The influence of nicergoline on reaction kinetics of synaptosomal adenosine triphosphatases from porcine brain.

10-Methoxy-1,6-dimethylergoline-8beta-methanol-5-bromonicotinate (nicergoline) has in vitro a modulatory effect upon reaction kinetics of two synaptosomal adenosine triphosphatases from porcine brain: Na,K-dependent ATPase and Ca,Mg-dependent ATPase. Nicergoline is a non-competitive inhibitor of synaptosomal Ca,Mg-dependent ATPase in vitro; thus, if its in vivo concentration reaches a sufficiently high level, the rate of exchange of Ca and Mg ions between the intra- and the extracellular spaces of neurons slows down. In vivo effect of nicergoline upon reaction kinetics of synaptosomal Na,K-dependent ATPase is complex; below 80 micromol/l ATP it is an activator, and above 80 micromol/l ATP it is an inhibitor or enzyme. It decreases Km for ATP from 310 micromol/l in the absence, to 70 micromol/l in the presence of 0.3 mmol/l drug. It is believed that, in vivo, nicergoline helps to level or normalize the rate of physiological processes energetically coupled to synaptosomal Na,K-dependent ATPase, by moderately accelerating the slow and strongly inhibiting the fast reaction rates by ATP hydrolysis.