Departments of 1 Medicine and 2 Physiology and Biophysics, Division of Nephrology, Albert Einstein College of Medicine, New York, New York 10461
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The PG transporter (PGT) is expressed in subapical vesicles in the kidney collecting duct. To gain insight into the possible function of the PGT in this tubule segment, we tagged rat PGT with green fluorescent protein at the COOH terminus and generated stable PGT-expressing Madin-Darby canine kidney cell lines. When grown on permeable filters, green fluorescent protein-PGT was expressed predominantly at the apical membrane. Although the basal-to-apical transepithelial flux of [3H]PGE2 was little changed by PGT expression, the apical-to-basolateral flux was increased 100-fold compared with wild-type cells. Analysis of driving forces revealed that this flux represents PGT-mediated active transepithelial PGE2 transport. We propose that endogenous PGT is exocytically inserted into the collecting duct apical membrane, where it could control the concentration of luminal PGs.
prostaglandin; eicosanoids; membrane transport; active transport; Madin-Darby canine kidney cells; prostaglandin transporter
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
PGS AND THROMBOXANES PLAY ubiquitous and vital pathophysiological and therapeutic roles in human health and disease (25), including pregnancy, labor, delivery, and abortion (10, 15); gastric protection and peptic ulcer formation (27); airway resistance and asthma (26); penile erection (18); blood pressure control (11); fever (24); bone metabolism (31); Alzheimer's disease (29); and cancer (2, 12). In the kidney, PGs and thromboxanes have major effects on renal blood flow and glomerular hemodynamics, renin secretion, Na excretion, and water excretion (3, 5, 6, 23).
Our laboratory identified the first known PG transporter (PGT) cDNA (17, 35). PGT mRNA is broadly expressed in rats, mice, and humans (17, 21, 30). It was recently found that endogenous PGT in the kidney is expressed in cell types known to synthesize and release eicosanoids, including glomerular endothelial and mesangial cells, arteriolar endothelial and muscularis cells, principal cells of the collecting duct, medullary interstitial cells, and the medullary vasa rectae endothelia (4). In the collecting duct, in particular, PGT is expressed in subapical vesicles (4).
Furthermore, recent evidence from our lab suggests that PGT is probably a lactate-PG exchanger and thus appears to be energetically poised for the uptake, but not the release, of PGs (8).
To determine the sorting pattern of PGT in the Madin-Darby canine kidney (MDCK) collecting duct cell line and to characterize PGT function when stably expressed in MDCK cells, we tagged rat PGT with green fluorescent protein (GFP) at the COOH terminus, generated stable MDCK cell lines, and assessed the function of the transporter. Our data indicate that expression of PGT is sufficient to induce active transepithelial prostanoid transport in MDCK cell monolayers.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The full-length rat PGT cDNA, cloned at an EcoR1 site in the vector pGEM3Z (17), was mutagenized at glycine 640 by using Gene Editor (Life Technologies) to remove the stop codon at position 643; this mutation introduced a new SmaI restriction site. Rat PGT was then cut with EcoR1 and SmaI and cloned in the vector pEGFP-N1 (Clontech, Palo Alto, CA) such that the NH2 terminus of a red-shifted variant of wild-type GFP was appended in-frame to the COOH terminus of PGT.
MDCK cells (strain II, American Type Culture Collection) were transfected with the PGT-GFP construct or with empty vector as a control and were subjected to neomycin antibiotic selection pressure, clonal selection, and expansion on the basis of their levels of GFP expression as judged by fluorescence microscopy. Separately, the same strain of MDCK cells was stably transfected with wild-type rat PGT cloned into the vector pcDNA3 and lacking the COOH-terminal GFP.
Stable cell lines expressing PGT-GFP were grown on plastic tissue culture dishes in DMEM with 5% fetal bovine serum containing penicillin and streptomycin. Timed uptake of [3H]PGE2 was determined as previously described (17).
In separate experiments, the stable cell lines were seeded at 200,000 cells/cm2 on permeable filter supports (Falcon PET) and were examined by laser scanning confocal microscopy between 4 and 7 days after seeding, i.e., at confluence.
Sided uptakes or transepithelial fluxes of [3H]PGE2 were determined at 37°C by using [14C]mannitol as an extracellular marker. For uptakes on filters, the monolayers were washed in Waymouth buffer [(in mM) 135 NaCl, 13 H-HEPES, 13 Na-HEPES, 2.5 CaCl2, 1.2 MgCl2, 0.8 MgSO4, 5 KCl, and 28 D-glucose] and then incubated with the [3H]PGE2 and [14C]mannitol on one side for a given time. They were then washed again, and the filters were excised from the holding ring and analyzed by liquid scintillation counting.
For transepithelial fluxes, the cells were washed and incubated on both sides in Waymouth buffer. Then [3H]PGE2 and [14C]mannitol were added to one side (A) and the buffer on the opposite side (B) was collected at timed intervals and analyzed by liquid scintillation counting. To calculate transcellular PGE2 fluxes, the ratio of [3H]PGE2 vs. [14C]mannitol counts/min was first calculated from side A. At the end of the flux experiment, the 3H and 14C counts/min of side B were determined. The side B 14C counts/min were then multiplied by the original ratio of 3H to 14C from side A to calculate the maximal 3H counts/min that could have appeared on side B by paracellular diffusion. Any 3H counts/min (PGE2) above that calculated value were deemed to have arrived at side B via a non-paracellular (i.e., transcellular) route.
Release of endogenous PGE2 into the surrounding buffer was determined over 10 min by using an enzyme-linked immunoadsorption assay (Cayman Chemical, Ann Arbor, MI) after stimulation of the MDCK cells with bradykinin.
Transepithelial voltage was measured directly, and transepithelial resistance was calculated from the transepithelial voltage deflections that resulted from passing 20 µA of alternating current across the monolayer (Voltohmmeter, World Precision Instruments, New Haven, CT). To obtain the specific voltage and resistance of the cell monolayer, the voltage and resistance of unseeded filters were subtracted from those of filters seeded with cells.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Wild-type MDCK cells or MDCK cells stably expressing the
GFP-tagged PGT were grown on plastic dishes, and the timed uptake of
[3H]PGE2 was determined. As shown in Fig.
1, wild-type MDCK cells exhibited very
low time-dependent PGE2 uptake. This is in keeping with our
results showing very low rates of entry of prostanoids into wild-type
HeLa cells and Xenopus laevis oocytes (9, 17). In contrast, MDCK cells expressing PGT exhibited rapid time-dependent uptake of [3H]PGE2 compared with wild-type
MDCK cells [(in fmol/dish) 356 (PGT) vs. 5.6 (wild-type) at 2 min and
506 (PGT) vs. 7.6 (wild-type) at 5 min]. We conclude that appending
the GFP peptide onto the COOH terminus of rat PGT has no discernable
effect on transporter function and that enough transporter is sorted to
the plasma membrane to make uptake assays possible.
|
To determine the intracellular sorting of the transporter, stable GFP-PGT MDCK cells were grown to confluence over 5 days as a monolayer on either glass coverslips or permeable filter supports. GFP-PGT MDCK cells formed normal-appearing monolayers. The protein content for both control and GFP-PGT cell lines averaged 1.02 ± 0.03 mg protein/filter.
Figure 2 shows confocal microscopy
Z-reconstructions. GFP-PGT in cells grown on glass was
distributed throughout the cytoplasm in what appears to be a vesicular
pattern, although there was perhaps some tendency for stronger
expression at the apical plasma membrane. In contrast, GFP-PGT MDCK
cells grown on filters demonstrated strong preferential expression at
the apical membrane, with much less expression in the cytoplasm.
|
The remaining experiments were carried out by using cells grown on
filters. We determined the sided uptake of PGE2 by
incubating wild-type or GFP-PGT MDCK monolayers in solutions containing
[3H]PGE2 and [14C]mannitol (the
latter acting as an extracellular volume marker), applied to either the
apical or the basolateral side. Figure 3 shows that expression of GFP-PGT induced a small and comparable increase in apparent basolateral and apical PGE2
permeabilities compared with wild-type MDCK cells [5-min
mannitol-corrected PGE2 uptakes: basolateral = 50 ± 6.8 (PGT) vs. 3.7 ± 0.1 fmol/mg protein (wild-type);
apical = 57 ± 12 (PGT) vs. 2.7 ± 1.7 fmol/mg protein (wild-type)]. PGT expression had no statistically significant effect
on the total PGE2 released in response to 1 µM bradykinin (in fact, the trend was for less PGE2 to be released in the
PGT-expressing cells: GFP-PGT, 663 ± 219 pg PGE2
released · mg protein1 · 10 min
1; control vector, 1,006 ± 167 pg
PGE2 released · mg
protein
1 · 10 min
1;
n = 5 each; P = not significant).
|
We performed transepithelial unidirectional flux measurements of
[3H]PGE2, again by using
[14C]mannitol as an extracellular volume marker. Although
the basal-to-apical transepithelial flux of
[3H]PGE2 was somewhat higher in the
PGT-expressing cells compared with wild-type cells [5-min flux in
fmol/mg protein: 8.7 ± 0.1 (PGT) vs. 2.7 ± 0 (wild-type)],
the apical-to-basolateral [3H]PGE2 flux was
much larger in the PGT-expressing cells [5-min flux: 277 ± 74 (PGT) vs. 2.7 ± 0 fmol/mg protein (wild-type)] (Fig.
4). The calculated net PGE2
flux was 268 fmol · mg protein1 · 5 min
1. Similar results were obtained in MDCK cell lines
stably expressing wild-type PGT without the GFP tag
(apical-to-basolateral PGE2 flux = 738 ± 16 fmol/mg protein, basolateral-to-apical flux = 13.8 ± 1.1 fmol/mg protein).
|
Because PGT can function in a PG/PG self-exchange mode (9), we inhibited endogenous PG production in the GFP-PGT MDCK monolayer by using aspirin (100 µM × 1 h). There was no effect on apical-to-basal tracer PGE2 flux across the MDCK monolayer (control = 224 ± 0.3 fmol/mg protein, aspirin = 240 ± 13 fmol/mg protein).
We have previously reported that MDCK monolayers of this strain
generate no detectable transepithelial voltage (32). Here, we again found that the transepithelial voltage was not significantly different from zero in the GFP-PGT monolayers (1.4 ± 0.4 mV) and in the control monolayers (
0.2 ± 0.3 mV). Similarly, the transepithelial resistance was relatively low in both groups
(GFP-PGT = 205 ± 19
· cm2,
control = 205 ± 14
· cm2). Because
the tracer PGE2 concentration gradients during the two
separate unidirectional fluxes were equal and opposite in direction and
the transepithelial voltage was zero, the Ussing flux ratio equation
predicts that passive transport alone would result in equal and
opposite unidirectional [3H]PGE2 fluxes
(36). Because the ratio of the two unidirectional fluxes
was 277 vs. 8.7, or 32, we conclude that PGT induces active PGE2 absorption.
We examined the effect of the organic anion transport inhibitor
bromcresol green (BCG), which inhibits cloned rat PGT in HeLa cells
with an inhibitory constant of 3.6 µM (17). As shown in Fig. 5, BCG (500 µM) strongly inhibited
the active [3H]PGE2 absorption by GFP-PGT
MDCK monolayers.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The major findings of the present study are as follows. Wild-type MDCK cells exhibit a very low permeability to PGE2, as judged by influx measurements. In contrast, stable expression of rat PGT in MDCK cells substantially increases the permeability of the plasma membrane to PGE2. When PGT-expressing MDCK cells are grown on filters, GFP-tagged PGT can be seen by confocal microscopy to be sorted primarily to the apical plasma membrane, where it induces robust active transport (absorption) of PGE2 across the monolayer. This PGT-mediated active transport is blocked by BCG, a known inhibitor of the PG carrier.
We chose to express PGT in MDCK cells for two reasons. First, there is a great deal of literature on protein sorting in MDCK cells that will be of help in future studies aimed at dissecting the sorting signals in PGT. Second, endogenous PGT is strongly expressed in the collecting duct (4), and MDCK cells derive from that nephron segment (13, 14, 28, 37). Thus MDCK cells probably reproduce the native cellular environment, despite the observation that endogenous PGT in the collecting duct is expressed in subapical vesicles; whereas in MDCK cells, it is sorted to the apical membrane. We hypothesize that the endogenous transporter in collecting ducts shuttles between subapical vesicles and the apical plasma membrane by means of exocytosis/endocytosis, as is the case with many membrane transporters (7). Studies are ongoing to determine those stimuli that induce exocytic insertion of PGT in vivo.
Expression of PGT in MDCK cells resulted in an equivalent increase in the cellular uptake, i.e., apparent permeability, of tracer PGE2 across both the apical and the basolateral membranes (Fig. 3). Permeability is the product of the permeability coefficient and the membrane area, and the basolateral membrane area in these strain II MDCK cells is approximately fourfold that of the apical membrane (38). Therefore, the uptakes shown in Fig. 3 indicate that the PGT-dependent apical membrane permeability coefficient is roughly fourfold that of the basolateral membrane, in keeping with the confocal localization.
An important aspect of the present experiments is the unequivocal evidence that PGT mediates active, uphill transport. On previous studies from our laboratory, we demonstrated that X. laevis oocytes-expressing PGT appear to be able to concentrate PGE2 against an electrochemical gradient (9). However, the limitations of the oocyte experimental system left open the possibility that PGT was a permease that made the tracer PG accessible to an intracellular binding protein(s). The present studies, on the other hand, definitively demonstrate that PGT energetically translocates PGE2 uphill across an epithelial monolayer from one aqueous compartment to another, i.e., carries out active transport. Given the predominantly apical membrane localization of PGT (Fig. 2), a likely model is that PGT mediates the energetically uphill influx of PG across the apical membrane, whereupon the PG exits the cell by passive, diffusional efflux across the basolateral membrane. In this regard, we have demonstrated previously that PGs can efflux from cells by simple diffusion (9).
We can make some statements about the likely driving force for active
PG uptake. Previous studies from our laboratory indicated that
transport of PGs by PGT is independent of H+,
Na+, and Cl (17) and that PGT is
an anion exchanger (9). Moreover, we have found that the
ability of PGT to transport PGs is dependent on glycolysis and has the
characteristics of lactate/PG exchange (8). Because
collecting ducts (16, 19, 20, 34, 39) and MDCK cells
(16, 22) engage in substantial aerobic glycolysis, both
cell types would generate a sufficient outwardly directed lactate
gradient to drive a lactate/PG exchanger in the direction of active PG
uptake into the cell. Cytoplasmic lactate might compete with
cytoplasmic PGs for binding to PGT, thus accounting for the lack of
augmented PGE2 release by PGT.
The biological function of active PG absorption from the collecting duct lumen remains unclear. Two laboratories have provided evidence for luminal PG receptors in the cortical collecting duct, activation of which suppresses Na transport and increases osmotic water permeability (1, 33). We speculate that PGT could control the net PGE2 available to these receptors by clearing the lumen of PGs derived from upstream nephron segments or of PGs that had entered the lumen by nondirectional diffusion from the collecting duct itself. Further experiments are required to test these hypotheses.
![]() |
ACKNOWLEDGEMENTS |
---|
We acknowledge the assistance of the Einstein Analytical Imaging Facility in generating the confocal micrographs.
![]() |
FOOTNOTES |
---|
A portion of this work was supported by grants to V. L. Schuster from the National Institute of Diabetes and Digestive and Kidney Diseases (DK-49688), the National Kidney Foundation, and the American Heart Association.
Address for reprint requests and other correspondence: V. L. Schuster, Rm. 615, Ullmann Bldg., Albert Einstein College of Medicine, 1300 Morris Park Ave., New York, NY 10461 (E-mail: schuster{at}aecom.yu.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
10.1152/ajprenal.00150.2001
Received 15 May 2001; accepted in final form 18 September 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ando, Y,
and
Asano Y.
Luminal prostaglandin E2 modulates sodium and water transport in rabbit cortical collecting ducts.
Am J Physiol Renal Fluid Electrolyte Physiol
268:
F1093-F1101,
1995
2.
Badawi, AF.
The role of prostaglandin synthesis in prostate cancer.
BJU Int
85:
451-462,
2000[ISI][Medline].
3.
Badr, KF,
and
Jacobson HR.
Arachidonic acid metabolites and the kidney.
In: The Kidney, edited by Brenner BM,
and Rector FC, Jr.. Philadelphia, PA: Saunders, 1991, p. 584-619.
4.
Bao Y, Pucci ML, Chan BS, Lu R, Ito S, and Schuster VL. The
prostaglandin transporter PGT is expressed in cell types that
synthesize and release prostanoids. Am J Physiol Renal
Physiol. In press.
5.
Bonventre, JV,
and
Nemenoff R.
Renal tubular arachidonic acid metabolism.
Kidney Int
39:
438-449,
1991[ISI][Medline].
6.
Breyer, MD,
Zhang Y,
Guan YF,
Hao CM,
Hebert RL,
and
Breyer RM.
Regulation of renal function by prostaglandin E receptors.
Kidney Int
67:
S88-S94,
1998.
7.
Brown, D.
Membrane recycling and epithelial cell function.
Am J Physiol Renal Fluid Electrolyte Physiol
256:
F1-F12,
1989
8.
Chan BS, Endo S, Kanai N, and Schuster VL. Identification of
lactate as a substrate and a driving force for prostanoid transport by
the prostaglandin transporter PGT. Am J Physiol Renal
Physiol. In press.
9.
Chan, BS,
Satriano JA,
Pucci ML,
and
Schuster VL.
Mechanism of prostaglandin E2 transport across the plasma membrane of HeLa cells and Xenopus oocytes expressing the prostaglandin transporter "PGT."
J Biol Chem
273:
6689-6697,
1998
10.
Christin-Maitre, S,
Bouchard P,
and
Spitz IM.
Medical termination of pregnancy.
N Engl J Med
342:
946-956,
2000
11.
Colina-Chourio, JA,
Godoy-Godoy N,
and
Avila-Hernandez R. M.
Role of prostaglandins in hypertension.
J Hum Hypertens
14:
S16-S19,
2000[ISI][Medline].
12.
Dannenberg, AJ,
and
Zakim D.
Chemoprevention of colorectal cancer through inhibition of cyclooxygenase-2.
Semin Oncol
26:
499-504,
1999[ISI][Medline].
13.
Devuyst, O,
Beauwens R,
Denef JF,
Crabbe J,
and
Abramow M.
Subtypes of Madin-Darby canine kidney (MDCK) cells defined by immunocytochemistry: further evidence for properties of renal collecting duct cells.
Cell Tissue Res
277:
231-237,
1994[ISI][Medline].
14.
Gekle, M,
Wunsch S,
Oberleithner H,
and
Silbernagl S.
Characterization of two MDCK-cell subtypes as a model system to study principal cell and intercalated cell properties.
Pflügers Arch
428:
157-162,
1994[ISI][Medline].
15.
Gibb, W.
The role of prostaglandins in human parturition.
Ann Med
30:
235-241,
1998[ISI][Medline].
16.
Gstraunthaler, G,
Pfaller W,
and
Kotanko P.
Biochemical characterization of renal epithelial cell cultures (LLC-PK1 and MDCK).
Am J Physiol Renal Fluid Electrolyte Physiol
248:
F536-F544,
1985
17.
Kanai, N,
Lu R,
Satriano JA,
Bao Y,
Wolkoff AW,
and
Schuster VL.
Identification and characterization of a prostaglandin transporter.
Science
268:
866-869,
1995[ISI][Medline].
18.
Khan, MA,
Thompson CS,
Sullivan ME,
Jeremy JY,
Mikhailidis DP,
and
Morgan RJ.
The role of prostaglandins in the aetiology and treatment of erectile dysfunction.
Prostaglandins Leukot Essent Fatty Acids
60:
169-174,
1999[ISI][Medline].
19.
Lawrence, GM,
Jepson MA,
Trayer IP,
and
Walker DG.
The compartmentation of glycolytic and gluconeogenic enzymes in rat kidney and liver and its significance to renal and hepatic metabolism.
Histochem J
18:
45-53,
1986[ISI][Medline].
20.
Lawrence, GM,
Trayer IP,
and
Walker DG.
Histochemical and immunohistochemical localization of hexokinase isoenzymes in normal rat liver.
Histochem J
16:
1099-1111,
1984[ISI][Medline].
21.
Lu, R,
Kanai N,
Bao Y,
and
Schuster VL.
Cloning, in vitro expression, and tissue distribution of a human prostaglandin transporter cDNA (hPGT).
J Clin Invest
98:
1142-1149,
1996
22.
Lynch, RM,
and
Balaban RS.
Coupling of aerobic glycolysis and Na+-K+-ATPase in renal cell line MDCK.
Am J Physiol Cell Physiol
22:
C269-C276,
1987.
23.
Menè, P,
and
Dunn MJ.
Vascular, glomerular, and tubular effects of angiotensin II, kinins, and prostaglandins.
In: The Kidney: Physiology and Pathophysiology, , edited by Seldin DW,
and Giebisch G.. New York: Raven, 1992, p. 1205-1248.
24.
Milton, AS.
Prostaglandins and fever.
Prog Brain Res
115:
129-139,
1998[ISI][Medline].
25.
Narumiya, S,
Sugimoto Y,
and
Ushikubi F.
Prostanoid receptors: structures, properties, and functions.
Physiol Rev
79:
1193-226,
1999
26.
Pang, L,
Pitt A,
Petkova D,
and
Knox AJ.
The cox-1/cox-2 balance in asthma.
Clin Exp Allergy
28:
1050-1058,
1998[ISI][Medline].
27.
Peskar, BM,
and
Maricic N.
Role of prostaglandins in gastroprotection.
Dig Dis Sci
43:
23S-29S,
1998[ISI][Medline].
28.
Pfaller, W,
Gstraunthaler G,
Kersting U,
and
Oberleithner H.
Carbonic anhydrase activity in Madin-Darby canine kidney cells. Evidence for intercalated cell properties.
Renal Physiol Biochem
12:
328-337,
1989[ISI][Medline].
29.
Prasad, KN,
Hovland AR,
La Rosa FG,
and
Hovland PG.
Prostaglandins as putative neurotoxins in alzheimer's disease.
Proc Soc Exp Biol Med
219:
120-125,
1998[Abstract].
30.
Pucci, ML,
Bao Y,
Chan B,
Itoh S,
Lu R,
Copeland NG,
Gilbert DJ,
and
Schuster VL.
Cloning of mouse prostaglandin transporter PGT cDNA: species-specific substrate affinities.
Am J Physiol Regulatory Integrative Comp Physiol
277:
R734-R741,
1999
31.
Raisz, LG.
Prostaglandins and bone: physiology and pathophysiology.
Osteoarthritis Cartilage
7:
419-421,
1999[ISI][Medline].
32.
Rosenberg, SO,
Berkowitz PA,
Li L,
and
Schuster VL.
Imaging of filter-grown epithelial cells: MDCK Na+-H+ exchanger is basolateral.
Am J Physiol Cell Physiol
260:
C868-C876,
1991
33.
Sakairi, Y,
Jacobson HR,
Noland TD,
and
Breyer MD.
Luminal prostaglandin E receptors regulate salt and water transport in rabbit cortical collecting duct.
Am J Physiol Renal Fluid Electrolyte Physiol
269:
F257-F265,
1995
34.
Schmid, H,
Mall A,
Scholz M,
and
Schmidt U.
Unchanged glycolytic capacity in rat kidney under conditions of stimulated gluconeogenesis. Determination of phosphofructokinase and pyruvate kinase in microdissected nephron segments of fasted and acidotic animals.
Hoppe-Seyler's Z Physiol Chem
361:
819-827,
1980[ISI][Medline].
35.
Schuster, VL.
Molecular mechanisms of prostaglandin transport.
Annu Rev Physiol
60:
221-242,
1998[ISI][Medline].
36.
Ussing, HH.
The distinction by means of tracers between active transport and diffusion. The transfer of iodide across the isolated frog skin.
Acta Physiol Scand
19:
43-56,
1949[ISI].
37.
Valentich, JD.
Morphological similarities between the dog kidney cell line MDCK and the mammalian cortical collecting tubule.
Ann NY Acad Sci
372:
384-404,
1981[Medline].
38.
Von Bonsdorff, CH,
Fuller S,
and
Simons K.
Apical and basolateral endocytosis in Madin-Darby canine kidney (MDCK) cells grown on nitrocellulose filters.
EMBO J
4:
2781-2792,
1985[Abstract].
39.
Wirthensohn, G,
and
Guder WG.
Renal substrate metabolism.
Physiol Rev
66:
469-497,
1986