Effects of bupivacaine on the membrane properties of nerve cell soma

While the effects of local anaesthetics on axonal conduction and axonal membrane have been extensively studied, there is little information about the actions of these agents on nerve cell soma. Therefore, the effects of the amide local anaesthetic bupivacaine on the electrophysiologic properties of the nerve cell soma were studied on isolated superfused superior cervical ganglia of rats. Administration of 100-200 nM of bupivacaine to the preparation produced marked changes in membrane properties of the cell soma. The resting membrane potential did not change, but the membrane resistance decreased 20% (P less than 0.01). The firing threshold, the action potential duration at 50% of maximal amplitude, and the intracellular current threshold for firing the cells increased significantly (P less than 0.01), while the action potential amplitude decreased significantly (P less than 0.01), before its complete blockade. The results show that the cell soma is a major site of action of local anaesthetics. The implication of the results is that when local anaesthetics are applied to areas where cell bodies and processes (axons and dendrites) are present together, such as during celiac plexus block, lumbar sympathetic block, stellate ganglion block, etc., they will all be effectively depressed and/or blocked.