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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Osmotic and diffusion permeabilities (P(f) and P(d)) of invertebrate nerve fibers to tritiated water were measured to determine what water flux studies could reveal about "the nerve membrane" and to directly test the possibility of active transport of water into or out of invertebrate nerve fibers. P(f)/P(d) ratios for lobster walking leg nerve fibers were found to be about 20 +/- 7 at 14 degrees C. P(d) measurements were made for squid giant axons at 25 degrees C. and found to yield a value of 4 x 10(-4) cm.(-1) sec.(-1). When combined with the data of D. K. Hill for P(f), a P(f)/P(d) ratio of 21 +/- 5 is obtained. These P(f)/P(d) ratios correspond to "effective pore radii" of about 16 +/- 4 angstrom units, according to theories developed by Koefoed-Johnsen and Ussing and independently by Pappenheimer and his colleagues. Variations of water flux ratios with temperatures were studied and apparent activation energies calculated for both diffusion experiments and osmotic filtration experiments using the Arrhenius equation, and found to be close to 3 to 5 cal. per mole of water transferred. Cyanide (5 x 10(-3) molar) and iodoacetate (1 x 10(-3) molar) poisoned lobster leg nerve fibers showed no appreciable change in diffusion or osmotic filtration water effluxes. Caution in interpreting these proposed channels as simple pores was emphasized, but the possibility that such channels exist and are related to ionic flow is not incompatible with electrophysiological data.
J Gen Physiol 1958 May 20
PMID:Water transport in invertebrate peripheral nerve fibers. 1352 75

A study is presented on the effect of temperature on unidirectional active ion transport, resting electrolyte equilibrium (electrolyte composition), and oxygen consumption in isolated frog skin. The aims were twofold: first, to find out whether the rate of active transport can be changed without affecting the Na(+) and K(+) balance of skin itself; second, to arrive at minimal DeltaNa/DeltaO(2) values by correlating quantitatively inhibition of active ion transport with inhibition of O(2) consumption. NaCl transport was maximal at 20 degrees C. At 28 degrees and at temperatures below 20 degrees , rate of NaCl transport was diminished. In many instances NaCl transport was diminished in skins which maintained their normal Na(+) and K(+) content. In several cases, however, neither rate of transport nor resting electrolyte equilibrium was affected; in other cases, both were. O(2) consumption decreased when lowering the temperature over the range from 28 to 10 degrees C. From a plot of log Q(OO2) against 1/T an activation energy of micro 13,700 cal. was calculated, valid for the range from 10 to 20 degrees C. It appeared that micro was smaller for temperatures above 20 degrees C. Working between 10 and 20 degrees , it was found that, on the average, 4 to 5 equivalents of Na(+) were transported for one mole of O(2) consumed in skins with undisturbed resting electrolyte equilibrium.
J Gen Physiol 1959 Jan 20
PMID:Effect of temperature on electrolyte metabolism of isolated frog skin. 1362 Aug 83

The dependence of PC(1) and ATP(1) dephosphorylation on the number of isometric twitches in the iodoacetate-nitrogen-poisoned muscle has been examined. There is no net dephosphorylation of adenosinetriphosphate. PC dephosphorylation varies linearly with the number of twitches and produces equivalent amounts of C(1) and P(1i).(1) Iodoacetate concentrations which block the enzyme, creatine phosphokinase, render the muscle non-contractile. A value of 0.286 micromole/gm. for the amount of PC split per twitch is obtained which gives a value of -9.62 kcal./mole for the "physiological" heat of hydrolysis of PC in agreement with expectations based on thermochemical data. In a single maximal isometric twitch it is estimated that 2 to 3 PC molecules are dephosphorylated per myosin molecule, or 1 per actin molecule. The results support the view that under the conditions of these experiments PC dephosphorylation is the net energy yielding reaction. The in vivo stoichiometry of the mechano-chemistry of contraction revealed by these studies on the one hand, and the known stoichiometry of actin polymerization and its coupling to the creatine phosphokinase system on the other are strikingly similar and strongly suggest that the reversible polymerization of actin is involved in a major way in the contraction-relaxation-recovery cycle of muscle.
J Gen Physiol 1960 Sep
PMID:The mechanochemistry of muscular contraction. I. The isometric twitch. 1369 Aug 28

Charge transfer through the receptor membrane of the nonmyelinated ending of Pacinian corpuscles is markedly affected by temperature. The rate of rise and the amplitude of the generator potential in response to a constant mechanical stimulus increase with temperature coefficients of 2.5 and 2.0 respectively. The duration of the falling phase, presumably a purely passive component, and the rise time of the generator potential are but little affected by temperature. The following interpretation is offered: Mechanical stimulation causes the conductance of the receptor membrane to increase and ions to flow along their electrochemical gradients. An energy barrier of about 16,000 cal/mole limits the conductance change. The latter increases, thus, steeply with temperature, causing both the rate of rise and the intensity of the generator current to increase. The membrane of the adjacent Ranvier node behaves in a distinctly different manner. The amplitude of the nodal action potential is little changed over a wide range of temperature, while the durations of its rising and falling phases increase markedly. The electrical threshold of the nodal membrane is rather constant between 40 and 12 degrees C. Below 12 degrees C the threshold rises, and the mechanically elicited generator current fails to meet the threshold requirements of the first node. Cold block of nerve impulse initiation then ensues, although the receptor membrane still continues to produce generator potentials in response to mechanical stimulation.
J Gen Physiol 1961 Sep
PMID:Effects of temperature on the generator and action potentials of a sense organ. 1371 6

A quantitative study was made of the repetitive response of the salt receptor cell of the blowfly taste receptor. The response begins at a high frequency and declines to a steady frequency during brief stimuli. The initial response was found to be a sigmoid function of the log of stimulus intensity over a short range of intensities. It was shown that a theory (Beidler, 1954; for mammalian salt receptors) that relates the magnitude of the steady response to stimulus intensity applies to this receptor. From the theory, it was calculated that the relative free energy change of the reaction between salt and receptor site was in the range 0 to -1 kcal/mole; and, therefore, the reaction probably involves weak physical forces. Evidence is given that the salt-combining sites of the receptor are anionic and strongly acidic and that consequently the cation of a salt largely dominates stimulation. Preliminary evidence suggests that the receptor has a high degree of specificity toward salts, being stimulated primarily by monovalent inorganic cations.
J Gen Physiol 1962 Mar
PMID:Stimulation of a primary taste receptor by salts. 1389 Sep 72

An attempt has been made to assess the validity of applying the frictional and viscous coefficients of bulk water to the movement of water and solutes through the urinary bladder of the toad. The temperature dependence of diffusion of THO, C(14)-urea, C(14)-thiourea, and net water transfer across the bladder was determined in the presence and absence of vasopressin. The activation energy for diffusion of THO was 9.8 kcal per mole in the absence of vasopressin and 4.1 kcal per mole with the hormone present. Activation energies simultaneously determined following vasopressin for diffusion and net transfers of water were similar, and in the same range as known activation energies for diffusion and viscous flow in water. Urea had activation energies for diffusion of 4.1 and 3.9 kcal per mole in the absence and presence of vasopressin, respectively. Thiourea had a high activation energy for diffusion of 6.3 kcal per mole, which was unchanged, 6.6 kcal per mole, following hormone. These findings suggest that in its rate-limiting permeability barrier, water is present in a structured state, offering a high resistance to penetration by water. Vasopressin enlarges the aqueous channels so that the core of water they contain possesses the physical properties of ordinary bulk water. Urea penetrates the tissue via these aqueous channels while thiourea is limited by some other permeability barrier.
J Gen Physiol 1962 May
PMID:The state of water in the isolated toad bladder in the presence and absence of vasopressin. 1390 90

The present study is concerned with the measurement of the unidirectional K flux in E. coli. Methods are described by means of which a fairly dense suspension of cells may be maintained in a well defined steady-state with respect to the intracellular K concentration and the pH of the medium. The kinetics of K(42) exchange under these conditions are consistent with the presence of a single intracellular K compartment with a unidirectional K flux of 1 pmol/(cm(2) sec.). This rate is independent of the extracellular K concentration over the range studied. The simultaneous rate of H secretion averages 16 pmols/(cm(2) sec.) indicating that in the steady-state the efflux of metabolically produced H is not linked mole for mole to K movement.
J Gen Physiol 1962 Nov
PMID:Cation transport in Escherichia coli. III. Potassium fluxes in the steadystate. 1398 37

Twice washed mitochondria from rat kidney cortex can accumulate sulfate ions from low (10(-7)M) ambient concentrations to create virtual gradients of several hundred to one. This sulfate is subsequently released. The activation energy for the uptake is 12,000 calories per mole; for release it is about 30,000 calories per mole. Variations in the sulfate concentration of the medium show that there is a straight line Freundlich adsorption isotherm over a million-fold range of concentration of sulfate in the medium. There are 9 x 10(4) sites at 10(-5)M and 9 x 10(5) sites at 10(-3)M sulfate per average single mitochondrion. Preincubation at 30 degrees C rapidly destroys the ability to accumulate sulfate. Partial protection occurs if oxidative phosphorylation is proceeding during the preincubation. The concentration of the endogenous inorganic sulfate of twice washed mitochondria is 4.2 x 10(-4) moles per liter of mitochondrial pellet water; 99.85 per cent of this endogenous sulfate is inexchangeable with external sulfate in vitro. It is all exchangeable in vivo. The pH optimum for accumulation of radiosulfate from dilute external sulfate concentrations is 5.5. These observations show that there is a delicate and specific mechanism in mitochondria from kidney cortex which accumulates sulfate. The chemical nature of the accumulated sulfate is unknown.
J Gen Physiol 1962 Mar
PMID:Accumulation of sulfate by mitochondria of rat kidney cortex. 1400 18

Using frog's sartorius muscles we have found no correlation between phosphocreatine hydrolysis and shortening under conditions (iodoacetate poisoning and anoxia) where this reaction was the only expected source of energy. Phosphocreatine hydrolysis did, however, show a constant term corresponding to the activation heat of A.V. Hill, and a linear term with work. It was concluded that shortening heat comes from some other chemical reaction, or else Hill's equation (E = A + W + ax) fails to describe correctly the energy output in a complete cycle of contraction and relaxation. To decide between these possibilities direct measurements of heat and work during a complete cycle were made. Also, experiments were performed in which heat, work, and phosphocreatine breakdown were measured simultaneously on the same muscles. The total energy output in a complete twitch could be most simply represented by a fixed "activation" heat, plus the work. There was no term corresponding to the shortening heat. Hill's equation must, therefore, be held as invalid for the complete isotonic twitch. A value of 9.8 +/- 0.5 (sE) kcal/mole was obtained for the in vivo heat of hydrolysis of phosphocreatine. This quantity showed no significant dependence on load, and it is in good agreement with the value obtained from thermochemical data. It is concluded that phosphocreatine hydrolysis and its associated buffer reactions can account quantitatively for the total energy output of isometric and isotonic twitches.
J Gen Physiol 1963 May
PMID:Total energy production and phosphocreatine hydrolysis in the isotonic twitch. 1401 93

Certain of the metabolic events associated with anaerobic sodium transport by the isolated bladder of the fresh water turtle have been investigated. The data suggest that energy for this transport arises from glycolysis and that endogenous glycogen was the major and perhaps the sole source of substrate. The rate of anaerobic glycolysis, as determined by lactate formation, correlates well with the rate as determined by glycogen utilization. Using lactate formation as the index of anaerobic glycolysis, a linear relationship was observed between glycolysis and net anaerobic sodium transport. In the absence of sodium transport, glycolysis decreased by approximately 45 per cent. Tissue ATP concentrations were maintained at about the same level under anaerobic as under aerobic conditions. Finally if it is assumed that in the conversion of glycogen to lactate anaerobically, 3 moles of ATP are generated per mole of glucose residue, an average of over 15 equivalents of sodium were transported for every mole of ATP generated.
J Gen Physiol 1965 Mar
PMID:ENERGETICS OF ANAEROBIC SODIUM TRANSPORT BY THE FRESH WATER TURTLE BLADDER. 1432 76


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