Secretion is normal in exPKO acinar cells. (A) Amylase secretion. The fraction of secreted amylase to total cellular amylase content was measured enzymatically for both basal and carbachol-stimulated pancreatic lobules. This is a representative result from 4 independent experiments. Lobules were isolated from P17 β-Perk; Perk+/+ (WT) and β-Perk; Perk-/- (PKO). The β-Perk; Perk-/-(PKO) mice are rescued for Perk in endocrine β-cells with all other tissues remaining PERK-deficient, whereas the β-Perk; Perk+/+ (WT) control mice harbor the rescuing Perk transgene in an otherwise WT background. The β-Perk; Perk-/- (PKO) mice are analogous to the exPKO mice with respect to their exocrine pancreas. Each data point represents three replicate samples. (B) Pulse-chase analysis of protein secretion. The average of two independent experiments is shown. Lobules were isolated from exPKO (PKO) and wild-type (WT) littermates (P17-18). Lobules were labeled with [35S]Met/Cys as described in Figure 3 and then chased in "cold" media over 2 hours. The fraction of TCA-precipitable radioactivity in the media to total cellular TCA-precipitable counts was calculated for each time point for both "basal," (without a secretagogues) and secretagogues-stimulated conditions ("Cch"; with 0.5 μM carbachol).