NICARDIPINE ENHANCES CYTOPLASMIC CALCIUM-CONCENTRATION IN MOUSE THYMOCYTES IN-VITRO

AIM: To study the effect of nicardipine (Nic) on the cytoplasmic free calcium concentration ([Ca2+](i)) in thymocytes and on the proliferati on of thymus lymphocytes from mice in vitro. METHODS: The [Ca2+](i) wa s measured by loading cells with the fluorescent dye Fura-2. The lymph ocyte proliferation was determined by [H-3]thymidine incorporation. RE SULTS: Nic 1 - 30 mu mol . L(-1) elevated [Ca2+](i) of resting thymocy tes with the percentages of its increase 43 % - 192 % and 12 % - 148 % in the presence and absence of extracellular Ca2+ respectively. Mitog en Con A 5 mg . L(-1) also released Ca2+ from intracellular stores. Ni c decreased the enhancement of [Ca2+](i) induced by Con A. The IC50 (m u mol . L(-1)) was 26. 8 (95 % limit: 24. 8 - 29. 0) and approximated to 10 in the presence and absence of extracellular Ca2+ respectively. Nic 1 - 30 mu mol . L(-1) did not stimulate the proliferation of resti ng lymphocytes from mouse thymuses (P>0.05), but inhibited the prolife ration when the lymphocytes had been stimulated by Con A (P<0.01). CON CLUSION: Nic elevated [Ca2+](i), which decreased the response of lymph ocytes to mitogen.