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At least 19 recordsLinked to original sources
PubMed1979

Calculation of the concentrations of free cations and cation-ligand complexes in solutions containing multiple divalent cations and ligands.

The method described permits the computation of the concentrations of free ions and ion-ligand complexes in a solution containing arbitrary numbers of divalent cations and ligands. It is required that the pH be known, along with appropriate sets of ligand-hydrogen and ligand-divalent cation concentration binding constants. It is assumed that these sets of constants are chosen to be consistent with the ionic strength of the complete solution which contains the divalent cations and ligands. The technique is an iterative one which provides upper and lower bounds for the values of the unknowns. The method does not require initial guesses at the values of the unknowns, and it gives correct answers even when the concentrations involved are many orders of magnitude apart. The present formulation of the problem is restricted to the case where only one cation can bind to a given ligand at any one time. The method is applicable to large molecules with multiple "sub-ligands" provided these sub-ligands are independent in their function as ion-binding sites. These sub-ligands need not all have the same properties. It is also shown that a simple modification of the method permits the determination of the subset of total ion concentrations that are required in order to produce a specified subset of free ion concentrations. The modifications required to include monovalent cation binding are presented in outline form.

Adenosine Triphosphate↗
PubMed1976

Cation control of chlorophyll a fluorescence yield in chloroplasts. Location of cation sensitive sites.

We have compared the effect of various cations on the fluorescence yield of chloroplasts under several different conditions in vitro. 1. In the absence of a high energy state but in the presence of low (10 mM) concentrations of monovalent cations, divalent metal cations increase steady state chlorophyll a fluorescence yield in a manner which does not involve transport of these cations across the thylakoid membranes. 2. The kinetics of this cation-induced fluorescence rise are relatively slow, and seem to reflect cation binding (or subsequent conformational changes) to sites on the outer surface of the thylakoid membrane. 3. In the absence of monovalent cations, the apparent binding constant for Mg2+ to sites on the outer side of the membrane is low. Addition of low concentrations of monovalent cations (10 mM) competitively inhibits divalent cation binding. 4. Control of fluorescence yield is also exerted by the high energy state, and seems to involve proton/metal cation exchange at sites on the inner side of the thylakoid. 5. When isolated chloroplasts are washed and resuspended in a medium containing no added cations, the initial fluorescence level is high, but is quenched on addition of monovalent cations, sodium EDTA being much more effective than sodium chloride. It is argued that when isolated under these conditions, chloroplasts retain sufficient divalent cations to saturate external negative sites, and that the fluorescence lowering is due to their removal. 6. Some other cations, such as poly(L-lysine), can displace divalent cations from their external sites in an irreversible manner, resulting in a fixed low fluorescence yield.

Binding, Competitive↗
PubMed1976

The lethal hit stage of mouse T and non-T cell-mediated cytolysis: differences in cation requirements and characterization of an analytical "cation pulse" method.

We investigated in detail the cation requirements of two different systems of mouse cell-mediated cytolysis in vitro, at their recognition, post-recognition hit and target cell disintegration stages. In T cell-mediated cytolysis, respectively Mg++ or Ca++, Ca++, and no cations, were required. In non-T cell-mediated hemolysis, respectively no cations, Mg++, and no cations, were required. Two main conclusions can be drawn. First, the cation requirements are different from one system to the other especially at the post-recognition hit stage, which strongly suggests the existence of differences between both systems as to the actual mechanism of lysis. Second, the cation requirements are different within each system from one step to another. This formed the basis of a step-by-step analysis of the lytic process, leading to the characterization of a cation pulse method for the experimental isolation and further study of the post-recognition hit stage of cell-mediated cytolysis.

Animals↗
PubMed1976

The biphasic effect of organic cations on the excretion of other organic cations.

The renal excretion of 14C-choline or 14C-acetylcholine was increased by the infusion of another organic cation at low rates but was decreased by infusion of the same added organic cation at higher rates with the Sperber technique in hens. The range of low rates of infusion was from 1 X 10(-15) to 1 X 10(-8) mol/min. At infusion rates greater than 1 X 10(-8) mol/min, inhibition of tubular excretion was found. At the low infusion rates, thiamine, lysine, quinine, atropine, acetylcholine and methylguanidine were found to increase 14C-choline excretion. The same compounds with the exception of lysine and acetylcholine inhibited 14C-choline excretion at the higher infusion rates. A biphasic effect on 14C-acetylcholine excretion was also observed with added atropine, thiamine and choline over the same infusion range. Increases in 14C-choline excretion occurred during a choline infusion rate that normally produced an excretory tubular maximum for choline whereas increases in 14C-acetylcholine excretion occurred during infusion of tracer amounts of 14C-acetylcholine. The effect of the addition of organic cations was selective for cations since the tubular excretion of organic anions was not affected by the addition of organic cations. The tubular excretion ratio of 14C-thiamine/p-aminohippuric acid increased from 0.25 to 0.95 when the infusion rate of added unlabeled thiamine was increased from 1 X 10(-11) to 1 X 10(-8) mol/min. Enhanced tubular excretion of 14C-thiamine may represent the effect of the increased load of unlabeled thiamine to protect the labeled thiamine from conversion to a nontransportable metabolite. Enhancement of excretion of 14C-choline and 14C-acetyocholine produced by very small amounts of other organic cations may represent either inhibition of tubular reabsorptive transport or induction of tubular excretory transport.

Acetylcholine↗
PubMed1975

Studies on ram acrosin. Isolation from spermatozoa, activation by cations and organic solvents, and influence of cations on its reaction with inhibitors.

1. A simple method is given for isolating from ram spermatozoa a water-soluble form of acrosin (a trypsin-like enzyme) which is about 25% pure. It is free from an acrosin inhibitor which is located in the spermatozoa. 2. In the hydrolysis of N-alpha-benzoyl-l-arginine ethyl ester the degree of activation of acrosin by Ca(2+), and by some other cations, is dependent on the extent of contamination by the inhibitor. In 50mm-Tris-HCl buffer (pH8.2) activation by Ca(2+) did not exceed 40%, but acrosin that is partially inhibited may be activated by up to 300%: this is due to cation-mediated protection of acrosin against the inhibitor. 3. Increasing concentrations of buffers (e.g. Tris) also activate acrosin but at above certain buffer concentrations Ca(2+) no longer exerts an activating effect and may become inhibitory. Ca(2+) is also inhibitory when added to assay systems involving anionic buffers with chelating properties. This is due to a fall in pH. 4. The above results suggest reasons for conflicting conclusions in papers dealing with the effects of Ca(2+) on acrosin activity. 5. Inhibition of acrosin by the Kunitz pancreatic trypsin inhibitor is increased on addition of Ca(2+). Inhibitions of trypsin by the acrosin inhibitor and by the Kunitz inhibitor are insensitive to Ca(2+). 6. Like trypsin, acrosin is activated, up to 60%, by 2-methyl-propan-2-ol, dimethyl sulphoxide, and some other water-miscible solvents. Effects of cations and solvents tend to be additive and a common maximum acrosin activity can be achieved with various concentrations of solvent, salts and buffer in the assay system. Activation by solvents is increased when low concentrations of the acrosin inhibitor are present. 7. Activations of acrosin by salts and by solvents are more pronounced when the substrate is N-alpha-benzoyl-dl-arginine 2-naphthylamide. 8. K(m) values for ram acrosin (about 0.2mm) are much higher than those for trypsin, and k(cat.) values are slightly higher than those for trypsin. Considerations of the influences of ions and dimethyl sulphoxide on the activities and kinetic constants of acrosin and trypsin suggest that conformational changes are the factors mainly responsible for the reported activations of acrosin. 9. The following conclusions are reached. (a) Acrosin plays a role in the penetration of the sperm cell into the egg without becoming detached from the acrosomal membrane. (b) The enzyme is a peripheral membrane protein which may be classed as a cathepsin. (c) The susceptibility of the activity of soluble acrosin to cations and solvents points to a flexible molecule, i.e. one lacking conformational restraints imposed by association (presumably ionic) with the acrosomal membrane.

Acrosin↗
PubMed1978

Cation permeability alterations during sickling: relationship to cation composition and cellular hydration of irreversibly sickled cells.

Sickle erythrocytes (RBC) incubated under 100% nitrogen for 4 hr manifested marked Na gain with an equivalent K loss. There were no changes in cell total cation or water content under these conditions, and no irreversible sickle cells (ISC) were formed. In contrast, sickle RBC incubated for 24 hr under 100% nitrogen in a glucose-free Na medium containing calcium manifested marked ISC formation. ISC formed under these conditions also had elevated Na content, although K content was much more reduced, and consequently ISC were cation depleted and dehydrated. When sickle RBC were incubated 24 hr under 100% nitrogen in a glucose-free K medium containing calcium no ISC formed and there were no major changes in cation or water content. These studies indicate that the Na+K content and dehydration of ISC was not directly related to the increased cation permeability associated with sickling. Rather, the ISC changes appear to reflect the well-known Gardos effect (K and water loss occurring in ATP-depleted RBC incubated with calcium). In addition, these studies suggest that ISC formation per se is related to K and water loss, since no ISC were formed when ATP-depleted sickle RBC were deoxygenated in calcium-containing high-K media that prevented K loss and dehydration.

Adenosine Triphosphate↗
PubMed1977

The effects of amphiphilic cationic drugs and inorganic cations on the activity of phosphatidate phosphohydrolase.

1. Phosphatidate phosphohydrolase from the particle-free supernatant of rat liver was assayed by using emulsions of phosphatidate as substrate. 2. The inhibition of the phosphohydrolase by chlorpromazine was of a competitive type with respect to phosphatidate. The potency of various amphiphilic cationic drugs as inhibitors of this reaction was related to their partition coefficients into a phosphatidate emulsion. 3. The effect of chlorpromazine on the phosphohydrolase activity was complementary rather than antagonistic towards Mg2+. Chlorpromazine stimulated the phosphohydrolase activity in the absence of added Mg2+ and was able to replace the requirement for Mg2+. However, at optimum concentrations of Mg2+, chlorpromazine inhibited the reaction, as did Ca2+. The phosphohydrolase activity was also stimulated by Co2+ and to a lesser extent by Mn2+, Fe2+, Fe3+, Ca2+, spermine and spermidine when Mg2+ was not added to the assays. 4. It is concluded that the inhibition of phosphatidate phosphohydrolase by amphiphilic cations can largely be explained by the interaction of these compounds with phosphatidate, which changes the physical properties of the lipid, making it less available for conversion into diacylglycerol. 5. The implications of these results to the effects of amphiphilic cations in redirecting glycerolipid synthesis at the level of phosphatidate are discussed.

Animals↗
PubMedDate not supplied

Plasma and erythrocyte cations and permeability of the erythrocyte membrane to cations in essential hypertension.

Untreated African patients with essential hypertension were found to have high plasma sodium and low plasma potassium. The red cel contents of these cations determined from the same sample of blood were found to be high for sodium and normal for potassium. The passive permeability of the erythrocytes for potassium was lower in hypertensives than in controls. The ouabain-sensitive active sodium efflux was lower in hypertensives than in controls. The relationships between the erythrocyte cation content and the total body content of the cations, and between the membrane function in red cells and other cells of the body are discussed.

Adult↗
PubMed1976

The use of ionophores of rapid loading of human red cells with radioactive cations for cation-pump studies.

Techniques are described for the rapid loading of intact human red cells with radioactive isotopes of alkali cations or Ca2+ by using ionophorous compounds (nigericin, gramicidin D and A 23187). Loading was rapid and efficient if the membrane potential of the cells was rendered more negative inside. After cation loading the ionophores could be bound to albumin and removed by repeated washings. The ATP and 2,3-DPG contents of the cells were practically unaltered by this treatment. Passive membrane permeability to Na+ and Ca2+ returned to normal. Loaded erythrocytes pumped out Na+ in a ouabain-sensitive and Ca2+ in a lanthanum-sensitive way. Ca2+ -loaded red cells were microspherocytes and exhibited a rapid K+ -efflux. Parallel with the extrusion of Ca2+ cells regained their biconcave shape and normal passive permeability to K+.

Adenosine Triphosphate↗
PubMed1977

Enhancement (by ATP, insulin, and lack of divalent cations) of ouabain inhibition of cation transport and ouabain binding in frog skeletal muscle; effect of insulin and ouabain on sarcolemmal (Na + K)MgATPase.

Using small, intact frog muscles, the basic properties of Na+ and K+ transport were shown to resemble those of the (Na+ + K+)Mg2+ATPase (EC 3.6.1.3) isolated from skeletal muscle. (a) External K+ is essential for Na+ exit and K+ entry after the muscles are Na+-loaded and K+-depleted; (b) the ouabain concentration causing maximum inhibition of recovery is the same for transport as for the inhibition of the isolated enzyme. Ouabain causes a decrease in the sorbitol space and causes muscle fibre swelling. Absence of Ca2+ and Mg2+ inhibits recovery of normal Na+ and K+ concentrations and increases the sorbitol space. Insulin stimulates K+ uptake and Na+ loss in intact muscles but has no effect on the isolated sarcolemmal (Na+ + K+)Mg2+ATPase. Absence of divalent cations, addition of external ATP and of insulin enhance the ouabain inhibition of recovery. Bound ouabain was measured using [3H]ouabain and [14C]sorbitol (to measure the extracellular space). The process of binding was slowly reversible and was saturable within a range of ouabain concentrations from 1.48 X 10(-7) to 5.96 X 10(-7) M. From the nonexchangeable ouabain bound, the density of glycoside receptors was estimated to be 650 molecules per square micrometre of membrane surface. The absence of divalent cations, addition of external ATP and of insulin significantly enhanced the amount of ouabain bound. Substitution of Na+ and K+ by choline greatly reduced the bound ouabain.

Adenosine Triphosphatases↗
PubMed1976

The role of divalent cations in activation of the sea urchin egg. I. Effect of fertilization on divalent cation content.

The Ca and Mg content of unfertilized sea urchin eggs (3 and 21 mumole/ml eggs) remains remarkably constant over periods of hours, even when the eggs are suspended in Ca- or Mg-free sea water. After fertilization the Ca content of eggs in regular sea water increases sharply by about 20%, followed by a decrease to the unfertilized level by 40 minutes. However, if the fertilized eggs are washed three minutes in Ca-free sea water a sharp decrease in the Ca content occurs amounting to 30% of the total in the first 40 minutes, with little change thereafter. Suspension of the eggs in Ca-free sea water results in an even greater loss of Ca amounting to about 43% of the total in the same time interval, followed by a continuing slow loss. It is concluded that fertilization initiates the intracellular release of Ca, which is then extruded. For unwashed eggs this change is masked by the simultaneous generation of new extra-cellular coats with high affinity for Ca. Changes in the Mg content of fertilized eggs follow the same general pattern except that absorption of this divalent cation to the extracellular coats is minimal.

Animals↗
PubMed1977

[Clinical significance of cationic proteins of leukocyte lysosomes: cationic leukocyte antigen (CLA) as a marker of blast crisis in chronic myelocytic leukaemia (author's transl)].

Cationic leukocyte antigen (CLA) was estimated in urine of acute and chronic leukaemics using quantitative immuno-precipitation techniques. The studies demonstrated that CLA is a marker of the (myelo-) blast crisis in patients with chronic myelocytic leukaemia (CML). By these studies the value of the determination of CLA for the differential diagnosis of acute myeloblastic leukaemia versus initial (myelo-) blast crisis in CML and the lymphatic leukaemias, respectively, was evident. The terminal blastic transformation in CML was indicated early by an elevation of the urinary CLA-level. The blast-crisis was accompanied by a heavy CLA-uria. The results are documented by demonstration of special studies of characteristic cases and discussed in the light of recent results of immunological and cytochemical findings on the nature of blast crisis in CML.

Aged↗
PubMed1992

Rat hepatocyte hyaluronan/glycosaminoglycan binding proteins: evidence for distinct divalent cation-independent and divalent cation-dependent activities.

We have previously shown (Biochemistry, 29, 10425, 1990) that hepatocytes contain intracellular specific binding sites for hyaluronan (HA). Although HA-binding activity is not dependent on divalent cations, it is increased in the presence of Ca+2. Here we report that a novel photoaffinity HA derivative (ASD-HA) crosslinks specifically to different proteins in permeable cells in the presence or absence of Ca+2. With Ca+2 present, two proteins of approximately 24 kD and 43 kD were labeled. Additionally, a broad zone of specific crosslinking was observed in the region of 40-100 kD. However, in the presence of the chelator EGTA this zone was absent and the 24 and 43 kD proteins were also not cross-linked to the HA photoaffinity derivative. In the absence of Ca+2, only a 54 kD protein was specifically labeled. The results indicate that different intracellular hepatocyte proteins are responsible for the Ca+2-independent and the Ca+2-dependent binding of HA.

Animals↗
PubMed1978

Glucose and cation transport in rat jejunum, ileum and colon in vivo: control experiments, and effect of cationic surfactant.

Osmotically balanced solutions of glucose (0.5-300 mM) and sodium chloride, containing cetrimonium bromide (cetrimide, 0.8-4.1 mM), were instilled into the jejunum, ileum and colon of anaesthetized rats. Net transport of glucose, sodium and potassium was studied by their disappearance from, or accumulation into the intestinal lumen during 15 min incubation. Cetrimide caused the following shifts in normal jejunal and ileal glucose absorption: At low luminal glucose levels, absorption was strongly depressed and may be converted to net secretion. At intermediate levels, inhibition was less pronounced, and at high luminal glucose levels absorption was enhanced. Similar changes were seen in the colon. Furthermore, cetrimide caused a three-fold change in the regression lines relating net sodium fluxes to the initial sodium concentration: The lines became steeper, the correlation was improved and the sodium concentration value corresponding to zero net transport was elevated. Net potassium secretion was increased. These changes are all consistent with the view that surfactants cause an increase in passive permeability. Quantitatively, the effect of cetrimide increased with localization in the order colon greater than ileum greater than jejunum. Benzalkonium chloride (0.5-1.7 mM) was tested in the ileum only, and caused quite similar effects.

Animals↗
PubMed1975

Effects of divalent cations, cation chelators and an ionophore on morphine analgesia and tolerance.

The analgesic effect of morphine was antagonized in mice by intracerebroventricular injection of Ca++, Mg++ and Mn++ and was potentiated by ethylene glycol tetraacetic acid but was not altered by Sr++, Ba++, Ni++, Hg++, Cd++ or ethylenediamine tetraacetic acid. The antagonistic effect of Ca++ was not altered by pretreatment with pargyline or 6-hydroxydopamine indicating that altered release of catecholamines or serotonin was not involved in this action of Ca++. Induction of morphine tolerance by pellet implantation also did not alter the antagonistic effect of Ca++. The antagonistic effects of Ca++ and naloxone were additive in both nontolerant and tolerant animals and the apparent affinity of naloxone for its receptors, as estimated by in vivo pA2 determinations, was not altered by Ca++. However, the ionophore X537A was found to increase greatly the narcotic antagonist effect of a low dose of Ca++ although the ionophore alone did not alter the effects of morphine. This indicates that Ca"++ must penetrate cell membranes in order to reduce the analgesic effects of morphine. These findings indicate the importance of Ca++ localization in the actions of narcotic agonists and antagonists.

Analgesia↗
PubMed1978

Effects of divalent cations, lanthanum, cation chelators and an ionophore on acetylcholine antinociception.

The antinociceptive effect of intracerebroventricularly administered acetylcholine as measured in the mouse tail-flick test was reduced by intracerebroventricularly injected calcium, magnesium and manganese. Maximum antagonism of acetylcholine-induced antinociception was observed with a 1-hour calcium pretreatment. Significant reduction existed at 2- but not 4-hour pretreatment. Barium and strontium were inactive. The antinociceptive effect of acetylcholine was potentiated by lanthanum and ethylene glycol tetraacetic acid but not by ethylenediamine tetraacetic acid. The ionophore A23187 was shown to increase greatly the antagonistic effect of a low dose of calcium. The ionophore alone did not significantly alter the effect of acetylcholine. Thus, it appears that calcium must penetrate cell membranes to reduce the effect of acetylcholine. In addition to acetylcholine, it was found that the antinociceptive effects of oxotremorine and physostigmine could also be reduced by calcium. These data indicate that alterations in intracellular calcium are involved in cholinergically induced antinociception.

Acetylcholine↗