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1.
Effect of endothelin-1 and chemically induced hypoxia on Na+−K+−Cl− cotransport activity in cultured rat brain capillary endothelial cells was examined by using86Rb+ as a tracer for K+; bumetanide-sensitive K+ uptake was defined as Na+−K+−Cl− cotransport activity. Endothelin-1, phorbol 12-myristate 13-acetate (PMA), or thapsigargin increased Na+−K+−Cl− cotransport activity. A protein kinase C inhibitor, bisindolylmaleimide, inhibited PMA- and endothelin-1- (but not thapsigargin-)
induced Na+−K+−Cl− cotransport activity, indicating the presence of both protein kinase C-dependent regulatory mechanisms and protein kinase
C-independent mechanisms which involve intracellular Ca2+. Oligomycin, sodium azide, or antimycin A increased Na+−K+−Cl− cotransport activity by 80–200%. Oligomycin-induced Na+−K+−Cl− cotransport activity was reduced by an intracellular Ca2+ chelator (BAPTA/AM) but not affected by bisindolylmaleimide, suggesting the involvement of intracellular Ca2+, and not protein kinase C, in hypoxia-induced Na+−K+−Cl− cotransport activity.
Portions were presented at “27th Annual Meeting, The American Society for Neurochemistry” Philadelphia, Pennsylvania, March
2–6, 1996. 相似文献
2.
Summary To study the physiological role of the bidirectionally operating, furosemide-sensitive Na+/K+ transport system of human erythrocytes, the effect of furosemide on red cell cation and hemoglobin content was determined in cells incubated for 24 hr with ouabain in 145mm NaCl media containing 0 to 10mm K+ or Rb+. In pure Na+ media, furosemide accelerated cell Na+ gain and retarded cellular K+ loss. External K+ (5mm) had an effect similar to furosemide and markedly reduced the action of the drug on cellular cation content. External Rb+ accelerated the Na+ gain like K+, but did not affect the K+ retention induced by furosemide. The data are interpreted to indicate that the furosemide-sensitive Na+/K+ transport system of human erythrocytes mediates an equimolar extrusion of Na+ and K+ in Na+ media (Na+/K+ cotransport), a 1:1 K+/K+ (K+/Rb+) and Na+/Na+ exchange progressively appearing upon increasing external K+ (Rb+) concentrations to 5mm. The effect of furosemide (or external K+/Rb+) on cation contents was associated with a prevention of the cell shrinkage seen in pure Na+ media, or with a cell swelling, indicating that the furosemide-sensitive Na+/K+ transport system is involved in the control of cell volume of human erythrocytes. The action of furosemide on cellular volume and cation content tended to disappear at 5mm external K+ or Rb+. Thein vivo red cell K+ content was negatively correlated to the rate of furosemide-sensitive K+ (Rb+) uptake, and a positive correlation was seen between mean cellular hemoglobin content and furosemide-sensitive transport activity. The transport system possibly functions as a K+ and waterextruding mechanism under physiological conditiosin vivo. The red cell Na+ content showed no correlation to the activity of the furosemide-sensitive transport system. 相似文献
3.
Electrophysiological studies on renal thick ascending limb segments indicate the involvement of a luminal Na+/K+/Cl− cotransport system and a K+ channel in transepithelial salt transport. Sodium reabsorption across this segment is blocked by the diuretics furosemide and bumetanide. The object of our study has been to identify in intact membranes and reconstitute into phospholipid vesicles the Na+/K+/Cl− cotransporter and K+ channel, as an essential first step towards purification of the proteins involved and characterization of their roles in the regulation of transepithelial salt transport. Measurements of 86Rb+ uptake into membrane vesicles against large opposing KCl gradients greatly magnify the ratio of specific compared to non-specific isotope flux pathways. Using this sensitive procedure, it has proved possible to demonstrate in crude microsomal vesicle preparations from rabbit renal outer medulla two 86Rb+ fluxes. (A) A furosemide-inhibited 86Rb+ flux in the absence of Na+ (K+-K+ exchange). This flux is stimulated by an inward Na+ gradient (Na+/K+ cotransport) and is inhibited also by bumetanide. (B) A Ba2+-inhibited 86Rb+ flux, through the K+ channel. Luminal membranes containing the Na+/K+/Cl− cotransporter and K+ channels, and basolateral membranes containing the Na+/K+ pumps were separated from the bulk of contaminant protein by metrizamide density gradient centrifugation. The Na+/K+/Cl− cotransporter and K+ channel were reconstituted in a functional state by solubilizing both luminal membranes and soybean phospholipid with octyl glucoside, and then removing detergent on a Sephadex column. 相似文献
4.
Tai Akera Satoshi Yamamoto Kyosuke Temma Dong-Hee Kim Theodore M. Brody 《生物化学与生物物理学报:生物膜》1981,640(3):779-790
- 1. (1) The significance of the specific (ouabain-sensitive) 86Rb+ or 42K+ uptake by cardiac muscle preparations which are not ‘sodium-loaded’ was studied.
- 2. (2) In left atrial preparations of guinea-pig heart, resting 86Rb+ uptake was relatively low. It was markedly increased by electrical stimulation. This stimulated uptake was further enhanced by isoproterenol and inhibited by verapamil.
- 3. (3) In rat atria, the resting 86Rb+ uptake was somewhat higher than in guinea-pig atria, and the increase in uptake caused by electrical stimulation was smaller. In guinea-pig right ventricular papillary muscle, the resting uptake was highest among those tissues studied, and the response to electrical stimulation was smallest. In the latter tissue, verapamil produced only a minimal inhibition of the specific 86Rb+ uptake.
- 4. (4) The effect of the frequency of electrical stimulation on 86Rb+ uptake paralleled its influence on the force of contraction, suggesting the involvement of intracellular sodium in both events.
- 5. (5) In both left atrial and right papillary muscle preparations of guinea-pig heart, specific 42K+ uptake observed with 5.8 mM K+ was relatively high, and was increased only slightly by electrical stimulation. This electrical stimulation, however, increased ouabain-induced inhibition of 42K+ uptake, suggesting that the stimulation increases the amount of Na+ available to the sodium pump.
- 6. (6) When the K+ concentration was 1 mM, the resting 42K+ uptake was low, and could be enhanced by electrical stimulation.
Keywords: Rb+ uptake; K+ uptake; Electrical stimulation; Na+ influex; (Cardiac muscle) 相似文献
5.
Toshitaka Ikehara Hisao Yamaguchi Keiko Hosokawa Akira Takahashi Hiroshi Miyamoto 《The Journal of membrane biology》1993,132(2):115-124
Summary The effects of intracellular K+ and Na+ (K+
c, Na+
c) on the Na+,K+,Cl+– cotransport pathway of HeLa cells were studied by measuring ouabain-insensitive, furosemide-sensitive Rb+ influx (JRb) at various intracellular concentrations of K+ and Na+ ([K+]c, [Na+]c). When [K+]c was increased and [Na+]c was decreased, keeping the sums of their concentrations almost constant, JRb as a function of the extracellular Rb+ or Na+ concentration ([Rb+]e, [Na+]e) was stimulated. However, the apparent K
0.5 for Rb+
e or Na+
e remained unchanged and the ratio of the apparent K
+0.5 for K+
c and the apparent K
i for Na+
c was larger than 1. When JRb was increased by hypertonicity by addition of 200 mM mannitol, the apparent maximum JRb increased without change in the apparent K
0.5 for Rb+
e. These results show that K+
c stimulates and Na+
c inhibits JRb, without change in the affinities of the pathway for Rb+
e and Na+
e. The affinity for K+
c is slightly lower than that for Na+
c. Hypertonicity enhances JRb without any change in the affinity for Rb+
e. We derived a kinetic equation for JRb with respect to K+
c and Na+
c and proposed a general and a special model of the pathway. The special model suggests that, in HeLa cells, JRb takes place when Rb+
e binds to the external K+ binding site of the pathway after the binding of K+
c to the internal regulatory site.We thank Mr. T. Masuya for technical assistance. This study was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas (No. 03202136) from the Japanese Ministry of Education, Science and Culture. 相似文献
6.
Jochen Duhm 《The Journal of membrane biology》1987,98(1):15-32
Summary The effect of extracellular and intracellular Na+ (Na
o
+
, Na
i
+
) on ouabain-resistant, furosemide-sensitive (FS) Rb+ transport was studied in human erythrocytes under varying experimental conditions. The results obtained are consistent with the view that a (1 Na++1 K++2 Cl–) cotransport system operates in two different modes: modei) promoting bidirectional 11 (Na+–K+) cotransport, and modeii) a Na
o
+
-independent 11 K
o
+
/K
i
+
exchange requiring Na
i
+
which, however, is not extruded. The activities of the two modes of operation vary strictly in parallel to each other among erythrocytes of different donors and in cell fractions of individual donors separated according to density. Rb+ uptake through Rb
o
+
/K
i
+
exchange contributes about 25% to total Rb+ uptake in 145mm NaCl media containing 5mm RbCl at normal Na
i
+
(pH 7.4). Na+–K+ cotransport into the cells occurs largely additive to K+/K+ exchange. Inward Na+–Rb+ cotransport exhibits a substrate inhibition at high Rb
o
+
. With increasing pH, the maximum rate of cotransport is accelerated at the expense of K+/K+ exchange (apparent pK close to pH 7.4). The apparentK
m
Rb
o
+
of Na+–K+ cotransport is low (2mm) and almost independent of pH, and high for K+/K+ exchange (10 to 15mm), the affinity increasing with pH. The two modes are discussed in terms of a partial reaction scheme of (1 Na++1 K++2 Cl–) cotransport with ordered binding and debinding, exhibiting a glide symmetry (first on outside = first off inside) as proposed by McManus for duck erythrocytes (McManus, T.J., 1987,Fed. Proc., in press). N-ethylmaleimide (NEM) chemically induces a Cl–-dependent K+ transport pathway that is independent of both Na
o
+
and Na
i
+
. This pathway differs in many properties from the basal, Na
o
+
-independent K+/K+ exchange active in untreated human erythrocytes at normal cell volume. Cell swelling accelerates a Na
o
+
-independent FS K+ transport pathway which most probably is not identical to basal K+/K+ exchange. K
o
+
o
+
o
+
o
2+
reduce furosemide-resistant Rb+ inward leakage relative to choline
o
+
. 相似文献
7.
Two cDNAs isolated from Cymodocea nodosa, CnSOS1A, and CnSOS1B encode proteins with high-sequence similarities to SOS1 plant transporters. CnSOS1A expressed in a yeast Na+-efflux mutant under the control of a constitutive expression promoter mimicked AtSOS1 from Arabidopsis; the wild type cDNA did not improve the growth of the recipient strain in the presence of Na+, but a cDNA mutant that expresses a truncated protein suppressed the defect of the yeast mutant. In similar experiments,
CnSOS1B was not effective. Conditional expression, under the control of an arabinose responsive promoter, of the CnSOS1A and CnSOS1B cDNAs in an Escherichia coli mutant defective in Na+ efflux was toxic, and functional analyses were inconclusive. The same constructs transformed into an E. coli K+-uptake mutant revealed that CnSOS1A was also toxic, but that it slightly suppressed defective growth at low K+. Truncation in the C-terminal hydrophilic tail of CnSOS1A relieved the toxicity and proved that CnSOS1A was an excellent
low-affinity K+ and Rb+ transporter. CnSOS1B mediated a transient, extremely rapid K+ or Rb+ influx. Similar tests with AtSOS1 revealed that it was not toxic and that the whole protein exhibited excellent K+ and Rb+ uptake characteristics in bacteria. 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.
Four Na+/H+ antiporters, Mrp, TetA(L), NhaC, and MleN have so far been described in Bacillus subtilis 168. We identified an additional Na+/H+ antiporter, YvgP, from B. subtilis that exhibits homology to the cation: proton antiporter-1 (CPA-1) family. The yvgP-dependent complementation observed in a Na+(Ca2+)/H+ antiporter-defective Escherichia coli mutant (KNabc) suggested that YvgP effluxed Na+ and Li+. In addition, effects of yvgP expression on a K+ uptake-defective mutant of E. coli indicated that YvgP also supported K+ efflux. In a fluorescence-based assay of everted membrane vesicles prepared from E. coli KNabc transformants, YvgP-dependent Na+ (K+, Li+, Rb+)/H+ antiport activity was demonstrated. Na+ (K+, Li+)/H+ activity was higher at pH 8.5 than at pH 7.5. Mg2+, Ca2+ and Mn2+ did not serve as substrates but they inhibited YvgP antiport activities. Studies of yvgP expression in B. subtilis, using a reporter gene fusion, showed a significant constitutive level of expression that was highest in stationary phase,
increasing as stationary phase progressed. In addition, the expression level was significantly increased in the presence of
added K+ and Na+. 相似文献
10.
Fusicoccin (FC) has long been known to promote K+ uptake in higher plant cells, including stomatal guard cells, yet the precise mechanism behind this enhancement remains uncertain. Membrane hyperpolarization, thought to arise from primary H+ pumping stimulated in FC, could help drive K+ uptake, but the extent to which FC stimulates influx and uptake frequently exceeds any reasonable estimates from Constant Field Theory based on changes in the free-running membrane potential (V
m) alone; furthermore, unidirectional flux analyses have shown that in the toxin K+ (86Rb+) exchange plummets to 10% of the control (G.M. Clint and E.A.C. MacRobbie 1984, J. Exp. Bot.35 180–192). Thus, the activities of specific pathways for K+ movement across the membrane could be modified in FC. We have explored a role for K+ channels in mediating these fluxes in guard cells ofVicia faba L. The correspondence between FC-induced changes in chemical (86Rb+) flux and in electrical current under voltage clamp was followed, using the K+ channel blocker tetraethylammonium chloride (TEA) to probe tracer and charge movement through K+-selective channels. Parallel flux and electrical measurements were carried out when cells showed little evidence of primary pump activity, thus simplifying analyses. Under these conditions, outward-directed K+ channel current contributed appreciably to charge balance maintainingV
m, and adding 10 mM TEA to block the current depolarized (positive-going)V
m; TEA also reduced86Rb+ efflux by 68–80%. Following treatments with 10 M FC, both K+ channel current and86Rb+ efflux decayed, irreversbly and without apparent lag, to 10%–15% of the controls and with equivalent half-times (approx. 4 min). Fusicoccin also enhanced86Rb+ influx by 13.9-fold, but the influx proved largely insensitive to TEA. Overall, FC promotednet cation uptake in 0.1 mM K+ (Rb+), despite membrane potentials which were 30–60 mVpositive of the K+ equilibrium potential. These results tentatively link (chemical) cation efflux to charge movement through the K+ channels. They offer evidence of an energy-coupled mechanism for K+ uptake in guard cells. Finally, the data reaffirm early suspicions that FC alters profoundly the K+ transport capacity of the cells, independent of any changes in membrane potential.Abbreviations and symbols
E
K
equilibrium potential for K+
- FC
fusicoccin
- Hepes
4-(2-hydroxyethyl)-1-piperazineeth-anesulfonic acid
-
G
m
membrane (slope) conductance atV
m
- I-V
current-voltage (relationship)
-
apparent rate constant for exchange
- K
i
+
, K
0
+
intracellular, extracellular K+ (concentration)
- TEA
tetraethylammonium chloride
-
V
m
free-running membrane potential (difference) 相似文献
11.
Putative potassium-transport-deficient mutant strains of Chlamydomonas reinhardtii Dang. were induced by ultra-violet mutagenesis and were identified by their dependence on abnormally high concentrations of potassium for growth. Potassium transport studies employing 86Rb as a tracer were carried out with wild-type cells and with three independently isolated KDP (potassium-dependent phenotype) clones. Wildtype cells exhibit two transport activities. Transport activity A was expressed when cells were grown in medium supplemented with 10 mM KCl. The transporter with type-A activity does not discriminate between either Rb+ or K+ as a substrate and has a Km for Rb+ equal to 1 mM and a Vmax equal to 31 nmol Rb+ h-1 10-6 cells. Transport activity B was expressed when cells were starved of potassium for 24 h. The transporter with type-B activity prefers K+ to Rb+ as a substrate; it has a Km for Rb+ equal to 2.5 mM and a Vmax equal to 210 nmol Rb+ h-1 10-6 cells. All three mutant clones exhibit transport activity comparable to type-A when grown in 10 mM KCl. When starved of potassium for 24 h, two KDP clones demonstrate no transport activity and the third clone continues to exhibit only type-A activity.Abbreviations CCCP
carbonyl cyanide m-chlorophenylhydrazone
- DES
diethylstilbesterol
- KDP
potassium-dependent phenotype 相似文献
12.
The K+ uptake pathways in yeast mitochondria are still undefined. Nonetheless, the K+-mediated mitochondrial swelling observed in the absence of phosphate (PO4) and in the presence of a respiratory substrate has led to propose that large K+ movements occur in yeast mitochondria. Thus, the uptake of K+ by isolated yeast mitochondria was evaluated. Two parallel experiments were conducted to evaluate K+ transport; these were mitochondrial swelling and the uptake of the radioactive K+ analog 86Rb+. The opening of the yeast mitochondrial unspecific channel (YMUC) was regulated by different PO4 concentrations. The high protein concentrations used to measure 86Rb+ uptake resulted in a slight stabilization of the transmembrane potential at 0.4 mM PO4 but not at 0 or 4 mM PO4. At 4 mM PO4 swelling was inhibited while, in contrast, 86Rb+ uptake was still observed. The results suggest that an energy-dependent K+ uptake mechanism was unmasked when the YMUC was closed. To further analyze the properties of this K+ uptake system, the Mg2+ and quinine sensitivity of both swelling and 86Rb+ uptake were evaluated. Under the conditions where the unspecific pore was closed, K+ transport sensitivity to Mg2+ and quinine increased. In addition, when Zn2+ was added as an antiport inhibitor, uptake of 86Rb+ increased. It is suggested that in yeast mitochondria, the K+ concentration is highly regulated by the equilibrium of uptake and exit of this cation through two specific transporters. 相似文献
13.
Summary It is shown that the ouabain-resistant (OR) furosemide-sensitive K+(Rb+) transport system performs a net efflux of K+ in growing mouse 3T3 cells. This conclusion is based on the finding that under the same assay conditions the furosemidesensitive K+(Rb+) efflux was found to be two- to threefold higher than the ouabain-resistant furosemide-sensitive K+(Rb+) influx. The oubain-resistant furosemide-sensitive influxes of both22Na and86Rb appear to be Cl– dependent, and the data are consistent with coupled unidirectional furosemide-sensitive influxes of Na+, K+ and Cl– with a ratio of 1 1 2. However, the net efflux of K+ performed by this transport system cannot be coupled to a ouabain-resistant net efflux of Na+ since the unidirectional ouabain-resistant efflux of Na+ was found to be negligible under physiological conditions. This latter conclusion was based on the fact that practically all the Na+ efflux appears to be ouabainsensitive and sufficient to balance the Na+ influx under such steady-state conditions. Therefore, it is suggested that the ouabain-resistant furosemide-sensitive transport system in growing cells performs a facilitated diffusion of K+ and Na+, driven by their respective concentration gradients: a net K+ efflux and a net Na+ influx. 相似文献
14.
The initial response of coleoptile cells to growth hormones and light is a rapid change in plasma-membrane polarization. We have isolated protoplasts from the cortex of maize (Zea mays L.) coleoptiles to study the electrical properties of their plasma membrane by the patch-clamp techniqueUsing the whole-cell configuration and cell-free membrane patches we could identify an H+-ATPase, hyperpolarizing the membrane potential often more negative than -150 mV, and a voltage-dependent, inward-rectifying K+ channel (unit conductance 5–7 pS) as the major membrane conductan-ces Potassium currents through this channel named CKC1in (for Coleoptile K
+ Channel inward rectifier) were elicited upon voltage steps negative to -80 mV, characterized by a half-activation potential of -112 mV. The kinetics of activation, well described by a double-exponential process, were strongly dependent on the degree of hyperpolarization and the cytoplasmic Ca2+ level. Whereas at nanomolar Ca2+ concentrations K+ currents increased with a t1/2=16 ms (at -180 mV), higher calcium levels slowed the activation process about fourto fivefoldUpon changes in the extracellular K+ concentration the reversal potential of the K+ channel followed the Nernst potential for potassium with a 56-mV shift for a tenfold increaseThe absence of a measurable conductance for Na+, Rb+, Cs+ and a permeability ratio PNH
4
+
/PK+ around 0.25 underlines the high selectivity of CKC1in for K+In contrast to Cs+, which at submillimolar concentration blocks the channel in a voltage-dependent manner, Rb+, often used as a tracer for K+, does not permeate this type of K+ channelThe lack of Rb+ permeability is unique with respect to other K+ transporters. Therefore, future molecular analysis of CKC1in, considered as a unique variation of plant inward rectifiers, might help to understand the permeation properties of K+ channels in general.Abbreviations CKC1in
Coleoptile K
+ Channel inward rectifier
- U
membrane voltage
- Iss
steady-state currents
- Itail
tail currents
Experiments were conducted in the laboratory of F.G. during the stay of RHas a guest professor sponsored by Special Project RAISA, subproject N2.1, paper N2155. 相似文献
15.
Steady-state fluxes of 86Rb+ (as a tracer for K+) were measured in Chinese hamster ovary cells (CHO-K1) and a mutant (CR1) defective in the regulation of cholesterol biosynthesis; the membrane cholesterol content of this mutant was varied by growing it on a range of cholesterol supplements to lipid-free medium (Sinensky, M. (1978) Proc. Natl. Acad. Sci. U.S. 75, 1247–1249).Analogous to previous findings in ascites tumor cells, 86Rb+ influx in the parent strain was differentiated into a ouabain-inhibitable ‘pump’ flux, furosemide-sensitive, chloride-dependent exchange diffusion, and a residual ‘leak’ flux.On the basis of this flux characterization, 86Rb+ pump and leak fluxes were measured in the mutant as a function of membrane cholesterol content. Pump and leak fluxes, when expressed per ml cell water, were independent of the cholesterol content of the mutant. Moreover, 86Rb+ fluxes in the mutant were equal to those in the parent strain. Our data imply that the flux behavior of K+ in the steady state is independent of the ordering of membrane lipid acyl chains. 相似文献
16.
Summary The specific activity of the Na+/K+/Cl– cotransporter was assayed by measuring the initial rates of furosemide-inhibitable86Rb+ influx and efflux. The presence of all three ions in the external medium was essential for cotransport activity. In cultured smooth muscle cells furosemide and bumetanide inhibited influx by 50% at 5 and 0.2 m, respectively. The dependence of furosemide-inhibitable86Rb+ influx on external Na+ and K+ was hyperbolic with apparentK
m values of 46 and 4mm, respectively. The dependence on Cl– was sigmoidal. Assuming a stoichiometry of 112 for Na+/K+/Cl–, aK
m of 78mm was obtained for Cl–. In quiescent smooth muscle cells cotransport activity was approximately equal to Na+ pump activity with each pathway accounting for 30% of total86Rb+ influx. Growing muscle cells had approximately 3 times higher cotransport activity than quiescent ones. Na+ pump activity was not significantly different in the gorwing and quiescent cultures. Angiotensin II (ANG) stimulated cotransport activity as did two calcium-transporting ionophores, A23187 and ionomycin. The removal of external Ca2+ prevented A23187, but not ANG, from stimulating the cotransporter. Calmodulin antagonists selectively inhibited86Rb+ influx via the cotransporter. Beta-adrenoreceptor stimulation with isoproterenol, like other treatments which increase cAMP, inhibited cotransport activity. Cultured porcine endothelial cells had 3 times higher cotransport activity than growing muscle cells. Calmodulin antagonists inhibited cotransport activity, but agents which increase cAMP or calcium had no effect on cotransport activity in the endothelial cells. 相似文献
17.
Summary Delta endotoxin, a 68 kilodalton protein isolated fromBacillus thuringiensis spp.Kurstaki, is a potent entomocidal agent that alters a K+ current across midgut tissue of many phytophagous insects. This toxin completely inhibited the vanadate-sensitive86Rb+ uptake and mimicked the vanadate-induced decrease in cytosolic pH in a cell line (CHE) originating fromManduca sexta embryonic tissue. The toxin also inhibited a K+-sensitive-ATPase in the plasma membranes isolated from these cells. Using the K+-sensitive-ATPase substratp-nitrophenyl phosphate, delta endotoxin was found to have aK
i
of 0.4 m. These data suggest that the toxin inhibits a K+-ATPase responsible for86Pb+ uptake in the CHE cells. The relationship between the toxin inhibition of K+-ATPase and toxin-altered K+ current is discussed. 相似文献
18.
Summary
86Rb+ fluxes have been measured in suspensions of vesicles prepared from the epithelium of toad urinary bladder. A readily measurable barium-sensitive, ouabain-insensitive component has been identified; the concentration of external Ba2+ required for half-maximal inhibition was 0.6mm. The effects of externally added cations on86Rb+ influx and efflux have established that this pathway is conductive, with a selectivity for K+, Rb+ and Cs+ over Na+ and Li+. the Rb+ uptake is inversely dependent on external pH, but not significantly affected by internal Ca2+ or external amiloride, quinine, quinidine or lidocaine. It is likely, albeit not yet certain, that the conductive Rb+ pathway is incorporated in basolateral vesicles oriented right-side-out. It is also not yet clear whether this pathway comprises the principle basolateral K+ channel in vivo, and that its properties have been unchanged during the preparative procedures. Subject to these caveats, the data suggest that the inhibition by quinidine of Na+ transport across toad bladder does not arise primarily from membrane depolarization produced by a direct blockage of the basolateral channels. It now seems more likely that the quinidine-induced elevation of intracellular Ca2+ activity directly blocks apical Na+ entry. 相似文献
19.
The primary leaves of kidney bean (Phaseolus vulgaris L.) openunder light and close in the dark by the deformation of thepulvinus resulting from diurnal distribution changes of K+,Cl, organic acid (or H+) and NO3. When Rb+ was added as a tracer of K+ to the seedlings throughtheir roots, it was transported to the pulvinus cells duringthe light period but not during the dark period. Transpirationoccurred vigorously in the light but almost stopped in the dark.We concluded that Rb+ absorbed by the roots was carried to thepulvinus by the transpiration stream. Phaseolus vulgaris L., pulvinus, Rb+, diurnal transport transpiration stream 相似文献
20.
Summary Cultured HeLa cells behave as ideal osmometers when subjected to hyperosmolar media, and show no volume regulatory behavior. In hypoosmolar solutions, cell swelling is not as great as predicted, and this is due largely to a loss of intracellular KCl. In hyperosmolar solutions there is a stimulation of the ouabain-insensitive but loop diuretic-sensitive86Rb+ (K+) pathway. Analysis of the K+, Na+ and Cl– dependency of this K+ flux pathway demonstrates that the increase is principally due to an increase in its maximal velocity (V
max). The sensitivity of this pathway to diuretic inhibition is unchanged in hyperosmolar media. Diuretic-sensitive86Rb+ (K+) efflux stimulated by hypertonicity shows no marked dependence on external K+. The K+ loss observed in hypoosmolar media is distinct from the K+ transport pathway stimulated by hyperosmolar media on the basis of its sensitivity to furosemide and anion dependence. 相似文献