scholarly journals Role of cAMP and neuronal K+channels on α2-AR-induced inhibition of ACh release in equine trachea

1998 ◽  
Vol 274 (5) ◽  
pp. L827-L832
Author(s):  
Xiang-Yang Zhang ◽  
Feng-Xia Zhu ◽  
N. Edward Robinson
Keyword(s):  
Electrical Field Stimulation ◽  
Intracellular Camp ◽  
Field Stimulation ◽  
Ach Release ◽  
Electrical Field ◽  
K Channels ◽  
Parasympathetic Nerves ◽  
Pathway Activation ◽  
Before And After

To investigate the effects of changes in intracellular cAMP on α2-adrenoceptor (AR)-induced inhibition of airway acetylcholine (ACh) release, we examined the effects of the α2-AR agonist clonidine on electrical field stimulation-evoked ACh release from equine tracheal parasympathetic nerves before and after treatment with 8-bromo-cAMP or forskolin. We also tested whether charybdotoxin (ChTX)- or iberiotoxin (IBTX)-sensitive Ca2+-activated K+ channels mediate α2-AR-induced inhibition by examining the effect of clonidine in the absence and presence of ChTX or IBTX on ACh release. The amount of released ACh was measured by HPLC coupled with electrochemical detection. Clonidine (10−7 to 10−5 M) dose dependently inhibited ACh release before and after treatment with 8-bromo-cAMP (10−3 M) or forskolin (3 × 10−5M). ChTX and IBTX, both at the concentration of 5 × 10−7 M, significantly increased ACh release; however, they did not alter the magnitude of clonidine-induced inhibition. These results indicated that in equine tracheal parasympathetic nerves, α2-AR-induced inhibition of ACh release is via an intracellular cAMP-independent pathway. Activation of both ChTX- and IBTX-sensitive Ca2+-activated K+ channels inhibits the electrical field stimulation-evoked ACh release, but these channels are not involved in the α2-AR-induced inhibition of ACh release.

Origin and modulation of ACh release from rat airway cholinergic nerves

1997 ◽  
Vol 272 (1) ◽  
pp. L8-L14 ◽  
Author(s):  
F. X. Zhu ◽  
X. Y. Zhang ◽  
N. E. Robinson
Keyword(s):  
Synaptic Vesicles ◽  
High Performance ◽  
Electrical Field Stimulation ◽  
Cyclooxygenase Inhibitors ◽  
Ach Release ◽  
Electrical Field ◽  
Parasympathetic Nerves ◽  
Release Of Acetylcholine ◽  
Rat Trachea

The release of acetylcholine (ACh) from airway parasympathetic nerves was studied in rat trachea. We established stimulus parameters, examined the role of extracellular Ca2+, and investigated the origin of the released ACh by use of vesamicol, an inhibitor of ACh uptake in synaptic vesicles. The role of muscarinic autoreceptors and prostanoids on ACh release was also studied. Tracheal rings were incubated in Krebs-Henseleit solution containing neostigmine and guanethidine with or without atropine. ACh release was measured by high-performance liquid chromatography with electrochemical detection. ACh release was dependent on frequency (0.5-16 Hz), voltage (10-25 V), and pulse duration (0.5-4 ms). At 4 Hz, one-fifth of electrical field stimulation-induced ACh release was extracellular Ca2+ independent and vesamicol resistant, indicating its nonvesicular origin. Three-fifths were Ca2+ dependent and vesamicol sensitive, indicating that it was newly synthesized, and one-fifth was Ca2+ dependent but vesamicol resistant, indicating its origin from prestored vesicles. At 16 Hz, two-fifths were nonvesicular and three-fifths were newly synthesized. Blockade of the muscarinic autoreceptor by atropine potentiated the release of ACh four- to fivefold. Neither of the cyclooxygenase inhibitors indomethacin or meclofenamate nor exogenous prostaglandin E2 affected ACh release, indicating that inhibitory prostanoids do not modulate ACh release.

Alpha-adrenergic and muscarinic cholinergic inhibition of ACh release in guinea pig trachea: role of neuronal K+ channels

1994 ◽  
Vol 266 (6) ◽  
pp. L698-L704
Author(s):  
D. G. Baker ◽  
H. F. Don ◽  
J. K. Brown
Keyword(s):  
Guinea Pig ◽  
High Performance ◽  
Electrical Field Stimulation ◽  
Ach Release ◽  
Adrenergic Agonist ◽  
Electrical Field ◽  
K Channels ◽  
Adrenergic Antagonist ◽  
Muscarinic Cholinergic

Our goals were to establish that an alpha 2-adrenergic agonist (clonidine) inhibits ACh release from airway nerve endings and to test effects of iberiotoxin (IBTX), an inhibitor of fast-conductance, Ca(2+)-activated K+ channels on alpha 2-adrenergic and muscarinic attenuation of ACh release. Guinea pig tracheas were mounted between electrodes in buffer containing indomethacin and neostigmine, and high-performance liquid chromatography with electrochemical detection was used to measure ACh release during electrical field stimulation. Clonidine inhibited ACh release in a concentration-dependent fashion [maximum reduction: 48 +/- 3%; 50% inhibitory constant (IC50): 0.1 microM], and idazoxan, alpha 2-adrenergic antagonist, reversed the effect. However, IBTX failed to alter clonidine-induced attenuation of ACh release. In contrast, IBTX did cause an increase in tracheal tension. In addition, IBTX failed to reverse any of the potent autoinhibitory effects of endogenous ACh. Our results confirm the presence of inhibitory alpha 2-adrenergic receptors. However, activation of IBTX-sensitive K+ channels does not appear necessary for either alpha 2-adrenergic or muscarinic cholinergic inhibition of ACh release.

K+-induced alterations in airway muscle responsiveness to electrical field stimulation

1986 ◽  
Vol 61 (1) ◽  
pp. 61-67 ◽  
Author(s):  
C. Murlas ◽  
G. Ehring ◽  
J. Suszkiw ◽  
N. Sperelakis
Keyword(s):  
Electrical Field Stimulation ◽  
Field Stimulation ◽  
Ach Release ◽  
Electrical Field ◽  
Before And After ◽  
Voltage Dependent ◽  
Cholinergic Nerve Terminals ◽  
Short Stimulus ◽  
K Concentration ◽  
Short Stimulus Duration

We investigated possible pre- and postsynaptic effects of K+-induced depolarization on ferret tracheal smooth muscle (TSM) responsiveness to cholinergic stimulation. To assess electromechanical activity, cell membrane potential (Em) and tension (Tm) were simultaneously recorded in buffer containing 6, 12, 18, or 24 mM K+ before and after electrical field stimulation (EFS) or exogenous acetylcholine (ACh). In 6 mM K+, Em was -58.1 +/- 1.0 mV (mean +/- SE). In 12 mM K+, Em was depolarized to -52.3 +/- 0.9 mV, basal Tm did not change, and both excitatory junctional potentials and contractile responses to EFS at short stimulus duration were larger than in 6 mM K+. No such potentiation occurred at a higher K+, although resting Em and Tm increased progressively above 12 mM K+. The sensitivity of ferret TSM to exogenous ACh appeared unaffected by K+. To determine whether the hyperresponsiveness in 12 mM K+ was due, in part, to augmented ACh release from intramural airway nerves, experiments were done using TSM preparations incubated with [3H]choline to measure [3H]ACh release at rest and during EFS. Although resting [3H]ACh release increased progressively in higher K+, release evoked by EFS was maximal in 12 mM K+ and declined in higher concentrations. We conclude that small elevations in the extracellular K+ concentration augment responsiveness of the airways, by increasing the release of ACh both at rest and during EFS from intramural cholinergic nerve terminals. Larger increases in K+ appear to be inhibitory, possibly due to voltage-dependent effects that occur both pre- and postsynaptically.

Release of epithelium-derived PGE2 from canine trachea after antigen inhalation

1998 ◽  
Vol 274 (2) ◽  
pp. L220-L225 ◽  
Author(s):  
I. McGrogan ◽  
L. J. Janssen ◽  
J. Wattie ◽  
P. M. O’Byrne ◽  
E. E. Daniel
Keyword(s):  
Smooth Muscle ◽  
Electrical Field Stimulation ◽  
Tracheal Smooth Muscle ◽  
Organ Bath ◽  
Field Stimulation ◽  
Electrical Field ◽  
Concentration Response Curve

To investigate the role of prostaglandin (PG) E2 in allergen-induced hyperresponsiveness, dogs inhaled either the allergen Ascaris suum or vehicle (Sham). Twenty-four hours after inhalation, some animals exposed to allergen demonstrated an increased responsiveness to acetylcholine challenge in vivo (Hyp-Resp), whereas others did not (Non-Resp). Strips of tracheal smooth muscle, either epithelium intact or epithelium denuded, were suspended on stimulating electrodes, and a concentration-response curve to carbachol (10−9 to 10−5 M) was generated. Tissues received electrical field stimulation, and organ bath fluid was collected to determine PGE2content. With the epithelium present, all three groups contracted similarly to 10−5 M carbachol, whereas epithelium-denuded tissues from animals that inhaled allergen contracted more than tissues from Sham dogs. In response to electrical field stimulation, Hyp-Resp tissues contracted less than Sham tissues in the presence of epithelium and more than Sham tissues in the absence of epithelium. PGE2release in the muscle bath was greater in Non-Resp tissues than in Sham or Hyp-Resp tissues when the epithelium was present. Removal of the epithelium greatly inhibited PGE2release. We conclude that tracheal smooth muscle is hyperresponsive in vitro after in vivo allergen exposure only when the modulatory effect of the epithelium, largely through PGE2 release, is removed.

Modulation of ACh release from airway cholinergic nerves in horses with recurrent airway obstruction

1999 ◽  
Vol 276 (5) ◽  
pp. L769-L775 ◽  
Author(s):  
Xiang-Yang Zhang ◽  
N. Edward Robinson ◽  
Feng-Xia Zhu
Keyword(s):  
Airway Obstruction ◽  
Muscarinic Receptors ◽  
Electrical Field Stimulation ◽  
Field Stimulation ◽  
Recurrent Airway Obstruction ◽  
Similar Magnitude ◽  
Cholinergic Nerves ◽  
Ach Release ◽  
Electrical Field ◽  
Catecholamine Concentration

To evaluate the functional status of neuronal α2-adrenoceptors (ARs) and β2-ARs on ACh release in horses with recurrent airway obstruction (RAO), we examined the effects of the physiological agonists epinephrine (Epi) and norepinephrine (NE) and the β2-agonists RR- and RR/ SS-formoterol on ACh release from airway cholinergic nerves of horses with RAO. Because SS-formoterol, a distomer of the β2-agonist, increases ACh release from airways of control horses only after the autoinhibitory muscarinic receptors are blocked by atropine, we also tested the hypothesis that if there is an M2-receptor dysfunction in equine RAO, SS-formoterol should increase ACh release even in the absence of atropine. ACh release was evoked by electrical field stimulation and measured by HPLC. Epi and NE caused less inhibition of ACh release in horses with RAO than in control horses. At the catecholamine concentration achieved during exercise (10−7 M), the inhibition induced by Epi and NE was 10.8 ± 13.2 and 3.4 ± 6.8%, respectively, in equine RAO versus 41.0 ± 6.4 and 27.1 ± 5.6%, respectively, in control horses. RR- and RR/ SS-formoterol (10−8 to 10−5 M) increased ACh release to a similar magnitude as that in control horses. These results indicate that neuronal β2-ARs are functioning; however, the α2-ARs are dysfunctional in the airways of horses with RAO in response to circulating catecholamines. SS-formoterol (10−8 to 10−5 M) facilitated ACh release in horses with RAO even in the absence of atropine. Addition of atropine did not cause significantly more augmentation of ACh release over the effect of SS-formoterol alone. The magnitude of augmentation in horses with RAO in the absence of atropine was similar to that in control horses in the presence of atropine. The latter observations could be explained by neuronal muscarinic-autoreceptor dysfunction in equine RAO.

Subtypes of muscarinic receptors regulating gallbladder cholinergic contractions

1999 ◽  
Vol 276 (5) ◽  
pp. G1243-G1250 ◽  
Author(s):  
Henry P. Parkman ◽  
Anthony P. Pagano ◽  
James P. Ryan
Keyword(s):  
Smooth Muscle ◽  
Electrical Field Stimulation ◽  
Receptor Subtypes ◽  
Muscarinic Receptor Subtypes ◽  
Cholinergic Nerves ◽  
Ach Release ◽  
Electrical Field ◽  
And Function

The aim of this study was to determine the functional role of muscarinic receptor subtypes regulating gallbladder cholinergic contractions. Electrical field stimulation (EFS; 16 Hz) produced contractile responses of guinea pig gallbladder muscle strips in vitro that were inhibited by 1 μM tetrodotoxin (2 ± 2% of control) and 1 μM atropine (1 ± 1% of control), indicating activation of intrinsic cholinergic nerves. Exogenous ACh (5 μM)-induced contractions were inhibited by atropine (1 ± 1% of control) but not tetrodotoxin (102 ± 1% of control), indicating a direct effect on smooth muscle. The M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh-induced contractions but inhibited EFS-induced contractions by 11 ± 3%. The M2 antagonist methoctramine (10 nM) had no effect on ACh-induced contractions but augmented EFS-induced contractions by 5 ± 2%. The M3 antagonist 4-DAMP (10 nM) inhibited ACh-induced contractions by 14 ± 4% and EFS-induced contractions by 22 ± 5%. In conclusion, specific M1, M2, and M3 receptors modulate gallbladder muscle contractions by regulating ACh release from cholinergic nerves and mediating the contraction. Cholinergic contractions are mediated by M3 receptors directly on the smooth muscle. M2 receptors are on cholinergic nerves and function as prejunctional inhibitory autoreceptors. M1 receptors are on cholinergic nerves and function as prejunctional facilitatory autoreceptors.

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