The Microtubule-Microfilament System in Beta-Cell Secretion

Abstract

This chapter discusses the histochemical properties of microtubule–microfilament system in beta-cell secretion. Glucose is the major physiologic stimulus for beta cell secretion resulting in the rapid release of insulin as well as the initiation of insulin synthesis. The mechanism of insulin release was studied initially by electron microscopic examination of the islets following acute stimulation of insulin secretion by either glucose or tolbutamide administered in vivo . With improved methods of fixation for electron microscopy, microtubules have been demonstrated in a wide variety of mammalian, plant cells, and in fungi. Microfilaments can be destroyed by cytochalasin B which is an antimitotic agent that apparently acts only on the microfilaments and does not destroy microtubules. Thus, it would appear that the microtubular–microfilament system may be a very primitive, intracellular structure that has been modified through cellular differentiation and specialization to serve a functional role either as an internal cytoskeleton or as a means of providing rhythmic movement to cytoplasmic projections or to provide an intracellular transport system for the movement of particles and secretory granules.