共查询到20条相似文献,搜索用时 31 毫秒
1.
The uptake of glycine in rabbit renal brush border membrane vesicles was shown to consist of glycine transport into an intravesicular space. An Na+ electrochemical gradient (extravesicular>intravesicular) stimulated the initial rate of glycine uptake and effected a transient accumulation of intravesicular glycine above the steady-state value. This stimulation could not be induced by the imposition of a K+, Li+ or choline+ gradient and was enhanced as extravesicular Na+ was increased from 10 mM to 100 mM. Dissipation of the Na+ gradient by the ionophore gramicidin D resulted in diminished Na+-stimulated glycine uptake. Na+-stimulated uptake of glycine was electrogenic. Substrate-velocity analysis of Na+-dependent glycine uptake over the range of amino acid concentrations from 25 μM to 10 mM demonstrated a single saturable transport system with apparent Km = 996 μM and Vmax = 348 pmol glycine/mg protein per min. Inhibition observed when the Na+-dependent uptake of 25 μM glycine was inhibited by 5 mM extravesicular test amino acid segregated dibasic amino acids, which did not inhibit glycine uptake, from all other amino acid groups. The amino acids d-alanine, d-glutamic acid, and d-proline inhibited similarly to their l counterparts. Accelerative exchange of extravesicular [3H]glycine was demonstrated when brush border vesicles were preloaded with glycine, but not when they were preloaded with l-alanine, l-glutamic acid, or with l-proline. It is concluded that a single transport system exists at the level of the rabbit renal brush border membrane that functions to reabsorb glycine independently from other groups of amino acids. 相似文献
2.
Marc R. Hammerman 《生物化学与生物物理学报:生物膜》1982,685(1):71-77
Na+-independent l-arginine uptake was studied in rabbit renal brush border membrane vesicles. The finding that steady-state uptake of l-arginine decreased with increasing extravesicular osmolality and the demonstration of accelerative exchange diffusion after preincubation of vesicles with l-arginine, but not d-arginine, indicated that the uptake of l-arginine in brush border vesicles was reflective of carrier-mediated transport into an intravesicular space. Accelerative exchange diffusion of l-arginine was demonstrated in vesicles preincubated with l-lysine and l-ornithine, but not l-alanine or l-proline, suggesting the presence of a dibasic amino acid transporter in the renal brush border membrane. Partial saturation of initial rates of l-arginine transport was found with extravesicular [arginine] varied from 0.005 to 1.0 mM. l-Arginine uptake was inhibited by extravesicular dibasic amino acids unlike the Na+-independent uptake of l-alanine, l-glutamate, glycine or l-proline in the presence of extravesicular amino acids of similar structure. l-Arginine uptake was increased by the imposition of an H+ gradient (intravesicular pH<extravesicular pH) and H+ gradient stimulated uptake was further increased by FCCP. These findings demonstrate membrane-potential-sensitive, Na+-independent transport of l-arginine in brush border membrane vesicles which differs from Na+-independent uptake of neutral and acidic amino acids. Na+-independent dibasic amino acid transport in membrane vesicles is likely reflective of Na+-independent transport of dibasic amino acids across the renal brush border membrane. 相似文献
3.
Andrew M. Weigensberg Rose M. Johnstone Rhoda Blostein 《Journal of bioenergetics and biomembranes》1982,14(5-6):335-345
Inside-out membrane vesicles have been prepared from sheep reticulocytes. With these vesicles, Na+-dependent glycine uptake and net accumulation have been demonstrated to occur in reverse, i.e., from extravesicular (normal cytoplasmic) to intravesicular (normal extravesicular) surface. Uptake and accumulation are inhibited by energization of the sodium pump by ATP whereby the Na+ electrochemical gradient is dissipated. Glycine-dependent Na+ uptake was also observed, providing evidence that Na+-dependent glycine influx into these vesicles, equivalent to normal efflux, is characterized by Na+-glycine co-transport. 相似文献
4.
The uphill uptake of l-arginine by renal brush border membrane vesicles was found to be energized by a Na+ gradient (extravesicular > intravesicular) in the presence of a membrane potential (inside negative). The uptake was specific for Na+. Either a K+-diffusion potential, generated by valinomycin, or a H+-diffusion potential, generated by the mitochondrial uncoupler, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, provided the electrical driving force. The Na+ gradient-dependent l-arginine transport system was shared by specific basic amino acids and l-cystine, but not by d-arginine nor other classes of amino acids. The molecular structure of the basic amino acid recognized by the carrier was postulated. 相似文献
5.
Abstract: The inhibitory effects of Na+/Ca2+ exchange inhibitory peptide (XIP), which corresponds to residues 219–238 of the Na+/Ca2+ exchange protein from canine heart, were studied in both rat and human brain plasma membrane vesicles. XIP had very high potency with respect to the inhibition of the initial velocity of intravesicular Na+-dependent Ca2+ uptake in both rat brain [IC50 = 3.05 ± 0.69 µM (mean ± SE)] and human brain (IC50 = 3.58 ± 0.58 µM). The maximal inhibition seen in rat brain vesicles was ~80%, whereas human brain vesicles were inhibited 100%. XIP also inhibited extravesicular Na+-dependent Ca2+ release, and the inhibitory effect was enhanced by increasing the extravesicular Na+ concentration. In contrast, the inhibitory effect of bepridil was competitive with respect to extravesicular Na+. When XIP was added at steady state (5 min after the initiation of intravesicular Na+-dependent Ca2+ uptake), it was found that the intravesicular Ca2+ content declined with time. Analysis of unidirectional fluxes for Ca2+ at steady state showed that 50 µM XIP inhibited Ca2+ influx and efflux ~85 and 70%, respectively. This result suggested that XIP inhibited both Na+/Ca2+ exchange and Ca2+/Ca2+ exchange but had no effect on the passive release pathway for Ca2+. The results suggest structural homology among cardiac, rat, and human brain exchangers in the XIP binding domain and that the binding of Na+ or other monovalent cations, e.g., K+, is required for XIP to have its inhibitory effect on Ca2+ transport. 相似文献
6.
Summary Glucose transport was studied in marine mussels of the genusMytilus. Initial observations, with intact animals and isolated gills, indicated that net uptake of glucose occurred in mussels by a carrier-mediated, Na+-sensitive process. Subsequent studies included use of brush-border membrane vesicles (BBMV) in order to characterize this transport in greater detail. The highest activity of Na+-dependent glucose transport was found in the brush-border membrane fractions used in this study, while basal-lateral membrane fractions contained the highest specific binding of ouabain. Glucose uptake into BBMV showed specificity for Na+, and concentrative glucose transport was observed in the presence of an inwardly directed Na+ gradient. There was a single saturable pathway for glucose uptake, with an apparentK
t of 3 m in BBMV and 9 m in intact gills. The kinetics of Na+ activation of glucose uptake were sigmoidal, with apparent Hill coefficients of 1.5 in BBMV and 1.2 in isolated gills, indicating that more than one Na+ may be involved in the transport of each glucose. Harmaline inhibited glucose transport in mussel BBMV with aK
i of 44 m. The uptake of glucose was electrogenic and stimulated by an inside-negative membrane potential. The substrate specificity in intact gills and BBMV resembled that of Na+-glucose cotransporters in other systems;d-glucose and -methyl glucopyranoside were the most effective inhibitors of Na+-glucose transport,d-galactose was intermediate in its inhibition, and there was little or no effect ofl-glucose,d-fructose, 2-deoxy-glucose, or 3-O-methyl glucose. Phlorizin was an effective inhibitor of Na+-glucose uptake, with an apparentK
i of 154nm in BBMV and 21nm in intact gills. While the qualitative characteristics of glucose transport in the mussel gill were similar to those in other epithelia, the quantitative characteristics of this process reflect adaptation to the seawater environment of this animal. 相似文献
7.
Vazhaikkurichi M. Rajendran Alfred Berteloot Yoshinori Ishikawa Abdul H. Khan Krishnamurthy Ramaswamy 《生物化学与生物物理学报:生物膜》1984,778(3):443-448
The characteristics of carnosine (β-alanyl-l-histidine) transport have been studied using purified brush-border membrane vesicles from mouse small intestine. Uptake curves did not exhibit any overshoot phenomena, and were similar under Na+, K+ or choline+ gradient conditions (extravesicular > intravesicular). However, uptake of histidine showed an overshoot phenomenon in the presence of a Na+-gradient. There was no detectable hydrolysis of carnosine during 15 min of incubation with membrane vesicles under conditions used for transport experiments. Analysis of intravesicular contents further showed the complete absence of the constituent free amino acids of carnosine, and indicates that intact carnosine is transported. Studies on the effect of concentration on peptide uptake revealed that transport occurred by a saturable process conforming to Michaelis-Menten kinetics with a Km of 9.6 ± 1.4 mM and a Vmax of 2.9 ± 0.2 nmol / mg protein per 0.4 min. Uptake of carnosine was inhibited by both di- and tripeptides with a maximum inhibition of 68% by glycyl-l-leucyltyrosine. These results clearly demonstrate that carnosine is transported intact by a carrier-mediated, Na+-independent process. 相似文献
8.
The Na+-dependent transport of 5-oxoproline into rabbit renal brush-border vesicles was stimulated by a K+ diffusion potential (interior-negative) induced by valinomycin. Na+ salts of two anions of different epithelial permeabilities also affected 5-oxoproline transport. These results show that the Na+-dependent 5-oxoproline transport in renal brush-border vesicles is an electrogenic process which results in a net transfer of positive charge. Maximum transport of 5-oxoproline occurred at an extravesicular pH of 6.0 to 8.0 and over that pH range, 5-oxoproline exists completely as an anion with a negative charge. The simplest stoichiometry consistent with this process is, therefore, the cotransport of one 5-oxoproline anion with two sodium ions. The presence of K+ inside the vesicles stimulated the Na+-dependent transport of 5-oxoproline. This stimulatory effect was specific for K+ and required the presence of Na+. The presence of Na+ gradient was not mandatory for the K+ action. The stimulation by the intravesicular K+ was seen in the presence as well as in the absence of a K+ gradient. Therefore, the increased influx of 5-oxoproline was not coupled to the simultaneous efflux of K+. The presence of K+ in the extravesicular medium alone did not affect the Na+-dependent transport of 5-oxoproline, showing that the site of K+ action was intravesicular. Glutamate did not interact with the Na+-dependent 5-oxoproline transport even in the presence of an outward K+ gradient. 相似文献
9.
Carolee K. Hunter L.Lockie Treanor J.Patrick Gray Susan A. Halter Anastacio Hoyumpa Frederick A. Wilson 《生物化学与生物物理学报:生物膜》1983,732(1):256-265
Ethanol, at concentrations found in the intestinal lumen after moderate drinking, has been shown to inhibit carrier-mediated intestinal transport processes. This inhibition could occur by direct interaction with membrane transporters, dissipation of the energy producing Na+ electrochemical gradient and/or nonspecific alteration of membrane integrity. The latter alteration may be reflected by changes in membrane fluidity, chemical composition or vesicular size. These possibilities were examined with studies in purified brush border membrane vesicles of rat intestine. Ethanol inhibited concentrative Na+-dependent d-glucose uptake in a dose-dependent manner. In contrast, ethanol did not inhibit concentrative d-glucose uptake under conditions of d-glucose trans-stimulation in the absence of a Na+ electrochemical gradient. Ethanol also inhibited initial, concentrative Na+-dependent taurocholic acid uptake, as well as equilibrium uptake. That ethanol exerted a dual effect on transport by increasing membrane conductance for Na+ while decreasing intravesicular space was supported by direct studies of Na+ uptake. Morphometric analysis confirmed that ethanol-treated membranes had a decreased intravesicular size when compared to untreated membranes. Finally, membrane fluidity measured by EPR showed that ethanol had a significant fluidizing effect without producing qualitative changes in membrane proteins, as determined by SDS gel electrophoresis. These results suggest that ethanol inhibits carrier-mediated transport by dissipation of the Na+ electrochemical gradient and alteration of membrane integrity rather than by direct interaction with membrane transporters. 相似文献
10.
Amiloride and harmaline were tested as inhibitors of proton movements in brush-border membrane vesicles from rat kidney cortex. Transmembrane pH differences were visualized using acridine orange. Fluorescence quenching due to Na+ gradient-driven intravesicular acidification was inhibited by amiloride and harmaline. However, a similar inhibition was observed for the Na+ gradient-driven electrogenic proton movements in the presence of gramicidin. Moreover, amiloride and harmaline decreased the fluorescence signal of electrogenic proton movements driven by a K+ gradient in the presence of valinomycin. The degree of inhibition of intravesicular acidification by both drugs was concentration dependent. Half-maximal inhibition (I50) of Na+/H+ exchange and K+ gradient-driven proton movements occurred at 0.21 and 0.6 amiloride, respectively. The I50 for harmaline was 0.21 mM in both cases. Amiloride also decreased the initial quenching of acridine orange fluorescence due to a preset pH gradient without affecting the rate of dissipation of the pH gradient. This effect was independent of the buffer capacity. In contrast, harmaline seemed to dissipate pH gradient in the same way as a permeant buffer. Amiloride and harmaline led to a concentration-dependent fluorescence decrease even in aqueous solution. The results suggest an interaction of amiloride and harmaline with acridine orange which overlaps a possible specific inhibition of Na+/H+ exchange by these drugs. 相似文献
11.
The present study aimed to clarify the existence of a Na+/Ca2+ antiport device in kidney tubular epithelial cells discussed in the literature to represent the predominant mechanistic device for Ca2+ reabsorption in the kidney. (1) Inside-out oriented plasma membrane vesicles from tubular epithelial cells of guinea-pig kidney showed an ATP-driven Ca2+ transport machinery similar to that known to reside in the plasma membrane of numerous cell types. It was not affected by digitalis compounds which otherwise are well-documented inhibitors of Ca2+ reabsorption. (2) The vesicle preparation contained high, digitalis-sensitive (Na++K+-ATPase activities indicating its origin from the basolateral portion of plasma membrane. (3) The operation of Na+/Ca2+ antiport device was excluded by the findings that steep Ca2+ gradients formed by ATP-dependent Ca2+ accumulation in the vesicles were not discharged by extravesicular Na+, and did not drive 45Ca2+ uptake into the vesicles via a Ca2+-45Ca2+ exchange. (4) The ATP-dependent Ca2+ uptake into the vesicles became increasingly depressed with time by extravesicular Na+. This was not due to an impairment of the Ca2+ pump itself, but caused by Na+/Ca2+ competition for binding sites on the intravesicular membrane surface shown to be important for high Ca2+ accumulation in the vesicles. (5) Earlier observations on Na+-induced release of Ca2+ from vesicles pre-equilibrated with Ca2+, seemingly favoring the existence of a Na+/Ca2+ antiporter in the basolateral plasma membrane, were likewise explained by the occurrence of Na+/Ca2+ competition for binding sites. The weight of our findings disfavors the transcellular pathway of Ca2+ reabsorption through tubule epithelium essentially depending on the operation of a Na+/Ca2+ antiport device. 相似文献
12.
The findings that the equilibrium uptake of β-alanine decreased with increasing medium osmolarity and preincubation with β-alanine increased uptake of the amino acid indicate that the uptake of β-alanine by rabbit renal brush border membranes represents transport into membrane vesicles. A Na+ electrochemical gradient (extravesicular > intravesicular) stimulated the initial rate of β-alanine uptake about three times and effected a transient accumulation of the amino acid twice the equilibrium value. Stimulation of the uptake was specific for Na+. Gramicidin abolished the overshoot, presumably by dissipating the gradient by accelerating the electrogenic entrance of Na+ into the vesicle via a pathway not coupled to uptake of β-alanine. In K+-loaded vesicle, valinomycin enhanced the Na+ gradient-dependent uptake of β-alanine. These findings indicate that the Na+ gradient-dependent transport of β-alanine is an electrogenic process and suggest that the membrane potential is a determinant of β-analine transport. Uptake of β-aniline, at a given concentration, reflected the sum of contributions from Na+ gradient-dependent and -independent transport systems. The dependent system saturated at 100 μM. The independent system did not saturate. At physiological concentrations the rate of the Na+ gradient-dependent uptake was four times that in the absence of the gradient. The Na+ gradient-dependent rate of β-alanine uptake was strongly inhibited by taurine, suggesting that β-amino acids have a common transport system, α-Amino acids, i.e. l-arginine, l-glutamate, l-proline, and glycine, representing previously reported specific α-amino acid transport systems in the brush border membrane, did not inhibit the uptake of β-alanine. These findings indicate that the brush border membrane has a distinct transport system for β-amino acids. 相似文献
13.
The Na+/Mg2+ exchanger represents the main Mg2+ extrusion mechanism operating in mammalian cells including hepatocytes. We have previously reported that this exchanger, located in the basolateral domain of the hepatocyte, promotes the extrusion of intravesicular trapped Mg2+ for extravesicular Na+ with ratio 1. This electrogenic exchange is supported by the accumulation of tetraphenyl-phosphonium within the vesicles at the time when Mg2+ efflux occurs. In this present study, the role of extra- and intra-vesicular Cl? on the Na+/Mg2+ exchange ratio was investigated. The results reported here suggest that Cl? ions are not required for the Na+ to Mg2+ exchange to occur, but the stoichiometry ratio of the exchanger switches from electrogenic (1Na in + :1 Mg out 2+ ) in the presence of intravesicular Cl? to electroneutral (2Na in + :1 Mg out 2+ ) in their absence. In basolateral liver plasma membrane vesicles loaded with MgCl2 labeled with 36Cl?, a small but significant Cl? efflux (~30 nmol Cl?/mg protein/1 min) is observed following addition of NaCl or Na-isethionate to the extravesicular medium. Both Cl? and Mg2+ effluxes are inhibited by imipramine but not by amiloride, DIDS, niflumic acid, bumetanide, or furosemide. In vesicles loaded with Mg-gluconate and stimulated by Na-isethionate, an electroneutral Mg2+ extrusion is observed. Taken together, these results suggest that the Na+/Mg2+ exchanger can operate irrespective of the absence or the presence of Cl? in the extracellular or intracellular environment. Changes in trans-cellular Cl? content, however, can affect the modus operandi of the Na+/Mg2+ exchanger, and consequently impact "cellular" Na+ and Mg2+ homeostasis as well as the hepatocyte membrane potential. 相似文献
14.
The absorbance change of the weak base dye probe, Acridine orange, was used to monitor alterations of pH gradients across renal brush border membrane vesicles. The presence of Na+/H+ or Li+/H+ exchange was demonstrated by diluting Na2SO4 or Li2SO4 loaded vesicles into Na+- or Li+-free solutions, which caused dye uptake. About 20% of the uptake was abolished by lipid permeable cations such as valinomycin-K+ or tetraphenylphosphonium, indicating perhaps the presence of a finite Na+ conductance smaller than electroneutral Na+/H+ exchange. The protonophore tetrachlorosalicylanilide raised the rate of dye uptake under these conditions, hence the presence of an Na+ conductance greater than the H+ conductance was suggested. K+ gradients also induced changes of pH, at about 10% of the Na+ or Li+ rate. Partial inhibition (21%) was seen with 0.1 mM amiloride indicating that K+ was a low affinity substrate for the Na+/H+ exchange. Acceleration both by tetrachlorosalicylanilide (2-fold) and valinomycin (4-fold) suggested the presence of 2 classes of vesicles, those with high and those with low K+ conductance. The larger magnitude of the valinomycin dependent signal suggested that 75% of the vesicles had a low K+ conductance. Inward Cl? gradients also induced acidification, partially inhibited by the presence of tetraphenylphosphonium, and accelerated by tetrachlorosalicylanilide. Thus both a Cl? conductance greater than the H+ conductance and a Cl?/OH? exchange were present. The rate of Na+/H+ exchange was amiloride sensitive with a pH optimum of 6.5 and an apparent Km for Na+ or Li+ of about 10 mM and an EA of 14.3 kcal per mol. A 61-fold Na2SO4 gradient resulted in a pH gradient of 1.64 units which increased to 1.8 with gramicidin. An equivalent NaCl gradient gave a much lower ΔpH even in the presence of gramicidin showing that the H+ and Cl? pathways could alter the effects of the Na+/H+ exchange. 相似文献
15.
Na+-ATPase of high-K+ and low-K+ sheep red cells was examined with respect to the sidedness of Na+ and K+ effects, using inside-out membrane vesicles and very low ATP concentrations (?2 μM). With varying amounts of Na+ in the medium, i.e., at the cytoplasmic surface, Nacyt+, the activation curves show that high-K+ Na+-ATPase has a higher affinity for Nacyt+ compared to low-K+. The apparent affinity for Nacyt+ is also increased by increasing the ATP concentrations in high-K+ but not low-K+. With Nacyt+ present, Na+-ATPase is stimulated by intravesicular Na+, i.e., Na+ at the originally external surface, Naext+, to a greater extent in low-K+ than high-K+. Intravesicular K+ (Kext+) activates Na+-ATPase in high-K+ but not in low-K+ vesicles and extravesicular K+ (Kcyt+) inhibits low-K+ but not high-K+ Na+-ATPase. Thus, the genetic difference between high-K+ and low-K+ is expressed as differences in apparent affinities for both Na+ and K+ and these differences are evident at both cytoplasmic and external membrane surfaces. 相似文献
16.
Selenate and selenite uptakes by isolated intestinal brush border membrane vesicles (BBMV) from pig, sheep, and rat were investigated.
Selenate uptake into jejunal and ileal, but not duodenal, BBMV from pig was stimulated by an inwardly directed transmembrane
Na+ gradient (Na
out
+
>Na
in
+
). Selenate transport into rat ileal and sheep jejunal BBMV was also enhanced in the presence of a Na+ gradient. Unlike selenate uptake, selenite uptake was not Na+ dependent, neither in pig small intestine nor in sheep jejunum and rat ileum. Uptake of selenate represented real uptake
into the vesicular lumen, whereas selenite uptake was a result of an extensive binding of75Se to the membranes. Thiosulfate at a 250-fold concentration of selenate completely inhibited Na+-dependent selenate uptake into pig jejunal BBMV. Furthermore, Na+-dependent sulfate uptake was totally inhibited in the presence of a 250-fold selenate concentration. The results clearly
show that selenate transport across the BBM of pig jejunum and ileum, sheep jejunum, and rat ileum is partially energized
by a transmembrane Na+ gradient. Moreover, it is concluded from the results that there exists a common transport mechanism for sulfate and selenate
in the BBM. The extensive binding of75Se from75Se-labeled selenite to the membranes could be from a spontaneous reaction of selenite with membrane-associated SH groups. 相似文献
17.
The transport of d-glucose by brush border membranes isolated from the rabbit renal cortex was studied. At concentrations less than 2 mM, the rate of d-glucose uptake increased linearly with the concentration of the sugar. No evidence was found for a “high-affinity” (μM) saturable site. Saturation was indicated at concentrations of d-glucose greater than 5 mM. The uptake of d-glucose was stereospecific and selectively inhibited by d-galactose and other sugars. Phlorizin inhibited the uptake of d-glucose in the presence and absence of Na+. The glycoside was a potent inhibitor of the efflux of d-glucose. Preloading the brush border membrane vesicles with d-glucose, but not with l-glucose, accelerated exchange diffusion of d-glucose. These results demonstrate that the uptake of d-glucose by renal brush borders represents transport into an intravesicular space rather than solely binding. The rate of d-glucose uptake was increased when the Na+ in the extravesicular medium was high and the membranes were preloaded with a Na+-free medium. The rate of d-glucose uptake was inhibited by preloading the brush border membranes with Na+. These results are consistent with the Na+ gradient hypothesis for d-glucose transport in the kidney. Thus, the presence of a Na+-dependent facilitated transport of d-glucose in isolated renal brush border membranes is indicated. This finding is consistent with what is known of the transport of the sugar in more physiologically intact preparations and suggests that the membranes serve as an effective model system in examining the mechanism of d-glucose transport in the kidney. 相似文献
18.
In the present study, we documented the promising role of thyroid hormones status in animals in modulation of Na+–Pi transport activity in intestinal brush border membrane vesicles (BBMV) which was accompanied with alterations in BBM lipid
composition and fluidity. Augmentation of net Pi balance in hyperthyroid (Hyper-T) rats was fraternized with accretion of Pi transport across BBMV isolated from intestine of Hyper-T rats as compared to hypothyroid (Hypo-T) and euthyroid (Eu-T) rats
while Na+–Pi transport across BBMV was decreased in Hypo-T rats relative to Eu-T rats. Increment in Na+–Pi transport in intestinal BBMV isolated from Hyper-T rats was manifested as an increase in the maximal velocity (Vmax) of Na+–Pi transport system. Furthermore, BBMV lipid composition profile in intestinal BBM from Hyper-T was altered to that of Hypo-T
rats and Eu-T rats. The molar ratio of cholesterol/phospholipids was higher in intestinal BBM from Hypo-T rats. Fluorescence
anistropy of diphenyl hexatriene (rDPH) and microviscosity were significantly decreased in the intestinal BBM of Hyper-T rats
and decreased in Hypo-T rats as compared to Eu-T rats which corroborated with the alteration in membrane fluidity in response
to thyroid hormone status of animals. Therefore, thyroid hormone mediated change in membrane fluidity might play an important
role in modulating Na+–Pi transport activity of intestinal BBM. (Mol Cell Biochem 278: 195–202, 2005) 相似文献
19.
The uptake of l-glutamic acid into brush-border membrane vesicles isolated from rat renal proximal tubules is Na+-dependent. In contrast to Na+-dependent uptake of d-glucose, pre-equilibration of the vesicles with K+ stimulates l-glutamic acid uptake. Imposition of a K+ gradient () further enhances Na+-dependent l-glutamic acid uptake, but leaves K+-dependent glucose transport unchanged. If K+ is present only at the outside of the vesicles, transport is inhibited. Intravesicular Rb+ and, to a lesser extent, Cs+ can replace intravesicular K+ to stimulate l-glutamic acid uptake. Changes in membrane potential incurred by the imposition of an H+-diffusion potential or anion replacement markedly affect Na+-dependent glutamic acid uptake only in the presence of K+. Experiments with a potential-sensitive cyanine dye also indicate that, in the presence of intravesicular K+ a charge movement is involved in Na+-dependent transport of l-glutamic acid.The data indicate that Na+-dependent l-glutamic acid transport can be additionally energized by a K+ gradient. Furthermore, intravesicular K+ renders Na+-dependent l-glutamic acid transport sensitive to changes in the transmembrane electrical potential difference. 相似文献
20.
Intracellular Ca++ is known to influence Na+ flux in luminal membranes. Abnormally elevated Ca++ levels in some cells is believed to be the primary pathophysiologic defect in cystic fibrosis (CF). This in turn is thought to alter Na+ transport which accounts for certain clinical manifestations of this disease. Two Na+-dependent intestinal transport mechanisms have been reported to be suppressed or missing in CF. To examine whether alterations in cell Ca++ may account for these findings, studies were performed to examine the influence of Ca++ on Na+-solute co-transport across intestinal luminal membranes. Purified brush border membrane vesicles prepared from rat small bowel were preincubated in either Ca++-free buffer or buffer containing 2.5 mM CaCl2. Ca++ loaded vesicles showed marked inhibition of Na+ co-transport of taurocholic acid, taurochenodeoxycholic acid, glucose and valine when compared to controls. The uptake of Na+ was also significantly reduced by intravesicular Ca++. These data demonstrate that intravesicular Ca++ inhibits Na+-coupled solute transport as well as Na+ influx across intestinal brush border membranes. These data suggest that intracellular Ca++ may suppress Na+-dependent solute absorption in the intestine. Results presented here further support the theory that elevated intracellular Ca++ may account for intestinal malabsorption and other altered transport phenomena reported in CF. 相似文献