Ca2+ Influx, But Not Ca2+ Release From Internal Stores, Is Required for the PACAP-Induced Increase in Excitability in Guinea Pig Intracardiac Neurons

2006 ◽  
Vol 95 (4) ◽  
pp. 2134-2142 ◽  
Author(s):  
John D. Tompkins ◽  
Jean C. Hardwick ◽  
Sarah A. Locknar ◽  
Laura A. Merriam ◽  
Rodney L. Parsons
Keyword(s):  
Guinea Pig ◽  
Action Potentials ◽  
Action Potential Firing ◽  
Pituitary Adenylate Cyclase ◽  
Whole Mount ◽  
Voltage Dependent ◽  
Potential Firing ◽  
Intracellular Ca ◽  
Indicator Dye ◽  
Intracardiac Neurons

Mechanisms modulating the pituitary adenylate cyclase activating polypeptide (PACAP)-induced increase in excitability have been studied using dissociated guinea pig intrinsic cardiac neurons and intact ganglion preparations. Measurements of intracellular calcium (Ca2+) with the fluorescent Ca2+ indicator dye fluo-3 indicated that neither PACAP nor vasoactive intestinal polypeptide (VIP) at either 100 nM or 1 μM produced a discernible elevation of intracellular Ca2+ in dissociated intracardiac neurons. For neurons in ganglion whole mount preparations kept in control bath solution, local application of PACAP significantly increased excitability, as indicated by the number of action potentials generated by long depolarizing current pulses. However, in a Ca2+-deficient solution in which external Ca2+ was replaced by Mg2+ or when cells were bathed in control solution containing 200 μM Cd2+, PACAP did not enhance action potential firing. In contrast, in a Ca2+-deficient solution with Ca2+ replaced by strontium (Sr2+), PACAP increased excitability. PACAP increased excitability in cells treated with a combination of 20 μM ryanodine and 10 mM caffeine to interrupt release of Ca2+ from internal stores. Experiments using fluo-3 showed that ryanodine/caffeine pretreatment eliminated subsequent caffeine-induced Ca2+ release from intracellular stores, whereas exposure to the Ca2+-deficient solution did not. In dissociated intracardiac neurons voltage clamped with the perforated patch recording technique, 100 nM PACAP decreased the voltage-dependent barium current ( IBa). These results show that, in the guinea pig intracardiac neurons, the PACAP-induced increase in excitability apparently requires Ca2+ influx through Cd2+-sensitive calcium permeable channels other than voltage-dependent Ca2+ channels, but not Ca2+ release from internal stores.

scholarly journals Enhancement of Ih, but not inhibition of IM, is a key mechanism underlying the PACAP-induced increase in excitability of guinea pig intrinsic cardiac neurons

2009 ◽  
Vol 297 (1) ◽  
pp. R52-R59 ◽  
Author(s):  
John D. Tompkins ◽  
Yancey T. Lawrence ◽  
Rodney L. Parsons
Keyword(s):  
Guinea Pig ◽  
Action Potentials ◽  
Action Potential Firing ◽  
M Current ◽  
Cardiac Ganglia ◽  
Cation Current ◽  
Pituitary Adenylate Cyclase ◽  
Whole Mount ◽  
Potential Firing

Pituitary adenylate cyclase-activating polypeptide (PACAP) increases excitability of guinea pig cardiac neurons, an effect mediated by PACAP-selective PAC1 receptors. In dissociated guinea pig cardiac neurons, PACAP causes a positive shift of the voltage dependence of activation of the hyperpolarization-activated nonselective cation current ( Ih). This observation suggested that an enhancement of Ih contributed to the increase in excitability in neurons within whole-mount cardiac ganglia preparations. To evaluate the role of Ih in the PACAP-induced increase in excitability, we compared the increase in action potentials generated by 10 nM PACAP in control neurons and in neurons treated with ZD7288 (10 or 100 μM) or CsCl (2 or 2.5 mM), drugs known to inhibit Ih. In control cells exposed to PACAP, 1-s depolarizing current pulses elicited multiple action potential firing in 79% of the neurons. In ZD7288- or CsCl-containing solutions, the 10 nM PACAP-induced increase in excitability was markedly suppressed, with 7% and 21% of the neurons generating multiple action potentials, respectively. Prior results indicated that PACAP initiates depolarization by activating an inward current, which is separate from its enhancement of Ih. Here, we show that a PACAP-induced depolarization was comparable in control neurons and neurons bathed in a CsCl-containing solution, an observation indicating that CsCl did not interfere with activation of the PAC1 receptor by PACAP. Additional experiments indicated that pretreatment with the putative M current ( IM) inhibitor 1 mM BaCl2, but not 10 μM XE991, initiated multiple firing in a majority of neurons, with resting potentials maintained at approximately −60 mV. Furthermore, in Ba2+-treated cells, 10 nM PACAP increased the number of action potentials generated. Our results indicate that PACAP enhancement of Ih, rather than inhibition of IM and other 1 mM Ba2+-sensitive K+ currents, is a key ionic mechanism contributing to the peptide-induced increase in excitability for neurons within whole-mount cardiac ganglia preparations.

Mitochondrial transport in processes of cortical neurons is independent of intracellular calcium

2006 ◽  
Vol 291 (6) ◽  
pp. C1193-C1197 ◽  
Author(s):  
Luis Beltran-Parrazal ◽  
Héctor E. López-Valdés ◽  
K. C. Brennan ◽  
Mauricio Díaz-Muñoz ◽  
Jean de Vellis ◽  
...  
Keyword(s):  
Cortical Neurons ◽  
Action Potentials ◽  
Synaptic Activity ◽  
Action Potential Firing ◽  
Mitochondrial Movement ◽  
Neuronal Processes ◽  
Potential Firing ◽  
Intracellular Ca ◽  
Rat Cortical Neurons ◽  
And Function

Mitochondria show extensive movement along neuronal processes, but the mechanisms and function of this movement are not clearly understood. We have used high-resolution confocal microscopy to simultaneously monitor movement of mitochondria and changes in intracellular [Ca2+] ([Ca2+]i) in rat cortical neurons. A significant percentage (27%) of the total mitochondria in cortical neuronal processes showed movement over distances of >2 μM. The average velocity was 0.52 μm/s. The velocity, direction, and pattern of mitochondrial movement were not affected by transient increases in [Ca2+]i associated with spontaneous firing of action potentials. Stimulation of Ca2+ transients with forskolin (10 μM) or bicuculline (10 μM), or sustained elevations of [Ca2+]i evoked by glutamate (10 μM) also had no effect on mitochondrial transit. Neither removal of extracellular Ca2+, depletion of intracellular Ca2+ stores with thapsigargin, or inhibition of synaptic activity with TTX (1 μM) or a cocktail of CNQX (10 μM) and MK801 (10 μM) affected mitochondrial movement. These results indicate that movement of mitochondria along processes is a fundamental activity in neurons that occurs independently of physiological changes in [Ca2+]i associated with action potential firing, synaptic activity, or release of Ca2+ from intracellular stores.

scholarly journals Zinc Enhances the Inhibitory Effects of Strychnine-Sensitive Glycine Receptors in Mouse Hippocampal Neurons

2007 ◽  
Vol 98 (6) ◽  
pp. 3666-3676 ◽  
Author(s):  
Hai Xia Zhang ◽  
Liu Lin Thio
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Hippocampal Slices ◽  
Glycine Receptors ◽  
Inhibitory Effects ◽  
Action Potential Firing ◽  
Embryonic Mouse ◽  
Potential Firing

Although extracellular Zn2+ is an endogenous biphasic modulator of strychnine-sensitive glycine receptors (GlyRs), the physiological significance of this modulation remains poorly understood. Zn2+ modulation of GlyR may be especially important in the hippocampus where presynaptic Zn2+ is abundant. Using cultured embryonic mouse hippocampal neurons, we examined whether 1 μM Zn2+, a potentiating concentration, enhances the inhibitory effects of GlyRs activated by sustained glycine applications. Sustained 20 μM glycine (EC25) applications alone did not decrease the number of action potentials evoked by depolarizing steps, but they did in 1 μM Zn2+. At least part of this effect resulted from Zn2+ enhancing the GlyR-induced decrease in input resistance. Sustained 20 μM glycine applications alone did not alter neuronal bursting, a form of hyperexcitability induced by omitting extracellular Mg2+. However, sustained 20 μM glycine applications depressed neuronal bursting in 1 μM Zn2+. Zn2+ did not enhance the inhibitory effects of sustained 60 μM glycine (EC70) applications in these paradigms. These results suggest that tonic GlyR activation could decrease neuronal excitability. To test this possibility, we examined the effect of the GlyR antagonist strychnine and the Zn2+ chelator tricine on action potential firing by CA1 pyramidal neurons in mouse hippocampal slices. Co-applying strychnine and tricine slightly but significantly increased the number of action potentials fired during a depolarizing current step and decreased the rheobase for action potential firing. Thus Zn2+ may modulate neuronal excitability normally and in pathological conditions such as seizures by potentiating GlyRs tonically activated by low agonist concentrations.

Rectification of muscarinic K+ current by magnesium ion in guinea pig atrial cells

1987 ◽  
Vol 253 (1) ◽  
pp. H210-H214
Author(s):  
M. Horie ◽  
H. Irisawa
Keyword(s):  
Guinea Pig ◽  
Action Potentials ◽  
Single Channel ◽  
Outward Current ◽  
Atrial Cells ◽  
Voltage Dependent ◽  
K Current ◽  
Single Channel Currents ◽  
Channel Currents ◽  
Low K

Rectifying properties of the acetylcholine (ACh)-sensitive K+ channels were studied using a patch-clamp method in single atrial cells prepared enzymatically from adult guinea pig hearts. In the presence of micromolar concentration of nonhydrolyzable guanosine 5'-triphosphate (GTP) analogue 5'-guanylylimidodiphosphate (GppNHp) and the absence of Mg2+ at the inner surface of patch membrane [( Mg2+]i), the channel activity recovered in inside-out patch condition. The single channel conductance became ohmic between -80 and +80 mV (symmetrical 150 mM K+ solutions). The rapid relaxation of outward single channel currents was disclosed on a depolarization. [Mg2+]i blocked the outward current through the channel dose- and voltage-dependently and also induced a dose-dependent increase in the channel activation. The apparent paradoxical role of [Mg2+]i is important for the cholinergic control in the heart; voltage-dependent Mg block ensures a low K+ conductance of cell membrane at the plateau of action potentials during the exposure to ACh, thereby slowing the heart rate without unfavorable shortening of the action potentials.

scholarly journals Nicotine suppresses hyperexcitability of colonic sensory neurons and visceral hypersensivity in mouse model of colonic inflammation

2012 ◽  
Vol 302 (7) ◽  
pp. G740-G747 ◽  
Author(s):  
Galya R. Abdrakhmanova ◽  
Minho Kang ◽  
M. Imad Damaj ◽  
Hamid I. Akbarali
Keyword(s):  
Mouse Model ◽  
Action Potential ◽  
Action Potentials ◽  
Drg Neurons ◽  
Action Potential Firing ◽  
Colonic Inflammation ◽  
Single Action ◽  
Nicotine Administration ◽  
Potential Firing

Recently, we reported that nicotine in vitro at a low 1-μM concentration suppresses hyperexcitability of colonic dorsal root ganglia (DRG; L1-L2) neurons in the dextran sodium sulfate (DSS)-induced mouse model of acute colonic inflammation ( 1 ). Here we show that multiple action potential firing in colonic DRG neurons persisted at least for 3 wk post-DSS administration while the inflammatory signs were diminished. Similar to that in DSS-induced acute colitis, bath-applied nicotine (1 μM) gradually reduced regenerative multiple-spike action potentials in colonic DRG neurons to a single action potential in 3 wk post-DSS neurons. Nicotine (1 μM) shifted the activation curve for tetrodotoxin (TTX)-resistant sodium currents in inflamed colonic DRG neurons (voltage of half-activation changed from −37 to −32 mV) but did not affect TTX-sensitive currents in control colonic DRG neurons. Further, subcutaneous nicotine administration (2 mg/kg b.i.d.) in DSS-treated C57Bl/J6 male mice resulted in suppression of hyperexcitability of colonic DRG (L1-L2) neurons and the number of abdominal constrictions in response to intraperitoneal injection of 0.6% acetic acid. Collectively, the data suggest that neuronal nicotinic acetylcholine receptor-mediated suppression of hyperexcitability of colonic DRG neurons attenuates reduction of visceral hypersensitivity in DSS mouse model of colonic inflammation.

scholarly journals Temporal coupling of field potentials and action potentials in the neocortex

2017 ◽  
Author(s):  
Brendon O. Watson ◽  
Mingxin Ding ◽  
György Buzsáki
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Field Potential ◽  
Electromyographic Activity ◽  
Action Potential Firing ◽  
Firing Rates ◽  
Potential Firing ◽  
Temporal Coupling ◽  
Potential Activity ◽  
The Relationship

AbstractThe local field potential (LFP) is an aggregate measure of group neuronal activity and is often correlated with the action potentials of single neurons. In recent years investigators have found that action potential firing rates increase during elevations in power high-frequency band oscillations (50-200 Hz range). However action potentials also contribute to the LFP signal itself, making the spike–LFP relationship complex. Here we examine the relationship between spike rates and LFPs in varying frequency bands in rat neocortical recordings. We find that 50-180Hz oscillations correlate most consistently with high firing rates, but that other LFPs bands also carry information relating to spiking, including in some cases anti-correlations. Relatedly, we find that spiking itself and electromyographic activity contribute to LFP power in these bands. The relationship between spike rates and LFP power varies between brain states and between individual cells. Finally, we create an improved oscillation-based predictor of action potential activity by specifically utilizing information from across the entire recorded frequency spectrum of LFP. The findings illustrate both caveats and improvements to be taken into account in attempts to infer spiking activity from LFP.

scholarly journals Substance P modulates nicotinic responses of intracardiac neurons to acetylcholine in the guinea pig

2001 ◽  
Vol 281 (6) ◽  
pp. R1792-R1800 ◽  
Author(s):  
Lili Zhang ◽  
John D. Tompkins ◽  
John C. Hancock ◽  
Donald B. Hoover
Keyword(s):  
Substance P ◽  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Neuronal Excitability ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Local Pressure ◽  
Slow Depolarization ◽  
Intracardiac Neurons

—Application of substance P (SP) to intracardiac neurons of the guinea pig causes slow depolarization and increases neuronal excitability. The present study was done to determine the influence of SP on fast excitatory responses of intracardiac neurons to ACh. Intracellular recording methods were used to measure responses of intracardiac neurons in whole mount preparations of atrial ganglionated nerve plexus from guinea pig hearts. Local pressure ejection of 100 μM SP (1 s) from a glass micropipette caused slow depolarization of all neurons ( n = 38) and triggered action potential generation in 47% of the cells tested. Bath application of SP (0.5–100 μM) caused a dose-dependent depolarization of intracardiac neurons but rarely evoked action potentials, even at the highest concentration. However, such treatment with SP enhanced nicotinic responses evoked by local pressure ejections of ACh (10 mM, 10- to 100-ms duration) in 77% of intracardiac neurons studied ( n = 52). A significant increase in amplitude of ACh-evoked fast depolarization occurred during treatment with 0.5 μM SP (13.0 ± 1.8 mV for control vs. 17.7 ± 1.9 mV with SP present, n = 7, P = 0.019). At higher concentrations of SP, enhancement of the response to ACh resulted mainly in action potential generation. However, responses to ACh were attenuated by SP in 15% of the intracardiac neurons studied. This attenuation occurred primarily during exposure to 10 and 100 μM SP and was manifest as a reduction in amplitude of nicotinic fast depolarization or inhibition of ACh-evoked action potentials. These findings support the conclusion that SP could function as a neuromodulator and neurotransmitter in intracardiac ganglia of the guinea pig.

Mechanisms underlying the modulation of arrhythmogenic events by components of ischemia in guinea pig cardiac myocytes

1994 ◽  
Vol 72 (4) ◽  
pp. 382-393 ◽  
Author(s):  
Qi-Ying Liu ◽  
Mario Vassalle
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Voltage Clamp ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Resting Potential ◽  
Spontaneous Discharge ◽  
High K ◽  
Voltage Dependent ◽  
Dependent Mechanism

The effects of some components of ischemia on the oscillatory (Vos) and nonoscillatory (Vex) potentials and respective currents (Ios and Iex), as well as their mechanisms, were studied in guinea pig isolated ventricular myocytes by means of a single-microelectrode, discontinuous voltage clamp method. Repetitive activations induced not only Vos and Ios, but also Vex and Iex. A small decrease in resting potential caused an immediate increase in Vos followed by a gradual increase due to the longer action potential. Immediate and gradual increases in Ios also occurred during voltage clamp steps. A small depolarization increased Vos and Vex, and facilitated the induction of spontaneous discharge by fast drive. At Vh where INa is inactivated, depolarizing steps induced larger Ios and Iex, indicating the importance of the Na-independent Ca loading. High [K]odecreased the resting potential, but also Vos, Vex, Ios, Iex, and ICa. In high [K]o, depolarization still increased Vos and Vex. Norepinephrine (NE) enhanced Vos and Vex, and also Ios and Iex, during voltage clamp steps. High [K]o antagonized NE effects, and NE those of high [K]o. In conclusion, on depolarization, Vos and Ios immediately increase through a voltage-dependent mechanism; and then Vos and Ios gradually increase, apparently through an increased Ca load related to the longer action potentials and the Na–Ca exchange. The depolarization induced by Vex may contribute to increase Vos size. Vos and Vex are similarly influenced by different procedures that modify Ca load. The arrhythmogenic events are enhanced by the simultaneous presence of depolarization, faster rate, or NE. Instead, high [K]o decreases Vos and Vex by decreasing ICa and opposes the effects of NE. The voltage clamp results show that potentiation and antagonism between different components of ischemia are due primarily to changes in Ca loading and not to changes in action potential configuration.Key words: ischemia, arrhythmias, oscillatory and nonoscillatory potentials and currents, norepinephrine, potassium.

Carbachol-induced synchronized rhythmic bursts in CA3 neurons of guinea pig hippocampus in vitro

1994 ◽  
Vol 72 (1) ◽  
pp. 131-138 ◽  
Author(s):  
R. Bianchi ◽  
R. K. Wong
Keyword(s):  
Membrane Potential ◽  
Guinea Pig ◽  
Mossy Fiber ◽  
Field Potential ◽  
Pyramidal Cells ◽  
Input Resistance ◽  
Gamma Aminobutyric Acid ◽  
Action Potential Firing ◽  
Potential Firing

1. Carbachol effects on CA3 hippocampal cells were studied in the absence of ionotropic glutamatergic and GABAergic transmission with intracellular and extracellular recordings from guinea pig septohippocampal slices. 2. In all experiments the perfusing solution contained ionotropic glutamate and gamma-aminobutyric acid (GABA) receptor blockers [6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10–20 microM), 3-((+/-)-2-carboxypiperazin-4-il)propyl-1-phosphonic acid (CPP, 10–20 microM), and picrotoxin (50 microM), respectively]. Under these conditions, the excitatory and early inhibitory postsynaptic potentials, evoked in CA3 pyramidal cells by mossy fiber stimulation before the addition of the blockers, were completely suppressed. 3. Carbachol (50 microM) introduced via bath perfusion or pulse application elicited a series of rhythmic bursts with overriding action potentials. Each rhythmic burst lasted up to 30 s and repeated at intervals of 0.7–6 min. Rhythmic bursts were blocked by atropine (1 microM). 4. At membrane potentials more depolarized than -70 mV, carbachol also elicited a sustained depolarization associated with an increase in membrane input resistance and action-potential firing. This response was blocked by atropine (1 microM). 5. Carbachol can induce both rhythmic bursts and sustained depolarizations in the same cell. Rhythmic bursts were elicited when the membrane potential of the cell was more hyperpolarized than -70 mV; sustained depolarizing responses were activated by carbachol when the cell membrane potential was more depolarized than -70 mV. 6. Extracellular field potential responses in the CA3 region occurred simultaneously with rhythmic bursts, indicating the synchronization of the event in the CA3 field. Dual intracellular recordings confirmed that rhythmic bursts occurred simultaneously in CA3 hippocampal pyramidal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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