Summary
Cells ofChironomus salivary glands communicate through intercellular connections of high permeability. Electron micrographs of salivary glands show two kinds of junctions between the membranes of adjacent cells, which may be responsible for cell coupling: septate junctions and close membrane junctions.
A large fraction of lateral cell surfaces is occupied by septate junctions, while the area of close membrane junctions appears to be very small. Consequently septate junctions have been considered as likely sites for intercellular coupling. There are however some indications that intercellular communication is provided by structures which seem to be unstable. As osmotic effects are among the factors which can disrupt cellular communications, we have tried to eliminate possible effects of the fixing solutions on the ultrastructure of intercellular connections by using isoosmotic fixatives. Under these conditions large regions of close membrane junctions of the nexus kind have been observed to occur between gland cells. They are of similar size as septate junctions. It seems to be possible that as in other communicating cell systems nexus could be the sites for intercellular coupling of salivary gland cells.
Zusammenfassung
Speicheldrüsen von Mückenlarven (Chironomus Thummi) haben eine ausgedehnte interzelluläre Kommunikation. In elektronenmikroskopischen Bildern der Speicheldrüsen wurden zwei Arten von interzellulären Verbindungen gefunden, die für die Zellkopplung verantwortlich sein könnten: septate junctions und close membrane junctions. Da die räumliche Ausdehnung der septate junctions viel größer zu sein scheint als die der close junctions, wurden erstere als wahrscheinliche Kopplungsstrukturen angesehen. Es gibt jedoch Hinweise, daß die Strukturen, welche die Zellkopplung bewirken, sehr labil sind. Unter den Faktoren, die zu einer Unterbrechung der zellulären Kommunikationen führen können, sind auch osmotische Effekte. Um mögliche Einflüsse dieser Art auf die Ultrastruktur zu verhindern, wurden die Drüsen für die mikroskopische Inspektion in isoosmotischen Lösungen fixiert. Unter diesen Bedingungen lassen sich ausgedehnte Membrankontakte vom nexus-Typ zwischen den Drüsenzellen erkennen. Ihre Ausdehnung scheint ebenso groß zu sein wie die der septate junctions. Es besteht nach diesen Befunden die Möglichkeit, daß wie in anderen kommunizierenden Zellsystemen, so auch in Speicheldrüsen die interzelluläre Kommunikation durch nexus bewirkt wird.
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Supported by financial grants of the Deutsche Forschungsgemeinschaft SFB38.
The authors would like to thank Prof. Dr. H. Leonhardt, Institut für Anatomie I, Homburg, for the use of his electron microscope (Zeiss EM 9-DFG grant LE 69−8) during part of this work and Prof. Dr. H. Kroeger, Institut für Genetik, Saarbrücken for the supply withChironomus larvae.
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Berger, W.K., Uhrík, B. Membrane junctions between salivary gland cells ofChironomus thummi. Z.Zellforsch 127, 116–126 (1972). https://doi.org/10.1007/BF00582761
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DOI: https://doi.org/10.1007/BF00582761