Xenopus oocytes has been utilized to analyze the intracellular signaling and coupling mechanisms between neurotransmitter receptors and ion channels. (1) The GTP-binding protein-coupled intracellular signaling pathway was analyzed in oocytes expressing metabotropic receptors by brain mRNA. These metabotropic receptors are commonly linked to the sequence of phosphoinositide metabolism, intracellular Ca2+ increase and opening of Ca2+-dependent Cl- channels. An antisense DNA study indicated that a specific subtype of GTP-binding protein is involved in the coupling of each metabotropic receptor. (2) Effects of central acting drugs on the functions of glutamate receptor subtypes and voltage-dependent Ca2+ channels were evaluated, and the data were compared with the results from conventional in vitro assays using brain preparations. (3) A series of experiments on κ-opioid receptors indicated that is κ-opioid receptors can couple with multiple signaling systems in the oocytes via GTP-binding proteins Gi/Go, which involves mobilization of intracellular Ca2+ through phosphoinositide metabolism, synergistic potentiation of cyclic AMP production, and inhibition of voltage-dependent Ca2+ channels.
To study the physiological regulation of the receptor protein, a fluorescent probe and detection system for α1B-adrenergic receptors have been developed. By using the anti-peptide antibody developed against the α1B-adrenergic receptor NH2-terminus, we have examined the agonistregulated α1B-adrenergic receptor redistribution in desensitized cells. Flow cytometry analysis showed that anti-peptide antibody against α1B-adrenergic receptor specifically identifies the receptor in CHO cells, COS-7 cells that were transfected with α1B-adrenergic receptor cDNA and rat hepatocytes. Using a fluoro-labeled receptor ligand, BODIPY FL-prazosin, as a probe, cell surface α1-adrenergic receptor subtypes can be detected by flow cytometry. Laser scanning confocal microscopy visualized the agonist-regulated redistribution process of α1B-adrenergic receptor in living cells; thus, following phenylephrine (10-6 M) stimulation, receptor antigen at the cell surface rapidly internalized and clustered together in a cell within 30 min. The results showed that the antibody and fluoro-labeled ligand are valuable tools for studying the localization and functional role of the α1-adrenergic receptor subtype.