R-type calcium channels in myenteric neurons of guinea pig small intestine

2004 ◽  
Vol 287 (1) ◽  
pp. G134-G142 ◽  
Author(s):  
Xiaochun Bian ◽  
Xiaoping Zhou ◽  
James J. Galligan
Keyword(s):  
Guinea Pig ◽  
Calcium Channels ◽  
Calcium Current ◽  
Calcium Currents ◽  
Voltage Sensitivity ◽  
Total Calcium ◽  
Myenteric Neurons ◽  
Combined Application ◽  
Inward Currents ◽  
Rapid Activation

Currents carried by L-, N-, and P/Q-type calcium channels do not account for the total calcium current in myenteric neurons. This study identified all calcium channels expressed by guinea pig small intestinal myenteric neurons maintained in primary culture. Calcium currents were recorded using whole cell techniques. Depolarizations (holding potential = −70 mV) elicited inward currents that were blocked by CdCl2 (100 μM). Combined application of nifedipine (blocks L-type channels), Ω-conotoxin GVIA (blocks N-type channels), and Ω-agatoxin IVA (blocks P/Q-type channels) inhibited calcium currents by 56%. Subsequent addition of the R-type calcium channel antagonists, NiCl2 (50 μM) or SNX-482 (0.1 μM), abolished the residual calcium current. NiCl2 or SNX-482 alone inhibited calcium currents by 46%. The activation threshold for R-type calcium currents was −30 mV, the half-activation voltage was −5.2 ± 5 mV, and the voltage sensitivity was 17 ± 3 mV. R-type currents activated fully in 10 ms at 10 mV. R-type calcium currents inactivated in 1 s at 10 mV, and they inactivated (voltage sensitivity of 16 ± 1 mV) with a half-inactivation voltage of −76 ± 5 mV. These studies have accounted for all of the calcium channels in myenteric neurons. The data indicate that R-type calcium channels make the largest contribution to the total calcium current in myenteric neurons. The relatively positive half-activation voltage and rapid activation kinetics suggest that R-type channels could contribute to calcium entry during somal action potentials or during action potential-induced neurotransmitter release.

scholarly journals L-type calcium channels refine the neural population code of sound level

2016 ◽  
Vol 116 (6) ◽  
pp. 2550-2563 ◽  
Author(s):  
Calum Alex Grimsley ◽  
David Brian Green ◽  
Shobhana Sivaramakrishnan
Keyword(s):  
Calcium Channels ◽  
Calcium Current ◽  
Dynamic Range ◽  
Sound Level ◽  
Neural Population ◽  
Total Calcium ◽  
Local Networks ◽  
Sound Levels ◽  
Local Circuits

The coding of sound level by ensembles of neurons improves the accuracy with which listeners identify how loud a sound is. In the auditory system, the rate at which neurons fire in response to changes in sound level is shaped by local networks. Voltage-gated conductances alter local output by regulating neuronal firing, but their role in modulating responses to sound level is unclear. We tested the effects of L-type calcium channels (CaL: CaV1.1–1.4) on sound-level coding in the central nucleus of the inferior colliculus (ICC) in the auditory midbrain. We characterized the contribution of CaL to the total calcium current in brain slices and then examined its effects on rate-level functions (RLFs) in vivo using single-unit recordings in awake mice. CaL is a high-threshold current and comprises ∼50% of the total calcium current in ICC neurons. In vivo, CaL activates at sound levels that evoke high firing rates. In RLFs that increase monotonically with sound level, CaL boosts spike rates at high sound levels and increases the maximum firing rate achieved. In different populations of RLFs that change nonmonotonically with sound level, CaL either suppresses or enhances firing at sound levels that evoke maximum firing. CaL multiplies the gain of monotonic RLFs with dynamic range and divides the gain of nonmonotonic RLFs with the width of the RLF. These results suggest that a single broad class of calcium channels activates enhancing and suppressing local circuits to regulate the sensitivity of neuronal populations to sound level.

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.

Low-Voltage Activated T-Type Calcium Currents Are Differently Expressed in Superficial and Deep Layers of Guinea PigPiriform Cortex

1998 ◽  
Vol 79 (2) ◽  
pp. 808-816 ◽  
Author(s):  
Jacopo Magistretti ◽  
Marco de Curtis
Keyword(s):  
Guinea Pig ◽  
Calcium Current ◽  
Low Voltage ◽  
Piriform Cortex ◽  
Neuronal Firing ◽  
Calcium Currents ◽  
Patch Clamp Technique ◽  
Voltage Range ◽  
Deep Layers ◽  
Group 2

Magistretti, Jacopo and Marco de Curtis. Low-voltage activated T-type calcium currents are differently expressed in superficial and deep layers of guinea pig piriform cortex. J. Neurophysiol. 79: 808–816, 1998. A variety of voltage-dependent calcium conductances are known to control neuronal excitability by boosting peripheral synaptic potentials and by shaping neuronal firing patterns. The existence and functional significance of a differential expression of low- and high-voltage activated (LVA and HVA, respectively) calcium currents in subpopulations of neurons, acutely isolated from different layers of the guinea pig piriform cortex, were investigated with the whole cell variant of the patch-clamp technique. Calcium currents were recorded from pyramidal and multipolar neurons dissociated from layers II, III, and IV. Average membrane capacitance was larger in layer IV cells [13.1 ± 6.2 (SD) pF] than in neurons from layers II and III (8.6 ± 2.8 and 7.9 ± 3.1 pF, respectively). Neurons from all layers showed HVA calcium currents with an activation voltage range positive to −40 mV. Neurons dissociated from layers III and IV showed an LVA calcium current with the biophysical properties of a T-type conductance. Such a current displayed the following characteristics: 1) showed maximal amplitude of 11–16 pA/pF at −30 mV, 2) inactivated rapidly with a time constant of ∼22 ms at −30 mV, and 3) was completely steady-state inactivated at −60 mV. Only a subpopulation of layer II neurons (group 2 cells; circa 18%) displayed an LVA calcium current similar to that observed in deep layers. The general properties of layer II-group 2 cells were otherwise identical to those of group 1 neurons. The present study demonstrates that LVA calcium currents are differentially expressed in neurons acutely dissociated from distinct layers of the guinea pig piriform cortex.

Patch-clamp recording in myenteric neurons of guinea pig small intestine

1992 ◽  
Vol 262 (6) ◽  
pp. G1074-G1078 ◽  
Author(s):  
L. V. Baidan ◽  
A. V. Zholos ◽  
M. F. Shuba ◽  
J. D. Wood
Keyword(s):  
Small Intestine ◽  
Patch Clamp ◽  
Guinea Pig ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Myenteric Neurons ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Current Clamp Mode

The results of our research established the feasibility of applying patch-clamp methods in the study of the cellular neurophysiology of myenteric neurons enzymatically dissociated from adult guinea pig small intestine. Recording in current-clamp mode revealed two populations of neurons. One population discharged repetitively during depolarizing current pulses and displayed anodal-break excitation reminiscent of S/type 1 myenteric neurons. In the second population, spike discharge was limited to one or two spikes at the onset of depolarizing pulses and was similar to the behavior of AH/type 2 neurons. Recording in voltage-clamp mode revealed a complex of overlapping inward and outward whole cell currents. Fast and slow components of inward current were interpreted as sodium and calcium currents, respectively. Outward currents were blocked by cesium and consisted of components with properties of delayed rectifier current and A-type potassium current.

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.

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.

Characterization of inward currents and channels underlying burst activity in motoneurons of crab cardiac ganglion

2013 ◽  
Vol 110 (1) ◽  
pp. 42-54 ◽  
Author(s):  
Joseph L. Ransdell ◽  
Simone Temporal ◽  
Nicole L. West ◽  
Megan L. Leyrer ◽  
David J. Schulz
Keyword(s):  
Calcium Channel ◽  
Calcium Current ◽  
Sodium Current ◽  
Large Cell ◽  
Calcium Currents ◽  
Cardiac Ganglion ◽  
Cancer Borealis ◽  
Cationic Current ◽  
Inward Currents

Large cell motoneurons in the Cancer borealis cardiac ganglion generate rhythmic bursts of action potentials responsible for cardiac contractions. While it is well known that these burst potentials are dependent on coordinated interactions among depolarizing and hyperpolarizing conductances, the depolarizing currents present in these cells, and their biophysical characteristics, have not been thoroughly described. In this study we used a combined molecular biology and electrophysiology approach to look at channel identity, expression, localization, and biophysical properties for two distinct high-voltage-activated calcium currents present in these cells: a slow calcium current ( ICaS) and a transient calcium current ( ICaT). Our data indicate that CbCaV1 is a putative voltage-gated calcium channel subunit in part responsible for an L-type current, while CbCaV2 (formerly cacophony) is a subunit in part responsible for a P/Q-type current. These channels appear to be localized primarily to the somata of the motoneurons. A third calcium channel gene (CbCaV3) was identified that encodes a putative T-type calcium channel subunit and is expressed in these cells, but electrophysiological studies failed to detect this current in motoneuron somata. In addition, we identify and characterize for the first time in these cells a calcium-activated nonselective cationic current ( ICAN), as well as a largely noninactivating TTX-sensitive current reminiscent of a persistent sodium current. The identification and further characterization of these currents allow both biological and modeling studies to move forward with more attention to the complexity of interactions among these distinct components underlying generation of bursting output in motoneurons.

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.

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