Possible involvement of botulinum ADP-ribosyltransferase sensitive low molecular G-protein on 5-hydroxytryptamine (5-HT)-induced inositol phosphates formation in 5-HT_2c cDNA transfected cells

To clarify the involvement of botulinum ADP-ribosyltransferase sensitive low molecular G-proteins in 5-hydroxytryptamine (5-HT)-induced stimulation of phosphatidylinositol turnover, we examined the effects of 5-HT on inositol phosphates formation in COS 7 cells transfected with serotonin 2C subtype (5-HT_2c) receptor cDNA. 5-HT at 1 and 10 μM stimulated inositol phosphates formation in the cells transfected with 5-HT_2c receptor cDNA, but did not in non-transfected or vector-transfected cells. A typical 5-HT_2c receptor antagonist mianserin (0.3-3 μM) inhibited the 5-HT-induced inositol phosphates formation. Treatment with botulinum toxin D preparation (20 μg/ml, 8 h) that contained botulinum C3 ADP-ribosyltransferase, blocked the 5-HT-induced inositol phosphate formation, although botulinum toxin A preparation that did not contain the enzyme did not have an influence. These results support our previous findings suggesting that low molecular weight G-proteins ADP-ribosylated by botulinum ADP-ribosyltransferase are involved in phospholipase C activity.