Endomorphins inhibit high-threshold Ca2+ channel currents in rodent NG108-15 cells overexpressing mu-opioid receptors.
1. Extracellular application of the novel brain peptides endomorphin 1 (EM1) and endomorphin 2 (EM2) inhibited high-threshold Ca2+ channel currents in NGMO-251 cells, a daughter clone of NG108-15 mouse neuroblastoma x rat glioma hybrid cells, in which mu-opioid receptors are overexpressed. 2. In contrast, EM1 and EM2 did not induce this inhibition in the parental NG108-15 cells that predominantly express endogenous delta-receptors. 3. The IC50 for EM1 and EM2 was 7.7 and 23.1 nM, respectively. 4. EM-induced Ca2+ channel current inhibition was blocked by treatment or pretreatment of the cells with 100 microM N-methylmaleimide or 100 ng ml-1 pertussis toxin. 5. These results show that a decrease in conductance of Ca2+ channels results following interaction of EMs with cloned mu-receptors, which couple via Gi/Go-type G proteins, and that EMs fulfill one of the necessary synaptic conditions for them to be identified as neurotransmitters.
Higashida
H
H
Department of Biophysics, Kanazawa University School of Medicine, Kanazawa 920, Japan. haruhiro@med.kanazawa-u.ac.jp
Hoshi
N
N
Knijnik
R
R
Zadina
J E
JE
Kastin
A J
AJ
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004056:Differential Threshold / Q000502:physiology; D004553:Electric Conductivity; D051379:Mice; D009842:Oligopeptides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D037342:Pertussis Toxin; D051381:Rats; D017450:Receptors, Opioid, mu / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; D010566:Virulence Factors, Bordetella; C105293:endomorphin 1; C105294:endomorphin 2; D037342:Pertussis Toxin