Figure 5.

Storage of prolactin by GH4C1 cell clones expressing PC1. Cells were metabolically labeled to approach steady state, as described in the text. The cells were then either tested directly for secretion under unstimulated (UNSTIM) or stimulated (STIM) conditions (A) or tested after 3 initial unstimulated hours to further enrich for slow-turnover pools of secretory protein (B). As a consequence, in B, a majority of the remaining intracellular prolactin was exported to the media upon secretagogue exposure. From quantitative scanning of the media and cell lysate bands from each gel (the sum in each case was considered 100%), the percentages recovered in the media under unstimulated (open bars) and stimulated (closed bars) conditions are shown (bar graphs).