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Journal of Cell Science, Vol 90, 167-171, Copyright © 1988 by Company of Biologists

Submitted on January 26, 1988
Accepted on February 15, 1988

Release of lysosomal enzymes in Tetrahymena: a Ca2+-dependent secretory process

A. TIEDTKE 1, L. RASMUSSEN 2, J. FLORIN-CHRISTENSEN 3, and M. FLORIN-CHRISTENSEN 4

1 Zoological Institute, University of Münster Schlo{beta}platz 5, D-4400 Münster, FRG
2 Institute of Anatomy and Cytology, University of Odense Campusvej 55, DK 5230 Odense M, Denmark
3 Center for Parasite and Vector Research, National University of La Plata Calle 2, No. 584, 1900 La Plata, Argentina
4 Center for Parasite and Vector Research, National University of La Plata, Calle 2, No. 584, 1900 La Plata, Argentina

The ciliate Tetrahymena thermophila releases lysosomal enzymes into nutrient and starvation media. We show here that this process occurs selectively, i.e. without leakage of cytoplasmic components, as indicated by lack of release of isocitrate dehydrogenase, a cytosolic enzyme with high activity in Tetrahymena. The role of intracellular Ca2+ in the process was also investigated. The Ca2+ ionophore A23187 has strong stimulatory effects on this release. Ionophore stimulation is maximal in the presence of extracellular Ca2+ but can occur also in its absence. Quin 2 fluorescence measurements indicate that intracellular Ca2+ increases in both cases. Mg2+ completely prevents the stimulatory effects of A23187. Ionomycin, another Ca2+ ionophore, also stimulates lysosomal enzyme release with a maximal response in the presence of extracellular Ca2+. Measurements of extracellular isocitrate dehydrogenase showed that ionophore-stimulated lysosomal enzyme release can take place without leakage of cytoplasmic components. The observations that divalent cation ionophores stimulate selective lysosomal enzyme release and that this effect is strongest in the presence of external Ca2+ indicate that this cation plays a crucial role in the control of this process in Tetrahymena. Together with other observations they support the view that a subpopulation of Tetrahymena lysosomes has properties like those of secretory vesicles.

Key words: lysosomal enzymes, secretion, Tetrahymena thermophila

Submitted on January 26, 1988
Accepted on February 15, 1988






© The Company of Biologists Ltd 1988