Fig. 4. Potentiation of isoproterenol-stimulated amylase secretion by BFA and by K⁺ depletion. Parotid lobules were pulse-labeled and chased as in Fig. 1. (A) Effects of BFA treatment on amylase secretion. Lobules were pretreated with 10 µg/ml BFA or carrier Me₂SO for 30 minutes. Subsequently samples were treated with 10 µg/ml BFA alone (BFA), 1 µM Iso and carrier Me₂SO (Iso) or 10 µg/ml BFA (Iso + BFA) and incubation was continued for 60 minutes with complete changes of medium every 10 minutes. A parallel sample was treated with 1 µM Iso and 10 µg/ml BFA and subsequently with 1 µM Iso alone (BFA take-away). The results shown are representative of four separate experiments. (B) Potentiation of isoproterenol-induced amylase secretion in K⁺-depleted medium. Samples were incubated in DMEM or K⁺-free DMEM (Na⁺ replacing K⁺) for 30 minutes before adding 1 µM isoproterenol. Subsequently, incubation was continued with complete changes of medium every 10 minutes. The results shown are representative of four separate experiments.