Changes in microfilament distribution during amylase exocytosis in rat parotid salivary glands in vitro.

In parotid acini, microfilaments were predominantly localized at the luminal border when visualized with the fluorescent probe, rhodamine-phalloidin. There was no fluorescence in the cytoplasm. When acini were stimulated by isoprenaline, the membranes of the secretory granules appeared to become undercoated by microfilaments immediately after fusion with the luminal membrane. The intensity of fluorescence was correlated with the extent of enlargement of the lumina. These findings indicate that the microfilament system (actin-myosin contractile system) may play a role in regulating the movement of the luminal plasma membrane rather than in the control of transport and access of secretory granules to the lumen.