Localization of Amiloride-Sensitive Sodium Current and Voltage-Gated Calcium Currents in Rat Fungiform Taste Cells

2007 ◽  
Vol 98 (4) ◽  
pp. 2483-2487 ◽  
Author(s):  
Albertino Bigiani ◽  
Valeria Cuoghi
Keyword(s):  
Low Voltage ◽  
Calcium Influx ◽  
Sodium Current ◽  
Calcium Currents ◽  
Nerve Endings ◽  
Repetitive Firing ◽  
High Threshold ◽  
Sodium Currents ◽  
Voltage Gated ◽  
Taste Cells

Recent studies have shown that taste cells transducing bitter, sweet, and umami stimuli do not possess high-threshold voltage-gated calcium channels required for synaptic transmission at conventional synapses, suggesting some sort of signal processing inside taste buds prior to the activation of nerve endings. To evaluate whether this is a general paradigm for the physiology of taste reception, we studied the transduction pathway underlying the detection of sodium ions (salty stimulus). In laboratory rodents, Na+ is thought to be transduced, at least in part, through amiloride-sensitive sodium channels (ASSCs). Therefore we used the patch-clamp techniques to analyze the occurrence pattern of amiloride-sensitive sodium currents and voltage-gated calcium currents (both low-voltage-activated T-type current and high-voltage-activated L-type current) among taste cells in rat fungiform papillae. Because taste cells turnover, we focused our attention on cells possessing large voltage-gated sodium currents, a sign of “mature” cells. We found that cells expressing functional ASSCs either did not possess any calcium currents or exhibited only T-type calcium currents, which is believed to play a role in repetitive firing. On the contrary, cells lacking functional ASSCs were endowed with L-type calcium currents, which are thought to mediate calcium influx required for neurotransmitter exocytosis. Therefore our data suggest that sodium-detecting cells are unlikely to use conventional synaptic communication to transfer taste information to nerve endings. Our findings on sodium taste detection support the recent model of taste transduction, involving separate groups of taste cells: chemosensitive cells and cells forming conventional synapses.

Voltage-gated calcium and sodium currents of starburst amacrine cells in the rabbit retina

2001 ◽  
Vol 18 (5) ◽  
pp. 799-809 ◽  
Author(s):  
ETHAN D. COHEN
Keyword(s):  
Calcium Channel ◽  
Calcium Current ◽  
Sodium Current ◽  
Amacrine Cells ◽  
Calcium Currents ◽  
Adult Rabbit ◽  
Rabbit Retina ◽  
Sodium Currents ◽  
Voltage Gated ◽  
Starburst Amacrine Cells

The voltage-gated calcium and sodium currents of starburst amacrine cells were examined in slices of the adult rabbit retina. ON-center starburst amacrine cells were targeted for whole-cell recording by prelabeling the retina with the nuclear dye 4′-6-diamidino-2-phenylindole hydrochloride (DAPI). Calcium currents were isolated using an external Ringer that contained tetrodotoxin to block sodium currents and barium to block potassium channels. When starburst amacrine cells were stepped to holding potentials positive to −50 mV, a series of voltage-dependent calcium currents were activated. The calcium current peaked at −10 mV. The calcium currents kinetics were mainly sustained in nature, showing only a small amount of slow inactivation. Nickel (100 μM), a T-type channel blocker, had no effect on the calcium current. Application of the L-type channel agonist BAY K8644 (1–2.5 μM) had small variable effects on the calcium current while the L-type channel antagonist nifedipine (10 μM) had no effect. However, addition of a reported N-type calcium channel antagonist, omega-conotoxin G6A (1 μM), blocked a large portion of the calcium current, as did a more nonselective antagonist, omega-conotoxin M7C (200 nM). Agatoxin 4A (500 nM) reduced a smaller sustained calcium current component, implying a P/Q-type calcium channel was present on these neurons. In addition to the calcium currents, a fast voltage-gated sodium current was observed in many starburst cells. This current could be blocked by tetrodotoxin (200–500 nM). The differing kinetics and durations of the sodium and calcium currents could play important roles in the regulation of synaptic release and in the coordination of spiking by starburst amacrine cell dendrites during retinal development and in the encoding of motion across the retinal surface.

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.

Pharmacologically and Functionally Distinct Calcium Currents of Stomatogastric Neurons

1998 ◽  
Vol 79 (4) ◽  
pp. 2070-2081 ◽  
Author(s):  
Laura M. Hurley ◽  
Katherine Graubard
Keyword(s):  
Neuromuscular Junction ◽  
Calcium Channel ◽  
Calcium Current ◽  
Calcium Influx ◽  
Outward Current ◽  
Calcium Currents ◽  
High Threshold ◽  
Channel Blockers ◽  
Postsynaptic Potentials ◽  
Different Types

Hurley, Laura M. and Katherine Graubard. Pharmacologically and functionally distinct calcium currents of stomatogastric neurons. J. Neurophysiol. 79: 2070–2081, 1998. Previous studies have suggested the presence of different types of calcium channels in different regions of stomatogastric neurons. We sought to pharmacologically separate these calcium channel types. We used two different preparations from different regions of stomatogastric neurons to screen a range of selective calcium channel blockers. The two preparations were isolated cell bodies in culture, in which calcium current was measured directly, and isolated neuromuscular junction, in which synaptic transmission was the indirect assay for presynaptic calcium influx. The selective blockers were two different dihydropyridines, ω-Agatoxin IVA, and ω-Conotoxin GVIA. Cultured cell bodies possessed both high-threshold calcium current and calcium-activated outward current, similar to intact neurons. The calcium current had transient and maintained components, but both components had the same voltage dependence of activation and inactivation. Dihydropyridines at ≥10 μM blocked both high-threshold calcium current and calcium-activated outward current. Nanomolar doses of ω-Agatoxin IVA did not block calcium current, but micromolar doses did. ω-Conotoxin GVIA did not block either current. In contrast, at the neuromuscular junction, dihydropyridines reduced the amplitude of postsynaptic potentials by only a modest amount, whereas ω-Agatoxin IVA at doses as low as 64 nM reduced the amplitude of postsynaptic potentials almost entirely. These effects were presynaptic. ω-Conotoxin GVIA did not change the amplitude of postsynaptic potentials. The different pharmacological profiles of the two isolated preparations suggest that there are at least two different types of calcium channel in stomatogastric neurons and that ω-Agatoxin IVA and dihydropridines can be used to pharmacologically distinguish them.

Glutamate metabotropic receptor inhibition of voltage-gated calcium currents in visceral sensory neurons

1994 ◽  
Vol 72 (1) ◽  
pp. 421-430 ◽  
Author(s):  
M. Hay ◽  
D. L. Kunze
Keyword(s):  
Calcium Current ◽  
Metabotropic Glutamate Receptors ◽  
Threshold Current ◽  
Calcium Currents ◽  
High Threshold ◽  
Inhibitory Effects ◽  
Sensory Afferents ◽  
Metabotropic Receptor ◽  
Voltage Gated ◽  
Metabotropic Glutamate

1. Metabotropic glutamate receptors (mGluRs) have been suggested to modulate neurotransmission of glutamatergic pathways via autoreceptive action. Visceral sensory afferents and baroreceptor afferents in particular are thought to utilize L-glutamate (L-glu) as a primary neurotransmitter. The purpose of this study was to investigate whether visceral sensory afferents possess a mGluR and determine the effect of mGluR activation on voltage-gated calcium currents in these neurons. 2. Activation of mGluRs by the selective agonist trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD) reversibly suppressed the voltage-gated calcium currents in visceral sensory afferents of the nodose ganglion. Concentrations of t-ACPD ranging from 50 to 1,000 microM consistently decreased the evoked calcium current with a maximum suppression of the peak current of 25–30%. This response was repeatable and reversible within a given cell. 3. Metabotropic GluR activation selectively decreased the high-threshold calcium current evoked from step potentials greater than -30 mV and had no effect on the low-threshold calcium current. The inhibitory effects of t-ACPD on the high-threshold channel was partially blocked by omega-conotoxin (omega-CTx-GVIA) suggesting that at least part of the effects of mGluR inhibition of the voltage-gated calcium current is because of a modulation of the omega-CTx-GVIA sensitive high-threshold current. 4. Finally, the inhibitory effects of quisqualate (quis) on the high-threshold calcium current were blocked by pretreatment of the neurons with pertussis toxin (PTX). These results suggest that visceral sensory afferents do possess a PTX-sensitive mGluR and activation of this receptor results in the inhibition of a omega-CTx-GVIA sensitive high-threshold calcium channel.

T-type current modulation by the actin-binding protein Kelch-like 1

2010 ◽  
Vol 298 (6) ◽  
pp. C1353-C1362 ◽  
Author(s):  
K. A. Aromolaran ◽  
K. A. Benzow ◽  
L. L. Cribbs ◽  
M. D. Koob ◽  
E. S. Piedras-Rentería
Keyword(s):  
Calcium Influx ◽  
Binding Protein ◽  
Noise Analysis ◽  
Calcium Currents ◽  
Actin Binding ◽  
Binding Motif ◽  
Open Probability ◽  
Brain Membrane ◽  
Voltage Gated ◽  
Actin Binding Protein

We report a novel form of modulation of T-type calcium currents carried out by the neuronal actin-binding protein (ABP) Kelch-like 1 (KLHL1). KLHL1 is a constitutive neuronal ABP localized to the soma and dendritic arbors; its genetic elimination in Purkinje neurons leads to dendritic atrophy and motor insufficiency. KLHL1 participates in neurite outgrowth and upregulates voltage-gated P/Q-type calcium channel function; here we investigated KLHL1's role as a modulator of low-voltage-gated calcium channels and determined the molecular mechanism of this modulation with electrophysiology and biochemistry. Coexpression of KLHL1 with CaV3.1 or CaV3.2 (α1G or α1H subunits) caused increases in T-type current density (35%) and calcium influx (75–83%) when carried out by α1H but not by α1G. The association between KLHL1 and α1H was determined by immunoprecipitation and immunolocalization in brain membrane fractions and in vitro in HEK-293 cells. Noise analysis showed that neither α1H single-channel conductance nor open probability was altered by KLHL1, yet a significant increase in channel number was detected and further corroborated by Western blot analysis. KLHL1 also induced an increase in α1H current deactivation time (τdeactivation). Interestingly, the majority of KLHL1's effects were eliminated when the actin-binding motif (kelch) was removed, with the exception of the calcium influx increase during action potentials, indicating that KLHL1 interacts with α1H and actin and selectively regulates α1H function by increasing the number of α1H channels. This constitutes a novel regulatory mechanism of T-type calcium currents and supports the role of KLHL1 in the modulation of cellular excitability.

scholarly journals Knock-in model of Dravet syndrome reveals a constitutive and conditional reduction in sodium current

2014 ◽  
Vol 112 (4) ◽  
pp. 903-912 ◽  
Author(s):  
Ryan J. Schutte ◽  
Soleil S. Schutte ◽  
Jacqueline Algara ◽  
Eden V. Barragan ◽  
Jeff Gilligan ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Sodium Current ◽  
Dravet Syndrome ◽  
Repetitive Firing ◽  
Gabaergic Interneurons ◽  
Sodium Currents ◽  
Channel Gene ◽  
Sodium Channel Gene ◽  
Current Activity ◽  
Scn1a Mutation

Hundreds of mutations in the SCN1A sodium channel gene confer a wide spectrum of epileptic disorders, requiring efficient model systems to study cellular mechanisms and identify potential therapeutic targets. We recently demonstrated that Drosophila knock-in flies carrying the K1270T SCN1A mutation known to cause a form of genetic epilepsy with febrile seizures plus (GEFS+) exhibit a heat-induced increase in sodium current activity and seizure phenotype. To determine whether different SCN1A mutations cause distinct phenotypes in Drosophila as they do in humans, this study focuses on a knock-in line carrying a mutation that causes a more severe seizure disorder termed Dravet syndrome (DS). Introduction of the DS SCN1A mutation (S1231R) into the Drosophila sodium channel gene para results in flies that exhibit spontaneous and heat-induced seizures with distinct characteristics and lower onset temperature than the GEFS+ flies. Electrophysiological studies of GABAergic interneurons in the brains of adult DS flies reveal, for the first time in an in vivo model system, that a missense DS mutation causes a constitutive and conditional reduction in sodium current activity and repetitive firing. In addition, feeding with the serotonin precursor 5-HTP suppresses heat-induced seizures in DS but not GEFS+ flies. The distinct alterations of sodium currents in DS and GEFS+ GABAergic interneurons demonstrate that both loss- and gain-of-function alterations in sodium currents are capable of causing reduced repetitive firing and seizure phenotypes. The mutation-specific effects of 5-HTP on heat-induced seizures suggest the serotonin pathway as a potential therapeutic target for DS.

Effects of osmotic swelling on voltage-gated calcium channel currents in rat anterior pituitary cells

2003 ◽  
Vol 285 (4) ◽  
pp. C840-C852 ◽  
Author(s):  
Shlomo Ben-Tabou De-Leon ◽  
Edna Blotnick ◽  
Itzhak Nussinovitch
Keyword(s):  
Calcium Channel ◽  
Calcium Influx ◽  
Membrane Surface ◽  
Hormone Secretion ◽  
Calcium Currents ◽  
Type I ◽  
Pituitary Cells ◽  
Voltage Gated ◽  
Channel Currents ◽  
Stimulation Of

Decrease in extracellular osmolarity ([Os]e) results in stimulation of hormone secretion from pituitary cells. Different mechanisms can account for this stimulation of hormone secretion. In this study we examined the possibility that hyposmolarity directly modulates voltage-gated calcium influx in pituitary cells. The effects of hyposmolarity on L-type ( IL) and T-type ( IT) calcium currents in pituitary cells were investigated by using two hyposmotic stimuli, moderate (18-22% decrease in [Os]e) and strong (31-32% decrease in [Os]e). Exposure to moderate hyposmotic stimuli resulted in three response types in IL (a decrease, a biphasic effect, and an increase in IL) and in increase in IT. Exposure to strong hyposmotic stimuli resulted only in increases in both IL and IT. Similarly, in intact pituitary cells (perforated patch method), exposure to either moderate or strong hyposmotic stimuli resulted only in increases in both IL and IT. Thus it appears that the main effect of decrease in [Os]e is increase in calcium channel currents. This increase was differential ( IL were more sensitive than IT) and voltage independent. In addition, we show that these hyposmotic effects cannot be explained by activation of an anionic conductance or by an increase in cell membrane surface area. In conclusion, this study shows that hyposmotic swelling of pituitary cells can directly modulate voltage-gated calcium influx. This hyposmotic modulation of IL and IT may contribute to the previously reported hyposmotic stimulation of hormone secretion. The mechanisms underlying these hyposmotic effects and their possible physiological relevance are discussed.

scholarly journals The modulation of two motor behaviors by persistent sodium currents in Xenopus laevis tadpoles

2017 ◽  
Vol 118 (1) ◽  
pp. 121-130 ◽  
Author(s):  
Erik Svensson ◽  
Hugo Jeffreys ◽  
Wen-Chang Li
Keyword(s):  
Action Potentials ◽  
Sodium Current ◽  
Repetitive Firing ◽  
Sodium Currents ◽  
Spinal Neurons ◽  
Motor Behaviors ◽  
Low Concentrations ◽  
Descending Interneurons ◽  
Lateral Sclerosis

Persistent sodium currents ( INaP) are common in neuronal circuitries and have been implicated in several diseases, such as amyotrophic lateral sclerosis (ALS) and epilepsy. However, the role of INaP in the regulation of specific behaviors is still poorly understood. In this study we have characterized INaP and investigated its role in the swimming and struggling behavior of Xenopus tadpoles. INaP was identified in three groups of neurons, namely, sensory Rohon-Beard neurons (RB neurons), descending interneurons (dINs), and non-dINs (neurons rhythmically active in swimming). All groups of neurons expressed INaP, but the currents differed in decay time constants, amplitudes, and the membrane potential at which INaP peaked. Low concentrations (1 µM) of the INaP blocker riluzole blocked INaP ~30% and decreased the excitability of the three neuron groups without affecting spike amplitudes or cellular input resistances. Riluzole reduced the number of rebound spikes in dINs and depressed repetitive firing in RB neurons and non-dINs. At the behavior level, riluzole at 1 µM shortened fictive swimming episodes. It also reduced the number of action potentials neurons fired on each struggling cycle. The results show that INaP may play important modulatory roles in motor behaviors. NEW & NOTEWORTHY We have characterized persistent sodium currents in three groups of spinal neurons and their role in shaping spiking activity in the Xenopus tadpole. We then attempted to evaluate the role of persistent sodium currents in regulating tadpole swimming and struggling motor outputs by using low concentrations of the persistent sodium current antagonist riluzole.

scholarly journals Impaired Inhibitory G-Protein Function Contributes to Increased Calcium Currents in Rats With Diabetic Neuropathy

2001 ◽  
Vol 86 (2) ◽  
pp. 760-770 ◽  
Author(s):  
Karen E. Hall ◽  
Jackie Liu ◽  
Anders A. F. Sima ◽  
John W. Wiley
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Dorsal Root ◽  
Calcium Influx ◽  
Opiate Receptors ◽  
Calcium Currents ◽  
High Threshold ◽  
Drg Neurons ◽  
Protein Activity ◽  
Inhibitory G Protein

There is a growing body of evidence that sensory neuropathy in diabetes is associated with abnormal calcium signaling in dorsal root ganglion (DRG) neurons. Enhanced influx of calcium via multiple high-threshold calcium currents is present in sensory neurons of several models of diabetes mellitus, including the spontaneously diabetic BioBred/Worchester (BB/W) rat and the chemical streptozotocin (STZ)-induced rat. We believe that abnormal calcium signaling in diabetes has pathologic significance as elevation of calcium influx and cytosolic calcium release has been implicated in other neurodegenerative conditions characterized by neuronal dysfunction and death. Using electrophysiologic and pharmacologic techniques, the present study provides evidence that significant impairment of G-protein-coupled modulation of calcium channel function may underlie the enhanced calcium entry in diabetes. N- and P-type voltage-activated, high-threshold calcium channels in DRGs are coupled to μ opiate receptors via inhibitory Go-type G proteins. The responsiveness of this receptor coupled model was tested in dorsal root ganglion (DRG) neurons from spontaneously-diabetic BB/W rats, and streptozotocin-induced (STZ) diabetic rats. Intracellular dialysis with GTPγS decreased calcium current amplitude in diabetic BB/W DRG neurons compared with those of age-matched, nondiabetic controls, suggesting that inhibitory G-protein activity was diminished in diabetes, resulting in larger calcium currents. Facilitation of calcium current density ( I DCa) by large-amplitude depolarizing prepulses (proposed to transiently inactivate G proteins), was significantly less effective in neurons from BB/W and STZ-induced diabetic DRGs. Facilitation was enhanced by intracellular dialysis with GTPγS, decreased by pertussis toxin, and abolished by GDPβS within 5 min. Direct measurement of GTPase activity using opiate-mediated GTPγ[35S] binding, confirmed that G-protein activity was significantly diminished in STZ-induced diabetic neurons compared with age-matched nondiabetic controls. Diabetes did not alter the level of expression of μ opiate receptors and G-protein α subunits. These studies indicate that impaired regulation of calcium channels by G proteins is an important mechanism contributing to enhanced calcium influx in diabetes.

scholarly journals Brivaracetam Differentially Affects Voltage‐Gated Sodium Currents Without Impairing Sustained Repetitive Firing in Neurons

2014 ◽  
Vol 21 (3) ◽  
pp. 241-251 ◽  
Author(s):  
Isabelle Niespodziany ◽  
Véronique Marie André ◽  
Nathalie Leclère ◽  
Etienne Hanon ◽  
Philippe Ghisdal ◽  
...  
Keyword(s):  
Repetitive Firing ◽  
Sodium Currents ◽  
Voltage Gated
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