| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
,1,#
* Centre for Molecular Biology and Neuroscience, and
Nordic Centre for Water Imbalance Related Disorders (WIRED), and
¶ Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway; and
# Department of Woman and Child Health, Karolinska Institutet, Stockholm, Sweden
1 Correspondence: Centre for Molecular Biology and Neuroscience, University of Oslo, P.O. Box 1105 Blindern, N-0317 Oslo, Norway. E-mail: mahmo{at}medisin.uio.no
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
25 kDa band in immunoblots. This isoform is likely to correspond to a new AQP9 mRNA that is obtained by alternative splicing and has a shorter ORF than the liver isoform. Subfractionation experiments and high-resolution immunogold analyses revealed that this novel AQP9 isoform is enriched in mitochondrial inner membranes. AQP9 immunopositive mitochondria occurred in astrocytes throughout the brain and in a subpopulation of neurons in the substantia nigra, ventral tegmental area, and arcuate nucleus. In the latter structures, the AQP9 immunopositive mitochondria were located in neurons that were also immunopositive for tyrosine hydroxylase, as demonstrated by double labeling immunogold electron microscopy. Our findings suggest that mitochondrial AQP9 is a hallmark of astrocytes and midbrain dopaminergic neurons. In physiological conditions, the flux of lactate and other metabolites through AQP9 may confer an advantage by allowing the mitochondria to adjust to the metabolic status of the extramitochondrial cytoplasm. We hypothesize that the complement of mitochondrial AQP9 in dopaminergic neurons may relate to the vulnerability of these neurons in Parkinson’s disease.—Amiry-Moghaddam, M., Lindland, H., Zelenin, S., Roberg, B. A., Gundersen, B. B., Petersen, P., Rinvik, R., Torgner, I. A., Ottersen, O. P. Brain mitochondria contain aquaporin water channels: evidence for the expression of a short AQP9 isoform in the inner mitochondrial membrane.
Key Words: water channels • mitochondria • Parkinson’s disease • astrocytes • substantia nigra
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
. The predominant aquaporin in brain is AQP4, which has been shown to be implicated in the pathophysiology of brain edema (for a review, see ref 2
). AQP1 also plays an important role in the brain as the primary aquaporin involved in the production of cerebrospinal fluid (3
, 4)
.
In addition to AQP4 and AQP1, the brain contains AQP9 (5
, 6)
, which is permeable for glycerol as well as water and thus belongs to the subfamily of aquaporins called aquaglyceroporins (1)
. It is unique among the aquaporins in having a very broad substrate specificity and a high permeability for urea and the monocarboxylates lactate and ß-hydroxybutyrate (7)
. Permeability for the monocarboxylates shows strong pH sensitivity, suggesting that these metabolites are transported in their neutral (protonated) form. In the brain, light microscopic immunocytochemistry has provided evidence of AQP9 expression in astrocytes and catecholaminergic neurons in the brain stem (5
, 8
, 9)
.
AQP9 is the aquaporin most closely related to GlpF, a bacterial aquaglyceroporin that fluxes water as well as glycerol (10
, 11)
. The sequence homology between the two molecules is 37% compared with 28% homology between AQP9 and the archetypical aquaporin AQP1 (10
, 12
, 13)
. As mitochondria are believed to be of bacterial origin, we hypothesized that AQP9 could be the elusive mitochondrial aquaporin. That mitochondria have retained aquaporins through phylogeny is supported by the observation that mammalian inner mitochondrial membranes have an unusually high water permeability (14)
.
Here we provide experimental data showing that the brain contains two novel isoforms of AQP9. One is concentrated to brain mitochondria. A key finding is that mitochondrial AQP9 occurs in astrocytes throughout the brain but also in select neuronal subpopulations, most notably in midbrain dopaminergic neurons.
AQP9 is the first mitochondrial protein that has been shown to be selectively expressed in dopaminergic neurons. As such, this protein should figure prominently in further attempts to unravel the molecular mechanisms of Parkinson’s disease.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Antibodies
For AQP9 immunolabeling, the antibodies used were obtained from Alpha Diagnostics (San Antonio, TX, USA) (5 µg/mL) or Chemicon (El Segundo, CA, USA) (5 µg/mL). Both antibodies were rabbit polyclonal and were raised against the C-terminal end of AQP9. We also employed antibodies to AQP4 (Chemicon, 1 µg/mL), phosphate-activated glutaminase (PAG; antibody directed to C-terminal part, and affinity purified as described in Roberg et al. (15)
; 1:100 000), tyrosine hydroxylase (rabbit polyclonal antibody from Chemicon, 0.4 µg/mL), the mitochondrial matrix marker mitochondrial HSP70 (mHSP70, 1:2000 dilution of the commercial preparation), and the mitochondrial outer membrane marker BCL-XL (Santa Cruz, Santa Cruz, CA, USA; 1 µg/mL).
Preparation of samples and immunoblotting
Fractionation of brain tissue and mitochondria
The animals were placed for few seconds into a CO2 chamber and decapitated prior to removal of the brains. Purified nonsynaptic mitochondria from fresh rat brains were prepared as in Roberg et al. (16)
. The membrane fraction (microsomal fraction) was isolated as in Roberg et al. (17)
.
Briefly, working at 4°C, rat brain homogenates (1:10) in a mannitol-sucrose buffer (mitochondrial buffer: mannitol: 0.25 M; sucrose: 0.7 M; HEPES: 0.01 M; pH 7.4; protease inhibitor (Complete, Roche, Nutley, NJ, USA) were centrifuged at 480 x g for 10 min. The nonsynaptic mitochondria were pelleted from the postnuclear supernatant through 1.2 M sucrose, 10 mM HEPES, pH 7.4 by ultracentrifugation at 161 000 x g for 25 min. To reduce microsomal contamination, the mitochondrial pellet was washed five times by centrifugation with mitochondrial buffer. The membrane fraction (microsomal fraction) was isolated from the crude synaptosomes (P2, pelleted by centrifugation at 18 800 x g for 6 min of the postnuclear supernatant and taken up in mitochondrial buffer) by ultracentrifugation at 161 000 x g for 1 h 15 min. Synaptosomal and membrane fractions were obtained from six brains.
The nonsynaptic mitochondria were further fractionated into inner membrane, matrix, and outer membrane essentially as described for liver mitochondria by DaCruz et al. (18)
. Eleven brains were used to prepare the submitochondrial fractions.
Briefly, mitoplasts were prepared by homogenization of the purified mitochondria in H2O and pelleted twice at 12 000 x g for 5 min. The resulting supernatant was the source of outer membrane, which was pelleted by ultracentrifugation at 161 000 x g for 50 min. The mitoplasts were treated with Na2CO3 (0.1 M, pH 11.5), and the inner membrane practically devoid of matrix proteins was pelleted by ultracentrifugation at 161 000 x g for 25 min. The resulting supernatant containing the matrix fraction was dialyzed against distilled water and freeze-dried.
For immunoblotting, the fractions were dissolved in 2% SDS in TE-bf (Tris: 0.05 M; EDTA: 0.001 M), pH 8.0.
Immunoblotting
Western blots were performed with enhanced chemiluminescence (ECL plus) essentially as described in Roberg et al. (15)
. Briefly, after SDS-PAGE the proteins were electrotransferred to polyvinylidene difluoride (PVDF) membranes (Hybond P, Amersham) and the blots were developed with ECL Plus (Amersham).
Protein concentration was determined by the bicinchoninic acid method (BCA protein assay kit; Pierce, Rockford, IL, USA).
Immunocytochemistry and immunoelectron microscopy
For immunocytochemical studies the animals (n=3) were anesthetized deeply with sodium pentobarbital (7.5 mg/kg), followed by intracardiac perfusion with 4% paraformaldehyde and 0.1% glutaraldehyde in phosphate buffer. For quantitative immunogold studies, different brain regions (neocortex, cerebellum, striatum, hypothalamus, and mesencephalon) were cut into 0.5 to 1.0 mm slices, cryoprotected, quick-frozen in liquid propane (–170°C), and subjected to freeze substitution (19
, 20)
. Specimens were then embedded in methacrylate resin (Lowicryl HM20) and polymerized by UV light at <0°C. Ultrathin sections were incubated with antibodies to AQP9, followed by goat anti-rabbit IgG coupled to 15 nm colloidal gold. For double labeling, the sections were first incubated with rabbit polyclonal anti-AQP9 (Alpha Diagnostics, 5 µg/mL), followed by goat anti-rabbit IgG coupled to 10 nm colloidal gold. The sections were then exposed to formaldehyde vapor at 80°C for 1 h and thereafter incubated with rabbit polyclonal antibody to tyrosine hydroxylase (Chemicon, 0.4 µg/mL), followed by goat anti-rabbit IgG coupled to 15 nm colloidal gold. The sections were then contrasted with uranyl acetate and lead citrate and examined with a Philips CM 10 electron microscope at 60 kV (19)
.
Preadsorption with the immunizing peptide and omission of the primary antibody were used as negative controls both for immunoblotting and immunogold cytochemistry.
Reverse transcription-polymerase chain reaction (RT-PCR) analysis
Total RNA was isolated from brains of adult male Sprague Dawley rats (B&K Universal, Stockholm, Sweden) using RNeasy Mini Kit (Qiagen, Chatsworth, CA, USA). RNA (1 µg) was reverse transcribed using Molony murine leukemia virus reverse transcriptase and oligo dT (Promega, Madison, WI, USA). The AQP9 cDNA was amplified by PCR using the rAQP9.U0063 5'-ATCCAGCTGTCTGAGGAGAGAAGA-3' and rAQP9.L1351 primer 5'-CTACATGATGACACTGAGCTCG -3' primers, corresponding to rat AQP9 mRNA (GeneBank accession numbers NM_022960). Primers were selected using software Vector NTI Suite (InforMax). PCR conditions were optimized on TGradient (Biometra) using AmpliTaq Gold (Applied Biosystems, Foster City, CA, USA). PCR was performed under the following conditions: 5 min at 95°C, 6 cycles (30 s at 94°C; 2 min at 72°C), 6 cycles (30 s at 94°C; 30 s at 70°C; 90 s at 72°C), 38 cycles (30 s at 94°C; 30 s at 65°C; 90 s at 72°C), 3 min at 72°C, store at 4°C. PCR fragments were separated on 1.5% agarose gel and visualized with ethidium bromide staining. Size of PCR fragments was determined using GeneRuler 100 bp DNA ladder Plus (Fermentas).
DNA sequencing
Detected RT PCR fragments were extracted from the agarose gel using GFX PCR DNA and Gel Band Purification Kit (Amersham Bioscience, Arlington Heights, IL, USA). DNA amount was quantified on agarose gel using MassRuler DNA Ladder Mix (Fermentas). PCR fragments were sequenced using AQP9 specific primers and BigDyeTM Terminator v 3.1 Cycle Sequencing Kit (Applied Biosystems). Sequence data were assembled into a contig using SEQMAN II program of Lasergene Software (DNA*DNASTAR) and rat AQP9 mRNA sequence (accession numbers NM_022960).
Quantification and statistical analysis
For the evaluation of AQP9 immunogold labeling, digital images of sections from two rat cerebelli (100 images, obtained randomly from each section) were acquired and quantified with a commercial image analysis program (Soft Imaging Systems, Münster, Germany) (21)
. Mitochondrial and cytoplasmic labeling density was recorded as no. of gold particles per unit area excluding all nuclei. Comparisons among different cell types and between different compartments within the same cell type were made by Student's unpaired t test and ANOVA-Scheffe test. P < 0.05 was considered significant. Data are presented as mean ± SE.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). These bands (at 25 and 27 kDa) were aligned with two weaker bands that occurred in the crude synaptosomal fraction. Absorption with the immunizing peptide caused the lower band to disappear but did not reduce significantly the labeling intensity of the upper band.
|
Subfractions enriched in the inner mitochondrial membrane displayed a band at 25 kDa whereas the subfraction of mitochondrial matrix proteins exhibited a 27 kDa band (Fig. 1C, D
). Neither band occurred in the fraction of outer mitochondrial membranes. Immunoblots of the plasma membrane fraction revealed a weak band with a higher molecular mass (30 kDa) and no bands corresponding to the bands from the mitochondrial fractions (Fig. 1A
). This finding suggests that the plasma membrane contains a modest amount of an AQP9 variant different from that present in mitochondrial membranes.
The results obtained with the antibody from Alpha Diagnostics were reproduced using a different anti-AQP9 antibody (Chemicon) (Fig. 2
). Notably, the bands in the mitochondrial fraction were located at identical positions with the two antisera.
|
These data suggest that the 25 kDa band represents an AQP9 isoform that is enriched in mitochondrial inner membranes. Labeling of the crude synaptosomal (P2) fraction is consistent with the admixture of free mitochondria in this fraction. The 27 kDa band is likely to reflect a cross-reacting protein restricted to the mitochondrial matrix.
To validate the fractionation procedure we used antibodies to phosphate-activated glutaminase (PAG)—a mitochondrial protein)—and AQP4, known to be restricted to the plasma membrane. The two antibodies produced selective labeling of the respective fractions (Fig. 3
). The labeling pattern of PAG mimicked that of AQP9 except that PAG was enriched in the P2 fraction relative to AQP9. This would be expected if the crude synaptosome fraction contains a predominance of neuronal mitochondria. Thus, PAG is a neuronal enzyme whereas AQP9 occurs predominantly in glia (see below). Specific antibodies (to BCL-XL and mHSP70) attested to the purity of the outer mitochondrial membrane and mitochondrial matrix fractions, respectively (data not shown).
|
To validate the immunoblot data, an immunocytochemical analysis was performed on an embedded P2 fraction. This fraction contains mitochondria in intact nerve terminals, as well as free mitochondria (of neuronal and glial origin). Strong AQP9 immunoreactivity occurred in mitochondria, particularly in those mitochondria that were not associated with nerve terminal-like profiles. A large fraction of the gold particles were close to, or superimposed on, the inner mitochondrial membrane (Fig. 4
A). The mitochondrial labeling that remained after absorption with the immunizing peptide showed no clear association with the cristae (Fig. 4B
). This is consistent with the idea that the residual labeling represents a cross-reacting matrix protein.
|
The results generated by the use of the two C-terminal AQP9 antibodies suggested that the brain contains two isoforms of AQP9 and that one of these is substantially smaller than the published AQP9 isoform from liver. These results were confirmed by RT PCR (Fig. 5
).
|
Diverse bands were amplified in the RT PCR reaction using upstream primer rAQP9.U0063 located within 3'UTR and the downstream primer rAQP9.L1351 located at the 5' end of AQP9 coding region (Fig. 5)
. Agarose gel analysis revealed two major amplification products with size 1290 bp and 880 bp, suggesting the presence of two AQP9 mRNA splice variants in rat brain. This could be confirmed by sequence analysis (Fig. 6
). Sequence analysis of AQP9 PCR fragment 1290 bp revealed alternative splicing in 5'UTR (Fig. 6A
) compared with AQP9 mRNA expressed in leukocytes and liver (accession numbers NM_022960 and BC085731). The ORF of this novel brain AQP9 mRNA was identical to the previously published ORF of AQP9 mRNA expressed in leukocytes and liver, encoding a protein of 295 aa and a predicted Mr of 32 kDa. The second mRNA splice variant lacks the last 281 bp of 5'UTR and the first 111 bp of the AQP9 mRNA coding region, and has a shorter ORF than rat liver AQP9 mRNA (Fig. 6B
).
|
Perfusion fixed brains were analyzed to determine whether AQP9 is also expressed in mitochondria in situ. The antibodies used were directed to the C terminus, implying they would bind to the translation products of both AQP9 splice variants. In all brain regions investigated (neocortex, cerebellum, striatum, hypothalamus, and mesencephalon), an immunogold signal was recorded over mitochondria of astrocytes (Fig. 7
). In the latter cell type, immunoreactive mitochondria occurred in the cell bodies, major processes, as well as in the endfeet. A quantitative analysis based on gold particle counts (data not shown) did not reveal any significant differences between these three compartments. Astrocyte and endothelial plasma membranes exhibited a weak immunogold signal.
|
Quantitative analysis (Fig. 8
) confirmed that glial mitochondria were strongly enriched in AQP9 immunoreactivity relative to the extramitochondrial cytoplasmic matrix. The weak signal that was recorded over the glial cytoplasmic matrix could be attributed to gold particles associated with membranes of the endoplasmic reticulum. Tissue-free resin was virtually devoid of gold particles.
|
Generally, neuronal mitochondria were weakly labeled compared with the mitochondria of astrocytes. The pattern observed in most of the hypothalamus (Fig. 7A
) and in the cerebellum (Fig. 7B
, Fig. 8
) is representative of that of most brain regions. Quantitative analysis of cerebellum revealed uniformly low immunogold signals in mitochondria of terminals as well as dendrites. In fact, unlike the situation for astrocytes, neuronal profiles in the cerebellum did not exhibit any significant difference in signal intensity between mitochondria and extramitochondrial compartments.
Among the brain regions investigated, the substantia nigra, ventral tegmental area, and arcuate nucleus of the hypothalamus stood out as the only structures with a distinct enrichment of AQP9 immunoreactivity in neuronal mitochondria. In pars reticulata of the substantia nigra, the labeled mitochondria occurred in dendritic profiles that were typically surrounded by nerve terminals establishing contacts with the dendritic stem (Fig. 9
). These nerve terminals were devoid of a mitochondrial immunogold signal. Immunopositive mitochondria occurred in neuronal cell bodies, particularly at the dorsal aspect of substantia nigra corresponding to pars compacta. AQP9-positive mitochondria were also found in dendrites of the arcuate nucleus (not shown).
|
The AQP9 immunolabeled neuronal profiles were double labeled with an antibody to tyrosine hydroxylase. In double-labeled sections, large particles signaling tyrosine hydroxylase were strictly extramitochondrial whereas small particle signaling AQP9 occurred in mitochondria (Fig. 10
). Similar results were obtained in the arcuate nucleus (not shown). Dendrites that were immunonegative for tyrosine hydroxylase did not display any AQP9 immunopositive mitochondria. Taken together with the ultrastructural analysis, the double labeling data suggest that the population of AQP9 immunopositive neurons is identical to the population of dopaminergic neurons in the substantia nigra, ventral tegmental area, and arcuate nucleus.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
.
In immunoblots of mitochondrial fractions the AQP9 antibodies identified a major band at 25 kDa. This AQP9 isoform probably corresponds to the short fragment identified by RT PCR, which predicts a 24.5 kDa translation product starting from the second start codon. This start codon is associated with a perfect Kozak consensus site (Fig. 6)
(23)
. The RT PCR experiments also pointed to the presence in brain of a longer mRNA splice variant that may code for the plasma membrane pool of AQP9, identified in immunoblots as well as in immunogold preparations. The latter pool is minor compared with the mitochondrial pool and will not be considered further. Suffice it to say that the plasma membrane pool of AQP9 may carry out functions similar to those of AQP9 in liver, where the first detailed investigations of AQP9 were performed (9
, 24)
. In liver, AQP9 is believed to be expressed primarily in the plasma membrane and to function as an uptake mechanism for glycerol and urea (25)
. The rat liver AQP9 has 295 amino acids and a predicted Mr of 32 kDa. The weak band presently observed at 30 kDa may correspond to the liver isoform; alternatively, it might be a translation product of the short mRNA splice variant with translation initiation at the first start codon (Fig. 6B
). As for the small endothelial pool of AQP9, this may contribute to the permeability of the blood-brain barrier to water as well as the organic substrates of AQP9.
AQP9 was not expressed in all brain mitochondria but showed a preference for mitochondria of astrocytes and a subset of neurons. Previous light microscopic analyses have shown that AQP9-positive neurons are immunopositive for tyrosine hydroxylase (5)
. Here we extend the latter observation by demonstrating, by double labeling immunogold cytochemistry, that the AQP9 pool of tyrosine hydroxylase-positive neurons is concentrated in the mitochondria and that immunolabeled mitochondria occur in dendrites as well as in the cell bodies. In fact, our data are consistent with the idea that all dopaminergic neurons in the substantia nigra and ventral tegmental area express mitochondrial AQP9. Among the brain structures analyzed, neurons with other transmitter signatures were found to be devoid of this aquaporin. This makes AQP9 the first mitochondrial protein to be selectively expressed in dopaminergic (or catecholaminergic) (5)
neurons.
AQP9 has a broad substrate specificity (7)
. Its permeability coefficient for water is on a par with (7)
, or somewhat lower than (25)
, that of AQP1 and AQP4. In line with its classification as an aquaglyceroprin, AQP9 fluxes glycerol but also a number of other organic molecules, including urea, polyols other than glycerol (mannitol, sorbitol), purines, pyrimidines (adenine, uracil), and monocarboxylates (ß-hydroxybutyrate and lactate). Permeability for the monocarboxylates increases severalfold at low pH, suggesting that AQP9 preferentially admits lactate and ß-hydroxybutyrate in their neutral, protonated form (7)
.
Transport of lactic acid into the mitochondria could be a major role of AQP9. When lactic acid is exposed to the relatively high pH of the mitochondrial matrix, it will become deprotonated and serve to reduce the proton gradient across the inner mitochondrial membrane. Such transport would manifest itself as a mild uncoupling: It would allow protons to bypass F0F1-ATP synthase and consequently the inner membrane will be slightly depolarized (26
, 27)
. A modest depolarization of the inner membrane is known to reduce the formation of free radicals in the mitochondrial matrix (26
, 28
, 29)
.
As for any substrate transported by aquaporins, the driving force for lactic acid through AQP9 is provided by its concentration gradient. The concentration gradient would be particularly pronounced in ischemia and hypoxia, which are characterized by an increased lactate formation and a reduction in cytoplasmic pH. These two factors combined would favor AQP9 mediated uptake of lactic acid into the mitochondria. Based on the evidence referred to above, cells equipped with mitochondrial AQP9 would be expected to display an increased resistance to ischemia. Not only would such cells show a reduced formation of free radicals compared with other cells, they would be better positioned to use alternative substrates, like lactate and ß-hydroxybutyrate, for energy production (30)
. Beta-hydroxybutyrate has been shown to be beneficial under hypoglycemic, hypoxic, and ischemic conditions in the brain (31
32
33)
. The same holds true for lactate under hypoxia and ischemia (34
35
36
37)
.
Based on the above line of reasoning, it can be assumed that the mitochondrial pool of AQP9 in astrocytes contributes to their relatively high tolerance to ischemia (38)
. Similarly, in several experimental paradigms, dopaminergic cells stand out as less vulnerable to ischemia than other neuronal populations (35
, 39)
. The up-regulation of AQP9 observed after focal cerebral ischemia (8
, 35)
may reflect its importance for cell survival under ischemia and could represent a novel mechanism for ischemic preconditioning.
However, it may well be that the endowment of AQP9 turns into a disadvantage in certain pathophysiological situations. AQP9 has been shown to be permeable to arsenite (40)
, and it is likely that it is permeable to or affected by several metals. Copper inhibits water and glycerol permeability of AQP3 (the aquaporin with the highest homology to AQP9 (41)
, and AQP8 (which is expressed in kidney proximal tubule mitochondria) is permeable to Cd2+ (42)
. It is widely believed that Parkinson’s disease may be precipitated by exposure to certain environmental toxins and metals, including copper, and that mitochondria are prime targets for the toxic effects (43
, 44)
. A pathophysiological role of AQP9 in the mediation of copper or iron toxicity would be consistent with the distribution of AQP9 reported here, as astrocytes and dopaminergic neurons are particularly sensitive to the deleterious effects of exposure to these metals (43
, 45)
. AQP9 is inhibited by mercury, but no association has been demonstrated between mercury load and Parkinson’s disease (44)
.
When AQP9 knockout animals become available, it should be an issue of priority to test whether these animals exhibit an increased or reduced resistance to drugs that normally generate symptoms of Parkinson’s disease.
|
ACKNOWLEDGMENTS |
|---|
Received for publication December 30, 2004. Accepted for publication April 27, 2005.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  T. M. Rodela, J. S. Ballantyne, and P. A. Wright Carrier-mediated urea transport across the mitochondrial membrane of an elasmobranch (Raja erinacea) and a teleost (Oncorhynchus mykiss) fish Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2008; 294(6): R1947 - R1957. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Uehlein, B. Otto, D. T. Hanson, M. Fischer, N. McDowell, and R. Kaldenhoff Function of Nicotiana tabacum Aquaporins as Chloroplast Gas Pores Challenges the Concept of Membrane CO2 Permeability PLANT CELL, March 1, 2008; 20(3): 648 - 657. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. J. Yool Aquaporins: Multiple Roles in the Central Nervous System Neuroscientist, October 1, 2007; 13(5): 470 - 485. [Abstract] [PDF]
|
|
|
|
 |
|
 A. Kaasik, D. Safiulina, A. Zharkovsky, and V. Veksler Regulation of mitochondrial matrix volume Am J Physiol Cell Physiol, January 1, 2007; 292(1): C157 - C163. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. S. Frydenlund, A. Bhardwaj, T. Otsuka, M. N. Mylonakou, T. Yasumura, K. G. V. Davidson, E. Zeynalov, O. Skare, P. Laake, F.-M. Haug, et al. Temporary loss of perivascular aquaporin-4 in neocortex after transient middle cerebral artery occlusion in mice PNAS, September 5, 2006; 103(36): 13532 - 13536. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W.-K. Lee and F. Thevenod A role for mitochondrial aquaporins in cellular life-and-death decisions? Am J Physiol Cell Physiol, August 1, 2006; 291(2): C195 - C202. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K.-Q. Hu, C. Liu, H. Ernst, N. I. Krinsky, R. M. Russell, and X.-D. Wang The Biochemical Characterization of Ferret Carotene-9', 10'-Monooxygenase Catalyzing Cleavage of Carotenoids in Vitro and in Vivo J. Biol. Chem., July 14, 2006; 281(28): 19327 - 19338. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. Yang, D. Zhao, and A. S. Verkman Evidence against Functionally Significant Aquaporin Expression in Mitochondria J. Biol. Chem., June 16, 2006; 281(24): 16202 - 16206. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||
