Membrane Electrical Behaviour in Nitellopsis Obtusa

Findlay, G. P.

doi:10.1071/bi9701033

Cited by 44 publications

(25 citation statements)

References 9 publications

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“…Later, studying the relation between excitation of tonoplast and plasmalemma, Findlay suggested that tonoplast is activated by some ion entering through the plasmalemma channels [12]. Our results support and detail these ideas.…”

Section: Ca-channelsupporting

confidence: 86%

Excitation ofCharaceae cell membranes as a result of activation of calcium and chloride channels

Lunevsky¹,

Zherelova²,

Vostrikov³

et al. 1983

J. Membrain Biol.

200

122

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Summary. Ionic channels responsible for excitation of plasmalemma and tonoplast of fresh-water Nitellopsis obtusa were studied using the voltage-clamp technique. Voltage was clamped on each separate membrane. Chloride channels were inhibited with ethacrynic acid. 1. Along with anion (chloride) channels the cation channels have been revealed in the membranes. The corresponding channels are similar in both types of membranes. 2. The cation channels are controlled by membrane voltage being activated under membrane depolarization. The channels possess activation-inactivation kinetics. For N. obtusa characteristic times of activation and inactivation are 0.1 and 0.5 sec, respectively. 3. Conductance of cation channels depends on the type of cation and the orders of conductivity decrease are the following: Rb + >K § >Cs + >Na + >Li + and Ba 2 § > Sr 2 + > Ca 2 + > Mg 2 +. Ratio of conductance for bivalent ions to that of monovalent ones decreases with the increase of normal concentrations. When the external medium contains both mono-and bivalent cations in comparable concentrations, the current is mainly determined by the latter. In natural environment of the algae such conditions are realized for Ca 2+ ions which create the bulk of the inward current through cation channels under cell excitation. That is why we term these channels "calcium" ones. 4. Ca 2 + ions entering the cytoplasm through the calcium channels located in both membranes activate the chloride channels. Ba 2+ and Mg 2+ also activate the chloride channels but to a lesser extent than Ca; § does. Characteristic inactivation time of these channels in N. obtusa is about 1 to 2 sec.

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Section: Ca-channelsupporting

confidence: 86%

Excitation ofCharaceae cell membranes as a result of activation of calcium and chloride channels

Lunevsky¹,

Zherelova²,

Vostrikov³

et al. 1983

J. Membrain Biol.

200

122

View full text Add to dashboard Cite

show abstract

“…(c) The AP across both membranes (top curve), the AP across plasma membrane (middle curve) and the AP across tonoplast in Nitella flexilis (Shimmen and Nishikawa 1988). (d) AP across tonoplast (upper curve) and plasma membrane (bottom curve) in Nitellopsis obtusa (Findlay 1970) (Coleman 1986;Laver 1991;McCulloch et al 1997), but their properties did not make them suitable for a role in the AP. However, the patch clamp experiments of Okihara et al (1991Okihara et al ( , 1993 on Chara plasma membrane found two types of Cl À channels.…”

Section: Ionic Basis Of the Depolarising Stagementioning

confidence: 97%

Electrophysiology of the Detached Cell Under Stress

Beilby

Casanova

2013

The Physiology of Characean Cells

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This chapter summarises the research on characean detached cells, subjected to calibrated and primarily abiotic types of stress. Responses to touch, wounding, voltage clamp to both depolarised and hyperpolarised potential difference (PD) levels and to osmotic and saline stress are described. Both salt-tolerant and saltsensitive Characeae have been investigated under osmotic and saline stress. Many of the cell responses involve an increase in cytoplasmic calcium concentration. However, the manner of calcium increase is specific to different stressors: mechanical stimulation opens stretch-activated (SA) channels on internal stores, depolarisation to excitation threshold opens IP 6 -activated channels on internal stores, hypo-osmotic stress opens SA channels on internal stores and possibly the vacuole, hyperpolarisation opens channels on the plasma membrane. The increase in the calcium concentration in the cytoplasm opens calcium-activated chloride channels on the plasma membrane (and possibly the tonoplast), leading to an outflow of chloride and depolarisation that can take a form of receptor potential (RPD), action potential (AP) or variation potential (VP). From all these responses, the AP fits the role of a signal: its form is relatively constant and it can propagate speedily from cell to cell. The responses to hyperosmotic and saline stress show interesting differences between salt-tolerant and salt-sensitive Characeae. In salt-tolerant Characeae, the proton pump is activated by both a decrease in turgor and an increase in salinity. The activation by turgor decrease is transient as turgor is regulated, while activation by salt is permanent and graded according to salt concentration. The turgor sensors may be located at the ends of nodal cells. In salt-sensitive Characeae, on the other hand, non-plasmolysing turgor decrease elicits no change in pump activity, while an increase in salinity shuts down the pump and opens H + /OH À channels, depolarising the membrane PD further. Spontaneous APs with long durations and opening of outward rectifying channels lead to a loss of potassium and death. Both salt-sensitive and salt-tolerant Characeae employ Na + /H + antiporter to remove Na + from the cytoplasmic compartment under saline stress and the water channels on the plasma membrane are closed by high osmolarity.

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“…In Characeae cells R., at the peak of A.P. was only 1/10-1/20 the resting value (3,4,11). At the peak of the slow depolarization accompanied by the streaming cessation, Rm was less than 1/10 the original value (Fig.…”

Section: Discussionmentioning

confidence: 99%

Cessation of Cytoplasmic Streaming Accompanying Osmosis-induced Membrane Depolarization in Nitella flexilis

Hayama

Tazawa

1978

Cell Struct. Funct.

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ABSTRACT. The transcellular osmosis induced both slow membrane depolarization (<50 mV sec-1) and cessation of cytoplasmic streaming in the endosmotic cell half of an internodal cell of Nitella flexilis. Membrane depolarization and streaming cessation occurred in cells made inexcitable by bathing in 10 mM KCl, suggesting that Ca2+ in the external medium is not essential for streaming cessation.Depolarization preceded the streaming cessation, suggesting that some membrane event induced by endosmosis may directly induce the streaming cessation. The larger the rate of depolarization, the stronger the streaming inhibition and the shorter the time needed for the cessation. The maximum rate of depolarization of the action potential was more than 10 times that of osmosis-induced depolarization.The all-or-none nature of the streaming cessation accompanying the action potential is interpreted as indicating that the rate of depolarization is high enough to always cause instant cessation.Streaming cessation was observed even when the membrane potential was clamped at the same level as before the start of transcellular osmosis. The membrane electromotive force and membrane resistance decreased significantly as in the case where the membrane potential was not clamped.In Characeae internodal cells, cytoplasmic streaming stops suddenly at the moment an action potential (A.P.) is generated (cf 6). When electric stimulus is applied to the internodal cell, the so-called all-or-none law is valid not only for the generation of A.P. but also for the cessation of streaming (16). The threshold for cessation is the same as that for the A.P. This suggests that the streaming cessation is not a direct consequence of the electrical stimulus itself but is caused by the A.P. However, Kishimoto and Akabori (9) found cases where the streaming does not stop but decelerates temporarily when the A.P. is not large enough.In Nitella flexilis, transcellular-osmosis (t-osmosis) (7) induces a very slow depolarization compared with A.P. only in the endosmotic cell half (19,5). The membrane depolarization induced by t-osmosis is often accompanied by A.P. However, the membrane is depolarized slowly by t-osmosis without eliciting A.P. when the concentration of KCl in the external medium is high. This type of membrane depolariza-*Present address:

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Membrane Electrical Behaviour in Nitellopsis Obtusa

Cited by 44 publications

References 9 publications

Excitation ofCharaceae cell membranes as a result of activation of calcium and chloride channels

Excitation ofCharaceae cell membranes as a result of activation of calcium and chloride channels

Electrophysiology of the Detached Cell Under Stress

Cessation of Cytoplasmic Streaming Accompanying Osmosis-induced Membrane Depolarization in Nitella flexilis

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