To study the mechanism of insulin release, we examined β-granule movement in the cytoplasm of monolayer-cultured B-cells. The majority of the granules do not move, while about 2% of the granules moved per minute. The velocities of 90% of the moving granules exceeded 0.4 μm/s and showed saltatory type of movement. This movement may have a role in transport of the beta granule from Golgi to B-cell membrane.

We studied the mechanism of this movement using colchicine. Granule movement decreased exponentially by treatment with colchicine (10−6 M to 10−4 M). Almost 60 min was necessary to get a full inhibitory effect of colchicine on granule movement.

Colchicine (10−8 M to 10−4 M) inhibits insulin release in a dose-dependent manner. Maximum inhibition of insulin release (by about 40%) by colchicine (10−4 M) required 60 min. Granule movement also decreased when insulin release was inhibited by lowering glucose from 16.5 mM to 2.7 mM. Thus, granule movement participates in the mechanism of insulin release and may be related to the microtubular system.

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