Nerve-Myoepithelium and Nerve-Glandular Epithelium Contacts in the Lacrimal Gland of the Sheep

Electron microscope studies of several types of secretory glands (6, 17, 18) have shown that myoepithelial cells envelop the acini and resemble smooth muscle cells in their fine structure (15). No close nerve-myoepithelium contacts with a separation of less than 0.1 /i have been described, and it has been suggested, for example in the rat submaxillary gland, that activation of the myoepithelium may occur by diffusion of transmitter substance over relatively long distances (18). In examining the fine structure of the lacrimal gland of sheep, we have observed that nerves are in close association with both the myoepithelium and the acinar epithelium. The material was taken from an animal under fluothane anesthesia, fixed with 1 % Os0 in a phosphate buffer, pH 7.6 (10), and embedded in Araldite (8). Unsupported sections, about 1,000 A thick, cut with glass knives in a Cambridge-Huxley-pattern microtome, and double-stained with uranyl nitrate (Merrillees, unpublished observations) and with lead citrate (11), were examined in a Hitachi 1iB electron microscope. A montage of electron micrographs (15,000 magnification) was prepared to cover the entire profile of an acinus of the gland (Fig. 1). The myoepithelium was identified by the presence of myofilaments and dense bodies in the dark ground FIGURE 1 Photograph of a montage of electron micrographs, showing profiles of one entire acinus (Al) and parts of two other acini (A2, AS). Two myoepithelial cells, MEl and ME2, appear to envelop two acini, Al + AA and Al + A3, respectively. Squares a-d indicate the presence of nerve axons. IC = epithelium of the intercalary duct. ME1-5 = myoepithelium. N? = a probable axon. X 3,300.