Inhibition of human erythrocyte acetylcholinesterase by succinyldicholine

When human erythrocyte acetylcholinesterase (AChE) is inhibited by succinyldicholine (SuCh) at low ionic strength, mu = 0.03, two apparent affinity constants for the inhibitor can be distinguished, KI(1) = 5.4 X 10-5 M and KI(2) = 1.3 X 10-5 M. Increasing the ionic strength to mu = 0.58 increases KI(1) to 1.1 X 10-4 M, but abolishes the contribution of KI(2) completely. It is suggested that a similar process may underlie the apparently continuous variation in affinity constant with ionic strength which has been reported for many bifunctional cationic inhibitors. Since KI(2) is in a concentration range commonly attained therapeutically, some of the clinical manifestations of succinyldicholine administration, e.g., muscarinic effects, may be explained by its anticholinesterase action.