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1.
The anoxia-dependent elevation of cytosolic Ca2+ concentration, [Ca2+]cyt, was investigated in plants differing in tolerance to hypoxia. The [Ca2+]cyt was measured by fluorescence microscopy in single protoplasts loaded with the calcium-fluoroprobe Fura 2-AM. Imposition of
anoxia led to a fast (within 3 min) significant elevation of [Ca2+]cyt in rice leaf protoplasts. A tenfold drop in the external Ca2+ concentration (to 0.1 mM) resulted in considerable decrease of the [Ca2+]cyt shift. Rice root protoplasts reacted upon anoxia with higher amplitude. Addition of plasma membrane (verapamil, La3+ and EGTA) and intracellular membrane Ca2+-channel antagonists (Li+, ruthenium red and cyclosporine A) reduced the anoxic Ca2+-accumulation in rice. Wheat protoplasts responded to anoxia by smaller changes of [Ca2+]cyt. In wheat leaf protoplasts, the amplitude of the Ca2+-shift little depended on the external level of Ca2+. Wheat root protoplasts were characterized by a small shift of [Ca2+]cyt under anoxia. Plasmalemma Ca2+-channel blockers had little effect on the elevation of cytosolic Ca2+ in wheat protoplasts. Intact rice seedlings absorbed Ca2+ from the external medium under anoxic treatment. On the contrary, wheat seedlings were characterized by leakage of Ca2+. Verapamil abolished the Ca2+ influx in rice roots and Ca2+ efflux from wheat roots. Anoxia-induced [Ca2+]cyt elevation was high particularly in rice, a hypoxia-tolerant species. In conclusion, both external and internal Ca2+ stores are important for anoxic [Ca2+]cyt elevation in rice, whereas the hypoxia-intolerant wheat does not require external sources for [Ca2+]cyt rise. Leaf and root protoplasts similarly responded to anoxia, independent of their organ origin. 相似文献
2.
The change in cytosolic free concentration of calcium ([Ca2+]cyt) plays a key role in regulating apoptosis in animal cells. In our experiment, we tried to investigate the function of Ca2+ in programmed cell death (PCD) in tobacco (Nicotiana tobacum, cultivar BY-2) protoplasts induced by salt stress. An obvious increase in [Ca2+]cyt was observed a few minutes after treatment and the onset of a decrease in mitochondrial membrane potential (ΔΨm) was also observed before the appearance of PCD, pre-treatment of protoplasts with EGTA or LaCl3 effectively retarded the increase in [Ca2+]cyt, which was concomitant with the decrease in the percentage of cell death and higher ΔΨm, pre-treatment with cyclosporine A (CsA) also effectively retarded the increase in [Ca2+]cyt, the decrease in ΔΨm and the onset of PCD. All these results suggest that Ca2+ is a necessary element in regulating PCD and the increase in [Ca2+]cyt and the opening of mitochondrial permeability transition pore (MPTP) could promote each other in regulating PCD in tobacco protoplasts induced by salt stress.Jiusheng Lin and Yuan Wang-These authors contributed equally for this work. 相似文献
3.
Outward and inward currents, mainly carried by K+, were detected in protoplasts of pollen grains (PG) and pollen tubes (PT) of Lilium longiflorum Thunb. by using the whole-cell configuration of the patch-clamp technique. The outward K+ current (IK+
out) was similar in both protoplast types, while the inward K+ current (IK+
in) was higher in pollen tube protoplasts. In PT but not in PG protoplasts, inward K+ currents were already detectable at negative membrane voltages usually monitored in lily pollen. IK+
in consisted of a slow and a fast current component, as revealed by fitting a sum of two exponential functions to the time-dependent current. The contribution of the fast component to the total inward current was higher in PT than in PG protoplasts, which was even more evident at acidic pH of the external medium. Therefore, based on the measured characteristics, the IK+
in of PT protoplasts may contribute to the endogenous K+ currents surrounding a growing pollen tube.
Abbreviations: BS, bath solution; BTP, bis-Tris-propane; MES, 2-N-morpholinoethane sulfonic acid; Vact, activation voltage; VM, membrane voltage; Erev, reversal potential; IK+
in, inward K+ current; IK+
out, outward K+ current; PG, pollen grain; PT, pollen tube; PM, pipette medium 相似文献
4.
Juyou Wu Cong Jin Haiyong Qu Xueting Jiang Jun Wu Guohua Xu Shaoling Zhang 《Acta Physiologiae Plantarum》2012,34(3):969-975
Calcium (Ca2+) plays crucial roles in regulation of pollen tube growth. The influx of Ca2+ into the pollen tube is mediated by ion channels, and the density and activity of Ca2+ channels in pollen plasma membranes critically determines their electrical properties. In this report, using whole-cell and single-channel patch-clamping techniques, we investigated developmental changes of hyperpolarization-activated Ca2+ channel activity in pear (Pyrus pyrifolia) pollen and its relationship with pollen viability. For both pollen and pollen tubes, hyperpolarization-activated Ca2+ channels had the same conductance and cAMP sensitivity, indicating that they were the same channels. However, the Ca2+ current density in pollen tube protoplasts was greater than that in pollen protoplasts. Compared with day-3 flowers’ pollen, hyperpolarization-activated Ca2+ current density was significantly lower in day 0 and day 3 flowers’ pollen, which was consistent with the pollen germination and pollen tube growth, indicating that pollen protoplasts’ increased Ca2+ current density may have enhanced the pollen viability. During pollen tube elongation, pollen tube plasma membrane Ca2+ current density increased with increased length pollen tubes up to 300 μm. All of these results indicated that hyperpolarization-activated Ca2+ channel activity was associated with in pear pollen development and may have a causal link between Ca2+ channel activity and pollen viability. 相似文献
5.
Takayanagi T Hirokawa Y Yamamoto M Ohki T Fujiwara S Tsuzuki M 《Marine biotechnology (New York, N.Y.)》2007,9(1):56-65
Both coccolith-bearing cells (C-cells) and naked cells (N-cells) of the coccolithophorid Pleurochrysis haptonemofera can grow in salinities of more than 7‰ (about 20% of a “normal” sea water salinity [35‰]), with the highest growth rates
in salinities of more than 14‰. Microscopic observations of cells suspended in 100 mM NaCl (7‰) showed that, while N-cells
were swelling uniformly all over the cell surface, C-cells were bulging the plasma membrane from the hole of the coccosphere
at the apical (flagellar) pole of the cell. Effects of several cations and anions on the morphological change of C-cells under
hypoosmotic pressure were investigated. When 100 mM K+ was used, protoplasts were released from the coccosphere completely in almost all the cells. This phenomenon was shown with
K+ most effectively. The protoplasts could grow in the fresh medium and form the first coccolith within 9 h. 相似文献
6.
The electrical properties of protoplasts of the turgor pressure-regulating giant marine alga Valonia utricularis were investigated by using the patch-clamp technique. In the whole-cell configuration, large inward currents were elicited by negative-going voltage pulses. The time-dependent component was predominantly carried by Cl-, as revealed by 'tail current' analysis. When experiments were performed on protoplasts directly after mechanical release from the 'mother cell', small outward currents were additionally observed at membrane voltages more positive than ECl-. These outward currents disappeared to a large extent after treatment of the protoplasts with a mixture of cell wall-degrading enzymes. Plots of the chord conductance versus the clamped membrane voltage revealed that enzymatic treatment affected the gating properties. By fitting Boltzmann distributions to the data, a midpoint potential of + 5 +/- 5 mV (n = 7) was obtained in symmetrical Cl- solutions for mechanically released protoplasts. In contrast, protoplasts treated additionally with enzymes exhibited a midpoint potential of -13 +/- 5 mV (n = 8). By varying the external and internal Cl- concentration, gating was also shown to depend on the Cl- gradient across the plasmalemma both in enzymatically treated and untreated protoplasts. Plotting of the midpoint potential against the Nernst potential of Cl- rendered a slope less than 1 (0.70 and 0.64, respectively) indicating that gating did not strictly depend on the electrochemical Cl- gradient. The voltage- and Cl--dependence as well as inhibition experiments with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) suggested that the Cl- conductance of the membrane is dominated by the Valonia Anion Channel 1 (VAC1) described by Heidecker, M., Wegner, L.H., Zimmermann, U. 1999: A patch-clamp study of ion channels in proto-plasts prepared from the marine alga Valonia utricularis. J. Membrane Biol. 172:235-247. The relevance of the findings for membrane potential control and turgor regulation in V. utricularis as well as the general implications of the data for electrophysiological work on protoplasts (that are usually obtained by enzymatic digestion of plant tissue) are discussed. 相似文献
7.
In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K+-release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K+ channels as the major K+ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.Electronic Supplementary Material Supplementary material is available for this article at
Matthias Arend and Andrea Stinzing contributed equally to this work 相似文献
8.
La3+ ions are known to antagonize Ca2+ and are used as a Ca2+ channel blocker but little is known on the direct effects of La3+. Micromolar La3+ concentrations promoted root growth while higher concentrations were inhibitory. The uptake of La3+ in maize root protoplasts revealed a membrane binding component (0.14 and 0.44 pmol min–1 protoplast–1 for 100 and 1,000 M La3+) followed by a slower concentration and time-dependent uptake. Uptake was reduced by Ca2+, but had no substantial effect on other ions. La3+ shifted microtubule organization from random to parallel but caused aggregation of microfilaments. Our data suggest that La3+ is taken up into plant cells and affects growth via stabilization of the cytoskeleton. 相似文献
9.
Xiang Zhao Xiao-wei Zhao Hui He Yan-xiao Wang Xiao Zhang 《Journal of Plant Biology》2010,53(4):275-281
Our previous studies suggested the cross talk of nitric oxide (NO) with Ca2+ in regulating stomatal movement. However, its mechanism of action is not well defined in plant roots. In this study, sodium
nitroprusside (SNP, a NO donor) showed an inhibitory effect on the growth of wheat seedling roots in a dose-dependent manner,
which was alleviated through reducing extracellular Ca2+ concentration. Analyzing the content of Ca2+ and K+ in wheat seedling roots showed that SNP significantly promoted Ca2+ accumulation and inhibited K+ accumulation at a higher concentration of extracellular Ca2+, but SNP promoted K+ accumulation in the absence of extracellular Ca2+. To gain further insights into Ca2+ function in the NO-regulated growth of wheat seedling roots, we conducted the patch-clamped protoplasts of wheat seedling
roots in a whole cell configuration. In the absence of extracellular Ca2+, NO activated inward-rectifying K+ channels, but had little effects on outward-rectifying K+ channels. In the presence of 2 mmol L−1 CaCl2 in the bath solution, NO significantly activated outward-rectifying K+ channels, which was partially alleviated by LaCl3 (a Ca2+ channel inhibitor). In contrast, 2 mmol L−1 CaCl2 alone had little effect on inward or outward-rectifying K+ channels. Thus, NO inhibits the growth of wheat seedling roots likely by promoting extracellular Ca2+ influx excessively. The increase in cytosolic Ca2+ appears to inhibit K+ influx, promotes K+ outflux across the plasma membrane, and finally reduces the content of K+ in root cells. 相似文献
10.
Aminoacyl-tRNA synthetases (aaRSs) decipher the genetic code, covalently linking amino acids to cognate tRNAs, thus preparing substrates for the process of translation. Although aaRSs funtion primarily in translation and are localized in cytosol, mitochondria and chloroplasts there are many reports on their additional functions and subcellular destinations beyond translation. However, data on plant aaRSs are scarce. Initial analysis of amino acid sequence of Arabidopsis thaliana seryl-tRNA synthetase (SerRS) suggested that protein contains putative nuclear localization signals. GFP-localization experiments in transiently transformed epidermal onion cells and Arabidopsis protoplasts gave ambiguous results because in some cells SerRS appeared to be dually localized to both cytosol and nucleus. However, data obtained on transgenic lines expressing SerRS-TAP and GFP-SerRS revealed exclusive cytosolic location of SerRS. Subcellular distribution of SerRS did not change during stress. Cytosolic Arabidopsis SerRS was expressed and purified. The enzyme efficiently aminoacylated eukaryotic and bacterial tRNAsSer, that are structurally very different. Given the fact that the same behavior was previously shown for monocot maize SerRS, it seems that plant SerRSs exhibit unusually broad tRNASer specificity, unlike SerRSs from other organisms. Possible functional implications of this unique characteristic of plant SerRSs are discussed. 相似文献
11.
The effects of oligomycin on photosynthesis and respiration in relation to ATP production in chloroplasts and mitochondria
were investigated in protoplasts isolated from the detached pea (Pisum sativum L cv. Iłowiecki.) and barley (Hordeum vulgare L. cv. Gunilla) leaves treated 5 mM Pb(NO3)2. The oligomycin (OM), an inhibitor of oxidative phosphorylation at 0.1 μM concentration caused the inhibition of photosynthesis
rate in the protoplasts from both the control and the Pb-treated pea leaves. The respiration rate and ATP/ADP ratio in the
protoplasts and the activity of ATPase in mitochondria, were also diminished in the control protoplasts. These effects were
not observed in the protoplasts and mitochondria isolated from the Pb-treated leaves. Oligomycin, an inhibitor of photophosphorylation
at 10 μM concentration decreased ATPase activity in chloroplasts from both the control and the Pb- treated leaves.
Using the method of rapid fractionation of barley protoplasts it was shown that the ATP/ADP ratio in the mitochondria from
Pb-treated leaves was largely suppressed (from 1.8 to 0.4) by OM under nonphotorespiratory conditions (high CO2), whereas under photorespiratory conditions (low CO2) this ratio was high (5.3) and under OM decreased less (to 3.1).
Our results indicate that oligomycin, in organelle isolated from Pb-treated leaves, had no inhibitory effect on the mitochondrial
ATPase, whereas it inhibited chloroplasts ATPase. We suggest that Pb ions affected the catalytic cycle and/or conformational
changes of ATPase in pea chloroplasts differently than in mitochondria. The differences in Pb responses may reflect fine mechanisms
for the regulation of ATP production in the plant cells under stress conditions. 相似文献
12.
Bertini I Felli IC Kümmerle R Luchinat C Pierattelli R 《Journal of biomolecular NMR》2004,30(3):245-251
13C-13C NOESY experiments were performed under long mixing time conditions on reduced human superoxide dismutase (32 kDa, 15N, 13C and 70% 2H labeled). 13C-13C couplings were successfully eliminated through post-processing of in-phase-anti-phase (IPAP) data. It appears that at mixing time m of 3.0 s the spin diffusion mechanism allows the detection of 96% of the two-bond correlations involving C and C. The interpretation was confirmed by simulations. This approach broadens the range of applicability of 13C-13C NOESY spectroscopy. 相似文献
13.
Significant resolution improvement in 13C,13C-TOCSY spectra of uniformly deuterated and 13C, 15N-labeled protein and 13C,15N-labeled RNA samples is achieved by introduction of multiple-band-selective 13C-homodecoupling applied simultaneously with 1H- or 2H- and 15N-decoupling at all stages of multidimensional experiments including signal acquisition period. The application of single, double or triple band-selective 13C-decoupling in 2D-[13C,13C]-TOCSY experiments during acquisition strongly simplifies the homonuclear splitting pattern. The technical aspects of complex multiple-band homonuclear decoupling and hardware requirements are discussed. The use of this technique (i) facilitates the resonance assignment process as it reduces signal overlap in homonuclear 13C-spectra and (ii) possibly improves the signal-to-noise ratio through multiplet collapse. It can be applied in any 13C-detected experiment. 相似文献
14.
This study is a comparison of four methods to induce calli formation in a protoplast culture of Chrysanthemum indicum. Culture in liquid medium (17.6 calli/105 protoplasts) was preferable to culture in solid agarose beads, although the efficiency of the latter could be improved by
layering them on glass beads (12.5 vs. 0.83 calli/105 protoplasts). Culture of protoplasts on moistened filter paper was unsuccessful. In the liquid media, microcalli and calli
were induced efficiently and easily after 6 weeks. These effects may be explained by reduced toxicity due to cell breakdown
and improved aeration. 相似文献
15.
A system for plant regeneration from protoplasts of the moss, Atrichum undulatum (Hedw.) P. Beauv. in vitro, is first reported. Viable protoplasts were isolated at about 9 × 105 protoplasts g−1 fresh weight from 10 to 18 days protonemata. For regeneration of protoplasts, viable protoplasts were cultured in liquid–solid medium containing surface liquid medium MS (0.4 M mannitol) and subnatant solid medium Benecke (0.3 M mannitol) at 20 °C under a 16-h photoperiod white light after 12 h preculture in darkness at 20 °C. The great majority of protoplasts follow a regenerative sequence: formation of asymmetric cells in 2–3 days; division of the asymmetric cells to 2–3 cells in 4–5 days, and further develop to produce a new chloronemal filament in 15 days. Juvenile gametophyte can be visible in 20 days. The plating ratio of cell cluster regenerated from protoplasts reaches up to 45%. Transient expression experiments indicate the electroporation uptake of DNA is possible. 相似文献
16.
C. Derrick QuarlesJr. R. Kenneth Marcus Julia L. Brumaghim 《Journal of biological inorganic chemistry》2011,16(6):913-921
Competitive binding of Fe3+, Cr3+, and Ni2+ to transferrin (Tf) was investigated at various physiological iron to Tf concentration ratios. Loading percentages for these
metal ions are based on a two M
n+ to one Tf (i.e., 100% loading) stoichiometry and were determined using a particle beam/hollow cathode–optical emission spectroscopy
(PB/HC-OES) method. Serum iron concentrations typically found in normal, iron-deficient, iron-deficient from chronic disease,
iron-deficient from inflammation, and iron-overload conditions were used to determine the effects of iron concentration on
iron loading into Tf. The PB/HC-OES method allows the monitoring of metal ions in competition with Fe3+ for Tf binding. Iron-overload concentrations impeded the ability of chromium (15.0 μM) or nickel (10.3 μM) to load completely
into Tf. Low Fe3+ uptake by Tf under iron-deficient or chronic disease iron concentrations limited Ni2+ loading into Tf. Competitive binding kinetic studies were performed with Fe3+, Cr3+, and Ni2+ to determine percentages of metal ion uptake into Tf as a function of time. The initial rates of Fe3+ loading increased in the presence of nickel or chromium, with maximal Fe3+ loading into Tf in all cases reaching approximately 24%. Addition of Cr3+ to 50% preloaded Fe3+–Tf showed that excess chromium (15.0 μM) displaced roughly 13% of Fe3+ from Tf, resulting in 7.6 ± 1.3% Cr3+ loading of Tf. The PB/HC-OES method provides the ability to monitor multiple metal ions competing for Tf binding and will
help to understand metal competition for Tf binding. 相似文献
17.
Kirti Dhingra Petra Fousková Goran Angelovski Martin E. Maier Nikos K. Logothetis Éva Tóth 《Journal of biological inorganic chemistry》2008,13(1):35-46
Two new bismacrocyclic Gd3+ chelates containing a specific Ca2+ binding site were synthesized as potential MRI contrast agents for the detection of Ca2+ concentration changes at the millimolar level in the extracellular space. In the ligands, the Ca2+-sensitive BAPTA-bisamide central part is separated from the DO3A macrocycles either by an ethylene (L1) or by a propylene (L2) unit [H4BAPTA is 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid; H3DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid]. The sensitivity of the Gd3+ complexes towards Ca2+ and Mg2+ was studied by 1H relaxometric titrations. A maximum relaxivity increase of 15 and 10% was observed upon Ca2+ binding to Gd2L1 and Gd2L2, respectively, with a distinct selectivity of Gd2L1 towards Ca2+ compared with Mg2+. For Ca2+ binding, association constants of log K = 1.9 (Gd2L1) and log K = 2.7 (Gd2L2) were determined by relaxometry. Luminescence lifetime measurements and UV–vis spectrophotometry on the corresponding Eu3+ analogues proved that the complexes exist in the form of monohydrated and nonhydrated species; Ca2+ binding in the central part of the ligand induces the formation of the monohydrated state. The increasing hydration number
accounts for the relaxivity increase observed on Ca2+ addition. A 1H nuclear magnetic relaxation dispersion and 17O NMR study on Gd2L1 in the absence and in the presence of Ca2+ was performed to assess the microscopic parameters influencing relaxivity. On Ca2+ binding, the water exchange is slightly accelerated, which is likely related to the increased steric demand of the central
part leading to a destabilization of the Ln–water binding interaction.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
19.
Govind Ragupathi Payal Damani Geeta Srivastava Om Srivastava Steven J. Sucheck Yoshi Ichikawa Philip O. Livingston 《Cancer immunology, immunotherapy : CII》2009,58(9):1397-1405
Sialyl Lewisa (sLea), also termed CA19-9 antigen, is recognized by murine mAb19-9 and is expressed on the cancer cell surface as a glycolipid
and as an O-linked glycoprotein. It is highly expressed in a variety of gastrointestinal epithelial malignancies including
colon cancer and pancreatic cancer, and in breast cancer and small cell lung cancer, but has a limited expression on normal
tissues. sLea is known to be the ligand for endothelial cell selectins suggesting a role for sLea in cancer metastases and adhesion. For these reasons, sLea may be a good target for antibody mediated immunotherapy including monoclonal antibodies and tumor vaccines. However, sLea is structurally similar to sLex and other blood group related carbohydrates which are widely expressed on polymorphonucleocytes and other circulating cells,
raising concern that immunization against sLea will induce antibodies reactive with these more widely expressed autoantigens. We have shown previously both in mice and
in patients that conjugation of a variety of carbohydrate cancer antigen to keyhole limpet hemocyanin (KLH) and administration
of this conjugate mixed with saponin adjuvants QS-21 or GPI-0100 are the most effective methods for induction of antibodies
against these cancer antigens. We describe here for the first time the total synthesis of pentenyl glycoside of sLea hexasaccharide and its conjugation to KLH to construct a sLea-KLH conjugate. Groups of five mice were vaccinated subcutaneously four times over 6 weeks. Sera were tested against sLea-HSA by ELISA and against sLea positive human cell lines adenocarcinoma SW626 and small cell lung cancer (SCLC) DMS79 by FACS. As expected, mice immunized
with unconjugated sLea plus GPI-0100 or unconjugated sLea mixed with KLH plus GPI-0100 failed to produce antibodies against sLea. However, mice immunized with sLea-KLH conjugate without GPI-0100 produced low levels of antibodies and mice immunized with sLea-KLH plus GPI-0100 produced significantly higher titer IgG and IgM antibodies against sLea by ELISA. These antibodies were highly reactive by FACS and mediated potent complement mediated cytotoxicity against sLea positive SW626 and DMS79 cells. They showed no detectable cross reactivity against a series of other blood group-related
antigens, including Ley, Lex, and sLex by dot blot immune staining. This vaccine is ready for testing as an active immunotherapy for treating sLea positive cancer in clinical settings.
Govind Ragupathi and Philip O. Livingston are paid consultants and shareholders in MabVax Therapeutics, Inc., San Diego, CA
92121. The sLea vaccine is licensed to MabVax. 相似文献
20.
Ca2+ concentration in retinal photoreceptor rod outer segment (OS) strongly affects the generator potential kinetics and the receptor
light adaptation. The response to intense light stimuli delivered in the dark produce potential changes exceeding 40 mV: since
the Ca2+ extrusion in the OS is entirely controlled by the Na+:Ca2+, K+ exchanger, it is important to assess how the exchanger ion transport rate is affected by the voltage and, in general, by
intracellular factors. It is indeed known that the cardiac Na+:Ca2+ exchanger is regulated by Mg-ATP via a still unknown metabolic pathway. In the present work, the Na+:Ca2+, K+ exchanger regulation was investigated in isolated OS, recorded in whole-cell configuration, using ionic conditions that activated
maximally the exchanger in both forward and reverse mode. In all species examined (amphibia: Rana esculenta and Ambystoma mexicanum; reptilia: Gecko gecko), the forward (reverse) exchange current increased about linearly for negative (positive) voltages and exhibited outward
(inward) rectification for positive (negative) voltages. Since hyperpolarisation increases Ca2+ extrusion rate, the recovery of the dark level of Ca2+ (and, in turn, of the generator potential) after intense light stimuli results accelerated. Mg-ATP increased the size of
forward and reverse exchange current by a factor of ∼2.3 and ∼2.6, respectively, without modifying their voltage dependence.
This indicates that Mg-ATP regulates the number of active exchanger sites and/or the exchanger turnover number, although via
an unknown mechanism.
Proceedings of the XVIII Congress of the Italian Society of Pure and Applied Biophysics (SIBPA), Palermo, Sicily, September
2006. 相似文献