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The role of cyclic AMP and its protein kinase in mediating acetylcholine release and the action of adenosine at frog motor nerve endings
Author(s) -
Hirsh Jody K.,
Silinsky Eugene M.,
Solsona Carles S.
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb12707.x
Subject(s) - adenosine , acetylcholine , protein kinase a , endocrinology , medicine , chemistry , adenylate kinase , phosphorylation , biophysics , biology , receptor , biochemistry
1 The importance of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) and its protein kinase (protein kinase A, PKA) in promoting acetylcholine (ACh) release was studied at frog motor nerve endings. The effects of cyclic AMP‐dependent protein phosphorylation on the action of adenosine receptor agonists were also investigated. 2 Cyclic AMP was delivered to a local region of the cytoplasm just beneath the plasma membrane of motor nerve endings using phospholipid vesicles (liposomes) as a vehicle. Cyclic AMP in liposomes produced a parallel reduction in the mean level of evoked ACh release (m) and spontaneous ACh release (miniature endplate potential frequency; m.e.p.p. f ) in most experiments. These inhibitory effects of cyclic AMP on quantal ACh release resemble the action of adenosine. 3 The effects of global increases in cytoplasmic cyclic AMP concentrations using lipophilic cyclic AMP analogues were generally different from those observed with cyclic AMP. 8‐(4‐Chlorophenylthio) cyclic AMP (CPT cyclic AMP) produced approximately two fold increases in m and m.e.p.p. f . Dibutyryl cyclic AMP (db cyclic AMP) also increased m and m.e.p.p. f , with the effect on m being smaller and more variable. 4 All three cyclic AMP analogues reduced the effects of adenosine receptor agonists on spontaneous and evoked ACh release. 5 The roles of protein phosphorylation in mediating ACh release and the inhibitory effects of adenosine were studied with the protein kinase inhibitor H7. H7 (30–100 μ m ) produced no consistent effect on evoked or spontaneous ACh release. At these concentrations, however, H7 exerted an unfortunate inhibitory action on the nicotinic ACh receptor/ion channel. 6 H7 prevented the increases in spontaneous ACh release produced by CPT cyclic AMP (250 μ m ). Thus H7 is likely to inhibit PK A in frog motor nerve endings. 7 H7 did not alter the inhibitory effect of adenosine on evoked and spontaneous ACh release. 8 The results suggest: (i) that the adenylyl cyclase‐cyclic AMP‐PK A system is compartmentalized within the motor nerve terminal, (ii) that phosphorylation does not play a major role in ACh release and (iii) the cyclic AMP‐PK A system modulates rather than mediates the inhibitory effects of adenosine.