Recombinant human serotonin 5A receptors stably expressed in C6 glioma cells couple to multiple signal transduction pathways.
Human serotonin 5A (5-HT5A) receptors were stably expressed in undifferentiated C6 glioma. In 5-HT5A receptors-expressing cells, accumulation of cAMP by forskolin was inhibited by 5-HT as reported previously. Pertussis toxin-sensitive inhibition of ADP-ribosyl cyclase was also observed, indicating a decrease of cyclic ADP ribose, a potential intracellular second messenger mediating ryanodine-sensitive Ca2+ mobilization. On the other hand, 5-HT-induced outward currents were observed using the patch-clamp technique in whole-cell configuration. The 5-HT-induced outward current was observed in 84% of the patched 5-HT5A receptor-expressing cells and was concentration-dependent. The 5-HT-induced current was inhibited when intracellular K+ was replaced with Cs+ but was not significantly inhibited by typical K+ channel blockers. The 5-HT-induced current was significantly attenuated by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) in the patch pipette. Depleting intracellular Ca2+ stores by application of caffeine or thapsigargin also blocked the 5-HT-induced current. Blocking G protein, the inositol triphosphate (IP3) receptor, or pretreatment with pertussis toxin, all inhibited the 5-HT-induced current. IP3 showed a transient increase after application of 5-HT in 5-HT5A receptor-expressing cells. It was concluded that in addition to the inhibition of cAMP accumulation and ADP-ribosyl cyclase activity, 5-HT5A receptors regulate intracellular Ca2+ mobilization which is probably a result of the IP3-sensitive Ca2+ store. These multiple signal transduction systems may induce complex changes in the serotonergic system in brain function.
Noda
Mami
M
Laboratory of Pathophysiology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka, Japan. noda@phar.kyushu-u.ac.jp
Yasuda
Satsuki
S
Okada
Mitsuko
M
Higashida
Haruhiro
H
Shimada
Aki
A
Iwata
Nakao
N
Ozaki
Norio
N
Nishikawa
Kaori
K
Shirasawa
Sakiko
S
Uchida
Mayumi
M
Aoki
Shunsuke
S
Wada
Keiji
K
D036541:ADP-ribosyl Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D005910:Glioma / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000067956:Adenylyl Cyclase Inhibitors; D026902:Potassium Channel Blockers; D011985:Receptors, Serotonin; C078730:serotonin 5 receptor; D012701:Serotonin; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D000242:Cyclic AMP; D036541:ADP-ribosyl Cyclase; D019204:GTP-Binding Proteins; D002118:Calcium