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1.
Synchronization modulation (SM) electric field has been shown to effectively activate function of Na+/K+ pumps in various cells and tissues, including skeletal muscle cells, cardiomyocyte, monolayer of cultured cell line, and peripheral blood vessels. We are now reporting the in vivo studies in application of the SM electric field to kidney of living rats. The field-induced changes in the transepithelial potential difference (TEPD) or the lumen potential from the proximal convoluted tubules were monitored. The results showed that a short time (20 s) application of the SM electric field can significantly increase the magnitude of TEPD from 1–2 mV to about 20 mV. The TEPD is an active potential representing the transport current of the Na/K pumps in epithelial wall of renal tubules. This study showed that SM electric field can increase TEPD by activation of the pump molecules. Considering renal tubules, many active transporters are driven by the Na+ concentration gradient built by the Na+/K+ pumps, activation of the pump functions and increase in the magnitude of TEPD imply that the SM electric field may improve reabsorption functions of the renal tubules. 相似文献
2.
We previously described a model for the electrical transfer of excitation from one cell to the next which utilized the electric potential generated in the junctional cleft between the cells. Low-resistance connections between the cells were not used in the model, and it was assumed that the junctional membranes were excitable. This model was analyzed for the static case without capacitances and for the dynamic case in which capacitances were part of the circuit elements. For simplicity, the Na+ resistance (RNa), after a threshold potential was exceeded, was allowed to decrease exponentially (to 1% of its initial value) within 0·25–1·0 ms, and possible changes in the K+ resistance were ignored. In this paper, we have incorporated the Hodgkin-Huxley equations into the operation of the lumped membrane units for the electrical equivalent circuit of the cell membrane. The parameters varied are the membrane capacitances, resistances, maximum Na+ conductance (), and the radial cleft resistance (Rjc). We demonstrated that our model worked very well, i.e. the successful transfer of action potentials was achieved, with the membrane units following Hodgkin-Huxley dynamics for changes in gNa and gK. The calculations indicate that transmission is facilitated when the junctional units have a higher and a lower capacitance and when Rjc is elevated. Lowering the resistance of the junctional membrane units several fold, relative to the surface membrane units, also facilitated transmission; however, the absolute resistance of the junctional membrane was still well above the maximum value that would allow sufficient local-circuit current to flow to effect transmission. Thus, the electric field model provides an alternative means of cell-to-cell propagation between myocardial cells which is electrical in nature but does not require the presence of low-resistance connections between cells. 相似文献
3.
Georg Petschenka Anurag A. Agrawal 《Proceedings. Biological sciences / The Royal Society》2015,282(1818)
Insect resistance to plant toxins is widely assumed to have evolved in response to using defended plants as a dietary resource. We tested this hypothesis in the milkweed butterflies (Danaini) which have progressively evolved higher levels of resistance to cardenolide toxins based on amino acid substitutions of their cellular sodium–potassium pump (Na+/K+-ATPase). Using chemical, physiological and caterpillar growth assays on diverse milkweeds (Asclepias spp.) and isolated cardenolides, we show that resistant Na+/K+-ATPases are not necessary to cope with dietary cardenolides. By contrast, sequestration of cardenolides in the body (as a defence against predators) is associated with the three levels of Na+/K+-ATPase resistance. To estimate the potential physiological burden of cardenolide sequestration without Na+/K+-ATPase adaptations, we applied haemolymph of sequestering species on isolated Na+/K+-ATPase of sequestering and non-sequestering species. Haemolymph cardenolides dramatically impair non-adapted Na+/K+-ATPase, but had systematically reduced effects on Na+/K+-ATPase of sequestering species. Our data indicate that major adaptations to plant toxins may be evolutionarily linked to sequestration, and may not necessarily be a means to eat toxic plants. Na+/K+-ATPase adaptations thus were a potential mechanism through which predators spurred the coevolutionary arms race between plants and insects. 相似文献
4.
Francisco C. Herrera Arlec Rodriguez Ildemaro López Henny Weitzmann I. Perey Zanders 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1986,156(4):591-597
Summary Maintenance of intracellular ion contents and their relations to transmembrane potential were studied in tentacles ofCondylactis gigantea. Tentacles leached at 2°C in 10 mMK+ and 2 mM K+ artificial seawaters (10K ASW and 2K ASW) with and without 2 MM ouabain, and in 0K ASW, lost cell K+ and gained Na+. Rewarming to 25°C in 10K ASW resulted in a marked accumulation of K+ and extrusion of Na+ in tentacles leached in 10K ASW and in 0K ASW. Initial rate of Na+ extrusion was twice the initial rate of K+ accumulation, suggesting a pump coupling ratio of 2. In tentacles leached and rewarmed in 2K ASW, no net reaccumulation of K+ and little net extrusion of Na+ was observed; i.e., the pump just kept pace with the leaks. Ouabain inhibited K+ reaccumulation and Na+ extrusion. This effect was less marked in 10K ASW than in 2K ASW confirming, in anemone tentacles, the well documented ouabain-K+ antagonism observed in other systems. In no case did K
i
+
/K
0
+
equal Cl
0
–
/Cl
i
–
; therefore, the distribution of these ions did not fit a Donnan distribution. Transmembrane potential difference was –22±3 mV in 10K ASW at 25°C. It fitted a modified Nernst equation which includes the pump coupling ratio and a Na+ to K+ permeability ratio of 0.31.A moderately high permeability of the cell membrane to Na+, and a ouabain and K+ sensitive ion pump, exchanging 2 Na+ for 1 K+, appear to be responsible for the observed ionic distribution and transmembrane potential in anemone cells. 相似文献
5.
(Na+, K+)-ATPase (EC 3.6.1.3) from kidney is more sensitive to inhibition by vanadate than red cell (Na+,K+)-ATPase. The difference appears to be in the apparent affinities of the two enzymes for K+ and Na+ at sites where K+ promotes and Na+ opposes vanadate binding. As a result of Na+-K+ competition at these sites, reversal of vanadate inhibition was accomplished at lower Na+ concentrations in red cell than in kidney (Na+,K+)-ATPase. It is possible that vanadate could selectively regulate Na+ transport in the kidney. 相似文献
6.
Summary The mechanism of salt tolerance was studied using isolated internodal cells of the charophyteNitellopsis obtusa grown in fresh water. When 100 mM NaCl was added to artificial pond water (0.1 mM each of NaCl, KC1, CaCl2), no cell survived for more than one day. Within the first 30 minutes, membrane potential (Em) depolarized and membrane resistance (Rm) decreased markedly. Simultaneously, cytoplasmic Na+ increased and K+ decreased greatly. At steady state the increase in Na+ content was roughly equal to the decrease in K+ content. The Cl– content of the cytoplasm did not change. These results suggest that Na+ enters the cytoplasm by exchange with cytoplasmic K+. Both the entry of Na+ and the exit of K+ are assumed to be passive and the latter being caused by membrane depolarization. Vacuolar K+, Na+, and Cl– remained virtually constant, suggesting that rapid influx of Na+ from the cytoplasm did not occur.In 100 mM NaCl containing 10 mM CaCl2, membrane depolarization, membrane resistance decrease and changes in cytoplasmic [Na+] and [K+] did not occur, and cells survived for many days. When cells treated with 100 mM NaCl were transferred within 1 hour to 100 mM NaCl containing 10 mM CaCl2, Em decreased, Rm increased, cytoplasmic Na+ and K+ returned to their initial levels, and cells survived. Two possible mechanisms for the role of Ca2+ in salt tolerance inNitellopsis are discussed; one a reduction in plasmalemma permeability to Na+ and the other a stimulation of active Na+-extrusion. 相似文献
7.
The carbocyanine dye, diS-C3-(5) was used to quantitate the plasma membrane potential of the bullfrog corneal endothelium. It was shown that valinomycin hyperpolarized the endothelial cell and that in the presence of the ionophore the membrane potential largely reflected the K+ equilibrium potential. Using calibration curves constructed by changing medium K+ concentration in the presence of valinomycin, and nigericin and ouabain to abolish ion gradients and electrogenic pump activity, the cell membrane potential was calculated to be 28.6 ± 4.2 mV. The major source of this potential was a K+ diffusion potential, and the membrane Na+ conductance reduced the cell potential to less than the apparent K+ equilibrium potential of 51.5 ± 5.1 mV. About 20% of the cell potential could be ascribed to the rheogenic (Na++K+)-ATPase. 相似文献
8.
Effect of sodium on potassium fluxes at the cell membrane and vacuole membrane of red beet 总被引:3,自引:2,他引:1
Poole RJ 《Plant physiology》1971,47(6):731-734
Slices of red beet (Beta vulgaris) washed for 5 to 6 days are known to accumulate Na+ in preference to K+ from solutions containing both ions. The present work, using ion concentrations of 1.0 mm or less, with Ca2+ added in some cases, shows that Na+ strongly inhibits K+ influx at the cell membrane (plasmalemma) while K+ efflux is increased to a lesser extent. This result from compartmental analysis is confirmed by short (15-minute) influx experiments, which indicate an immediate inhibitory effect of Na+ on K+ influx at the cell membrane. It is concluded that cation selectivity, even when Na+ is favored for uptake, is primarily determined at the cell membrane. Nevertheless, a high level of K+ in the cytoplasm is maintained during Na+ influx, by an inhibition of K+ transfer to the vacuole. 相似文献
9.
Margaret R. Clark John C. Guatelli Anthony T. White Stephen B. Shohet 《生物化学与生物物理学报:生物膜》1981,646(3):422-432
Using the antibiotic Nystatin, we have developed a systematic method for the preparation of red blood cells with independently selected levels of intracellular Na+ concentrations and water content. Such cells provided an experimental model to study the effect of Na+/K+ pump stimulation on red cell water content. Even in initially dehydrated cells, stimulation of the Na+/K+ pump by elevated intracellular Na+ caused subsequent further loss of cell water. Cell water loss was reflected in decreased monovalent cation content per unit mass of hemoglobin and by a shift in the density distribution of the cell populations to higher densities on discontinuous Stractan gradients. We conclude that the 3 Naout+ : 2 Kin+ stoichiometry of the Na+/K+ pump results in a net desalting effect with increased pump activity. Under the conditions of these experiments, the cell appears to have no effective mechanism to compensate for a net loss of ions and water. 相似文献
10.
Interactions among Ca2+, Na+ and K+ in salinity toxicity: quantitative resolution of multiple toxic and ameliorative effects 总被引:5,自引:0,他引:5
Root elongation by wheat seedlings (Triticum aestivum
L. cv. Scout 66) was not inhibited by NaCl or KCl up to 130 mM in culture
solutions or by high Na+ (2 mg
g-1 FW) or K+ (4 mg
g-1 FW) in the root tissue, provided that
[Ca2+]>2 mM in the rooting medium. At [NaCl],
[KCl], or [mannitol] >250 mOs, root elongation was progressively
inhibited, irrespective of high [Ca2+]. In contrast,
shoot elongation was sensitive to any diminution of water potential, and
Ca2+ alleviated the toxicity only weakly. At solute
concentrations <250 mOs, the following interactions were observed.
Ca2+ alleviated Na+ and
K+ toxicity to roots by at least three separate
mechanisms. K+ was more toxic to roots than
Na+, but Na+ was more toxic
to shoots. Low levels of K+ relieved
Na+ toxicity, but low levels of
Na+ enhanced K+ toxicity.
Tissue concentrations of Na+ were reduced by
Ca2+ and K+ in the rooting
medium, and tissue concentrations of K+ were
enhanced by Ca2+ and Na+.
Several hypotheses relating to salinity toxicity can be evaluated, at least
for wheat seedlings. The osmoticant hypotheses (salinity intoxication
occurs because of diminished water potential) is true for shoots at all
salinity levels, but is true for roots only at high salinity. The
Ca2+-displacement hypothesis
(Na+ is toxic because it displaced
Ca2+ from the cell surface) is correct, but often of
minor importance. The K+-depletion hypothesis
(Na+ is toxic because it causes a loss of
K+ from plant tissues) is false. The
Cl--toxicity hypothesis (the apparent toxicity of
Na+ is induced by associated
Cl-) is false. The results indicate that, apart from
osmotic effects, high levels of Na+ in the rooting
medium and in the tissues are not toxic unless Ca2+
is also deficient, a condition probably leading to inadequate
compartmentation and excessive cytoplasmic accumulation. This study related
growth to ion activities at plasma-membrane surfaces. These activities were
computed by a Gouy-Chapman-Stern model then incorporated into non-linear
growth models for growth versus toxicants and ameliorants.Key
words: Calcium, potassium, salinity, sodium, toxicity
相似文献
11.
Verena Schneider Michaela L. Krieger Gerd Bendas Ulrich Jaehde Ganna V. Kalayda 《Journal of biological inorganic chemistry》2013,18(2):165-174
Decreased cellular accumulation of cisplatin is a frequently observed mechanism of resistance to the drug. Beside passive diffusion, several cellular proteins using ATP hydrolysis as an energy source are assumed to be involved in cisplatin transport in and out of the cell. This investigation aimed at clarifying the contribution of intracellular ATP as an indicator of energy-dependent transport to cisplatin resistance using the A2780 human ovarian adenocarcinoma cell line and its cisplatin-resistant variant A2780cis. Depletion of intracellular ATP with oligomycin significantly decreased cellular platinum accumulation (measured by flameless atomic absorption spectrometry) in sensitive but not in resistant cells, and did not affect cisplatin efflux in both cell lines. Inhibition of Na+,K+-ATPase with ouabain reduced platinum accumulation in A2780 cells but to a lesser extent compared with oligomycin. Western blot analysis revealed lower expression of Na+,K+-ATPase α1 subunit in resistant cells compared with sensitive counterparts. The basal intracellular ATP level (determined using a bioluminescence-based assay) was significantly higher in A2780cis cells than in A2780 cells. Our results highlight the importance of ATP-dependent transport, among other processes mediated by Na+,K+-ATPase, for cisplatin influx in sensitive cells. Cellular platinum accumulation in resistant cells is reduced and less dependent on energy sources, which may partly result from Na+,K+-ATPase downregulation. Our data suggest the involvement of other ATP-dependent processes beside those regulated by Na+,K+-ATPase. Higher basal ATP level in cisplatin-resistant cells, which appears to be a consequence of enhanced mitochondrial ATP production, may represent a survival mechanism established during development of resistance. 相似文献
12.
Summary Movements of K+, Na+, and Cl}- ions during transcellular osmosis were studied in internodal cells ofNitella flexilis. Much K+ was released from the endosmotic cell part, but only a little from the exosmotic cell part. The amount of K+ released depended on the osmotic gradient driving transcellular osmosis. Movement of Na+ was hardly detected. Cl}- was released in nearly the same amounts as K+. Release of K+ from the endosmotic cell half was stimulated remarkably by lowering the temperature from 20 to 1 °C, and also by lowering the internal osmotic pressure but inhibited by raising it.The dependence of K+ release on osmotic gradient, internal osmotic pressure and temperature can be explained by their effects on membrane depolarization and membrane resistance (Hayama
et al. 1978). We concluded thatP
K
remained unchanged, whileP
Cl
increased a great deal in the endosmotic cell part. 相似文献
13.
Na+/K+-ATPase plays a key role in the transport of Na+ throughout the nephron, but ageing appears to be accompanied by changes in the regulation and localization of the pump. In
the present study, we examined the effect of in vitro cell ageing on the transport of Na+ and K+ ions in opossum kidney (OK) cells in culture. Cells were aged by repeated passing, and Na+/K+-ATPase activity and K+ conductance were evaluated using electrophysiological methods. Na+K+-ATPase α1– and β1-subunit expression was quantified by Western blot techniques. Na+/H+ exchanger activity, changes in membrane potential, cell viability, hydrogen peroxide production and cellular proliferation
were determined using fluorimetric assays. In vitro cell ageing is accompanied by an increase in transepithelial Na+ transport, which results from an increase in the number of Na+/K+-ATPase α1- and β1-subunits, in the membrane. Increases in Na+/K+-ATPase activity were accompanied by increases in K+ conductance as a result of functional coupling between Na+/K+-ATPase and basolateral K+ channels. Cell depolarization induced by both KCl and ouabain was more pronounced in aged cells. No changes in Na+/H+ exchanger activity were observed. H2O2 production was increased in aged cells, but exposure for 5 days to 1 and 10 μM of H2O2 had no effect on Na+/K+-ATPase expression. Ouabain (100 nM) increased α1-subunit, but not β1-subunit, Na+/K+-ATPase expression in aged cells only. These cells constitute an interesting model for the study of renal epithelial cell
ageing. 相似文献
14.
Maximum ATPase activities in the cell wall fraction of English ryegrass (Lolium perenne L.) roots were stimulated by foru discrete millimole ratios of (Na++ K+); 40:0, 35:5, 5:35, and 0:40. The optimal pH for stimlation was found to be 6.5. Contrary to data in the literature, Mg2+ inhibited all stimulatory ratios of (Na++ K+) when plants were cultured on an adequate nutrient solution. When grown on a dilute solution, Mg2+ enhanced (Na++ K+)-stimulated ATPase activity in this membrane preparation. The single optimal combined concentration of (Na++ K+) for all stimulatory ratios was 40 MM. The ratios of (Na++ K+) which stimulated ATPase activity in the cell wall fraction varied with position along the root axis such that all rarely existed simultaneously nor did any exist in the terminal millimetre of the root. Both cell wall and microsomal fractions showed stimulation by (Na++ K+) at all the above ratios indicating the possible presence of plasma membrane fragments in both fractions. Only the 35:5 ratio was stimulations were found in the supernatant. Implications of ion-stimulated ATPase involvement in ion transport were drawn from the appearance of ATPase activity at a 40:0 ratio of (Na++ K+) and the disappearance of stimulations at 35:5, 5:35, and 0:40 ratios when plants were moved from a strong (35 mM total concentration) to a dilute (0.75 mM) nutrient solution. 相似文献
15.
The K+ content and the K+ flux were measured in the cell lines ME2 and MF2 isolated from plasmocytoma MOPC 173. Both cell lines were shown to have the same K+ content and the same K+ steady state flux per unit of surface area.In ME2 cells, no modification of the exchange movement was observed during contact inhibition. However, contact-inhibited cells exhibited an increased resistance to depletion, characterized by a lower K+ net movement.The (Na+ + K+)-ATPase measured in homogenates is poorly correlated to in vivo cation fluxes both because of the enhancement due, presumably, to the drop of K+ concentration on the cytoplasmic face of the membrane and because of losses during preparation which can be conspicuous, especially in contact-inhibited cells.The K+ net flux is considerably increased when the intracellular K+ level is reduced after preincubation of the cells in a K+-free medium. Thus, internal K+ seems to regulate the K+ influx. 相似文献
16.
Ning Xu 《The Journal of membrane biology》2013,246(1):75-90
In animal cells, the resting potential is established by the concentration gradients of sodium and potassium ions and the different permeabilities of the cell membrane to them. The large concentration gradients of sodium and potassium ions are maintained by the Na+/K+ pump. Under physiological conditions, the pump transports three sodium ions out of and two potassium ions into the cell per ATP hydrolyzed. However, unlike other primary or secondary active transporters, the Na+/K+ pump does not work at the equilibrium state, so the pumping ratio is not a thermodynamic property of the pump. In this article, I propose a dipole-charging model of the Na+/K+ pump to prove that the three Na+ to two K+ pumping ratio of the Na+/K+ pump is determined by the ratio of the ionic mobilities of potassium to sodium ions, which is to ensure the time constant τ and the τ-dependent processes, such as the normal working state of the Na+/K+ pump and the propagation of an action potential. Further, the concentration ratios of potassium ions outside and inside the cell to sodium ions inside and outside the cell are 0.3027 and 0.9788, respectively, and the sum of the potassium and sodium equilibrium potentials is ?30.3 mV. A comparative study on these constants is made for some marine, freshwater and terrestrial animals. These findings suggest that the pumping ratio of the Na+/K+ pump and the ion concentration ratios play a role in the evolution of animal cells. 相似文献
17.
Ehrlich cells actively accumulate neutral amino acids even if both the Na+ and K+ gradients are inverted. The seeming contradiction of this observation to the gradient hypothesis is, however, explained by the presence of a powerful electrogenic Na+ pump, which stongly raises the electrochemical potential gradient of Na+ under these conditions. Since the evidence of this pump has so far been found only during abnormal concentrations of alkali ions (low K+, high Na+) in these cells, the question arises whether the pump is equally powerful with completely normal cells, when the pump is not ‘needed’ for amino acid transport. Using the initial rate of uptake of the test amino acid (2-aminoisobutyrate) as a sensitive monitor of the electrical potential at constant cation distribution between cell and medium, a procedure has been devised to split the overall electrical potential into the diffusional and the pump component. With this procedure it could be shown that the electrogenic pump per se is most powerful in K+-depleted and Na+-rich cells but declines to a lower ‘resting’ value according as the electrolyte content of the cell approaches normality. A strong positive correlation between cellular Na+ content and the electrogenic pumping activity suggests that the intracellular activity of this ion regulates the rate of the electrogenic pump. The low activity of the pump under normal conditions may explain why the existance of this pump has rarely come to attention previously. 相似文献
18.
In leech P neurons the inhibition of the Na+-K+ pump by ouabain or omission of bath K+ leaves the membrane potential unaffected for a prolonged period or even induces a marked membrane hyperpolarization, although
the concentration gradients for K+ and Na+ are attenuated substantially. As shown previously, this stabilization of the membrane potential is caused by an increase
in the K+ conductance of the plasma membrane, which compensates for the reduction of the K+ gradient. The data presented here strongly suggest that the increased K+ conductance is due to Na+-activated K+ (KNa) channels. Specifically, an increase in the cytosolic Na+ concentration ([Na+]i) was paralleled by a membrane hyperpolarization, a decrease in the input resistance (Rin) of the cells, and by the occurrence of an outwardly directed membrane current. The relationship between Rin and [Na+]i followed a simple model in which the Rin decrease was attributed to K+ channels that are activated by the binding of three Na+ ions, with half-maximal activation at [Na+]i between 45 and 70 mM. At maximum channel activation, Rin was reduced by more than 90%, suggesting a significant contribution of the KNa channels to the physiological functioning of the cells, although evidence for such a contribution is still lacking. Injection
experiments showed that the KNa channels in leech P neurons are also activated by Li+. 相似文献
19.
The balance of K+, Na+, and Cl− fluxes across the cell membrane with the Na+/K+ pump, ion channels, and Na+K+2Cl− (NKCC) and Na+-Cl− (NC) cotransport was calculated to determine the mechanism of cell shrinkage in apoptosis. It is shown that all unidirectional
K+, Na+, and Cl− fluxes; the ion channel permeability; and the membrane potential can be found using the principle of the flux balance if
the following experimental data are known: K+, Na+, and Cl− concentrations in cell water; total Cl− flux; total K+ influx; and the ouabain-inhibited pump component of the Rb+(K+) influx. The change in different ionic pathways during apoptosis was estimated by calculations based on the data reported
in the preceded paper (Yurinskaya et al., 2010). It is found that cell shrinkage and the shift in ion balance in U937 cells
induced to apoptosis with 1 μM staurosporine occur due to the coupling of reduced pump activity with a decrease in the integral
permeability of Na+ channels, whereas K+ and Cl− channel permeability remains almost unchanged. Calculations show that only a small part of the total fluxes of K+, Na+, and Cl− account for the fluxes mediated by NKCC and NC cotransporters. Despite the importance of cotransport fluxes for maintaining
the nonequilibrium steady-state distribution of Cl−, they cannot play a significant role in apoptotic cell shrinkage because of their minority and cannot be revealed by inhibitors. 相似文献
20.
Summary The plasma membrane potential of Lettré cells has been determined with the optical indicator oxonol-V and found to be –57 mV at 37°C (range –20 to –80 mV depending on the physiological condition of the cells). Increasing extracellular K+ does not depolarize cells: even in the presence of 155mM K+ the potential is –41 mV; membrane potential is also insensitive to the chemical gradient of Na+,Mg2+, Ca2+ or Cl–. Ouabain depolarizes the cells; H+ efflux from cells is stimulated by extracellular Na+. We propose that in Lettré cells the plasma membrane potential is generated by electrogenic cation pumps. The balancing fluxes of Na+ and K+ are mainly through electroneutral cation exchanges (Na+/K+ and Na+/H+) and the magnitude of the potential is limited by organic anion leaks. Such a mechanism may operate in other biological membranes also. 相似文献