mu-Opioid receptor-independent fashion of the suppression of sodium currents by mu-opioid analgesics in thalamic neurons.
Most reports in the literature have shown that the effects of opioid analgesics are primarily mediated by mu-opioid receptor (MOR), whereas other potential targets of opioid analgesics have not been thoroughly characterized. In this study, we found that extracellular application of morphine, fentanyl or oxycodone, which are all considered to be MOR agonists, at relatively high concentrations, but not endogenous mu-opioid peptides, produced a concentration-dependent suppression of sodium currents in cultured thalamic neurons. These effects of opioids were not affected by either a MOR antagonist naloxone or a deletion of MOR gene. Among these opioids, fentanyl strongly suppressed sodium currents to the same degree as lidocaine, and both morphine and oxycodone slightly but significantly reduced sodium currents when they were present extracellularly. In contrast, the intracellular application of morphine, but not oxycodone, fentanyl or lidocaine, reduced sodium currents. These results suggest that morphine, fentanyl and oxycodone each produce the MOR-independent suppression of sodium currents by distinct mechanisms in thalamic neurons.
Department of Toxicology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan.
Keisuke
K
Hashimoto
Taku
T
Amano
Akiko
A
Kasakura
George R
GR
Uhl
Ichiro
I
Sora
Norio
N
Sakai
Naoko
N
Kuzumaki
Tsutomu
T
Suzuki
Minoru
M
Narita
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D005283:Fentanyl / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009020:Morphine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018847:Opioid Peptides / Q000378:metabolism; D010098:Oxycodone / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013788:Thalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D000701:Analgesics, Opioid; D018847:Opioid Peptides; D017450:Receptors, Opioid, mu; D009020:Morphine; D012964:Sodium; D010098:Oxycodone; D005283:Fentanyl