Orexin receptor type-1 couples exclusively to pertussis toxin-insensitive G-proteins, while orexin receptor type-2 couples to both pertussis toxin-sensitive and -insensitive G-proteins.
Signal transduction pathways of orexin receptors were examined using a nerve-like cell line transfected with orexin receptor type-1 (OX1R) and orexin receptor type-2 (OX2R). Forskolin-stimulated cyclic adenosine 3,5-monophosphate (cAMP) accumulation in OX2R-expressing cells was inhibited by orexin in a dose-dependent manner, and the effect was abolished by pretreatment with pertussis toxin (PTX). The inhibitory effect of orexin on forskolin-stimulated cAMP accumulation was not observed in OX1R-expressing cells. Administration of orexin to these cells resulted in a transient increase of intracellular calcium concentration ([Ca(2+)](i)). Orexin-stimulated increases in [Ca(2+)](i) in OX1R- or OX2R-expressing cells were not affected by the PTX pretreatment. These observations suggest that OX1R couples exclusively to PTX-insensitive G-proteins, while OX2R couples to both PTX-sensitive and -insensitive G-proteins. To examine the relative contributions of these G-proteins in OX2R-mediated activation of neurons, we used histaminergic tuberomammillary nucleus neurons, in which OX2R is abundantly expressed. We found that a phospholipase C (PLC)-inhibitor, U73122, inhibits orexin-mediated neuronal activation, but PTX showed no effect on it. This suggests that although OX2R couples to multiple G-proteins, activation of neurons by orexins through OX2R is mediated via a PTX-insensitive, PLC dependent pathway.
Zhu
Yun
Y
Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Japan.
Miwa
Yoshihiro
Y
Yamanaka
Akihiro
A
Yada
Toshihiko
T
Shibahara
Megumi
M
Abe
Yoichiro
Y
Sakurai
Takeshi
T
Goto
Katsutoshi
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009479:Neuropeptides / Q000494:pharmacology; D064446:Orexin Receptors; D000068797:Orexins; D037342:Pertussis Toxin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide / Q000819:agonists / Q000378:metabolism*
D002352:Carrier Proteins; C578626:HCRTR2 protein, human; C578627:Hcrtr1 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium