The exocytotic exposure of antigens of chromaffin granule membranes was studied with chromaffin cells isolated from bovine adrenal medulla. Antigens on the cell surface were visualized by indirect membrane immunofluorescence employing antisera against glycoprotein III and dopamine ß-hydroxylase . With unstimulated cells, only weak immunofluorescence on the cell surface was observed, whereas stimulated cells (with carbachol or Bat +) exhibited much stronger reactions . In all cases the staining appeared as dots and patches . To quantitatively prove these observations, we analyzed the immunostained cells using a fluorescenceactivated cell sorter . After stimulation, the average fluorescence intensity of the cell population was enhanced . This increase correlated with the degree of catecholamine secretion . The fluorescence intensity of stimulated cells varied over a broad range indicating that individual cells reacted variably to the secretagogues . When stimulated cells were incubated at 37°C for up to 45 min after stimulation, a decrease of membrane immunofluorescence approaching that of unstimulated control cells was observed . Apparently, the membranes of chromaffin granules, which had been incorporated into the plasma membrane, were retrieved by a specific and relatively fast process . This retrieval of the antigen from the cell surface was blocked by sodium azide, but not influenced by colchicine, cytochalasin B, and trifluoperazine . The quantitative methods established in this paper should prove useful for further study of the kinetics of the exo-endocytotic cycle in secretory tissues .Secretion of catecholamines from adrenal medulla occurs by exocytosis (23,27) . During this process the membranes of the secretory organelles, i .e ., the chromaffin granules, are incorporated into the plasma membrane . In order to prevent enlargement of the cell surface, membrane retrieval has to accompany exocytotic activity (17). In adrenal medulla, evidence for endocytotic processes subsequent to secretion has been obtained by studying the uptake of exogenous markers (10,16,26). These investigations have not established whether the membranes of chromaffin granules are retrieved specifically and, if so, how fast this specific endocytosis proceeds. To answer these questions, specific components of the membranes of chromaffin granules have to be followed through the exo-endocytotic cycle . The biochemical composition and topology of these membranes has already been characterized

The synthesis rate of the membrane proteins of the catecholamine-storing vesicles (chromaffin granules) of the adrenal medulla is lower than that of the secretory proteins of the contents. Based on these results we proposed that after exocytosis the membranes of chromaffin granules are retrieved and are re-used for several secretion cycles (see also ref. 4). This concept of re-use of granule membranes has been further strengthened by the finding that exogenous markers which are taken up by secretory cells during stimulation can be traced to the Golgi region and to immature secretory organelles. However, one basic question remains: are the membranes of secretory organelles specifically and completely removed from the plasma membrane and if so, how fast is this process? By using an antiserum against a membrane glycoprotein of chromaffin granules we have now obtained quantitative data which demonstrate that during exocytosis this antigen becomes exposed on the cell surface and disappears again to a large degree within 30 min.

Conventional radiography is still regarded the gold standard for imaging techniques in rheumatoid arthritis (RA). It is a very important tool for the diagnosis, the differential diagnosis, and the evaluation of the course and prognosis of the disease. Special advantages of conventional radiography are the worldwide availability and experience with the method over decades and the relatively low costs. Moreover, x-rays can be stored and re-evaluated over long periods of time. Joint damage caused by RA can be quantified by means of scoring methods. The amount of destruction correlates well with functional disability over time. The inhibition of damage progression seen on radiographs is the most important characteristic of a DMARD. Typical radiographic changes are part of the ACR classification criteria of RA. Technically, bone structure can be demonstrated with a high local resolution better than with all other imaging techniques, whereas only indirect conclusions can be drawn concerning soft tissue and cartilage lesions. This review includes recommendations given by the "Commission on Imaging Techniques" of the German Society of Rheumatology regarding technical and personal preconditions, costs, indication as well as practical performance of radiography in RA. In addition, radiographic changes that can be expected in RA including destruction and repair are discussed briefly.

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