Potentiation of acetylcholine release from tracheal parasympathetic nerves by cAMP.
We tested the hypothesis that increasing intracellular levels of adenosine 3', 5'-cyclic monophosphate (cAMP) increases acetylcholine (ACh) release from airway parasympathetic nerves. Muscle strips from equine trachea were preincubated for 60 min with 10(-7)M atropine, 10(-6)M neostigmine, and 10(-5) M guanethidine. The ACh release was evoked by electrical field stimulation (EFS, 20 V, 0.5 ms, 0.5 Hz) and measured by high-performance liquid chromatography with electrochemical detection. Agents known to increase cAMP, i.e., forskolin (10(-6) - 10(-4) M), 8-bromoadenosine 3', 5'-cyclic monophosphate (8-BrcAMP; 10(-5)-10(-3) M), and 3-isobutyl-1-methylxanthine (IBMX ; 10(-5)-10(-3)M) was potentiated by IBMX but not mimicked by 1,9 dideoxyforskolin. To determine if the augmentation of Ach release facilitated EFS-induced ACh release in a concentration-dependent manner. Forskolin-induced augmentation of ACh release induced by activation of beta 2-adrenoceptors is mediated via cAMP-dependent pathways, we also examined the additive effects of 8-BrcAMP, forskolin, and IBMX with 10(-6)M isoproterenol (ISO), the concentration that maximally augments ACh release. Neither forskolin nor 8-BrcAMP potentiated the maximal augmentation produced by ISO, but inhibition of phosphodiesterase with IBMX (10(-4) and 10(-3)M) augmented the maximal effect of ISO. These observations indicate that neuronal cAMP is a physiological modulator of ACh release from airway parasympathetic nerves and mediates ISO-induced augmentation of ACh release. Bronchodilators that increase cAMP may therefore paradoxically augment ACh release while relaxing smooth muscle.
Zhang
X Y
XY
Department of Large Animal Clinical Science, Michigan State University, East Lansing 48824, USA.
Robinson
N E
NE
Zhu
F X
FX
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D004558:Electric Stimulation; D006736:Horses; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000378:metabolism*; D014132:Trachea / Q000294:innervation*
D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D007545:Isoproterenol; D000109:Acetylcholine; D015056:1-Methyl-3-isobutylxanthine