scholarly journals cADP-ribose potentiates cytosolic Ca2+ elevation and Ca2+ entry via L-type voltage-activated Ca2+ channels in NG108-15 neuronal cells

2000 ◽  
Vol 345 (2) ◽  
pp. 207-215 ◽  
Author(s):  
Minako HASHII ◽  
Yoshio MINABE ◽  
Haruhiro HIGASHIDA
Keyword(s):  
Membrane Potential ◽  
Ryanodine Receptors ◽  
Neuronal Cells ◽  
Resting Membrane Potential ◽  
Hybrid Cells ◽  
External Application ◽  
Whole Cell ◽  
Fura 2 ◽  
Retrograde Signal ◽  
Ca2 Channels

The effects of cADP-ribose (cADPR), a metabolite of β-NAD+, on the elevation of cytoplasmic free Ca2+ concentration ([Ca2+]i) and Ca2+ influx through voltage-activated Ca2+ channels (VACCs) were studied in NG108-15 neuroblastoma×glioma hybrid cells. NG108-15 cells were pre-loaded with fura-2 and whole-cell patch-clamped. Application of cADPR through patch pipettes did not by itself trigger any [Ca2+]i rise at the resting membrane potential. A rise in [Ca2+]i was evoked upon sustained membrane depolarization, and was significantly larger in cADPR-infused cells than in non-infused cells. This potentiation in the [Ca2+]i elevation was reproduced by infusion of β-NAD+, and was blocked by 8-bromo-cADPR and antagonized by external application of ryanodine or by pretreatment of cells with FK506. Nicotinamide inhibited β-NAD+-induced, but not cADPR-elicited, potentiation. [Ca2+]i increases or Ca2+ influx, measured by Mn2+ quenching, elicited by the same protocol of depolarization was blocked completely by nifedipine but not by Ω-conotoxin. Ca2+ influx in cADPR- or β-NAD+-infused cells was steeper and greater than that in control cells, and was inhibited partly by ryanodine. In contrast, ryanodine accelerated Ca2+ influx in non-infused cells. These results show that cADPR amplifies both depolarization-induced [Ca2+]i increase and Ca2+ influx through L-type VACCs. These results suggest that cADPR functions on ryanodine receptors as a direct agonist and also interacts with L-type VACCs as an indirect agonist, i.e. via a retrograde signal.

scholarly journals Grayanotoxin, veratrine, and tetrodotoxin-sensitive sodium pathways in the Schwann cell membrane of squid nerve fibers.

1976 ◽  
Vol 67 (3) ◽  
pp. 369-380 ◽  
Author(s):  
J Villegas ◽  
C Sevcik ◽  
F V Barnola ◽  
R Villegas
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Schwann Cell ◽  
Nerve Fiber ◽  
Schwann Cells ◽  
Giant Axon ◽  
Nerve Fibers ◽  
Resting Membrane Potential ◽  
External Application ◽  
Axon Membrane

The actions of grayanotoxin I, veratrine, and tetrodotoxin on the membrane potential of the Schwann cell were studied in the giant nerve fiber of the squid Sepioteuthis sepioidea. Schwann cells of intact nerve fibers and Schwann cells attached to axons cut lengthwise over several millimeters were utilized. The axon membrane potential in the intact nerve fibers was also monitored. The effects of grayanotoxin I and veratrine on the membrane potential of the Schwann cell were found to be similar to those they produce on the resting membrane potential of the giant axon. Thus, grayanotoxin I (1-30 muM) and veratrine (5-50 mug-jl-1), externally applied to the intact nerve fiber or to axon-free nerve fiber sheaths, produce a Schwann cell depolarization which can be reversed by decreasing the external sodium concentration or by external application of tetrodotoxin. The magnitude of these membrane potential changes is related to the concentrations of the drugs in the external medium. These results indicate the existence of sodium pathways in the electrically unexcitable Schwann cell membrane of S. sepioidea, which can be opened up by grayanotoxin I and veratrine, and afterwards are blocked by tetrodotoxin. The sodium pathways of the Schwann cell membrane appear to be different from those of the axolemma which show a voltage-dependent conductance.

Activation of L-type Ca2+ channels after purinoceptor stimulation by ATP in an alveolar epithelial cell (L2)

1995 ◽  
Vol 269 (6) ◽  
pp. L873-L883 ◽  
Author(s):  
P. Dietl ◽  
T. Haller ◽  
B. Wirleitner ◽  
H. Volkl ◽  
F. Friedrich ◽  
...  
Keyword(s):  
Epithelial Cell ◽  
Alveolar Epithelial Cell ◽  
Alveolar Epithelium ◽  
Bay K 8644 ◽  
Epithelial Cell Line ◽  
Apparent Dissociation Constant ◽  
Whole Cell ◽  
Fura 2 ◽  
Alveolar Epithelial ◽  
Ca2 Channels

In the alveolar epithelium, ATP increases the intracellular Ca2+ concentration ([Ca2+]i) and stimulates the secretion of surfactant. We investigated the effects of extracellular ATP on the membrane potential (Vm), the whole cell current, and [Ca2+]i in a cloned rat alveolar epithelial cell line (L2). In microelectrode experiments, ATP caused a sustained depolarization of Vm, resulting from the activation of cation and Cl- conductances, as revealed by ion replacements. The depolarizing phase of the Vm shift was superimposed by Ca(2+)-dependent depolarizing spikes. Spikes were also induced by depolarizing Vm with charybdotoxin or maitotoxin. Replacement of bath Ca2+ with Ba2+ or Sr2+ also evoked repetitive spikes. Ca2+ (Ba2+, Sr2+)-induced spikes were unaffected by pretreatment with ionomycin or thapsigargin. They were, however, completely abolished by (+)-isradipine (100 nM) and stimulated by BAY K 8644 (100 nM). Whole cell L-type Ca2+ (Ba2+, Sr2+) currents were similarly abolished by (+)-isradipine and enhanced by BAY K 8644. L-type Ca2+ channels were further confirmed by demonstrating high-affinity dihydropyridine receptors stereoselectively labeled by (+)-[3H]-isradipine, apparent dissociation constant < 1 nM. In fura 2 experiments, ATP evoked a transient elevation of [Ca2+]i in the absence of Ca2+ and a biphasic sustained elevation in the presence of Ca2+, indicating intracellular Ca2+ release and Ca2+ entry. The ATP-induced fura 2 signals were unaffected by (+)-isradipine. We conclude that in L2 cells, L-type Ca2+ channels are activated after purinoceptor stimulation by ATP. The overall [Ca2+]i response is, however, mediated by Ca2+ entry through and (+)-isradipine-insensitive mechanism and by intracellular Ca2+ release.

scholarly journals Large-conductance calcium-activated potassium current modulates excitability in isolated canine intracardiac neurons

2013 ◽  
Vol 304 (3) ◽  
pp. C280-C286 ◽  
Author(s):  
Guillermo J. Pérez ◽  
Mayurika Desai ◽  
Seth Anderson ◽  
Fabiana S. Scornik
Keyword(s):  
Membrane Potential ◽  
Calcium Release ◽  
Single Channel ◽  
Calcium Influx ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Release Mechanism ◽  
Dependent Manner ◽  
Whole Cell ◽  
Intracardiac Neurons

We studied principal neurons from canine intracardiac (IC) ganglia to determine whether large-conductance calcium-activated potassium (BK) channels play a role in their excitability. We performed whole cell recordings in voltage- and current-clamp modes to measure ion currents and changes in membrane potential from isolated canine IC neurons. Whole cell currents from these neurons showed fast- and slow-activated outward components. Both current components decreased in the absence of calcium and following 1–2 mM tetraethylammonium (TEA) or paxilline. These results suggest that BK channels underlie these current components. Single-channel analysis showed that BK channels from IC neurons do not inactivate in a time-dependent manner, suggesting that the dynamic of the decay of the fast current component is akin to that of intracellular calcium. Immunohistochemical studies showed that BK channels and type 2 ryanodine receptors are coexpressed in IC principal neurons. We tested whether BK current activation in these neurons occurred via a calcium-induced calcium release mechanism. We found that the outward currents of these neurons were not affected by the calcium depletion of intracellular stores with 10 mM caffeine and 10 μM cyclopiazonic acid. Thus, in canine intracardiac neurons, BK currents are directly activated by calcium influx. Membrane potential changes elicited by long (400 ms) current injections showed a tonic firing response that was decreased by TEA or paxilline. These data strongly suggest that the BK current present in canine intracardiac neurons regulates action potential activity and could increase these neurons excitability.

scholarly journals Membrane potential responses of paramecium caudatum to bitter substances: existence of multiple pathways for bitter responses

1998 ◽  
Vol 201 (1) ◽  
pp. 13-20
Author(s):  
K Oami
Keyword(s):  
Membrane Potential ◽  
Action Potentials ◽  
Bathing Solution ◽  
Transduction Pathway ◽  
Paramecium Caudatum ◽  
External Application ◽  
Common Component ◽  
Voltage Gated ◽  
Mutant Cells ◽  
Ca2 Channels

The membrane potential responses of Paramecium caudatum to the external application of bitter substances were examined by employing conventional electrophysiological techniques. Mutant cells defective in voltage-gated Ca2+ channels were used to record the potential responses in the absence of contamination by Ca2+ action potentials. The cells produced a transient depolarization followed by a transient hyperpolarization in response to a rapid whole-cell application of chloroquine, strychnine nitrate or brucine. Of these chemicals, chloroquine was the most potent. Cells produced a simple depolarization in response to a localized application of test chemicals to the anterior region, whereas they produced a transient hyperpolarization in response to an application to the posterior region. Membrane potential responses to an application of chloroquine declined with repeated application. The presence of chloroquine in the external bathing solution strongly inhibited the membrane potential responses to an application of brucine or strychnine. However, the presence of chloroquine did not affect the membrane potential responses to an application of quinine. It is suggested that chloroquine, strychnine and brucine share a common component of their transduction pathways, but that the transduction pathway for quinine is different.

Endurance training alters outward K+current characteristics in rat cardiocytes

2001 ◽  
Vol 90 (4) ◽  
pp. 1327-1333 ◽  
Author(s):  
Korinne N. Jew ◽  
M. Charlotte Olsson ◽  
Eric A. Mokelke ◽  
Bradley M. Palmer ◽  
Russell L. Moore
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Primary Culture ◽  
Left Ventricular ◽  
Resting Membrane Potential ◽  
Sprague Dawley ◽  
Whole Cell ◽  
Time To Peak ◽  
Time Required ◽  
In Cells

The effect of endurance run training on outward K+ currents with rapidly inactivating ( I to) and sustained or slowly inactivating ( I sus) characteristics was examined in left ventricular (LV) cardiocytes isolated from sedentary (Sed) and treadmill-trained (Tr) female Sprague-Dawley rats. Isolated LV cardiocytes were used in whole cell patch-clamp studies to characterize whole cell I to and I sus. Peak I to was greatest in cells isolated from the Tr group. When I to was corrected for cell capacitance to yield a current density, most, but not all, of the Sed vs. Tr differences in I to magnitude were eliminated. Regardless of how I to was expressed (e.g., I to or I todensity), the time required to achieve a peak value was markedly shortened in the cardiocytes isolated from the Tr group. Training elicited a reduction in I sus density. Action potential characteristics were determined in Sed and Tr cardiocytes in primary culture. Training did not affect resting membrane potential, whereas peak membrane potential was reduced and time to peak membrane potential was prolonged in the Tr group. In addition, time to 50% repolarization was significantly increased in cells from the Tr group. Collectively, these data indicate that I to and I sus characteristics are altered by training in isolated LV cardiocytes. These alterations in I to and I sus may be responsible, at least in part, for the training-induced alterations in action potential configuration in cardiocytes in primary culture.

HERG-Like Potassium Current Regulates the Resting Membrane Potential in Glomus Cells of the Rabbit Carotid Body

2000 ◽  
Vol 83 (3) ◽  
pp. 1150-1157 ◽  
Author(s):  
Jeffrey L. Overholt ◽  
Eckhard Ficker ◽  
Tianen Yang ◽  
Hashim Shams ◽  
Gary R. Bright ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Carotid Body ◽  
Cell Voltage ◽  
Resting Membrane Potential ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Whole Cell ◽  
Glomus Cells ◽  
Tail Current

Direct evidence for a specific K+ channel underlying the resting membrane potential in glomus cells of the carotid body has been absent. The product of the human ether-a-go-go–related gene (HERG) produces inward rectifier currents that are known to contribute to the resting membrane potential in other neuronal cells. The goal of the present study was to determine whether carotid body glomus cells express HERG-like K+ current, and if so, to determine whether a HERG-like current regulates the resting membrane potential. Freshly dissociated rabbit glomus cells under whole cell voltage clamp exhibited slowly decaying outward currents that activated 20–30 mV positive to the resting membrane potential. Raising extracellular K+revealed a slowly deactivating inward tail current indicative of HERG-like K+ current. HERG-like currents were not found in cells resembling type II cells. The HERG-like current was blocked by dofetilide (DOF) in a concentration-dependent manner (IC50 = 13 ± 4 nM, mean ± SE) and high concentrations of Ba2+ (1 and 10 mM). The biophysical and pharmacological characteristics of this inward tail current suggest that it is conducted by a HERG-like channel. The steady-state activation properties of the HERG-like current ( V h = −44 ± 2 mV) suggest that it is active at the resting membrane potential in glomus cells. In whole cell, current-clamped glomus cells (average resting membrane potential, − 48 ± 4 mV), DOF, but not tetraethylammonium, caused a significant (13 mV) depolarizing shift in the resting membrane potential. Using fluorescence imaging, DOF increased [Ca2+]i in isolated glomus cells. In an in-vitro carotid body preparation, DOF increased basal sensory discharge in the carotid sinus nerve in a concentration-dependent manner. These results demonstrate that glomus cells express a HERG-like current that is active at, and responsible for controlling the resting membrane potential.

Voltage-dependent effects of isoproterenol on cytosolic Ca concentration in rat heart

1987 ◽  
Vol 252 (4) ◽  
pp. H697-H703 ◽  
Author(s):  
S. S. Sheu ◽  
V. K. Sharma ◽  
M. Korth
Keyword(s):  
Membrane Potential ◽  
Calcium Concentration ◽  
Ventricular Myocytes ◽  
Cytosolic Calcium ◽  
Resting Membrane Potential ◽  
Beta Adrenoceptor ◽  
Adrenoceptor Agonist ◽  
Voltage Dependent ◽  
K Concentration ◽  
Ca2 Channels

The effect of the beta-adrenoceptor agonist, isoproterenol, on cytosolic calcium concentration ([Ca2+]i) was studied with the Ca2+-sensitive fluorescent indicator quin 2 in enzymatically dissociated rat ventricular myocytes. Under conditions in which cells have normal polarized resting membrane potential, isoproterenol (1 microM) produced a decrease in [Ca2+]i. In contrast, in the depolarized cells (by raising extracellular K+ concentration to 50 mM), isoproterenol (1 microM) caused an increase in [Ca2+]i. This isoproterenol-induced increase in [Ca2+]i in depolarized cells could be reversed by prior exposure of the cells to the Ca2+ channel blocker, verapamil (5 microM). The results indicate that isoproterenol can either decrease or increase [Ca2+]i depending on membrane potential. The actual effect of isoproterenol on [Ca2+]i at any given membrane potential probably reflects the relative contributions of isoproterenol-induced stimulation of Ca2+ buffering or effluxing activities (which favor a decrease in [Ca2+]i) and enhancement of Ca2+ influx through voltage-sensitive Ca2+ channels (which favors an increase in [Ca2+]i).

Metabolic communication from cardiac myocytes to vascular endothelial cells

2005 ◽  
Vol 288 (5) ◽  
pp. H2232-H2237 ◽  
Author(s):  
Anna K. Brzezinska ◽  
Daphne Merkus ◽  
William M. Chilian
Keyword(s):  
Endothelial Cells ◽  
Membrane Potential ◽  
Cardiac Myocytes ◽  
Vascular Tone ◽  
Vascular Endothelial Cells ◽  
Resting Membrane Potential ◽  
Vascular Endothelial ◽  
Whole Cell ◽  
Cell Current ◽  
Whole Cell Current

The endothelium releases substances that affect both vascular and cardiac myocytes. However, under conditions of augmented metabolic demands and cardiac work, signals from the cardiac myocytes may be critical for the endothelium to fulfill its secretory and regulatory function in the vascular bed. Therefore, we hypothesized that cardiac myocytes produce substances that alter the resting membrane potential of endothelial cells and thus vascular tone. Isolated rat cardiac myocytes were electrically stimulated at the rate of 0 and 400 beats/min (Po2 = 150 mmHg), and supernatants were collected from each group (Sup-0; control) and (Sup-400) and used within 6 mo. These supernatants were applied to human coronary endothelial cells that were subsequently analyzed by using the whole cell and cell-attached patch-clamp modes. Sup-0 had no effect on the whole cell current and the zero-current potential. The Sup-0 from myocytes treated with aprotinin, an inhibitor of kallikrein and serine protease, reduced whole cell current between −120 and −60 mV. Sup-400 depolarized endothelial cells from the resting membrane potential of −45 to −5 mV ( P < 0.05), increased the magnitude of an inward current, and activated an outward current. Moreover, Sup-400 cells assayed in cell-attached patches increased single channel amplitude and the probability of a channel being in the open state. These effects were reversed by the Sup-400 from aprotinin-treated cells. We conclude that under certain metabolic conditions, isolated cardiac myocytes produce and release vasoactive substances that alter the function of K+ channels in vascular endothelial cells. Thus cardiac myocytes seem to communicate metabolic information to the endothelium, which could potentially influence vascular tone.

Inhibition of voltage-dependent Ca2+influx by extracellular ATP in salivary cells of the leech Haementeria ghilianii

1996 ◽  
Vol 199 (6) ◽  
pp. 1335-1341
Author(s):  
W Wuttke ◽  
T Munsch ◽  
J Deitmer
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Extracellular Atp ◽  
Threshold Concentration ◽  
Resting Membrane Potential ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
K Concentration ◽  
Gamma S ◽  
Ca2 Channels

The effects of extracellular ATP on intracellular free Ca2+ concentration ([Ca2+]i) and depolarization-induced elevations of [Ca2+]i were investigated in salivary cells of the leech Haementeria ghilianii using the fluorescent Ca2+ indicator Fura-2. Simultaneously, the membrane potential was monitored or controlled by voltage-clamp. The cell membrane was depolarized either by transient elevations of the extracellular K+ concentration ([K+]o) to 90 mmol l-1 or by depolarizing steps under voltage-clamp. The resulting transient elevations of [Ca2+]i (Ca2+ transients) could be repeatedly elicited with little variability in amplitude. Ca2+ transients were completely inhibited by 2 mmol l-1 Ni2+ or in Ca2+-free saline. The transients are, therefore, dependent on Ca2+ influx from the external medium through voltage-gated Ca2+ channels. The Ca2+ influx was rapidly and reversibly inhibited by extracellular application of ATP. The effect was dose-dependent with a threshold concentration below 10(-7) mol l-1. A 50 % reduction in the amplitude of Ca2+ transients was obtained by application of 1&shy;2 &micro;mol l-1 ATP or ATP-gamma-S (apparent IC50, 1.6 &micro;mol l-1 ATP) and Ca2+ transients were almost completely inhibited by 30&shy;100 &micro;mol l-1 ATP. Resting [Ca2+]i, the resting membrane potential and membrane potential changes induced by 90 mmol l-1 [K+]o were not affected by ATP. Adenosine (10 &micro;mol l-1) did not affect resting [Ca2+]i, the resting membrane potential or membrane potential changes induced by 90 mmol l-1 [K+]o and had little effect on Ca2+ transients. Suramin, an antagonist of vertebrate P2 receptors, was without effect on the inhibitory actions of ATP. We conclude that activation of a suramin-insensitive purinoceptor by ATP inhibits Ca2+ influx through voltage-gated Ca2+ channels in the salivary cells of Haementeria ghilianii.

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