Do protozoa conceal a high potency of nucleoside triphosphate hydrolysis present in Toxoplasma gondii?

ATP hydrolytic activity in whole cell homogenates of some protozoa was assayed in the presence or absence of dithiothreitol. The activities in all protozoan cell homogenates, except Toxoplasma gondii, ranged from 0.6 to 32 mumol/mg protein/hr, irrespective of the presence or absence of dithiothreitol. A remarkably higher activity, 11,690 mumol/mg protein/hr, was observed for T. gondii in the presence of dithiothreitol. These results indicate that the higher ATP hydrolytic potency observed for T. gondii is not universal to protozoa, rather it is unique to T. gondii.     

Enhanced susceptibility of target KMT-17 cells to activated macrophages by treatment with the antitumor agent bleomycin

Summary We observed that after KMT-17 cells had been treated with bleomycin (BLM), even with a dose as high as 160 g/ml, they were still able to form colonies in soft agar. We then studied the susceptibility of KMT-17 cells treated with BLM to activated macrophages. During a colony inhibition assay, BLM-treated KMT-17 cells were found to be much more susceptile to activated macrophages than nontreated KMT-17 cells, moreover, a tumor neutralizing assay showed that the growth of BLM-treated KMT-17 cells was also significantly inhibited by activated macrophages as compared with nontreated KMT-17 cells. Macrophages activated by both BLM and the Nocardia rubra cell wall skeleton were able to mediate such tumor inhibition activity in BLM-treated KMT-17 cells. Activated macrophages did not seem to have strong antitumor activity against nontreated KMT-17 cells in vivo, however, the life span of the rats which were inoculated i. p. with KMT-17 cells was significantly expanded after the tumorbearing rats were given BLM i.p. The data presented here suggest that not only does BLM have a direct tumoricidal effect on KMT-17 cells, it also regulates immunosensitivity of targets to immune effectors. We also discuss the mechanism for enhancing the susceptibility of KMT-17 cells to activated macrophages brought about by treatment with BLM.Supported in part by a Grant-in-Aid for Cancer Research from the Japanese Ministry of Education, Science, and Culture     

Postnatal reorganization of actin filaments and differentiation of intercellular boundaries in the rat aortic endothelial cells

Postnatal change in the distribution of actin filaments in endothelial cells was studied in the rat aorta by use of rhodamine-phalloidin staining and confocal laser scanning microscopy. Endothelial cells of the rat aorta possessed two populations of actin filament bundles, namely, peripheral bands at the cell border and stress fibers running longitudinally in the cytoplasm. Aortic endothelial cells of the neonatal rat contained only stress fibers, whereas those of the 10-day-old rat developed both peripheral bands and stress fibers. After 20 days of age, aortic endothelial cells had predominantly peripheral bands with occasional stress fibers around the branch orifices. During postnatal development the length density of stress fibers in aortic endothelial cells decreased, whereas individual stress fibers in endothelial cells were shortened. Electron-microscopic observation revealed that the high intercellular boundaries of aortic endothelial cells at birth decreased in height and developed cytoplasmic interdigitations after 20 days of age. The occurrence of peripheral bands at the cell border is thought to be closely related to formation of cytoplasmic interdigitation which strengthens the mechanical connection between endothelial cells against increasing transmural pressure. Expression of stress fibers in aortic endothelial cells of the neonatal rat is supposed to be affected by longitudinal elongation of the developing aorta, whereas their postnatal decrease is though to be correlated with the change of fluid shear stress loaded in the aortic endothelium.     

Physiological role of the chaA gene in sodium and calcium circulations at a high pH in Escherichia coli.

Ohyama et al. previously isolated Escherichia coli mutant RS1, which had a negligible activity for sodium ion extrusion at alkaline pH (T. Ohyama, R. Imaizumi, K. Igarashi, and H. Kobayashi, J. Bacteriol. 174:7743-7749, 1992). Our present study showed that the mutation of RS1 was compensated for by a cloned chaA gene. It has been proposed that sodium ion extrusion by ChaA is prevented under physiological conditions (D. M. Ivey, A. A. Guffanti, J. Zemsky, E. Pinner, R. Karpel, E. Padan, S. Schuldiner, and T. A. Krulwich, J. Biol. Chem. 268:11296-11303, 1993). In order to clarify the physiological role of chaA in sodium ion circulation at alkaline pH, we constructed a delta chaA mutant. The resultant mutant, TO112, deficient in both nhaA and chaA, was unable to grow at pH 8.5 in medium containing 0.1 M sodium chloride and had negligible sodium ion extrusion activity. However, TO112 grew at pH 7.0 in medium containing 0.4 M sodium chloride. Sodium ions were extruded from TO112 cells at neutral pH. The extrusion activity at pH 7.5 was greatly reduced by the deletion of nhaB. These data demonstrate that the activity of nhaB is low at high pH and that ChaA extrudes sodium ions at alkaline pH. The uptake of calcium ions by everted membrane vesicles prepared from the delta chaA mutant TO110 was 60% of the activity observed in the vesicles of the wild-type strain at pH 8.5, but the activity at neutral pH was not reduced by the deletion of chaA. Therefore, it was also suggested that ChaA plays a role in calcium ion circulation at alkaline pH.