[The influence of pentifylline and theophylline on reaction kinetics on rat brain ATPase stimulatable by catecholamines (author's transl)].

The effects of 1-hexyl-3,7-dimethyl-xanthine (pentifylline, Cosaldon) and theophylline on rat brain Na+-, K+-, Mg2+ ATPase activities were investigated in in vitro experiments. It was established that pentifylline inhibits catecholamine sensitive ATPase in a dose dependent manner. Theophylline was without effect. Pentifylline also inhibited the Mg2+-dependent portion of Na+, K+-, Mg2+-ATPase. The effect of pentifylline on the kinetic parameters of Na+-, K+-, Mg2+-ATPase of synaptosomes was studied in detail. It was shown by a Lineweaver-Burk plot under the influence of pentifylline that the Michaelis constant (Km) increases from 1.0 x 10(-4) mol/l to 6.7 x 10(-4) mol/l. Km by norepinephrine stimulated ATPase decreases from 3.7 x 10(-4) mol/l to 2.9 x 10(-4) mol/l. In both experimental situations a decrease of maximal reaction velocity (Vmax) was observed. At high concentration of potassium in incubation medium the ATPase of synaptosomes was significantly more sensitive to pentifylline than at low concentration of potassium. The inhibition of ATPase by pentifylline was not influenced by the change in Na+/K+ ratio in the incubation medium. In all these experiments, theophylline used as a standard xanthine, was virtually without effect on the reaction kinetic of Na+-, K+-ATPase.