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N Kolassa

Publications and source records attributed to N Kolassa.

At least 37 records · Page 2Linked to original sources
PubMed1982

Uptake of cytidine by isolated, perfused mouse liver.

Mouse livers were perfused at 22 degrees C with an oxygenated salts medium containing [5-3H]cytidine and [carboxyl-14C]inulin. The cellular uptake of cytidine was determined from the 3H content of liver samples less that present in the extracellular (inulin) space of the samples. Time courses of cytidine uptake were biphasic with initial phases which were approximately linear for 15 s and had time zero values that approximated the extracellular space. Rates of cytidine uptake derived from the initial phase of uptake evidently represented rates of membrane transport because (i) initial rates were saturable, and (ii) cytidine uptake was blocked by the nucleoside transport inhibitor, nitrobenzylthioinosine (NBMPR). Treatment of mice with the 5'-monophosphate of NBMPR (greater than 0.2 mg/kg, injected i.p.) 30-40 min prior to the perfusion also blocked cytidine entry into livers. An apparent half-saturation constant of about 10(-3) M and a maximum rate of about 1 mumol . g-1 . min-1 were estimated for the NBMPR-sensitive transport of cytidine into mouse liver cells.

Adenine Nucleotides↗
PubMed1981

Absence of binding sites for the transport inhibitor nitrobenzylthioinosine on nucleoside transport-deficient mouse lymphoma cells.

Cells of an adenosine-resistant clone (AE1) of S49 mouse lymphoma cells were compared with cells of the parental line with respect to (a) characteristics of nucleoside transport, (b) high affinity binding of the inhibitor of nucleoside transport, nitrobenzylthioinosine (NBMPR), and (c) the antiproliferative effects of the nucleoside antibiotics, tubercidin, arabinosyladenine and showdomycin. Rates of inward transport of uridine, thymidine, adenosine, 2'-deoxyadenosine, tubercidin, showdomycin, and arabinosyladenine in AE1 cells were less than 1% of those in cells of the parental S49 line. The inhibitor of nucleoside transport, NBMPR, reduced rates of inward nucleoside transport in S49 cells to levels comparable to those seen in the transport-defective mutant. S49 cells possessed high affinity sites that bound NBMPR (6.6 X 10(4) sites/cell, Kd = 0.2 nM), whereas site-specific binding of NBMPR to AE1 cells was not demonstrable, indicating that loss of nucleoside transport activity in AE1 cells was accompanied by loss of the high affinity NBMPR binding sites. Relative to S49 cells, AE1 cells were resistant to the antiproliferative effects of tubercidin and showdomycin, but differences between the two cell lines in sensitivity toward arabinosyladenine were minor, suggesting that nucleoside transport activity was required for cytotoxicity of tubercidin and showdomycin, but not for that of arabinosyladenine.

Adenosine↗
PubMed1981

Formation of magnesium-phosphoenzyme and magnesium-calcium-phosphoenzyme in the phosphorylation of adenosine triphosphatase by orthophosphate in sarcoplasmic reticulum. Models of a reaction sequence.

The aim of the present study was to test simple reaction sequences which describe calcium-independent plus calcium-dependent phosphorylation of sarcoplasmic reticulum transport. ATPase by orthophosphate including the function of magnesium in phosphoenzyme formation. The reaction schemes considered were based on the reaction sequence for calcium-independent phosphorylation proposed previously; namely that the transport enzyme (E) forms a ternary complex (Mg . E . Pi), by random binding of free magnesium and free orthophosphate, which is in equilibrium with the magnesium-phosphoenzyme (Mg . E-P). Phosphorylation, performed at pH 7.0 20 degrees C and a constant free orthophosphate concentration using sarcoplasmic reticulum vesicles either unloaded or loaded passively with calcium in the presence of 5 mM or 40 mM CaCl2, resulted in a gradual decrease in the apparent magnesium half-saturation constant and an increase in maximum phosphoprotein formation with increasing calcium loads. When phosphorylation of sarcoplasmic reticulum vesicles preloaded in the presence of 5 mM CaCl2 was performed at a constant free magnesium concentration, a decrease in the apparent orthophosphate half-saturation constant and an increase in maximum phosphoprotein formation was observed as compared with vesicles from which calcium inside has been removed by ionophore X-537A plus EGTA treatment; however, both parameters remained unchanged by increasing free magnesium from 20 mM to 30 mM. When phosphorylation of sarcoplasmic reticulum vesicles passively loaded with calcium in the presence of 40 mM CaCl2, at which the saturation of the low-affinity calcium binding sites of the ATPase is presumably near maximum, was performed at increasing concentrations of free orthophosphate, there was a parallel shift of phosphoprotein formation as a function of free magnesium and vice versa, with no change in the maximum phosphoenzyme formation. Comparison of the experimental data with the pattern of phosphoprotein formation predicted from model equations for various theoretical possible reaction sequences suggests that phosphoenzyme formation from orthophosphate possesses the following features. Firstly, calcium present at the inside of the sarcoplasmic reticulum membrane binds to the free enzyme and in sequential order to E . Mg . Pi or Mg . E-P or to both, but neither to E. Mg nor to E . Pi. Secondly, calcium-independent and calcium-dependent phosphoproteins are magnesium-phosphoenzymes. Calcium-dependent phosphoenzyme is a magnesium-calcium-enzyme phosphate complex with 1 magnesium, 2 calciums and 1 orthophosphate (the last covalently) bound to the enzyme [Mg . E-P . (Cai)2], and not a 'calcium-phosphoprotein' without bound magnesium.

Adenosine Triphosphatases↗
PubMed1980

Induction of drug metabolism in the rat by taglutimide, a sedative-hypnotic glutarimide derivative.

Pretreatment with taglutimide significantly decreased the plasma dicoumarol level and shortened the duration of hexobarbital-induced narcosis in rats. Furthermore, taglutimide pretreatment accelerated the in vitro metabolism of dicoumarol, hexobarbital, o-nitrophenyl acetate and procaine, but not of 3,4-benzypyrene, as assayed in the 10,000xg supernatant fraction of rat liver homogenate. No definite increase was observed in liver wet weight, nor in the amount of microsomal and total liver protein in comparison with the control values. No marked differences were found between the effects of short- (4-day) and long-term (17-day) pretreatment on any of the studied parameters. The changes in drug metabolism and liver protein observed after taglutimide pretreatment differed from those observed after pretreatment with either phenobarbital or 3,4-benzypyrene. Taglutimide, like other inducing agents, is lipophilic, but differs from them in not being a substrate of monooxygenases.

Animals↗
PubMed1980

Active secretion of hypoxanthine and xanthine by guinea pig jejunum in vitro.

Isolated epithelium of guinea pig jejunum secretes hypoxanthine and xanthine by a transport process that is capable of uphill transport and dependent on metabolic energy supply. Unidirectional influx of hypoxanthine across both the luminal and the contraluminal cell membrane appears to be saturable; influx across the contraluminal membrane is inhibited by 2,4-dinitrophenol (DNP). Efflux across the luminal membrane is diminished by DNP; efflux across the contraluminal membrane is increased by DNP. This evidence suggests the existence of a mediated transport system both in the luminal and the contraluminal cell membrane. Additionally, intracellular metabolism of hypoxanthine seems to regulate transepithelial permeation: increased hypoxanthine salvage by the phosphoribosyltransferase reduces the rate of secretion. However, the incorporation of hypoxanthine into the nucleotides is limited when the hypoxanthine is added to the luminal side of the epithelium, and the permeation rate in the absorptive direction is not markedly influenced by the rate of hypoxanthine salvage. These findings are a further example of the functional orientation of the jejunal epithelial cells with respect to enzymic activity and transepithelial transport properties.

Animals↗
PubMed1980

[Characterization of the calcium transport cycle of sarcoplasmic reticulum by inorganic phosphate including the function of magnesium (author's transl)].

The present study presents experiments on ATP-Pi exchange and phosphorylation of the calcium-transport-ATPase of sarcoplasmic reticulum vesicles by orthophosphate under conditions of ATP-Pi exchange, as well as on Ca-independent and Ca-dependent phosphorylation in the absence of ATP, ADP and calcium outside. The rate of the ATP-Pi exchange correlates with the phosphoprotein steady state level labelled from orthophosphate. Ca-independent phosphorylation is due to magnesium-phosphoprotein formation and Ca-dependent phosphorylation is due to magnesium-calcium-phosphoprotein formation. A reaction sequence which probably accounts for phosphorylation of the transport enzyme by orthophosphate and its significance in characterizing the intermediate steps of the calcium transport cycle is discussed.

Animals↗
PubMed1980

[Membrane transport of antineoplastic drugs and its relevance to tumour chemotherapy (author's transl)].

The permeation of cell membranes by several antineoplastic drugs (AD) exhibits characteristics of carrier-mediated transport processes (facilitated diffusion or active transport); the main representatives among these AD are mechlorethamine, cyclophosphamide, melphalan, methotrexate, 6-mercaptopurine, 5-fluorouracil, cytarabine, 5-fluorodeoxyuridine, vincristine, vinblastine, adriamycin, daunorubicin and dactinomycin. Inhibition or stimulation of the membrane transport of AD influences absorption, distribution, elimination, therapeutic effectiveness and toxicity. The choice of certain combination therapies may increase the selectivity of AD by influencing membrane transport. A change in the properties of transport systems is one possible reason for the resistance of tumour cells to various AD.

Animals↗
PubMed1979

Ionized and bound calcium inside isolated sarcoplasmic reticulum of skeletal muscle and its significance in phosphorylation of adenosine triphosphatase by orthophosphate.

Calcium loading of skeletal muscle sarcoplasmic reticulum performed passively by incubation with high calcium concentrations (0.5--15 mM) on ice gives calcium loads of 50--60 nmol/mg sarcoplasmic reticulum protein. This accumulated calcium is not released by EGTA [ethyleneglycol bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid], but almost completely released by ionophore X-537A plus EGTA or phospholipase A plus EGTA treatment and is therefore assumed to be inside the sarcoplasmic reticulum. This calcium is distributed in one saturable and one non-saturable calcium compartment, as derived from the dependence of the calcium load on the calcium concentration in the medium. These compartments are assigned to bound and ionized calcium inside the sarcoplasmic reticulum, respectively. Maximum calcium binding under these conditions was 33 nmol/mg protein with an apparent half-saturation constant of 5,8 nmol/mg free calcium inside, or between 1.2 and 0.6 mM free calcium inside, assuming an average vesicular water space of 5 or 10 microliter/mg protein, respectively. Calcium-dependent phosphorylation of sarcoplasmic reticulum calcium-transport ATPase from orthophosphate depends on the square of free calcium inside, whilst inhibition of phosphorylation depends on the square of free calcium in the medium. Calcium-dependent phosphorylation appears to be determined by the free calcium concentrations inside or outside allowing calcium binding to the ATPase according to the two classes of calcium binding constants for low affinity calcium binding or high affinity calcium binding, respectively. It is further suggested that the saturation of the low-affinity calcium-binding sites of the ATPase facing the inside of the sarcoplasmic reticulum membrane is responsible for the greater apparent orthophosphate and magnesium affinity in calcium-dependent phosphorylation than in calcium-independent phosphorylation from orthophosphate. Maximum calcium-dependent phosphoprotein formation at 20 degrees C and pH 7.0 is about 4 nmol/mg sarcoplasmic reticulum protein.

Adenosine Triphosphatases↗
PubMed1979

Pharmacological properties of taglutimide, a new sedative-hypnotic drug.

2-[Bicyclo(2,2,1)heptane-2-endo-3-endo-dicarboximido]-glutarimide (taglutimide, K-2004) proved to be a new sedative-hypnotic drug which did not produce any toxic effects when administered orally to mice even at a very high dosage. Central-nervous depression was demonstrated by a reduction in spontaneous motor activity, potentiation of the central-depressant effect of pentobarbital, antagonism of the central-stimulant effect of amphetamine after oral administration and by narcotic activity after i.v. administration of the drug. Furthermore, oral administration of taglutimide potentiated the analgesic action of morphine without being effective on its own. Only weak potentiation of chlorpromazine-induced catalepsy, but not of reserpine-induced catalepsy was observed after taglutimide pretreatment. The drug influenced neither motor co-ordination nor the toxicity of ethanol. Taglutimide exhibited no anticonvulsant activity with respect to maximum electroshock or strychnine-induced seizures. No effect on heart rate or blood pressure was demonstrable after taglutimide treatment in conscious dogs.

Animals↗
PubMed1979

Plasma level of the prodrug midodrine and its active metabolite in comparison with the alpha-mimetic action in dogs.

Midodrine, i.v. or orally administered, causes a prolonged elevation of blood pressure and a reduction in heart rate. These cardiovascular changes are not correlated to the plasma levels of the intact drug. On administration of either midodrine or its metabolite, ST-1059, formed by cleavage of the glycine residue, the elevation of blood pressure and the reduction in heart rate were significantly correlated to the plasma level of ST-1059. The results are in agreement with the assumption that the pressor activity of midodrine is mainly exerted by its metabolite ST-1059.

Adrenergic alpha-Agonists↗
PubMed1978

pH and temperature dependence of adenosine uptake in human erythrocytes.

Kinetic analysis of the saturable adenosine uptake in human erythrocytes suggests the existence of two saturable components, distinguished by different Km values (1.4 and 260 micron, respectively, at pH 7.4 and 25 degrees C). Both components were abolished by p-nitrobenzylthioguanosine or dipyridamole. Total uptake was significantly higher at pH 8 than at pH 7 at adenosine concentrations above 2 micron. The increase in uptake at the higher pH was brought about mainly by an increase in the maximum rate of transport of the low-affinity uptake system. With rising temperature the Km and the V of both uptake components increased. No transition temperature was observed between 12 and 37 degrees C.

Adenosine↗
PubMed1978

Calcium gradient-dependent and calcium gradient-independent phosphorylation of sarcoplasmic reticulum by orthophosphate. The role of magnesium.

Phosphorylation of the calcium-transport ATPase of skeletal muscle sarcoplasmic reticulum by inorganic phosphate was investigated in the presence or absence of a calcium gradient. The maximum phosphoprotein formation in the presence of a calcium gradient at 20 degrees C and pH 7.0 is approximately 4 nmol/mg sarcoplasmic reticulum protein, but only between 2.4 and 2.8 nmol/mg protein in the absence of a calcium gradient, using Ionophore X-537 A or phospholipase-A-treated sarcoplasmic reticulum vesicles. Maximum phosphoprotein formation independent of calcium gradient at 20 degrees C and pH 6.2 is in the range of 3.6--4 nmol/mg protein. Half-maximum phosphoprotein formation dependent on calcium gradient was achieved with 0.1--0.2 mM free orthophosphate at 10 mM free magnesium or at 0.1--0.2 mM free magnesium at 10 mM free orthophosphate. Phosphoprotein formation independent of calcium gradient is in accordance with a model which assumes, firstly, the formation of a ternary complex of the ATPase protein with orthophosphate and magnesium (E . Pi . Mg) in equilibrium with the phosphoprotein (E-Pi . Mg) and, secondly, an interdependence of both ions in the formation of the ternary complex. The apparent equilibrium constant was 0.6 and the apparent dissociation constants KMg, KMg', KPi and KPi' were 8.8, 1.9, 7.2 and 1.5 mM respectively, assuming a total concentration of the phosphorylation site per enzyme of 7 nmol/mg protein.

Animals↗
PubMed1978

Influence of hexobendine, dipyridamole, dilazep, lidoflazine, inosine and purine riboside on adenosine uptake by the isolated epithelium of guinea pig jejunum.

The uptake of (14C)adenosine by isolated epithelium of guinea pig jejunum, administered on the blood side, was inhibited by hexobendine, dipyridamole, dilazep and lidoflazine. On the lumen side, however, weak inhibition was observed with lidoflazine only and no significant change was recorded with hexobendine, dipyridamole or dilazep. This difference was not altered when the degradation of hexobendine by the jejunal epithelium was blocked by physostigmine. When adenosine uptake was already reduced by purine riboside, further addition of hexobendine, dipyridamole, dilazep or lidoflazine caused divergent changes depending on the side of administration. Adenosine uptake was further diminished on the blood side, but raised towards control values on the lumen side. By contrast, inosine inhibited adenosine uptake on both sides of the epithleium. The results suggest that the mechanism of adenosine uptake is different on either side with respect to inhibition characteristics, corresponding to differences in morphology and function of the two sides of the intestinal epithelium.

Adenosine↗