Partial Uncoupling of Neurotransmitter Release From [Ca2+]i by Membrane Hyperpolarization

1999 ◽  
Vol 81 (6) ◽  
pp. 3044-3053 ◽  
Author(s):  
R. Ravin ◽  
H. Parnas ◽  
M. E. Spira ◽  
I. Parnas
Keyword(s):  
Membrane Potential ◽  
Neurotransmitter Release ◽  
Quantal Content ◽  
Presynaptic Membrane ◽  
Release Process ◽  
Membrane Hyperpolarization ◽  
Quantal Release ◽  
Asynchronous Release ◽  
Frequency Of Stimulation ◽  
Different Levels

Partial uncoupling of neurotransmitter release from [Ca2+]i by membrane hyperpolarization. The dependence of evoked and asynchronous release on intracellular calcium ([Ca2+]i) and presynaptic membrane potential was examined in single-release boutons of the crayfish opener neuromuscular junction. When a single bouton was depolarized by a train of pulses, [Ca2+]iincreased to different levels according to the frequency of stimulation. Concomitant measurements of evoked release and asynchronous release, from the same bouton, showed that both increased in a sigmoidal manner as a function of [Ca2+]i. When each of the depolarizing pulses was immediately followed by a hyperpolarizing pulse, [Ca2+]i was elevated to a lesser degree than in the control experiments, and the rate of asynchronous release and the quantal content were reduced; most importantly, evoked quantal release terminated sooner. The diminution of neurotransmitter release by the hyperpolarizing postpulse (HPP) could not be entirely accounted for by the reduction in [Ca2+]i. The experimental results are consistent with the hypothesis that the HPP reduces the sensitivity of the release machinery to [Ca2+]i, thereby not only reducing the quantal content but also terminating the quantal release process sooner.

scholarly journals Fusicoccin (FC)-Induced Rapid Growth, Proton Extrusion and Membrane Potential Changes in Maize (Zea mays L.) Coleoptile Cells: Comparison to Auxin Responses

2021 ◽  
Vol 22 (9) ◽  
pp. 5017
Author(s):  
Małgorzata Polak ◽  
Waldemar Karcz
Keyword(s):  
Membrane Potential ◽  
Rapid Growth ◽  
Proton Pumps ◽  
Proton Extrusion ◽  
Membrane Hyperpolarization ◽  
Fungal Toxin ◽  
Maize Coleoptile ◽  
Lag Times ◽  
Kinetics Of ◽  
Indole 3 Acetic Acid

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.

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

1998 ◽  
Vol 80 (6) ◽  
pp. 2954-2962 ◽  
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.

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

1987 ◽  
Vol 89 (2) ◽  
pp. 185-213 ◽  
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.

Measuring Absolute Membrane Potential Across Space and Time

2021 ◽  
Vol 50 (1) ◽  
Author(s):  
Julia R. Lazzari-Dean ◽  
Anneliese M.M. Gest ◽  
Evan W. Miller
Keyword(s):  
Membrane Potential ◽  
Neurotransmitter Release ◽  
Cell Cycle Control ◽  
The Other ◽  
Annual Review ◽  
Publication Date ◽  
Short Term ◽  
Cellular Processes ◽  
Sensing Platform ◽  
The One

Membrane potential (Vmem) is a fundamental biophysical signal present in all cells. Vmem signals range in time from milliseconds to days, and they span lengths from microns to centimeters. Vmem affects many cellular processes, ranging from neurotransmitter release to cell cycle control to tissue patterning. However, existing tools are not suitable for Vmem quantification in many of these areas. In this review, we outline the diverse biology of Vmem, drafting a wish list of features for a Vmem sensing platform. We then use these guidelines to discuss electrode-based and optical platforms for interrogating Vmem. On the one hand, electrode-based strategies exhibit excellent quantification but are most effective in short-term, cellular recordings. On the other hand, optical strategies provide easier access to diverse samples but generally only detect relative changes in Vmem. By combining the respective strengths of these technologies, recent advances in optical quantification of absolute Vmem enable new inquiries into Vmem biology. Expected final online publication date for the Annual Review of Biophysics, Volume 50 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Fractional SR Ca release is regulated by trigger Ca and SR Ca content in cardiac myocytes

1995 ◽  
Vol 268 (5) ◽  
pp. C1313-C1319 ◽  
Author(s):  
J. W. Bassani ◽  
W. Yuan ◽  
D. M. Bers
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Load Condition ◽  
Standard Test ◽  
Ca Current ◽  
Release Process ◽  
Contraction Coupling ◽  
Ca Uptake ◽  
High Load Condition ◽  
Different Levels

The release of sarcoplasmic reticulum (SR) Ca in cardiac muscle during excitation-contraction coupling is known to be graded by the amount of activating Ca outside the SR (i.e., Ca-induced Ca release). However, little is known about how intra-SR Ca affects the release process. In this study we assessed how the fractional SR Ca release as described by Bassani et al. [Am. J. Physiol. 265 (Cell Physiol. 34): C533-C540, 1993] is affected by alteration of trigger Ca and of SR Ca content. Experiments were done with isolated ferret ventricular myocytes using indo 1 to measure Ca concentration, perforated patch to measure Ca current (ICa), caffeine application to release SR Ca, and thapsigargin to completely block SR Ca uptake. For what we consider a Normal SR Ca load and trigger Ca [action potential at 0.5 Hz with 2 mM extracellular Ca concentration ([Ca]o)], 35 +/- 3% of the SR Ca content was released at a twitch. Changing trigger Ca by altering [Ca]o (to 0.5 and 8 mM) at a test twitch changed this fractional SR Ca release to 10 +/- 2 and 59 +/- 6%, with the same SR Ca load (and peak ICa changed in a parallel manner in separate voltage-clamp experiments). Three different levels of SR Ca load were studied (Low, Normal, and High; by action potential stimulation at different frequencies from 0.05 to 0.8 Hz) using the same standard test trigger Ca (2 mM). Surprisingly, the High-load condition only increased SR Ca content by approximately 4% but appeared to be very close to the limiting SR Ca capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Determining the Relative Efficacy of Positive Allosteric Modulators of the GABAA Receptor

2013 ◽  
Vol 19 (3) ◽  
pp. 462-467 ◽  
Author(s):  
Philippe Ghisdal ◽  
Nadine Noel ◽  
Nathalie Pacico ◽  
Murielle Martini ◽  
Patrik Foerch ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Patch Clamp ◽  
Multiple Drug ◽  
Allosteric Modulators ◽  
Relative Efficacy ◽  
Subtype Selectivity ◽  
Automated Patch Clamp ◽  
Positive Allosteric Modulators ◽  
New Generation ◽  
Different Levels

Gamma amino butyric acid receptors (GABA) are major therapeutic targets for the development of drugs in neurological and psychiatric disorders. The new generation of GABAA modulators is targeting subtype selectivity and low/partial efficacy on the receptor to potentially overcome the adverse effects described for drugs with full agonist profile. We evaluated a screening approach to measure the relative efficacy of GABAA positive allosteric modulators (PAM) using automated patch clamp and fluorescence membrane potential assays. We determined that the use of an internal comparator (zolpidem), tested on each cell in parallel to the test compound, provides a reliable approach to measure and compare the relative efficacy of PAM ligands. Patch clamp recordings on recombinant GABAA receptors, using a multiple drug addition protocol, allows us to rank PAM ligands with different levels of efficacies. We observed that fluorescence membrane potential assays are not predictive of the relative efficacies of GABAA PAM ligands.

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)

Stimulus-Dependent Alterations in Quantal Neurotransmitter Release

2006 ◽  
Vol 96 (6) ◽  
pp. 3082-3087 ◽  
Author(s):  
Chad P. Grabner ◽  
Aaron P. Fox
Keyword(s):  
Neurotransmitter Release ◽  
Chromaffin Cells ◽  
Time Course ◽  
Ion Concentration ◽  
Fusion Pore ◽  
Release Process ◽  
Large Dense Core Vesicles ◽  
Intracellular Calcium Ion ◽  
Individual Vesicle ◽  
Digitonin Permeabilization

Neurotransmitter release is a steep function of the intracellular calcium ion concentration ([Ca2+]i) at the release sites. Both the Ca2+ amplitude and the time course appear to be important for specifying neurotransmitter release. Ca2+ influx regulates the number of vesicles exocytosed as well as the amount of neurotransmitter each individual vesicle releases. In our study we stimulated mouse chromaffin cells in two different ways to alter Ca2+ presentation at the release sites. One method, digitonin permeabilization followed by exposure to Ca2+, allows for a large uniform global elevation of [Ca2+]i, whereas the second method, application of nicotine, depolarizes chromaffin cells and activates voltage-dependent Ca2+ channels, thereby producing more phasic and localized changes in [Ca2+]i. Using amperometry to monitor catecholamine release, we show that both kinds of stimuli elicit the exocytosis of similar quantities of neurotransmitter per large dense core vesicles (LDCVs) released. Even so, the release process was quite different for each stimulus; nicotine-elicited events were small and slow, whereas digitonin events were, in comparison, large and fast. In addition, the transient opening of the fusion pore, called the “foot,” was essentially absent in digitonin-stimulated cells, but was quite common in nicotine-stimulated cells. Thus even though both strong stimuli used in this study elicited the release of many vesicles it appears that the differences in the Ca2+ levels at the release sites were key determinants for the fusion and release of individual vesicles.

Effect of membrane potential on cytosolic calcium of bovine aortic endothelial cells

1989 ◽  
Vol 257 (3) ◽  
pp. H778-H784 ◽  
Author(s):  
W. P. Schilling
Keyword(s):  
Endothelial Cells ◽  
Membrane Potential ◽  
Cytosolic Calcium ◽  
Membrane Depolarization ◽  
K Channel ◽  
Membrane Hyperpolarization ◽  
Aortic Endothelial Cells ◽  
Bovine Aortic Endothelial Cells ◽  
K Concentration ◽  
Aortic Endothelial

The effect of bradykinin on membrane potential of cultured bovine aortic endothelial cells (BAECs) was estimated by measuring the uptake of the lipophilic cation, tetra[3H]phenylphosphonium ([3H]TPP+). Uptake of [3H]TPP+ was found to be 1) a function of extracellular K+ concentration, 2) sensitive to valinomycin, and 3) decreased by the K+ channel inhibitor, Ba2+, suggesting that the uptake of [3H]TPP+ responds to changes in membrane potential of the BAEC. Bradykinin (50 nM) produced an increase in [3H]TPP+ uptake in low K+ buffer consistent with a bradykinin-induced membrane hyperpolarization. The effect of membrane depolarization with high K+ buffer on the bradykinin-stimulated changes in cytosolic Ca2+ was determined using the fluorescent Ca2+ indicator, fura-2. The results of these experiments demonstrated that both basal cytosolic Ca2+ and bradykinin-stimulated release of Ca2+ from internal stores were not affected by membrane depolarization. However, bradykinin-stimulated influx of Ca2+ from the extracellular space decreased with membrane depolarization in a manner consistent with the movement of Ca2+ through a channel.

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