RESUMEN
Dexmedetomidine (DMED) is a potent and highly selective α2-adrenergic receptor agonist and is widely used for short-term sedation. However, the mechanism of DMED-induced sedation has not been deciphered. In the present study, we investigated the mechanism of Gαi and Gßγ subunits on DMED-induced sedation. An ED50 of DMED-induced loss of righting reflex (200.0nmol/kg) was increased to 375.0 or 433.3nmol/kg after pre-treatment with cAMP analog dbcAMP (50nmol/5⯵l/mouse, i.c.v.) or the phosphodiesterase 4 inhibitor rolipram (100nmol/5⯵l/mouse, i.c.v.). Conversely, the ED50 of DMED-induced LORR decreased to 113.6 or 136.5 nmol/kg after pre-treated with Gßγ subunit inhibitor M119 (100â¯mg/kg, i.p.) or gallein (100â¯mg/kg, i.p.) respectively. Administration of dbcAMP, rolipram, gallein or M119 alone had no effect on LORR. Gallein (10⯵M) significantly inhibited forskolin-stimulated cAMP accumulation in α2A-AR -CHO cells. Compared with Gßγ subunit inhibitors or DMED alone, [Ca2+]i and pERK1/2 was significantly increased after co-administration with Gßγ subunit inhibitors and DMED. DbcAMP (5⯵M) or rolipram (5⯵M) alone had no effect on ERK1/2 phosphorylation, but decreased DMED-induced ERK1/2 phosphorylation after co-administration with DMED. Gßγ subunit inhibitor treatment increased DMED-induced phosphorylation of CREB, whereas dbcAMP or rolipram had no effect on pCREB induced by DMED. From our results we conclude that, Gßγ subunit may inhibit DMED-induced sedation through the cAMP and pERK1/2 pathway.
Asunto(s)
Agonistas de Receptores Adrenérgicos alfa 2/farmacología , Conducta Animal/efectos de los fármacos , Estado de Conciencia/efectos de los fármacos , Dexmedetomidina/farmacología , Subunidad alfa de la Proteína de Unión al GTP Gi2/efectos de los fármacos , Subunidades beta de la Proteína de Unión al GTP/efectos de los fármacos , Subunidades gamma de la Proteína de Unión al GTP/efectos de los fármacos , Hipnóticos y Sedantes/farmacología , Animales , Bucladesina/farmacología , Células CHO , Cricetulus , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Relación Dosis-Respuesta a Droga , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Subunidad alfa de la Proteína de Unión al GTP Gi2/metabolismo , Subunidades beta de la Proteína de Unión al GTP/metabolismo , Subunidades gamma de la Proteína de Unión al GTP/metabolismo , Masculino , Ratones , Inhibidores de Fosfodiesterasa 4/farmacología , Fosforilación , Receptores Adrenérgicos alfa 2/efectos de los fármacos , Receptores Adrenérgicos alfa 2/genética , Receptores Adrenérgicos alfa 2/metabolismo , Reflejo de Enderezamiento/efectos de los fármacos , Rolipram/farmacología , Transducción de Señal/efectos de los fármacosRESUMEN
G(q), a heterotrimeric guanine nucleotide-binding protein, plays important roles such as the regulation of calcium mobilization and cell proliferation. This protein is considered as a promising drug target for the treatment of cardiac hypertrophy. Selective activation of G(q) would be quite useful for analyzing the role of G(q) in signaling pathways. We synthesized m3i3c-a peptide with 16 amino acid residues that corresponds to the junction between the C-terminus of the third intracellular loop and the sixth transmembrane helix (TM-VI) of human m3 muscarinic acetylcholine receptor, which couples to G(q) but not G(i2). At micromolar concentrations, this peptide was found to activate G(q) but not G(i2). This peptide is the first small compound that selectively activates G(q) but not G(i2).