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Coupling of Canine Serotonin 5‐HT 1B and 5‐HT 1D Receptor Subtypes to the Formation of Inositol Phosphates by Dual Interactions with Endogenous G i/o and Recombinant G α15 Proteins
Author(s) -
Wurch Thierry,
Pauwels Petrus J.
Publication year - 2000
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.1471-4159.2000.0751180.x
Subject(s) - inositol phosphate , receptor , pertussis toxin , inositol , ketanserin , ritanserin , 5 ht5a receptor , 5 ht receptor , 5 ht1 receptor , phospholipase c , g protein , biology , gq alpha subunit , chemistry , biochemistry , serotonin
Molecular cloning and expression of canine (ca) serotonin 5‐HT 1B and ca 5‐HT 1D receptor subtypes showed that besides the lower binding affinity of ketanserin for the ca 5‐HT 1D receptor, the ligand binding profiles were similar to their human homologues. Site‐directed mutagenesis studies suggest that a Gln 189 residue in the second extracellular loop of the ca 5‐HT 1D receptor may partially account for the lower binding affinity of ketanserin. The coupling of ca 5‐HT 1B and ca 5‐HT 1D receptor subtypes to the phospholipase C pathway was analyzed by measuring stimulation of inositol phosphate formation in COS‐7 cells. Zolmitriptan potently stimulated (EC 50 = 4.9 n M ) the inositol phosphate formation at ca 5‐HT 1D receptors in a fully pertussis toxin (PTX)‐dependent manner, whereas only a weak PTX‐resistant inositol phosphate response (26‐29% at 10 μ M zolmitriptan) could be detected for the ca 5‐HT 1B receptor at a similar expression level. In contrast, both ca 5‐HT 1B and ca 5‐HT 1D receptor subtypes yielded a similar maximal magnitude of inositol phosphate formation (300‐340% at 10 μ M zolmitriptan) upon co‐expression with a mouse (m) G α15 protein. PTX treatment and co‐expression with a β‐adrenergic receptor kinase C‐terminal polypeptide partially (20‐46%) abolished the m G α15 protein‐dependent ca 5‐HT 1B and ca 5‐HT 1D receptor‐mediated stimulation of inositol phosphate formation. This study suggests both 5‐HT receptor subtypes can activate βγ subunits of endogenous G i/o proteins besides their coupling to recombinant m G α15 protein.