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  • 1
    Electronic Resource
    Electronic Resource
    Alanine and taurine transport by the gill epithelium of a marine bivalve: Effect of sodium on influx (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 37-45 
    Details
    ISSN: 1432-1424
    Keywords: epithelia ; integument ; coupled transport ; amino-acid transport ; taurine ; alanine ; marine bivalve ; Mytilus californianus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Marine mussels can accumulate amino acids from seawater into the epithelial cells of the gill against chemical gradients in excess of 5×106 to 1. Uptake of both alanine and taurine into gill tissue isolated fromMytilus californianus was found to be dependent upon Na+ in the external solution. Uptake of these amino acids was described by Michaelis-Menten kinetics, and a reduction in external [Na+] (from 425 to 213mm) increased the apparent Michaelis constants (alanine, from 8 to 17 μm; taurine, from 4 to 39 μm) without a significant influence on theJ max's of these processes. Fivemm harmaline, an inhibitor of Na-cotransport processes in many systems, reduced both alanine and taurine uptake by more than 95%; this inhibition appeared to be competitive in nature, with an apparentK i of 43 μm for the interaction with alanine uptake. Increasing the external [Na+] from 0 to 510mm produced a sigmoid activation of alanine and taurine uptake withK Na's of approximately 325mm. The apparent Hill coefficients for this activation were 7.3 and 7.4 for alanine and taurine, respectively. These data are consistent with uptake mechanisms which require comparatively high concentrations of Na+ to activate transport, and which couple several Na+ ions to the transport of each amino acid. These characteristics, in conjunction with the previously demonstrated low passive permeability of the apical membrane to amino acids, result in systems capable of i) accumulating amino acids from seawater to help meet the nutritional needs of this animal, and ii) maintaining the high intracellular amino-acid concentrations associated with volume regulation in the gill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869628
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  • 2
    Electronic Resource
    Electronic Resource
    l-Alanine uptake in brush border membrane vesicles from the gill of a marine bivalve (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 209-223 
    Details
    ISSN: 1432-1424
    Keywords: alanine transport ; neutral amino acid transport ; brush border membrane vesicles ; marine bivalve gills ; Mytilus edulis ; epithelia ; integument
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Brush border membrane vesicles were prepared from mussel gills using differential and sucrose density gradient centrifugation. These vesicles contained both the maximal Na+-dependent alanine transport activity found in the gradient and the maximal activities of γ-glutamyl transpeptidase and alkaline phosphatase. Electron micrographs showed closed vesicles of approximately 0.1–0.5 μm diameter. Transport experiments using these vesicles demonstrated a transient 18-fold overshoot in intravesicular alanine concentration in the presence of an inwardly directed Na+ gradient, but not under Na+ equilibrium conditions. A reduced overshoot (10-fold) was seen with an inwardly directed K+ gradient. Further studies revealed a broad cation selectivity, with preference for Na+, which was characteristic of alanine transport but not glucose transport in these membranes. The apparent amino acid specificity of the uptake pathway(s) was similar to that of intact gills and supported the idea of at least four separate pathways for amino acid transport in mussel gill brush border membranes. The apparent Michaelis constant for alanine uptake was approximately 7μm, consistent with values forK t determined with intact tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869303
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  • 3
    Electronic Resource
    Electronic Resource
    Sodiumd-glucose cotransport in the gill of marine mussels: Studies with intact tissue and brush-border membrane vesicles (1989)
    Springer
    The journal of membrane biology 107 (1989), S. 77-88 
    Details
    ISSN: 1432-1424
    Keywords: Glucose transport ; Na-glucose cotransport ; brush-border membrane vesicles ; marine bivalve gills ; Mytilus edulis ; integument
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Glucose transport was studied in marine mussels of the genusMytilus. Initial observations, with intact animals and isolated gills, indicated that net uptake of glucose occurred in mussels by a carrier-mediated, Na+-sensitive process. Subsequent studies included use of brush-border membrane vesicles (BBMV) in order to characterize this transport in greater detail. The highest activity of Na+-dependent glucose transport was found in the brush-border membrane fractions used in this study, while basal-lateral membrane fractions contained the highest specific binding of ouabain. Glucose uptake into BBMV showed specificity for Na+, and concentrative glucose transport was observed in the presence of an inwardly directed Na+ gradient. There was a single saturable pathway for glucose uptake, with an apparentK t of 3 μm in BBMV and 9 μm in intact gills. The kinetics of Na+ activation of glucose uptake were sigmoidal, with apparent Hill coefficients of 1.5 in BBMV and 1.2 in isolated gills, indicating that more than one Na+ may be involved in the transport of each glucose. Harmaline inhibited glucose transport in mussel BBMV with aK i of 44 μm. The uptake of glucose was electrogenic and stimulated by an inside-negative membrane potential. The substrate specificity in intact gills and BBMV resembled that of Na+-glucose cotransporters in other systems;d-glucose and α-methyl glucopyranoside were the most effective inhibitors of Na+-glucose transport,d-galactose was intermediate in its inhibition, and there was little or no effect ofl-glucose,d-fructose, 2-deoxy-glucose, or 3-O-methyl glucose. Phlorizin was an effective inhibitor of Na+-glucose uptake, with an apparentK i of 154nm in BBMV and 21nm in intact gills. While the qualitative characteristics of glucose transport in the mussel gill were similar to those in other epithelia, the quantitative characteristics of this process reflect adaptation to the seawater environment of this animal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871085
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  • 4
    Electronic Resource
    Electronic Resource
    A choline transporter in renal brush-border membrane vesicles: Energetics and structural specificity (1992)
    Springer
    The journal of membrane biology 126 (1992), S. 51-65 
    Details
    ISSN: 1432-1424
    Keywords: choline ; TEA ; organic cation ; transport ; proximal tubule ; kidney ; reabsorption ; secretion ; molecular modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Choline is a quaternary ammonium compound that is normally reabsorbed by the renal proximal tubule, despite its acknowledged role as a substrate for the renal organic cation (OC) secretory pathway. The basis for choline reabsorption was examined in studies of transport in rabbit renal brush-border membrane vesicles (BBMV). Although an outwardly directed H+ gradient (pH 6.0in ∶ 7.5out) stimulated uptake of tetraethylammonium (TEA), a model substrate of the OC/H+ exchanger in renal BBMV, it had no effect on uptake of 1 μ m choline. A 5 mm trans concentration gradient of choline did, however, drive countertransport of both TEA and choline, although trans TEA had no effect on choline accumulation in BBMV. A 20 mm concentration of unlabeled choline blocked uptake of both choline and TEA by 〉85%, whereas 20 mm TEA blocked only TEA uptake. The kinetics of choline uptake into vesicles preloaded with 1 mm unlabeled choline appeared to involve two, saturable transport processes, one of high affinity for choline (K t of 97 μ m) and a second of low affinity (K t of ∼10 mm), the latter presumably reflecting a weak interaction of choline with the OC/H+ exchanger. An inside-negative electrical PD stimulated the rate of uptake and supported the transient concentrative accumulation of choline in BBMV. The high affinity transporter showed a marked specificity for choline and closely related analogues. A model of the molecular determinants of substrate-transporter interaction is described. We conclude that the electrogenic high affinity pathway plays a central role in renal reabsorption of choline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233460
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  • 5
    Electronic Resource
    Electronic Resource
    Specificity of the Na+-dependent monocarboxylic acid transport pathway in rabbit renal brush border membranes (1983)
    Springer
    The journal of membrane biology 72 (1983), S. 213-221 
    Details
    ISSN: 1432-1424
    Keywords: monocarboxylate carrier ; lactate ; renal brush border membranes ; Na+-cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The substrate specificity of a Na+-dependent transport pathway forl-lactate was studied in rabbit renal brush border membrane vesicles.J max forl-lactate transport was unaffected by the presence of a fixed concentration of two different short-chain monocarboxylic acids, while the apparentK t (K a ) forl-lactate increased, and this is compatible with competitive inhibition. The inhibitor constants (“K i ”'s) for the transport pathway for the two solutes examined closely corresponded to the respective “K i ”'s derived from a Dixon plot. A broad range of compounds were then tested as potential inhibitors ofl-lactate transport, and the “K i ”'s thereby derived yielded specific information regarding optimal substrate recognition by the carrier. A single carboxyl group is an absolute requirement for recognition, and preference is given to 3 to 6 C chain molecules. Addition of ketone, hydroxyl and, particularly, amine groups at any carbon position, diminishes substrate-carrier interaction. Intramolecular forces, notably the inductive effects of halogens, may play a role in enhancing substrate-carrier interaction; however, no correlation was found between pK a and “K i ” for the substrates examined. We conclude that a separate monocarboxylic acid transport pathway, discrete from either thed-glucose, α or β neutral amino-acid, or dicarboxylic acid carriers, exists in the renal brush border, and this handles a broad range of monocarboxylates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870588
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  • 6
    Electronic Resource
    Electronic Resource
    Specificity of the transport system for tricarboxylic acid cycle intermediates in renal brush borders (1980)
    Springer
    The journal of membrane biology 57 (1980), S. 73-82 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Uptake studies employing renal brush border membranes were used to examine the structural specificity of the TCA cycle intermediate transport system. The kinetics of reciprocal inhibition between succinate and citrate revealed these compounds to be transported by a common mechanism. The Michaelis constant for succinate (0.11mm) was significantly lower than that of citrate (0.28mm), indicating that the system has a higher affinity for succinate than for citrate. The specificity of the transport system was determined from the relative inhibitory constants of 40 organic acids on the transport of succinate. The results established that the system is highly specific for 4-carbon, terminal dicarboxylic acids in thetrans-configuration, including the major intermediates of the TCA cycle. The system is comparatively insensitive to monocarboxylates. Substitution of one of several polar, noncharged residues on the α-carbon of succinate permitted interaction of the substrate with the transport system, but substitutions on both the α and \-carbons did not. The structural specificity of the system is fundamentally different from that of the dicarboxylate and tricarboxylate exchange systems of mitochondria. The role of this transport system in the reabsorption of TCA cycle intermediates from the proximal tubule is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868987
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  • 7
    Electronic Resource
    Electronic Resource
    Uptake of lysine and prolinevia separate α-neutral amino acid transport pathways inMytilus gill brush border membranes (1989)
    Springer
    The journal of membrane biology 107 (1989), S. 237-247 
    Details
    ISSN: 1432-1424
    Keywords: alanine transport ; lysine transport ; proline transport ; brush-border membrane vesicles ; Na-cotransport ; Mytilus edulis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Brush border membrane vesicles (BBMV) were prepared from the gills of the marine mussel,Mytilus edulis. These membranes contained two distinct pathways for cotransport of Na+ and α-neutral amino acids. The major pathway in mussel gill BBMV was the alanine-lysine (AK) pathway, which had a high affinity for alanine and for the cationic amino acid, lysine. The AK pathway was inhibited by nonpolar α-neutral amino acids and cationic amino acids, but was not affected by β-neutral amino acids or imino acids. The kinetics of lysine transport were consistent with a single saturable process, with aJ max of 550 pmol/mg-min and aK t of 5 μm. The AK pathway did not have a strict requirement for Na+, and concentrative transport of lysine was seen in the presence of inwardly directed gradients of Li+ and K+, as well as Na+. Harmaline inhibited the transport of lysine in solutions containing either Na+ or K+. The alanine-proline (AP) pathway transported both alanine and proline in mussel gill BBMV. The AP pathway was strongly inhibited by nonpolar α-neutral amino acids, proline, and α-(methylamino)isobutyric acid (Me-AIB). The kinetics of proline transport were described by a single saturable process, with aJ max of 180 pmol/mg-min andK t of 4 μm. In contrast to the AK pathway, the AP pathway appeared to have a strict requirement for Na+. Na+-activation experiments with lysine and proline revealed sigmoid kinetics, indicating that multiple Na+ ions are involved in the transport of these substrates. The transport of both lysine and proline was affected by membrane potential in a manner consistent with electrogenic transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871939
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  • 8
    Electronic Resource
    Electronic Resource
    Autoradiographic analysis of amino acid uptake by the gill ofMytilus (1984)
    Springer
    Journal of comparative physiology 154 (1984), S. 249-256 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Autoradiography was used to examine the influence of lateral ciliary activity on the pattern of leucine uptake into isolated gill tissue from the mussel,Mytilus californianus. Metachronal activity of the lateral cilia, normally absent in the in vitro gill, was reestablished by application of 10 μM 5-hydroxytryptamine (5-HT). This treatment produced a 5–7 fold stimulation in the rate of leucine uptake into isolated gills. The treatment with 5-HT did not, however, affect the fractional incorporation of leucine into alcohol insoluble vs alcohol soluble material. Autoradiograms of gills treated with 5-HT showed extensive labelling of frontal, lateral, and abfrontal surfaces of gill filaments compared to the control condition in which label was largely confined to the frontal region of the gill. Quantitative analyses of the autoradiograms revealed a 4-fold increase in the number of silver grains over lateral and abfrontal surfaces compared to control gills. Autoradiograms of gills from intact mussels exposed to3H-leucine showed a pattern of silver grain deposition similar to that observed in in vitro gills treated with 5-HT. It is concluded that the capacity for amino acid transport exists in cells from the frontal, lateral, and abfrontal surfaces of gill filaments, butaccess to dissolved substrates by transport sites on lateral and abfrontal surfaces is dependent upon lateral ciliary activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464404
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  • 9
    Electronic Resource
    Electronic Resource
    Multiple pathways for amino acid transport inMytilus gill (1985)
    Springer
    Journal of comparative physiology 156 (1985), S. 259-267 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The epidermal tissues of marine mussels can accumulate amino acids from surrounding sea water. In the present study, gill tissue isolated from the California coastal mussel,Mytilus californianus, was used in conjunction with intact, actively pumping mussels to study epidermal transport processes. There appeared to be at least four pathways for this uptake: i) a β-neutral pathway which transports taurine; ii) an α-acidic pathway specific for substrates such as aspartate; iii) an α-neutral pathway having a general specificity for this class of compound, but which also accepts the basic amino acid, lysine; and iv) a second α-neutral pathway, also of broad specificity, capable of accepting the imino acid, proline, as a substrate. Replacement of Naα in sea water with choline reduced uptake of leucine, taurine, aspartate, and proline by more than 95%, and reduced lysine uptake by 75%, suggesting that Naα-independent pathways play no significant role in epidermal transport in the gill. Isolated gill tissue was used to estimate the maximum transport capacities (J max's) of the pathways, which ranged from approximately 5 to 25 μmol/(g·hr). Apparent Michaelis constants (K t *'s) of the epidermal transporters were estimated using a convection-diffusion model introduced previously (Wright and Secomb, Am J Physiol 247:R346–R355, 1984). TheseK t *'s ranged from 1 to 5 μM. The characteristics of the epidermal transporters are such that they can play a significant role in both animal nutrition and in the reacumulation of endogenous amino acids lost from surface cells through passive diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00695781
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  • 10
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    Unstirred Water Layers and the Kinetics of Organic Cation Transport (2015)
    Springer
    Details
    Publication Date: 2015-03-20
    Print ISSN: 0724-8741
    Electronic ISSN: 1573-904X
    Topics: Chemistry and Pharmacology
    Published by Springer
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