Phosphorprotein intermediate in the Ca2+-dependent ATPase reaction of macrophage plasma membrane

Biocompatibility of wound management products: a study of the effects of various polysaccharides on murine L929 fibroblast proliferation and macrophage respiratory burst

An in-vitro screening method to examine the biocompatibility of materials used in wound management has been evaluated. This involved the use of a macrophage respiratory-burst assay and a fibroblast proliferation assay to represent respectively the inflammatory and the granulation phases in wound healing. Standard polysaccharides (calcium and sodium alginates, l-carrageenan, chitin, chitosan lactate, chondroitin sulphate and pectic acid) were used as test compounds. None of the polysaccharide samples caused a significant increase in L929 fibroblast cell numbers relative to control after 6 days incubation. The overall effect of exposure of the fibroblast cultures to the alginates, carrageenan and chondroitin sulphate was an extension of lag phase followed by an enhanced rate of cell proliferation in the logarithmic phase. Only calcium and sodium alginates and chondroitin sulphate enhanced the respiratory burst activity of murine macrophages; l-carrageenan and chitosan lactate were markedly inhibitory. The results suggest that a macrophage activity assay should be included as part of an in-vitro screening program to evaluate the biocompatibility of wound management materials and to detect intrinsic biological activity.

Characterization of a (Ca2+ + Mg2+)-ATPase system in the osteoblast plasma membrane

A high affinity, calmodulin-sensitive (Ca2 + Mg2+)-ATPase was demonstrated in the plasma membrane preparation of three different osteosarcoma cell lines previously demonstrated to respond to parathyroid hormone with an increase in cytosolic calcium and a decrease in pH. The maximal velocity of the enzyme activity in the membrane preparations ranged from 0.83 to 2.42 nmol Pi released per min per mg protein with half-saturation constants of 26 nM of free Ca. The enzyme activity was not affected by Na+, K+, ouabain and azide, and exhibited an absolute requirement for Mg2+ ions. These results suggest a possible role for a membrane Ca2 + Mg2+-ATPase in initiating and perpetuating the ionic control of osteoblastic function.

Identification of Ca2+-pump-related phosphoprotein in plasma membrane vesicles of Ehrlich ascites carcinoma cells

Plasma membrane vesicles of Ehrlich ascites carcinoma cells have been isolated to a high degree of purity. In the presence of Mg2+, the plasma membrane preparation exhibits a Ca2+-dependent ATPase activity of 2 mumol Pi per h per mg protein. It is suggested that this (Ca2+ + Mg2+)-ATPase activity is related to the measured Ca2+ transport which was characterized by Km values for ATP and Ca2+ of 44 +/- 9 microM and 0.25 +/- 0.10 microM, respectively. Phosphorylation of plasma membranes with [gamma-32P]ATP and analysis of the radioactive species by polyacrylamide gel electrophoresis revealed a Ca2+-dependent hydroxylamine-sensitive phosphoprotein with a molecular mass of 135 kDa. Molecular mass and other data differentiate this phosphoprotein from the catalytic subunit of (Na+ + K+)-ATPase and from the catalytic subunit of (Ca2+ + Mg2+)-ATPase of endoplasmic reticulum. It is suggested that the 135 kDa phosphoprotein represents the phosphorylated catalytic subunit of the (Ca2+ + Mg2+)-ATPase of the plasma membrane of Ehrlich ascites carcinoma cells. This finding is discussed in relation to previous attempts to identify a Ca2+-pump in plasma membranes isolated from nucleated cells.

A high affinity, calmodulin-responsive (Ca2+ + Mg2+)-ATPase in isolated bone cells

Although acute alterations in Ca2+ fluxes may mediate the skeletal responses to certain humoral agents, the processes subserving those fluxes are not well understood. We have sought evidence for Ca2+-dependent ATPase activity in isolated osteoblast-like cells maintained in primary culture. Two Ca2+-dependent ATPase components were found in a plasma membrane fraction: a high affinity component (half-saturation constant for Ca2+ of 280 nM, Vmax of 13.5 nmol/mg per min) and a low affinity component, which was in reality a divalent cation ATPase, since Mg2+ could replace Ca2+ without loss of activity. The high affinity component exhibited a pH optimum of 7.2 and required Mg2+ for full activity. It was unaffected by potassium or sodium chloride, ouabain or sodium azide, but was inhibited by lanthanum and by the calmodulin antagonist trifluoperazine. This component was prevalent in a subcellular fraction which was also enriched in 5'-nucleotidase and adenylate cyclase activities, suggesting the plasma membrane as its principal location. Osteosarcoma cells, known to resemble osteoblasts in their biological characteristics and responses to bone-seeking hormones, contained similar ATPase activities. Inclusion of purified calmodulin in the assay system caused small non-reproducible increases in the Ca2+-dependent ATPase activity of EGTA-washed membranes. Marked, consistent calmodulin stimulation was demonstrated in membranes exposed previously to trifluoperazine and then washed in trifluoperazine-free buffer. These results indicate the presence of a high affinity, calmodulin-sensitive Ca2+-dependent ATPase in osteoblast-like bone cells. As one determinant of Ca2+ fluxes in bone cells, this enzyme may participate in the hormonal regulation of bone cell function.

ATP-driven Ca2+ pump activity of macrophage and neutrophil plasma membrane

The results of the investigations here described permit us to conclude that macrophages and neutrophils have a peripheral, outwardly directed Ca2+ extrusion system, which is very similar to the well known Ca2+ pump of the red cell, with regard to capacity and mechanism (16, 21, 29). In fact, all the three cell types have similar maximum pumping rates (about 0.1-0.2 microgram-ions Ca2+/min/ml cells) and use ATP for extruding Ca2+. Furthermore, the plasma membrane of all the three cell types catalyzes a Ca2+-dependent ATPase reaction, which is very likely the enzyme manifestation of the Ca2+ pump activity. Further investigation is needed to establish whether the peripheral Ca2+ pump system of macrophages and neutrophils is utilized to restore steady-state levels of cytosolic Ca2+ upon cell stimulation, or is somehow involved in the triggering of cell response to various stimuli. In fact impairment of the pump activity by a cell stimulant would unbalance Ca2+ passive leaks and active cation extrusion, thereby leading to higher steady-state levels of Ca2+ in the cytosol and to stimulation of Ca2+-dependent functions (1-12).

Localization of phosphatases in Trypanosoma rhodesiense

Phosphatase activity in Trypanosoma rhodesiense has been examined histochemically by light and electron microscopy and by enzymatic assay in homogenate fractions. Using a method with lead as capture ion, acid phosphatase was found in lysosome-like vesicles and in the flagellar pocket. No alkaline adenosine triphosphatase (ATPase) was detectable by this method. Direct assay of p-nitrophenylphosphatase activity in homogenate fractions showed that acid phosphatase activity was strongly membrane-bound, but that activity at pH 9 was minimal in both soluble and particulate fractions. "Endogenous" ATPase activity was localized specifically and reproducibly in the mitochondrial membranes and under the plasma membrane of he flagellum. This nonenzymic reaction product could not be eradicated by glycerol extraction or glucose depletion. Unlike the membrane staining, which was manifest only after lead treatment, heat-resistant electron-dense material was found in the matrix of lysosomal vesicles in trypanosomes fixed in glutaraldehyde only and not subjected to further treatment with heavy metal reagents. X-ray emission analysis showed the presence of calcium and phosphorus, indicating that the matrix might have a phosphate storage function.