction of the released Ca++ with myofibrils in vitro. For this purpose, the glycerol-extracted fiber was selected as a muscle model, since it contains both sarcoplasmic reticulum and myofibrils. It was found that electrical stimulation of skeletal and heart glycerol-extracted fibers resulted in the contraction of fibers. It appeared that the contraction of glycerol fibers by electrical stimulation was caused by the Ca++ release from sarcoplasmic reticulum by stimulation.
Cellular Electrophoretic Mobility and the Mitotic Cycle
Authors: Mayhew E.
Published: May 2004

The electrophoretic mobility of RPMI No. 41 cells grown in suspension, parasynchronized by double thymidine blocking and cold shock, is reported. No. 41 cells have a higher electrophoretic mobility during the mitotic peak phase than at other times in the mitotic cycle. Treatment of parasynchronous cells by neuraminidase reduces the mobility to the same value irrespective of the stage of the cells in the mitotic cycle. The higher electrophoretic mobility of cells in mitotic peak phase is probably due to a higher surface charge density at this time, possibly caused by a higher concentration of ionized neuraminic acid carboxyl groups at the hydrodynamic shear layer. The mobility of nonsynchronous rapidly and slowly growing cells differs; neuraminidase reduces their mobility by proportionately similar amounts. The results suggest that the differences in mobility between rapidly and slowly growing cells cannot be accounted for exclusively by differences in the amount of neuraminic acid groups at the shear layer.
The Cellular Transport of Calcium in Rat Liver
Authors: Wallach Stanley , Reizenstein David L. , Bellavia Josephine V.
Published: May 2004

The bidirectional transport of calcium in rat liver was studied using slices labeled with Ca47 in a closed two compartment system. Steady-state conditions were observed with influx and efflux transfer coefficients of 0.070 and 0.018 per minute, respectively. The rapidly exchanging cell fraction of calcium existed at a concentration three times higher than the average cell concentration of calcium and occupied cell loci comprising less than 25% of the cell mass, suggesting that calcium associated with the cell membranes, nuclei, and mitochondria participated in the rapidly exchanging fraction. At pH 7.4 and 377deg;C, the influx transfer coefficient was 25% above the steady-state condition and accumulation of calcium by the slices occurred. Studies of the effects of varied physical and chemical conditions revealed that the influx transfer coefficient was increased by elevated pH, strontium, certain metabolic inhibitors, and 2 mM concentrations of cyclic adenosinemonophosphate and adenosinetriphosphate. The influx transfer coefficient was decreased by reduced temperature, decreased pH, magnesium, and 10 mM adenosinetriphosphate. The efflux transfer coefficient was increased by elevated pH, strontium, iodoacetate, and adenosinetriphosphate, and was decreased by reduced temperature and by N-ethylmaleimide. These data support the thesis that cell transport of calcium is accomplished by the attachment of calcium atoms to the cell surface and transport through the plasma membrane bound to either specific carriers or to membrane constituents. Conditions which change the affinities, capacities, and mobilities of plasma membrane ligands that bind calcium or cause extracellular chelation of calcium are capable of altering the rate of calcium transport.
Temperature Characteristics of Excitation in Space-Clamped Squid Axons
Authors: Guttman Rita ,   with the technical assistance of Robert Barnhill
Published: May 2004

Temperature characteristics of excitability in the squid giant axon were measured for the space-clamped axon with the double sucrose gap technique. Threshold strength-duration curves were obtained for square wave current pulses from 10 µsec to 10 msec and at temperatures from 5°C to 35°C. The threshold change of potential, at which an action potential separated from a subthreshold response, averaged 17 mv at 20°C with a Q10 of 1.15. The average threshold current density at rheobase was 12 µa/cm2 at 20°C with a Q10 of 2.35 compared to 2.3 obtained previously. At short times the threshold charge was 1.5·10-8 coul/cm2. This was relatively independent of temperature and occasionally showed a minimum in the temperature range. At intermediate times and all temperatures the threshold currents were less than for both the single time constant model and the two factor excitation process as developed by Hill. FitzHugh has made computer investigations of the effect of temperature on the excitation of the squid axon membrane as represented by the Hodgkin-Huxley equations. These are in general in good agreement with our experimental results.
A Kinetic Model for Adaptation and the Light Responses of Phycomyces
Authors: Castle Edward S.
Published: May 2004

A kinetic model is described consisting of two sequential first order processes connected by two parallel reaction pathways, one of which is light-catalyzed. A change in light flux changes the rate constant of the light-dependent process, whereupon the levels of two chemical intermediaries readjust. The model's output duplicates all the main features of the cell's light-growth and dark-growth responses except their latent periods. An asymmetric modification of the model reproduces the two types of phototropic inversion discovered by Reichardt and Varjú and by Dennison. Simple exponential equations describe these responses of the model, as well as the theoretical course of its light and dark adaptation. It is concluded that adaptation in Phycomyces consist in the photocatalytic adjustment of the level of a metabolic reservoir.
Theoretical Effect of Temperature on Threshold in the Hodgkin-Huxley Nerve Model
Authors: Fitzhugh Richard
Published: May 2004

In the squid giant axon, Sjodin and Mullins (1958), using 1 msec duration pulses, found a decrease of threshold with increasing temperature, while Guttman (1962), using 100 msec pulses, found an increase. Both results are qualitatively predicted by the Hodgkin-Huxley model. The threshold vs. temperature curve varies so much with the assumptions made regarding the temperature-dependence of the membrane ionic conductances that quantitative comparison between theory and experiment is not yet possible. For very short pulses, increasing temperature has two effects. (1) At lower temperatures the decrease of relaxation time of Na activation (m) relative to the electrical (RC) relaxation time favors excitation and decreases threshold. (2) For higher temperatures, effect (1) saturates, but the decreasing relaxation times of Na inactivation (h) and K activation (n) factor accommodation and increased threshold. The result is a U-shaped threshold temperature curve. R. Guttman has obtained such U-shaped curves for 50 µsec pulses. Assuming higher ionic conductances decreases the electrical relaxation time and shifts the curve to the right along the temperature axis. Making the conductances increase with temperature flattens the curve. Using very long pulses favors effect (2) over (1) and makes threshold increase monotonically with temperature.
Some Properties of DNA from Phage-Infected Bacteria
Authors: Smith M. G. , Skalka A.
Published: May 2004

Replicating T5 or λ phage DNA has been labeled by adding tritiated thymidine for short periods to cultures of phage-infected Escherichia coli before isolation of intracellular DNA. Two procedures are described for separating T5 replicating DNA from DNA of intracellular phage particles. Both T5 and λ replicating DNA had the same bouyant density in cesium chloride as DNA from phage particles but sedimented faster when centrifuged in sucrose density gradients. The fast sedimentation did not appear to be caused by DNA protein or DNA-RNA complexes or by aggregation of DNA, but is probably due to DNA molecules of unusual structure. Experiments involving hydrodynamic shear and sucrose density gradient centrifugation at alkaline pH have suggested that with λ the replicating form of DNA is a linear molecule considerably longer than the DNA molecules of λ-phage particles. The constituent polynucleotide chains of λ but not T5 replicating DNA also appear to be longer than those of phage DNA.
On the Mechanism of Integration of Transforming Deoxyribonucleate
Authors: Fox Maurice S.
Published: May 2004

The characteristics of the intermediates in the reaction, between DNA and pneumococcus, that results in genetic transformation are described in so far as they have been characterized. Transformation with DNA isolated from bacteria carrying in addition to genetic markers 32P as a radioactive label and 2H and 15N as density labels has permitted the characterization of the product of recombination between the newly introduced DNA and the DNA of a recipient bacterium. The evidence for a single strand displacement mechanism producing a hybrid structure in the DNA of the recipient bacteria is presented. Progeny of single transformants have been examined. The results of these segregation studies permit the further characterization of this hybrid product of transformation as a genetically heterozygous structure.
On the Nature of Recombinants Formed during Transformation in Hemophilus influenzae
Authors: Notani Nihal , Goodgal Sol H.
Published: May 2004

During the process of transformation in Hemophilus influenzae integration of donor DNA, i.e. the formation of recombinant DNA, involves the incorporation of single-stranded DNA. Evidence was obtained from cesium chloride density gradient centrifugation of DNA from donor-recipient complexes that integration was accompanied by the formation of hybrid DNA with a density intermediate with respect to heavy, 2H, 15N, donor and light, 1H, 4N recipient DNA. On denaturation the position of the heavy donor DNA moved closer to, but not all the way toward, the density position of the original donor DNA. In addition to supporting the idea of single-stranded incorporation, this evidence suggested that the integrated donor DNA was covalently linked to light recipient DNA. The DNA was taken up in the double-stranded form and no detectable amounts of denatured DNA could be found during the transformation process. However, during the process of integration an amount of donor atoms, equivalent to the amount of hybrid DNA formed, appeared in recipient DNA, and indicated that while one strand of DNA was integrated the other was broken down and resynthesized. The density of the hybrid DNA, as well as rebanding of denatured hybrid, indicated that the size of the integrated piece of DNA was large, approximately 6 x 106 daltons.
Genetic Studies of Recombining DNA in Pneumococcal Transformation
Authors: Ephrussi-Taylor Harriett , Gray Thomas C.
Published: May 2004

The results of genetic fine structure experiments, performed on the amiA locus of Pneumococcus are summarized. The peculiar feature of transformation genetics is that a given donor marker mutation transforms with an efficiency characteristic of the mutated site. In spite of this difficulty, mapping procedures have been devised and quantitative recombination studies performed. It is concluded from these studies that transformation, in this locus, is the consequence of frequent, and essentially random exchanges occurring between donor DNA and the chromosomal DNA of the recipient cell. The average length of uninterrupted donor DNA polynucleotide strand which could be inserted into the chromosome of a transformed cell is estimated, from genetic data, to be probably not greater than 3·105 daltons (for a double-stranded insertion). It is proposed, on the basis of genetic evidence, that following essentially random exchanges between donor DNA and recipient chromosome, a revision process, specific for certain types of mutated sites, occurs. The revision process appears to remove preferentially donor DNA sequences from the primary recombinant structure, and allow repair along the chromosomal template, leading to low efficiency in the genetic integration of these sites. A mechanism for this "destruction-choice" process is presented, and evidence in support of this mechanism discussed.
Integration of Deoxyribonuclease-Treated DNA in Bacillus subtilis Transformation
Authors: Bodmer Walter F.
Published: May 2004

Normal preparations of B. subtilis DNA have weight average native molecular weights of 10 to 30 x 106. For any given preparation the upper and lower 95% size limits may differ by a factor of ten or more. Single-stranded molecular weights indicate an average of 1 to 4 breaks per single strand of the native DNA. The reduction in transforming activity and viscosity following DNAase I digestion can be accounted for by a direct relationship between the transforming activity of a DNA and its single-stranded molecular weight. Uptake studies with DNAase I treated heavy (2H15N 3H) DNA show that single strand breaks inhibit integration less than transformation. A provisional estimate of the size of the integrated region based on correlating the single strand size of the donor-recipient complex with the donor-recipient density differences following alkali denaturation came to 1530 nucleotides. Using a competent, nonleaky thymine-requiring strain of B. subtilis grown in 5-BU medium before and after transformation, it was shown that (a) No detectable amount of DNA synthesis is necessary for the initial stages of integration, (b) Cells which have recently been replicating DNA are not competent. (c) Cells containing donor DNA show a lag in DNA replication following transformation, (d) When donor DNA is replicated it initially appears in a density region between light and hybrid. This indicates that it includes the transition point formed at the time of reinitiation of DNA synthesis in the presence of 5-BU following transformation. A model is proposed in which donor DNA is integrated at the stationary growing point of the competent cell, which is in a state of suspended DNA synthesis.
The Structure and Function of the DNA from Bacteriophage Lambda
Authors: Hogness David S.
Published: May 2004

The position and orientation of genes in lambda and lambda dg DNA are described. The position of six genes located in the right half of isolated lambda DNA was found to be -(N, iλ)--O-P---Q-R-(right end of DNA), which is their order on the genetic map of the vegetative phage. The order of the three genes of the galactose operon (k, t, and e) located in the left half of lambda dg DNA was found to be (left end of DNA)----k-t-e-, consistent with Campbell's model (5) for the formation of this variant. Gene orientation, defined as the direction of transcription along the DNA, is inferred to be from right to left for the galactose operon in lambda dg DNA. The strand of lambda DNA which functions as template in transcription of N, an "early" gene required for normal replication of lambda DNA, was determined as a first step in ascertaining the orientation of this gene. The method includes isolation of each strand, formation of each of two heteroduplex molecules consisting of one strand from wild-type and one from an N mutant) and comparison of their N activities. The second step, which consists of ascertaining the 5'-to-3' direction of each strand, is discussed, as is a determination of the orientation of gene R.
Enzymatic Mechanisms of DNA Replication
Authors: Mitra Sankar , Kornberg Arthur
Published: May 2004

DNA polymerases purified from several sources are characterized by replication of the 3'-hydroxy-terminated strand of a helical template. Failure to achieve simultaneous replication of the 5'-strand leads to aberrations in the synthesized DNA, described as nondenaturability and branching. Aberrations in synthesized DNA were not observed when (a) the 5'-strand was destroyed by a specific nuclease during the course of replication or (b) a single-stranded (circular) phage (M13) DNA served as template. Replication of a single-stranded, circular DNA produced a helical product, but the nature of initiation of a new strand by the circular template remains to be explained. Hypothetical mechanisms for simultaneous replication of the 5'-strand are presented as is the possibility that the tertiary structure of the DNA, as for example, a circular form of the helix, is of prime importance in in vivo replication.
Caffeine- and Potassium-Induced Contractures of Frog Striated Muscle Fibers in Hypertonic Solutions
Authors: Caputo Carlo
Published: May 2004

The effect of hypertonic solutions on the caffeine- and KCl-induced contractures of isolated fibers of frog skeletal muscle was tested. Hypertonic solutions, twice the normal osmotic strength, prepared by adding NaCl or sucrose, potentiate the caffeine-induced contractures. The fibers may develop tensions of 3.6 kg/cm2 of fiber transverse section. The same hypertonic medium reduced the peak tension of KCl-induced contractures. Thus the hypertonic condition does not affect the contractile mechanism itself. These findings give further support to the view that the differential effect of hypertonic solution is on the excitation-contraction coupling mechanism. Extracellular calcium is not essentially required for the first few of a series of caffeine-induced contractures either in hypertonic or in isotonic solutions.