INHIBITORY EFFECTS OF BOTULINUM TOXIN ON 5-HT(1C) RECEPTOR-INDUCED CL- CURRENT IN XENOPUS-OOCYTES

Several low molecular weight G proteins have been identified, but thei r functional roles remain unclear. To clarify the involvement of low m olecular weight G protein in receptor-stimulated turnover of polyphosp hoinositide (PI) turnover, influences of botulinum toxins on serotonin (5-HT)-stimulated Cl- current mediated by PI turnover were investigat ed using Xenopus oocytes injected with rat brain mRNA. Treatment with botulinum toxin C, D or purified ADP-ribosyltransferase of botulinum t oxin (botulinum toxin C3 enzyme) inhibited the 5-HT-induced Cl- curren t in oocytes, and ADP-ribosylated 23 kDa proteins. Both botulinum toxi n C3 enzyme-induced inhibition of the current and ADP-ribosylation wer e suppressed by pretreatment with antibotulinum toxin C3 enzyme antibo dy. Botulinum toxin D treatment of oocytes was ineffective in the resp onse of Cl- current induced by injection of 50 pmol inositol 1,4,5-tri sphosphate and 50 pmoI Ca2+. It is suggested that low molecular weight G proteins ADP-ribosylated by botulinum toxin C3 enzyme are involved in phospholipase C activation in Xenopus oocytes.