Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones

A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer.     

Development of the embryonic chick phagocytic system: Intraembryonic erythrophagocytosis induced by phenylhydrazine

The intraembryonic reticuloendothelial response to phenylhydrazine-induced hemolytic anemia was studied embryonic chicks (days 13–16) by light and electron microscopy and histochemical and biochemical assays for acid phosphatase. Phenylhydrazine was given on day 13 and tissue taken at 2, 5, and 10 h and at 1, 2, and 3 days after injections. The response varied in the three major reticuloendothelial organs. The spleen first demonstrated an increase in erythrophagocytosis that was accompanied by increased acid phosphatase levels. Erythrophagocytosis occurred primarily in the red pulp resulting in increased numbers of macrophages, increased size of macrophages, and retention of erythrocytes, which together combined to enlarge the spleens. By 2 days after phenylhydrazine injection, greatly enlarged macrophages began to migrate into the venous system, where some erythrophagocytosis continued to occur. The liver was also a major erythroclastic organ in which Kupffer cells became increasingly erythrophagocytic. However, erythrophagocytosis began later than in the spleen, and as measured by acid phosphatase levels, the liver was not as effective in removing damaged erythroid cells. Marrow erythrophagocytosis was only slightly enhanced; however, the marrow responded by increasing its production of red blood cells. Thus, the intraembryonic reticuloendothelial organs of the embryonic chick responded to phenylhydrazine-induced hemolytic anemia in much the same manner as might be expected of the adult bird.     

Sexually different actions of leptin in proopiomelanocortin neurons to regulate glucose homeostasis

Leptin regulates energy balance and glucose homeostasis, at least in part, via activation of receptors in the arcuate nucleus of the hypothalamus located in proopiomelanocortin (POMC) neurons. Females have greater sensitivity to central leptin than males, suggested by a greater anorectic effect of central leptin administration in females. We hypothesized that the regulation of energy balance and peripheral glucose homeostasis of female rodents would be affected to a greater extent than in males if the action of leptin in POMC neurons were disturbed. Male and female mice lacking leptin receptors only in POMC neurons gained significantly more body weight and accumulated more body fat. However, female mice gained disproportionately more visceral adiposity than males, and this appeared to be largely the result of differences in energy expenditure. When maintained on a high-fat diet (HFD), both male and female mutants had higher levels of insulin following exogenous glucose challenges. Chow- and HFD-fed males but not females had abnormal glucose disappearance curves following insulin administrations. Collectively, these data indicate that the action of leptin in POMC neurons is sexually different to influence the regulation of energy balance, fat distribution, and glucose homeostasis.