A B S T R A C TIn order to ascertain the role of calcium in maintaining the structure of the junctional complex between oxyntic cells, control gastric mucosae of the frog Rana pipiens were compared with those exposed to 1 to 4 mM ethylenediaminetetraacetic acid (EDTA). Changes in transmucosal potential difference and mucosal conductance were monitored. In one case a piece of EDTA-treated mucosa was washed and placed in a Ca++-containing solution. Material from all three categories was prepared for electron microscopy (glutaraldehyde and OsO4 fixation with Epon 812 embedding). Electron micrographs showed that after Ca ++ depletion the intercellular electron-opaque material of the desmosome disappears and the walls of this component separate. Similar changes were observed in the

A B S T R A C TThe fine structure of the oxyntic cell from the gastric glands of the bullfrog was studied in lead hydroxide-stained sections of gastric mucosa fixed in buffered osmium tetroxide and embedded in n-butyl methacrylate. The oxyntic cell in non-acid-secreting stomachs (gastric juice pH, 7.4-7.8) is characterized by: (a) numerous closely packed smooth surfaced vesicular and tubular profiles disposed randomly in the cell; some of these elements show interconnections making it possible to identify this component with smooth surfaced endoplasmic reticula of certain other cell types, (b) a small percentage of rough surfaced profiles characteristic of endoplasmic reticula possessing RNP particles on the outer membrane surfaces, (c) a Golgi complex consisting of multiple isolated non-polarized arrays of smooth surfaced parallel elongated profiles and associated vesicular elements, (d) a sparse granular component (140 A) scattered freely in the cytoplasmic matrix, (e) numerous mitochondria with a dense matrix and containing an unusually large number of closely approximated cristae, (f) a number of zymogen granules consisting of either a dense body limited by a membrane or surrounded by a halo of less dense material which is in turn limited by a membrane, and (g) a number of granules (~260 A) containing several smaller granules (~8 0 A) identified presumably as glycogen. Intracellular canaliculi were not observed. Instead the free surface of the oxyntic cell facing the lumen of the gastric gland shows a complicated plication of the plasma membrane. Intercellular canaliculi are seen frequently between adjacent oxyntic cells. The walls of these canaliculi are made up of folded and ruffled cell membranes. The basal surface of the cell also exhibited this type of configuration. Occasional smooth surfaced profiles are seen communicating with the free surface, the wall of an intercellular canaliculus, or the basal surface of the cell. Although nerve endings were not found in association with oxyntic cells, unmyelinated nerves were observed in the vicinity of the gastric glands.

The electron microscope was used to study the structure and three dimensional relationships of the components of the body cortex in thin sections of Paramecium multimicronucleatum. Micrographs of sections show that the cortex is covered externally by two closely apposed membranes (together ∼250 A thick) constituting the pellicle. Beneath the pellicle the surface of the animal is molded into ridges that form a polygonal ridgework with depressed centers. It is these ridges that give the surface of the organism its characteristic configuration and correspond to the outer fibrillar system of the light microscope image. The outer ends of the trichocysts with their hood-shaped caps are located in the centers of the anterior and posterior ridges of each polygon. The cilia extend singly from the depressed centers of the surface polygons. Each cilium shows two axial filaments with 9 peripheral and parallel filaments embedded in a matrix and the whole surrouned by a thin ciliary membrane. The 9 peripheral filaments are double and these are evenly spaced in a circle around the central pair. The ciliary membrane is continuous with the outer member of the pellicular membrane, whereas the plasma membrane is continuous with the inner member of the pellicular membrane. At the level of the plasma membrane the proximal end of the cilium is continuous with its tube-shaped basal body or kinetosome. The peripheral filaments of the cilium, together with the material of cortical matrix which tends to condense around them, form the sheath of the basal body. The kinetodesma connecting the ciliary kinetosomes (inner fibrillar system of the light microscopist) is composed of a number of discrete fibrils which overlap in a shingle-like fashion. Each striated kinetosomal fibril originates from a ciliary kinetosome and runs parallel to other kinetosomal fibrils arising from posterior kinetosomes of a particular meridional array. Sections at the level of the ciliary kinetosomes reveal an additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli extending into the matrix of the organelle from the inner membrane of the paired mitochondrial membrane. The cortical cytoplasm contains also a particulate component and a system of vesicles respectively comparable to the nucleoprotein particles and to the endoplasmic reticulum described in various metazoan cell types. An accessory kinetosome has been observed in oblique sections of a number of non-dividing specimens slightly removed from the ciliary kinetosome and on the same meridional line as the cilia and trichocysts. Its position corresponds to the location of the kinetosome of the newly formed cilium in animals selected as being in the approaching fission stage of the life cycle.

The endothelium-dependent contractile responses of subepicardial coronary resistance arteries (286 +/- 18 microns ID, n = 22) from rabbits fed either a 0.5 or 2.0% cholesterol-enriched diet or a control diet for 10-12 wk were determined under isometric conditions at the optimum length for active force production (Lo). After the development of tone with 29 mM K+-Krebs, arteries from control rabbits treated with acetylcholine (0.1-10 microM) showed a concentration-dependent relaxation, with a maximum decrease in tone of 63%. In contrast, coronary arteries from animals fed 0.5 and 2.0% cholesterol contracted to acetylcholine (approximately 210% increase in tone). A similar phenomenon was seen with arteries precontracted with 10 nM 9,11-methanoepoxy-prostaglandin H2 (U 46,619), a thromboxane A2 mimetic. The contractile responses to acetylcholine occurred in arteries in which the endothelium was structurally intact and which were devoid of plaque. Arteries from cholesterol-fed animals were poorly responsive to ADP (0.01-10.0 microM), whereas arteries from normal animals relaxed. All arteries relaxed to an equal degree when exposed to acidified nitrite, which produces nitric oxide (NO). The data suggest that as a result of hypercholesterolemia, there may be a dysfunction in the synthesis or release of endothelium-derived relaxing factor (EDRF) by the endothelial cells of coronary resistance arteries, rather than an abnormality of the smooth muscle cells per se.