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Up‐Regulation of the Neuronal Form of Nitric Oxide Synthase in Response to Prolonged Muscarinic M 1 Receptor Stimulation
Author(s) -
Cuadra Adolfo E.,
ElFakahany Esam E.
Publication year - 1998
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.1471-4159.1998.71020571.x
Subject(s) - agonist , muscarinic acetylcholine receptor , endocrinology , carbachol , medicine , chemistry , inositol phosphate , receptor , muscarinic agonist , muscarinic acetylcholine receptor m3 , nitric oxide synthase , muscarinic acetylcholine receptor m1 , ionomycin , muscarinic acetylcholine receptor m2 , stimulation , nitric oxide , biology , inositol , biochemistry
It is generally believed that the neuronal form of nitric oxide synthase (nNOS) is constitutively expressed and that regulation of this enzyme's activity is mediated solely by changes in cytosolic calcium concentration. Serendipitously, however, we observed that pretreatment of Chinese hamster ovary (CHO) cells, which coexpress muscarinic M 1 receptors and nNOS, with 3.3 µ M or 1 m M carbachol (CCh) for 48 h resulted in marked enhancement of maximal muscarinic receptor‐stimulated nNOS activity as determined by l ‐[ 3 H]citrulline and cyclic [ 3 H]GMP production. This was accompanied by a decrease in the potency of CCh. Muscarinic receptor density was reduced in the agonist‐pretreated cells, as determined by specific [ N‐methyl ‐ 3 H]scopolamine methyl chloride binding, whereas competition binding studies revealed no changes in agonist affinity. Both receptor‐stimulated inositol phosphate formation and elevation of intracellular calcium concentrations were found to be desensitized in agonist‐pretreated cells in a manner dependent on CCh pretreatment concentration. It is interesting that ionomycin‐stimulated nNOS activity was greater in CCh‐pretreated cells. Also, western analysis revealed increased nNOS immunoreactivity in pretreated cells. A similar increase in nNOS immunoreactivity following agonist treatment was demonstrated in N1E‐115 neuroblastoma cells, which endogenously express nNOS and muscarinic M 1 receptors. Thus, the enhancement of maximal receptor‐stimulated nNOS activity following agonist pretreatment can be attributed to up‐regulation of nNOS. It is interesting that this augmentation of the response takes place in spite of receptor down‐regulation and desensitization of multiple steps involved in nNOS activation.