Inhibition of dog kidney Na+, K+-ATPase activity by procaine, tetracaine and dibucaine

The potency of local anesthetics as inhibitors of Na+, K+-ATPase and K+- NPPase activities correlated with lipid solubility. The order of potencies was: dibucaine greater than tetracaine much greater than procaine. Na+-ATPase activity was remarkably more sensitive to inhibition by tetracaine and procaine, and inhibitory potency did not correlate with lipid solubility. The order of potencies for inhibition of Na+-ATPase activity was: tetracaine greater than dibucaine greater than procaine. We examined interactions between the local anesthetics and monovalent cations in an attempt to explain this observation. Inhibition of Na+-K+-ATPase by tetracaine and dibucaine was competitive with respect to Na+, and inhibition of Na+-ATPase activity by all three agents was competitive with respect to Na+. Inhibition of Na+, K+-ATPase activity by procaine and tetracaine was competitive with respect to K+, and inhibition of K+- NPPase activity by all three agents was competitive with respect to K+. Dibucaine, the most lipid soluble agent, was equipotent as an inhibitor of all three activities and was generally less effective as a competitor with respect to activation by monovalent cations. These results suggest that dibucaine may interact nonspecifically with membrane lipids to inhibit enzyme activity whereas less lipid soluble agents, such as tetracaine and procaine, may interact more selectively with cation binding sites. It appears that the presence of K+ in the assay medium specifically decreases the inhibitory potency of tetracaine and procaine. Direct competition between these agents and K+ may prevent inhibition or, alternately, the presence of K+ may convert the enzyme to a conformation less susceptible to inhibition by agents of low to intermediate lipid solubility.