Inhibitory effects of botulinum toxin on 5-HT1C receptor-induced Cl- current in Xenopus oocytes

Several low molecular weight G proteins have been identified, but their functional roles remain unclear. To clarify the involvement of low molecular weight G protein in receptor-stimulated turnover of polyphosphoinositide (PI) turnover, influences of botulinum toxins on serotonin (5-HT)-stimulated Cl- current mediated by PI turnover were investigated using Xenopus oocytes injected with rat brain mRNA. Treatment with botulinum toxin C, D or purified ADP-ribosyltransferase of botulinum toxin (botulinum toxin C3 enzyme) inhibited the 5-HT-induced Cl- current in oocytes, and ADP-ribosylated 23 kDa proteins. Both botulinum toxin C3 enzyme-induced inhibition of the current and ADP-ribosylation were suppressed by pretreatment with antibotulinum toxin C3 enzyme antibody. Botulinum toxin D treatment of oocytes was ineffective in the response of Cl- current induced by injection of 50 pmol inositol 1,4,5-trisphosphate and 50 pmol 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.