DOPAMINE SECRETION BY PC12 CELLS MICROENCAPSULATED IN A HYDROXYETHYL METHACRYLATE METHYL-METHACRYLATE COPOLYMER

A rat pheochromocytoma cell line (PC12) was encapsulated in a water-in soluble hydroxyethyl methacrylate-methyl methacrylate copolymer by int erfacial precipitation from a polyethylene glycol 200 solution into ph osphate-buffered saline. The resulting capsules (660 +/- 44 mu m in di ameter; 84 +/- 27 mu m wall thickness) contained viable PC12 cells in a spheroidal arrangement, much like tumour spheroids, the latter grown on surfaces unsuitable for cell attachment. In these spheroids, the v iable cells formed a band approximately 100 mu m thick, surrounding an inner core of necrotic cells. A similar arrangement was seen 14, 28 a nd 42 days after encapsulation, with capsules maintained in an in vitr o tissue culture environment; the annular ring was roughly constant in size, although the packing density appeared to increase over the 6 we ek observation period. During the first 4 weeks, when measurements wer e made the encapsulated cells converted a tetrazolium dye (MTT) into a n insoluble formazan product, in a time-after-encapsulation-dependent manner. This indicated that PC12 cells retained viability despite enca psulation and an ability to increase (at least in part) their metaboli c capacity, presumably by a combination of proliferation and altered c ellular activity. The encapsulated PC12 cells also secreted dopamine w hen incubated in a high potassium release medium but not in a low pota ssium, conventional tissue culture medium (RPMI 1640). Consistent with the MTT results, the amount of dopamine released was also dependent o n the time after encapsulation, as well as the cell density at the tim e of encapsulation.