Figure 4.

Insulin synthesis and secretion in trans-differentiated hepatic oval cells. Trans-differentiated hepatic oval cell cultures were maintained 7 days in the absence or presence of 10 mM nicotinamide, then stimulated for 2 h with glucose (23 mM) in serum-free medium. Insulin contents within the cells and insulin secretions were measured after collection of the media or preparation of cell lysates. The cell lysates and culture medium were pooled from three independent culture flasks. Insulin was immunoprecipitated from either the cell lysates (Left) or media (Right). The precipitated material was separated on SDS/PAGE, transferred to nylon membranes, and developed with anti-insulin antibodies. Insulin control (lane 1), normal rabbit serum (lanes 2 and 5), rabbit anti-rat insulin antibody (lanes 3–4 and 6–8). Growth of the cells in nicotinamide before glucose stimulation increased the levels of insulin detected (lane 4 versus 3; lanes 7 and 8 versus 6).