Abstract
The pharmacological properties of the recently described antagonist for capacitative Cat+ entry LU 52396 were investigated and compared to known Ca 2+ antagonists in Jurkat T-lymphocytes. In the first set of experiments, cells were stimulated with the anti-CD3 monoclonal antibody OKT3 and, subsequently, Cat+ antagonists were added. Under such conditions SK-F 96365, econazole, nitrendipine and ZnCl 2 dose-dependently antagonized Ca 2+ signaling, whereas LU 52396 in concentrations up to 100 μM did not. In contrast, when LU 52396 was added a few minutes before OKT3, a dose-dependent inhibition of the OKT3-stimulated Cat+ signals by LU 52396 was observed. Likewise, by prior addition of LU 52396 to thapsigargin-stimulated Jurkat T cells, a dose-dependent inhibition of Ca 2+ signals was achieved. The IC 50 value of LU 52396 for both agonists was about 5 μM. LU 52396 also inhibited Jurkat T cell proliferation, but showed cytotoxic effects at concentrations > 50 μ M. Our data indicate that, in contrast to the other Ca 2+ antagonists SK-F 96365, econazole, nitrendipine and ZnCI 2, LU 52396 recognized the channel for capacitative Ca 2+ entry only when intracellular Ca 2+ was low and the channel was in its closed state.
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