Motile events in pancreatic endocrine cells

Monolayer cultures of neonatal rat endocrine pancreatic cells were examined by time lapse cinematography. Motion analysis revealed two major types of motile events. On one hand, particles (0.3 micrometers in diameter) tentatively identified as secretory granules were found to undergo back and forth saltatory movements along oriented pathways. The existence of such pathways was statistically validated by the large prevalence of angles close to either 0 degrees of 180 degrees between successive movements of the same particle. The movements occurred at a mean speed of 0.8 micrometers/sec. Glucose (16.7 mM) increased the frequency of such movements. Vincristine (10 microM) caused a progressive inhibition of saltatory movements, which may depend, therefore, on the integrity of the microtubular apparatus. On the other hand, areas of the cell boundary displayed contractile-like movements, which were stimulated by insulinotropic agents, such as glucose and the ionophore A23187. Cytochalasin B also affected this second type of motile event, which is thought to reflect the activity of actin-like microfilaments. These findings suggest that the microtubular apparatus serves as a guiding cytoskeleton for the oriented translocation of secretory granules, whereas the microfilamentous cell web may control the eventual access of the granules to exocytotic sites.