scholarly journals Facilitation of Somatic Calcium Channels Can Evoke Prolonged Tail Currents in Rat Hypoglossal Motoneurons

2007 ◽  
Vol 98 (2) ◽  
pp. 1042-1047 ◽  
Author(s):  
Anna T. Moritz ◽  
Gregory Newkirk ◽  
Randall K. Powers ◽  
Marc D. Binder
Keyword(s):  
Voltage Clamp ◽  
Calcium Currents ◽  
Whole Cell ◽  
Persistent Inward Currents ◽  
Hypoglossal Motoneurons ◽  
Pharmacological Tests ◽  
Voltage Ramp ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Whole Cell Recordings

Voltage-dependent persistent inward currents (PICs) make an important contribution to the input-output properties of alpha motoneurons. PICs are thought to be mediated by membrane channels located primarily on the dendrites as evidenced by prolonged tail currents following the termination of a voltage step and by a clockwise hysteresis in the whole cell inward currents recorded in response to depolarizing then repolarizing voltage ramp commands. We report here, however, that voltage-clamp currents with these same features can be generated in isolated somatic membrane patches from rat hypoglossal motoneurons. Long-lasting (200–800 ms) tail currents after 1-s voltage-clamp pulses were observed in nucleated patches from 16 of 23 cells. Further, these somatic PICs display “facilitation” in response to conditioning depolarization as previously observed in whole cell recordings from intact neurons. Pharmacological tests suggest that the PICs were primarily mediated by Cav1 channels. Our results show that many of the features of persistent calcium currents recorded from intact motoneurons do not necessarily reflect a remote dendritic origin but can also be ascribed to the intrinsic properties of their Cav1 channels.

Persistent Sodium and Calcium Currents in Rat Hypoglossal Motoneurons

2003 ◽  
Vol 89 (1) ◽  
pp. 615-624 ◽  
Author(s):  
Randall K. Powers ◽  
Marc D. Binder
Keyword(s):  
Calcium Channels ◽  
Voltage Clamp ◽  
Developmental Stages ◽  
Calcium Currents ◽  
Neonatal Rat ◽  
Negative Slope ◽  
Channel Blockers ◽  
Whole Cell ◽  
Persistent Inward Currents ◽  
Inward Currents

Voltage-dependent persistent inward currents are thought to make an important contribution to the input–output properties of α−motoneurons, influencing both the transfer of synaptic current to the soma and the effects of that current on repetitive discharge. Recent studies have paid particular attention to the contribution of L-type calcium channels, which are thought to be widely distributed on both the somatic and the dendritic membrane. However, the relative contribution of different channel subtypes as well as their somatodendritic distribution may vary among motoneurons of different species, developmental stages, and motoneuron pools. In this study, we have characterized persistent inward currents in juvenile (10- to 24-day-old) rat hypoglossal (HG) motoneurons. Whole-cell, voltage-clamp recordings were made from the somata of visualized rat HG motoneurons in 300-μm brain stem slices. Slow (10 s), triangular voltage-clamp commands from a holding potential of −70 to 0 mV and back elicited whole-cell currents that were dominated by outward, potassium currents, but often showed a region of negative slope resistance on the rising phase of the command. In the presence of potassium channel blockers (internal cesium and external 4-aminopyridine and tetraethylammonium), net inward currents were present on both the rising and falling phases of the voltage-clamp command. A portion of the inward current present on the ascending phase of the command was mediated by TTX-sensitive sodium channels, whereas calcium channels mediated the remainder of the current. We found roughly the same relative contributions of P-, N-, and L-type channels to the calcium currents recorded at the soma that had previously been found in neonatal rat HG motoneurons. In most cells, the somatic voltage thresholds for calcium current onset and offset were similar and the peak current was largest on the ascending phase of the clamp command. However, about one-third of the cells exhibited a substantial clockwise current hysteresis, i.e., inward currents were present at lower voltages on the descending phase of the clamp command. In the same cells, 1-s depolarizing voltage-clamp commands were followed by prolonged tail currents, consistent with a prominent contribution from dendritic channels. In contrast to previous reports on turtle and mouse motoneurons, blocking L-type calcium channels did not eliminate these presumed dendritic currents.

Dopamine Modulation of Calcium Currents in Pyloric Neurons of the Lobster Stomatogastric Ganglion

2003 ◽  
Vol 90 (2) ◽  
pp. 631-643 ◽  
Author(s):  
Bruce R. Johnson ◽  
Peter Kloppenburg ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Calcium Channel ◽  
Transmitter Release ◽  
Stomatogastric Ganglion ◽  
Calcium Currents ◽  
Voltage Gated ◽  
Pyloric Network ◽  
Pyloric Dilator ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Dopamine Modulation

We examined the dopamine (DA) modulation of calcium currents (ICa) that could contribute to the plasticity of the pyloric network in the lobster stomatogastric ganglion. Pyloric somata were voltage-clamped under conditions designed to block voltage-gated Na+, K+, and H currents. Depolarizing steps from –60 mV generated voltage-dependent, inward currents that appeared to originate in electrotonically distal, imperfectly clamped regions of the cell. These currents were blocked by Cd2+ and enhanced by Ba2+ but unaffected by Ni2+. Dopamine enhanced the peak ICa in the pyloric constrictor (PY), lateral pyloric (LP), and inferior cardiac (IC) neurons and reduced peak ICa in the ventricular dilator (VD), pyloric dilator (PD), and anterior burster (AB) neurons. All of these effects, except for the AB, are consistent with DA's excitation or inhibition of firing in the pyloric neurons. Enhancement of ICa in PY and LP neurons and reduction of ICa in VD and PD neurons are also consistent with DA-induced synaptic strength changes via modulation of presynaptic ICa. However, the reduction of ICa in AB suggests that DA's enhancement of AB transmitter release is not directly mediated through presynaptic ICa. ICa in PY and PD neurons was more sensitive to nifedipine block than in AB neurons. In addition, nifedipine blocked DA's effects on ICa in the PY and PD neurons but not in the AB neuron. Thus the contribution of specific calcium channel subtypes carrying the total ICa may vary between pyloric neuron classes, and DA may act on different calcium channel subtypes in the different pyloric neurons.

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.

Sequential activation of multiple persistent inward currents induces staircase currents in serotonergic neurons of medulla in ePet-EYFP mice

2020 ◽  
Vol 123 (1) ◽  
pp. 277-288
Author(s):  
Yi Cheng ◽  
Qiang Zhang ◽  
Yue Dai
Keyword(s):  
High Voltage ◽  
Low Voltage ◽  
Spinal Neurons ◽  
Serotonergic Neurons ◽  
Persistent Inward Currents ◽  
Functional Roles ◽  
Bath Application ◽  
Voltage Ramp ◽  
Inward Currents ◽  
Sequential Activation

Persistent inward currents (PICs) are widely reported in rodent spinal neurons. A distinctive pattern observed recently is staircase-like PICs induced by voltage ramp in serotonergic neurons of mouse medulla. The mechanism underlying this pattern of PICs is unclear. Combining electrophysiological, pharmacological, and computational approaches, we investigated the staircase PICs in serotonergic neurons of medulla in ePet-EYFP transgenic mice (postnatal days 1–7). Staircase PICs induced by 10-s voltage biramps were observed in 70% of serotonergic neurons ( n = 73). Staircase PICs activated at −48.8 ± 5 mV and consisted of two components, with the first PIC of 45.8 ± 51 pA and the second PIC of 197.3 ± 126 pA ( n = 51). Staircase PICs were also composed of low-voltage-activated sodium PIC (Na-PIC; onset −46.2 ± 5 mV, n = 34), high-voltage-activated calcium PIC (Ca-PIC; onset −29.3 ± 6 mV, n = 23), and high-voltage-activated tetrodotoxin (TTX)- and dihydropyridine-resistant sodium PIC (TDR-PIC; onset −16.8 ± 4 mV, n = 28). Serotonergic neurons expressing Na-PIC, Ca-PIC, and TDR-PIC were evenly distributed in medulla. Bath application of 1–2 μM TTX blocked the first PIC and decreased the second PIC by 36% ( n = 23, P < 0.05). Nimodipine (25 μM) reduced the second PIC by 38% ( n = 34, P < 0.001) without altering the first PIC. TTX and nimodipine removed the first PIC and reduced the second PIC by 59% ( n = 28, P < 0.01). A modeling study mimicked the staircase PICs and verified experimental conclusions that sequential activation of Na-PIC, Ca-PIC, and TDR-PIC in order of voltage thresholds induced staircase PICs in serotonergic neurons. Further experimental results suggested that the multiple components of staircase PICs play functional roles in regulating excitability of serotonergic neurons in medulla. NEW & NOTEWORTHY Staircase persistent inward currents (PICs) are mediated by activation of L-type calcium channels in dendrites of mouse spinal motoneurons. A novel mechanism is explored in this study. Here we report that the staircase PICs are mediated by sequentially activating sodium and calcium PICs in serotonergic neurons of mouse medulla.

Serotonin Modulates Dendritic Calcium Influx in Commissural Interneurons in the Mouse Spinal Locomotor Network

2007 ◽  
Vol 98 (4) ◽  
pp. 2157-2167 ◽  
Author(s):  
Manuel Díaz-Ríos ◽  
Daniel A. Dombeck ◽  
Watt W. Webb ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Spinal Cord ◽  
Voltage Clamp ◽  
Neuronal Excitability ◽  
Calcium Influx ◽  
Active Role ◽  
Calcium Currents ◽  
Detectable Effect ◽  
Lumbar Region ◽  
Fictive Locomotion ◽  
Voltage Dependent

Commissural interneurons (CINs) help to coordinate left–right alternating bursting activity during fictive locomotion in the neonatal mouse spinal cord. Serotonin (5-HT) plays an active role in the induction of fictive locomotion in the isolated spinal cord, but the cellular targets and mechanisms of its actions are relatively unknown. We investigated the possible role of serotonin in modifying dendritic calcium currents, using a combination of two-photon microscopy and patch-clamp recordings, in identified CINs in the upper lumbar region. Dendritic calcium responses to applied somatic voltage-clamp steps were measured using fluorescent calcium indicator imaging. Serotonin evoked significant reductions in voltage-dependent dendritic calcium influx in about 40% of the dendritic sites studied, with no detectable effect in the remaining sites. We also detected differential effects of serotonin in different dendritic sites of the same neuron; serotonin could decrease voltage-sensitive calcium influx at one site, with no effect at a nearby site. Voltage-clamp studies confirmed that serotonin reduces the voltage-dependent calcium current in CINs. Current-clamp experiments showed that the serotonin-evoked decreases in dendritic calcium influx were coupled with increases in neuronal excitability; we discuss possible mechanisms by which these two seemingly opposing results can be reconciled. This research demonstrates that dendritic calcium currents are targets of serotonin modulation in a group of spinal interneurons that are components of the mouse locomotor network.

Voltage-clamp analysis of a Ca2+- and voltage-dependent chloride conductance in cultured mouse spinal neurons

1986 ◽  
Vol 55 (6) ◽  
pp. 1115-1135 ◽  
Author(s):  
D. G. Owen ◽  
M. Segal ◽  
J. L. Barker
Keyword(s):  
Voltage Clamp ◽  
Reversal Potential ◽  
Gamma Aminobutyric Acid ◽  
Spinal Neurons ◽  
Exponential Process ◽  
Voltage Clamp Analysis ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Ca 50 ◽  
O 10

Current and voltage-clamp recordings were made at room temperature from cultured mouse spinal neurons using conventional two-electrode voltage-clamp techniques and electrodes filled with either 3 M KCl, 3 M CsCl, or 3 M Cs2SO4. In the presence of tetraethylammonium and tetrodotoxin, “fast” (rapidly rising and falling) action potentials (FAP) of variable duration were recorded in most neurons. “Slow” (slowly rising and falling) depolarizing potentials (SDP) occurred in 23% of the cells, when using KCl-filled electrodes, and in 82% of the cells with CsCl-filled electrodes. The SDP was frequently preceded by an FAP, although in some cells activation of the SDP occurred before the FAP threshold was reached and in a graded fashion. Both the FAP and SDP were abolished by Cd2+ and other Ca2+ antagonists. In cells exhibiting SDPs, voltage-clamp analysis revealed a sustained (noninactivating) inward current (Isin) during depolarizing steps to potentials more positive than -45 mV. Repolarizing steps resulted in slowly decaying inward tail currents (Itail). Both Isin and Itail were abolished in solutions nominally free of Cao2+, or containing Ca2+-channel antagonists. Bao2+ did not support Isin. The data indicated a U-shaped activation curve for Isin, peaking at about -10 mV. Activation of Isin occurred exponentially with a time constant of approximately 140 ms at -23 mV, becoming faster at more depolarized potentials (ca. 50 ms at -2 mV). Deactivation was slow, giving rise to tail currents lasting seconds. In some cases deactivation could be described by a single exponential process, although frequently the kinetics were more complex. Deactivation was faster at hyperpolarized potentials and sensitive to extracellular ([Ca2+]o), duration of activating voltage steps, and the degree of activation of Isin. Using CsCl-filled electrodes, the reversal potential (Erev) for Isin was -1.7 mV (SEM 3.5 mV, n = 20). Erev always corresponded to the reversal potential for gamma-aminobutyric acid-evoked currents in the same cell. In experiments in which Cs2SO4-filled electrodes were used, Erev was estimated to be -44 mV (SEM 2.3 mV, n = 9). Neither complete substitution of Nao+ with choline ions nor elevation of [K+]o 10-fold significantly affected the estimated Erev. However, substitution of Cl0- with isethionate or methanesulphonate increased the amplitude of inward currents (recorded with CsCl-filled electrodes) and shifted Erev to more depolarized potentials. The results indicate that Cl- are the primary charge carriers for this current and that Cai2+ is required for its activation, leading us to identify it as ICl(Ca).(ABSTRACT TRUNCATED AT 400 WORDS)

Whole-cell patch-clamp analysis of voltage-dependent calcium conductances in cultured embryonic rat hippocampal neurons

1989 ◽  
Vol 61 (3) ◽  
pp. 467-477 ◽  
Author(s):  
D. E. Meyers ◽  
J. L. Barker
Keyword(s):  
Patch Clamp ◽  
Hippocampal Neurons ◽  
Calcium Currents ◽  
Tetraacetic Acid ◽  
Whole Cell ◽  
Inward Current ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Cells Cultured ◽  
In Cells

1. Voltage-dependent calcium currents in embryonic (E18) hippocampal neurons cultured for 1-14 days were investigated using the whole-cell patch-clamp technique. 2. Calcium currents were isolated by removing K+ from both the internal and external solutions. In most recordings the external solution contained tetrodotoxin, tetraethylammonium ions, and low concentrations of Na+, whereas the internal solution contained the large cations and anions, N-methyl-D-glucamine and methanesulphonate, and an adenosine 5'-triphosphate (ATP) regenerating system (Forscher and Oxford, 1985) to retard “run-down” of Ca currents. 3. Under these conditions, the sustained inward current triggered during depolarizing steps was enhanced when extracellular [Ca2+] ([Ca2+]0) was raised from 2 to 10 mM and abolished when [Ca2+]0 was lowered to 0.1 mM or by addition of Co2+ ions. These results indicate that the inward current was carried primarily by Ca2+ ions and was designated ICa. This current may be comparable to the “high-voltage-activated” Ca current described in other preparations. 4. In cells cultured for 1-3 days, ICa was small or absent (less than 20 pA for cells 1 day in culture and less than 80 pA for cells 3 days in culture). Although ICa decayed considerably during depolarizing steps, there was little evidence of the transient calcium current (T current) that was recorded in approximately 40% of cells cultured longer than 6 days. Maximal (i.e., the largest) ICa increased from 20 to 80 pA in 1- to 3-day cells to 150–450 pA in cells cultured for longer than 6 days. 5. The decay of ICa elicited by depolarizations from holding potentials of -60 mV or more negative was usually greatest for the maximal ICa. Replacement of extracellular Ca2+ (4 mM) with Ba2+ (2 mM) resulted in a substantial decrease in the extent of decay of ICa and a shift of the I-V relation in the hyperpolarizing direction. 6. Qualitative data obtained from experiments in which different levels of internal Ca2+ buffering were employed demonstrated that, on average, the decay of ICa was reduced as the capacity and/or rate of buffering was increased. The mean decay of ICa in cells buffered with 5 mM 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) was 9 +/- 7 (SD) %, (n = 12) and 25 +/- 12%, (n = 12) for cells buffered with the same concentration of ethyleneglycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA).(ABSTRACT TRUNCATED AT 400 WORDS)

Protein kinase C stimulates Ca2+ current in pregnant rat myometrial cells

1994 ◽  
Vol 72 (11) ◽  
pp. 1304-1307 ◽  
Author(s):  
Keiichi Shimamura ◽  
Masumi Kusaka ◽  
Nicholas Sperelakis
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Pregnant Rat ◽  
Whole Cell ◽  
Myometrial Cells ◽  
Kinase C ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent

The factors that regulate the voltage-dependent Ca2+ channels in pregnant uterine smooth muscle cells have not been elucidated, including any roles for protein kinase C (PKC). Therefore, the role of PKC in the regulation of the slow (L type) Ca2+ channels was examined in myometrial cells isolated from late pregnant (18–19 day) rat uterus, using the nystatin-perforated whole-cell voltage clamp. A PKC activator, phorbol 12, 13-dibutyrate (PDB), increased the L-type Ca2+ current (ICa(L)). Bath application of PDB (0.03 and 0.3 μM) increased the peak amplitude of ICa(L) by 21 ± 14% (n = 6) and 37 ± 8% (n = 9, p < 0.01), respectively. PDB did not change the holding current or shift the current–voltage relationship for ICa(L). The PKC inhibitors, H-7 (20 μM) or staurosporine (10 nM), reversed the effect of PDB. These results indicate that PKC may play a role in regulating Ca2+ channel function in pregnant rat myometrial cells and, therefore, may be involved in control of uterine contraction.Key words: protein kinase C, phorbol ester, calcium current, myometrial cell, nystatin-perforated patch, whole-cell voltage clamp.

Nicotinic and muscarinic activation of motoneurons in the crayfish locomotor network

1994 ◽  
Vol 72 (4) ◽  
pp. 1622-1633 ◽  
Author(s):  
D. Cattaert ◽  
A. Araque ◽  
W. Buno ◽  
F. Clarac
Keyword(s):  
Voltage Clamp ◽  
Injection Pressure ◽  
Rhythmic Activity ◽  
Membrane Resistance ◽  
Membrane Depolarization ◽  
Muscarinic Agonist ◽  
Electrode Voltage ◽  
Voltage Dependent ◽  
Inward Currents

1. We investigated the effects of acetylcholine (Ach) on identified motoneurons (MNs) using an in vitro preparation of the crayfish thoracic nervous system. Discontinuous current-clamp and single electrode voltage-clamp recordings from 50 MNs were performed along with micropipette pressure ejection of Ach (or agonists) close to the recording electrode. 2. Localized ejections of relatively large volumes (500–2,500 pl) of Ach (10(-2) M) or of the muscarinic agonist oxotremorine (Oxo, 10(-2)M) onto the MN neuropile region, usually (90% of the cases) induced a slow, alternating rhythmic activity in antagonistic MNs. In other cases (4 experiments), with similar deliveries of Ach or Oxo, MNs developed the ability to fire rhythmically but only when depolarized by sustained current injection. Pressure ejections of smaller volumes (50–200 pl) of Ach (10(-2)M) close to the recorded MN could give rise to a fast (1–2 s) large amplitude (< or = 20 mV) membrane depolarization (12%), a long-lasting (10 s to several minutes) and small (2–5 mV) depolarization (14%), and a combination of the two (74%). These responses appeared to involve different regions of the neurite because they changed when the drug-ejection pipette was displaced in the neuropile. Moreover, fast and long-lasting depolarizing components resulted from a direct effect of Ach onto the MNs because they persisted under tetrodotoxin (TTX, 10(-6)M) and cobalt (Co2+, 5 x 10(-3) M) superfusion. 3. Whereas the membrane resistance decreased during the fast Ach-induced depolarization, it increased during the long-lasting depolarization. The increase in membrane resistance was more pronounced at depolarized potentials more than -55 mV and involve a reduction in K+ conductance. 4. Superfusion with nicotinic and muscarinic antagonists revealed that the fast Ach-induced depolarization involved nicotinic receptors, muscarinic receptors, or both, whereas the slow depolarization was exclusively muscarinic. 5. The Ach-evoked inward currents were studied under voltage clamp. The fast nicotinic component (Inic) increased with hyperpolarizing holding potentials and decreased with depolarizing potentials, reversing at between 10 and 30 mV. The fast muscarinic current (Ifmus) displayed similar characteristics and reversed at about -10 mV. Whereas both fast components were voltage independent, the long-lasting muscarinic component (Ismus) was voltage dependent. The response grew with membrane depolarization, but when the holding potential was hyperpolarized below resting level, the response declined to disappear at about -60 mV and beyond.(ABSTRACT TRUNCATED AT 400 WORDS)

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