Two different modes of inhibition of the rat brain Na+, K(+)-ATPase by triterpene glycosides, psolusosides A and B from the holothurian Psolus fabricii

Effects of two triterpene glycosides, isolated from the holothurian Psolus fabricii, on rat brain Na+, K(+)-ATPase (Na, K-pump; EC 3.6.1.3) were investigated. Psolusosides A and B (PsA and PsB) inhibited rat brain Na+, K(+)-ATPase with I50 values of 1 x 10(-4) M and 3 x 10(-4) M, respectively. PsA significantly stimulated [3H]ATP binding to Na+, K(+)-ATPase, weakly increased [3H]ouabain binding to the enzyme, and inhibited K(+)-phosphatase activity to a smaller degree than the total reaction of ATP hydrolysis. In contrast, PsB decreased [3H]ATP binding to Na+, K(+)-ATPase, and had no effect on [3H]ouabain binding to the enzyme. K(+)-Phosphatase activity was inhibited by PsB in parallel with Na+, K(+)-ATPase activity. The fluorescence intensity of tryptophanyl residues of Na+, K(+)-ATPase was increased by PsA and decreased by PsB in a dose-dependent manner. The excimer formation of pyrene, a hydrophobic fluorescent probe, was decreased by PsA only. The different characteristics of inhibition mode for these substances were explained by peculiarities of their chemical structures and distinctive affinity to membrane cholesterol.     

Effects of cytapheresis on cell cycle distribution of peripheral blood and bone marrow cells in some hematological malignancies

Feulgen-DNA cytophotometry and 3H-thymidine autoradiography were used to evaluate therapeutic cytapheresis effects on cell cycle distributions of peripheral blood leukemic cells in 15 acute leukemia, 5 CML and 8 CLL patients and of bone marrow erythroblasts in 18 PV patients. Both individual cytapheresis procedures and a long-term program of cytapheresis altered cell cycle distributions and biochemistry which may be summarized as follows: An increase in percentage of cells in S-phase (acute leukemia, CML); a decrease in the differences between values of S-cell number obtained by cytophotometry and autoradiography (acute leukemia, CML, PV); a decrease in some cases in enlarged fraction of cells in G2 (blast crisis of CML, PV); an activation of G0----G1 transition and an increase in the PAS-positive lymphocyte fraction in CLL patients. An apparent increase of blasts in S-phase was found after a pheresis in acute leukemia patients who responded to subsequent chemotherapy. In "nonresponders", a pheresis had no effect on cell cycle distributions. The results of the study demonstrate that despite the wide variability of individual responses, cytapheresis activates cell proliferation and metabolic processes in patients with hematological malignancies.