scholarly journals THE KINETICS OF PENETRATION

1935 ◽  
Vol 18 (6) ◽  
pp. 967-985 ◽  
Author(s):  
A. G. Jacques ◽  
W. J. V. Osterhout

The rate of entrance of potassium into Nitella flexilis has been investigated, and it has been shown that (a) at the concentrations studied the rate is independent of the external pH between 6 and 8 but it is possible that at lower concentrations a dependence may be found; (b) that it does not vary much with the external potassium concentration between 0.01 and 0.001 M, but appears to vary more with the potassium concentration below this limit. It has also been shown that the rate is independent of the illumination, in contrast with the penetration of halides into Nitella clavata studied by Hoagland. It has been found that potassium leaves the cells in distilled water, and since this does not seem to be the result of injury, there is apparently a concentration between 0 and 0.0001 M at which potassium neither enters nor leaves the cell. In Valonia increase of external potassium increases the rate of entrance as shown in the increase in moles of potassium in the sap. In Nitella this is true below an external concentration of 0.001 M. In Valonia this increase is paralleled by the increase in entrance of water so that little or no change in concentration occurs, but in Nitella no growth occurred during the experiment and in consequence the concentration of potassium in the sap increased. It has been shown that the potassium content of the raw gelatinous sap is no greater than that of its ultrafiltrate, so that it is not possible to assume that any of the potassium is bound up in the cell in colloidal compounds. It has been pointed out that all the gradients between the sap and the external solution are unfavorable to the entrance of potassium except the potassium bicarbonate gradient. However, on other grounds entrance as potassium bicarbonate is not considered to be very probable. Various modes of entrance are discussed and it has been concluded that the subject must be investigated further before a definite answer can be given.

1937 ◽  
Vol 20 (5) ◽  
pp. 737-766 ◽  
Author(s):  
A. G. Jacques

When 0.1 M NaI is added to the sea water surrounding Valonia iodide appears in the sap, presumably entering as NaI, KI, and HI. As the rate of entrance is not affected by changes in the external pH we conclude that the rate of entrance of HI is negligible in comparison with that of NaI, whose concentration is about 107 times that of HI (the entrance of KI may be neglected for reasons stated). This is in marked contrast with the behavior of sulfide which enters chiefly as H2S. It would seem that permeability to H2S is enormously greater than to Na2S. Similar considerations apply to CO2. In this respect the situation differs greatly from that found with iodide. NaI enters because its activity is greater outside than inside so that no energy need be supplied by the cell. The rate of entrance (i.e. the amount of iodide entering the sap in a given time) is proportional to the external concentration of iodide, or to the external product [N+]o [I-lo, after a certain external concentration of iodide has been reached. At lower concentrations the rate is relatively rapid. The reasons for this are discussed. The rate of passage of NaI through protoplasm is about a million times slower than through water. As the protoplasm is mostly water we may suppose that the delay is due chiefly to the non-aqueous protoplasmic surface layers. It would seem that these must be more than one molecule thick to bring this about. There is no great difference between the rate of entrance in the dark and in the light.


1978 ◽  
Vol 235 (1) ◽  
pp. C35-C48 ◽  
Author(s):  
L. J. Mandel

The short circuit current as a function of Na concentration in both solutions was found to obey Michaelis-Menten kinetics under a variety of experimental conditions. Values of maximal transport rate (Im) and half-maximal Na concentrations (Kt) were determined from these experiments. Three type of results were obtained: 1) Im and Kt both decreased by approximately the same fraction when the pH of both solutions was reduced by increasing PCO2, 2) Im decreased and Kt increased when the external pH was decreased, and 3) Im increased with ADH and theophylline, decreased with external Ca, and Kt remained unchanged. Various criteria were utilized to determine that these were properties of the entry barrier for Na into the "transport pool." The results are explained in terms of a model that separates three different types of actions on the entry barrier: 1) competition of Na with other ions in the external solution for entry, 2) modulation of the number of sites available for Na translocation by changing the cytoplasmic pH, and 3) alterations in the rate of Na translocation caused by changes in the Na permeability or the electrochemical gradient across the entry barrier.


1976 ◽  
Vol 22 (2) ◽  
pp. 245-253 ◽  
Author(s):  
Willard A. Taber

Claviceps purpurea PRL 1980 grew on partially dissociated succinic acid (pH 4) but not on fully dissociated succinic acid (pH 7.2). Mycelium suspended in 42 mM solution of partially ionized succinic acid (pH 4; 60.1% nonionized, 39% monoanion, and 0.9% dianion, K+ salt) over a period of 25 min accumulated more succinic acid carbon than mycelium suspended in highly ionized solution (pH 6.8; 0.01% nonionized, 4.8% monoanion, and 95% dianion). The greater accumulation from partially ionized solution was not attributable solely to metabolism of succinic acid nor to the lower external concentration of potassium ion. Rate of uptake by sodium azide and iodoacetate-treated mycelium was proportional to external concentration at least up to 200 μmol/ml. External potassium or sodium ion was not required for uptake by inhibited or uninhibited mycelium and external sodium ion and glucose did not allow concentration of succinic acid. The internal concentrations of succinic acid carbon expressed as succinic acid in cell water were about the same as the external concentrations. Uptake was not appreciably affected by extent of ionization of external succinic acid but accumulation was markedly affected. A plot of accumulated succinic acid carbon against external pH produced a bimodal curve with the two maxima corresponding to the maximal concentrations of nonionized and monoanion succinic acid. The bimodal curve probably results from overlapping of two separate curves; the nonionized form accumulating efficiently because of one interaction with the cell and the monoanion form accumulating efficiently because of another interaction. Uptake from concentrated solution is by diffusion and efflux is rapid but not complete. Efflux is not retarded by presence of phosphate in the external solution.


1936 ◽  
Vol 19 (3) ◽  
pp. 397-418 ◽  
Author(s):  
A. G. Jacques

The rate of entrance of H2S into cells of Valonia macrophysa has been studied and it has been shown that at any given time up to 5 minutes the rate of entrance of total sulfide (H2S + S-) into the sap is proportional to the concentration of molecular H2S in the external solution. This is in marked contrast with the entrance of ammonia, where Osterhout has shown that the rate of entrance of total ammonia (NH3 + NR4+) does not increase in a linear way with the increase in the external concentration of NH3, but falls off. The strong base guanidine also acts thus. It has been shown that the rate of entrance of H2S is best explained by assuming that it enters by diffusion of molecular H2S through the non-aqueous protoplasmic surface. It has been pointed out that the simple diffusion requires that the rate of entrance might be expected to be monomolecular. Possible causes of the failure of H2S to follow this relationship have been discussed.


1971 ◽  
Vol 49 (10) ◽  
pp. 879-888 ◽  
Author(s):  
J. G. Foulks ◽  
Florence A. Perry ◽  
H. D. Sanders

Increased [K]0 sufficient to produce submaximum depolarization contractures of frog toe muscle enhanced the tension produced during subsequent caffeine contractures, but caffeine-contracture tension was depressed after an increase in [K]0 sufficient to produce maximum or near-maximum depolarization contractures.Reduced external concentration of divalent cations often augmented caffeine-contracture tension at normal [K]0 but did not do so after [K]0 was increased to levels which produce maximum K contractures. Increased [Mg]0 or [Ca]0 had little direct effect on caffeine contractures but shifted the effect of [K]0 on caffeine contractures toward higher [K]0 in accordance with the shift in [K]0 required to produce depolarization contractures. Replacement of external chloride with acetate, which shifts the relation between [K]0 and depolarization-contracture tension toward lower [K]0, produced a similar shift in the effect of [K]0 on caffeine contractures. Maximum depolarization contractures relaxed rapidly when superimposed on submaximum caffeine contractures, often to a level of residual tension which was less than that developed by the initial caffeine contracture. This effect was particularly marked in media containing acetate in place of chloride.


In the first paper of this series (Burgoyne 1937) the kinetics of the isothermal oxidation above 400° C of several aromatic hydrocarbons was studied. The present communication extends this work to include the phenomena of ignition in the same temperature range, whilst the corresponding reactions below 400° C form the subject of further investigations now in progress. The hydrocarbons at present under consideration are benzene, toluene, ethylbenzene, n -propylbenzene, o-, m - and p -xylenes and mesitylene.


MRS Bulletin ◽  
1990 ◽  
Vol 15 (1) ◽  
pp. 41-47 ◽  
Author(s):  
Nikola Kallay

The adhesion of particles at solid surfaces in liquid media has attracted the attention of scientists because of its various applications as well as the theoretical significance of the processes involved. Early studies were characterized either by poorly defined systems or limited by the properties of a few morphologically well-defined model colloids, such as latex dispersions. Consequently, results were either of semiquantitative nature or were related to some specific cases, which eluded general conclusions. New methods for preparing uniform particles of different compositions, shapes, and sizes make it possible to approach the problem in a more comprehensive manner. For example, to demonstrate difficulties caused by polydispersity, it is sufficient to mention that the electrostatic interaction energy between a plane surface and a particle is approximately proportional to the particle radius, yet the rate of deposition depends exponentially on the height of the energy barrier.In principle, static and dynamic approaches may be employed in the study of particle adhesion. The static method yields the force required to detach an adhered particle, while kinetic investigations of attachment and detachment give the rates of the respective processes. Both methods offer information on the stability of the system in terms of the bond strength of adhered solids. For small colloid particles, which are the subject of thermal random Brownian motion, the dynamic approach is more appropriate. This article emphasizes the kinetics of deposition and detachment of small colloid particles in liquid media.


1976 ◽  
Vol 64 (2) ◽  
pp. 311-322
Author(s):  
M. J. Berridge ◽  
B. D. Lindley ◽  
W. T. Prince

1. Potassium is the major cation in the secretion of the salivary glands of Calliphora and is necessary for full secretory rates. 2. Other ions (rubidium and sodium) can support secretion in the absence of potassium. 39. During stimulation with 5-HT a Nernst plot of the basal membrane potential has a slope of 53 mV for a tenfold change in external potassium concentration and the slope at rest deviates from this over the range I-20 mM external potassium. 4. Hyperpolarization of the basal membrane by 5-HT is abolished if the chloride in the bathing medium is replaced by isethionate. 5. The diuretic agent amiloride inhibits fluid secretion by a mechanism which may include a reduction in calcium entry in addition to its recognized effect on sodium permeability. 6. A model is proposed in which fluid secretion is driven by the active transport of potassium across the apical membrane with chloride following passively.


1894 ◽  
Vol 40 (169) ◽  
pp. 249-251

With the publication in the “Pall Mall Magazine” of the first of Lord Wolseley's articles on “The Decline and Fall of Napoleon,” the inveterate controversy as to the position of the “Corsican Parvenu” in the military and general history of the world assumes a new aspect, the development of which, as psychologists, we shall watch with much interest. There have already been three great epochs in this protracted conflict of opinion. To his contemporaries and rivals of the type of Dumouriez, Bonaparte was a magnificent charlatan of mediocre ability, fit only to serve as a divisional commander under men of light and leading like themselves. The school of thought, however, which saw no genius in the famous march from Boulogne to Ulm and Austerlitz necessarily wielded an ephemeral influence, and was quickly superseded by the reactionary school, of whose views Thiers was at once the founder and the ablest exponent. Over the veteran author of “The Consulate and the Empire” the spirit of Napoleon exercised a fascination of which the records of hero-worship furnish few analogies. Then came the school of Lanfrey, Taine, and Seeley. The method which these great writers sought to pursue in investigating the life and character of Bonaparte was excellent. They set before themselves as the object to be attained a cold, critical survey, detached alike from the rancour of Dumouriez and the adulation of Thiers. But they failed, and failed badly. In spite of all their critical acumen—and perhaps because of it—the Napoleonic idea eluded their grasp. They were no better fitted for their task than Bunyan would have been for that of writing an impartial biography of Charles the Second, and the writer who will raise a real living Napoleon from the 32 volumes of “Correspondance” in which his life and thoughts are entombed has still to appear above the literary horizon. Lord Wolseley makes no attempt to fill this vacant rôle. Indeed, we doubt whether it could be adequately filled by one who believes Napoleon to have been “the greatest of all the great men” that ever lived. But he makes a contribution of much interest and value to a question that has been occasionally mooted of late years, viz., What was the mysterious malady from which the French Emperor suffered at the close of his public life in Europe? Perhaps we ought to suspend a definite answer to this question till we see what else Lord Wolseley has to say on the subject in his remaining articles. But in the meantime a rapid summary of the evidence on the point available to any student of modern French literature may not be inopportune. Of course, the matter to be considered is whether there was, in fact, at the end of Napoleon's military career a failing in his powers. Our ancestors would, no doubt, have deemed it unpatriotic to question that the “Boney” whom Wellington beat at Waterloo not only knew his best and did it, but was as competent a general as the hero of Arcola and Rivoli. But this comforting position is no longer tenable. Lord Wolseley points to the fatal delay of Napoleon at Wilna in the Russian campaign of 1812, and his equally fatal omission to support Ney at the crisis of the battle of Borodino; and, if we mistake not, the campaigns of Leipsic and Waterloo yield evidences still more cogent that the very faculty of commandership repeatedly deserted Bonaparte at the time when its presence was essential to his fortunes. The direct testimony of his contemporaries to the same fact is not wanting. Marshal Augereau (as we learn from Macdonald's memoirs) noticed it, although his coarsely-grained and jealous mind saw in it only a proof of the incompetence which he preferred to consider as a characteristic of his master, and the officers who received the fugitive Corsican on his return from Elba were astounded at his alternate fits of garrulity and silence, tremendous energy and hopeless lassitude. If, then, the fact of Napoleon's mental and physical decline is established, what was the cause? Lord Wolseley goes no further at present than “mental and moral prostration,” and there is certainly nothing extraordinary in the theory that the prodigious and continuous strain to which the mighty intellect of the great captain had for years been subjected was at last destroying its machinery. But there is also positive evidence, we think, that Napoleon had become the victim of epilepsy, and without dwelling on the subject further just now, till Lord Wolseley's series has been completed, we may point out that the theory here suggested derives some corroboration from the circumstance on which his lordship's first article offers abundant proof, that while Napoleon's power of executing his plans was impaired, the splendour of his military imagination survived, and even increased in apparent brilliancy at the last.


1985 ◽  
Vol 119 (1) ◽  
pp. 275-285
Author(s):  
JAMES N. CAMERON

In the days immediately after moulting, manipulations of external pH, [HCO3−], and [Ca2+] were used to determine the nature of the rapid net Ca2+ influx and attendant apparent net H+ efflux in the blue crab (Callinectes sapidus Rathbun). Both fluxes were strongly inhibited by reductions in external [Ca2+], [HCO3−], or pH. The net Ca2+ influx was reversed at an external concentration of 2.5 mmol l−1, and both fluxes were reversed by reducing the external [HCO3−] to 0.2 mmol l−1. The correlation between net Ca2+ flux and apparent net H+ flux was 0.61 (P<0.01), but the variability and the time course of most experiments indicated that the link was indirect, rather than a direct coupling or cotransport. This conclusion was also borne out by acid-base disturbances that occurred in the low-[Ca2+] treatment. The results are consistent with the hypothesis that inward calcium transport is accompanied by both inward HCO3− transport and outward H+ transport, probably by separate exchanges with ions of like charge such as Na+ and Cl−. Crustecdysone (β-ecdysone) does not appear to be involved in control of these post-moult fluxes and calcification.


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