scholarly journals A carrier-mediated transport for folate in basolateral membrane vesicles of rat small intestine

1987 ◽  
Vol 247 (1) ◽  
pp. 141-146 ◽  
Author(s):  
H M Said ◽  
R Redha
Keyword(s):  
Folic Acid ◽  
Anion Exchange ◽  
Membrane Surface ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Basolateral Membrane Vesicles ◽  
Exchange Inhibitor ◽  
Carrier Mediated Transport ◽  
Structural Analogues ◽  
Disulphonic Acid

The mechanism of exit of folate from the enterocyte, i.e. transport across the basolateral membrane, is not known. In this study we examined, using basolateral membrane vesicles, the transport of folic acid across the basolateral membrane of rat intestine. Uptake of folic acid by these vesicles represents transport of the substrate into the intravesicular compartment and not binding to the membrane surface. The rate of folic acid transport was linear for the first 1 min of incubation but decreased thereafter, reaching equilibrium after 5 min of incubation. The transport of folic acid was: (1) saturable as a function of concentration with an apparent Km of 0.6 +/- 0.17 microM and Vmax. of 1.01 +/- 0.11 pmol/30 s per mg of protein; (2) inhibited in a competitive manner by the structural analogues 5-methyltetrahydrofolate and methotrexate (Ki = 2 and 1.4 microM, respectively); (4) electroneutral; (5) Na+-independent; (6) sensitive to the effect of the anion exchange inhibitor 4,4′-di-isothiocyanatostilbene-2,2′-disulphonic acid (DIDS). These data indicate the existence of a carrier-mediated transport system for folic acid in rat intestinal basolateral membrane and demonstrate that the transport process is electroneutral, Na+-independent and sensitive to the effect of anion exchange inhibition.

scholarly journals Mechanism of n-butyrate uptake in the human proximal colonic basolateral membranes

2002 ◽  
Vol 282 (4) ◽  
pp. G676-G682 ◽  
Author(s):  
S. Tyagi ◽  
J. Venugopalakrishnan ◽  
K. Ramaswamy ◽  
P. K. Dudeja
Keyword(s):  
Fatty Acid ◽  
Anion Exchange ◽  
Short Chain Fatty Acid ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Organ Donor ◽  
Chain Fatty Acid ◽  
Ph Gradient ◽  
Basolateral Membrane Vesicles ◽  
Exchange Inhibitor

Current studies were undertaken to characterize the mechanism of short-chain fatty acid (SCFA) transport in isolated human proximal colonic basolateral membrane vesicles (BLMV) utilizing a rapid-filtration n-[14C]butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO[Formula: see text]/SCFA exchanger in these membranes, are summarized as follows: 1) n-[14C]butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO[Formula: see text] and an inwardly directed pH gradient; 2) n-[14C]butyrate uptake was markedly inhibited (∼40%) by anion exchange inhibitor niflumic acid (1 mM), but SITS and DIDS (5 mM) had no effect; 3) structural analogs e.g., acetate and propionate, significantly inhibited uptake of HCO[Formula: see text] and pH-gradient-driven n-[14C]butyrate; 4) n-[14C]butyrate uptake was saturable with a Kmfor butyrate of 17.5 ± 4.5 mM and a Vmaxof 20.9 ± 1.2 nmol · mg protein−1· 5 s−1; 5) n-[14C]butyrate influx into the vesicles demonstrated a transstimulation phenomenon; and 6) intravesicular or extravesicular Cl−did not alter the anion-stimulated n-[14C]butyrate uptake. Our results indicate the presence of a carrier-mediated HCO[Formula: see text]/SCFA exchanger on the human colonic basolateral membrane, which appears to be distinct from the previously described anion exchangers in the membranes of colonic epithelia.

Transport of tetraethylammonium by rabbit renal brush-border and basolateral membrane vesicles

1987 ◽  
Vol 253 (5) ◽  
pp. F1040-F1050 ◽  
Author(s):  
S. H. Wright ◽  
T. M. Wunz
Keyword(s):  
Brush Border ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Electrical Potential Difference ◽  
Basolateral Membrane Vesicles ◽  
Equilibrium Conditions ◽  
Electrically Conductive ◽  
Conductive Pathway ◽  
Carrier Mediated Transport

Brush-border and basolateral membrane vesicles (BBMV and BLMV, respectively) from rabbit renal cortex were used to study transport of the organic cation, tetraethylammonium (TEA). Outwardly directed proton gradients stimulated uptake of TEA into BBMV and supported concentrative accumulation. Furthermore, an inwardly directed H+ gradient accelerated TEA efflux from BBMV. These data suggest that TEA transport in BBMV involved exchange with H+. The Jmax and Kt for TEA transport into BBMV under pH equilibrium conditions (pH 7.5) were 2.1 nmol.mg-1.min-1 and 0.15 mM, respectively. Under pH gradient conditions (6.0in:7.5out), Jmax increased by 270% with no effect on Kt. Uptake of TEA into BBMV was stimulated by an inside-positive electrical potential difference (PD), although exchange of TEA for H+ appeared to be one for one. In BLMV, H+ gradients had little effect on TEA uptake and were incapable of supporting concentrative transport. The Jmax and Kt for TEA transport in BLMV were 0.33 nmol.mg-1.min-1 and 0.37 mM, respectively. Inside-negative PDs stimulated this uptake, suggesting that it involved an electrically conductive pathway. TEA transport in BBMV and BLMV was inhibited by amiloride and cimetidine, although p-aminohippuric acid was without effect. Thus, secretion of TEA involves carrier-mediated transport steps at both the luminal and peritubular membranes, although an active step is not evident in isolated BLMV.

Evidence for carrier-mediated Cl-SO4 exchange in rabbit ileal basolateral membrane vesicles

1987 ◽  
Vol 253 (3) ◽  
pp. G404-G410 ◽  
Author(s):  
C. M. Schron ◽  
R. G. Knickelbein ◽  
P. S. Aronson ◽  
J. W. Dobbins
Keyword(s):  
Anion Exchange ◽  
Brush Border ◽  
Initial Velocity ◽  
Brush Border Membrane ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Disulfonic Acid ◽  
Basolateral Membrane Vesicles ◽  
Beta Hydroxybutyrate

In rabbit ileal basolateral membrane (BLM) vesicles, an outwardly directed Cl gradient ([Cl] in/out = 60/6 mM) stimulated the initial velocity of SO4 uptake compared with uptake in the absence of Cl. Under Cl gradient conditions, SO4 was transiently accumulated at a concentration twice that found at equilibrium ("overshoot"). Chloride gradient-stimulated SO4 uptake was markedly reduced by inhibitors of anion exchange (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid) and was saturable (SO4 Km = 0.302 +/- 0.064 mM; Vmax = 1.59 +/- 0.22 nmol SO4 . mg protein-1 . min-1). SO4 uptake by BLM vesicles was not stimulated by imposition of an inside-positive electrical potential, suggesting that the stimulation by a Cl gradient was not due to an induced electrical potential. Oxalate, nitrate, iodide, and bromide inhibited the initial velocity of Cl gradient-stimulated SO4 uptake, whereas phosphate, beta-hydroxybutyrate, lactate, and p-aminohippurate had no effect. When SO4 uptake by BLM vesicles was compared with that of brush-border membrane vesicles, Cl gradient-stimulated SO4 uptake was found predominantly in the BLM preparation. In conclusion, these findings provide evidence for a carrier on the ileal basolateral membrane that mediates Cl-SO4 exchange.

Characterization of Cl-HCO3 exchange in basolateral membrane of rat distal colon

2003 ◽  
Vol 285 (4) ◽  
pp. C912-C921 ◽  
Author(s):  
Mutsuhiro Ikuma ◽  
John Geibel ◽  
Henry J. Binder ◽  
Vazhaikkurichi M. Rajendran
Keyword(s):  
Anion Exchange ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Distal Colon ◽  
Basolateral Membranes ◽  
Exchange Inhibitor ◽  
Rat Distal Colon ◽  
Different Types ◽  
Voltage Clamping

Sodium-independent Cl movement (i.e., Cl-anion exchange) has not previously been identified in the basolateral membranes of rat colonic epithelial cells. The present study demonstrates Cl-HCO3 exchange as the mechanism for 36Cl uptake in basolateral membrane vesicles (BLMV) prepared in the presence of a protease inhibitor cocktail from rat distal colon. Studies of 36Cl uptake performed with BLMV prepared with different types of protease inhibitors indicate that preventing the cleavage of the COOH-terminal end of AE2 protein by serine-type proteases was responsible for the demonstration of Cl-HCO3 exchange. In the absence of voltage clamping, both outward OH gradient (pHout/pHin: 7.5/5.5) and outward HCO3 gradient stimulated transient 36Cl uptake accumulation. However, voltage clamping with K-ionophore, valinomycin, almost completely (87%) inhibited the OH gradient-driven 36Cl uptake, whereas HCO3 gradient-driven 36Cl uptake was only partially inhibited (38%). Both electroneutral HCO3 and OH gradient-driven 36Cl uptake were 1) completely inhibited by DIDS, an anion exchange inhibitor, with a half-maximal inhibitory constant ( Ki) of ∼26.9 and 30.6 μM, respectively, 2) not inhibited by 5-nitro-2-(3-phenylpropylamino)benzoic acid(NPPB), a Cl channel blocker, 3) saturated by increasing extravesicular Cl concentration with a Km for Cl of ∼12.6 and 14.2 mM, respectively, and 4) present in both surface and crypt cells. Intracellular pH (pHi) was also determined with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-acetomethylester (BCECF-AM) in an isolated superfused crypt preparation. Removal of Cl resulted in a DIDS-inhibitable increase in pHi both in HCO3-buffered and in the nominally HCO3-free buffered solutions (0.28 ± 0.02 and 0.11 ± 0.02 pH units, respectively). We conclude that a carrier-mediated electroneutral Cl-HCO3 exchange is present in basolateral membranes and that, in the absence of HCO3, Cl-HCO3 exchange can function as a Cl-OH exchange and regulate pHi across basolateral membranes of rat distal colon.

Depression of calcium pump activity in renal cortex of vitamin D-deficient rats with secondary hyperparathyroidism

1990 ◽  
Vol 123 (4) ◽  
pp. 438-444 ◽  
Author(s):  
Yusuke Tsukamoto ◽  
Teiichi Tamura ◽  
Michiyo Saitoh ◽  
Yumiko Takita ◽  
Toshiaki Nakano
Keyword(s):  
Vitamin D ◽  
Secondary Hyperparathyroidism ◽  
Hormonal Regulation ◽  
Serum Calcium Level ◽  
Renal Cortex ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Calcium Pump ◽  
Basolateral Membrane Vesicles ◽  
Pump Activity

Abstract. To examine the hormonal regulation of the ATP-dependent Ca2+ pump in the kidneys, the ATP-dependent Ca2+ uptake by the basolateral membrane vesicles in the renal cortex was measured using radioactive calcium (45Ca2+) in rats with vitamin D deficiency or rats undergoing thyroparathyroidectomy. The Vmax of the Ca2+ pump activity was increased not only by administering calcitriol, but also by normalizing the serum calcium level in vitamin D-deficient rats. PTH suppressed the Ca2+ pump activity in normocalcemic vitamin D-deficient rats. Thyroparathyroidectomy did not affect the Ca2+ pump activity in the kidneys of normal rats. It was concluded that the ATP-dependent Ca2+ pump activity was depressed by secondary hyperparathyroidism in vitamin D-deficient rats.

scholarly journals Characterization of sodium-dependent and sodium-independent nucleoside transport systems in rabbit brush-border and basolateral plasma-membrane vesicles from the renal outer cortex

1989 ◽  
Vol 264 (1) ◽  
pp. 223-231 ◽  
Author(s):  
T C Williams ◽  
A J Doherty ◽  
D A Griffith ◽  
S M Jarvis
Keyword(s):  
Brush Border ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Facilitated Diffusion ◽  
Basolateral Membrane Vesicles ◽  
Plasma Membrane Vesicles ◽  
Outer Cortex ◽  
Overshoot Phenomenon

The transport of uridine into rabbit renal outer-cortical brush-border and basolateral membrane vesicles was compared at 22 degrees C. Uridine was taken up into an osmotically active space in the absence of metabolism for both types of membrane vesicles. Uridine influx by brush-border membrane vesicles was stimulated by Na+, and in the presence of inwardly directed gradients of Na+ a transient overshoot phenomenon was observed, indicating active transport. Kinetic analysis of the saturable Na+-dependent component of uridine flux indicated that it was consistent with Michaelis-Menten kinetics (Km 12 +/- 3 microM, Vmax. 3.9 +/- 0.9 pmol/s per mg of protein). The sodium:uridine coupling stoichiometry was found to be consistent with 1:1 and involved the net transfer of positive charge. In contrast, uridine influx by basolateral membrane vesicles was not dependent on the cation present and was inhibited by nitrobenzylthioinosine (NBMPR). NBMPR-sensitive uridine transport was saturable (Km 137 +/- 20 microM, Vmax. 5.2 +/- 0.6 pmol/s per mg of protein). Inhibition of uridine flux by NBMPR was associated with high-affinity binding of NBMPR to the basolateral membrane (Kd 0.74 +/- 0.46 nM). Binding of NBMPR to these sites was competitively blocked by adenosine and uridine. These results indicate that uridine crosses the brush-border surface of rabbit proximal renal tubule cells by Na+-dependent pathways, but permeates the basolateral surface by NBMPR-sensitive facilitated-diffusion carriers.

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