Cellular mechanisms of anaesthetic agents

Abstract: Anaesthesia is given to approximate 5% of the Swedish population annually, with the great advantage of painless surgery, but it also has side effects such as depression of blood pressure that might give a heart infarction. Exactly how anaesthetic agents cause anaesthesia is poorly known. Most anaesthetics have been shown to interact with the GABAA receptor, whose endogenous ligand GABA causes down-regulation of the brain and sleep. To further explore the cellular signal system used by anaesthetics this study was performed.First, two different malignant cell lines, PC-12 and SH-SY5Y, were tested, to evaluate if they could replace animal cells; however, they did not respond with increased intracellular calcium [Ca2+]i upon stimulation with propofol, as the normal rat neurons do. This is probably due to differences in the intracellular signaling systems in these malignant cells. Therefore, the studies in this thesis were performed on rat neurons.Propofol, an intravenous anaesthetic, was shown to cause a bicucullin insensitive increase in [Ca2+]i, where the release from intracellular stores was dependent on a tyrosine kinase. Sevoflurane, a volatile anaesthetic, also caused an ilrunediate increase in [Ca2+]i, but not nitrous oxide. Increased [Ca2+], is supposed to augment the influx of chloride ions through the GABAA receptor, hence hyperpolarising the neuron, and thereby make it anaesthetised.Tyrosine phosphorylation of the GABAA receptor is necessary for its function. Propofol tyrosine phosphorylates another ß2 subunit in the membrane then GABA. Propofol, but not GABA, also caused a tyrosine phosphorylation of actin in both the cytoskeletal and cell membrane fraction. Together these changes might explain the difference between sleep and anaesthesia. Isoflurane, sevoflurane and nitrous oxide all tyrosine phosphmylate a protein, suggested to be the GABAA receptor ß subunit, in different cellular compartments. This might explain their different clinical effects.Propofol and sevoflurane, but not GABA, causes actin rings to be formed in the cell, and for propofol the signal goes via rhoA and rho kinase, that also are involved in the translocation of actin to the cellular membrane. An unl~own 160 kDa protein is tyrosine phosphorylated by propofol, is part of the rho signalling pathway and is regulated by rho, This unknown protein might be involved in the actin reorganisation.