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1.
Palytoxin (PTX) inhibits the (Na(+) + K+)-driven pump and simultaneously opens channels that are equally permeable to Na+ and K+ in red cells and other cell membranes. In an effort to understand the mechanism by which PTX induces these fluxes, we have studied the effects of PTX on: 1) K+ and Na+ occlusion by the pump protein; 2) phosphorylation and dephosphorylation of the enzyme when a phosphoenzyme is formed from ATP and from P(i); and 3) p-nitro phenyl phosphatase (p-NPPase) activity associated with the (Na+, K+)-ATPase. We have found that palytoxin 1) increases the rate of deocclusion of K+(Rb+) in a time- and concentration-dependent manner, whereas Na+ occluded in the presence of oligomycin is unaffected by the toxin; 2) makes phosphorylation from P(i) insensitive to K+, and 3) stimulates the p-NPPase activity. The results are consistent with the notion that PTX produces a conformation of the Na+, K(+)-pump that resembles the one observed when ATP is bound to its low-affinity binding site. Further, they suggest that the channels that are formed by PTX might arise as a consequence of a perturbation in the ATPase structure, leading to the loss of control of the outside "gate" of the enzyme and hence to an uncoupling of the ion transport from the catalytic function of the ATPase. 相似文献
2.
A triple mutant strain of Saccharomyces cerevisiae lacking its own Na+-ATPases and Na+/H+ antiporters (enal-4delta nha1delta nhx1delta) was used for the expression of the Oryza sativa NHX1 gene encoding a putative vacuolar Na+/H+ exchanger. Upon expression in yeast cells, the OsNhx 1p is not a transport system specific only for sodium cations but it has a broad substrate specificity for at least four alkali metal cations (Na+, Li+, K+ and Rb+) and is able to substitute for the endogenous yeast ScNhx1 antiporter. Its activity contributes to sequestration of alkali metal cations in intracellular vesicles. 相似文献
3.
Mechanism of luminal Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> action on the vacuolar slowly activating channels 总被引:2,自引:0,他引:2
The non-selective slow vacuolar (SV) channel can dominate tonoplast conductance, making it necessary to tightly control its activity. Applying the patch-clamp technique to vacuoles from sugar beet (Beta vulgaris L.) taproots we studied the effect of divalent cations on the vacuolar side of the SV channel. Our results show that the SV channel has two independent binding sites for vacuolar divalent cations, (i) a less selective one, inside the channel pore, binding to which impedes channel conductance, and (ii) a Ca2+-selective one outside the membrane-spanning part of the channel protein, binding to which stabilizes the channels closed conformations. Vacuolar Ca2+ and Mg2+ almost indiscriminately blocked ion fluxes through the open channel pore, decreasing measured single-channel current amplitudes. This low-affinity block displays marked voltage dependence, characteristic of a permeable blocker. Vacuolar Ca2+—with a much higher affinity than Mg2+—slows down SV channel activation and shifts the voltage dependence to more (cytosol) positive potentials. A quantitative analysis results in a model that exactly describes the Ca2+-specific effects on the SV channel activation kinetics and voltage gating. According to this model, multiple (approximately three) divalent cations bind with a high affinity at the luminal interface of the membrane to the channel protein, favoring the occupancy of one of the SV channels closed states (C2). Transition to another closed state (C1) diminishes the effective number of bound cations, probably due to mutual repulsion, and channel opening is accompanied by a decrease of binding affinity. Hence, the open state (O) is destabilized with respect to the two closed states, C1 and C2, in the presence of Ca2+ at the vacuolar side. The specificity for Ca2+ compared to Mg2+ is explained in terms of different binding affinities for these cations. In this study we demonstrate that vacuolar Ca2+ is a crucial regulator to restrict SV channel activity to a physiologically meaningful range, which is less than 0.1% of maximum SV channel activity.Abbreviation SV Slow vacuolar 相似文献
4.
The thermostabilities of Fe2+ ligation in rubredoxins (Rds) from the hyperthermophile Pyrococcus furiosus (Pf) and the mesophiles Clostridium pasteurianum (Cp) and Desulfovibrio vulgaris (Dv) were compared. Residue 44 forms an NH...S(Cys) hydrogen bond to one of the cysteine ligands to the [Fe(SCys)4] site, and substitutions at this location affect the redox properties of the [Fe(SCys)4] site. Both Pf Rd and Dv Rd have an alanine residue at position 44, whereas Cp Fd has a valine residue. Wild-type proteins were examined along with V44A and A44V exchange mutants of Cp and Pf Rds, respectively, in order to assess the effects of the residue at position 44 on the stability of the [Fe(SCys)4] site. Stability of iron ligation was measured by temperature-ramp and fixed-temperature time course experiments, monitoring iron release in both the absence and presence of more thiophilic metals (Zn2+, Cd2+) and over a range of pH values. The thermostability of the polypeptide fold was concomitantly measured by fluorescence, circular dichroism, and 1H NMR spectroscopies. The A44V mutation strongly lowered the stability of the [FeII(SCys)4] site in Pf Rd, whereas the converse V44A mutation of Cp Rd significantly raised the stability of the [FeII(SCys)4] site, but not to the levels measured for wild-type Dv Rd. The region around residue 44 is thus a significant contributor to stability of iron coordination in reduced Rds. This region, however, made only a minor contribution to the thermostability of the protein folding, which was found to be higher for hyperthermophilic versus mesophilic Rds, and largely independent of the residue at position 44. These results, together with our previous studies, show that localized charge density, solvent accessibility, and iron site/backbone interactions control the thermostability of the [Fe(SCys)4] site. The iron site thermostability does make a minor contribution to the overall Rd thermostability. From a mechanistic standpoint, we also found that attack of displacing ions (H+, Cd2+) on the Cys42 sulfur ligand at the [Fe(SCys)4] site occurs through the V8 side and not the V44 side of the iron site.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00775-004-0525-4Abbreviations BPS bathophenanthroline sulfonate, sodium salt - Cp Rd (Pf Rd, Dv Rd) recombinant rubredoxin from Clostridium pasteurianum (Pyrococcus furiosus, Desulfovibrio vulgaris) - HEPES hydroxyethylpiperazineethanesulfonic acid - MES morpholinoethanesulfonic acid - Tris tris(hydroxymethyl)aminomethane - wt wild-type - ZnRd recombinant rubredoxin containing a [Zn(SCys)4] site 相似文献
5.
Using a microfluidic volume sensor, we studied the dynamic effects of Hg2+ on hypotonic stress-induced volume changes in CHO cells. A hypotonic challenge to control cells caused them to swell but did not evoke a significant regulatory volume decrease (RVD). Treatment with 100 muM HgCl2 caused a substantial increase in the steady-state volume following osmotic stress. Continuous hypotonic challenge following a single 10-min exposure to HgCl2 produced a biphasic volume increase with a steady-state volume 100% larger than control cells. Repeated hypotonic challenges to cells exposed once to Hg2+ resulted in a sequential approach to the same steady-state volume. Stimulation after reaching steady state caused a reduction in peak cell volume. Repeated stimulation was different than continuous stimulation resulting in a more rapid approach to steady state. Substituting extracellular Na+ with impermeant NMDG+ in the hypotonic solution produced a rapid RVD-like volume decrease and eliminated the Hg2+-induced excess swelling. The volume decrease in the presence of Hg2+ was inhibited by tetraethylammonium and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium, blockers of K+ and Cl(-) channels, respectively, suggesting that part of the Hg2+ effect was increasing NaCl influx over KCl efflux. The presence of multiple phases of steady-state volume and their sensitivity to the stimulation history suggests that factors beyond solute fluxes, such as modification of mechanical stress within the cytoskeleton also plays a role in the response to hypotonic stress. 相似文献
6.
Gusev GP Ivanova TI 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2003,173(5):429-435
The present study was designed to evaluate the role of protein phosphatases in regulation of sodium transport in the marsh frog erythrocytes using 22Na as a tracer. For this purpose the cells were treated with several known inhibitors of protein phosphatases. In standard isotonic medium, exposure of the cells to 10 mmol l(-1) NaF, 20 nmol l(-1) calyculin A or 0.1 mmol l(-1) cantharidin resulted in a significant (1.7-fold) increase in unidirectional ouabain-insensitive Na+ influx. The Na+ influx in frog red cells was progressively activated as the medium osmolality was increased by addition of 100, 200 or 300 mmol l(-1) sucrose to standard isotonic medium. The stimulatory effect of protein phosphatase blockers on Na+ influx was much higher in hypertonic medium containing 100 or 200 mmol l(-1) sucrose than that in isotonic medium. Stimulation of Na+ transport enhanced with increasing concentrations of calyculin A, and half-maximal activation (EC50) was obtained at 16 nmol l(-1). However, Na+ influx induced by strong hypertonic treatment (+300 mmol l(-1) sucrose) was not altered further in the presence of protein phosphatase inhibitors. The changes in Na+ influx evoked by protein phosphatase inhibitors and hypertonic treatment were associated with a rise in the intracellular Na+, but not K+, content. Enhancement in Na+ influx after addition of protein phosphatase blockers to cell suspension in isotonic or hypertonic media was almost completely inhibited by Na+/H+ exchange inhibitors, amiloride and ethyl-isopropyl-amiloride. The basal Na+ influx in frog erythrocytes in isotonic medium was relatively low (1.7 mmol/l cells/h) and not affected by 1 mmol l(-1) amiloride. Thus, the data obtained clearly indicate that Na+/H+ exchanger in the marsh frog red blood cells is under tight regulatory control, in all likelihood via protein phosphatases of types PP-1 and PP-2A. 相似文献
7.
The work describes the original application of biosensors based on enzyme immobilised by electropolymerisation to heavy metal determination. An inhibition detection scheme has been employed for detecting Hg2+ by an established glucose biosensor based on glucose oxidase immobilised in poly-o-phenylenediamine. The investigated enzymatic inhibition appears reversible and mixed, in agreement with data for the enzyme in solution. A low response time (<2 min) and a rapid recovery of response by EDTA seem the most interesting characteristics of the proposed biosensor at the present stage of development, along with the well known easy preparation of this kind of biosensors. The occurrence of a high response also for Cu2+ opens the possibility to apply the biosensor in total toxic metal content determination. 相似文献
8.
Capo JA Mandal PK Eyyunni S Ahearn GA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2005,175(1):13-20
The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether 65Zn2+ transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10–15 s and approached equilibrium by 120 s. In the absence of sodium, 65Zn2+ influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 M ATP (increase in Km and Jmax) and inhibited by the simultaneous presence of 150 mol l–1 ATP+250 mol l–1 vanadate (decrease in both Km and Jmax). In the absence of ATP, 65Zn2+ influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l–1) and exhibited a Hill Coefficient of 4.03±1.14, consistent with the exchange of 3 Na+/1Zn2+. Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle 65Zn2+ influx by both the ATP-dependent (Ki=205 nmol l–1 Ca2+) and sodium-dependent (Ki=2.47 mol l–1 Ca2+) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.Communicated by: I.D. Hume 相似文献
9.
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
10.
The toxic effect of Pb2+ has been studied in eukaryotic cells by using Tetrahymena as a target. The maximum power (P
m) and the growth rate constant (k) were determined, which showed that values of P
m and k were linked to the concentration (C) of Pb2+. The addition of Pb2+ caused a decrease of the maximum heat production and growth rate constant, indicating that Tetrahymena growth was inhibited in the presence of Pb2+, and Pb2+ took part in the metabolism of cells. From micrographs, morphological changes of Tetrahymena were observed with addition of Pb2+, indicating that the toxic effect of Pb2+ derived from destroying the membrane of surface of Tetrahymena. According to the thermogenic curves and photos of Tetrahymena under different conditions, it is clear that metabolic mechanism of Halobacterium halobium R1 growth has been changed with the addition of Pb2+. 相似文献
11.
Aertsen A Masschalck B Wuytack EY Michiels CW 《Extremophiles : life under extreme conditions》2003,7(6):499-504
Sodium concentrations as low as 2 mM exerted a significant protective effect on the high-pressure inactivation (160–210 MPa) of Rhodotorula rubra at pH 6.5, but not on two other yeasts tested (Shizosaccharomyces pombe and Saccharomyces cerevisiae). A piezoprotective effect of similar magnitude was observed with Li+ (2 and 10 mM), and at elevated pH (8.0–9.0), but no effect was seen with K+, Ca2+, Mg2+, Mn2+, or NH4
+. Intracellular Na+ levels in cells exposed to low concentrations of Na+ or to pH 8.0–9.0 provided evidence for the involvement of a plasma membrane Na+/H+ antiporter and a correlation between intracellular Na+ levels and pressure resistance. The results support the hypothesis that moderate high pressure causes indirect cell death in R. rubra by inducing cytosolic acidification.Communicated by K. Horikoshi 相似文献
12.
Mutoh H Yoshino M 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2004,174(1):21-28
The Ca2+-conducting pathway of myocytes isolated from the cricket lateral oviduct was investigated by means of the whole-cell patch clamp technique. In voltage-clamp configuration, two types of whole cell inward currents were identified. One was voltage-dependent, initially activated at –40 mV and reaching a maximum at 10 mV with the use of 140 mM Cs2+-aspartate in the patch pipette and normal saline in the bath solution. Replacement of the external Ca2+ with Ba2+ slowed the current decay. Increasing the external Ca2+ or Ba2+ concentration increased the amplitude of the inward current and the current–voltage (I–V) relationship was shifted as expected from a screening effect on negative surface charges. The inward current could be carried by Na+ in the absence of extracellular Ca2+. Current carried by Na+ (I
Na) was almost completely blocked by the dihydropyridine Ca2+ channel antagonist, nifedipine, suggesting that the I
Na is through voltage-dependent L-type Ca2+ channels. The other inward current is voltage-independent and its I–V relationship was linear between –100 mV to 0 mV with a slight inward rectification at more hyperpolarizing membrane potentials when 140 mM Cs+-aspartate and 140 mM Na+-gluconate were used in the patch pipette and in the bath solution, respectively. A similar current was observed even when the external Na+ was replaced with an equimolar amount of K+ or Cs+, or 50 mM Ca2+ or Ba2+. When the osmolarity of the bath solution was reduced by removing mannitol from the bath solution, the inward current became larger at negative potentials. The I–V relationship for the current evoked by the hypotonic solution also showed a linear relationship between –100 mV to 0 mV. Bath application of Gd3+ (10 M) decreased the inward current activated by membrane hyperpolarization. These results clearly indicate that the majority of current activated by a membrane hyperpolarization is through a stretch-activated Ca2+-permeable nonselective cation channel (NSCC). Here, for the first time, we have identified voltage-dependent L-type Ca2+ channel and stretch-activated Ca2+-permeable NSCCs from enzymatically isolated muscle cells of the cricket using the whole-cell patch clamp recording technique.Abbreviations
I
Ca
Ca2+ current
-
I
Na
Na+ current
-
I–V
current–voltage
-
NSCC
nonselective cation channel
Communicated by G. Heldmaier 相似文献
13.
14.
Removal of heavy metals (Pb2+, Zn2+) from aqueous solution by dried biomass of Spirulina sp. was investigated. Spirulina rapidly adsorbed appreciable amount of lead and zinc from the aqueous solutions within 15 min of initial contact with the
metal solution and exhibited high sequestration of lead and zinc at low equilibrium concentrations. The specific adsorption
of both Pb2+ and Zn2+ increased at low concentration and decreased when biomass concentration exceeded 0.1 g l−1. The binding of lead followed Freundlich model of kinetics where as zinc supported Langmuir isotherm for adsorption with
their r
2
values of 0.9659 and 0.8723 respectively. The adsorption was strongly pH dependent as the maximum lead biosorption occurred
at pH 4 and 10 whereas Zn2+ adsorption was at pH 8 and 10. 相似文献
15.
Bucking C Wood CM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(3):349-360
A diet containing an inert marker (ballotini beads, quantified by X-radiography) was used to quantify the transport of two
essential minerals, Ca2+ and Mg2+ from the diet during the digestion and absorption of a single meal of commercial trout food (3% ration). Initially, net uptake
of Ca2+ was observed in the stomach followed by subsequent Ca2+ fluxes along the intestine which were variable, but for the most part secretory. This indicated a net secretion of Ca2+ along the intestinal tract resulting in a net assimilation of dietary Ca2+ of 28%. Similar handling of Ca2+ and Mg2+ was observed along the gastrointestinal tract (GI), although net assimilation differed substantially between the cations,
with Mg2+ assimilation being close to 60%, mostly a result of greater uptake by the stomach. The stomach displayed the highest net
uptake rates for both cations (1.5 and 1.3 mmol kg−1 fish body mass for Ca2+ and Mg2+, respectively), occurring within 2 h following ingestion of the meal. Substantial secretions of both Ca2+ and Mg2+ were observed in the anterior intestine, which were attributed to bile and other intestinal secretions, while fluxes in the
mid and posterior intestine were small and variable. The overall patterns of Ca2+ and Mg2+ handling in the GI tract were similar to those observed for Na+ and K+ (but not Cl−) in a previous study. Overall, these results emphasize the importance of dietary electrolytes in ionoregulatory homeostasis. 相似文献
16.
Supplementation with CaCl2·2H2O (50 mg l−1) or CuSO4·5H2O (10 mg l−1) improved mannitol production by Candida magnoliae by 14.5 and 18.6% (25 and 32 g/L), respectively. When used in combination, they acted synergistically: Ca2+ decreased the intracellular concentration of mannitol 30%, whereas Cu2+ increased the intracellular activity of mannitol dehydrogenase 1.6-times more than control. Ca2+ probably works by altering the permeability of cells to mannitol, whereas, Cu2+ increases the activity of an enzyme responsible for mannitol biosynthesis. 相似文献
17.
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
18.
Urease (urea amidohydrolase, EC 3.5.1.5) was extracted from the mixed rumen bacterial fraction of bovine rumen contents and purified 60-fold by (NH4)2SO4 precipitation, calcium phosphate-gel adsorption and chromatography on hydroxyapatite. The purified enzyme had maximum activity at pH 8.0. The molecular weight was estimated to be 120000-130000. The Km for urea was 8.3 X 10(-4) M+/-1.7 X 10(-4) M. The maximum velocity was 3.2+/-0.25 mmol of urea hydrolysed/h per mg of protein. The enzyme was stabilized by 50 mM-dithiothreitol. The enzyme was not inhibited by high concentrations of EDTA or phosphate but was inhibited by Mn2+, Mg2+, Ba2+, Hg2+, Cu2+, Zn2+, Cd2+, Ni2+ and Co2+. p-Chloromercuribenzenesulfphonate and N-ethylmaleimide inhibited the enzyme almost completely at 0.1 mM. Hydroxyurea and acetohydroxamate reversibly inhibited the enzyme. Polyacrylamide-gel electrophoresis showed that the mixed rumen bacteria produce ureases which have identical molecular weights and electrophoretic mobility. No multiple forms of urease were detected. 相似文献
19.
20.
The K+-agitated (Kag) mutant of Paramecium caudatum shows prolonged backward swimming in K+-rich solution. To understand the regulation mechanisms of the ciliary motility in P. caudatum, we examined the membrane electrical properties of the Kag mutant. The duration of the backward swimming of the Kag in K+-rich solution was about 10 times longer than that of the wild type. In response to an injection of the outward current, the wild type produced an initial action potential and a subsequent membrane depolarization due to I-R potential drop, while the Kag exhibited repetitive action potentials during the depolarization. Under voltage-clamp conditions, the depolarization-activated transient inward current exhibited by the Kag was slightly smaller than that exhibited by the wild type. In response to an application of K+-rich solution, both the wild type and the Kag exhibited a depolarizing afterpotential representing the activation of the K+-induced Ca2+ conductance. The inactivation time course of the K+-induced Ca2+ conductance of Kag was about 10 times longer than that of the wild type. This difference corresponds well with the difference in behavioral responses between Kag and wild type to K+-rich solution. We conclude that the overreaction of the Kag mutant to the K+-rich solution is caused by slowing down of the inactivation of the K+-induced Ca2+ conductance. 相似文献