Anaesthetic sensitivity of fMLP-induced cell signalling in Xenopus oocytes

FMLP stimulation of Xenopus oocytes expressing fMLP receptors leads to a concentration-dependent biphasic inward current. To identify the evolution of these currents we have examined the effects of blocking various cell signalling pathways. In addition we have analysed the effects of three intravenous anaesthetics on these fMLP-induced currents. Xenopus oocytes were microinjected with cRNA encoding the fMLP receptor and fMLP-stimulated (100 nM) currents measured, using two-electrode voltage-clamp (-70 mV), before and after injection of heparin (120 ng ml-1), wortmannin (1 microM), U73122 (5 microM) or buffer. Concentration-response curves were established for the action on fMLP-stimulated currents of thiopentone (5-500 microM), methohexitone (0.2-200 microM) and propofol (0.5-500 microM). Heparin significantly enhanced the fast current (p<0.05). Wortmannin had no effect on either current. U73122 inhibited only the slow current (p<0.05). All anaesthetics inhibited both currents, with the maximum inhibition for the fast/slow currents 70%/100%, 60%/60% and 100%/100% for thiopentone (IC50 147/120 microM), methohexitone (IC50 4.7/2.2 microM) and propofol (IC50 33/8 microM), respectively. We suggest (a) the slow current arises via the PLC/PKC pathway because it is reduced by the PLC inhibitor U73122, (b) the PI3K- and PLD-mediated pathways are not involved because wortmannin had no effect and (c) activation of the two conductance channels must be different because U73122 reduced the slow but not the fast current. Since both currents are decreased by all three anaesthetics, their inhibition might be mediated through an action at the agonist/receptor, although, since the slow current is consistently more sensitive than the fast, there may be additionally an action on cell signalling.