EPIXENOSOMES, PECULIAR EPIBIONTS OF THE CILIATE EUPLOTIDIUM-ITOI - INVOLVEMENT OF MEMBRANE-RECEPTORS AND THE ADENYLATE CYCLASE-CYCLIC-AMP SYSTEM IN THE EJECTING PROCESS

The extrusive apparatus is the most prominent and complex structure of epixenosomes. In the present paper the mechanisms activating its ejec ting process were investigated by means of in vivo treatments and cyto chemical procedures at the ultrastructural level. The results obtained clearly demonstrated that the ejecting process in epixenosomes is tri ggered by the detection of external signals through membrane receptors and the consequent activation of the adenylate cyclase-cyclic AMP sys tem as a transduction mechanism. The membrane receptors coming into pl ay have an affinity for soybean agglutinin and have a precise localiza tion at the top of the organism, just where a membrane interruption ap pears as a first step in the whole process. The factors that trigger e jection in nature are still unknown. In the laboratory, ejection was o btained in the presence of adrenalin, which has been proved to bind to the same receptors shown to have affinity for soybean agglutinin. So epixenosomes appear to possess specific binding molecules for a mammal ian hormone in the appropriate location, i.e., in the plasma membrane, and this hormone induces a precise biological response. These results are particularly interesting if we consider that epixenosomes are eni gmatic organisms in which prokaryotic and eukaryotic characteristics a ppear to coexist.