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1.
Summary Taking advantage of prolonged action potential under low temperature, we studied temporal relationship among the action potential, increase of cytoplasmic Ca2+ concentration and cessation of cytoplasmic streaming inNitella. The Ca2+ concentration began to increase at a very early stage of the action potential and the cessation of streaming followed that increase.Abbreviations APW
artificial pond water 相似文献
2.
Takeshi Abe 《Journal of plant research》1981,94(4):379-383
The shortening, action potential and Cl−-efflux of the excised lower half cortex in the main pulvinus ofMimosa pudica were simultaneously recorded. The mean values±(S.E.) for Cl−-efflux and shortening were 183±18 picomoles/mg fresh weight/impulse and 87.0±2.2 μm, respectively. 相似文献
3.
Axonal demyelination leads to an increase in the refractory period for propagation of the action potential. Computer simulations were used to investigate the mechanism by which changes in the passive properties of the internodal membrane increase the refractory period. The properties of the voltage dependent ion channels can be altered to restore conduction in demyeliated nerve fibers. The ability of these alterations to decrease the refractory period of demyelinated model nerve fibers was compared. The model nerve fiber contained six nodes. The action potential was stimulated at node one and propagated to node six. The internode between nodes three and four was demyelinated in a graded manner. The absolute refractory period for propagation of the action potential through the demyelinated internode increased as the number of myelin wraps was reduced to less than 25% of the normal value. The increase in refractory period was found to be due to a reduction in the rate or repolarization of the action potential at node three. The delay in repolarization reduced the rate of recovery of inactivated Na channels and slowed the closing of K channels. The rate of repolarization of node three was reduced by the conduction delay for the depolarization of node four caused by demyelination of the preceeding internode. In these simulations the increase in refractory period due to demyelination was eliminated by slowing the onset of Na channel inactivation. A small reduction of the K conductance also decreased the refractory period. However, larger reductions eliminated this effect. 相似文献
4.
Gerhard Thiel 《European biophysics journal : EBJ》1995,24(2):85-92
TheCl– and K+ currents underlying the action potential (AP) in the giant alga Chara were directly recorded with the action potential clamp method. An electrically triggered action potential was recorded and repetitively replayed as command voltage to the same cell under voltage clamp. The resulting clamp current was close to zero. Only the initial rectangular current used for stimulation was approximately reproduced by the clamp circuit. Inhibition of Cl– channels with niflumic acid or ethacrynic acid and of K+ channels with Ba2+ evoked characteristic compensation currents because the amplifier had to add the selectively inhibited currents. Integration of the compensation currents revealed a mean flux through Cl– and K+ channels of 3.3 10–6 and 2.1 10–6 mole M–2 AP–1 respectively. The dynamics of CI– and K+ channel activation/inactivation were obtained by converting the relevant clamp currents to ionic permeabilities using the Goldman-Hodgkin-Katz current equation. During the AP the Cl– permeability reaches a peak 370 ms, on average, after termination of the stimulating pulse. The following inactivation proceeds 3.6 times slower than the activation. The increase in K+ permeability lags behind the rise in Cl– permeability, reaching a peak approximately 2 s after the latter. 相似文献
5.
Summary Amounts and temporal changes of the release of the tracer ions K+ (86Rb+),22Na+, and36Cl– as well as of H+ in the course of action potentials inAcetabularia have been recorded. New results and model calculations confirm in quantitative terms the involvement of three major ion transport systemsX in the plasmalemma: Cl– pumps, K+ channels, and Cl– channels (which are marked in the following by the prefixes,P, K andC) with their equilibrium voltages
X
V
e
and voltage/time-dependent conductances, which can be described by the following, first approximation. Let the maximum (ohmic) conductance of each of the three populations of transporter species be about the same (P
L,
KL,C
L=1) but voltage gating be different: the pump (
p
V
e
about –200 mV) being inactivated (open,oclosed,c) at positive going transmembrane voltages,V
m; the K+ channels (K
V
e about –100 mV) are inactivated at negative goingV
m; and the Cl– channels (C
V
e: around 0 mV), which are normally closed (c) at a restingV
m (nearPVe) go through an intermediate open (o) state at more positiveV
m before they enter a third shut state (s) in series. Model calculations, in which voltage sensitivities are expressed by the factorf=exp(V
mF/(2RT)), simulate, the action potential fairly well with the following parameters (PKco10/f ks–1,PKoc1000·f ks–1,KKco200·f ks–1,Kkoc2/f ks–1,cKco500·f ks–1,CKoc5/f ks–1,CKso0.1/f ks–1,Ckos20·f ks–1). It is also shown that the charge balance for the huge transient Cl– efflux, which frequently occurs during an action potential, can be accounted for by the observation of a corresponding release of Na+. 相似文献
6.
(1) Fluctuations of the membrane potential states are essential for the brain functions from the response of individual neurons
to the cognitive function of the brain. It has been reported in slice preparations that the action potential duration is dependent
on the membrane potential states. (2) In order to examine whether dependence of action potential duration on the membrane
potential could happen in isolated individual neurons that have no network connections, we studied the membrane potential
dependence of the action potential duration by artificially setting the membrane potentials to different states in individual
cultured rat hippocampal neurons using patch-clamp technique. (3) We showed that the action potential of individual neurons
generated from depolarized membrane potentials had broader durations than those generated from hyperpolarized membrane potentials.
(4) Furthermore, the membrane potential dependence of the action potential duration was significantly reduced in the presence
of voltage-gated K+ channel blockers, TEA, and 4-AP, suggesting involvement of both delayed rectifier I
K and transient I
A current in the membrane potential dependence of the action potential duration. (5) These results indicated that the dependence
of action potential duration on the membrane potential states could be an intrinsic property of individual neurons.
Bo Gong and Mingna Liu contributed equally to this work. 相似文献
7.
Olli Varis 《Hydrobiologia》1993,268(3):129-145
Several explanations have been presented for the formation of lacustrine cyanobacteria blooms. These include elevated water temperature, nutrient enrichment, low N/P ratios, low light energy requirements, high pH and/or low carbon dioxide concentration, selective zooplankton grazing, excretion of compounds which suppress the growth of competing algae, and migration. The impact of the first four were studied in Lake Tuusulanjärvi, a eutrophic Finnish lake, using deterministic simulation. The study, which covered 15 years, included a sequence of cases on the recovery of the lake after the implementation of two restoration measures: aeration of the hypolimnion, and termination of municipal waste discharge, both of which were done during the study period. The focus was on Microcystis and Oscillatoria, and on the N-fixing cyanobacteria, Anabaena and Aphanizomenon. Eukaryotic phytoplankton were also included in the study. Monitoring data were used. The roles of the hypotheses were discussed, from the point of view of the utility of the information in water resources management. 相似文献
8.
Crown architecture was analyzed forScaphium macropodum (Sterculiaceae), a common shade-tolerant emergent tree of a tropical rain forest in West Kalimantan, Indonesia. Saplings
and poles shorter than 12 m in height had no branches, and gathered their leaves at the ends of the stem. The leaves changed
from entire to palmately-parted with increasing tree size. The parted leaves increased the light penetration through the clustered
foliage. The size of leaves including the blade and petiole ranged from 22 cm to 147 cm. Because the weight of petiole per
blade increased with leaf size, the leaf could not be enlarged infinitely. Taller trees with lateral branches bore small (about
40 cm in length) entire leaves. The light intensity in the forest increased from the ground to about 12 m tall and was nearly
constant from 12 m to 18 m. Crown architecture ofS. macropodum adapted to this light environment. The monoaxial trees lower than 12 m could thus increase the amount of light with vertical
elongation, and the branched trees higher than 12 m could increase it by means of lateral extension of crown area. 相似文献
9.
Bożena Pawlikowska-Pawlěga Kazimierz Trěbacz Elżbieta Król Antoni Gawron 《Acta Physiologiae Plantarum》2000,22(1):61-67
Quercetin is a very common flavonoid widely distributed in many plants. The flavonoid intake has been linked to the prevention
of human diseases including cancer. Flavonoids possess also a broad spectrum of effects on plants. Quercetin is involved in
Ca2+ transport and metabolism. The present study was designed to check the effects of quercetin alone and in combination with
verapamil on the resting and action potentials in the liverwort Conocephalum conicum. The application of 59·10−6 mol·dm−3 quercetin caused an increase of action potential amplitudes. During the 3rd and 4th hour of treatment an increase by 20–22
% with respect to the control was observed. No changes were found in the resting potential in quercetin treated plants. Verapamil,
a calcium channel inhibitor, caused gradual decrease of action potential amplitudes. Quercetin, when added together with verapamil,
prevented its inhibitory effect. Interactions between quercetin and Ca2+ transport are discussed. 相似文献
10.
Summary Species ofPediastrum, a genus in which the colonies assemble from aggregating zoospores, differ in the number and form of prongs on peripheral cells and the amount of space between cells of the colony; cell shape appears to be genetically based. Peripheral cells of theP. boryanum colony, for example, have two prongs per cell;P. simplex has one prong per cell. Prong extension is suppressed in the interior cells ofP. boryanum, but prong sites have been reported in scanning electron micrographs of the cell walls. A mutant unicellular strain in which cells of the colony separate after attaining typical form reveals several prong sites (6 or more) in each cell. Multiple suppressed prong sites are evident inP. simplex cells as well. Polyeders, 4- and 5-pronged unicells, occur in the life cycle ofP. simplex. Based on these observations and a recent report byMarchant (1979) of a microtubule organizing center associated with the prongs, it is suggested that several microtubule organizing centers are to be found in zoospores ofPediastrum species and may be related to species differences in cell shape.Research supported in part by Argonne Center for Educational Affairs, U.S. Department of Energy, under contract No. W-31-109-ENG-38. 相似文献
11.
The intention of this investigation was to acquire more concise information about the nature of the action potential of Dionaea muscipula Ellis and the different types of cells generating and conducting it. It is shown by microelectrode measurements that, besides the sensory cells, all the major tissues of the trap lobes are excitable, firing action potentials with pronounced after-hyperpolarizations. The action potentials are strictly dependent on Ca2+. Their peak depolarizations are shifted 25–27 mV in a positive direction after a tenfold increase in external Ca2+ concentration. Perfusions with 1 mM ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) or 1 mM LaCl3 completely inhibit excitability. Magnesium ions only slightly affect the peak depolarizations but considerably prolong action potentials. Sodium azide and 2,4-dinitrophenol also abolish excitation, probably by reducing the intracellular ATP concentration. Furthermore, it is tested whether the sensory cells can be distinguished from the other cells of the trap by their electrical behaviour. The resting potentials of sensory cells (-161±7 mV) and mesophyll cells (-155±8 mV) are of the same magnitude. Changes in external ion concentrations affect resting and action potentials in both cell types in a similar way. Additional freeze-fracture studies of both cell types reveal similar numbers and distributions of intramembrane particles on the fracture faces of the plasma membrane, which is most likely the mechanosensor. These findings stress the view that the high mechanosensitivity of the sensory hair results from its anatomy and not from a specialized perception mechanism. It is proposed that trap closure is triggered by a rise in the cytoplasmic concentration of Ca2+ or a Ca2+-activated regulatory complex, which must exceed a threshold concentration. Since the Ca2+ influx during a single action potential does not suffice to reach this threshold, at least two stimulations of the trap are necessary to elicit movement.Abbreviations DNP
2,4-dinitrophenol
- EF
exoplasmic fracture face
- EGTA
ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid
- Em
membrane potential
- Em,r
resting potential
- PF
protoplasmic fracture face
Dedicated to Professor Karl-Ernst Wohlfarth-Bottermann on the occasion of his 65th birthdayA preliminary report was presented at the 14th International Botanical Congress, Berlin, July 1987. This work is part of the dissertation (D5) of D.H. 相似文献
12.
13.
Teruo Shimmen 《Journal of plant research》1994,107(4):371-375
A unique after-hyperpolarization was found in internodal cells ofChara globularis. The cells generated an ordinary action potential due to regenerative depolarization induced by the outward electric current pulse larger than a threshold stimulus. After reaching a depolarizing peak, the membrane potential repolarized and overshooted the resting potential to a value which was somehow 40 mV more negative than the resting potential before stimulation (after-hyperpolarization). Since the membrane resistance increased during the after-hyperpolarization, the after-hyperpolarization is thought to be caused by an increase in the resistance (decrease in the conductance) of the passive diffusion channel. 相似文献
14.
Hybridization is increasingly recognized as a significant creative force in evolution. Interbreeding among species can lead to the creation of novel genotypes and morphologies that lead to adaptation. On the Hawaiian island of Oahu, populations of two species of plants in the endemic genus Lipochaeta grow at similar elevations in the northern Waianae Mountains. These two species represent extremes of the phenotypic distribution of leaf shape: the leaves of Lipochaeta tenuifolia individuals are compound and highly dissected while leaves of L. tenuis are simple. Based primarily on leaf shape morphology, a putative hybrid population of Lipochaeta located at Puu Kawiwi was identified. Individuals in this population exhibit a range of leaf shapes intermediate in varying degrees between the leaf shapes of the putative parental species. We analyzed individuals from pure populations of L. tenuifolia, L. tenuis and the putative hybrids using 133 AFLP markers. Genetic analysis of these neutral markers provided support for the hybrid origin of this population. The correlation between genetic background and leaf morphology in the hybrids suggested that the genome of the parental species with simple leaves might have significantly contributed to the evolution of a novel, compound leaf morphology. 相似文献
15.
P. Zeman 《Entomologia Experimentalis et Applicata》1993,67(1):31-39
A computer model was applied to simulate responses of German cockroach populations to feeding on juvenoid baits during an
equilibrium, exponential, and the earliest phase of population growth. The simulations show that the renewal potential of
the cockroach populations will be exhausted when about 80% or more adults become sterile. The attainment of this activity
threshold will be preceded by a lag time with no apparent control effect. The time delay appears substantially shorter for
both growing populations (30–60 days) than for the equilibrious one (90–120 days), but, the former ones will continue growing
throughout this lag. The simulations predict that even a worse baits' performance can give sufficient control effect in the
field if the baits are laid in an early phase of population growth. Thus, optimum tactics should integrate administration
of juvenoid baits with an introductory reduction of cockroach population. 相似文献
16.
The polarity protein Par6 is coupled to the microtubule network during molluscan early embryogenesis
Cell polarity, which directs the orientation of asymmetric cell division and segregation of fate determinants, is a fundamental feature of development and differentiation. Regulators of polarity have been extensively studied, and the critical importance of the Par (partitioning-defective) complex as the polarity machinery is now recognized in a wide range of eukaryotic systems. The Par polarity module is evolutionarily conserved, but its mechanism and cooperating factors vary among different systems. Here we describe the cloning and characterization of a pond snail Lymnaea stagnalis homologue of partitioning-defective 6 (Lspar6). The protein product LsPar6 shows high affinity for microtubules and localizes to the mitotic apparatus during embryonic cell division. In vitro assays revealed direct binding of LsPar6 to tubulin and microtubules, which is the first evidence of the direct interaction between the two proteins. The interaction is mediated by two distinct regions of LsPar6 both located in the N-terminal half. Atypical PKC, a functional partner of Par6, was also found to localize to the mitotic spindle. These results suggest that the L. stagnalis Par complex employs the microtubule network in cell polarity processes during the early embryogenesis. Identical sequence and localization of LsPar6 for the dextral and the sinistral snails exclude the possibility of the gene being the primary determinant of handedness. 相似文献
17.
Chromaffin cells of the adrenal medulla receive cholinergic input from the splanchnic nerve. Upon sympathetic activity, chromaffin cells fire action potentials that open voltage-gated calcium channels and evoke the exocytic release of catecholamines. Catecholamines then regulate homeostatic processes such as cardiac output and vascular tone. Thus control of the Ca(2+) influx in chromaffin cells represents a target for the regulation of multiple physiological functions. Previous reports utilized square pulse depolarizations to quantify the proportional exocytic response as a function of Ca(2+) channel subtype. In this study, we use perforated patch voltage clamp and action potential waveforms to depolarize cells in situ. We analyze Ca(2+) current components under conditions that match the dynamic native cell behavior. This approach revealed a greater role for P/Q-type calcium channels in evoked exocytosis than previously reported. Thus, the P/Q-type channels represent a more important control point for the regulation of catecholamine-dependent processes than previously believed. 相似文献
18.
Silvana Grandillo Hsin-Mei Ku Steven D. Tanksley 《Molecular breeding : new strategies in plant improvement》1996,2(3):251-260
In two previous quantitative trait locus (QTL) mapping studies conducted inLycopersicon esculentum x L. pimpinellifolium BC1 and BC2 populations we had localized a major QTL for fruit shape,fs8.1, to a ca. 20 cM interval on the short arm of chromosome 8, flanked by markers TG176 and CT92. At this QTL the allele from the wild species reduces the length of fruit, giving round-shaped fruit. In order to define more precisely the location offs8.1, near-isogenic lines (NILs) segregating for the region of interest were developed. The results from substitution mapping show that no recombination occurred betweenfs8.1 and the marker CD40 in 322 meioses. The gene action forfs8.1 was determined in a BC4F3 population to be partial dominance. The main effect offs8.1 is exerted on fruit length while fruit diameter is not significantly affected. A highly significant correlation (r=0.89;P<0.01) was found between fruit shape and ovary shape indicating that thefs8.1 gene product acts early in ovary development (preanthesis). Implications for the evolution of fruit shape and the feasibility of map-based cloning of this QTL are discussed. 相似文献
19.
In young Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva) the formation of the lateral hair whorls can be induced by a short pulse of blue light after continuous red preillumination. In this paper we describe the experimental conditions for optimum response and the properties of the action spectrum. The probit of the cells which eventually form hair whorls is linearly correlated to the logarithm of the incident quanta of blue light. Parallel fluence-response curves for all wavelengths indicate the involvement of only one photoreceptor pigment. The action spectrum shows no effectiveness of wavelengths above 520 nm, a high action peak at 470 nm and two lower ones at 425 and 370 nm, and is in accordance with those of cryptochrome-like photoreceptors. 相似文献
20.
Characteristic shape parameters, light intensities and relative water velocities were estimated in thalli of free-moving seaweeds, using threeGracilaria-like species:G. cornea, G. conferta andGracilariopsis lemaneiformis. Relative velocities over the branches were determined mostly by rotation of the algae in the water as opposed to linear translation. The tree major shape parameters of the thallus, weight, volumetric specific weight and areal specific weight, explain the differences in relative velocity. Relative velocities near the center of the thallus were about 50% to 80% of the external velocity. Light intensities at the vicinity of the center ofG. cornea ranged between 60% to 90% of the external light intensity. Light attenuation in the center was proportional to the weight of the thallus. The significance of light and velocity attenuation as a function of shape parameters is discussed.Author for correspondence 相似文献