Regulation of Nicotinic Acetylcholine Receptor Desensitization by Ca2+

2007 ◽  
Vol 97 (1) ◽  
pp. 93-101 ◽  
Author(s):  
Xiaochuan Guo ◽  
Robin A. J. Lester
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Relative Weight ◽  
Recovery Phase ◽  
Nicotinic Acetylcholine ◽  
Voltage Gated ◽  
Whole Cell Patch Clamp ◽  
Medial Habenula ◽  
Intracellular Ca ◽  
Two Phases

The relationship between the concentration of intracellular Ca2+ ([Ca2+]i) and recovery from desensitization of nicotinic acetylcholine receptors (nAChRs) in rat medial habenula (MHb) neurons was investigated using the whole cell patch-clamp techniques in combination with microfluoresecent [Ca2+]i measurements. Recovery from desensitization was assessed with a paired-pulse agonist application protocol. Application of 100 μM nicotine (5 s) caused pronounced desensitization of nAChRs, after which recovery proceeded with two components. The relative weight of the two phases of recovery was sensitive to the nature of the intracellular Ca2+ chelator, with a greater fraction of channels recovering during the fast phase in the presence of BAPTA than EGTA. Recovery was affected by differential Ca2+ buffering only when Ca2+ was present in the extracellular solution, implying that Ca2+ influx through nAChRs was responsible for slowing the recovery. Simultaneous [Ca2+]i measurements showed that recovery from desensitization was inversely correlated with the instantaneous [Ca2+]i, further supporting the suggestion that elevation of [Ca2+]i limits the return of nAChRs to the resting state. In a separate set of experiments, activation of voltage-gated Ca2+ channels during the recovery phase produced a sufficiently large increase in [Ca2+]i to reduce recovery from desensitization even in the absence of Ca2+ influx through nAChRs. Overall, it is suggested that Ca2+ entry through both nAChRs and voltage-gated Ca2+ channels exerts a negative feedback on nAChR activity through stabilization of desensitized states. The interaction of these two Ca2+ sources could form the basis of a coincidence detector under specific circumstances.

scholarly journals Ca2+ Flux and Signaling Implications by Nicotinic Acetylcholine Receptors in Rat Medial Habenula

2007 ◽  
Vol 97 (1) ◽  
pp. 83-92 ◽  
Author(s):  
Xiaochuan Guo ◽  
Robin A. J. Lester
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Nicotinic Receptors ◽  
Close Agreement ◽  
Hydrolysis Product ◽  
Synaptic Activity ◽  
Nicotinic Acetylcholine ◽  
Medial Habenula ◽  
Low Concentrations ◽  
Intracellular Ca

The fraction of inward current carried by Ca2+ ( FCa2+) through nicotinic acetylcholine receptors (nAChRs) on acutely isolated rat medial habenula (MHb) neurons was calculated from experiments that simultaneously monitored agonist-induced membrane currents and intracellular [Ca2+], measured with patch-clamp and indo-1 fluorescence, respectively. In physiological concentrations of extracellular Ca2+ (2 mM) at −50 mV, the percentage of current carried by Ca2+ was determined to be roughly 3–4%, which is in close agreement with measurements from other heteromeric nicotinic receptors expressed in peripheral tissue. Among factors that may have affected this measurement, such as Ca2+ influx through voltage-gated Ca2+ channels, the concentration of intracellular Ca2+ buffer, and Ca2+ sequestration and release from intracellular stores, only Ca2+ uptake by mitochondria was shown to confound the analysis. Furthermore, we find that because of the high density of nAChRs on MHb cells, low concentrations of ACh (10 μM) and its hydrolysis product, choline (1 mM), can significantly elevate intracellular Ca2+. Moreover, during persistent activation of nAChRs, the level of intracellular Ca2+ is proportional to its extracellular concentration in the physiological range. Together, these findings support the suggestion that nAChRs may be capable of sensing low concentrations of diffusely released neurotransmitter and, in addition, transfer information about ongoing local synaptic activity by changes in extracellular Ca2+.

Expression of functional nicotinic acetylcholine receptors in neuroepithelial bodies of neonatal hamster lung

2003 ◽  
Vol 285 (6) ◽  
pp. L1203-L1212 ◽  
Author(s):  
Xiao Wen Fu ◽  
Colin A. Nurse ◽  
Suzanne M. Farragher ◽  
Ernest Cutz
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Respiratory Control ◽  
Hill Coefficient ◽  
Neuroepithelial Bodies ◽  
Patch Clamp Technique ◽  
Nicotinic Acetylcholine ◽  
Whole Cell Patch Clamp ◽  
Inward Currents ◽  
Double Label

Pulmonary neuroepithelial bodies (NEB) are presumed airway chemoreceptors involved in respiratory control, especially in the neonate. Nicotine is known to affect both lung development and control of breathing. We report expression of functional nicotinic acetylcholine receptors (nAChR) in NEB cells of neonatal hamster lung using a combination of morphological and electrophysiological techniques. Nonisotopic in situ hybridization method was used to localize mRNA for the β2-subunit of nAChR in NEB cells. Double-label immunofluorescence confirmed expression of α4-, α7-, and β2-subunits of nAChR in NEB cells. The electrophysiological characteristics of nAChR in NEB cells were studied using the whole cell patch-clamp technique on fresh lung slices. Application of nicotine (∼0.1-100 μM) evoked inward currents that were concentration dependent (EC50 = 3.8 μM; Hill coefficient = 1.1). ACh (100 μM) and nicotine (50 μM) produced two types of currents. In most NEB cells, nicotine-induced currents had a single desensitizing component that was blocked by mecamylamine (50 μM) and dihydro-β-erythroidine (50 μM). In some NEB cells, nicotine-induced current had two components, with fast- and slow-desensitizing kinetics. The fast component was selectively blocked by methyllcaconitine (MLA, 10 nM), whereas both components were inhibited by mecamylamine. Choline (0.5 mM) also induced an inward current that was abolished by 10 nM MLA. These studies suggest that NEB cells in neonatal hamster lung express functional heteromeric α3β2, α4β2, and α7 nAChR and that cholinergic mechanisms could modulate NEB chemoreceptor function under normal and pathological conditions.

scholarly journals Activation of Nicotinic Acetylcholine Receptors Increases the Frequency of Spontaneous GABAergic IPSCs in Rat Basolateral Amygdala Neurons

2005 ◽  
Vol 94 (5) ◽  
pp. 3081-3091 ◽  
Author(s):  
Ping Jun Zhu ◽  
Randall R. Stewart ◽  
J. Michael McIntosh ◽  
Forrest F. Weight
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Basolateral Amygdala ◽  
Bathing Solution ◽  
Patch Clamp Recording ◽  
Nicotinic Acetylcholine ◽  
Whole Cell Patch Clamp ◽  
Agonist And Antagonist ◽  
Subunit Combination ◽  
Conditioned Responses

The basolateral amygdala (BLA) is a critical component of the amygdaloid circuit, which is thought to be involved in fear conditioned responses. Using whole cell patch-clamp recording, we found that activation of nicotinic acetylcholine receptors (nAChRs) leads to an action potential-dependent increase in the frequency of spontaneous GABAergic currents in principal neurons in the BLA. These spontaneous GABAergic currents were abolished by a low-Ca2+/high-Mg2+ bathing solution, suggesting that they are spontaneous inhibitory postsynaptic currents (sIPSCs). Blockade of ionotropic glutamate receptors did not prevent this increased frequency of sIPSCs nor did blockade of α7 nAChRs. Among the nAChR agonists tested, cystisine was more effective at increasing the frequency of the sIPSCs than nicotine or 1,1-dimethyl-4-phenyl piperazinium iodide, consistent with a major contribution of β4 nAChR subunits. The nicotinic antagonist, dihydro-β-erythroidine, was less effective than d-tubocurarine in blocking the increased sIPSC frequency induced by ACh, suggesting that α4-containing nAChR subunits do not play a major role in the ACh-induced increased sIPSC frequency. Although α2/3/4/7 and β2/4 nAChR subunits were found in the BLA by RT-PCR, the agonist and antagonist profiles suggest that the ACh-induced increase in sIPSC frequency involves predominantly α3β4-containing nAChR subunits. Consistent with this, α-conotoxin-AuIB, a nAChR antagonist selective for the α3β4 subunit combination, inhibited the ACh-induced increase in the frequency of sIPSCs. The observations suggest that nicotinic activation increases the frequency of sIPSCs in the BLA by acting mainly on α3β4-containing nicotinic receptors on GABAergic neurons and may play an important role in the modulation of synaptic transmission in the amygdala.

Characterization of Neuronal Nicotinic Acetylcholine Receptors in the Membrane of Unmyelinated Human C-Fiber Axons by In Vitro Studies

2003 ◽  
Vol 90 (5) ◽  
pp. 3295-3303 ◽  
Author(s):  
P. M. Lang ◽  
R. Burgstahler ◽  
W. Sippel ◽  
D. Irnich ◽  
B. Schlotter-Weigel ◽  
...  
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Rank Order ◽  
Axonal Membrane ◽  
Nicotinic Acetylcholine ◽  
C Fibers ◽  
C Fiber ◽  
Intracellular Ca ◽  
Axonal Excitability

Application of acetylcholine to peripheral nerve terminals in the skin is a widely used test in studies of human small-fiber functions. However, a detailed pharmacological profile and the subunit composition of nicotinic acetylcholine receptors in human C-fiber axons are not known. In the present study, we recorded acetylcholine-induced changes of the excitability and of the intracellular Ca2+ concentration in C-fiber axons of isolated human nerve segments. In addition, using immunohistochemistry, an antibody of a subtype of nicotinic acetylcholine receptor was tested. Acetylcholine and agonists reduced the current necessary for the generation of action potentials in C fibers by ≤30%. This increase in axonal excitability was accompanied by a rise in the free intracellular Ca2+ concentration. The following rank order of potency for agonists was found: epibatidine >> 5-Iodo-A-85380 > 1,1-dimethyl-4-phenylpiperazinium iodide > nicotine > cytisine > acetylcholine; choline had no effect. The epibatidine-induced increase in axonal excitability was blocked by mecamylamine and, less efficiently, by methyllycacontine and dihydro-β-erythroidine. Many C-fiber axons were labeled by an antibody that recognizes the α5 subunit of nicotinic acetylcholine receptors. In summary, electrophysiological and immunohistochemical data indicate the functional expression of nicotinic acetylcholine receptors composed of α3, α5, and β4 but not of α4/β2 or of α7 subunits in the axonal membrane of unmyelinated human C fibers. In addition, the observations suggest that the axonal membrane of C fibers in isolated segments of human sural nerve can be used as a model for presumed cholinergic chemosensitivity of axonal terminals.

scholarly journals Nicotinic modulation of Ca2+ oscillations in rat cortical neurons in vitro

2016 ◽  
Vol 310 (9) ◽  
pp. C748-C754 ◽  
Author(s):  
JianGang Wang ◽  
YaLi Wang ◽  
FangLi Guo ◽  
ZhiBo Feng ◽  
XiangFang Wang ◽  
...  
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Cortical Neurons ◽  
Oscillation Frequency ◽  
Acetylcholine Receptors ◽  
Nicotinic Acetylcholine ◽  
Cultured Cortical Neurons ◽  
Intracellular Ca ◽  
Rat Cortical Neurons ◽  
20 Nm

The roles of nicotine on Ca2+ oscillations [intracellular Ca2+ ([Ca2+]i) oscillation] in rat primary cultured cortical neurons were studied. The spontaneous [Ca2+]i oscillations (SCO) were recorded in a portion of the neurons (65%) cultured for 7–10 days in vitro. Application of nicotine enhanced [Ca2+]i oscillation frequency and amplitude, which were reduced by the selective α4β2-nicotinic acetylcholine receptors (nAChRs) antagonist dihydro-β-erythroidine (DHβE) hydrobromide, and the selective α7-nAChRs antagonist methyllycaconitine citrate (MLA, 20 nM). DHβE reduced SCO frequency and prevented the nicotinic increase in the frequency. DHβE somewhat enhanced SCO amplitude and prevented nicotinic increase in the amplitude. MLA (20 nM) itself reduced SCO frequency without affecting the amplitude but blocked nicotinic increase in [Ca2+]i oscillation frequency and amplitude. Furthermore, coadministration of both α4β2- and α7-nAChRs antagonists completely prevented nicotinic increment in [Ca2+]i oscillation frequency and amplitude. Thus, our results indicate that both α4β2- and α7-nAChRs mediated nicotine-induced [Ca2+]i oscillations, and two nAChR subtypes differentially regulated SCO.

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