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Modification of Vmax of canine cardiac Purkinje fibers and of the effects of lidocaine by SC-72-14.

We used standard microelectrode techniques to determine the effects of SC-72-14, a monoclonal antibody to the fast sodium channel, on the transmembrane potentials and Vmax of canine cardiac Purkinje fibers, and to study the interactions of the monoclonal antibody with lidocaine. SC-72-14 was prepared with receptor-rich membrane fragments of homogenized eel electroplax as the antigen. It reduced Vmax in a concentration-dependent fashion, and depressed membrane responsiveness, as well. These effects were attributable specifically to SC-72-14, and not to other substances in the vehicle. At slow rates of stimulation, the actions of SC-72-14 and lidocaine on Vmax equaled the sum of their effects, administered alone. These results are consistent with the interpretation that SC-72-14 and the local anesthetic did not compete for the same binding site. In contrast, at fast stimulation rates, the use-dependent blocking effects of lidocaine were suppressed by SC-72-14. The basis for the interference with the use-dependent action of lidocaine is not readily apparent, but may be the result of SC-72-14-induced changes in channel state, receptor affinity for drug, or the availability of ionized drug molecules. These possibilities all await further testing.