Local anaesthetic effects on trophoblast membrane fluidity

Previous studies showed that anaesthesia with the barbiturate Thiopental induces an increase in membrane fluidity and a decrease in acetylcholinesterase activity in syncytiotrophoblast plasma membranes (SPM) obtained from placentas after Cesarean section. The aim of the present work was to compare the effect of a local anaesthetic (bupivacaine hydrochloride, trade name Marcaine) on SPM in vivo and to establish whether the anaesthetic is still present in the membrane after tissue preparation. The acetylcholinesterase activity was lower in Marcaine-anaesthetized SPM (27 +/- 3 against 39 +/- 6 in the control). The Marcaine action on the SPM can be ascribed to a competitive inhibition, similar to that reported for Thiopental. Fluorescence studies of the order parameter P showed it to be higher in SPM obtained from control (0.253 +/- 0.012) than in SPM obtained from Marcaine-exposed membranes (0.240 +/- 0.015). The local anaesthetic is still present in the SPM after their preparation (20.1 ng per mg membrane protein). It appears that the local anaesthetic exhibits an effect similar to that of the general anaesthetic, apparently due to binding to the membrane.