Dynamics of Insulin Release and Microtubular‐Microfilamentous System

Abstract. A model is proposed to account for the phasic nature of insulin release. It is suggested that one modality of secretion results from the mobilization of secretory granules already located in the close vicinity of the microfilamentous cell web. This corresponds to a fraction of the initial secretory response to a high glucose concentration, the residual release of insulin provoked by glucose in the presence of diazoxide, and the total release of insulin evoked by sulphonylurea at a low glucose concentration. A second modality of release, which is characteristic of the late phase of glucose‐induced insulin secretion, is thought to correspond to the mobilization of secretory granules transported to the periphery of the β‐cell along oriented microtubular pathways. Whether only one or both modalities of release are initiated by a given insulinotropic stimulus may depend on the magnitude and duration of the changes induced by secretagogues in the insular handling of calcium.