Modulation of a Delayed-Rectifier K+ Current by Angiotensin II in Rat Sympathetic Neurons

2007 ◽  
Vol 98 (1) ◽  
pp. 79-85 ◽  
Author(s):  
Eduardo Acosta ◽  
Víctor Mendoza ◽  
Elena Castro ◽  
Humberto Cruzblanca
Keyword(s):  
Angiotensin Ii ◽  
Pertussis Toxin ◽  
Sympathetic Neurons ◽  
Delayed Rectifier ◽  
Muscarinic Agonist ◽  
Muscarinic Agonists ◽  
Stimulatory Action ◽  
Delayed Rectifier Current ◽  
Cultured Sympathetic Neurons ◽  
Ganglion Neurons

It is well known that angiotensin II (Angio II) mimics most of the muscarinic-mediated excitatory actions of acetylcholine on superior cervical ganglion neurons. For instance, in addition to depolarization and stimulation of norepinephrine release, muscarinic agonists and Angio II modulate the M-type K+ current and the N-type Ca2+ current. We recently found that muscarinic receptors modulate the delayed rectifier current IKV as well. Therefore a whole cell patch-clamp experiment was carried out in rat cultured sympathetic neurons to assess whether Angio II modulates IKV. We found that Angio II increased IKV by about 30% with a time constant of approximately 30 s. In comparison, inhibition of M-current was faster (τ ∼ 8 s) and stronger (∼61%). Modulation of IKV was disrupted by the AT1 receptor-antagonist losartan but not by the AT2-antagonist PD123319. IKV enhancement was reduced by the G-protein inhibitor GDP-β-S, whereas current modulation remained unaltered after cell treatment with pertussis toxin. The peptidergic modulation of IKV was severely disrupted when internal ATP was replaced by its nonhydrolyzable analogue AMP-PNP. Angio II enhanced IKV and further reduced the stimulatory action of a muscarinic agonist on IKV. Likewise, the muscarinc agonist enhanced IKV and occluded the effect of Angio II on IKV. We have also found that the protein kinase C activator PMA enhanced IKV, thereby mimicking and further attenuating the action of Angio II on IKV. These results suggest that AT1 receptors by coupling to pertussis toxin–insensitive G proteins, stimulate an ATP-dependent and PKC-mediated pathway to modulate IKV.

Increase in [Ca2+]i by CCh in adult rat sympathetic neurons are not dependent on intracellular Ca2+ pools

1995 ◽  
Vol 268 (4) ◽  
pp. C829-C837 ◽  
Author(s):  
S. Foucart ◽  
S. J. Gibbons ◽  
J. R. Brorson ◽  
R. J. Miller
Keyword(s):  
Pertussis Toxin ◽  
Sympathetic Neurons ◽  
Inhibitory Effect ◽  
Muscarinic Agonist ◽  
Muscarinic Agonists ◽  
Action Potential Firing ◽  
Adult Rats ◽  
Adult Rat ◽  
Potential Firing ◽  
Nicotinic Agonist

We have examined the effects of the muscarinic agonists, carbachol (CCh) and oxotremorine (Oxo), on the intracellular free Ca2+ concentration ([Ca2+]i) in acutely dissociated sympathetic neurons from adult rats using fura 2-based microfluorometry. The drugs increased [Ca2+]i by 86 +/- 7 and 38 +/- 10 nM for CCh and Oxo, respectively (both 10 microM). Basal [Ca2+]i was 52 +/- 3 nM. Depletion of the caffeine-sensitive Ca2+ store or blockade of the Ca(2+)-adenosinetriphosphatase with thapsigargin did not alter the effect of either agonist on the rise in [Ca2+]i. On the other hand, the omission of Ca2+ from the perfusion solution or the use of TA-3090, a Ca2+ channel antagonist, blocked the effects of CCh and Oxo. In whole cell current-clamp recordings, the muscarinic agonists elicited a depolarization and action potential firing, which probably explained the rise in [Ca2+]i observed with microfluorimetric recording. In addition to their direct effects on the [Ca2+]i, muscarinic agonists also reduced the rise in [Ca2+]i induced by a nicotinic agonist. This inhibitory effect, observed in 68% of cells that responded to the nicotinic agonist, was blocked by atropine and pertussis toxin, whereas the muscarinic agonist-induced increase in [Ca2+]i was blocked by atropine but was pertussis toxin insensitive. These results suggest that at least two muscarinic receptors are present on sympathetic neurons and that they mediate opposite effect on the fluctuation of [Ca2+]i.

Actions of substance P on membrane potential and ionic currents in guinea pig stellate ganglion neurons

1998 ◽  
Vol 274 (4) ◽  
pp. C892-C903 ◽  
Author(s):  
Robert Gilbert ◽  
Jennifer S. Ryan ◽  
Magda Horackova ◽  
Frank M. Smith ◽  
Melanie E. M. Kelly
Keyword(s):  
Membrane Potential ◽  
Substance P ◽  
Guinea Pig ◽  
Channel Blocker ◽  
Sympathetic Neurons ◽  
Stellate Ganglion ◽  
Ionic Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Ganglion Neurons

Neuropeptides are known to modulate the excitability of mammalian sympathetic neurons by their actions on various types of K+ and Ca2+ channels. We used whole cell patch-clamp recording methods to study the actions of substance P (SP) on dissociated adult guinea pig stellate ganglion (SG) neurons. Under current-clamp conditions, SG neurons exhibited overshooting action potentials followed by afterhyperpolarizations (AHP). The K+ channel blocker tetraethylammonium (1 mM), the Ca2+ channel blocker Cd2+ (0.1–0.2 mM), and SP (500 nM) depolarized SG neurons, decreased the AHP amplitude, and increased the action potential duration. In the presence of Cd2+, the effect of SP on membrane potential and AHP was reduced. Under voltage-clamp conditions, several different K+ currents were observed, including a transient outward K+ conductance and a delayed rectifier outward K+ current ( I K) consisting of Ca2+-sensitive [ I K(Ca)] and Ca2+-insensitive components. SP (500 nM) inhibited I K. Pretreatment with Cd2+ (20–200 μM) or the high-voltage-activated Ca2+ channel blocker ω-conotoxin (10 μM) blocked SP’s inhibitory effects on I K. This suggests that SP reduces I K primarily through the inhibition of I K(Ca) and that this may occur, in part, via a reduction of Ca2+ influx through voltage-dependent Ca2+ channels. SP’s actions on I K were mediated by a pertussis toxin-insensitive G protein(s) coupled to NK1 tachykinin receptors. Furthermore, we have confirmed that 500 nM SP reduced an inward Cd2+- and ω-conotoxin-sensitive Ba2+ current in SG neurons. Thus the actions of SP on I K(Ca) may be due in part to a reduction in Ca2+influx occurring via N-type Ca2+channels. This study presents the first description of ionic currents in mammalian SG neurons and demonstrates that SP may modulate excitability in SG neurons via inhibitory actions on K+ and Ca2+ currents.

Kv3 channels contribute to the delayed rectifier current in small cultured mouse dorsal root ganglion neurons

2012 ◽  
Vol 303 (4) ◽  
pp. C406-C415 ◽  
Author(s):  
Elke Bocksteins ◽  
Gerda Van de Vijver ◽  
Pierre-Paul Van Bogaert ◽  
Dirk J. Snyders
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Neuronal Excitability ◽  
Dorsal Root Ganglion Neurons ◽  
Delayed Rectifier ◽  
Drg Neurons ◽  
M Current ◽  
Delayed Rectifier Current ◽  
Mouse Dorsal Root Ganglion ◽  
Ganglion Neurons

Delayed rectifier voltage-gated K+ (KV) channels are important determinants of neuronal excitability. However, the large number of KV subunits poses a major challenge to establish the molecular composition of the native neuronal K+ currents. A large part (∼60%) of the delayed rectifier current ( IK) in small mouse dorsal root ganglion (DRG) neurons has been shown to be carried by both homotetrameric KV2.1 and heterotetrameric channels of KV2 subunits with silent KV subunits (KVS), while a contribution of KV1 channels has also been demonstrated. Because KV3 subunits also generate delayed rectifier currents, we investigated the contribution of KV3 subunits to IK in small mouse DRG neurons. After stromatoxin (ScTx) pretreatment to block the KV2-containing component, application of 1 mM TEA caused significant additional block, indicating that the ScTx-insensitive part of IK could include KV1, KV3, and/or M-current channels (KCNQ2/3). Combining ScTx and dendrotoxin confirmed a relevant contribution of KV2 and KV2/KVS, and KV1 subunits to IK in small mouse DRG neurons. After application of these toxins, a significant TEA-sensitive current (∼19% of total IK) remained with biophysical properties that corresponded to those of KV3 currents obtained in expression systems. Using RT-PCR, we detected KV3.1–3 mRNA in DRG neurons. Furthermore, Western blot and immunocytochemistry using KV3.1-specific antibodies confirmed the presence of KV3.1 in cultured DRG neurons. These biophysical, pharmacological, and molecular results demonstrate a relevant contribution (∼19%) of KV3-containing channels to IK in small mouse DRG neurons, supporting a substantial role for KV3 subunits in these neurons.

Speed of Ca2+ Channel Modulation by Neurotransmitters in Rat Sympathetic Neurons

1997 ◽  
Vol 77 (4) ◽  
pp. 2040-2048 ◽  
Author(s):  
Jiuying Zhou ◽  
Mark S. Shapiro ◽  
Bertil Hille
Keyword(s):  
G Protein ◽  
Sympathetic Neurons ◽  
Onset Time ◽  
Muscarinic Agonist ◽  
Single Population ◽  
Time Constants ◽  
Channel Modulation ◽  
Adult Rat ◽  
Time Courses ◽  
Ganglion Neurons

Zhou, Jiuying, Mark S. Shapiro, and Bertil Hille. Speed of Ca2+ channel modulation by neurotransmitters in rat sympathetic neurons. J. Neurophysiol. 77: 2040–2048, 1997. We have measured the onset and recovery speed of inhibition of N-type Ca2+ channels in adult rat superior cervical ganglion neurons by somatostatin (SS), norepinephrine (NE), and oxotremorine-M (oxo-M, a muscarinic agonist), using the whole cell configuration of the patch-clamp method with 5 mM external Ca2+. With a local perfusion pipette system that changed the solution surrounding the cell within 50 ms, we applied agonists at various times before a brief depolarization from −80 mV that elicited I Ca. At concentrations that produced maximal inhibition, the onset time constants for membrane-delimited inhibition by SS (0.5 μM), NE (10 μM), and oxo-M (20 μM) were 2.1, 0.7, and 1.0 s, respectively. The time constants for NE inhibition depended only weakly on the concentration, ranging from 1.2 to 0.4 s in the concentration range from 0.5 to 100 μM. Inhibition by oxo-M (20 μM) through a different G-protein pathway that uses a diffusible cytoplasmic messenger had a time constant near 9 s. The recovery rate constant from membrane-delimited inhibition was between 0.09 and 0.18 s−1, significantly higher than the intrinsic GTPase rate of purified G protein Go, suggesting that Ca2+ channels or other proteins in the plasma membrane act as GTPase activating proteins. We also measured the rate of channel reinhibition after relief by strong depolarizing prepulses, which should reflect the kinetics of final steps in the inhibition process. In the presence of different concentrations of NE, reinhibition was four to seven times faster than the onset of inhibition, indicating that the slowest step of inhibition must precede the binding of G protein to the channel. We propose a kinetic model for the membrane-delimited NE inhibition of Ca2+ channels. It postulates two populations of receptors with different affinities for NE, a single population of G proteins, and a single population of Ca2+ channels. This model closely simulated the time courses of onset and recovery of inhibition and reinhibition, as well as the dose-response curve for inhibition of Ca2+ channels by NE.

scholarly journals Morphological and biochemical studies on the development of cholinergic properties in cultured sympathetic neurons. I. Correlative changes in choline acetyltransferase and synaptic vesicle cytochemistry.

1980 ◽  
Vol 84 (3) ◽  
pp. 680-691 ◽  
Author(s):  
M I Johnson ◽  
C D Ross ◽  
M Meyers ◽  
E L Spitznagel ◽  
R P Bunge
Keyword(s):  
Synaptic Vesicle ◽  
Choline Acetyltransferase ◽  
Sympathetic Neurons ◽  
Culture Conditions ◽  
Neonatal Rat ◽  
Synaptic Contacts ◽  
Cervical Ganglion ◽  
Electron Microscopy Analysis ◽  
Cultured Sympathetic Neurons ◽  
Ganglion Neurons

Under certain culture conditions, neonatal rat superior cervical ganglion neurons display not only a number of expected adrenergic characteristics but, paradoxically, also certain cholinergic functions such as the development of hexamethonium-sensitive synaptic contacts and accumulation of choline acetyltransferase (ChAc). The purpose of this study was to determine whether the entire population of cultured neurons was aquiring cholinergic capabilities, or whether this phenomenon was restricted to a subpopulation. After 1--6 and 8 wk in culture, neurons were fixed in KMnO4 after incubation in norepinephrine and prepared for electron microscopy analysis of synaptic vesicle content to determine whether vesicles were dense cored or clear. ChAc, acetylcholinesterase (AChE), and DOPA-decarboxylase (DDC) activities were assayed in sister cultures. In the period from 1 to 8 wk in culture, the average ChAc activity per neuron increased 1,100-fold, and the DDC and AChE activities increased 20- and 30-fold, respectively. After 1 wk in culture, 48 of 50 synaptic boutons contained predominantly dense-cored vesicles, but by 8 wk the synaptic vesicle population was predominantly of the clear type. At intermediate times, the vesicle population in many boutons was mixed. The morphology of the synaptic contacts on neuronal surfaces was that characteristic of autonomic systems, with no definite clustering of the vesicles adjacent to the area of contact. Increased vesicle size correlated with increasing age in culture and the presence of a dense core. Considering these data along with available physiological studies, we conclude that these cultures contain one population of neurons that is initially adrenergic. Over time, under conditions of this culture system, this population develops cholinergic mechanisms. That a neuron may, at a given time, express both cholinergic and adrenergic mechanisms is suggested by the approximately equal numbers of clear and dense-cored vesicles in the boutons found at the intermediate times.

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