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Vol. 291, Issue 2, 492-502, November 1999
Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan (L.H.L., D.A.P.); and Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, Georgia (R.K.Z.)
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Abstract |
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 Top
 Abstract
 Introduction
Experimental Procedures
Results
Discussion
References
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Inorganic mercury (Hg2+) induced time- and
concentration-dependent cellular injury in freshly isolated proximal
tubular (PT) and distal tubular (DT) cells from normal (control) rats
or uninephrectomized (NPX) rats. PT cells from NPX rats were more
susceptible than PT cells from control rats, and DT cells were slightly
more susceptible than PT cells to cellular injury induced by
Hg2+ (not bound to a thiol). Preloading cells with
glutathione increased Hg2+-induced cellular injury in PT
cells from control rats. However, coincubation of PT or DT cells from
control or NPX rats with Hg2+ and glutathione (1:4)
provided significant protection relative to incubations with
Hg2+ alone. No support was obtained for a role for
-glutamyltransferase in glutathione-dependent protection. However,
the organic anion carrier does appear to play a role in accumulation
and toxicity of mercuric conjugates of cysteine in PT cells from
control, but not NPX, rats. Coincubation with Hg2+ and
cysteine (1:4) had little effect on, or slightly enhanced, Hg2+-induced cellular injury at low concentrations of
Hg2+ in all cells studied. Coincubation with
Hg2+ and albumin (1:4) markedly protected PT and DT cells
from control and NPX rats at all concentrations except the highest
concentration of Hg2+ in DT cells from NPX rats.
2,3-Dimercapto-1-propanesulfonic acid protected cells both when
preloaded or added simultaneously with Hg2+. Thus, renal
cells from NPX rats are more susceptible to Hg2+-induced
injury, PT and DT cells respond differently to exposure to
Hg2+, and thiols can significantly modulate the toxic
response to Hg2+.
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Introduction |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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The
kidneys are the primary organs that accumulate inorganic mercury
(Hg2+) and exhibit toxicity after in vivo
exposures to Hg2+ (Zalups, 1993a
).
Hg2+ accumulates selectively along the three
segments of the proximal tubule (Zalups, 1991a,b). Freshly isolated
proximal tubular (PT) and distal tubular (DT) cells (a nontarget renal
cell population) from rats accumulate comparable levels of
Hg2+ after exposure to
HgCl2 (Lash et al., 1998). Hence, although PT
cells are the primary in vivo target cells that accumulate, and are
intoxicated by, Hg2+, other renal cell
populations can accumulate Hg2+ in an in vitro model.
Protein and nonprotein thiols bind Hg2+ with high
affinity and are the major extracellular and intracellular ligands for
Hg2+ (Zalups and Lash, 1994). Alterations in the
cellular content of thiols, particularly glutathione (GSH), modulate
the intracellular uptake and accumulation of Hg2+
(Berndt et al., 1985; Baggett and Berndt, 1986; Girardi and Elias, 1993; Burton et al., 1995; Zalups and Lash, 1997a). Furthermore, coadministration of GSH or L-cysteine (Cys) with
Hg2+ both in vivo (de Ceaurriz et al., 1994;
Zalups and Barfuss, 1995a,b; Zalups, 1998) and in vitro (Lash et al.,
1998; Zalups and Barfuss, 1998a) alters the rate of renal tubular
uptake and accumulation of Hg2+. Data are
consistent with mercuric conjugates of GSH and/or Cys being
physiological transport forms of Hg2+ (Tanaka et
al., 1990; Zalups, 1995, 1998; Zalups and Barfuss, 1995a,b, 1998b;
Zalups and Minor, 1995; Zalups and Lash, 1997b). Luminal transport of
mercuric conjugates of GSH appears to require activity of renal
-glutamyltransferase (GGT; Tanaka et al., 1990; Zalups and Barfuss,
1995a; Zalups and Minor, 1995; Zalups and Lash, 1997a,b; Lash et al.,
1998). Mercuric conjugates of Cys may thus be the primary luminal
transport form because mercuric conjugates of GSH are likely processed
to the corresponding Cys conjugates before the uptake of
Hg2+. The organic anion transporter on the
basolateral membrane and Na+-dependent and
-independent amino acid transporters on the luminal membrane are
involved in the uptake of mercuric conjugates of Cys (Zalups, 1995,
1998; Zalups and Barfuss, 1995a,b, 1998a,b; Zalups and Minor, 1995;
Zalups and Lash, 1997b; Lash et al., 1998; V. T. Cannon, D. W. Barfuss, and R.K.Z., unpublished observations).
In vivo administration of, or in vitro exposure to, GSH (Lash and
Zalups, 1992; de Ceaurriz et al., 1994; Burton et al., 1995), Cys (Lash
and Zalups, 1992; Zalups and Barfuss, 1996), serum albumin (Lash and
Zalups, 1992), or 2,3-dimercapto-1-propanesulfonic acid (DMPS; Zalups
et al., 1991, 1998; Lash and Zalups, 1992; Zalups, 1993b) protects PT
cells from the toxic effects induced by Hg2+.
Although serum albumin and DMPS virtually completely protect from the
toxic effects induced by Hg2+ (which correlates
with their ability to nearly completely inhibit renal cellular uptake
and accumulation of Hg2+), GSH and Cys protect to
varying degrees (which appears to correlate with their influence on
renal cellular uptake and accumulation of Hg2+).
Moreover, at relatively low concentrations, coincubation in vitro with
Cys stimulates renal cellular uptake and accumulation of
Hg2+ and coincubation in vitro with GSH inhibits
renal cellular uptake and accumulation of Hg2+ to
a much lesser degree than coincubation with serum albumin or DMPS
(Zalups and Barfuss, 1995a, 1998a,b; Zalups and Lash, 1997b; Lash et
al., 1998; Zalups, 1998).
Compensatory renal growth, which occurs after reductions in renal mass,
is another major factor that influences the disposition and
nephrotoxicity of Hg2+. Remnant renal tissue
undergoes rapid changes after uninephrectomy, and the acute
hemodynamic, functional, and biochemical effects in rodents are nearly
complete within 7 to 10 days after surgery (Fine, 1986). These changes
include increased renal cellular synthesis and content of GSH and
metallothionein (Zalups and Lash, 1990; Zalups and Lash, 1994),
increased activities of several GSH-dependent enzymes (Lash and Zalups,
1994), and increased renal cellular uptake and accumulation of
Hg2+ (Zalups et al., 1987; Zalups and Diamond,
1987; Zalups and Lash, 1990; Zalups, 1997a) compared with kidneys or
renal tissue from control animals. The nephropathy and the in vitro
cytotoxicity induced by Hg2+ are also increased
(Houser and Berndt, 1986; Lash and Zalups, 1992; Zalups, 1997b).
In the present study, we used freshly isolated PT and DT cells from control and uninephrectomized (NPX) rats to determine: 1) the dose and time dependence of Hg2+-induced renal cellular injury, 2) the influence of albumin and low-molecular-weight thiols on Hg2+-induced renal cellular injury, and 3) the influence of modulating GSH-conjugate metabolism and the organic anion transporter in the renal cellular injury induced by mercuric conjugates of GSH or Cys.
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Experimental Procedures |
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Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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Materials.
Percoll, collagenase (type I), BSA
(fraction V), acivicin
L-(
S,5S)--amino-3-chloro-4,5-dihydro-5-isoxazoleacetic
acid], p-aminohippurate (PAH), and DMPS were
purchased from Sigma Chemical Co. (St. Louis, MO). All other chemicals
were of the highest purity available and were purchased from commercial sources.
Animals and Surgical Procedures.
Male Sprague-Dawley rats
(175-200 g at time of surgery; Harlan Sprague-Dawley, Indianapolis,
IN) were used in the present study. Animals were housed in the Wayne
State University vivarium, were allowed access to laboratory chow and
water ad libitum, and were kept in a room on a 12-h light/dark cycle.
The rats were divided into two surgical groups: one that underwent
uninephrectomy (NPX rats) and nonsurgical control rats. Animals were
anesthetized with i.p. injections of sodium pentobarbital (50 mg/kg
b.wt.) before surgery. Uninephectomies were performed by removal of the right kidney as described previously (Zalups and Lash, 1990). Previous
studies show that there is no difference in cells isolated from
untreated or sham-operated rats; hence, nonsurgically treated rats were
used as controls.
Isolation of Rat Renal PT and DT Cells.
Renal cortical cells
were isolated by collagenase perfusion, and enriched populations of PT
and DT cells were then obtained by Percoll density-gradient
centrifugation (Lash and Tokarz, 1989). Briefly, cortical cells (5 ml,
5-8 × 106 cells/ml) were layered on 35 ml of 45%
(v/v) isosmotic Percoll solution in 50-ml polycarbonate centrifuge
tubes and were centrifuged at 4°C for 30 min at
20,000g in a Sorvall RC2B centrifuge in an SS34 rotor.
Fractions were collected, and cell types of origin were identified by
the use of marker enzymes and cell type-specific respiratory responses
(Lash and Tokarz, 1989). Based on enzymology and morphology, the renal
PT cell preparation contains cells derived from both convoluted and
straight segments and is estimated to be at least 97% pure; the renal
DT cell preparation contains cells derived from the distal convoluted
tubule, the cortical collecting duct, and connecting tubules, but not
the thick ascending limbs, and is estimated to have less than 10%
contamination from PT cells, with a purity of approximately 88%.
Experimental Design.
Before incubations, cells were diluted
5-fold with Krebs-Henseleit buffer, pH 7.4, containing 25 mM HEPES and
metabolic substrates (5 mM glucose, 5 mM glutamine), washed to remove
Percoll, and then resuspended in fresh buffer at a concentration of
1.2 × 106 cells/ml. Cell concentrations were
determined in the presence of 0.2% (w/v) trypan blue using a
hemacytometer, and cell viability was estimated by either trypan blue
exclusion or by the release of lactate dehydrogenase (LDH) activity
from the cells (Lash and Tokarz, 1989). All buffers were equilibrated
with 95% O2/5% CO2, and cells were stored on
ice in 25-ml polyethylene Erlenmeyer flasks until used. Incubations
were performed in 25-ml polyethylene Erlenmeyer flasks in a 37°C
Dubnoff metabolic shaking incubator (60 cycles/min) under an atmosphere
of 95% O2/5% CO2.
). Free DMPS is transported into the renal
proximal tubule by the basolateral organic anion carrier (Klotzbach and
Diamond, 1988; Zalups et al., 1998), so the isolated cells should
accumulate DMPS under these incubation conditions. The organic anion
transporter is not present in distal cell populations. Thus, it is very
unlikely that a highly polar molecule like DMPS is transported into any distal cell population. However, the DT cells were preincubated with
DMPS to provide a parallel experimental design with measurements performed with PT cells.
To assess the influence of exogenous thiols on the severity of the
cellular injury induced by Hg2+, PT and DT cells
were coincubated with 5, 10, or 100 µM Hg2+ and
a 4-fold molar excess of either GSH, Cys, BSA, or DMPS.
Hg2+ forms 1:2 linear II coordinate complexes
with thiols (Rabenstein, 1989). A 4-fold molar excess of the thiols was
used to ensure that all the Hg2+ was in the form
of a mercuric-thiol conjugate consisting of two molecules of a thiol
bound to a single mercuric ion. In two experiments, cells were
coincubated with the indicated concentrations of
Hg2+ and either 5 mM GSH or 5 mM DMPS to parallel
the preloading experiments with GSH and DMPS described above.
To assess the role of activity of the brush-border membrane enzyme GGT
in the toxic effects of mercuric conjugates of GSH, cells were
preincubated for 15 min with 0.25 mM acivicin to inhibit GGT activity
before the addition of the mercuric conjugates of GSH. Acivicin would
be expected to decrease toxicity if metabolism of the glutathionyl
moiety is required for uptake and subsequent cytotoxicity of the
mercuric conjugates of GSH. Pretreatment of PT cells with this
concentration of acivicin inhibits more than 95% of GGT activity
(Visarius et al., 1996).
To assess the role of the organic anion carrier in the cellular uptake
and subsequent cytotoxicity of mercuric conjugates of Cys, cells were
coincubated with 1 mM PAH and the mercuric conjugates of Cys. PAH,
which is a substrate for the organic anion carrier, would be expected
to decrease toxicity if function of this carrier is required for the
uptake and subsequent cytotoxicity of mercuric conjugates of Cys.
Cytotoxicity Assay.
Cell viability after incubations with
Hg2+ or Hg2+ in the presence of various thiols
could not be measured by LDH release from cells because of direct
inhibition of LDH activity by Hg2+ (Lash and Zalups, 1992).
Total LDH activity (extracellular plus intracellular), however,
correlated with trypan blue uptake (Lash and Zalups, 1992) and was used
to demonstrate and quantify toxicity due to Hg2+.
Data Analysis. Results are expressed as mean ± S.E. values of measurements from the indicated number of separate cell preparations. Significant differences among selected mean values were first assessed by a one- or two-way ANOVA. When significant F values were obtained with ANOVA, the Fisher's protected least significant difference t test was performed to determine which mean values were significantly different from each other with two-tailed P values of <.05 considered significant.
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Results |
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Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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Time and Concentration Dependence of Hg2+-Induced
Cellular Injury.
Time courses of total cellular LDH activity in PT
and DT cells incubated with buffer or 0.5, 1, 10, or 100 µM
Hg2+ confirmed previous results (Lash and Zalups, 1992)
that in the absence of BSA in the extracellular buffer, PT cells from
NPX rats exhibited greater susceptibility to Hg2+-induced
cellular injury and higher LDH activity than did PT cells from control
rats (Fig. 1, A and B). Furthermore, in
control PT cells, a threshold effect was observed such that no
significant decrease in LDH activity was observed with Hg2+
concentrations of 10 µM and below, whereas 100 µM Hg2+
produced a 97% decrease in LDH activity after 2 h of incubation. In contrast, 10 µM Hg2+ produced significant decreases in
LDH activity after 1 and 2 h of incubation in PT cells from NPX
rats (19 and 42% decrease, respectively).
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), DT cells exhibited
higher LDH activity than PT cells. Hg2+-induced
cellular injury in DT cells from control rats (Fig. 1C) was greater
than that in PT cells from control rats, with 10 µM Hg2+ producing significant decreases in LDH
activity (18 and 31% decrease after 1 and 2 h of incubation,
respectively). In contrast to results with PT cells, compensatory renal
growth had no effect on Hg2+-induced cellular
injury in DT cells (Fig. 1D).
Modulation of Hg2+-Induced Cellular Injury by GSH. To assess the role of GSH in Hg2+-induced cytotoxicity, three experiments were performed, involving preloading of cells with GSH to increase the intracellular content of GSH, simultaneous incubation of cells with Hg2+ and GSH to form the mercuric conjugates of GSH, and alteration of the metabolism of the mercuric conjugates of GSH.
Preloading of PT cells from control rats with GSH significantly increased cellular injury induced by 10 µM Hg2+ (Fig. 2A). In contrast, PT cells from NPX rats (Fig. 2B) or DT cells from control (Fig. 2C) or NPX (Fig. 2D) rats were protected by preloading with GSH. Also note that in this set of experiments, 10 µM Hg2+ produced a small but statistically significant decrease in LDH activity in PT cells from control rats (Fig. 2A). This contrasts with results presented in Fig. 1A. However, in these experiments, the relative decrease in LDH activity was still smaller in PT cells from control rats than in PT cells from NPX rats (cf. Fig. 2A with Fig. 2B).
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Modulation of Hg2+-Induced Cellular Injury by Cys.
Simultaneous incubation of PT cells from control rats with
Hg2+ and a 4-fold molar excess of Cys had no effect on LDH
inactivation at 5 and 10 µM Hg2+ but almost completely
protected at 100 µM Hg2+ (Fig.
6A). In contrast, simultaneous incubation
with Cys had no significant effect on Hg2+-induced LDH
inactivation at 5 µM Hg2+ but almost completely protected
PT cells from NPX rats from Hg2+-induced cellular injury at
10 and 100 µM Hg2+ (Fig. 6B). Simultaneous incubation of
DT cells from control rats with Hg2+ and a 4-fold molar
excess of Cys partially protected cells from Hg2+-induced
cellular injury at 100 µM Hg2+ (Fig. 6C), whereas the
same experiment in DT cells from NPX rats showed partial protection at
both 10 and 100 µM Hg2+ (Fig. 6D).
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Modulation of Hg2+-Induced Cellular Injury by BSA.
Simultaneous incubation of PT cells from control rats with a 4-fold
molar excess of BSA completely protected the cells from Hg2+-induced LDH inactivation at all concentrations of
Hg2+ tested (Fig. 8A). In
contrast, BSA completely protected PT cells from NPX rats at 5 and 10 µM Hg2+ but only partially protected at 100 µM
Hg2+ (Fig. 8B). DT cells from control and NPX rats
exhibited a similar pattern as PT cells, except that at 100 µM
Hg2+, BSA had no effect on the extent of cellular injury
(Fig. 8, C and D).
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Modulation of Hg2+-Induced Cellular Injury by
DMPS.
To study the effect of the dithiol chelator DMPS on
Hg2+-induced cellular injury, cells were first preincubated
with 5 mM DMPS and then incubated with 5 or 10 µM
Hg2+ (Fig. 9). DMPS
preloading provided complete protection from Hg2+-induced
LDH inactivation in PT cells from either control or NPX rats but
provided only partial protection in DT cells.
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Discussion |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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The present study sought to define the susceptibility of PT cells
from control and NPX rats to Hg2+, to determine
whether DT cells are also susceptible to Hg2+,
and to determine the influence of thiols on
Hg2+-induced cellular injury. The use of
suspensions of freshly isolated PT cells as an in vitro model allowed
manipulation of incubation conditions in a controlled environment.
Earlier studies showed that isolated PT cells from NPX rats maintained
their hypertrophic state, increased cellular contents of protein and
GSH, and increased enzymatic activities that are observed in vivo (Lash
and Zalups, 1992, 1994). These cells are thus a suitable model in which
to explore the mechanisms by which compensatory renal cellular
hypertrophy alters Hg2+-induced cellular injury.
Relative Susceptibility of PT and DT Cells.
Although the PT
region of the nephron is the major site that accumulates
Hg2+ and exhibits pathological changes after exposure to
Hg2+ in vivo (Zalups, 1991a,b), freshly isolated DT cells
from control rats exhibited modestly greater susceptibility to
Hg2+ than PT cells from control rats. These results suggest
that the distal nephron can be intoxicated if it is exposed to
sufficient amounts of Hg2+, which may occur if the
transport activities in the proximal nephron that enable cellular
accumulation of Hg2+ are defective. This in turn may occur
under conditions such as energy depletion that lead to proximal tubular
dysfunction. Hg2+ may then be delivered to more distal
segments of the nephron, thereby leading to cellular injury in those
epithelial cells.
Effect of Compensatory Renal Growth.
PT cells from NPX rats
were indeed more sensitive to Hg2+ than were PT cells from
control rats. In contrast, no significant effect of compensatory renal
growth was observed in DT cells. This finding is consistent with the
minimal changes in cellular biochemistry observed in DT cells from NPX
rats (Lash and Zalups, 1994) and the heterogeneity with respect to
hypertrophy occurring in distal segments of the nephron.
). One possible reason why PT cells from NPX rats
were protected is that transport processes, possibly involving uptake
and/or efflux of GSH itself or mercuric conjugates of various thiols, may be altered as a result of compensatory cellular hypertrophy, leading to a state where net cellular accumulation of
Hg2+ was diminished.
Modulation by GSH. Mercuric conjugates with various extracellular thiols, rather than free Hg2+, are likely the principal forms of Hg2+ that renal epithelial cells are exposed to in vivo. As discussed above, the relevance of incubating cells with free Hg2+ (in the absence of ligands) is that data from these experiments can be used as a reference point from which to assess the effects of various intracellular and extracellular thiols.
GSH has a complex role in the regulation of renal cellular disposition and cytotoxicity of Hg2+. On the one hand, GSH can protect renal cells from Hg2+-induced cellular injury by preventing it from binding to other essential, cellular thiols (Johnson, 1982; Houser et al., 1992; Lash and Zalups,
1992; Girardi and Elias, 1993). On the other hand, mercuric conjugates
of GSH may be a physiological form by which Hg2+
is transported into the renal proximal tubule; this implies that the
presence of extracellular GSH may function to enhance renal cellular
accumulation of Hg2+ (Zalups and Lash, 1997b;
Lash et al., 1998; Zalups, 1998). Indeed, the present results and the
fact that other types of GSH conjugates are transported into renal PT
cells (Lash and Jones, 1985) support these conclusions.
The effect of preloading cells with GSH on
Hg2+-induced cellular injury differed in PT and
DT cells. As discussed above, PT cells from control rats whose
intracellular GSH content was enhanced exhibited more toxicity. DT
cells, however, were afforded protection under the same incubation
conditions. The difference in effect is likely due to cellular
heterogeneity along the nephron with respect to GSH-dependent
metabolism and transport (Lash and Tokarz, 1989; Lash and Putt, 1999).
Hence, the inability of DT cells to significantly accumulate GSH may
account for the protective, rather than enhancing, effect of GSH preincubation.
Mercuric conjugates of GSH may be transported at both basolateral and
brush-border membranes. However, it is likely that the corresponding
Cys conjugates are the primary species that are transported across the
brush-border membrane. In support of this are studies showing that
inhibition of GGT activity by acivicin diminishes the renal cellular
uptake and accumulation of Hg2+ (Berndt et al.,
1985; Tanaka et al., 1990; Zalups, 1995). In the present study,
however, acivicin had little or no effect on cellular injury induced by
mercuric conjugates of GSH. This suggests that at least in this in
vitro model, degradation of mercuric conjugates of GSH to the Cys
conjugates is not an obligate step in the processes leading from
cellular uptake and accumulation to injury because increased uptake of
mercuric conjugates of GSH across the basolateral membrane may occur
under these conditions.
Modulation by Cys.
Data from the present study support the
hypothesis that mercuric conjugates of Cys are important transport
forms of Hg2+. Exposure of PT cells from control rats to
mercuric conjugates of Cys resulted in slight enhancement or little
effect on cytotoxicity (depending on the concentration of
Hg2+ used) compared with PT cells from control rats
incubated with Hg2+ alone. This slight effect or lack of
effect of Cys is very significant because other thiols (i.e., DMPS and
BSA) provide almost complete protection from Hg2+-induced
injury (Lash and Zalups, 1992; present study).
Modulation by BSA and DMPS.
BSA and DMPS were by far the most
effective, protective thiols. Incubation of PT cells from control rats
with Hg2+ and either BSA or DMPS (presumably in the form of
a mercuric conjugate) provided nearly complete protection from the
toxic effects of Hg2+ at all three concentrations tested.
In contrast, exposure to mercuric conjugates of BSA or DMPS provided
partial protection to PT cells from NPX rats and DT cells from control
rats at 100 µM Hg2+ and partial to no protection in DT
cells from NPX rats with increasing Hg2+ concentrations.
Compensatory cellular hypertrophy and cell type-dependent differences
in the handling of BSA or mercuric conjugates of BSA may account for
the various observed effects. Mercuric conjugates of BSA may accumulate
in PT cells via a slow, low-capacity process involving endocytosis on
the luminal membrane. Differences in the ability to transport DMPS or
mercuric conjugates of DMPS or in the ability to reduce oxidized DMPS
may play a role in the varied responses observed during coexposure to
Hg2+ and DMPS. Results with DMPS are consistent with data
showing that once Hg2+ binds to DMPS, the complex is not
readily taken up by renal epithelial cells (Zalups et al., 1998). There
also is no evidence that DMPS can be transported into epithelial cells
from the distal nephron. Hence, the protection observed with DT cells
that were preincubated with DMPS was likely due to extracellular
chelation of Hg2+ rather than increases in intracellular
content of DMPS.
Summary and Conclusions.
The various pathways discussed above
are summarized in Fig. 11, which
illustrates the potential metabolic fates and action of several
transporters in delivering Hg2+, in the form of thiol
conjugates, to the renal PT cell. One important caveat is that the
isolated renal cell suspensions have lost the plasma membrane polarity
that is characteristic of the intact renal tubular epithelium. Hence,
transporters on both brush-border and basolateral plasma membrane
surfaces have equal and simultaneous access to substrates.
Consequently, inhibition of one transport mechanism may be more readily
compensated by increased transport via another carrier. Accordingly,
although all the data from various studies support the conclusion that
mercuric conjugates of Cys and GSH are primary transport forms of
Hg2+, a role for other types of mercuric conjugates and
other transport systems cannot be excluded.
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Footnotes |
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Accepted for publication June 30, 1999.
Received for publication April 8, 1999.
1 This work was supported by National Institute of Environmental Health Sciences Grant ES05157.
Send reprint requests to: Dr. Lawrence H. Lash, Department of Pharmacology, Wayne State University, School of Medicine, 540 East Canfield Ave., Detroit, MI 48201-1928. E-mail: l.h.lash{at}wayne.edu
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Abbreviations |
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Hg2+, inorganic mercury;
PT, proximal tubular;
acivicin, L-(S,5S)--amino-3-chloro-4,5-dihydro-5-isoxazoleacetic
acid;
Cys, L-cysteine;
DMPS, 2,3-dimercapto-1-propanesulfonic acid;
DT, distal tubular;
GGT, -glutamyltransferase;
GSH, glutathione;
LDH, lactate dehydrogenase;
NPX, uninephrectomized;
PAH, p-aminohippurate.
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References |
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Top
Abstract
Introduction
Experimental Procedures
Results
Discussion
References
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-glutamyltranspeptidase in the disposition and kidney toxicity of inorganic mercury in rats.
J Appl Toxicol
14:
201-206[Medline].-glutamyltranspeptidase in renal uptake and toxicity of inorganic mercury in mice.
Toxicology
60:
187-198[Medline].-glutamyl transpeptidase in kidney linked mechanistically to renal tubular uptake of inorganic mercury.
Toxicol Appl Pharmacol
132:
289-298[Medline].This article has been cited by other articles:
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L. H. Lash, D. A. Putt, and R. K. Zalups Influence of Compensatory Renal Growth on Susceptibility of Primary Cultures of Renal Cells to Chemically Induced Injury Toxicol. Sci., December 1, 2006; 94(2): 417 - 427. [Abstract] [Full Text] [PDF]
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, significantly different
(P < .05) from corresponding sample incubated
without GSH.
, significantly
different (P < .05) from corresponding sample
incubated without GSH.
) and is transported into
the lumen by a membrane potential-sensitive carrier, where it is
degraded in successive reactions by GGT and dipeptidase activities to
the cysteinylglycine (CG-Hg-CG) and, finally, the Cys conjugate. The
resulting luminal as well as serosal mercuric conjugates of Cys are
believed to be transported into the renal PT cell by carriers that may
or may not cotransport Na+ ions and are competitively
inhibited by cystine.