Specificity of the fluorescein transport process in Malpighian tubules of the cricket Acheta domesticus
1 Department of Biology, Eastern Mennonite University, Harrisonburg, VA
22802, USA
2 Ohio State University, School of Public Health, Columbus, OH 43210,
USA
* Author for correspondence (e-mail: neufeldd{at}emu.edu)
Accepted 23 March 2005
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Summary |
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Key words: Malpighian tubules, fluorescein, organic anion transport, Acheta domesticus, pesticide
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Introduction |
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The Malpighian tubule of insects performs a role analogous to that of
vertebrate kidneys, and is recognized as a model transport epithelia with
impressive capacities for both solute and water transport
(Maddrell, 1991). Studies of
transport function in this tissue have largely focused on elucidating
mechanisms for ion transport, and have demonstrated the critical physiological
role of this organ in surviving the wide range of conditions inhabited by
insects (Pannabecker, 1995
).
For instance, the fast response and high transport rate in Malpighian tubules
of blood-sucking insects are recognized as crucial adaptations for a feeding
strategy that relies on rapidly processing large, dilute blood meals
(Maddrell, 1991
). A number of
studies have pointed to a similar adaptive role for the transport of organic
substances by Malpighian tubules, including a role in the secretion of
xenobiotics (e.g. Hanson et al., 1980;
Meredith et al., 1984
).
Furthermore, evidence from several studies suggests that the upregulation of
xenobiotic transport may confer resistance to pesticides in insects
(Lanning et al., 1996
), or
other invertebrates (Cornwall et al.,
1995
). A role for transport in acquired xenobiotic resistance
would not be surprising, given that transport-mediated drug resistance in
vertebrate tissues is implicated in the ability of cells to tolerate
xenobiotic exposures (Ambudkar et al.,
1999
).
Given that the organic anion transport process appears to be present in
Malpighian tubules (Bresler et al.,
1990; Linton and O'Donnell,
2000
), and that this transport process handles environmentally
relevant compounds in other species (e.g.
Dawson and Renfro, 1993
), we
hypothesized that organic anion transport may play a key role in insect
survival during exposure to toxins. We report here on the specificity of this
process in the house cricket Acheta domesticus, and implicate the
process in the handling of at least one insecticide metabolite a
metabolic product of malathion.
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Materials and methods |
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Standard testing procedure was to measure uptake in two consecutive periods (Fig. 1). During the first measurement period, we exposed tubules to Ringer's solution containing 0.5 µmol l1 FL. We allowed chamber change-out for approximately 40 s, and then measured the rate of accumulation over the following 3040 s. For the second measurement period, solution was switched to either a control solution (an identical solution, Ringer's + 0.5 µmol l1 FL), or to a test solution (a solution containing 0.5 µmol l1 FL + the test compound). As with the first measurement period, we measured uptake rates for 3040 s after a 40 s chamber change-out period. After an uptake trial, the solution was switched back to plain Ringer's and tubules were allowed to recover (with FL washout) for at least 10 min. Multiple uptake tests could normally be performed for 23 h in this manner before there was a substantial decrease in FL accumulation; in no case was there evidence of obvious toxicity of the test compounds (i.e. lack of FL accumulation after the recovery period that followed a test exposure). All FL concentrations were 0.5 µmol l1, except for the trials to determine kinetics. In the kinetics trials, we calculated Km values for four tubules that were each exposed to FL concentrations of 0.5, 2, 3.5, 7 and 14 µmol l1.
Quantification of fluorescein accumulation in whole tubules by fluorescence photometry
In selected cases, FL accumulation was also assessed for whole Malpighian
tubules using fluorescence photometry. Individual Malpighian tubules were
digitally photographed under a dissecting microscope (for length
measurements), and then incubated in Ringer's containing 0.5 µmol
l1 FL in the presence or absence of a test compound. Tubules
were rinsed three times for 30 s each in Ringer's alone, and then digested in
200 µl of 0.1 mol l1 NaOH. Fluorescence intensity of
tubule extracts and standard solutions were then measured using a luminescence
spectrometer (LS-55, Perkin-Elmer) with excitation/emission wavelengths of 492
nm/520 nm, respectively. Uptake rates were standardized to the measured length
of the tubule.
HPLC measurement of pesticide metabolites in Malpighian tubules
Accumulations of 3-phenoxybenzoic acid (PBA) and malathion monocarboxylic
acid (MMA) in Malpighian tubules were measured directly by HPLC. Rather than
using single Malpighian tubules, we pooled groups of Malpighian tubules from
multiple crickets in order to increase the tissue mass to the point that we
could detect the presence of these compounds. For each experiment, we
dissected the complete complex of Malpighian tubules (representing
approximately 100 tubules; Spring and Kim,
1993) from five crickets. When cut at the ureter, near its
connection with the colon, each complex of Malpighian tubules stayed together
as a single unit, connected via the ampula.
Each complex of Malpighian tubules (from a single cricket) was cut approximately in half; one half was used as a control (for exposure to the metabolite alone), and the other half was used in test solution (for exposure to metabolite plus inhibitor). For control trials, each one-half of a Malpighian tubule complex was exposed to 1 mmol l1 of the metabolite for a 1 h period. The complex was then rinsed three times for 30 s each in Ringer's solution, and then extracted in 1 ml of HPLC grade water for at least 1 h. Each half-complex from the five crickets was combined into the same 1 ml extraction volume; each sample therefore represents the pooled tissue from five separate tubule complexes. Extracts were vortexed and then centrifuged prior to further processing. Test conditions followed the general procedure described above for controls, and took two forms. First, we tested the effect of organic anion transport inhibitors on metabolite accumulation. FL was used to test for inhibition of PBA accumulation. Because the FL retention time overlapped with the MMA metabolite peaks under the HPLC conditions used, we used PBD as an inhibitor of MMA accumulation. The second type of test condition exposed tubules for 1 min to HPLC-grade water, prior to exposure to the metabolite. Exposure to water alone for a short period stopped FL transport (data not shown), presumably by causing cellular rupture, but maintained some structural integrity of the tubule due to the basal lamina surrounding the cells of the Malpighian tubules. Metabolite accumulation after exposure to water is indicative of non-specific binding rather than mediated transport.
After extraction, samples were cleaned by solid-phase extraction (strong
anion exchange cartridge; Accubond II SAX, Agilent Technologies, Palo Alto,
CA, USA) based on the procedure of Abu-Qare and Abou-Donia
(2001). Prior to sample
loading, the SAX cartridge was prepared with 2 ml of retention buffer
(HPLC-grade water adjusted to pH 7 with acetic acid and NaOH). The cartridge
was loaded with 0.75 ml of centrifuged sample, rinsed with 2 ml of retention
buffer, and then extracted with 2 ml of extraction buffer (50 mmol
l1 citric acid, pH 2). Extraction by SAX cartridges of
standard solutions indicated a recovery of 89% for PBA, and 82% and 93% (for
the first and second isomer peaks, respectively) for MMA. All samples were
then run through a 0.45 µm filter (Millex-LH, Millipore, Billerica, MA,
USA) prior to HPLC injection. We used a gradient from 55:45 acetonitrile:water
(adjusted to pH 3.5 with acetic acid) to 100% ACN over a 20 min period on a 5
µm C18 column (Zorbax Eclipse XDB-C18, 4.6 mm x 250 mm). Compounds
were detected by UV absorbance at 210 nm: a single peak for PBA was detected
at approximately 7.9 min, and a double peak for MMA isomers eluted at 5.7 and
6.2 min.
Statistics
All uptake trials using fluorescence microscopy are reported as the rate of
uptake during the second measurement period relative to the rate of uptake
during the first measurement period. The effect of the presence of test
compounds on FL uptake was analyzed with a paired t-test by comparing
this change in uptake rate (between first and second measurement periods) in
the presence vs absence of test compound. All reported values are
means ± S.E.M.
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Results |
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Inhibition of fluorescein accumulation
Inhibitors of organic solute transport
We tested for inhibition of FL uptake by a range of compounds that
represent known inhibitors of various organic solute transport processes
(Table 1). Although the classic
organic anion transport inhibitor p-aminohippuric acid (PAH) did not
show inhibition at concentrations up to 3 mmol l1, other
known blockers of organic anion transport (probenecid (PBD),
bromosulfophthalein, methotrexate, salicyclic acid and penicillin) did block
uptake. As expected, the classic organic cation transport blocker
tetraethylammonium (TEA) showed no inhibition of FL uptake. Verapamil, a
blocker of p-glycoprotein (p-gp; multi-drug resistance
transporter) transport, was effective at blocking FL uptake.
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Carboxylic acids
Since the uptake by organic anion transport is typically inhibited by
aliphatic mono- and dicarboxylic acids in a defined size range
(Ullrich et al., 1987), we
tested for inhibition of FL uptake by carboxylic acids with a range of carbon
backbone lengths. Inhibition by monocarboxylic acids increased with length of
carbon chains (Fig. 3),
although this inhibition was evident only at the higher (3 mmol
l1) inhibitor concentrations. Evidence for inhibition by
dicarboxylic acids was weak, with only the longest chain compound (sebacic
acid with a 10 carbon backbone) showing any evidence of inhibition.
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Inhibition of FL accumulation in Drosophila
FL accumulation was also evident in Malpighian tubules of
Drosophila; we therefore tested several compounds for FL inhibition
in Drosophila (Fig.
5). As with Acheta, FL uptake was notably decreased by
PBD and PBA. However, unlike in Acheta, the classic organic anion
transport inhibitor PAH was effective at blocking FL uptake in
Drosophila.
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Discussion |
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The demonstration of the transport of organic anions in Acheta is
consistent with other studies that report organic anion transport in
Malpighian tubules of insects (Bresler et
al., 1990; Linton and
O'Donnell, 2000
; Maddrell and
Gardiner, 1975
). The specificity of the transport process in
Acheta and other insects shows similarities with specific organic
anion transporters in mammals. For instance, inhibition of organic anion
transport in insects by PBD (present study;
Linton and O'Donnell, 2000
), a
prototypical inhibitor of organic anion transport, mirrors results found in
mammalian systems (Burckhardt and
Burckhardt, 2003
). Likewise, bromosulfophthalein, salicylic acid,
penicillin, methotrexate, and the larger dicarboxylic acids all effectively
inhibited FL accumulation in Acheta, and are known substrates for one
or multiple isoforms of the OAT transporter in mammals
(Burckhardt and Burckhardt,
2003
).
In other respects, specificity of FL transport in Acheta does not
match the `classic' model for organic anion transport. A number of compounds
that commonly inhibit organic anion transport in other animals did not affect
FL accumulation in Acheta. FL accumulation was not affected by PAH, a
prototypical organic anion transport inhibitor in mammals that also inhibits
organic anion transport in Drosophila
(Linton and O'Donnell, 2000)
and several orthopteran species (Bresler et
al., 1990
). The monocarboxylate glutarate likewise had no effect
on FL accumulation. This is consistent with the finding of Linton and
O'Donnell (2000
) in
Drosophila who found that PAH transport was insensitive to preloading
by
-ketoglutarate. Monocarboxylic acids such as
-ketoglutarate
or glutarate act as a counterion in the classic model of organic anion
transport. However, recent evidence indicates that not all isoforms of organic
anion transporters in mammals have high affinity for PAH
(Zhang et al., 2004
), and that
some isoforms do not act as exchangers with monocarboxylic acids
(Burckhardt and Burckhardt,
2003
). Thus FL transport in Acheta is more consistent
with a basolateral transport step that does not follow the `classic' pattern
of specificity. Finally, organic anion transport in Acheta seemed to
prefer larger compounds than organic anion transport in mammals, based on
tests of related molecules of differing sizes. For instance, whereas
dicarboxylic acids with shorter (5 carbon) backbones are effective at blocking
FL in rat (Ullrich et al.,
1987
), dicarboxylic acids only inhibited FL in Acheta
when of a larger size, and at a higher concentration.
FL transport in Acheta was inhibited by several compounds normally
not associated with organic anion transport (OAT). Both verapamil and quinine,
typically considered substrates of the multidrug resistant transporter
p-gp (Ambudkar et al.,
1999), decreased FL accumulation in Acheta. However, the
decrease in FL accumulation seen in the presence of these, or other, test
compounds could have been due to effects on either the basolateral or apical
surfaces of the Malpighian tubule. In other systems, FL translocation across
the basolateral surface occurs via an OAT transporter, but its
translocation across the apical surface has been studied less. Thus,
inhibition of FL transport by verapamil and quinine in Acheta may not
indicate an OAT with unusual charge requirements.
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Inhibition of FL transport by the plant alkaloid quinine suggest that
organic anion transport may play a role in the excretion of naturally
occurring toxins associated with plant diets. This is consistent with a number
of other studies, suggesting that xenobiotic excretion allows insects to
utilize plants that contain toxic alkaloids
(Gaertner et al., 1998;
Lanning et al., 1996
).
Inhibition of FL transport by decyl-glutathione in Acheta suggests
that glutathione conjugates may represent a second class of xenobiotic
compounds that could be handled by the organic anion transport pathway. In
`Phase II' (conjugative) biotransformation that uses glutathione, potentially
toxic compounds are attached to the sulfhydryl group (on cysteine) of
glutathione, making them substrates for excretion. The process is well studied
in mammals, where organic anion transport is known to handle a variety of
glutathione conjugates (Ullrich et al.,
1989
). Many xenobiotics in fact go through Phase II
biotransformation as part of the detoxification process in insects
(Hemingway et al., 2004
). For
example, glutathione S-transferase activity is upregulated in
Anopheles mosquitoes resistant to DDT
(Ranson et al., 2001
). Thus,
organic anion transport could also be a pathway for moving conjugation
products through the Malpighian tubules for excretion.
Herbicides, insecticides and insecticide metabolites represent a third
class of compounds that are potential substrates for transport via
organic anion transport. One of the most common herbicides in use, 2,4-D, has
a moderate size and a carboxyl group, making it a likely substrate for organic
anion transport, as it is in other species (e.g.
Dawson and Renfro, 1993).
Indeed, both 2,4-D and 2,4-DB (a related herbicide with a longer carbon chain
on its carboxyl side group) were potent inhibitors of FL transport in
Acheta. Furthermore, 2,4-DB (the more effective inhibitor) stimulated
a net loss of FL from the tubule (Table
2), perhaps representing trans-stimulation of efflux (a
FL efflux that is stimulated by the increased influx of its counterion). A
similar trans-stimulation of organic anion transport was reported for
a number of other chlorophenoxy acid herbicides in flounder proximal tubules
(Dawson and Renfro, 1993
),
We tested a number of insecticides and their metabolites for FL transport. Although several parent compounds (permethrin and carbaryl) showed modest inhibition, a more marked effect was noted for the Phase I biotransformation products of malathion and permethrin (malathion monocarboxylic acid, MMA, and 3-phenoxybenzoic acid, PBA, respectively). In fact, the moderate size and carboxylic acid side groups of both compounds make them candidates for organic anion transport. Since inhibition of FL transport does not necessarily imply that the test compound is translocated, we quantified MMA and PBA accumulation more directly with HPLC. Both MMA and PBA clearly accumulated in Malpighian tubules, but only MMA showed evidence of mediated transport MMA accumulation was partially inhibited both by PBA, an organic anion transport inhibitor, and by pretreatment with water (which killed tubules). PBA accumulation, on the other hand, was unaffected by either FL or water pretreatment, suggesting that accumulation of this metabolite reflected nonspecific binding.
Acquired resistance to pesticides such as malathion clearly involves an
increase in enzymatic biotransformation (e.g.
Haubruge et al., 2002;
Pasteur et al., 2001
). During
acquisition of malathion resistance, carboxyesterases are commonly
upregulated, increasing MMA production and diverting malathion away from the
more toxic malathion oxon derivative (Fig.
7), which is not an organic anion transport substrate
(Table 2). In mosquitoes,
carboxyesterases are particularly common in the alimentary canal, where they
would be positioned to transform malathion into its carboxylic acid derivative
as the toxin is taken up into the insect body
(Pasteur et al., 2001
). Thus,
upregulation of MMA excretion by the Malpighian tubules of Acheta may
complement an upregulation of malathion biotransformation to MMA.
It has become clear that molecular mechanisms of resistance acquisition can
differ between strains of insects, even for the same insecticide (e.g.
Pasteur et al., 2001).
Likewise, different species have differing sensitivities to pesticides (e.g.
Karunaratne and Hemingway,
2001
). We suggest that, just as enzyme activity underlies some
differences in pesticide susceptibility between some species and strains, so
might differences in transport activity underlie differences in pesticide
susceptibility. Thus, the difference in the ability of organic anion transport
to use MMA and PBA as substrates could in part explain the observation that
insects sometimes do not show cross-resistance between malathion and
permethrin (Bisset et al.,
1991
): increased excretion of the malathion metabolite would not
imply an increased excretion of the permethrin metabolite. In addition,
competitive interactions at the site of the transporter could underlie the
effectiveness of some pesticide adjuvants. Inclusion of a transport inhibitor
in a pesticide mixture could effectively decrease the transport detoxification
mechanism for the insect, just as the use of inhibition of transport can
modulate chemical nephrotoxicity in mammals
(Berndt, 1998
).
In summary, we have demonstrated a robust process for the transport of
organic anions in Malpighian tubules of Acheta. Plant alkaloids,
glutathione conjugates and pesticide metabolites all interacted with the
transporter, and at least one pesticide metabolite (MMA) was accumulated by
Malpighian tubules via mediated transport. A similar handling of
pesticide metabolites by organic anion transport could occur in humans and
other mammals, given that MMA is rapidly produced and excreted from humans
(Tuomianen et al., 2002). To
our knowledge, there are no reports of whether MMA interacts with organic
anion transport in mammalian systems. From a functional standpoint, the
organic anion transport process in insects is thus poised to act as a key
component in acquired resistance to xenobiotics.
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Acknowledgments |
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References |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Abu-Qare, A. W. and Abou-Donia, M. B. (2001). Simultaneous determination of malathion, permethrin, DEET (N,N-diethyl-m-toluamide), and their metabolites in rate plasma and urine using high performance liquid chromatography. J. Pharmacol. Biomed. Anal. 26,291 -299.[CrossRef]
Ambudkar, S. V., Dey, S., Hrycyna, C. A., Ramachandra, M., Pastan, I. and Gottesman, M. M. (1999). Biochemical, cellular, and pharmacological aspects of the multidrug transporter. Annu. Rev. Pharmacol. Toxicol. 39,361 -398.[CrossRef][Medline]
Berndt, W. O. (1998). The role of transport in chemical nephrotoxicity. Toxicol. Pathol. 26, 52-57.[Medline]
Bisset, J. A., Rodriguez, M. M., Hemingway, J., Diaz, C., Small, G. J. and Ortiz, E. (1991). Malathion and pyrethroid resistance in Culex quinquefasciatus from Cuba: efficacy of pirimiphos-methyl in the presence of at least three resistance mechanisms. Med. Vet. Entomol. 5,223 -228.[Medline]
Bresler, V. M., Belyaeva, E. A. and Mozhayeva, M. G. (1990). A comparative study on the system of active transport of organic acids in Malpighian tubules of insects. J. Insect Physiol. 36,259 -270.[CrossRef]
Burckhardt, B. C. and Burckhardt, G. (2003). Transport of organic anions across the basolateral membrane of proximal tubule cells. Physiol. Biochem. Pharmacol. 146,95 -158.
Cornwall, R., Toomey, B. H., Bard, S., Bacon, C., Jarmon, W. M. and Epel, D. (1995). Characterization of multixenobiotic/multidrug transport in the gills of the mussel Mytilus californianus and identification of environmental substrates. Aquat. Toxicol. 31,277 -296.[CrossRef]
Dantzler, W. H. (2002). Renal organic anion transport: a comparative and cellular perspective. Biochim. Biophys. Acta 1566,169 -181.[Medline]
Dawson, M. A. and Renfro, J. L. (1993). Interaction of structurally similar pesticides with organic anion transport by primary cultures of winter flounder renal proximal tubule. J. Pharm. Exp. Ther. 266,673 -677.[Abstract]
Gaertner, L. S., Murray, C. L. and Morris, C. E.
(1998). Transepithelial transport of nicotine and vinblastine in
isolated Malpighian tubules of the tobacco hornworm (Manduca sexta)
suggests a P-glycoprotein-like mechanism. J. Exp.
Biol. 201,2637
-2645.
Hansen, C. R., Gauss, J. D. and Kawatski, J. A. (1980). Whole-body distribution and Malpighian tubule transport of 2',5-dichloro-4'-nitrosalicylanilide (Bayer 73) and 3-trifluoromethyl-4-nitrophenol in larvae of the aquatic midge Chironomus tentans. Xenobiotica 4,257 -263.
Haubruge, E., Amichot, M., Cuany, A., Berge, J. B. and Arnaud, L. (2002). Purification and characterization of a carboxylesterase involved in malathion-specific resistance from Tribolium castaneum (Coleoptera: Tenebrionidae). Insect Biochem. Mol. Biol. 32,1181 -1190.[CrossRef][Medline]
Hemingway, J., Hawkes, N. J., McCarroll, L. and Ranson, H. (2004). The molecular basis of insecticide resistance in mosquitoes. Insect Biochem. Mol. Biol. 34,653 -665.[CrossRef][Medline]
Karnaky, K. J., Jr, Sedmerova, M., Petzel, D., Bridges, J., Boatwright, S. W. and Miller, D. S. (2001). Mrp2-like transport in the Malpighian tubule of the cricket, Acheta domesticus.Bull. Mt. Des. Isl. Biol. Lab. 40, 53-55.
Karunaratne, S. H. P. P. and Hemingway, J. (2001). Malathion resistance and prevalence of the malathion carboxylesterase mechanism in populations of mosquito vectors of disease in Sri Lanka. B. World Health Organ. 79,1060 -1064.
Lanning, C. L., Fine, R. L., Corcoran, J. J., Ayad, H. M., Rose, R. L. and About-Donia, M. B. (1996). Tobacco budworm P-glycoprotein: biochemical characterization and its involvement in pesticide resistance. Biochim. Biophys. Acta 1291,155 -162.[Medline]
Linton, S. M. and O'Donnell, M. J. (2000).
Novel aspects of the transport of organic anions by the Malpighian tubules of
Drosophila melanogaster. J. Exp. Biol.
203,3575
-3584.
Maddrell, S. H. P. (1991). The fastest fluid-secreting cell known: the upper Malpighian tubule cell of Rhodnius.BioEssays 13,357 -362.[CrossRef]
Maddrell, S. H. P. and Gardiner, B. O. C.
(1975). Induction of transport of organic anions in Malpighian
tubules of Rhodnius. J. Exp. Biol.
63,755
-761.
Meredith, J., Moore, L. and Scudder, G. G. E. (1984). Excretion of ouabain by Malpighian tubules of Oncopeltus fasciatus. Am. J. Physiol. 246,R705 -R715.[Medline]
Pannabecker, T. (1995). Physiology of the Malpighian tubule. Annu. Rev. Entomol. 40,493 -510.[CrossRef]
Pasteur, N., Nance, E. and Bons, N. (2001). Tissue localization of overproduced esterases in the Mosquito Culex pipiens (Diptera: Culicidae). J. Med. Entomol. 38,791 -801.[Medline]
Ranson, H., Rossiter, L., Ortelli, F., Jensen, B., Wang, X., Roth, C. W., Collins, F. H. and Hemingway, J. (2001). Identification of a novel class of insect glutathione S-transferases involved in resistance of DDT in the malaria vector Anopheles gambiae.Biochem. J. 359,295 -304.[CrossRef][Medline]
Spring, J. H. and Hazelton, S. R. (1987). Excretion in the house cricket (Acheta domesticus): Stimulation of diuresis by tissue homogenates. J. Exp. Biol. 129, 63-81.
Spring, J. H. and Kim, I. S. (1993). Excretion in the house cricket: structural and functional differences between distal and mid-tubules. Mol. Comp. Physiol. 12,130 -145.
Tuomianen, A., Kangas, J. A., Meuling, W. J. A. and Glass, R. C. (2002). Monitoring of pesticide applicators for potential dermal exposure to malathion and biomarkers in urine. Toxicol. Lett. 134,125 -132.[CrossRef][Medline]
Ullrich, K. J. (1997). Renal transporters for organic anions and organic cations. Structural requirements for substrates. J. Membr. Biol. 158,95 -107.[CrossRef][Medline]
Ullrich, K. J., Rumrich, G., Fritzsch, G. and Kloss, S. (1987). Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney. II. Specificity: Aliphatic dicarboxylic acids. Pflugers Arch. 408, 38-45.[CrossRef][Medline]
Ullrich, K. J., Rumrich, G., Wieland, T. and Dekant, W. (1989). Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney. IV. Specificity: Amino acids, their N-methyl-, N-acetyl- and N-benzoylderivatives; glutathione- and cysteine conjugates, di- and oligopeptides. Pflugers Arch. 415,342 -350.[CrossRef][Medline]
Welborn, J. R., Shpun, S., Dantzler, W. H. and Wright, S. H.
(1998). Effect of -ketoglutarate on organic anion
transport in single rabbit renal proximal tubules. Am. J.
Physiol. 274,F165
-F174.[Medline]
Zhang, X., Groves, C. E., Bahn, A., Barendt, W. M., Prado, M. D., Rodiger, M., Chatsudthipong, V., Burckhardt, G. and Wright, S. H. (2004). Relative contribution of OAT and OCT transporters to organic electrolyte transport in rabbit proximal tubule. Am. J. Physiol. 287,F999 -F1010.
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