RESUMO
The pharmacological properties of the recently described antagonist for capacitative Ca2+ entry LU 52396 were investigated and compared to known Ca2+ antagonists in Jurkat T-lymphocytes. In the first set of experiments, cells were stimulated with the anti-CD3 monoclonal antibody OKT3 and, subsequently, Ca2+ antagonists were added. Under such conditions SK-F 96365, econazole, nitrendipine and ZnCl2 dose-dependently antagonized Ca2+ signaling, whereas LU 52396 in concentrations up to 100 microM did not. In contrast, when LU 52396 was added a few minutes before OKT3, a dose-dependent inhibition of the OKT3-stimulated Ca2+ signals by LU 52396 was observed. Likewise, by prior addition of LU 52396 to thapsigargin-stimulated Jurkat T cells, a dose-dependent inhibition of Ca2+ signals was achieved. The IC50 value of LU 52396 for both agonists was about 5 microM. LU 52396 also inhibited Jurkat T cell proliferation, but showed cytotoxic effects at concentrations > 50 microM. Our data indicate that, in contrast to the other Ca2+ antagonists SK-F 96365, econazole, nitrendipine and ZnCl2, LU 52396 recognized the channel for capacitative Ca2+ entry only when intracellular Ca2+ was low and the channel was in its closed state.
