The long-term objective of my research is to understand how do local anesthetics block the nerve conduction. The proposed project has placed the emphasis on discriminating between the specific effect of local anesthetics from their non-specific effects on nerve membranes. The specific effect will be studied by examining the drug-Na channel interactions and the non-specific effects will be investigated by using hydrophobic ions as probes of general membrane properties. Both types of experiments will be performed in voltage-clamped squid axons with the specific aims: (1) to determine the role of Na inactivation machinery in the drug channel blocking action with respect to the resting and use-dependent blocks by using different agents to remove Na inactivation. (2) To determine the role of the activation gate in modulating use-dependent block (a) by comparing the voltage dependence of use-dependent block to that for the activation of the Na channels, and (b) by comparing the voltage dependence for recovery from use-dependent block to that for the activation of the Na channels. (3) To determine the potency and voltage dependency of local anesthetic blocking action in the presence of different species of permenant ions at various concentrations in pronase-treated axons. These results will be interpreted using a barrier model with a provision for multi-ion occcupancy. (4) To define the role of external or internal H+ ions in modulating the recovery from use-dependent block. (5) To determine the effects of local anesthetics and other membrane perturbating agents on the artificial gating current induced by hydrophobic ions and compare these effects to their effects on the Na gating currents. Our understanding of mechanisms for producing local anesthetic action will also provide an understanding of how antiarrhythmic and anticonvulsant action is brought about by those agents exhibiting local anesthetic action.