Ref ID : 1201
Robert K. Peck and Francoise Duborgel; Effects of cations on phagocytosis in the ciliate Pseudomicrothorax dubius. J.Protozool. 32(3):501-508, 1985
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Various cations have been examined for their effects on phagocytosis. Media with high [Ca2+] and low [K+] favor phagocytosis, which is inhibited in media with high [K+], [Rb+], or [Ba2+] and low [Ca2+]. Microscopical observations of inhibited cells demonstrate that swimming behavior is not modified but they cannot perform the initial step of phagocytosis, attachment to food: when Ca2+ is added, cells attach to and ingest food, demonstrating rapid reversal of inhibition. Attachment is shown to be a linear function of the ratio [K+]/[Ca2+]1/2 or [Rb+]/[Ca2+]1/2 in the medium. The Ca2+ influx inhibitor Verpamil blocks attachment, as does La3+; the latter is believed to compete with Ca2+ for access to the Ca2+ channel. Likewise, treatment of cells with media containing no added Ca2+ inhibits attachment, and addition of 10 uM Ca2+ allows 90% of these cells to attach to and ingest food. The ionphore A23187, known to transport Ca2+ into a wide variety of cells, provokes lysosomal streaming movements typical of attachment. Based upon these observations, Ca2+ influx plays an essential role in attachment; K+ efflux also appears to be necessary since tetraethylammonium chloride blocks attachment. Treatment of cells with Tetrodotoxin, an inhibitor of Na+ transport, or suspending them in media containing no added Na+ does not affect attachment or ingestion, indicating that Na+ is not implicated in these processes. An hypothesis is presented which implicates Ca2+ in both direct adhesion and exocytosis phenomena during attachment.