Pharmacology & Pharmacy, 2011, 2, 173-179
doi:10.4236/pp.2011.23025 Published Online July 2011 (http://www.scirp.org/journal/pp)
173
Nonlinear Intestinal Absorption of Fluorescein
Isothiocyanate Dextran 4000 Caused by
Absorptive and Secretory Transporting System
Mikio Tomita, Rie Ohkubo, Shohei Ouchi, Chise Kawahata, Masahiro Hayashi
Department of Drug Absorption and Pharmacokinetics, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, To-
kyo, Japan.
Received April 5th, 2011; revised May 2nd, 2012; accepted June 6th, 2011.
ABSTRACT
The mechanism of the nonlinear concentration dependence of the intestinal absorption of fluorescein isothiocyanate
dextran 4,000 (FD-4) was studied using in situ rat intestinal loops and the in vitro Ussing-type chamber method. The
intestinal absorption rate constant of FD-4, as evaluated by the intestinal loop method, increased significantly in a
nonlinear fashion as the FD-4 concentration increased up to 0.2 mM and tended to decrease at concentrations higher
than 0.2 mM. The mucosal-to-serosal permeation of FD-4 across rat ileal sheets, as evaluated by the in vitro
Ussing-type chamber method, also increased in a nonlinear fashion in the low concentration range (0.01 - 0.02 mM),
before decreasing as the concentration increased further, whereas serosal-to-mucosal permeation decreased in a con-
centration-dependent manner. In addition, mucosal-to-serosal flux and serosal-to-mucosal flux were increased and
reduced in the presence of the metabolic inhibitor 2,4-dinitrophenol, respectively. These results suggest that FD-4 is
predominantly secreted into the intestinal lumen by an efflux transport system.
Keywords: Fluorescein Isothiocyanate Dextran 4000, Nonlinear Absorptive Transport, Nonlinear Secretory Transport,
Rat Ileal Intestine
1. Introduction
Under normal conditions, the intestinal epithelium acts
as a selective barrier that defines and maintains distinc-
tive luminal and subepithelial compartments. The barrier
function of the intestine permits the systemic absorption
of nutrients while it prevents systemic contamination by
luminal microbes or microbial products [1]. In both
clinical and experimental studies, the functional integrity
of the intestinal epithelial barrier has often been assessed
by measuring the mucosal permeability of certain hydro-
philic compounds, such as 51Cr-EDTA [2], lactulose [3],
cellobiose [4], polyethylene glycols [5], fluorescent dyes
[6], and fluorescein isothiocyanate (FITC)-labeled dex-
trans [7]. It is generally accepted that the transepithelial
movement of these hydrophilic probes occurs as a result
of passive diffusion through the paracellular channels
formed by adjacent enterocytes. The rate of transepithe-
lial permeation is thought to be regulated by the tight
junctions guarding the apical end of paracellular pores [8]
as well as the hydrodynamic size of the hydrophilic
probes used for the measurements [9]. In some in vivo
experimental studies, permeability was measured in the
lumen-to-plasma direction [5]; whereas in others, per-
meability was measured in the plasma-to-lumen direction
[7], and both types of studies were performed under the
assumption that directional permeation involves passive
diffusion and is not polarized.
However, it has become apparent that many substan-
ces are actively transported across intestinal epithelia.
For example, it has been reported that poorly absorbed β-
actam antibiotics, such as cefazolin and ampicillin, are
actively secreted in the serosal-to-mucosal direction by
one or more mechanisms that are inhibited by both or-
ganic anions and some organic cations. The multidrug
resistance (MDR) gene product, which is a 170-kD plas-
ma membrane glycoprotein and is commonly designated
Gp170 or P-glycoprotein (P-gp), has been implicated in
the active intestinal secretion of various hydrophobic or
amphipathic molecules, including cyclosporine A, dau-
nomycin, rhodamine 123, and some small molecular pep-

Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
174
tides.
On the other hand, we have demonstrated that the se-
cretion of fluorescein isothiocyanate dextran 4,000 (FD-
4; MW 4,400 Da), which is considered to be an impor-
tant paracellular probe for assessing transport in the se-
rosal to mucosal direction across rat colonic epithelial
cells and Caco-2 cell monolayers, is mediated by tran-
scytosis mechanisms, one of which shows substrate
specificity for dextran polysaccharides [10,11]. Thus, the
absorption mechanism of FD-4 is complex and needs to
be studied further.
In the present study, we investigated the absorptive
and secretory transport of FD-4 in the rat intestine and
revealed the participation of multiple transport mecha-
nisms.
2. Materials and Methods
2.1. Materials
Fluorescein isothiocyanate dextran 4,000 (FD-4); fluo-
rescein isothiocyanate dextran 40,000 (FD-40); 2,4-di-
nitrophenol (DNP); colchicine; chloroquine; methyl-β-
cyclodextrin; fucoidan; polyinosinic acid (5’) potassium
salt (poly (I)); cyclosporine A; probenecid; and gluta-
thione (GSH) were purchased from Sigma (St. Louis).
All other chemicals were commercial products of reagent
grade.
2.2. Measurement of Intestinal Absorption by
the in Situ Loop Method Materials
The intestinal absorption of FD-4 was evaluated using
the loop method [12,13]. The ileal of male Wistar/ST rats
weighing 200 g to 250 g (Japan SLC, Hamamatsu, Ja-
pan) were exposed by making an abdominal incision
along the midline, and two L-shaped glass cannulae (i.d.:
2 mm, o.d.: 4 mm) were inserted through small slits at
the proximal and distal ends (7 cm). The proximal and
distal cannulae were located at 12 cm and 5 cm above the
cecum, respectively. Each cannula was secured by liga-
tion with a silk suture, and the intestine was returned to
the abdominal cavity to maintain its integrity. A 4-cm
portion of Tygon tubing (i.d.: 3 mm, o.d.: 5 mm) was
attached to the exposed end of each cannula, and a 10-ml
hypodermic syringe fitted with a connecting tube and
containing loop solution pre-warmed at 37˚C was at-
tached to the proximal cannula. To clear the gut, saline
was slowly passed through it to the distal cannula and
discarded until the effluent was clear. The remaining
loop solution was carefully expelled from the intestine
by pumping air through the syringe, and 5 ml of FD-4
solution were immediately introduced into the intestine.
The distal cannula was connected to a 10-ml syringe fit-
ted with a three-way stopcock. At 15, 30, 45, and 60 min
after the administration of the drug solution, a 0.5-ml
aliquot of luminal solution was removed through the
attached syringe. The FD-4-containing test solution was
composed of 126 mM NaCl, 5.0 mM KCl, 1.4 mM
CaCl2, 3.5 mM NaHCO3, 4.85 mM NaH2PO4·2H2O, 0.95
mM Na2HPO4, and 2 g/L D (+)-glucose at pH 6.5, and
the solution was gassed with 95% O2/5% CO2 before and
during the transport experiment. The change in the vol-
ume of water in the intestinal luminal solution was cor-
rected for by measuring the change in the concentration
of the unabsorbable marker fluorescein isothiocyanate
dextran 40,000 (FD-40), which was administered simul-
taneously without FD-4. The concentration of FD-40
used in this study was 0.1%.
2.3. Transport Experiments Involving the
Ussing-Type Chamber Method
Rat ileal tissue sheets were prepared as described previ-
ously [14]. Tissue sheets consisting of the mucosa and
most of the muscularis mucosa were prepared by remov-
ing the submucosa and tunica muscularis with fine for-
ceps. They were then mounted vertically in an Ussing-
type chamber that provided an exposed area of 0.75 cm2.
The volume of bathing solution on each side was 11 ml,
and the solution temperature was maintained at 37˚C in a
water-jacketed reservoir. The FD-4-containing test solu-
tion was composed of 126 mM NaCl, 5.0 mM KCl, 1.4
mM CaCl2, 3.5 mM NaHCO3, 4.85 mM NaH2PO4·2H2O,
0.95 mM Na2HPO4, and 2g/L D (+)-glucose at pH 6.5,
and the solution was gassed with 95% O2/5% CO2 before
and during the transport experiment. To examine the
effects of 2,4-dinitrophenol (DNP), a metabolic inhibitor,
and colchicines [15] , chloroquine [16], methyl-β-cyclo-
dextrin [17], fucoidan [18], poly (I) [19], cyclosporine A
[20], and probenecid +GSH [21], which inhibit various
transport systems, the mucosal reservoir was filled with
test solution containing one of the above inhibitors. The
pH of the test solution containing DNP was adjusted to
6.5 using sodium hydroxide. Samples were taken from
the acceptor side at intervals of 10 min.
2.4. Assay and Data Analysis
The concentration of FD-4 was determined using a fluo-
rescence spectrophotometer after appropriate dilution of
the samples in phosphate-buffered saline (pH7.4). The
excitation and emission wavelengths of FD-4 were 492
and 515 nm, respectively.
The absorption rate constant was evaluated from the
slope of the decline in the FD-4 concentration of the lu-
minal fluid over time.
Permeation clearance was obtained as follows:
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Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
175
Permeation clearance = (dQ/dt)/(A × C0),
where dQ/dt is the transport rate (µg/min) and corre-
sponds to the slope of the linear regression line between
the amount transported and time. C0 is the initial concen-
tration in the donor chamber (µg/mL), and A is the area
of the membrane (0.75 cm2).
2.5. Statistical Analysis
All results are expressed as the mean value ± standard
error (Mean ± S.E.). The statistical significance of dif-
ferences between two groups was analyzed using Dun-
nett’s test. Differences were considered to be significant
at a level of p < 0.05.
3. Results
3.1. Concentration Dependence of the Intestinal
Absorption Rate of FD-4 in Rats
The relationship between the first-order absorption rate
constant and the FD-4 concentration was evaluated by
the loop method. When 0.01 to 1 mM FD-4 was admin-
istered to the ileal loop, the intestinal absorption rate
changed nonlinearly, as shown in Figure 1. The intesti-
nal absorption rate increased from 0.01 mM to 0.2 mM,
and then decreased from 0.2 mM to 1 mM. The absorp-
tion rate constant at 0.2 mM was significantly higher
than that at 0.01 or 0.02 mM (p < 0.05). This result sug-
gests that at least two nonlinear events are involved in
Figure 1. Concentration dependence of the FD-4 ileal ab-
sorption rate constant in rats. The intestinal absorption rate
constant (ka) of FD-4 (0.01 mM - 1 mM) was evaluated
throughout the time course of the decrease in the luminal
FD-4 concentration measured by the in situ loop method;
Each point represents the mean ±S.E. of seven experiments.
***Significantly different from the absorption rate constant
observed at 0.01 µM FD-4 (p < 0.001). N.S. not significantly
different from the absorption rate constant measured at 0.2
mM FD-4.
the I testinal absorption of FD-4.
The transport of FD-4 in rat intestinal tissue was ex-
amined further using the diffusion chamber method. The
permeation of FD-4 at various concentrations across a rat
ileal sheet was measured in both the mucosal-to-serosal
and serosal-to-mucosal directions. As shown in Figure 2,
the serosal-to-mucosal permeation coefficient signifi-
cantly decreased in a concentration-dependent manner,
whereas the mucosal-to-serosal permeation coefficient
increased up to 0.02 mM, and then tended to decrease at
concentrations higher than 0.02 mM. Furthermore, in the
presence of 1 mM DNP, the serosal-to-mucosal transport
clearance of 0.01 mM FD-4 significantly decreased,
whereas transport in the reverse direction increased sig-
nificantly (Figure 2). At FD-4 concentrations above 0.02
mM, no vectorial transport of FD-4 across the rat ileal
membrane was observed (Figure 2), and the effect of
DNP disappeared (data not shown)
3.2. Transcellular Transport of FD-4 across a
Rat Ileal Sheet
To determine whether the transport of FD-4 across a rat-
ileal sheet was temperature dependent, transport fluxes
Figure 2. Concentration dependence of FD-4 permeation
clearance across rat ileal tissue. The permeation of FD-4
was determined using a rat ileum mounted in an Ussing-
type chamber. The closed squares and closed circles re-
present the permeation clearance in the serosal-to-mucosal
and mucosal-to-serosal directions, respectively. The open
squares and open circles represent the serosal-to-mucosal
and mucosal-to serosal clearance of FD-4 in the presence of
1 mM 2,4-dinitrophenol. Each point represents the mean
±S.E. of seven experiments. Significantly different from the
mucosal-to-serosal clearance in the absence of 2,4-dini-
trophenol (p < 0.05). **Significantly different from the se-
rosal-to-mucosal clearance in the absence of 2,4-dinitro-
phenol (p < 0.01).

Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
176
were measured at 4˚C and 37˚C (Figure 3). The permea-
tion of FD-4 was linear over 120 min after an initial lag
time of a few minutes. The flux in the serosal-to mucosal
direction was about 2.0 - 3.3 times larger than the reverse
flux (Figure 3), and the flux observed at 4˚C, which is
regarded as a measure of passive permeability, was sig-
nificantly lower than that seen at 37˚C. Therefore, the
transport of FD-4 can be ascribed to active transcellular
permeation.
To investigate whether FD-4 interacts with receptors
or transporters present in rat ileal epithelial cells, the
effects of colchicines [15], chloroquine [16], methyl-β-
cyclodertin [17], fucoidan [18], poly(I) [19], cyclospo-
rine A [20], and probenecid + GSH [21] on the serosal to
mucosal transport of FD-4 were examined. When colchi-
cines, a typical inhibitor of transcytosis including endo-
cytosis and exocytosis, was used at a concentration of 2
mM, the transport of FD-4 in the serosal-to-mucosal di-
rection decreased (Figure 4), while that of FITC without
dextran was not decreased (Figure 5). When Cyclos-
porine A, a typical substrate for P-gp, was added at a
concentration that was 2 times higher than that of FD-4,
the transport of FD-4 was significantly decreased, and it
was also decreased in the presence of ABC transport
inhibitors such as a probenecid + GSH and various other
endocytosis inhibitors such as chloroquine, methyl-β-
cyclodextrin, and fucoidan (Figure 4). However, no
marked changes in the serosal-to-mucosal transport of
FITC were observed in the presence or absence of pro-
Figure 3. Effect of temperature on the polarized permeation
of FD-4 across rat ileal tissue. The concentration of FD-4
used in this study was 10 µM. The circles and triangles
represent the data obtained at 37˚C and 4˚C, respectively.
The white and black symbols represent the data for the
serosal-to-mucosal and mucosal-to-serosal directions, re-
spectively. Each point represents the mean ±S.E. of seven
experiments.
Figure 4. Effects of various inhibitors on the serosal to mu-
cosal transport of FD-4 across rat ileal tissue. The concen-
trations of colchicines, chloroquine, methyl-β-cyclodextrin,
fucoidan, poly (I), cyclosporine A, probenecid, and GSH
used in the present study were 2 mM, 0.1 mM, 5 mM, 0.2
mg/ml, 50 µg/ml, 20 µM, 1 mM, and 10 mM, respectively.
Each point represents the mean ±S.E. of seven experiments;
*( p < 0.05); **( p < 0.01); ***( p < 0.001), significantly differ-
ent from the data obtained without the inhibitor (no addi-
tive).
Figure 5. Effects of various inhibitors on the serosal to mu-
cosal transport of FITC across rat ileal tissue. The concen-
trations of colchicines, chloroquine, methyl-b-cyclodextrin,
fucoidan, poly (I), cyclosporine A, probenecid, and GSH
used in the present study were 2 mM, 0.1 mM, 5 mM, 0.2
mg/ml, 50 µg/ml, 20 µM, 1 mM, and 10 mM, respectively.
Each point represents the mean ±S.E. of seven experi-
ments.
benecid +GSH (Figure 5). Chloroquine, methyl-β-cy-
clodextrin, fucoidan, and cyclosporine A had no signifi-
cant effect on FITC transport (Figure 5).
4. Discussion
The concept that carrier-mediated intestinal absorption
and luminal secretion mechanisms as well as intestinal
tissue metabolic activity regulate the bioavailability of
various drugs has been established previously [22,23].
Such saturable physiological mechanisms can sometimes
produce nonlinear pharmacokinetic phenomena. The re-
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Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
177
FD-4.
sults obtained in the present study represent the first evi-
dence that a complex pattern of nonlinear FD-4 bio-
availability is generated by the interaction of intestinal
absorptive and secretory transport systems when FD-4 is
present at a concentration beyond that which induces
linear absorbability in the intestinal luminal fluid.
The intestinal absorption of FD-4 in rats, as assessed
by the in situ loop method, exhibited distinctive nonlin-
earity, involving a significant increase of the first-order
absorption rate constant at a drug concentration of 0.2
mM compared with those observed at 0.01 and 0.02 mM,
followed by a decrease at higher concentrations (1 mM)
(Figure 1). As the disappearance of intact FD-4 from the
intestinal luminal fluid was measured in this experiment,
the above observations can be accounted for by saturable
secretory and absorptive transport mechanisms as these
phenomena can not be induced by metabolism saturation
or a solubility limitation. Absorptive-directed (mucosal-
to-serosal) flux of FD-4 across ileal tissue preparations
mounted on an Ussing-type chamber increased with the
concentration of the drug up to 0.02 mM (Figure 2).
This result is consistent with that obtained by the in situ
loop method, both of which can be explained by a satur-
able secretory mechanism. This hypothesis is further
supported by our measurements of serosal-to-mucosal
flux using the Ussing-type chamber method, which
showed a marked decrease in the permeation coefficient
as the FD-4 concentration increased (Figure 2). The
break points shown in Figures 1 and 2 occurred at 0.2
mM and 0.02 mM, respectively. This concentration dif-
ference can be ascribed to the difference in the thick-
ness of the unstirred water layer between these two ex-
perimental systems because the loop method is expected
to have a thicker unstirred water layer than the isolated
ileal sheet chamber method. Conversely, in the in vitro
system, the solution in contact with the tissue was stirred
at 95% O2/5% CO2 throughout the experiment.
The vectorial transport of FD-4 across a rat ileal sheet
displayed a higher permeation constant in the serosal-to-
mucosal direction than in the reverse direction (Figure
3). Accordingly, concentration-dependent and vectorial
transport may operate during rat intestinal absorption.
Here, the mucosal-to-serosal flux of FD-4 at 37˚C was
significantly higher than that at 4˚C (Figure 3), support-
ing the active transport of FD-4 across rat ileal sheets.
In a previous study using an Ussing-type chamber, we
showed that the permeability of laminaran, a (1→3)-β-
D-glucan used as a water soluble and high molecular
weight probe, is greater in the serosal-to-mucosal direc-
tion than the mucosal-to-serosal direction [24]. Lamina-
ran is a dextran polysaccharide that consists of repeating
D-glucose units connected by α-glycoside linkages. The
polarized serosal-to-mucosal flux of FD-4 but not Luci-
fer yellow (a substrate of fluid-phase endocytosis) was
inhibited when excess dextran 10,000, a structurally
similar polysaccharide, was added to the FD-4 solution
[25]. These findings suggest that at least two distinct
polarized transport systems exist, one of which shows
some degree of substrate specificity for dextrans. We
also considered the possibility that the polarized trans-
port of FD-4 and laminaran was mediated by membrane
traffic such as fluid-phase endocytosis. This notion is not
a novel concept. Using primary cultures of canine
proximal tubular renal epithelial cells, Goligorsky et al.
reported that the flux of LY, which is generally regarded
as a marker of fluid-phase endocytosis, was 3-fold
greater in the basal-to-apical direction than in the api-
cal-to-basal direction [26]. In contrast, Pantzar et al. re-
ported that the net rate of fluid-phase transcytosis of [3H]
inulin across cultured MDCK epithelial cells was ap-
proximately equal in both directions, even though the
basolateral endocytotic rate was 6-fold greater than the
apical rate [27]. In our study, we observed that the mu-
cosa-to-serosal and serosal-to-mucosal fluxes of FD-4
involve nonlinear transport that is dependent on the con-
centration of FD-4 in the donor chamber. These findings
are consistent with transport in both directions occurring
as a result of membrane traffic and paracellular permea-
tion, or a combination of both processes. Our results are
insufficient to entirely exclude the possibility that polar-
ized fluid phase transcytosis (or some other nonsaturable
process) contributes to the vectorial transport of
In conclusion, fluorescein isothiocyanate dextran 4,000
(FD-4), displayed nonlinear intestinal absorption involv-
ing increases at lower concentrations followed by de-
creases at higher concentrations. Such nonlinearity can
be explained by the operation of absorptive and secretory
transporters or other mechanisms in the intestine, al-
though no specific secretory or absorptive transporters
have been identified yet. Clarification of the mechanistic
and kinetic features of the nonlinear intestinal absorption
of FD-4 is important to aid our understanding of the sys-
tems used to transport high molecular and hydrophilic
compounds in humans.
5. Acknowledgments
This research was supported partly by a Grant-in-Aid for
Scientific Research (No. 21590182) from the Ministry of
Education, Science, and Culture of Japan and by grants
from the Japan Health Sciences Foundation.
6. References
[1] J. S. Aranow and M. P. Fink, “Determinant of Intestinal
Barrier Failure in Critical Illness,” British Journal of An-

Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
178
esthesia, Vol. 77, 1996, pp. 71-81.
[2] D. W. Riddington, B. Venkatesh, C. M. Boivin, et al.,
“Intestinal Permeability, Gastric Intramucosal pH, and
Systemic Endotoxemia in Patients Undergoing Cardio-
pulmonaly Bypass,” The Journal of the American Medi-
cal Association, Vol. 275, 1996, pp. 1007-1012.
doi:10.1001/jama.275.13.1007
[3] P. L. Faries, R. J. Simon, A. T. Martella, et al., “Intestinal
Permeability Correlates with Severity of Injury in Trauma
Patients,” The Journal of Trauma, Vol. 44, No. 6, 1998,
pp. 1031-1036. doi:10.1097/00005373-199806000-00016
[4] H. M. Oudemans van Straaten, P. G. Jansen, F. J. Hoek,
et al., “Intestinal Permeability, Circulating Endotoxin,
and Postoperative Systemic Responses in Cardiac Sur-
gery Patients,” Journal of Cardiothoracic and Vascular
Anesthesia, Vol. 10, 1996, pp. 187-194.
doi:10.1097/00005373-199806000-00016
[5] R. Schleiffer and F. Raul, “Prophylactic Administration
of L-Arginine Improves the Intestinal Barrier Function
after Mesenteric Ischemia,” Gut, Vol. 39, No. 2, 1996, pp.
194-198. doi:10.1097/00005373-199806000-00016
[6] A. L. Salzman, P. S. Wollert, H. Wang, et al., “Intralu-
minal Oxygenation Ameliorates Ischemia/Reperfusion-in-
Duced Gut Mucosal Hyperpermeability in Pigs,” Cir-
culatory Shock, Vol. 40, No. 1, 1993, pp. 37-46.
[7] A. L. Salzman, H. Wang, P. S. Wollert, et al., “En-
dotoxin-Induced Ileal Mucosal Hyperpermeability in Pigs:
Role of Tissue Acidosis,” American Journal of Physiol-
ogy, Vol. 266, No. 4, 1994, pp. G633-G646.
[8] J. L. Madara, “Loosening Tight Junctions: Lessons from
the Intestine,” The Journal of Clinical Investgation, Vol.
83, No. 4, 1989, pp. 1089-1094. doi:10.1172/JCI113987
[9] T. Sawada, T. Ogawa, M. Tomita, et al., “Role of Para-
cellular Pathway in Nonelectrolyte Permeation across Rat
Colon Epithelium Enhanced by Sodium Caprate and
Sosium Caprylate,” Pharmaceutical Research, Vol. 8, No.
11, 1991, pp. 1365-1371. doi:10.1023/A:1015840921203
[10] M. Tomita, Y. Hotta, R. Ohkubo and S. Awazu, “Polar-
ized Transport Wa Observed not in Hydrophilic Com-
pounds but in Dextran in Caco-2 cell Monolayers,” Bio-
logical & Pharmaceutical Bulletin, Vol. 22, 1999, pp.
330-331.
[11] M. Tomita, M. J. Menconi, R. L. Delude and M. P. Fink.,
“Polarized Transport of Hydrophilic Compounds across
Rat Colonic Mucosa from Serosa to Mucosa is Tempera-
ture Dependent,” Gastroenterology, Vol. 118, No. 3,
2000, pp. 535-543.
doi:10.1016/S0016-5085(00)70259-9
[12] A. Iida, M. Tomita, Y. Matsuura, et al., “Improvement of
Intestinal Absorption of P-Glycoprotein Substrate by
D-Tartaric Acid,” Drug Metabolism and Pharmacokinet-
ics, Vol. 21, No. 5, 2006, pp. 424-428.
doi:10.2133/dmpk.21.424
[13] J. T. Doluisio, N. F. Billups, E. T. Sugita, et al., “Drug
Absorption I: An in Situ Rat Gut Technique Yielding Re-
alistic Absorption Rates,” Journal of Pharmaceutical
Sciences, Vol. 58, No. 10, 1969, pp. 1196-1202.
doi:10.1002/jps.2600581006
[14] M. Tomita, R. Ohkubo and M. Hayashi, “Lipopolysac-
charide Transport System across Colonic Epithelial Cells
in Normal and Infective Rat,” Drug Metabolism and
Pharmacokinetics, Vol. 19, No. 1, 2004, pp. 33-40.
doi:10.2133/dmpk.19.33
[15] K. Sandvig and B. van Deurs, “Selective Modification of
the Endocytic Uptake of Eicin and Fluid Phase Markers
without Alteration in Transferring Endocytosis,” The
Journal of Biological Chemistry, Vol. 265, 1990, pp.
6382-6388.
[16] S. Wu-Pong, T. L. Weiss and C. A. Hunt, “Antisense C-
myc Oligodeoxynucleotide Cellular Uptake,” Pharma-
ceutical Research, Vol. 9, No. 8, 1992, pp. 1010-1017.
doi:10.1023/A:1015846209681
[17] S. K. Rodal, G. Skretting, O. Garred, et al., “Extraction of
Cholesterol with Methyl-β-Cyclodextrin Perturbs Forma-
tion of Clathrin-Coated Endocytic Vesicles,” Molecular
Biology of the Cell, Vol. 10, No. 4, 1999, pp. 961-974.
[18] D. J. Falcone, “Heparin Stimulation of Plasminogen Acti-
vator Secretion by Macrophage-Like Cell Line RAW264.7:
Role of the Scavenger Receptor,” Journal of Cellular
Physiology, Vol. 140, No. 2, 1989, pp. 219-226.
doi:10.1023/A:1015846209681
[19] L. Rohrer, M. Freeman, T. Kodama, et al., “Coiled Coli
fibrous Domains Mediated Ligand Binding by Macro-
phage Scavenger Receptor Type II,” Nature, Vol. 343,
1990, pp. 570-572. doi:10.1038/343570a0
[20] B. L. Leu and J. D. Huang, “Inhibition of Intestinal P-
Glycoprotein and Effect on Etoposide Absorption,” Can-
cer Chemotherapy and Pharmacology, Vol. 35, No. 5,
1995, pp. 432-436. doi:10.1007/s002800050258
[21] G. Rappa, A. Lorico, R. A. Flavell, et al., “Evidence that
the Multidrug Resistance Protein (MRP) Function as a
Co-transporter of Glutathione and Natural Product Tox-
ins,” Cancer Research, Vol. 57, No. 23, 1997, pp. 5232-
5237.
[22] I. Tamai, A. Saheki, R. Saitoh, et al., “Nonlinear Intesti-
nal Absorption of 5-Hydroxytrip-Tamine Receptor An-
tagonist Caused by Absorptive and Secterory Transport-
ers,” The Journal of Pharmacology and Experimental
Therapeutics, Vol. 283, No. 1, 1997, pp. 108-115.
[23] L. Z. Benet, C. Y. Wu, M. F. Hebert, et al., “Intestinal
Drug Metabolism and Antiport Processes: A Potential
Paradigm I Oral Drug Delivery,” Journal of Controlled
Release, Vol. 39, 1996, pp. 139-143.
doi:10.1016/0168-3659(95)00147-6
[24] M. Tomita, M. Miwa, S. Ohuchi, et al., “Nonlinear Intes-
tinal Absorption of (1→3) β-D-Glucan Caused by Ab-
sorptive and Secretory Transporting System,” Biological
& Pharmaceutical Bulletin, Vol. 32, No. 7, 2009, pp.
1295-1297. doi:10.1248/bpb.32.1295
[25] M. Tomita, M. J. Menconi, R. L. Dekude, et al., “Polar-
ized Transport of Hydrophilic Compounds across Rat
Colonic Mucosa from Serosa to Mucosa is Temperature
C opyright © 2011 SciRes. PP

Nonlinear Intestinal Absorption of Fluorescein Isothiocyanate Dextran 4000 Caused by Absorptive and Secretory
Transporting System
179
Dependent,” Gastroenterology, Vol. 118, No. 3, 2000, pp.
535-543. doi:10.1016/S0016-5085(00)70259-9
[26] M. S. Goligorsky and K. A. Hruska, “Transcytosis in
Cultured Proximal Tubular Cells,” Journal of Membrane
Biology, Vol. 93, No. 3, 1986, pp. 237-247.
doi:10.1007/BF01871178
[27] N. Pantzar, S. Lundin and B. R. Westrom, “Bidirectional
Small-Intestinal Permeability in the Rat to Some Com-
mon Marker Molecules in Vitro,” Scandinavian Journal
of Gastroenterology, Vol. 29, 1994, pp. 703-709.
doi:10.3109/00365529409092497