Yasuo Oyama, Lumi Chikahisa (#1), Kaori Kanemaru, Mami Nakata, Sachi
Noguchi, Takayuki Nagano, Eisuke Okazaki and Akira Hirata (#2)
Laboratory of Cellular Signalling, Faculty of Integrated Arts and Sciences,
The University of Tokushima, Tokushima 770-8502, Japan
Present address:
(#1) Taiho Pharmaceutical Co., Ltd., Hanno 357-8527, Japan
(#2) Santen Pharmaceutical Co., Ltd., Osaka 533-8651, Japan
Abstract: Effects of FTY720 (2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol
HCI), a novel immunosuppressant, were examined on neurons and thymocytes
respectively dissociated from rat brains and thymus glands using a flow
cytometer to see if FTY720 exerts cytotoxic actions not only on spleen cells
as previously reported but also on the other cells. FTY720 at a concentration
of 10 microM deteriorated almost all of the thymocytes, while it was not
the case for brain neurons. FTY720 increased the intracellular concentration
of Ca2+ ([Ca2+]i) of thymocytes in both
the presence and absence of external Ca2+, although the [Ca2+]i
increased by FTY720 in the presence of external Ca2+ was much
greater than that in the absence of external Ca2+. Thus, FTY720
may increase the membrane permeability of Ca2+ and release Ca2+
from intracellular Ca2+ stores in thymocytes. Furthermore, the
number of thymocytes stained with ethidium, a dye impermeant to intact membranes,
time-dependently increased after drug application. Therefore, FTY720 at
concentrations of 3 - 10 microM non-specifically increases the membrane
permeability of thymocytes, resulting in necrotic cell death, although FTY720
at micromolar concentrations was reported to induce apoptosis of spleen
cells.
Keywords: Brain neuron, Cytotoxic action, Immunosuppressant, Thymocyte,
Flow cytometry