Membrane Potentials in Carrot Root Cells

1977 ◽  
Vol 4 (2) ◽  
pp. 241 ◽  
Author(s):  
W.P Anderson ◽  
R.N Robertson ◽  
B.J Wright
Keyword(s):  
Membrane Potentials ◽  
Xylem Parenchyma ◽  
Carrot Root ◽  
Root Cells ◽  
Membrane Hyperpolarization ◽  
Electrogenic Transport ◽  
Carbonyl Cyanide ◽  
External Conditions ◽  
Complete Nutrient Solution ◽  
Single Exponential

Membrane potentials in carrot root xylem parenchyma cells, aged for at least 5 days after excision from the parent organ, were measured under a variety of external conditions by standard intracellular electrode methods. The respiration blocking agents cyanide and carbon monoxide (in the dark) produced large (up to 90 mV) depolarizations which could be described by single exponential decay curves having rate constants (or half-times) of 0.065 s-1 (t*1/2 = 10.8 s) and 0.094 s-1 (t*1/2 = 7.4 s) respectively. The uncoupler carbonyl cyanide m-chlorophenylhydrazone caused a single exponential membrane depolarization with a rate constant of 0.0054 s-1(t*1/2 = 126 s). These effects are thought to reflect the action of an active electrogenic H+ extrusion pump at the plasmalemma. A second, minor electrogenic transport, causing depolarization of about 10 mV in the restlng state, and due to an obligate electrogenic coupling to Cl- influx has been confirmed in KCl-pretreated tissue. In tissue pretreated in more complete nutrient solution, there is no evidence of a Cl- -coupled electrogenic exchange. This seems to be the first report of two independent electrogenic mechanisms operating in a plant cell and, interestingly, they act in opposite senses, the major H+ extrusion causing membrane hyperpolarization, the minor Cl- -influx-coupled exchange causing depolarization, in the normal resting cell.

Conductance changes underlying a late synaptic hyperpolarization in hippocampal CA3 neurons

1987 ◽  
Vol 58 (1) ◽  
pp. 160-179 ◽  
Author(s):  
J. J. Hablitz ◽  
R. H. Thalmann
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Time Course ◽  
Membrane Potentials ◽  
Resting Membrane Potential ◽  
Extracellular Potassium ◽  
Voltage Sensitivity ◽  
Base Line ◽  
Membrane Hyperpolarization ◽  
Ca3 Neurons

1. Single-electrode current- and voltage-clamp techniques were employed to study properties of the conductance underlying an orthodromically evoked late synaptic hyperpolarization or late inhibitory postsynaptic potential (IPSP) in CA3 pyramidal neurons in the rat hippocampal slice preparation. 2. Late IPSPs could occur without preceding excitatory postsynaptic potentials at the resting membrane potential and were graded according to the strength of the orthodromic stimulus. The membrane hyperpolarization associated with the late IPSP peaked within 140-200 ms after orthodromic stimulation of mossy fiber afferents. The late IPSP returned to base line with a half-decay time of approximately 200 ms. 3. As determined from constant-amplitude hyperpolarizing-current pulses, the membrane conductance increase during the late IPSP, and the time course of its decay, were similar whether measurements were made near the resting membrane potential or when the cell was hyperpolarized by approximately 35 mV. 4. When 1 mM cesium was added to the extracellular medium to reduce inward rectification, late IPSPs could be examined over a range of membrane potentials from -60 to -140 mV. For any given neuron, the late IPSP amplitude-membrane potential relationship was linear over the same range of membrane potentials for which the slope input resistance was constant. The late IPSP reversed symmetrically near -95 mV. 5. Intracellular injection of ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid or extracellular application of forskolin, procedures known to reduce or block certain calcium-dependent potassium conductances in CA3 neurons, had no significant effect on the late IPSP. 6. Single-electrode voltage-clamp techniques were used to analyze the time course and voltage sensitivity of the current underlying the late IPSP. This current [the late inhibitory postsynaptic current (IPSC)] began as early as 25 ms after orthodromic stimulation and reached a peak 120-150 ms following stimulation. 7. The late IPSC decayed with a single exponential time course (tau = 185 ms). 8. A clear reversal of the late IPSC at approximately -99 mV was observed in a physiological concentration of extracellular potassium (3.5 mM).(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Studies in The Metabolism of Plant Cells

1950 ◽  
Vol 3 (4) ◽  
pp. 487 ◽  
Author(s):  
DC Weeks ◽  
RN Robertson
Keyword(s):  
Cytochrome Oxidase ◽  
Enzyme Inhibitor ◽  
Plant Cells ◽  
Carrot Root ◽  
Root Cells ◽  
Oxidase System

It has been established with the use of the enzyme inhibitor carbon monoxidethat the cyanide-sensitive salt respiration in carrot root cells is mediatedby the cytochrome-cytochrome oxidase system. The cyanide-stable ground respirationis not mediated by the cytochrome-cytochfome oxidase system.

scholarly journals Effects of beauvericin on root cell transmembrane electric potential, electrolyte leakage and respiration of maize roots with different susceptibility to Fusarium

2011 ◽  
Vol 52 (No. 11) ◽  
pp. 492-498 ◽  
Author(s):  
J. Pavlovkin ◽  
I. Mistríková ◽  
M. Luxová ◽  
I. Mistrík
Keyword(s):  
Electric Potential ◽  
Electrolyte Leakage ◽  
Cumulative Effect ◽  
Significant Inhibition ◽  
Membrane Potentials ◽  
Root Cell ◽  
Cortical Cells ◽  
Root Cells ◽  
Membrane Conductivity ◽  
Maize Roots

Effect of beauvericin on root cell transmembrane electric potential (E<sub>M</sub>), electrolyte leakage and respiration of roots were studied in two maize cultivars (Zea mays L.) with different susceptibility to this toxigenic metabolite produced by Fusarium. Beauvericin treatment induced rapid and significant depolarisation of membrane potentials of the outer cortical cells of maize roots of tolerant cv. Lucia. The range of depolarisation was dose dependent with maximum depolarisation of 55 mV (55 &plusmn; 7 mV, n = 7) at 200&micro;M beauvericin. In contrast, membrane potentials of beauvericin susceptible cv. Pavla was only slightly depolarised by identical concentrations of beauvericin and the value of depolarisation represented only half of the value of tolerant cv. Lucia (27 &plusmn; 6 mV, n = 8). The values of membrane potentials of root cells of tolerant cv. Lucia were higher (137 &plusmn; 9 mV, n = 26) and more electrogenic (60 &plusmn; 2 mV, n&nbsp;=&nbsp;3) than in susceptible cv. Pavla (125 &plusmn; 7 mV, n = 28), (47 &plusmn; 2 mV, n = 3), respectively. Our results confirmed that 2 h treatment with 50&micro;M beauvericin does not cause irreversible changes in plasma membrane H<sup>+</sup>-ATPase, because fusicoccin, an H<sup>+</sup>-ATPase activator diminished the depolarizing effect of beauvericin on the E<sub>M</sub>. Further experiments revealed beauvericin-induced increase of membrane conductivity in root cells of Pavla but not in root cells of Lucia. Time-coarse experiments showed that 25&micro;M beauvericin induced slight, but significant inhibition of root respiration in both cultivars during the first two hours of treatment, and the inhibition was higher in cv. Lucia than in cv. Pavla. The depolarisation of E<sub>M</sub> in the outer cortical cells of maize roots may be the result of a cumulative effect of beauvericin on ATP supply, activity of H<sup>+</sup>-ATPase and mainly on the permeability of plasmalemma. Increased beauvericin tolerance in maize might be associated with the increased ability of tolerant plant to maintain normal ion fluxes and membrane potentials across the plasmalemma of root cells in the presence of beauvericin.

scholarly journals Calcium-dependent inactivation of the calcium current activated upon hyperpolarization of Paramecium tetraurelia.

1992 ◽  
Vol 100 (2) ◽  
pp. 253-268 ◽  
Author(s):  
R R Preston ◽  
Y Saimi ◽  
C Kung
Keyword(s):  
Time Course ◽  
Membrane Potentials ◽  
Paramecium Tetraurelia ◽  
Calcium Dependent ◽  
Recovery From Inactivation ◽  
Dependent Inactivation ◽  
Dependent Pathway ◽  
Single Exponential Function ◽  
Lines Of Evidence ◽  
Single Exponential

The Ca2+ current activated upon hyperpolarization of Paramecium tetraurelia decays over a period of 150-200 ms during sustained steps under voltage clamp. At membrane potentials between -70 and approximately -100 mV, the time course of this inactivation is described by a single exponential function. Steps negative to approximately -100 mV elicit currents that decay biexponentially, however. Three lines of evidence suggest that this current's inactivation is a function of intracellular Ca2+ concentration rather than membrane potential: (a) Comparing currents with similar amplitudes but elicited at widely differing membrane potentials suggests that their time course of decay is a sole function of inward current magnitude. (b) The extent of current inactivation is correlated with the amount of Ca2+ entering the cell during hyperpolarization. (c) The onset and time course of recovery from inactivation can be hastened significantly by injecting cells with EGTA. We suggest that the decay of this current during hyperpolarization involves a Ca(2+)-dependent pathway.

scholarly journals Voltage dependence of acetylcholine receptor channel gating in rat myoballs.

1992 ◽  
Vol 100 (4) ◽  
pp. 729-748 ◽  
Author(s):  
L D Chabala
Keyword(s):  
Acetylcholine Receptor ◽  
Rate Constants ◽  
Voltage Dependence ◽  
Single Channel ◽  
Light Flash ◽  
Membrane Potentials ◽  
Concentration Jump ◽  
Membrane Hyperpolarization ◽  
Wide Range ◽  
Closing Rate

Whole-cell currents from nicotinic acetylcholine receptor (AChR) channels were studied in rat myoballs using a light-activated agonist to determine the voltage dependence of the macroscopic opening and closing rate constants. Myoballs were bathed in a solution containing a low concentration of the inactive isomer of the photoisomerizable azobenzene derivative, cis-Bis-Q. A light flash was then presented to produce a known concentration jump of agonist, trans-Bis-Q, across a wide range of membrane potentials in symmetrical solutions (NaCl or CsCl on both sides) or asymmetrical solutions (NaCl in the bath and CsCl in the pipette). At the low agonist concentration used in this study, the reciprocal of the macroscopic time constants gives an unambiguous measure of the effective closing rate. It showed an exponential decrease with membrane hyperpolarization between +20 and -100 mV, but tended to level off at more depolarized and at more hyperpolarized membrane potentials. The relative effective opening rate was derived from the steady-state conductance, the single-channel conductance, and the apparent closing rate; it decreased sharply in the depolarizing region and tended to level off and then turn up in the hyperpolarizing region. The two effective rate constants were shown to depend on the first, second, and third power of membrane potential.

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