Energy coupling for membrane hyperpolarization in Lemna: respiration rate, ATP level and membrane potential at low oxygen concentrations

The fungal toxin fusicoccin (FC) induces rapid cell elongation, proton extrusion and plasma membrane hyperpolarization in maize coleoptile cells. Here, these three parameters were simultaneously measured using non-abraded and non-peeled segments with the incubation medium having access to their lumen. The dose–response curve for the FC-induced growth was sigmoidal shaped with the maximum at 10−6 M over 10 h. The amplitudes of the rapid growth and proton extrusion were significantly higher for FC than those for indole-3-acetic acid (IAA). The differences between the membrane potential changes that were observed in the presence of FC and IAA relate to the permanent membrane hyperpolarization for FC and transient hyperpolarization for IAA. It was also found that the lag times of the rapid growth, proton extrusion and membrane hyperpolarization were shorter for FC compared to IAA. At 30 °C, the biphasic kinetics of the IAA-induced growth rate could be changed into a monophasic (parabolic) one, which is characteristic for FC-induced rapid growth. It has been suggested that the rates of the initial phase of the FC- and IAA-induced growth involve two common mechanisms that consist of the proton pumps and potassium channels whose contribution to the action of both effectors on the rapid growth is different.

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Opioid-Activated Postsynaptic, Inward Rectifying Potassium Currents in Whole Cell Recordings in Substantia Gelatinosa Neurons

Journal of Neurophysiology ◽

10.1152/jn.1998.80.6.2954 ◽

1998 ◽

Vol 80 (6) ◽

pp. 2954-2962 ◽

Cited By ~ 49

Author(s):

S. P. Schneider ◽

W. A. Eckert ◽

A. R. Light

Keyword(s):

Membrane Potential ◽

G Protein ◽

Potassium Currents ◽

Substantia Gelatinosa ◽

Opioid Agonist ◽

Membrane Hyperpolarization ◽

Whole Cell ◽

Protein Activation ◽

G Protein Activation ◽

Whole Cell Recordings

Schneider, S. P., W. A. Eckert III, and A. R. Light. Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons. J. Neurophysiol. 80: 2954–2962, 1998. Using tight-seal, whole cell recordings from isolated transverse slices of hamster and rat spinal cord, we investigated the effects of the μ-opioid agonist (d-Ala2, N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO) on the membrane potential and conductance of substantia gelatinosa (SG) neurons. We observed that bath application of 1–5 μM DAMGO caused a robust and repeatable hyperpolarization in membrane potential ( V m) and decrease in neuronal input resistance ( R N) in 60% (27/45) of hamster neurons and 39% (9/23) of rat neurons, but significantly only when ATP (2 mM) and guanosine 5′-triphosphate (GTP; 100 μM) were included in the patch pipette internal solution. An ED50 of 50 nM was observed for the hyperpolarization in rat SG neurons. Because G-protein mediation of opioid effects has been shown in other systems, we tested if the nucleotide requirement for opioid hyperpolarization in SG neurons was due to G-protein activation. GTP was replaced with the nonhydrolyzable GTP analogue guanosine-5′- O-(3-thiotriphosphate) (GTP-γ-S; 100 μM), which enabled DAMGO to activate a nonreversible membrane hyperpolarization. Further, intracellular application of guanosine-5′- O-(2-thiodiphosphate) (GDP-β-S; 500 μM), which blocks G-protein activation, abolished the effects of DAMGO. We conclude that spinal SG neurons are particularly susceptible to dialysis of GTP by whole cell recording techniques. Moreover, the depletion of GTP leads to the inactivation of G-proteins that mediate μ-opioid activation of an inward-rectifying, potassium conductance in these neurons. These results explain the discrepancy between the opioid-activated hyperpolarization in SG neurons observed in previous sharp electrode experiments and the more recent failures to observe these effects with whole cell patch techniques.

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Cytoplasmic [Ca2+] and intracellular pH in lymphocytes. Role of membrane potential and volume-activated Na+/H+ exchange.

The Journal of General Physiology ◽

10.1085/jgp.89.2.185 ◽

1987 ◽

Vol 89 (2) ◽

pp. 185-213 ◽

Cited By ~ 70

Author(s):

S Grinstein ◽

S Cohen

Keyword(s):

Protein Kinase C ◽

Membrane Potential ◽

Protein Kinase ◽

Intracellular Ph ◽

Enzyme Treatment ◽

Membrane Hyperpolarization ◽

Kinase C ◽

Free Media ◽

Stimulation Of

The effect of elevating cytoplasmic Ca2+ [( Ca2+]i) on the intracellular pH (pHi) of thymic lymphocytes was investigated. In Na+-containing media, treatment of the cells with ionomycin, a divalent cation ionophore, induced a moderate cytoplasmic alkalinization. In the presence of amiloride or in Na+-free media, an acidification was observed. This acidification is at least partly due to H+ (equivalent) uptake in response to membrane hyperpolarization since: it was enhanced by pretreatment with conductive protonophores, it could be mimicked by valinomycin, and it was decreased by depolarization with K+ or gramicidin. In addition, activation of metabolic H+ production also contributes to the acidification. The alkalinization is due to Na+/H+ exchange inasmuch as it is Na+ dependent, amiloride sensitive, and accompanied by H+ efflux and net Na+ gain. A shift in the pHi dependence underlies the activation of the antiport. The effect of [Ca2+]i on Na+/H+ exchange was not associated with redistribution of protein kinase C and was also observed in cells previously depleted of this enzyme. Treatment with ionomycin induced significant cell shrinking. Prevention of shrinking largely eliminated the activation of the antiport. Moreover, a comparable shrinking produced by hypertonic media also activated the antiport. It is concluded that stimulation of Na+/H+ exchange by elevation of [Ca2+]i is due, at least in part, to cell shrinking and does not require stimulation of protein kinase C.

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Sustained Aerobic Oxidation of Vinyl Chloride at Low Oxygen Concentrations

Environmental Science & Technology ◽

10.1021/es9033974 ◽

2010 ◽

Vol 44 (4) ◽

pp. 1405-1411 ◽

Cited By ~ 68

Author(s):

James M. Gossett

Keyword(s):

Vinyl Chloride ◽

Aerobic Oxidation ◽

Low Oxygen ◽

Oxygen Concentrations

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The Function of the Gills of Mayfly Nymphs from Different Habitats

Journal of Experimental Biology ◽

10.1242/jeb.16.3.363 ◽

1939 ◽

Vol 16 (3) ◽

pp. 363-373 ◽

Cited By ~ 2

Author(s):

C. A. WINGFIELD

Keyword(s):

Oxygen Consumption ◽

Oxygen Content ◽

The Body ◽

Gaseous Exchange ◽

Low Oxygen ◽

Respiratory Mechanism ◽

Tracheal Gills ◽

Cloeon Dipterum ◽

Gill Function ◽

Oxygen Concentrations

1. The oxygen consumption of normal and gill-less nymphs of the mayflies Baetis sp., Cloeon dipterum and Ephemera vulgata has been measured at various oxygen concentrations. 2. It has been found that over the complete range of oxygen concentrations studied, the tracheal gills do not aid oxygen consumption in Baetis sp. In Cloeon dipterum, at all oxygen concentrations tested, no gaseous exchange takes place through the gills; at low oxygen concentrations, however, the gills function as an accessory respiratory mechanism in ventilating the respiratory surface of the body and so aid oxygen consumption. In Ephemera Vulgata the gills aid oxygen consumption even at high oxygen concentrations. In this species the gills may function both as true respiratory organs and as a ventilating mechanism. 3. It is shown that the differences in gill function can be related to the oxygen content of the habitat of each species.

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