Somatostatin-14-Like Antigenic Sites in Fixed Islet D-Cells Are Unaltered by Cysteamine: A Quantitative Electron Microscopic Immunocytochemical Evaluation*

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Abstract
Exposure of somatostatin cells to cysteamine (CSH) produces a marked reduction in somatostatin-14-like immunoreactivity (S-14 LI) in cell extracts. In the present study we have evaluated the effects of CSH on S-14-like sites in fixed islet D-cells using immunofluorescence and quantitative electron microscopic immunocytochemistry. Monolayer cultures of rat islet cells exposed to CSH (10 mM) for 1 h and subsequently extracted in 1 M acetic acid exhibited a severe reduction in S-14 LI from 6.6 .+-. 0.48 to 0.7 .+-. 0.06 ng/dish. CSH-induced reduction in S-14 LI persisted when cells were fixed in Zamboni''s solution for 16 h and subsequently extracted and assayed. By immunofluorescence, however, the relative numbers of somatostatin-positive cells as well as the fluorescent intensity were identical in control and CSH-treated cells. CSH did not produce any identifiable abnormality in the ultrastructural appearance of D-cells. Protein A-gold labeling of the islet cells showed a uniform distribution of gold particles in both control and CSH-treated cultures. The density of gold particles over D-cell secretory granules from CSH-exposed cultures (36.6 .+-. 3.5 particles/.mu.m2) was not different from that in control D-cell granules (42.2 .+-. 5.9 particles/.mu.m2). These data clearly indicate that despite a profound reduction by CSH of S-14 LI in tissue extracts, there is no detectable decrease in the same antigenic sites in tissue sections when assessed immunocytochemically.