scholarly journals Nickel suppresses the PACAP-induced increase in guinea pig cardiac neuron excitability

2015 ◽  
Vol 308 (11) ◽  
pp. C857-C866 ◽  
Author(s):  
John D. Tompkins ◽  
Laura A. Merriam ◽  
Beatrice M. Girard ◽  
Victor May ◽  
Rodney L. Parsons
Keyword(s):  
Guinea Pig ◽  
Neuronal Excitability ◽  
Low Voltage ◽  
Calcium Influx ◽  
Quantitative Polymerase Chain Reaction ◽  
Intercellular Signaling ◽  
Neuron Excitability ◽  
Unique System ◽  
Cell Recording ◽  
Recording Conditions

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a potent intercellular signaling molecule involved in multiple homeostatic functions. PACAP/PAC1 receptor signaling increases excitability of neurons within the guinea pig cardiac ganglia, making them a unique system to establish mechanisms underlying PACAP modulation of neuronal function. Calcium influx is required for the PACAP-increased cardiac neuron excitability, although the pathway is unknown. This study tested whether PACAP enhancement of calcium influx through either T-type or R-type channels contributed to the modulation of excitability. Real-time quantitative polymerase chain reaction analyses indicated transcripts for Cav3.1, Cav3.2, and Cav3.3 T-type isoforms and R-type Cav2.3 in cardiac neurons. These neurons often exhibit a hyperpolarization-induced rebound depolarization that remains when cesium is present to block hyperpolarization-activated nonselective cationic currents ( Ih). The T-type calcium channel inhibitors, nickel (Ni2+) or mibefradil, suppressed the rebound depolarization, and treatment with both drugs hyperpolarized cardiac neurons by 2–4 mV. Together, these results are consistent with the presence of functional T-type channels, potentially along with R-type channels, in these cardiac neurons. Fifty micromolar Ni2+, a concentration that suppresses currents in both T-type and R-type channels, blunted the PACAP-initiated increase in excitability. Ni2+ also blunted PACAP enhancement of the hyperpolarization-induced rebound depolarization and reversed the PACAP-mediated increase in excitability, after being initiated, in a subset of cells. Lastly, low voltage-activated currents, measured under perforated patch whole cell recording conditions and potentially flowing through T-type or R-type channels, were enhanced by PACAP. Together, our results suggest that a PACAP-enhanced, Ni2+-sensitive current contributes to PACAP-induced modulation of neuronal excitability.

scholarly journals Activation of MEK/ERK signaling contributes to the PACAP-induced increase in guinea pig cardiac neuron excitability

2016 ◽  
Vol 311 (4) ◽  
pp. C643-C651 ◽  
Author(s):  
John D. Tompkins ◽  
Todd A. Clason ◽  
Jean C. Hardwick ◽  
Beatrice M. Girard ◽  
Laura A. Merriam ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Neuronal Excitability ◽  
Low Voltage ◽  
Ionic Currents ◽  
Erk Signaling ◽  
Repetitive Firing ◽  
Neuronal System ◽  
Cellular Mechanisms ◽  
Pac1 Receptor ◽  
Neuron Excitability

Pituitary adenylate cyclase (PAC)-activating polypeptide (PACAP) peptides ( Adcyap1) signaling at the selective PAC1 receptor ( Adcyap1r1) participate in multiple homeostatic and stress-related responses, yet the cellular mechanisms underlying PACAP actions remain to be completely elucidated. PACAP/PAC1 receptor signaling increases excitability of neurons within the guinea pig cardiac ganglia, and as these neurons are readily accessible, this neuronal system is particularly amenable to study of PACAP modulation of ionic conductances. The present study investigated how PACAP activation of MEK/ERK signaling contributed to the peptide-induced increase in cardiac neuron excitability. Treatment with the MEK inhibitor PD 98059 blocked PACAP-stimulated phosphorylated ERK and, in parallel, suppressed the increase in cardiac neuron excitability. However, PD 98059 did not blunt the ability of PACAP to enhance two inward ionic currents, one flowing through hyperpolarization-activated nonselective cationic channels ( Ih) and another flowing through low-voltage-activated calcium channels ( IT), which support the peptide-induced increase in excitability. Thus a PACAP - and MEK/ERK-sensitive, voltage-dependent conductance(s), in addition to Ih and IT, modulates neuronal excitability. Despite prior work implicating PACAP downregulation of the KV4.2 potassium channel in modulation of excitability in other cells, treatment with the KV4.2 current blocker 4-aminopyridine did not replicate the PACAP-induced increase in excitability in cardiac neurons. However, cardiac neurons express the ERK target, the NaV1.7 sodium channel, and treatment with the selective NaV1.7 channel inhibitor PF-04856264 decreased the PACAP modulation of excitability. From these results, PACAP/PAC1 activation of MEK/ERK signaling may phosphorylate the NaV1.7 channel, enhancing sodium currents near the threshold, an action contributing to repetitive firing of the cardiac neurons exposed to PACAP.

scholarly journals Proximal clustering between BK and CaV1.3 channels promotes functional coupling and BK channel activation at low voltage

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Oscar Vivas ◽  
Claudia M Moreno ◽  
Luis F Santana ◽  
Bertil Hille
Keyword(s):  
Single Molecule ◽  
Neuronal Excitability ◽  
Low Voltage ◽  
Calcium Influx ◽  
Sympathetic Neurons ◽  
Spatial Arrangement ◽  
Bk Channels ◽  
Bk Channel ◽  
Functional Coupling ◽  
Channel Activation

CaV-channel dependent activation of BK channels is critical for feedback control of both calcium influx and cell excitability. Here we addressed the functional and spatial interaction between BK and CaV1.3 channels, unique CaV1 channels that activate at low voltages. We found that when BK and CaV1.3 channels were co-expressed in the same cell, BK channels started activating near −50 mV, ~30 mV more negative than for activation of co-expressed BK and high-voltage activated CaV2.2 channels. In addition, single-molecule localization microscopy revealed striking clusters of CaV1.3 channels surrounding clusters of BK channels and forming a multi-channel complex both in a heterologous system and in rat hippocampal and sympathetic neurons. We propose that this spatial arrangement allows tight tracking between local BK channel activation and the gating of CaV1.3 channels at quite negative membrane potentials, facilitating the regulation of neuronal excitability at voltages close to the threshold to fire action potentials.

scholarly journals Calcium-Independent Afterdepolarization Regulated by Serotonin in Anterior Thalamus

2000 ◽  
Vol 83 (5) ◽  
pp. 3173-3176 ◽  
Author(s):  
Esther M. Chapin ◽  
Rodrigo Andrade
Keyword(s):  
Adenylate Cyclase ◽  
Intracellular Calcium ◽  
Neuronal Excitability ◽  
Thalamic Nucleus ◽  
Calcium Influx ◽  
Thalamic Nuclei ◽  
Electrophysiological Properties ◽  
Anterior Thalamus ◽  
Cell Recording ◽  
Hyperpolarization Activated Current

Previous studies have identified an afterdepolarization (ADP) in thalamocortical neurons that is mediated by an upregulation of the hyperpolarization-activated current I h. This ADP has been suggested to play a key role in the generation of spindle oscillations. In the lateral geniculate nucleus, upregulation of I h has been shown to be signaled by a rise in intracellular calcium leading to the activation of adenylate cyclase and formation of cAMP. However, it is unclear how generalizable this mechanism is to other thalamic nuclei. We have used whole cell recording to examine the electrophysiological properties of neurons of the anterodorsal thalamic nucleus, a nucleus thought not to undergo spindle oscillations. We now report that cells in this nucleus also display an ADP mediated by I h. Surprisingly, the ADP and the underlying upregulation of I h persisted even after buffering intracellular calcium and blocking calcium influx. These results indicate that, in neurons of the anterodorsal thalamic nucleus, an I h-mediated ADP can occur through a mechanism that does not involve a rise in intracellular calcium. We next examined the possibility that this calcium-independent ADP might be modulated by serotonin. Serotonin produced a robust enhancement in the amplitude of the ADP even after strong buffering of intracellular calcium and blockade of calcium channels. These results indicate that neurons of the anterodorsal thalamic nucleus display a calcium-independent, I h-mediated ADP and that this ADP is a target for regulation by serotonin. These findings identify a novel mechanism by which serotonin can regulate neuronal excitability.

scholarly journals Recruitment of endosomal signaling mediates the forskolin modulation of guinea pig cardiac neuron excitability

2017 ◽  
Vol 313 (2) ◽  
pp. C219-C227 ◽  
Author(s):  
Jean C. Hardwick ◽  
Todd A. Clason ◽  
John D. Tompkins ◽  
Beatrice M. Girard ◽  
Caitlin N. Baran ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Neuronal Excitability ◽  
Receptor Activation ◽  
Erk Signaling ◽  
Pac1 Receptor ◽  
Signaling Mechanism ◽  
Erk Activation ◽  
Neuron Excitability ◽  
Endosomal Signaling ◽  
Gated Channel

Forskolin, a selective activator of adenylyl cyclase (AC), commonly is used to establish actions of G protein-coupled receptors (GPCRs) that are initiated primarily through activation of AC/cAMP signaling pathways. In the present study, forskolin was used to evaluate the potential role of AC/cAMP, which is a major signaling mechanism for the pituitary adenylate cyclase-activating polypeptide (PACAP)-selective PAC1 receptor, in the regulation of guinea pig cardiac neuronal excitability. Forskolin (5–10 µM) increases excitability in ~60% of the cardiac neurons. The forskolin-mediated increase in excitability was considered related to cAMP regulation of a cyclic nucleotide gated channel or via protein kinase A (PKA)/ERK signaling, mechanisms that have been linked to PAC1 receptor activation. However, unlike PACAP mechanisms, forskolin enhancement of excitability was not significantly reduced by treatment with cesium to block currents through hyperpolarization-activated nonselective cation channels ( Ih) or by treatment with PD98059 to block MEK/ERK signaling. In contrast, treatment with the clathrin inhibitor Pitstop2 or the dynamin inhibitor dynasore eliminated the forskolin-induced increase in excitability; treatments with the inactive Pitstop analog or PP2 treatment to inhibit Src-mediated endocytosis mechanisms were ineffective. The PKA inhibitor KT5702 significantly suppressed the forskolin-induced change in excitability; further, KT5702 and Pitstop2 reduced the forskolin-stimulated MEK/ERK activation in cardiac neurons. Collectively, the present results suggest that forskolin activation of AC/cAMP/PKA signaling leads to the recruitment of clathrin/dynamin-dependent endosomal transduction cascades, including MEK/ERK signaling, and that endosomal signaling is the critical mechanism underlying the forskolin-induced increase in cardiac neuron excitability.

Modulation by Zn2+ of GABA responses in bipolar cells of the mouse retina

2000 ◽  
Vol 17 (2) ◽  
pp. 273-281 ◽  
Author(s):  
M. KANEDA ◽  
B. ANDRÁSFALVY ◽  
A. KANEKO
Keyword(s):  
Axon Terminal ◽  
Inhibitory Action ◽  
Phosphinic Acid ◽  
Amacrine Cells ◽  
Bipolar Cells ◽  
Mouse Retina ◽  
Induced Responses ◽  
Inhibitory Interaction ◽  
Cell Recording ◽  
Recording Conditions

The localization of endogenous Zn2+ in the mouse retina was examined histochemically and the inhibitory action of Zn2+ on GABA-induced responses was studied in bipolar cells isolated from the mouse retina. Accumulation of endogenous Zn2+ was detected in photoreceptors, bipolar, and/or amacrine cells by either the bromopyridylazo-diethylaminophenol method or the dithizone method. Under whole-cell recording conditions, GABA induced a Cl− current in isolated bipolar cells. The current consisted of two components. The first component was inhibited completely by application of 100 μM bicuculline, suggesting that this is a GABAA-receptor mediated current. The second component was inhibited completely by 100 μM 3-aminopropyl-(methyl)-phosphinic acid, suggesting that this is a GABAC-receptor mediated current. GABAC receptors were present at a higher density on the axon terminal than on dendrites. Zn2+ inhibited both GABAA and GABAC receptors. GABAC receptors were more susceptible to Zn2+; the IC50 for the GABAA receptor was 67.4 μM and that for the GABAC receptor was 1.9 μM. These results suggest that Zn2+ modulates the inhibitory interaction between amacrine and bipolar cells, particularly that mediated by the GABAC receptor.

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.

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.

scholarly journals Angiotensin receptors alter myocardial infarction-induced remodeling of the guinea pig cardiac plexus

2015 ◽  
Vol 309 (2) ◽  
pp. R179-R188 ◽  
Author(s):  
Jean C. Hardwick ◽  
Shannon E. Ryan ◽  
Emily N. Powers ◽  
E. Marie Southerland ◽  
Jeffrey L. Ardell
Keyword(s):  
Myocardial Infarction ◽  
Guinea Pig ◽  
Neuronal Excitability ◽  
Synaptic Function ◽  
Receptor Expression ◽  
Angiotensin Receptors ◽  
Ang Ii ◽  
Muscarinic Agonists ◽  
Neuronal Remodeling ◽  
Drug Treatments

Neurohumoral remodeling is fundamental to the evolution of heart disease. This study examined the effects of chronic treatment with an ACE inhibitor (captopril, 3 mg·kg−1·day−1), AT1 receptor antagonist (losartan, 3 mg·kg−1·day−1), or AT2 receptor agonist (CGP42112A, 0.14 mg·kg−1·day−1) on remodeling of the guinea pig intrinsic cardiac plexus following chronic myocardial infarction (MI). MI was surgically induced and animals recovered for 6 or 7 wk, with or without drug treatment. Intracellular voltage recordings from whole mounts of the cardiac plexus were used to monitor changes in neuronal responses to norepinephrine (NE), muscarinic agonists (bethanechol), or ANG II. MI produced an increase in neuronal excitability with NE and a loss of sensitivity to ANG II. MI animals treated with captopril exhibited increased neuronal excitability with NE application, while MI animals treated with CGP42112A did not. Losartan treatment of MI animals did not alter excitability with NE compared with untreated MIs, but these animals did show an enhanced synaptic efficacy. This effect on synaptic function was likely due to presynaptic AT1 receptors, since ANG II was able to reduce output to nerve fiber stimulation in control animals, and this effect was prevented by inclusion of losartan in the bath solution. Analysis of AT receptor expression by Western blot showed a decrease in both AT1 and AT2 receptors with MI that was reversed by all three drug treatments. These data indicate that neuronal remodeling of the guinea pig cardiac plexus following MI is mediated, in part, by activation of both AT1 and AT2 receptors.

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