Biomedical subjects

S H Wright

Publications and source records attributed to S H Wright.

At least 55 records · Page 3Linked to original sources

PubMed1995

Peritubular paraquat transport in isolated renal proximal tubules.

To better understand the characteristics of peritubular transport of organic cations (OCs), the uptake of the polyvalent OC dimethylbipyridinium (paraquat) and the structurally similar monovalent OC 1-methyl-4-phenylpyridinium (MPP+) was measured in suspensions of rabbit renal proximal tubules. Compared to the uptake of MPP+, the uptake of paraquat across the peritubular membrane was a low affinity, low capacity carrier-mediated process with a Jmax of 0.52 +/- 0.19 nmol.mg of protein.-1 min-1 and a Km of 162 +/- 25 microM. The uptake of MPP+ was a carrier-mediated process with a measured Jmax and Km of 1.8 +/- 0.09 nmol.mg of protein.-1min-1 and 28 +/- 8 microM, respectively. To determine whether paraquat is a substrate for the monovalent OC pathway, the effect of unlabeled MPP+ and tetraethylammonium (TEA) on paraquat uptake was examined. A 1 mM concentration of the monovalent OC MPP+ and TEA reduced the uptake of [14C]paraquat and [3H]MPP+ by approximately 30 and 90%, respectively, whereas 1 mM paraquat had no effect on [3H]MPP+ or [14C]TEA uptake. Thus, MPP+, but not paraquat, appears to interact with the monovalent OC transporter. On the other hand, the polyvalent OC substrates, including the polyamines putrescine and spermine, the herbicide diquat and the divalent hexamethonium bromidehydrate had no effect on either paraquat or MPP+ uptake. However, the synthetic polyamine methylglyoxal bis(guanyl-hydrazone)dihydrochloride (MGBG; 1 mM) reduced both paraquat and MPP+ uptake (by 60 and 90%, respectively). The ability of MGBG, unlike the other polyvalent substrates, to interact with paraquat transport may be related to structural similarities in the relative location of the two charged nitronium moieties in paraquat and MGBG.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenylpyridinium↗

PubMed1995

Kinetics of interactions of para-aminohippurate, probenecid, cysteine conjugates and N-acetyl cysteine conjugates with basolateral organic anion transporter in isolated rabbit proximal renal tubules.

Kinetics of the first 15 s of para-aminohippurate (PAH) uptake across the basolateral membrane of single isolated S2 segments of rabbit proximal renal tubules and the effects of probenecid and cysteine conjugates on them were determined. For PAH uptake in control tubules, Kt (the concentration of PAH at 1/2 Jmax) was about 110 microM and Jmax (maximal rate of PAH transport) was about 6.5 pmol min-1 nl-1. In tubules preloaded with alpha-ketoglutarate (alpha-KG), thereby stimulating PAH/alpha-KG countertransport, Jmax doubled with little change in Kt. Probenecid cis-inhibited PAH uptake with an apparent Ki of about 13 to 15 microM whether or not the tubules were preloaded with alpha-KG. High probenecid concentrations cis-inhibited PAH uptake by > 98%, indicating that essentially all movement of PAH across the basolateral membrane is carrier mediated. Zwitterionic nephrotoxic cysteine conjugate, S-(1,2-dichlorovinyl)-L-cysteine (DCVC), and nontoxic cysteine conjugate, S-(2-benzothiazole)-L-cysteine (BTC) cis-inhibited PAH uptake (apparent Ki: approximately 86 microM for DCVC; approximately 37 microM for BTC) at least as effectively as their negatively charged N-acetyl derivatives (NAC-DCVC and NAC-BTC) (apparent Ki: approximately 310 microM for NAC-DCVC; approximately 35 microM for NAC-BTC). The inhibition by both DCVC and NAC-DCVC was competitive in nature. NAC-DCVC also cis-inhibited net transepithelial secretion of PAH by isolated, perfused S2 segments. The presence of DCVC and NAC-DCVC, as well as PAH itself, in the bathing medium trans-stimulated the 15 s efflux of PAH across the basolateral membrane of single S2 segments with oil-filled lumens. These data indicate that these cysteine conjugates and their N-acetyl derivatives, not only interact competitively with the PAH transporter, but are transported by it.

Acetylcysteine↗

PubMed1994

Peritubular organic cation transport in isolated rabbit proximal tubules.

The physiological characteristics of peritubular organic cation transport were examined by measuring the transport of the organic cation tetraethylammonium (TEA) in rabbit renal proximal tubule suspensions and isolated nonperfused rabbit renal proximal tubules. Peritubular organic cation transport in both single S2 segments and suspensions of isolated renal proximal tubules was found to be a high-capacity, high-affinity, carrier-mediated process. For tubule suspensions, the maximal capacity of the carrier for TEA (Jmax) and the concentration of TEA at 1/2 Jmax (Kt) (1.49 +/- 0.21 nmol.min-1.mg dry wt-1 and 131 +/- 16 microM, respectively), did not differ significantly from those measured in single S2 segments (Jmax, 1.16 +/- 0.075 nmol.min-1.mg dry wt-1; Kt, 108 +/- 10 microM). In addition, the pattern of inhibition of peritubular TEA transport by long-chain n-tetraalkylammonium compounds (n = 1-5) was both qualitatively and quantitatively similar in single S2 segments and tubule suspensions, exhibiting an increase in inhibitory potency with increasing alkyl chain length. For example, in tubule suspensions, apparent Michaelis constants for inhibition of TEA uptake ranged from 1.3 mM for tetramethylammonium (TMA) to 0.8 microM for tetrapentylammonium (TPeA). To determine whether these compounds were substrates for the peritubular organic cation transporter, their effect on the efflux of [14C]TEA from tubule suspensions was examined. A concentration of 0.5 mM of the short-chain tetraalkyls TMA or TEA increased the efflux of [14C]TEA (i.e., trans-stimulated) from tubules in suspension. The longer-chain tetraalkyls tetrapropylammonium, tetrabutylammonium, and TPeA all decreased the efflux of [14C]TEA from tubules in suspension; TPeA completely blocked efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Short-term cell volume regulation in Mytilus californianus gill.

Long-term acclimation of Mytilus californianus to 60% artificial sea water (585 mosmol l-1; ASW) led to a 30-40% decrease in the taurine (53.5-36.9 mumol g-1 wet mass) and betaine (44.8-26.2 mumol g-1 wet mass) content of gill tissue, compared with that of control animals held in 100% ASW (980 mosmol l-1). The K+ content of gills did not change following long-term acclimation to reduced salinity. In contrast, losses of all three solutes during a brief (60 min) exposure to 60% ASW were less than or equal to 15%. Nevertheless, the swelling of gill cells that occurred after acute exposure to 60% ASW was followed by a return towards the control volume. Direct optical measurement of single gill filaments confirmed that, during an acute exposure to reduced salinity, ciliated lateral cells increased in cell height (volume) and then underwent a regulatory volume decrease (RVD) with a half-time of approximately 10 min. This short-term RVD was completely inhibited by exposure to 1 mmol l-1 quinidine, a K+ channel blocker, but only when the drug was applied to the basolateral aspect of the gill epithelium. Application of 1 mumol l-1 valinomycin relieved the inhibition by quinidine of the gill RVD. However, addition of valinomycin did not accelerate the rate of RVD observed in the absence of quinidine. These results indicate that long-term acclimation of Mytilus californianus gill in dilute sea water involves primarily losses of taurine and betaine, whereas short-term regulation of cell volume may involve an electrically conductive loss of intracellular K+ and a counter ion.

Acclimatization↗

PubMed1993

Seroepidemiological study of Taenia saginata cysticercosis in Swaziland.

A cross-sectional study of Taenia saginata cysticercosis in Swaziland using a serodiagnostic ELISA for parasite antigen is described. The seroprevalence and the levels of parasite antigen were compared in the sera of cattle from different geographical localities, and from areas of high or low population density. Cattle from the Lowveldt region, which has a hot and dry climate relative to the other areas investigated, exhibited significantly higher serum antigen levels. Seroprevalence was also higher in the Lowveldt but this difference was not found to be significant. Within the Lowveldt, antigen levels were found to be slightly elevated in cattle from more highly populated areas. It is suggested that either human behaviour and/or practices in animal husbandry, or increased susceptibility of cattle to reinfection at certain times of the year, may enhance transmission in the Lowveldt since climatic conditions in this region are not conducive to transmission.

Animals↗

PubMed1993

Betaine transport in rabbit renal brush-border membrane vesicles.

Transport of the organic osmolyte betaine was characterized in brush-border membrane vesicles (BBMV) isolated from rabbit renal cortex. Inwardly directed gradients of either Na+ or H+ supported concentrative uptake in a manner consistent with the presence of parallel Na(+)-betaine and H(+)-betaine cotransport processes. Concentrative uptake occurred in the presence of membrane potential alone, indicating that betaine transport is electrogenic. Accumulation of betaine was not dependent on chloride in the medium. Whereas L-proline inhibited both the H(+)- and Na(+)-sensitive components of betaine transport, glycine blocked the H(+)-sensitive pathway and had little effect on Na(+)-sensitive betaine transport. Both pathways were adequately described by Michaelis-Menten kinetics. Under Na(+)-gradient conditions (pH equilibrium), the maximal rate of total betaine transport (Jmax) = 50.8 +/- 13.3 nmol.mg-1.min-1 and the concentration of total betaine producing half-maximal uptake (Kt) = 4.1 +/- 0.5 mM. Under H(+)-gradient conditions (Na+ free), Jmax = 102.5 +/- 10.5 nmol.mg-1.min-1 and Kt = 2.8 +/- 0.3 mM. Imposition of both Na+ and H+ gradients increased Jmax (142 +/- 25.5 nmol.mg-1.min-1) to a level significantly greater than that noted in the presence of a Na+ gradient alone. We conclude that betaine transport in renal BBMV involves two distinct transport pathways that are differentiated on the basis of sensitivity to either Na+ or H+ and by their specificity to proline and glycine.

Animals↗

PubMed1993

Teaching word-finding strategies to severely language-impaired children.

The present study describes how four severely language-impaired pupils participated in an intervention programme aimed towards improving their word-finding skills. Short intervention sessions that concentrated upon a combination of both elaboration and retrieval techniques were conducted over a period of 4 weeks. Four control subjects received language therapy that was unrelated to word-finding activities. The subjects were matched for age, sex and word-finding difficulties. Results revealed that the two groups differed significantly on the accuracy of word retrieval. The four subjects that had received specific intervention improved in their ability to retrieve words. Two-tailed t-tests indicated that the improvement was highly significant at the probability level of p < 0.01 between the stages of testing. The contribution of the intervention sessions towards facilitating word-finding strategies of the four children is discussed.

Child↗

PubMed1992

High-affinity phlorizin binding in Mytilus gill.

The gill of the marine mussel, Mytilus, contains a high affinity, Na-dependent D-glucose transporter capable of accumulating glucose directly from sea water. We examined the ability of the beta-glucoside, phlorizin, to act as a high-affinity ligand of this process in intact gills and isolated brush border membrane vesicles (BBMV). The time course of association of nanomolar [3H]phlorizin to gills and BBMV was slow, with t50 values between 10 and 30 min, and a half-time for dissociation of approx. 30 min. 1 mM D-glucose reduced equilibrium binding of 1 nM phlorizin by 90-95%, indicating that there was little non-specific binding of this ligand to the gill. In addition, there was little, if any, hydrolysis by the gill of phlorizin to its constituents, glucose and phloretin. Phlorizin binding to gills and BBMV was significantly inhibited by the addition of 50 microM concentrations of D-glucose and alpha-methyl-D-glucose, and unaffected by the addition of L-glucose and fructose. Binding to gills and BBMV was reduced by greater than 90% when Na+ was replaced by K+. Replacement of Na+ by Li+ effectively blocked binding to the intact gill, although Li+ did support a limited amount of glucose-specific phlorizin binding in BBMV. The Kd values for glucose-specific phlorizin binding in intact gills and BBMV were 0.5 nM and 6 nM, respectively. We conclude that phlorizin binds with extremely high affinity to the Na-dependent glucose transporter of Mytilus gill, which may be useful in future efforts to isolate and purify the protein(s) involved in integumental glucose transport.

Animals↗

PubMed1992

A choline transporter in renal brush-border membrane vesicles: energetics and structural specificity.

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 microM 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 greater than 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 (Kt of 97 microM) and a second of low affinity (Kt of approximately 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.

Animals↗

PubMed1992

Betaine transport in the gill of a marine mussel, Mytilus californianus.

The integumental epithelium of Mytilus californianus gill accumulates amino acids directly from seawater against chemical gradients exceeding 10(7) to 1. In the present report, we confirm the presence of betaine in Mytilus tissue and identify a transport process in the gill for this organic osmolyte. Betaine content of gill tissue from animals acclimated to 100% seawater (980 mosM) was 45 mmol/kg wet wt, similar to that of taurine (53 mmol/kg). The kinetics of betaine uptake were adequately described by the Michaelis-Menten equation, with a Kt of 6 microM and Jmax of 7 mumol.g-1.h-1. Betaine transport was inhibited by L-proline and related structural analogues, and by alanine. L-Proline transport, which involves both high- and low-affinity pathways, was partially inhibited by betaine. The low-affinity proline pathway transports lysine. Betaine and L-lysine showed no reciprocal inhibitory interactions. This pattern of structural specificity suggested that betaine transport in the gill is confined to the alanine-proline pathway. Uptake of 0.5 microM betaine into gills was inhibited by 97% when Na+ in seawater was replaced with Li+. Activation of betaine transport in the gill was a near-linear function of the external Na+ concentration up through 100% artificial seawater (ASW, 425 mM Na+). Acute exposure of the gill to 60% ASW inhibited betaine uptake by 83%. Maintenance of normal osmotic concentration (980 mosM, by addition of mannitol to 60% ASW) reduced inhibition to 31%, similar to the level predicted from the availability of Na+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Integumental taurine transport in Mytilus gill: short-term adaptation to reduced salinity.

Taurine, a principal osmolyte in molluscan integument, is actively transported from sea water by Mytilus gill by means of a Na(+)-dependent process. In this study we examined the response of this transport to reductions in external salinity, i.e. the response to reductions in osmotic concentration as well as Na+ concentration. Acute exposure of isolated gill tissue to 60% artificial sea water (ASW) resulted in a greater than 85% inhibition of taurine uptake, substantially more than the 45% inhibition predicted on the basis of the acute reduction in external [Na+]. Within 60 min, however, taurine transport recovered to the level predicted by the Na+ concentration in dilute sea water. Isolated gills acutely exposed to 60% ASW made isosmotic to normal (100%) ASW with mannitol had rates of taurine uptake comparable to gills acclimated for 60 min. Taurine uptake by gill tissue exposed to 60% ASW for 60 min and then returned to 100% ASW for 90 min was not significantly different from that of control gills held in 100% ASW. Glucose uptake by the gill during acute exposure to reduced salinity responded in a pattern similar to that of taurine. Gill tissue increased by 20% in wet mass within 2 min of exposure to 60% ASW, but returned to control mass within 30-60 min, presumably reflecting cell volume regulation. Long-term (12 days) exposure to reduced salinities was not accompanied by increases in taurine transport over that of gills observed following the 60 min 'short-term' acclimation. These results suggest that Mytilus gill undergoes a rapid (albeit incomplete) recovery from the extreme inhibition of transport associated with abrupt changes in salinity, and the extent of recovery is defined by the availability of Na+ in the external medium. The extreme sensitivity of taurine uptake observed after acute exposure of gills to reduced salinity is related to the osmotic concentration of the medium, and is possibly linked to a change in cell volume.

Adaptation, Physiological↗

PubMed1992

A multicenter, randomized, controlled trial to evaluate the effect of prophylactic octreotide on ERCP-induced pancreatitis.

Eight-four patients undergoing endoscopic retrograde cholangiopancreatography (ERCP) were randomized to receive 100 micrograms of octreotide intravenously immediately prior to ERCP, and 100 micrograms subcutaneously 45 min after the initial dose, or placebo. Amylase, lipase, and glucose were measured and clinical assessment was performed before, and 2 and 24 h after, ERCP. We define clinical pancreatitis as the combination of elevated amylase or lipase with abdominal pain and tenderness. Interim analysis in 84 patients revealed an 11% incidence of clinical pancreatitis in the control group and 35% in the treatment group (p < 0.01). There were no differences in either group with respect to sphincterotomy, gender, age, duration of ERCP, number of cannulations of the pancreatic duct, degree of duct injection, or the volume of contrast injected. Analysis of group differences stratified by sphincterotomy revealed the following: 1) In patients who did not undergo a sphincterotomy, there was a significantly higher rate of pancreatitis in the treatment group [10/17 (59%) versus 1/17 (6%) RR 10.0 (95% CI 1.4-69.8)]. 2) Sphincterotomy reduced the rate of pancreatitis in patients who received octreotide from 10/17 (59% no sphincterotomy), to 3/20 (15% sphincterotomy) (p = 0.01), which equals the rate in patients who received placebo and underwent sphincterotomy [4/25 (16%)]. 3) Although the incidence of pancreatitis was higher in the treatment group, octreotide may reduce the severity of pancreatitis measured by the number of days NPO (Wilcoxon rank sum, p = 0.02), length of stay after ERCP (p = 0.13), the number of days of pain (p = 0.11), and the degree of amylase elevation (p = 0.04). We conclude that: 1) Octreotide appears to increase the incidence of pancreatitis when given prophylactically for diagnostic ERCP. 2) Although pancreatitis was more common in the octreotide group, it was less severe than the placebo group. 3) Sphincterotomy may afford protection against pancreatitis in patients who received octreotide. 4) We cannot recommend the use of prophylactic octreotide during diagnostic or therapeutic ERCP.

Amylases↗

PubMed1991

Tetraethylammonium transport by snake renal brush-border membrane vesicles.

Transport of tetraethylammonium (TEA) by snake (Thamnophis spp.) renal brush-border membrane vesicles (BBMV) was studied. An outwardly directed proton gradient (pH 6.0 in, pH 7.5 out) stimulated uptake of TEA into BBMV and supported concentrative accumulation. Uptake of radioactively labeled TEA was also stimulated by outwardly directed gradients of unlabeled TEA and choline. The initial rate of TEA uptake was a saturable process that was adequately described by Michaelis-Menten kinetics. TEA uptake was not influenced by changes in the electrical potential difference across the membranes. Although uptake of TEA was stimulated by an outwardly directed Na+ gradient and inhibited by an inwardly directed Na+ gradient, these effects were probably secondary to the generation of proton gradients via a Na+/H+ exchanger demonstrated in these same BBMV. In agreement with previous studies with intact snake renal tubules, the present results indicate that TEA transport across the brush-border membrane involves electroneutral countertransport for protons or organic cations.

Animals↗

PubMed1991

Basolateral tetraethylammonium transport in intact tubules: specificity and trans-stimulation.

To examine the specificity of proximal renal basolateral organic cation transport, the effects of unlabeled organic cation substrates in the bathing medium on the rate of uptake [14C]tetraethylammonium ([14C]TEA) by intact nonperfused proximal tubules and isolated basolateral membrane vesicles (BLMV) from rabbit kidneys were explored. The pattern of inhibition of transport by a battery of unlabeled organic cations was similar in intact tubules and BLMV. To determine if trans-stimulation could be demonstrated across the basolateral membrane of intact tubules, the effects of preloading tubules with unlabeled substrates on the rate of uptake of [14C]TEA and the effects of unlabeled substrates in the bathing medium on the rate of efflux of [14C]TEA from tubules preloaded with this labeled substrate were examined. Trans-stimulation was clearly demonstrated for the first time in intact tubules. However, of the compounds that significantly inhibited [14C]TEA uptake (TEA, amiloride, tetrapropylammonium, mepiperphenidol, isopropyl pyridinium, and choline), only TEA itself and choline produced a trans-stimulation of [14C]TEA uptake. Moreover, choline appeared to be at least as effective as TEA itself as a counter ion for TEA transport. Such trans-stimulation could play a physiological role in the net reabsorption of choline and the net secretion of most other organic cations.

Animals↗

PubMed1990

MPP+ is transported by the TEA(+)-H+ exchanger of renal brush-border membrane vesicles.

Rabbit renal brush-border membrane vesicles (BBMV) were used to study the transport of the cationic neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). An outwardly directed H(+)-gradient stimulated MPP+ uptake and led to the development of an active accumulation of MPP+ within the vesicles. H(+)-gradient driven MPP+ transport was saturable, with a maximal transport rate of 3 nmol.mg-1.min-1 and an apparent Michaelis constant (Kt) of 8 microM. MPP+ and tetraethylammonium (TEA) behaved as competitive inhibitors of one another's transport in renal BBMV, suggesting the presence of a common transport pathway for these organic cations. At an ambient pH of 7.5, preloading BBMV with MPP+ failed to stimulate TEA uptake, although trans TEA did stimulate MPP+ uptake. Increasing ambient pH to 8.5 (i.e., reducing competition between H+ and these organic cations for a common transport pathway) led to a clear reciprocal trans stimulation of TEA and MPP+ fluxes. With an equilibrium-shift protocol, a trans concentration of MPP+ energized uphill transport of TEA. We conclude that MPP+ and TEA share a common organic cation-H+ exchange pathway in the renal brush border, although turnover of an MPP(+)-loaded exchanger is slow compared with that for a TEA or H(+)-loaded exchanger.

1-Methyl-4-phenylpyridinium↗

PubMed1989

Sodium D-glucose cotransport in the gill of marine mussels: studies with intact tissue and brush-border membrane vesicles.

Glucose transport was studied in marine mussels of the genus Mytilus. 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 apparent Kt of 3 microM in BBMV and 9 microM 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 a Ki of 44 microM. 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 alpha-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 of L-glucose, D-fructose, 2-deoxy-glucose, or 3-O-methyl glucose. Phlorizin was an effective inhibitor of Na+-glucose uptake, with an apparent Ki of 154 nM in BBMV and 21 nM 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.

Animals↗

PubMed1989

Uptake of lysine and proline via separate alpha-neutral amino acid transport pathways in Mytilus gill brush border membranes.

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 alpha-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 alpha-neutral amino acids and cationic amino acids, but was not affected by beta-neutral amino acids or imino acids. The kinetics of lysine transport were consistent with a single saturable process, with a Jmax of 550 pmol/mg-min and a Kt of 5 microM. 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 alpha-neutral amino acids, proline, and alpha-(methylamino)isobutyric acid (Me-AIB). The kinetics of proline transport were described by a single saturable process, with a Jmax of 180 pmol/mg-min and Kt of 4 microM. 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.

Alanine↗

PubMed1989

Specific detection of circulating surface/secreted glycoproteins of viable cysticerci in Taenia saginata cysticercosis.

A mouse monoclonal antibody (MoAb), reactive with a repetitive carbohydrate epitope on lentil-lectin adherent glycoproteins present on the surface and in the secretions of Taenia saginata cysticerci, was used in the construction of a diagnostic ELISA assay to detect these glycoproteins in the serum of T. saginata infected cattle. The MoAb was used as the trapping layer and subsequently bound glycoprotein was revealed using the same MoAb and biotinylated peroxidase-streptavidin complex as the developing system. The assay was suitably specific. Exceptionally low background values were obtained with sera from animals with a range of commonly occurring tropical parasitic infections, including Taenia hydatigena, Echinococcus granulosus and Fasciola gigantica. The minimal detection level was approximately 200 live cysticerci in cattle. Parasite derived glycoprotein could be detected in serum from about 4-5 weeks post-infection onwards and was associated with a current infection, as drug treatment of infected cattle to kill the cysticerci resulted in the disappearance of these components from the circulation, while the titre of anti-parasite antibody remained high. The same assay also detected Taenia solium cysticercosis in humans.

Animals↗