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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 7 (1968), S. 2724-2730 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0899-0042
    Keywords: atenolol ; enantiomers ; pharmacokinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this study was to describe the pharmacokinetics of and heart rate and blood pressure responses to (S)-atenolol (SATN) and (R)-atenolol (RATN) after oral administration of (S)-atenolol and (R,S)-atenolol (Tenormin™) in man. Eight male subjects were given single oral doses of 50 mg of SATN as a single enantiomer formulation (SEF) and 100 mg of Tenormin™ (TMN) using a randomized, double-blind, 2-period, complete crossover study design. Subjects performed exercise tolerance tests (Bruce Protocol) before and 2, 4, 6, 8, 12, and 24 h after drug administration. Plasma samples were obtained 2 min before and 30 min, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 16, and 24 h after dosing. Urine was collected for the first 48 h after dosing. Plasma and urine samples were analyzed for SATN and RATN by an enantioselective HPLC method. SEF and Tenormin™ attenuated exercise-induced increases in heart rate and systolic blood pressure. Mean changes in exercise heart rates 4 h after dosing were -38 ± 3 bpm and -37 ± 3 bpm for SEF and TMN, respectively, P = 0.792. Mean changes in exercise systolic blood pressure were -42 ± 12 mm Hg and -55 ± 14 mm Hg for SEF and TMN, respectively, P = 0.484. Mean area under the plasma level time curve (AUC0-24) and mean Cmax for SATN for SEF were significantly lower than for SATN after TMN. Mean SATN AUCs0-24 were 1867 ± 261 and 2543 ± 223 ng · h/ml (P = 0.005) and mean Cmaxs were 225 ± 29 and 333 ± 30 ng/ml, for SEF and TMN, respectively (P = 0.011). Mean Tmax for SATN occurred significantly earlier after SEF than after TMN (2.9 ± 0.3 and 3.3 ± 0.3 h, P = 0.028). The amount of SATN excreted in urine was significantly lower after SEF than after TMN (18.7 ± 2.7 and 24.2 ± 2.0 mg, P = 0.017). AUC, Cmax, and amount excreted in urine (Au) were significantly higher for RATN than SATN after TMN. Mean AUCs, Cmaxs, and Aus for RATN compared to SATN were 2806 ± 239 vs 2543 ± 223 ng ± h/ml (P 〈 0.0001), 360 ± 31 vs 333 ± 30 ng/ml (P 〈 0.0001), and 25 ± 2.1 vs 24 ± 2 mg (P = 0.004), respectively. SEF and TMN are equieffective in attenuating exercise-induced increases in heart rate and systolic blood pressure. The SEF has lower bioavailability compared to TMN and RATN plasma levels are higher than SATN after TMN administration. © 1994 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The studies reported here were carried out to characterize further previously described changes in membrane localized amino acid transport associated with simian virus 40 transformation of the mammalian cell line, Balb/c3T3. Membrane vesicles were prepared from confluent cultures of both simian virus 40 transformed Balb/c3T3 (SV3T3) and the untransformed parent line, Balb/c3T3 (3T3). An initial, externally imposed out〉in, 100mm Na+ gradient produces acceleration of early ingress of α-aminoisobutyric acid (AIB) in vesicles from both cell lines, but transient, concentrative uptake (overshooting) only in SV3T3 vesicles. Early ingress ofl-leucine is also accelerated in SV3T3 vesicles by a Na+ gradient, and overshooting is also demonstrable. Na+-gradient independent AIB permeability of SV3T3 and 3T3 membranes was estimated using uptake data, a first order rate equation and measurements of vesicle size derived from quasi-elastic light-scattering studies. AIB permeability of SV3T3 membranes is greater than that of 3T3 membranes (113 Å/min and 43 Å/min, respectively), suggesting that overshooting in 3T3 vesicles is not attenuated by a Na+-independent AIB “leak”. Na+ permeability of the two membranes is similar, ruling out the possibility that a slower rate of Na+ equilibration across the SV3T3 membrane allows development of the overshoot. In SV3T3 vesicles the height of a Na+-gradient dependent overshoot varies with the initial [Na+] o /[Na+] i ratio, and [Na+] o /[Na+] i is linearly related to ln AIB uptake at overshoot peak/AIB uptake at equilibrium, consistent with the possibility that for [Na+] o /[Na+] i ratios in the range studied, AIB overshoot is energized by a constant proportion of the energy available from the initial electrochemical gradient for Na+. These results are consistent with the possibility that Na+-gradient dependent overshooting in SV3T3 vesicles is produced by Na+-amino acid carrier interactions resulting in either an increase in maximum transport velocity or an incrase in carrier affinity for AIB.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A model with a carrier having sites for both amino acid and Na+ can account for AIB (α-aminoisobutyric acid) transport kinetics observed in membrane vesicles from SV3T3 (simian virus 40-tranformed Balb/c3T3 cells) and 3T3 (the parent cell line). The main feature of this cotransport model is that Na+ binding to carrier decreases the effectiveK m for AIB transport, Na+ transport kinetics observed in both vesicle systems can be described by passive (possibly facilitated) diffusion. The lag of Na+ transport across the membrane compared to that for AIB, coupled to the Na+-dependent decrease in theK m for AIB, accounts for the overshoot in intravesicular AIB observed for SV3T3 in the presence of an initial Na+ gradient. Extra-vesicular Na+ maintains a derease in theK m for AIB influx before intra-vesicular Na+ has accumulated to balance it with a comparable decrease in theK m for AIB efflux. 3T3 vesicles display little overshoot, and this finding can be explained mostly by a lower carrier affinity for Na+.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Mixed membrane vesicle populations composed of plasma membrane and endoplasmic reticulum were prepared from Balb/c 3T3 and simian virus 40-transformed Balb/c 3T3 mouse fibroblasts. The initial rates of uptake of L-leucine and α-aminoisobutyric acid by these vesicles were stimulated by a NaCl gradient (external 〉 internal). Cation specificity for stimulation of L-leucine uptake was Na+ 〉 Li+ 〉 K+. NaSCN was as effective as NaCl. Stimulation of uptake of both amino acids by a NaCl gradient was twice as great in vesicles from transformed as compared to non-transformed cells. The NaCl gradient produced transient accumulation of both L-leucine and α-aminoisobutyric acid to twice the equilibrium level in vesicles from transformed cells. No such “overshoot” was observed in vesicles from nontransformed cells. In vesicles from the contact-inhibitable Balb/c 3T3 cells, transport of α-aminoisobutyric acid, but not L-leucine, exhibited a density-dependent decrease in Na+ gradient induced stimulation, from 248% for sub-confluent to 109% with confluent cells. No density-related changes in uptake were noted with vesicles from the transformed cells. These studies suggest that variations in amino acid uptake associated with viral transformation may be related, at least in part, to alterations in Na+ permeability of the surface membrane.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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