Fig. 1. HRA-19 monolayers grown for 4 days in culture medium containing 10% foetal calf serum-containing (A,C) or serum-free medium (B,D) and stained using immunocytochemistry for either chromogranin A (A,B) or type-IV collagen (C,D). Scattered chromogranin-A-positive endocrine cells are observed only under serum-free conditions (B) in similar numbers to collagen-IV-positive endocrine cells (D), which are also only present in serum-free conditions. Bar, 100 µm.

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