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A Nitric Oxide/Cyclic GMP‐Dependent Protein Kinase Pathway Alters Transmitter Release and Inhibition by Somatostatin at a Site Downstream of Calcium Entry
Author(s) -
Gray D. Bruce,
PoloParada Luis,
Pilar Guillermo R.,
Eang Peau,
Metzger Ryan R.,
Klann Eric,
Meriney Stephen D.
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.0721981.x
Subject(s) - somatostatin , nitric oxide , chemistry , cyclic gmp , calcium , protein kinase a , downstream (manufacturing) , cgmp dependent protein kinase , signal transduction , microbiology and biotechnology , biophysics , kinase , endocrinology , biochemistry , biology , mitogen activated protein kinase kinase , operations management , organic chemistry , economics
We have examined the somatostatin‐mediated modulation of acetylcholine release from intact chick embryo choroid tissue and compared these data with those obtained using acutely dissociated neuronal cell bodies from the chick ciliary ganglion. Acetylcholine release, evoked in a calcium‐dependent manner by a high potassium (55 m M KCl) stimulation in both preparations, was inhibited almost completely by 100 n M somatostatin. Measurement of intracellular calcium in these neurons revealed that somatostatin blocked the large calcium transient that was observed in control neurons following KCl exposure. The modulatory effect of somatostatin on transmitter release was significantly attenuated by pretreatment with pharmacologic agents that selectively block cyclic GMP (cGMP)‐dependent protein kinase (PKG) or nitric oxide (NO) synthase. It is interesting that this prevention of somatostatin‐mediated acetylcholine release inhibition occurred without reversal of the somatostatin‐mediated block of the KCl‐evoked calcium transient. Furthermore, a NO donor or cGMP analogue could block KCl‐evoked acetylcholine release, but only cGMP could reduce the KCl‐evoked calcium transient. Although cGMP could reduce the KCl‐evoked calcium transient, a cGMP analogue was shown to reduce calcium ionophore‐evoked transmitter release. Thus, somatostatin reduces acetylcholine release by modulating calcium influx, but the NO‐PKG pathway can inhibit acetylcholine release, and alter somatostatin‐mediated inhibition, by affecting transmitter release at some point after calcium entry.