Studies on an Epithelial (Gland) Cell Junction

Abstract

Membrane permeability of an epithelial cell junction (Drosophila salivary gland) was examined with intraccllular microclectrodes and with fluorescent tracers. In contrast to the non-junctional cell membrane surface, which has a low permeability to ions (I0 -4 mho/cm2), the junctional membranc surface is highly pcrmcable. In fact, it introduces no substantial restriction to ion flow beyond that in the cytoplasm; the resistance through a chain of cells (150 ~ cm) is only slightly greater than in extrudcd cytoplasm (100 ~ cm). Thc diffusion resistance along thc intcrccllular spacc to the cxtcrior, on thc other hand, is very high. Here, there exists an ion barrier of, at least, 10 4 ~ cm 2. As a result, small ions and fluorescein move rather freely from one cell to the next, but do not leak appreciably through the intercellular space to the exterior. The organ here, rather than the single cell, appears to be the unit of ion environment. The possible underlying structural aspects are discussed.

Fine Structure of the Epithelium of the Gut in the Crayfish (<i>Procambarus clarkii</i>) with Special Reference to the Cytoplasmic Microtubules

“…Just below this junction occurs the typical septate desmosome (Fig. 10) which has been known to be present in the wide phyla of invertebrates (WOOD, 1959, LOEWENSTEIN andKANNO, 1964;WIENER and LOEWENSTEIN, 1964;LOCKE, 1965). The septate desmosome is characterized by the presence of a septa across the interThe apical cytoplasm is particularly concentrated by abundant mitochondria.…”

Electrophysiological Study of Special Connections Between Cells in the Early Chick Embryo

“…references 10,11,14), certain alternatives should be mentioned. The existence of a high resistance barrier surrounding the whole blastodisc is excluded since virtually no potential changes were recorded unless both current and recording micropipettes were intracellular.…”

“…certain nerve cells, cardiac, and visceral muscle cells) (1,2,4,5), but also between certain nonexcitable cells (e.g. glial cells and epithelial cells in insects, amphibians, and mammals) (8)(9)(10)(11)13). In all the cases cited above, electron microscopy has shown that the cells are connected by regions of specialized membrane apposition (e.g.…”

“…"tight junctions") (3,7,12,15,20,21). The widespread presence of such connections, even between cells which do not generate action potentials, has led to the suggestion that these contacts play a role in addition to that of the intercellular transmission of electrical signals (10,14).…”

Polyomavirus middle T antigen downregulates junctional cell-to-cell communication.

“…The probe was microinjected into individual cells (23,31), and the fraction of first-order neighbors displaying LRB-Glu fluorescence within 5 min of the injection-the incidence of permeable interfaces-was scored. In all cases analyzed, including the transformed condition, the first-order neighbors could be clearly distinguished; regions with excessive cell overlap were not used.…”