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In the presence of SCH 23390, a potent blocker of D1 dopamine receptors, dopamine inhibits adenylate cyclase activity of synaptic plasma membranes isolated from rat striatum. Maximal inhibition corresponds to a 20-25% decrease of basal enzyme activity and is reached with 100 microM dopamine. The apparent IC50 of dopamine is 2.5 microM. The inhibitory effect(More)
There are five subtypes of muscarinic acetylcholine receptors (M(1) to M(5)) which control a large number of physiological processes, such as the function of heart and smooth muscles, glandular secretion, release of neurotransmitters, gene expression and cognitive functions as learning and memory. A selective ligand is very useful for studying the function(More)
We recently reported that clozapine behaves as a partial agonist at the cloned human m4 muscarinic receptor subtype. In the present study, we investigated whether the drug could elicit similar effects at the cloned human m1, m2, and m3 muscarinic receptor subtypes expressed in the Chinese hamster ovary (CHO) cells. Clozapine elicited a(More)
The activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC] by vasoactive intestinal peptide (VIP) was used as a model to investigate the molecular mechanisms triggered by the occupancy of dopamine recognition sites in rat anterior pituitary. Dopamine failed to change the basal enzyme activity, but it inhibited the stimulation of(More)
In synaptic plasma membranes of rat striatum, activation of dopamine receptors stimulates a high affinity GTPase activity. The rank order of potency of various dopamine receptor agonists in increasing GTP hydrolysis is the following: (-)-propylnorapomorphine greater than (-)-apomorphine = (+/-)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene(More)
The stimulation of GTP hydrolysis has been proposed as a mechanism by which hormones inhibit receptor-coupled adenylate cyclase activity. The present study attempts to verify whether this mechanism is also operative in transmitter-mediated receptor-coupled attenuation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC] located in synaptic(More)
Several studies have indicated the occurrence of an antagonistic interaction between muscarinic and dopamine D1-like receptors in the ventral striatum, but the subtype(s) of muscarinic receptor involved has not been characterized. We show that in membranes of rat nucleus accumbens, carbachol inhibited the stimulation of adenylyl cyclase activity by dopamine(More)