Fine structural distribution of microtubules in pancreatic B cells of the rat.

The distribution of microtubules has been studied in pancreatic B cells of normal rats and in animals infused with glucose for various periods of time. An array of microtubules extends from the outer nuclear membrane to the plasma membrane coursing in all directions of the cytoplasmic space. Microtubules are found between profiles of the endoplasmic reticulum, cisternae of the Golgi complex and in close proximity to mitochondria and secretion granules. Insertion of microtubules in the plasma membrane is best studied in tangential sections through the plane of the membrane, the fixation of microtubules might involve microfilaments and desmosomes. The possible role of microtubules in the different phases of the secretory process is discussed.