Inward membrane current inChara inflata: I. A voltage- and time-dependent Cl− component

Tyerman, Stephen D.; Findlay, G. P.; Paterson, G. J.

doi:10.1007/bf01869710

Cited by 35 publications

(13 citation statements)

References 24 publications

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“…We have offset Icl(toc) since it may have generally larger values as a result of not accounting for all of the non-C1-leak. The modified function is also still within the large range of observed values for Icl(to,) (Tyerman et al, 1985).…”

Section: Effect Of Low Concentrations Of Ammoniummentioning

confidence: 61%

Inward membrane current inChara inflata: II. Effects of pH, Cl−-channel blockers and NH 4 + , and significance for the hyperpolarized state

1986

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Summary. The C1 component of the voltage-and time-dependent inward current activated by hyperpolarizing the membrane of Chara inflata increases exponentially as the external pH, pH,,, is lowered from 7 with the membrane potential difference (PD) kept constant. Lanthanum and anthracene-9-carboxylic acid (A-9-C, a C1-channel blocker) both blocked the CI-component and removed the pHo sensitivity of the inward current. Lanthanum, however, also decreased the K + conductance. The hyperpolarized membrane is depolarized by A-9-C in a manner similar to that caused by the removal of external C1-. Low external concentrations of NH~-stimulated the CI-component of the inward current probably as a result of a change in cytoplasmic pH rather than as a result of a change in cytoplasmic [C1-], since the effect was observed in Cl--free solutions. The results show that the membrane PD, at hyperpolarized levels, is most likely determined by two factors: the proton extrusion pump, provided it has a reversal PD more negative than about -300 mV, and a voltagedependent C1-leak.

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Section: Effect Of Low Concentrations Of Ammoniummentioning

confidence: 61%

Inward membrane current inChara inflata: II. Effects of pH, Cl−-channel blockers and NH 4 + , and significance for the hyperpolarized state

1986

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“…A number of voltage-regulated anion channels have been observed previously but these are either hyperpolarisation-activated (Tyerman et al 1986;Schauf and Wilson 1987;Terry et al 1991) or depolarisation-activated but capable of passing inward current (anion efflux). Guardcell protoplasts contain depolarisation-activated anion channels, fast and slow (Schroeder and Keller 1992), that activate negative of Eanio n and allow anion efflux (Keller et al 1989;Hedrich et al 1990;Schroeder and Keller 1992;Marten et al 1992).…”

Section: Discussionmentioning

confidence: 92%

A channel that allows inwardly directed fluxes of anions in protoplasts derived from wheat roots

Skerrett

Tyerman

1994

Planta

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Abstract. An anion channel that only allows outward current flow (anion influx) has been identified in protoplasts derived from wheat (Triticum aestivum L., Triticum turgidum L.) roots. The anion outward rectifier (anion OR) measured by patch-clamp of whole cells activated very quickly, usually reaching a steady-state level in less than 100 ms and was easily distinguished from the cation outward rectifier (cation OR) which activated more slowly during membrane depolarisation. The anion OR is permeable to NO 3 and CI, moderately permeable to I-, and relatively impermeable to H2PO 4 and C104 . An anomalous mole-fraction effect between C104 and C1-was observed on the outward current, indicating that the channel is a multi-ion pore. The anion OR is gated by both voltage and external anion concentration such that it activates near to the equilibrium potential for the permeant anion. It activated at more negative membrane potentials when NO 3 was substituted for C1 in the external medium, indicating that the channel may function to allow NO 3 influx under luxuriant external NO 3-concentrations. For most experiments, K + and C1-were the main cation and anion in solution, and under these conditions it appeared likely that the anion OR functioned in membrane-potential regulation by facilitating a C1 influx at membrane potentials more positive than the chloride reversal potential (Ect). If Ecl was more negative than the K + reversal potential (EK) then the anion OR dominated but both the anion and cation ORs occurred together when the membrane potential difference (Vm) was positive of both Ecl and EK. The cation OR was inhibited by increasing external C1 concentrations, but the anion OR was not affected by external K + or Na + concentration. The anion-transport inhibitors, zinc and phenylglyoxal were ineffective in blocking the anion OR. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) irreversibly blocked about 34% of the current when applied Abbreviations: Bath = solution bathing the extracellular face of the membrane; DIDS = (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid); Ex = reversal potential for ion x; OR = outward rectifier; Pip = solution inside the pipette; TEAC1 = (tetraethyl-ammonium chloride); Vm = membrane potential difference Correspondence to: S.D. Tyerman; FAX: 61 (8) 2013015 extracellularly at a concentration of 25 gM, and about 69% at a concentration of 200 gM. However, DIDS (200 gM) also occasionally acted as an irreversible blocker of the cation OR. Perchlorate blocked irreversibly 75% of the current at an external concentration of 10 mM and did not block the cation OR. Whole-cell currents also indicated that the anion OR was insensitive to external pH(pH = 5-7) and calcium concentration ([Ca 2+] =0.1-10 mM). Increasing intracellular calcium concentration significantly increased the occurrence of the fast outward current in whole cells (P < 0.005, X 2 test). With approximately 10 nM calcium inside the cell the anion outward current was observed in 64% (n = 45) of cells and with 50 nM calcium...

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“…For Chara, two (or more?) K + channels (Beilby, 1985(Beilby, , 1986Sokolik & Yurin, 1986) and a CI-channel (Tyerman, Findlay & Paterson, 1986) can impart, voltage-and concentration-dependent, inward-and outward-rising currents to the whole membrane I-V characteristic. Even a nonlinear (Goldman) model will approximate the true leak I-V profile over a limited voltage range only under these conditions.…”

Section: Implications Of the Leak For Guard Cell K + Relationsmentioning

confidence: 99%

Electrical characteristics of stomatal guard cells: The contribution of ATP-dependent, “Electrogenic” transport revealed by current-voltage and difference-current-voltage analysis

Blatt

1987

J. Membrain Biol.

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Summary. The steady-state, current-voltage (I-V) characteristicsof stomatal guard cells from Vicia faba L. were explored by voltage clamp using conventional electrophysiological techniques, but with double-barrelled microelectrodes containing 50 mM K+-acetate. Attention was focused, primarily, on guard cell response to metabolic blockade. Exposures to 0.3-1.0 mM NaCN and 0.4 mM salicylhydroxamic acid (SHAM) lead consistently to depolarizing (positive-going) shifts in guard cell potentials (V~), as large as + 103 mV, which were generally complete within 60-90 sec (mean response half-time, 10.3 -+ 1.7 sec); values for V~ in NaCN plus SHAM were close or positive to -100 mV and well removed from the K + equilibrium potential. Guard cell ATP content, which was followed in parallel experiments, showed a mean half-time for decay of 1().8 + 1.9 sec ([ATP]t~0, 1.32 -+ 0.28 mM; lATP],=60-fs0 .... 0.29 -+ 0.40 mM). In respiring cells, the I-V relations were commonly sigmoid about V,, or gently concave to the voltage axis positive to V~. Inward-and outward-rectifying currents were also observed, especially near the voltage extremes (nominally -350 and +50 mV). Short-circuit currents (at V = 0 mV) were typically about 200-500 mAm -2. The principal effect of cyanide early on was to linearize the I-V characteristic while shifting it to the right along the voltage axis, to decrease the membrane conductance, and to reduce the short-circuit current by approx. 50-75%. The resulting difference-current-voltage (dl-V) curves (+cyanide) showed a marked sensitivity to voltages negative from -100 mV and, when clamp scans had been extended sufficiently, they revealed a distinct minimum near -300 mV before rising at still more negative potentials. The difference currents, along with changes in guard cell potential, conductance and ATP content are interpreted in context of a primary, ATPconsuming ion pump. Fitting dl-V curves to reaction kinetic model for the pump J. Membrane Biol. 63:165; Blatt, M.R. (1986)J. Membrane Biol. 92:91] implicates a stoichiometry of one (+) charge transported outward for each ATP hydrolyzed, with pump currents as high as 200 mA m 2 at the free-running potential. The analysis indicates that the pump can comprise more than half of the total membrane conductance and argues against modulations of pump activity alone, as an effective means to controlling K + transport for stomatal movements. Key Wordsstomatal guard cell -(difference-) current-voltage relation 9 conductance-voltage relation 9 H + pump . kinetic carrier model 9 K + transport -Vicia

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Inward membrane current inChara inflata: I. A voltage- and time-dependent Cl− component

Cited by 35 publications

References 24 publications

Inward membrane current inChara inflata: II. Effects of pH, Cl−-channel blockers and NH 4 + , and significance for the hyperpolarized state

Inward membrane current inChara inflata: II. Effects of pH, Cl−-channel blockers and NH 4 + , and significance for the hyperpolarized state

A channel that allows inwardly directed fluxes of anions in protoplasts derived from wheat roots

Electrical characteristics of stomatal guard cells: The contribution of ATP-dependent, “Electrogenic” transport revealed by current-voltage and difference-current-voltage analysis

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