Subcellular fractionation studies in resting human neutrophils indicated a bimodal distribution for cytochrome b. A major peak of cytochrome b co-sedimented with gelatinase under different experimental conditions. This localization was partially overlapped with specific granules (using lysozyme and lactoferrin as specific granule markers), but clearly resolved from azurophilic granules, plasma membrane, mitochondria, as well as from a novel alkaline phosphatase-rich intracellular organelle. A minor localization of cytochrome b was found in fractions enriched in both the plasma membrane marker 5'-nucleotidase and alkaline phosphatase. A significant portion of ubiquinone cell content co-fractionated with the gelatinase-containing granules. After phorbol myristate acetate (PMA)-cell stimulation, cytochrome b was mobilized to fractions showing respiratory burst activity and enriched in 5'-nucleotidase activity. This mobilization paralleled secretion of gelatinase and lysozyme to the extracellular medium. Furthermore, neutrophil stimulation with fluoride in the absence of cytochalasin B induced release of gelatinase and generation of superoxide anion with only minimal release of lysozyme. Preincubation of cells with the anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) prevented lysozyme release, but had only a minor effect on the release of gelatinase and did not inhibit the superoxide anion generation elicited by N-formyl-methionyl-leucyl-phenylalanine or PMA. These results suggest a main location of cytochrome b in mobilizable gelatinase-containing granules, which can constitute a subpopulation of specific granules. Furthermore, these findings show that the gelatinase-containing granule is functionally involved in the respiratory burst in neutrophils and that membrane fusion between plasma membrane and the gelatinase-containing granule occurs during activation of cells.

The levels of NTX uniquely discriminated between older adults with normal, osteopenic, or osteoporotic BMD levels. If confirmed, these data suggest that NTX levels could be used to predict current osteoporosis in older men and women.

The "erythroid/brain" glucose transporter (GT) isoform is expressed only in a subset of hepatocytes, those forming the first row around the terminal hepatic venules, while the "liver" GT is expressed in all hepatocytes. After 3 d of starvation, a threeto fourfold elevation of expression of the erythroid/brain GT mRNA and protein is detected in the liver as a whole; this correlates with the expression of this GT in more hepatocytes, those forming the first three to four rows around the hepatic venules. Starvation-dependent expression of the erythroid/ brain GT on the plasma membrane of these additional hepatocytes is lost within 3 h of glucose refeeding; however, by immunoblotting we show that the protein is still present. Its loss from the surface is possibly explained by internalization. (J.Clin. Invest. 1990. 86:986-992.) Key words: starvation * liver glucose transporter * glucose refeeding * regulation and internalization Introduction The liver plays a key role in glucose homeostasis. Of the blood entering the liver, 75% comes from the digestive system via the portal vein and 25% from the hepatic artery. During passage of blood through the liver, glucose in excess of 5 mM (after a meal) is removed; it is either stored as glycogen or catabolized by glycolysis. Between meals and during starvation, when blood glucose is lower then 5 mM, hepatic glycogen degradation and gluconeogenesis result in release of glucose into the blood. Thus, constant blood glucose concentration is maintained by the parenchymal cells (hepatocytes).

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Release and subcellular fractionation experiments indicate that fusion of a novel tertiary granule with the plasma membrane is concomitant with human neutrophil activation. Phorbol 1Zmyristate 13-acetate (PMA) induced a respiratory burst in human neutrophils as well as a high release of gelatinase, a marker of the tertiary granule. Preincubation of neutrophils with cytochalasin E induced a partially activated or 'primed' state, in which cells were unable to generate superoxide anion, but showed a reduced latency period for this activity. Fusion of tertiary granules with the cell surface also occurred during priming, although to a lesser extent than in PMA stimulation. The rapid tertiary granule degranulation, preceding that of specifics and azurophilics, seems to play an important role in the functionality and secretory properties of human neutrophils.