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1.
The existence of two primary chloride-binding sites was found on the basis of the study of halorhodopsin spectra at different chloride concentrations. SVD analysis of the spectra revealed two chloride-dependent components at low chloride concentration (0.1-10 mM). Global fitting of SVD components found K
D values of 0.47 mM and 5.2 mM with unitity Hill coefficients. The second K
D coincides with the apparent K
D of the photovoltage response of halorhodopsin. 相似文献
2.
Fast-2, a membrane mutant of Paramecium aurelia, is due to a single-gene mutation and has behavioral abnormalities. Intracellular recordings through changes of external solutions were made. The mutant membrane hyperpolarized when it encountered solutions with low K+ concentration. This hyperpolarization and other associated activities were best observed in Ca- or Na-solutions devoid of K+. Membrane potential was plotted against the concentration of K+ (0.5 to 16 mM) in solutions of fixed Na+ or Ca++ concentration. The slopes of the curves for the mutant membrane were steeper than those for the wild type at the lower concentrations of K+. Inclusion of 2 mM tetraethylammonium chloride (TEA-Cl) counteracted the mutational effects. Spontaneous action potentials in Ba-solution and the electrically evoked action potentials in various solutions are normal in this mutant. We conclude that the resting permeability to K+ relative to the permeabilities to Na+ and Ca++ has been increased by the mutation. 相似文献
3.
Salinization of the medium inhibits both K+ uptake by excised barley (Hordeum vulgare L.) roots and K+ release from their stele, as measured by short-term 86Rb uptake and xylem exudation, respectively. Although inhibition was not specific to chloride, mannitol caused a different response from that of inorganic sodium salts, indicating that inhibition was at least partly the result of an ion effect. In roots previously exposed to low levels of NaCl, NaCl stress directly affected stelar K+ release, whereas in low-sodium roots stelar K+ release was much less salt-sensitive than K+ uptake.Abbreviation chCl
choline chloride 相似文献
4.
PURIFICATION AND PROPERTIES OF CHOLINE ACETYLTRANSFERASE FROM THE NERVOUS SYSTEM OF DIFFERENT INVERTEBRATES 总被引:2,自引:2,他引:0
—Choline acetyltransferase has been purified from three invertebrate species, namely snail (Helix aspersa), cockroach (Periplaneta americana) and horse shoe crab (Limulus polyphemus.) All three enzymes followed a Theorell-Chance enzyme mechanism with a sequential addition of the substrates. All three enzymes were activated by sodium and potassium chloride and inhibited by high concentrations of magnesium or calcium chloride. The apparent Km for choline and acetyl-CoA was for snail: Kmch= 370 μm ,KmAcetyl-CoA= 51μm ; cockroach:KmCh= 550 μm , KmAcely-CoA= 16 μm horse shoe crab:KmCn= 2700 μm KmAcctyl-coA= 68 μm CoA inhibited the enzymes competitively with respect to acetyl-CoA and non-competitively with respect to choline. Acetylcholine inhibited the enzymes competitively with respect to choline and non-competitively with respect to acetyl-CoA. All the enzymes were inhibited strongly by 5,5′-dithiobis (2-nitrobenzoate), iodoacetate, acryloylcholine, chloracetylcholine and 3-bromacetonyltrimethyl-ammonium. The enzymes were only weakly inhibited by the styrylpyridine derivatives. The isoelectric points were 5.3 and 5.0 for the horse shoe crab and cockroach enzymes respectively. All three enzymes showed low affinity for a cation-exchanger (CM-Sephadex). 相似文献
5.
Chung-Yi Wang Yi-Ru Hsieh Chang-Chai Ng Helen Chan Hsin-Tang Lin Wen-Sheng Tzeng Yuan-Tay Shyu 《Enzyme and microbial technology》2009,44(6-7):373-379
A halostable cellulase with a molecular mass of 29 kDa was purified from culture supernatants of the halophilic bacterium Salinivibrio sp. NTU-05 by way of the Fast Protein Liquid Chromatography method and the biochemical properties of the halostable cellulase was studied. The enzyme was active over a range of 0–25% sodium chloride examined in culture broth. The optimum cellulase activity was observed at 5% sodium chloride. Results from the salinity stability test indicated 24% of enzyme activity was retained at 25% sodium chloride for 4 h. The enzyme was also shown to be slightly thermostable with 40% residual activity under 60 °C for 4 h. The enzyme has a Km of 3.03 mg/ml and a Vmax of 142.86 mol/min/mg when tested using carboxymethyl-cellulose (CMC). The enzyme activity increased in the presence of K+, Mg2+, Na+ ions and decreased when Hg2+ ions were present. The deduced internal amino acid sequence of the Salinivibrio sp. NTU-05 cellulase showed similarity to the sequence of the glycoside hydrolase family protein. These are some of the novel characteristics that make this enzyme have potential applications in cellulose biodegradation. 相似文献
6.
《Journal of enzyme inhibition and medicinal chemistry》2013,28(5):331-341
AbstractThree new mono-pyridinium compounds were prepared: 1-phenacyl-2-methylpyridinium chloride (1), 1-benzoylethylpyridinium chloride (2) and 1-benzoylethylpyridinium-4-aldoxime chloride (3) and assayed in vitro for their inhibitory effect on human blood acetylcholinesterase (EC 3.1.1.7, AChE). All the three compounds inhibited AChE reversibly; their binding affinity for the enzyme was compared with their protective effect (PI) on AChE phosphonylation by soman and VX. Compound 1 was found to bind to both the catalytic and the allosteric (substrate inhibition) sites of the enzyme with estimated dissociation constants of 6.9 μM (Kcat) and 27 μM (Kall), respectively. Compound 2 bound to the catalytic site with Kcat= 59 μM and compound 3 only to the allosteric site with Kall = 328 μM. PI was evaluated from phosphonylation measured in the absence and in presence of the compounds applied in a concentration corresponding to their Kcat or Kall value, and was also calculated from theoretical equations deduced from the reversible inhibition of the enzyme. Compounds 1 and 3 protected the enzyme from phosphonylation by soman and VX, whereas no protection was observed in the presence of compound 2 under the same conditions. Irrespective of the binding sites to AChE, PI for compounds 1 and 3 evaluated from phosphonylation agreed with PI calculated from reversible inhibition. Compound 3 was found to be a weak reactivator of methylphosphonylated AChE with kr = 1.1 × 102Lmol-1 min-1. 相似文献
7.
Joseph D. Robinson 《Journal of bioenergetics and biomembranes》1984,16(3):195-207
Reaction of a dog kidney (Na + K)-ATPase with pyridoxal phosphate, followed by borohydride reduction, reduced the catalytic activity when measured subsequently. The time course of inactivation did not follow a first-order process, and certain characteristics of the residual enzymatic activity were modified. Moreover, various catalytic activities were diminished differently: Na-ATPase activity was largely spared, K-phosphatase activity was diminished only by half that of the (Na + K)-ATPase, whereas (Na + K)-CTPase and Na-CTPase activities were diminished more. ATP, ADP, CTP, nitrophenyl phosphate, and Pi all protected against inactivation. Increasing salt concentrations increased inactivation, but KCl slowed and NaCl hastened inactivation when compared with choline chloride. Occupancy of certain substrate or cation sites seemed more crucial than selection of conformational states. For the residual (Na + K)-ATPase activity theK
0.5 for K+ was lower and theK
0.5 for Na+ higher, while the sensitivities to ouabain, oligomycin, and dimethylsulfoxide were diminished; for the residual K-phosphatase activity theK
0.5 for K+ was unchanged, the sensitivity to ouabain and oligomycin diminished, but the stimulation by dimethylsulfoxide increased. These properties cannot be wholly accommodated by assuming merely shifts toward either of the two major enzyme conformations. 相似文献
8.
Margaret Colden-Stanfield William P. Schilling Lourival D. Possani Diana L. Kunze 《The Journal of membrane biology》1990,116(3):227-238
Summary Bovine aortic endothelial cells (BAECs) respond to bradykinin with an increase in cytosolic-free Ca2+ concentration, [Ca2+]
i
, accompanied by an increase in surface membrane K+ permeability. In this study, electrophysiological measurement of K+ current was combined with86Rb+ efflux measurements to characterize the K+ flux pathway in BAECs. Bradykinin- and Ca2+-activated K+ currents were identified and shown to be blocked by the alkylammonium compound, tetrabutylammonium chloride and by the scorpion toxin,noxiustoxin, but not by apamin or tetraethylammonium chloride. Whole-cell and single-channel current analysis suggest that the threshold for Ca2+ activation is in the range of 10 to 100nm [Ca2+]
i
. The whole-cell current measurement show voltage sensitivity only at the membrane potentials more positive than 0 mV where significant current decay occurs during a sustained depolarizing pulse. Another K+ current present in control conditions, an inwardly rectifying K+ current, was blocked by Ba2+ and was not affected bynoxiustoxin or tetrabutylammonium chloride. Efflux of86Rb– from BAEC monolayers was stimulated by both bradykinin and ionomycin. Stimulated efflux was blocked by tetrabutyl- and tetrapentyl-ammonium chloride and bynoxiustoxin, but not by apamin or furosemide. Thus,86Rb+ efflux stimulated by bradykinin and ionomycin has the same pharmacological sensitivity as the bradykinin- and Ca2+-activated membrane currents. The results confirm that bradykinin-stimulated86Rb+ efflux occurs via Ca2+-activated K+ channels. The blocking agents identified may provide a means for interpreting the role of the Ca2+-activated K+ current in the response of BAECs to bradykinin. 相似文献
9.
HIGH AFFINITY CHOLINE UPTAKE: IONIC AND ENERGY REQUIREMENTS 总被引:20,自引:19,他引:1
Abstract— High affinity choline uptake into rat hippocampal synaptosomes was examined at 37°C when various ions were deleted from normal Kreb's-Ringer media. When sodium chloride was replaced by sucrose, lithium chloride, cesium chloride or rubidium chloride, choline uptake was markedly reduced. When the sodium concentrations of the Kreb's media were gradually reduced to zero, the uptake was gradually reduced in parallel. A kinetic analysis performed at low and normal sodium concentrations revealed changes in Km and Vmax values. When several non-chloride sodium salts were utilized, the uptake was reduced in all cases suggesting also a chloride-dependence in addition to the sodium-dependence. Omission of calcium chloride or magnesium sulfate from the media did not alter uptake. Sodium-dependent choline uptake was examined over a range of potassium concentrations (0–35 DIM). It was found that uptake was maximal between potassium concentrations of 0.35–4.8 mm but was reduced at both lower and higher potassium concentrations. The kinetics of uptake were examined under varying potassium concentrations, and at low potassium, only a change in Vmax was observed while at high potassium concentrations, there were changes in both Km and Vmax values. Preincubation and incubation of synaptosomes with 0.1 m -ouabain, 0.1 mm -2,4-dinitrophenol and 1 mm -KCN caused a reduction in sodium-dependent uptake. When dextrose was omitted from the preincubation and incubation media there was also a reduction in sodium-dependent uptake. By contrast, the sodium-independent uptake was unaffected by the metabolic inhibitors or omission of dextrose, and had a very low Q10. When various incubation temperatures were utilized in uptake experiments, the Q10 for the interval 37-27°C was 2.7 and the activation energy was 22.7 kcal/mol. Slightly different ionic dependences were observed when animals pretreated with pentobarbital of oentylenetetrazol were utilized as the source of synaptosomes. 相似文献
10.
Chandra Sekhar Gahan Jan‐Eric Sundkvist Mark Dopson Åke Sandström 《Biotechnology and bioengineering》2010,106(3):422-431
Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe2+ by a Leptospirillum ferriphilum‐dominated culture was completely inhibited by 12 g L?1 chloride. In addition, the effects of chloride on oxidation kinetics in a Fe2+ limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe2+ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (µmax) and an increase in the substrate constant (Ks) with increasing chloride concentrations, indicating an effect on the Fe2+ oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2–3 g L?1 chloride with a concomitant drastic decrease in the true yield (Ytrue). This model helps to understand the influence of chloride on Fe2+ biooxidation kinetics. Biotechnol. Bioeng. 2010; 106: 422–431. © 2010 Wiley Periodicals, Inc. 相似文献
11.
A. Martin M. Zade-Oppen Norma C. Adragna Daniel C. Tosteson 《The Journal of membrane biology》1988,103(3):217-225
Summary Ouabain-resistant effluxes from pretreated cells containing K+/Na+=1.5 into K+ and Na+ free media were measured.Furosemide-sensitive cation effluxes from cells with nearly normal membrane potential and pH were lower in NO
3
–
media than in Cl– media; they were reduced when pH was lowered in Cl– media. When the membrane potential was positive inside furosemide increased the effluxes of Na+ and K+ (7 experiments). With inside-positive membrane potential thefurosemideinsensitive effluxes were markedly increased, they decreased with decreasing pH at constant internal Cl– and also when internal Cl– was reduced at constant pH. The correlation between cation flux and the membrane potential was different for cells with high or low internal chloride concentrations. The data with chloride47mm showed a better fit with the single-barrier model than with the infinite number-of-barriers model. With low chloride no significant correlation between flux and membrane potential was found. The data are not compatible with pure independent diffusion of Na+ and K+ in the presence of ouabain and furosemide. 相似文献
12.
Yoshitaka Saito Keiichi Itoi Keisuke Horiuchi Tadao Watanabe 《The Journal of membrane biology》1980,53(2):85-93
Summary The effects of furosemide on the chloride-dependent short-circuit current across the toad ciliary epithelium were examined. Under control conditions, the short-circuit current obeyed Michaelis-Menten kinetics against medium chloride concentration, the Michaelis constant (K
m
) for chloride being 90mm and the maximal short-circuit current (V
max) 128 A/cm2. Furosemide added to the aqueous side of the epithelium rapidly reduced the short-circuit current; the effect was reversible. The effect of furosemide addition to the stromal side was much smaller and slower than that from the aqueous side. The dose-dependent range of furosemide action was from 0.1 m to 1mm with 50% inhibition occurring at about 3 m. Line-weaver-Burk plot of the short-circuit current against the chloride concentration showed that furosemide decreased the value ofV
max and increased theK
m
; the inhibition being of mixed type. A Hill plot of the dose-response curve yielding a slope of unity suggested one furosemide molecule combines with one chloride transport site. Probenecid, a competitive inhibitor of organic acid transport, reduced the effects of furosemide significantly when added simultaneously. The involvement of organic acid transport system in the mechanism of furosemide action on chloride transport was suggested.Department of Ophthalmology. 相似文献
13.
Effects of ammonium on the photosynthetic recovery of Nostoc flagelliforme Berk. et M. A. Curtis were assayed when being rehydrated in low‐K+ or high‐K+ medium. Its photosynthetic recovery was K+ limited after 3 years of dry storage. The potassium absorption of N. flagelliforme reached the maximum after 3 h rehydration in low‐K+ medium but at 5 min in high‐K+ medium. The K+ content of N. flagelliforme rehydrated in high‐K+ medium was much higher than that in low‐K+ medium. The maximal PSII quantum yield (Fv/Fm) value of N. flagelliforme decreased significantly when samples were rehydrated in low‐K+ medium treated with 5 mM NH4Cl. However, the treatment of 20 mM NH4Cl had little effect on its Fv/Fm value in high‐K+ medium. The relative Fv/Fm 24 h EC50 (concentration at which 50% inhibition occurred) value of NH4+ in high‐K+ medium (64.35 mM) was much higher than that in low‐K+ medium (22.17 mM). This finding indicated that high K+ could alleviate the inhibitory action of NH4+ upon the photosynthetic recovery of N. flagelliforme during rehydration. In the presence of 10 mM tetraethylammonium chloride (TEACl), the relative Fv/Fm 24 h EC50 value of NH4+ was increased to 46.34 and 70.78 mM, respectively, in low‐K+ and high‐K+ media. This observation suggested that NH4+ entered into N. flagelliforme cells via the K+ channel. Furthermore, NH4+ could decrease K+ absorption in high‐K+ medium. 相似文献
14.
Stephen D. McCormick 《Cell and tissue research》1990,260(3):529-533
Summary Anthroylouabain, a fluorescent derivative of ouabain, was used to localize Na+,K+-ATPase in transport epithelia of two species of teleosts. Exposure of the opercular membrane of seawater-adapted tilapia (Oreochromis mossambicus) and the jaw skin of the long-jawed mudsucker (Gillichthys mirabilis) to a 2 M anthroylouabain solution resulted in the appearance of cells stained bright blue. These were deemed to be chloride cells by their large size, distinct morphology and co-localization of DASPEI fluorescence, a mitochondrial stain. Addition of ouabain (1 mM final concentration) greatly decreased anthroylouabain fluorescent staining of chloride cells of seawater-adapted fish. Exposure of opercular membranes from freshwater tilapia to 2 M anthroylouabain did not result in significant staining. Anthroylouabain is therefore a useful vital stain for localizing Na+,K+-ATPase in chloride cells of seawater-adapted teleosts, and may be useful for fluorescent labelling of ouabain-sensitive Na+,K+-ATPase in other tissues and species. 相似文献
15.
H. Schnabl 《Planta》1978,144(1):95-100
Chloride ions are necessary to compensate for the positively charged potassium ions imported into guard cells of Allium cepa L. during stomatal opening. Therefore an external Cl- supply of intact Allium plants is important. But high levels of chloride have been found to reduce the sensitivity of the starch-lacking stomata and isolated guard cell protoplasts (GCPs) from Allium to potassium ions, fusicoccin and abscisic acid. Furthermore, with high levels of chloride, malate anions disappear from the guard cells of Allium, a finding which contrasts with situation in Vicia where the stomatal sensitivity to K+ ions, fusicoccin and ABA is not influenced by Cl- ions and malate levels are unaffected. It is suggested that the absence of malate as a proton yielding primer inhibits the mechanism of H+/K+ exchange in Allium.Abbreviations ABA
abscisic acid
- FC
fusicoccin
- GCPs
guard cell protoplasts 相似文献
16.
Summary Sodium (22Na) transport was studied in a basolateral membrane vesicle preparation from rabbit parotid. Sodium uptake was markedly dependent on the presence of both K+ and Cl– in the extravesicular medium, being reduced 5 times when K+ was replaced by a nonphysiologic cation and 10 times when Cl– was replaced by a nonphysiologic anion. Sodium uptake was stimulated by gradients of either K+ or Cl– (relative to nongradient conditions) and could be driven against a sodium concentration gradient by a KCl gradient. No effect of membrane potentials on KCl-dependent sodium flux could be detected, indicating that this is an electroneutral process. A KCl-dependent component of sodium flux could also be demonstrated under equuilibrium exchange conditions, indicating a direct effect of K+ and Cl– on the sodium transport pathway. KCl-dependent sodium uptake exhibited a hyperbolic dependence on sodium concentration consistent with the existence of a single-transport system withK
m
=3.2mm at 80mm KCl and 23°C. Furosemide inhibited this transporter withK
0.5=2×10–4
m (23°C). When sodium uptake was measured as a function of potassium and chloride concentrations a hyperbolic dependence on [K] (Hill coefficient =1.31±0.07) were observed, consistent with a Na/K/Cl stoichiometry of 112. Taken together these data provide strong evidence for the electroneutral coupling of sodium and KCl movements in this preparation and strongly support the hypothesis that a Na+/K+/Cl– cotransport system thought to be associated with transepithelial chloride and water movements in many exocrine glands is present in the parotid acinar basolateral membrane. 相似文献
17.
Summary In order to investigate whether the loop diuretic sensitive, sodium-chloride cotransport system described previously in shark rectal gland is in fact a sodium-potassium chloride cotransport system, plasma membrane vesicles were isolated from rectal glands ofSqualus acanthias and sodium and rubidium uptake were measured by a rapid filtration technique. In addition, the binding of N-methylfurosemide to the membranes was investigated. Sodium uptake into the vesicles in the presence of a 170mm KCl gradient was initially about five-fold higher than in the presence of a 170mm KNO3 gradient. In the presence of chloride, sodium uptake was inhibited 56% by 0.4mm bumetanide and 40% by 0.8mm N-methylfurosemide. When potassium chloride was replaced by choline chloride or lithium chloride, sodium uptake decreased to the values observed in the presence of potassium nitrate. Replacement of potassium chloride by rubidium chloride, however, did not change sodium uptake. Initial rubidium uptake into the membrane vesicles was about 2.5-fold higher in the presence of a 170mm NaCl gradient than in the presence of a 170mm NaNO3 gradient. The effect of chloride was completely abolished by 0.4mm bumetanide. Replacement of the sodium chloride gradient by a lithium chloride gradient decreased rubidium uptake by about 40%; replacement by a choline chloride gradient reduced the uptake even further. Rubidium uptake was also strongly inhibited by potassium. Sodium chloride dependence and bumetanide inhibition of rubidium flux were also found in tracer exchange experiments in the absence of salt gradients. The isolated plasma membranes bound3[H]-N-methylfurosemide in a dose-dependent manner. In Scatchard plots, one saturable component could be detected with an apparentK
D of 3.5×10–6
m and a number of sitesn of 104 pmol/mg protein. At 0.8 m, N-methylfurosemide binding decreased 51% when sodium-free or low-potassium media were used. The same decrease was observed when the chloride concentration was increased from 200 to 600mm or when 1mm bumetanide or furosemide were added to the incubation medium. These studies indicate that the sodium-chloride cotransport system described previously in the rectal gland is in fact a sodium-potassium chloride cotransport system. It is postulated that this transport system plays an essential role in the secondary active chloride secretion of the rectal gland. 相似文献
18.
P. GOMES M.P SERRO M.A VIEIRA-COELHO P. SOARES-DA-SILVA 《Cell biology international》1997,21(4):249-255
The present work was aimed at studying the kinetics and nature of the l-DOPA transporter in opossum kidney (OK) cells. Saturation experiments were performed in OK cells incubated for 6 min with increasing concentrations of l-DOPA (10 to 2500 μm); non-linear analysis of the saturation curve revealed for l-DOPA aKmof 129 μm (114, 145) and aVmaxof 30.0±0.4 nmol mg protein?16 min?1The uptake of l-DOPA (250 μm) was inhibited in a concentration-dependent manner by cyanine 863, an organic cation inhibitor, with aKivalue of 638 (430, 947) μmthe organic anion inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid (DIDS), was devoid of effect upon the uptake of l-DOPA. The uptake of l-DOPA (250 μm) was significantly (P<0.02) decreased (25% reduction) when cells were incubated in the presence of 137 mm K+plus 5 mm Na+when compared with the control condition (137 mm Na+plus 5 mm K+); substitution of NaCl by choline chloride (137 mm) did not affect l-DOPA uptake. Similarly, inwardly or outwardly directed proton gradients of 0.5 pH units (7.9, 7.4, 6.9, 6.4 and 5.9) were found not to change l-DOPA uptake. In conclusion, the l-DOPA uptake system in OK cells has the characteristics of an organic cation potential-dependent and proton-independent transporter. 相似文献
19.
CARRIER MEDIATED BLOOD-BRAIN BARRIER TRANSPORT OF CHOLINE AND CERTAIN CHOLINE ANALOGS 总被引:24,自引:19,他引:5
Blood-brain barrier (BBB) transport of choline and certain choline analogs was studied in adult and suckling rats, and additionally compared in the paleocortex and neocortex of adult rats. Saturable uptake was characterized by a single kinetic system in all cases examined, and in adult rat forebrains we determined a Km= 442 ± 60 μM and Vmax= 10.0 ± 0.6 nmol min-1 g-1. In 14–15-day-old suckling forebrains a similar Km (= 404 ± 88 μM) but higher Vmax (= 12.5 ± 1.5 nmol min-1 g-1) was determined. When choline uptake was compared in two regions of the forebrain, similar Michaelis-Menten constants were determined but a higher uptake velocity was found in the neocortex (i.e. neocortex Km= 310 ± 103 μM and Vmax= 12.6 ± 2.8 nmol min-1g-1; paleocortex Km= 217 ± 76 μM and Vmax= 7.2 ± 1.5 nmol min-1 g-1). Administration of radiolabelled choline at low (5 μM) and high (100 μM) concentrations, followed by microwave fixation 60 s later and chloroform-methanol-water separations of the homogenized brain did not suggest a relationship between concentration and the appearance of label in lipid or aqueous fractions as observed in another in-vitro study elaborating two-component kinetics of choline uptake. It was observed that 60s after carotid injection 12–14% of the radiolabel in the ipsilateral cortex was found in the chloroform-soluble fraction. Hemicholinium-3 (Ki= 111 μM), dimethylaminoethanol (Ki= 42 μM), tetraethyl ammonium chloride, tetramethyl ammonium chloride, 2-hydroxyethyl triethylammonium iodide, carnitine, normal rat serum, and to a lesser extent lithium and spermidine all inhibited choline uptake in the BBB. Unsubstituted ammonium chloride and imipramine did not inhibit choline uptake. No difference was observed in blood-brain barrier choline uptake of unanesthetised, carotid artery-catheterized animals, and comparable sodium pentobarbital-anesthetized controls. 相似文献
20.
Abstract— The swelling of intact, exposed primate cerebral cortex perfused in vioo under, isosmotic conditions was a linear function of the concentration of K+ in perfusate over the range 25–117 mM. The K+-dependent swelling was manifested throughout the depth of the cerebral cortex studied and was associated with an increased content of chloride in the swollen tissue, despite the constancy of the concentration of external chloride. The swelling of the cerebral cortex was a linear function of the temperature of the perfusate over the range 15–38°C, despite the constancy of the concentration of external K+. Moreover, the content of chloride in the swollen cerebral cortex was a linear function of the temperature of the overlying perfusate, despite the constancy of the external concentration of chloride. The changes in the contents of Na+ and K+ in the swollen cerebral cortex perfused with solutions containing constant concentrations of external Na+ and K+ but differing in temperature suggested that the fluid of swelling in the tissue was rich in both K+ and CI-, as had been shown previously in vitro. Perfusion of the exposed, intact cerebral cortex in uiuo with K+-rich fluids usually involved the reciprocal reduction of the concentrations of Na+ in the perfusate to maintain isotonicity. When comparable reductions in the concentration of external Na+ were achieved by replacement with choline (instead of K+), swelling of the perfused, exposed cortex was significantly less than that attributed to isotonic, K+-rich but Na+-poor fluids. These observations suggested that it was the elevated levels of K+ rather than lowered concentrations of Na+ that promoted the swelling of the perfused cerebral cortex. The apparent rate of influx of 36Cl from the perfusate into the underlying exposed and intact monkey cerebral cortex in vivo was a linear function of the concentration of K+ in perfusate over the range 25–117 mM and conformed to Michaelis-Menten kinetics when plotted according to Lineweaver and Burk. Moreover, the apparent influx of chloride from perfusate into swollen cerebral cortex was a linear function of the percentage swelling of cerebral cortex over the range 6–30 per cent. However, the apparent rate of influx of chloride from perfusate into unswollen cortex was not consistent with the linear correlation already described for swollen cerebral cortex. One reason for this discrepancy was the reduction in the size of the true (inulin) extracellular space associated with the K+-dependent swelling of cerebral cortex in vivo. The anatomical locus for this K+-dependent swelling of cerebral cortex was an expanded glial compartment, as demonstrated by electron-microscopy. The parenteral administration (50 mg/kg) or local perfusion (5 mM) of acetazolamide inhibited the K+-dependent swelling of cerebral cortex in vivo. Moreover, administration of acetazolamide inhibited the K+-dependent increase in content of C1- and the K+-dependent rate of influx of 36Cl into swollen cerebral cortex. We have discussed the possible enzymatic basis of these K+-dependent alterations in content of fluid and chloride and transport of chloride in mammalian cerebral cortex in viuo. 相似文献