[The Na,K-ATPase pump and the lymphocyte adenylate cyclase system]

The effects of the Na(+)-K(+)-pump inhibitor ouabain on the beta 2-adrenoreceptor-coupled adenylate cyclase system were examined in vitro using intact human mononuclear lymphocytes and cell homogenates. Ouabain caused a dose-dependent increase in basal adenylate cyclase (AC) activity from 0.1 to 100 microM. The density of surface binding sites for 125ICYP (4 degrees C) was decreased by almost 25% after ouabain action. Glycoside shifted to the right the dose-response curve for stimulation of the cAMP synthesis by 1-isoproterenol. This shift was due to a decrease in the affinity of beta 2-adrenoreceptors for 1-isoproterenol, as it was shown in the competition experiments with 125ICYP (control--IC50, 1-isoproterenol--0.5 microM, ouabain--1.25 microM). Ouabain did not change the forskolin-stimulated AC activity. The activity measured in the presence of Gpp(NH)p which stimulates AC via Gs-protein was increased by ouabain; lag-period of Gpp(NH)p action did not change after ouabain addition. N-ethylmaleimide which inactivates Gi-protein increased basal, 1-isoproterenol and ouabain-sensitive AC activities. The stimulation of lymphocyte AC activity by ouabain may be due to an enhancement of the activation of Gs-protein.