Voltage-Dependent Calcium Currents in Trigeminal Motoneurons of Early Postnatal Rats: Modulation by 5-HT Receptors

2005 ◽  
Vol 94 (3) ◽  
pp. 2063-2072 ◽  
Author(s):  
Chie-Fang Hsiao ◽  
Nanping Wu ◽  
Scott H. Chandler
Keyword(s):  
Ion Channels ◽  
Calcium Channels ◽  
Calcium Current ◽  
Calcium Currents ◽  
Input Output ◽  
Membrane Excitability ◽  
Oral Motor ◽  
Final Output ◽  
Voltage Dependent ◽  
Trigeminal Motoneurons

Trigeminal motoneurons relay the final output signals generated within the oral-motor pattern generating circuit(s) to muscles for execution of various motor patterns. In recent years, these motoneurons were shown to possess voltage dependent nonlinear membrane properties that allow them to actively participate in sculpting their final output. A complete understanding of the factors controlling trigeminal motoneuronal (TMN) discharge during oral-motor activity requires, at a minimum, a detailed understanding of the palette of ion channels responsible for membrane excitability and a determination of whether these ion channels are targets for modulation. Toward that end, we studied in detail the properties of calcium channels in TMNs and their susceptibility to modulation by 5-HT in rat brain slices. We found that based on pharmacological and voltage-dependent properties, high-voltage-activated (HVA) N-type [ω-conotoxin GVIA (ω-CgTX)]-sensitive, and to a lesser extent P/Q-type [ω-agatoxin IVA (ω-Aga IVA)]-sensitive, calcium channels make up the majority of the whole cell calcium current. 5-HT (5.0 μM) decreased HVA current by 31.3 ± 2.2%, and the majority of this suppression resulted from reduction of current flow through N- and P/Q-type calcium channels. In contrast, 5-HT had no effect on low-voltage-activated (LVA) current amplitude in TMNs. HVA calcium current inhibition was mimicked by 5-CT, a 5-HT1 receptor agonist, and by R(+)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT), a specific 5-HT1A agonist. The effects of 5-HT were blocked by the 5-HT1A antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine hydrobromide (NAN-190) but not by ketanserin, a 5-HT2/1C antagonist. Under current clamp, ω-CgTX and 5-HT were most effective in suppressing the mAHP and both increased the spike frequency and input/output gain in response to current injection. Calcium current modulation by 5-HT1A receptors likely is an important mechanism to fine tune the input/output gain of TMNs in response to small incoming synaptic inputs and accounts for some of the previously reported effects of 5-HT on TMN excitability during tonic and burst activity during oral-motor behavior.

scholarly journals Dopamine modulates in a differential fashion T- and L-type calcium currents in bass retinal horizontal cells.

1993 ◽  
Vol 102 (2) ◽  
pp. 277-294 ◽  
Author(s):  
C Pfeiffer-Linn ◽  
E M Lasater
Keyword(s):  
Cyclic Amp ◽  
Calcium Channels ◽  
Calcium Current ◽  
Horizontal Cell ◽  
Calcium Currents ◽  
Horizontal Cells ◽  
White Bass ◽  
Cell Calcium ◽  
Cone Type ◽  
Voltage Dependent

White bass (Roccus chrysops) retinal horizontal cells possess two types of voltage-activated calcium currents which have recently been characterized with regard to their voltage dependence and pharmacology (Sullivan, J., and E. M. Lasater. 1992. Journal of General Physiology. 99:85-107). A low voltage-activated transient current was identified which resembles the T-type calcium current described in a number of other preparations, along with a sustained high threshold, long-lasting calcium current that resembles the L-type calcium current. Here we report on the modulation of horizontal cell calcium channels by dopamine. Under whole-cell voltage clamp conditions favoring the expression of both calcium currents, dopamine had opposing actions on the two types of voltage-sensitive calcium currents in the same cone-type horizontal cell. The L-type calcium current was significantly potentiated by dopamine while the T-type current was simultaneously reduced. Dopamine had no effect on calcium currents in rod-type horizontal cells. Both of dopamine's actions were mimicked with the D1 receptor agonist, SKF 38393, and blocked by application of the D1 specific antagonist, SCH 23390. Dopamine's actions on the two types of calcium currents in white bass horizontal cells are mimicked by the cell membrane-permeant cyclic AMP derivative, 8-(4-chlorophenylthio)-cyclic AMP, suggesting that dopamine's action is linked to a cAMP-mediated second messenger system. Furthermore, the inhibitor of cAMP-dependent protein kinase blocked both of dopamine's actions on the voltage-dependent calcium channels when introduced through the patch pipette. This indicates that protein phosphorylation is involved in modulating horizontal cell calcium channels by dopamine. Taken together, these results show that dopamine has differential effects on the voltage-dependent calcium currents in retinal horizontal cells. The modulation of these currents may play a role in shaping the response properties of horizontal cells.

Voltage-dependent calcium channels in rat midbrain dopamine neurons: modulation by dopamine and GABAB receptors

1995 ◽  
Vol 74 (3) ◽  
pp. 1137-1148 ◽  
Author(s):  
D. L. Cardozo ◽  
B. P. Bean
Keyword(s):  
Calcium Channels ◽  
Calcium Current ◽  
Receptor Agonist ◽  
Gabab Receptor ◽  
Calcium Currents ◽  
Dopamine Neurons ◽  
Gabab Receptors ◽  
High Threshold ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

1. Voltage-dependent calcium channels were studied with whole cell voltage-clamp recordings from neurons enzymatically dispersed from the ventral mesencephalon of rat brains (postnatal days 3-10) and identified as dopamine neurons by 5,7-dihydroxytryptamine autofluorescence. 2. Dopamine neurons had large high-threshold calcium currents activated by depolarizations positive to -50 mV. Different components of calcium channel current were not readily distinguishable by voltage dependence or kinetics, but pharmacological experiments showed the existence of different channel types. The overall current had significant components blocked by nimodipine (28%), by omega-conotoxin GVIA (22%), and by omega-agatoxin-IVA (omega-Aga-IVA) (37%), and there was a significant amount of current (16%) remaining in saturating concentrations of all three blockers. 3. High-threshold calcium current was reversibly reduced by the gamma-aminobutyric acid-B (GABAB) receptor agonist baclofen and by dopamine and the D2 receptor agonist quinpirole. Inhibition by GABAB or dopamine agonists developed and reversed within seconds. 4. Quinpirole reduced both omega-conotoxin-sensitive and omega-Aga-IVA-sensitive components of calcium current. 5. With physiological ionic conditions, inward calcium currents were outweighed by outward currents, in part through calcium-activated potassium channels activated by omega-conotoxin-sensitive and omega-Aga-IVA-sensitive calcium entry.

A background sodium conductance is necessary for spontaneous depolarizations in rat pituitary cell line GH3

1994 ◽  
Vol 266 (3) ◽  
pp. C709-C719 ◽  
Author(s):  
S. M. Simasko
Keyword(s):  
Cell Line ◽  
Calcium Current ◽  
Membrane Conductance ◽  
Potassium Currents ◽  
Pituitary Cell ◽  
Calcium Currents ◽  
Gh3 Cells ◽  
Sodium Conductance ◽  
Rat Pituitary ◽  
Voltage Dependent

The role of Na+ in the expression of membrane potential activity in the clonal rat pituitary cell line GH3 was investigated using the perforated patch variation of patch-clamp electrophysiological techniques. It was found that replacing bath Na+ with choline, tris(hydroxymethyl)aminomethane (Tris), or N-methyl-D-glucamine (NMG) caused the cells to hyperpolarize 20-30 mV. Tetrodotoxin had no effect. The effects of the Na+ substitutes could not be explained by effects on potassium or calcium currents. Although all three Na+ substitutes suppressed voltage-dependent calcium current by 10-20%, block of voltage-dependent calcium current by nifedipine or Co2+ did not result in hyperpolarization of the cells. There was no effect of the Na+ substitutes on voltage-dependent potassium currents. In contrast, all three Na+ substitutes influenced calcium-activated potassium currents [IK(Ca)], but only at depolarized potentials. Choline consistently suppressed IK(Ca), whereas Tris and NMG either had no effect or slightly increased IK(Ca). These effects on IK(Ca) also cannot explain the hyperpolarization induced by removing bath Na+. Choline always hyperpolarized cells yet suppressed IK(Ca). Furthermore, removing bath Na+ caused an increase in cell input resistance, an observation consistent with the loss of a membrane conductance as the basis of the hyperpolarization. Direct measurement of background currents revealed a 12-pA inward current at -84 mV that was lost upon removing bath Na+. These results suggest that this background sodium conductance provides the depolarizing drive for GH3 cells to reach the threshold for firing calcium-dependent action potentials.

scholarly journals Proteolytic maturation of α2δ represents a checkpoint for activation and neuronal trafficking of latent calcium channels

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Ivan Kadurin ◽  
Laurent Ferron ◽  
Simon W Rothwell ◽  
James O Meyer ◽  
Leon R Douglas ◽  
...  
Keyword(s):  
Calcium Channels ◽  
Proteolytic Cleavage ◽  
Proteolytic Processing ◽  
Calcium Currents ◽  
Cleavage Sites ◽  
Voltage Dependent ◽  
Neuronal Processes ◽  
Associated Proteins ◽  
Synaptic Boutons

The auxiliary α2δ subunits of voltage-gated calcium channels are extracellular membrane-associated proteins, which are post-translationally cleaved into disulfide-linked polypeptides α2 and δ. We now show, using α2δ constructs containing artificial cleavage sites, that this processing is an essential step permitting voltage-dependent activation of plasma membrane N-type (CaV2.2) calcium channels. Indeed, uncleaved α2δ inhibits native calcium currents in mammalian neurons. By inducing acute cell-surface proteolytic cleavage of α2δ, voltage-dependent activation of channels is promoted, independent from the trafficking role of α2δ. Uncleaved α2δ does not support trafficking of CaV2.2 channel complexes into neuronal processes, and inhibits Ca2+ entry into synaptic boutons, and we can reverse this by controlled intracellular proteolytic cleavage. We propose a model whereby uncleaved α2δ subunits maintain immature calcium channels in an inhibited state. Proteolytic processing of α2δ then permits voltage-dependent activation of the channels, acting as a checkpoint allowing trafficking only of mature calcium channel complexes into neuronal processes.

scholarly journals Effect of FMRFamide on voltage-dependent currents in identified centrifugal neurons of the optic lobe of the cuttlefish, Sepia officinalis

2020 ◽  
Author(s):  
Abdesslam Chrachri
Keyword(s):  
Visual Processing ◽  
Calcium Current ◽  
Optic Lobe ◽  
Low Voltage ◽  
Sodium Current ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWhole-cell patch-clamp recordings from identified centrifugal neurons of the optic lobe in a slice preparation allowed the characterization of five voltage-dependent currents; two outward and three inward currents. The outward currents were; the 4-aminopyridine-sensitive transient potassium or A-current (IA), the TEA-sensitive sustained current or delayed rectifier (IK). The inward currents were; the tetrodotoxin-sensitive transient current or sodium current (INa). The second is the cobalt- and cadmium-sensitive sustained current which is enhanced by barium and blocked by the dihydropyridine antagonist, nifedipine suggesting that it could be the L-type calcium current (ICaL). Finally, another transient inward current, also carried by calcium, but unlike the L-type, this current is activated at more negative potentials and resembles the low-voltage-activated or T-type calcium current (ICaT) of other preparations.Application of the neuropeptide FMRFamide caused a significant attenuation to the peak amplitude of both sodium and sustained calcium currents without any apparent effect on the transient calcium current. Furthermore, FMRFamide also caused a reduction of both outward currents in these centrifugal neurons. The fact that FMRFamide reduced the magnitude of four of five characterized currents could suggest that this neuropeptide may act as a strong inhibitory agent on these neurons.SummaryFMRFamide modulate the ionic currents in identified centrifugal neurons in the optic lobe of cuttlefish: thus, FMRFamide could play a key role in visual processing of these animals.

Voltage-dependent calcium channels in ventricular cells of rainbow trout: effect of temperature changes in vitro

2000 ◽  
Vol 278 (6) ◽  
pp. R1524-R1534 ◽  
Author(s):  
Catherine S. Kim ◽  
Mary D. Coyne ◽  
Judith K. Gwathmey
Keyword(s):  
Rainbow Trout ◽  
Calcium Channels ◽  
Temperature Sensitivity ◽  
Calcium Currents ◽  
Temperature Dependency ◽  
Patch Clamp Technique ◽  
Ventricular Cells ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

Voltage-dependent calcium channels (VDCC) in ventricular myocytes from rainbow trout ( Oncorhynchus mykiss) were investigated in vitro using the perforated patch-clamp technique, which maintains the integrity of the intracellular milieu. First, we characterized the current using barium as the charge carrier and established the doses of various pharmacological agents to use these agents in additional studies. Second, we examined the current at several physiological temperatures to determine temperature dependency. The calcium currents at 10°C (acclimation temperature) were identified as l-type calcium currents based on their kinetic behavior and response to various calcium channel agonists and antagonists. Myocytes were chilled (4°C) and warmed (18 and 22°C), and the response of VDCC to varying temperatures was observed. There was no significant dependency of the current amplitude and kinetics on temperature. Amplitude decreased 25–36% at 4°C (Q10 ∼1.89) and increased 18% at 18°C (Q10 ∼1.23) in control, Bay K8644 (Bay K)-, and forskolin-enhanced currents. The inactivation rates (τi) did not demonstrate a temperature sensitivity for the VDCC (Q10 1.23–1.92); Bay K treatment, however, increased temperature sensitivity of τi between 10 and 18°C (Q10 3.98). The low Q10 values for VDCC are consistent with a minimal temperature sensitivity of trout myocytes between 4 and 22°C. This low-temperature dependency may provide an important role for sarcolemmal calcium channels in adaptation to varying environmental temperatures in trout.

Separation and modulation of calcium currents in bullfrog sympathetic neurons

1992 ◽  
Vol 70 (S1) ◽  
pp. S56-S63 ◽  
Author(s):  
Stephen W. Jones ◽  
Keith S. Elmslie
Keyword(s):  
G Protein ◽  
Calcium Current ◽  
Sympathetic Neurons ◽  
Calcium Currents ◽  
Dependent Manner ◽  
Activation Kinetics ◽  
Channel Opening ◽  
Voltage Dependent ◽  
Rapid Activation ◽  
Kinetics Of

The calcium current of frog sympathetic neurons has relatively rapid activation kinetics (τ < 3 ms) in response to changes in voltage. Pharmacologically, the current is blocked ~90% by ω-conotoxin, but < 10% by dihydropyridine antagonists. This suggests that nearly all of the current is N type. However, inactivation is slow and incomplete even for depolarizations lasting > 1 s, consistent with recent evidence that N-type channels do not always inactivate rapidly. The calcium current is partially inhibited via receptors for acetylcholine, luteinizing hormone releasing hormone, substance P, ATP, and norepinephrine. These effects are mimicked by internal dialysis with GTP-γ-S, suggesting involvement of a G protein. The transmitters affect the activation kinetics of the calcium current in a voltage-dependent manner, which can be modeled as a reversible shift of some channels to "reluctant" states in which strong depolarization is needed to produce channel opening. The effects of transmitters develop and recover with t½ ~ 1–2 s, so if a second messenger is involved in receptor – calcium channel coupling, it must act rapidly.Key words: norepinephrine, ω-conotoxin, dihydropyridine, inactivation, G protein.

scholarly journals Two components of voltage-dependent calcium influx in mouse neuroblastoma cells. Measurement with arsenazo III.

1986 ◽  
Vol 88 (2) ◽  
pp. 149-165 ◽  
Author(s):  
S R Bolsover
Keyword(s):  
Intracellular Calcium ◽  
Calcium Current ◽  
Calcium Influx ◽  
Neuroblastoma Cells ◽  
Calcium Currents ◽  
Arsenazo Iii ◽  
Optical Absorbance ◽  
Mouse Neuroblastoma ◽  
Calcium Indicator ◽  
Voltage Dependent

N1E-115 mouse neuroblastoma cells were injected with the calcium indicator dye arsenazo III. Optical absorbance changes during voltage-clamp depolarization were used to examine the properties of the two calcium currents present in these cells. The rapidly inactivating calcium current (Moolenar and Spector, 1979b, Journal of Physiology, 292:307-323) inactivates by a voltage-dependent mechanism. The slowly inactivating calcium current is dominant in raising intracellular calcium during depolarizations to greater than -20 mV. Lowering the extracellular calcium concentration affects the two calcium currents unequally, with the slowly inactivating current being reduced more. Intracellular calcium falls very slowly (tau greater than 1 min) after a depolarization. The rapidly inactivating calcium current is responsible for a calcium action potential under physiological conditions. In contrast, it is unlikely that the slowly inactivating calcium current has an important electrical role. Rather, its function may be to add a further increment of calcium influx over and above the calcium influx through the rapidly inactivating calcium channels.

Neurotransmitters acting via different G proteins inhibit N-type calcium current by an identical mechanism in rat sympathetic neurons

1995 ◽  
Vol 74 (6) ◽  
pp. 2251-2257 ◽  
Author(s):  
I. Ehrlich ◽  
K. S. Elmslie
Keyword(s):  
Calcium Channels ◽  
G Protein ◽  
G Proteins ◽  
Calcium Current ◽  
Voltage Dependence ◽  
Sympathetic Neurons ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Kinetics Of

1. We studied the mechanism of voltage-dependent inhibition of N-type calcium current by norepinephrine (NE) and vasoactive intestinal peptide (VIP) in adult rat superior cervical ganglion (SCG) neurons using the whole cell patch-clamp technique. 2. The voltage dependence of inhibition is manifest in the reversal of inhibition by strong depolarization. We tested the hypothesis that this voltage dependence results from disruption of G proteins binding to calcium channels. According to this hypothesis, the kinetics of calcium current reinhibition following a strong depolarization should become faster for higher concentrations of active G proteins. 3. Assuming that larger inhibitions result from higher concentrations of active G proteins, we used different concentrations of NE to alter the amplitude of inhibition and, thus, the active G protein concentration. We found that the kinetics of reinhibition at -80 mV following a depolarizing pulse to +80 mV were faster for larger inhibitions. 4. VIP induces voltage-dependent inhibition of N-current via a different G protein (Gs) than that of NE (Go). We found that the effect of VIP on reinhibition kinetics was identical to that produced by NE. 5. Combined application of NE and VIP did not greatly increase the amplitude of the inhibition but significantly increased the rate of reinhibition. Thus NE plus VIP appear to greatly increase the concentration of the molecule binding to the channel (G protein according to the hypothesis). 6. The kinetics of calcium current disinhibition during strong depolarization (step to +80 mV) did not change with the size of the inhibition induced by NE, VIP or application of NE and VIP together. 7. Both the concentration-dependent reinhibition kinetics and concentration-independent disinhibition kinetics are consistent with the hypothesis that active G proteins bind directly to N-type calcium channels to modulate their activity in rat sympathetic neurons.

Three distinct G protein pathways mediate inhibition of neuronal calcium current by bradykinin

1996 ◽  
Vol 76 (5) ◽  
pp. 3559-3562 ◽  
Author(s):  
M. A. Wilk-Blaszczak ◽  
W. D. Singer ◽  
F. Belardetti
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Calcium Current ◽  
Suppressive Effect ◽  
Calcium Currents ◽  
Tetraacetic Acid ◽  
Combined Application ◽  
Voltage Dependent ◽  
K Currents

1. In NG108-15 cells dialyzed with 10 mM ethylene glycolbis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or bis (o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), bradykinin (BK) selectively inhibited the N-type calcium current. This effect of BK was blocked by an antibody directed against the G protein G13. Thus under these conditions G13 mediates the inhibition of voltage-dependent calcium current (ICa, V) by BK. In contrast, activation of K+ currents by BK is mediated by Gq/11. BK also couples to Gi2. 2. We now examine the involvement of G proteins in the inhibition of ICa, V by BK when NG108-15 cells are dialyzed with 1 mM BAPTA. Under these conditions, BK inhibited both the N- and L-type, but not the T-type, calcium currents. Intracellular application of anti-G13 antibody did not suppress the response to BK. Applications of either anti-Gq/11 antibody or pertussis toxin (PTX, to block Gi2) were similarly ineffective. Even combined application of anti-Gq/11 and -G13 antibodies, or PTX together with either antibody, did not block inhibition of ICa, V by BK. However, the combination of both antibodies with PTX blocked the response to BK in low BAPTA. In conclusion, both Gq/11 and a PTX-sensitive G protein (presumably Gi2), together with G13, are involved in the inhibition of ICa, V by BK. 3. Gq/11 inhibited only the L-type calcium current, whereas the PTX-sensitive G protein inhibited both the N- and L-type calcium currents. 4. The BAPTA dependence of the Gq/11 and PTX-sensitive inhibitions may reflect a Ca2+ requirement of the pathway(s) acting on the L current and/or a direct suppressive effect of BAPTA.

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