Active accumulation of glutamate and aspartate by insect epidermal cells

Tomlin, E.; McLean, Heather; Caveney, Stanley

doi:10.1016/0965-1748(93)90029-r

Cited by 23 publications

(23 citation statements)

References 15 publications

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“…This glutamate uptake mechanism has a Na+-dependency similar to that described for co-transport in several vertebrate tissues (Fukuhara and Turner 1985;Erecinska 1987;Balcar 1992). We suspect that the epidermal Na +-dependent transporter for glutamate and aspartate is responsible for maintaining the plasma concentration of these amino acids in the low micromolar range (Tomlin et al 1993). …”

Section: Introductionmentioning

confidence: 71%

“…The amount of amino acid taken up by the tissue or remaining in the solution after incubation was determined by reverse-phase HPLC using a Beckman Gold HPLC system equipped with programmable pump module 126, programmable UV detector module 166 and autosampler 506. Amino acids were derivatized with phenylisothiocyanate and separated by gradient flow of two eluents through a CSC-Sil 80A 5 gm column at 40 ~ The method is described in Tomlin et al (1993). At the start of each experiment, a 25-gl aliquot of each experimental saline (containing 6.25 nmol of L-glutamate and inhibitor) was placed in 90 gl chilled acetone to which 5 nmol hydroxyproline was added as an internal standard amino acid, to determine the relative absorbances at 254 nm (response factors) of known amounts of the derivatized anaino acids.…”

Section: Detection Of Uptake Of Radiolabeled Compounds (1) [3h]l-glutmentioning

confidence: 99%

“…Despite its obvious importance, insect blood plasma has only micromolar amounts of L-glutamate and L-aspartate (Irving et al 1979a, b;Tomlin et al 1993) while containing millimolar amounts of other free amino acids [reviewed in Mullins (1985)]. It has been proposed (Irving et al 1979a, b) that the plasma levels of glutamate and aspartate are kept low in order to prevent the non-neuronal stimulation of motoneuron terminals in muscle, which in many insects are not sealed from the blood by glial elements (Osborne 1975).…”

Section: Introductionmentioning

confidence: 99%

“…It has been proposed (Irving et al 1979a, b) that the plasma levels of glutamate and aspartate are kept low in order to prevent the non-neuronal stimulation of motoneuron terminals in muscle, which in many insects are not sealed from the blood by glial elements (Osborne 1975). The tissue(s) responsible for suppressing the plasma levels of glutamate and aspartate in insects is not known, although recently epidermal tissue has been shown to be capable of selectively accumulating these two amino acids against steep concentration gradients (Tomlin et al 1993).…”

Section: Introductionmentioning

confidence: 99%

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Na+-dependent medium-affinity uptake of L-glutamate in the insect epidermis

McLean

Caveney

1993

J Comp Physiol B

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Abstract.It is proposed that the activity of an epidermal cotransport system for Na § and dicarboxylic amino acids accounts for the small amounts of L-glutamate and L-aspartate in the otherwise amino-acid-rich blood plasma of insects. This Na+-dependent transport system is responsible for more than 95% of the uptake of these amino acids into the larval epidermis of the beetle Tenebrio molitor. Kinetic analysis of uptake showed that the Na+-dependent co-transporter has medium affinity for L-glutamate and L-aspartate. The K m for L-glutamate uptake was 146 gmol.1 1, and the maximum velocity of uptake (Fmax) was 12.1 pmol.mm -2 of epidermal sheet per minute. The corresponding values for L-aspartate were 191gmol'l 1 and 8.4pmol.mm-2.min -1. The Na+/L-glutamate co-transporter has a stoichiometry of at least two Na § ions for each L-glutamate-ion transported (n=217). The co-transporter has an affinity for Na + equivalent to a K m of 21 mmol.1-1 Na +. Na + is the only external ion apparently required to drive L-glutamate uptake. Li + substitutes weakly for Na +. Removal of external K + or addition of ouabain decreases uptake slowly over 1 h, suggesting that these treatments dissipate the Na+/K + gradient by inhibiting epidermal Na+/ K + ATPase. Several structural analogues of L-glutamate inhibit the medium-affinity uptake of L-glutamate. The order of potency with which these competitive inhibitors block glutamate uptake is L-cysteate_ threo-3-hydroxy-DL-aspartate > D-aspartate > L-aspartate > L-cysteine sulphinate > L-homocysteate ~> D-glutamate. L-trans-Pyrrolidine-2,4-dicarboxylate, a potent inhibitor of L-glutamate uptake in mammalian synaptosomes, is a relatively weak blocker of epidermal uptake. The epidermis takes Abbreviations: ac, acetate; Ch, choline; CNS, central nervous system; cpm, counts per minute; CDTA, trans-l,2-diaminocyclohexane-N,N,N',N'-tetraacetic acids; HPLC, high performance liquid chromatography; Kin, Michaelis constant; napp, apparent number; NMG, N-methyl-D-glucamine; Pipes; Piperazine-N,N'-bis-[2-ethanesulfonic acid]; SD, standard deviation; TEA, tetraethyl-ammonium; V, velocity of uptake; Vmax, maximum velocity of uptake Correspondence to: H. McLean up substantially more L-glutamate by this Na+-dependent system than tissues such as skeletal muscle and ventral nerve cord. The epidermis may be a main site regulating blood L-glutamate levels in insects with high blood [Na+]. Because L-glutamate and L-aspartate stimulate skeletal muscle in insects, a likely role for epidermal Lglutamate/L-aspartate transporter is to keep the level of these excitatory amino acids in the blood below the postsynaptic activation thresholds.

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Section: Introductionmentioning

confidence: 71%

Section: Detection Of Uptake Of Radiolabeled Compounds (1) [3h]l-glutmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Na+-dependent medium-affinity uptake of L-glutamate in the insect epidermis

McLean

Caveney

1993

J Comp Physiol B

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“…Usually, the first step of amino acid absorption in insects is represented by transport from the gut lumen into the cells of the midgut and the hindgut (Wright and Ahearn, 1997). However, uptake of amino acids through epidermis has been described in some species (Tomlin et al, 1993;Giordana et al, 2003). In all instances, amino acid transport is apparently mediated by specific membrane proteins (transporters), which operate as secondary active transport systems (symporters) or mediate a facilitated diffusion (uniporters) (Wolfersberger, 2000).…”

Section: Introductionmentioning

confidence: 99%

Leucine transport in brush border membrane vesicles from freshwater insect larvae

Forcella

Berra

Giacchini

et al. 2006

Arch Insect Biochem Physiol

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Leucine transport across brush border membrane vesicles prepared from four insect species common to European freshwater streams has been characterized. The species studied were: Ephemera danica (Ephemeroptera: Ephemeridae), Isoperla grammatica (Plecoptera: Perlodidae), Hydropsyche pellucidula (Trichoptera: Hydropsychidae), and Hybomitra bimaculata (Diptera: Tabanidae). The transport differed among the studied taxa for several features, including pH and sodium dependence, substrate affinity and specificity, and efficiency. In H. pellucidula and E. danica, leucine uptake was higher at pH 7.4 than at more alkaline or acidic pH values, whereas in I. grammatica and H. bimaculata, the uptake was rather constant when pH varied from 5.0 to 7.4, then strongly decreased at pH 8.8. All but E. danica displayed a transient intravescicular leucine accumulation in the presence of sodium, suggesting the existence of a cation-leucine symport mechanism. The sodium dependence ranged according to the following order: H. pellucidula > I. grammatica > H. bimaculata > E. danica. Moreover, in H. pellucidula and I. grammatica, the sodium-dependence was stronger at pH 8.8 than at pH 7.4. In E. danica, leucine uptake was sodium-independent at all pH values. The highest value of V(max) (45.3 pmol.s(-1).mg proteins(-1)) was in E. danica, which, however, displayed the lowest affinity (K(m) 137 muM) when compared to the kinetic parameters of other taxa. The V(max) and K(m) values were: 40 and 52.5, 32.1 and 12.5, and 4.5 and 230 for H. bimaculata, H. pellucidula, and I. grammatica, respectively. The obtained results are discussed within our current knowledge of amino acid transport systems in insects.

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Insecticidal activity of glufosinate through glutamine depletion in a caterpillar

Kutlesa

Caveney

2001

Pest. Manag. Sci.

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The herbicide glufosinate-ammonium (GLA) is a competitive inhibitor of glutamine synthetase (GS), an enzyme converting glutamate to glutamine in both plants and animals. Because GS is essential for ammonia detoxification in plants, GLA treatment disrupts photorespiration by causing a build-up of ammonia and a loss of glutamine in plant tissues. This study reports that GLA applied to leaf surfaces is also toxic to 5th-instar caterpillars of the skipper butterfly Calpodes ethlius (LD50 = 400 mg kg-1). After ingesting GLA, caterpillars stopped feeding and became dehydrated through a loss of rectal function. Caterpillars showed symptoms of neurotoxicity, such as proleg tremors, body convulsions and complete paralysis before death. Incubation of several tissues isolated from normal feeding-stage caterpillars with the GS substrates glutamate and ammonium showed that GLA inhibited GS activity in vitro. Within 24 h of ingesting GLA, caterpillars had a greatly reduced glutamine content and the ammonium ion levels had more than doubled. Injection of ammonium chloride into non-GLA-treated caterpillars had no deleterious effect, suggesting that glutamine depletion, and not a rise in body ammonium, was the primary cause of GLA toxicity following GS inhibition. This was supported by the observation that the onset of the symptoms of GLA poisoning could be postponed by giving GLA-fed caterpillars several subsequent daily injections of glutamine. The effective GLA dose fed to 5th-instar caterpillars in this study was comparable to the amount that might realistically by acquired from feeding on GLA-treated crops.

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Active accumulation of glutamate and aspartate by insect epidermal cells

Cited by 23 publications

References 15 publications

Na+-dependent medium-affinity uptake of L-glutamate in the insect epidermis

Na+-dependent medium-affinity uptake of L-glutamate in the insect epidermis

Leucine transport in brush border membrane vesicles from freshwater insect larvae

Insecticidal activity of glufosinate through glutamine depletion in a caterpillar

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