Different rate of desensitization in the multiple signaling pathways of opioid receptor
Kaneko, S.; Yada, N.; Adachi, K.; Akaike, A.; Satoh, M.
Folia Pharmacologica Japonica 106(Suppl 1): 147P-151P
ISSN/ISBN: 0015-5691 DOI: 10.1254/fpj.106.supplement_147
RNA-injected Xenopus oocytes were used for studying homologous desensitization of opioid receptors to G-protein-coupled intracellular signaling pathways. In the oocytes expressing kappa opioid receptor, voltage-dependent Ca-2+ channel alpha-1 and beta subunits, the kappa agonist U50488H (1 mu-M) inhibited Ca-2+ channel current in a reversible manner, and the inhibition was diminished by sustained agonist exposure (homologous desensitization). More than 10 min was required to halve the inhibition of BI- or Q-type Ca-2+ channels by the K agonist, however, the t-1/2 for U50488H-induced inhibition of BIII- or N-type channels was only 6 +- 1 min. Moreover, in the oocytes expressing kappa opioid receptor, EP-4 prostaglandin receptor and CFTR channel, no apparent desensitization was observed in the kappa receptor-mediated potentiation of the cyclic AMP production by prostaglandin E-2 even when the oocytes were treated with U50488H for 2 hours or more. The time-course of desensitization of mu opioid receptor was also different in the effector molecules. These observations suggest that rate of homologous desensitization of opioid receptor is not only dependent on the receptor molecule itself but also on its intracellular signaling systems.