adenosine-5--(n-ethylcarboxamide) and Leukemia

Using the ratiometric Ca2+ indicator, indo-1, the antigen-induced increase in intracellular Ca2+ concentration ([Ca2+]i) was measured in individual RBL-2H3 cells which had been passively sensitized with monoclonal antibody to the dintrophenyl (DNP) haptenic group. Antigenic stimulation using DNP-human serum albumin conjugate (DNP-HSA) induced concentration-dependent asynchronous Ca2+ oscillations, or irregular spikes. To achieve a quantitative comparison of the effects of different concentrations of antigen on changes in Ca2+[i, the area under the curve (AUC) of Ca2+ oscillations in each cell was calculated. The dose-response curve of the calculated AUC is consistent with the bell-shaped dose-response curve for antigen-induced mediator release, depolarization and 86Rb(+)-efflux. Ca2+ oscillations induced by antigenic stimulation were abolished by removal of external Ca2+ and the subsequent reintroduction of external Ca2+ caused their resumption. To investigate the role of Ca2+ oscillations in the secretory response, changes in [Ca2+]i induced by concanavalin A (Con-A), A23187, thapsigargin and NECA were also monitored. Con-A mimicked the response induced by antigen, whilst A23187 and thapsigargin induced a large transient non-oscillatory response. NECA, an adenosine receptor agonist, induced only a small transient rise in Ca2+[i without oscillatory behaviour. Since all these stimuli accept NECA-induced degranulation in these cells, it is suggested that, although Ca2+ oscillations are not essential for the initiation of secretion, they probably underlie the in-vivo physiological response of mast cells and basophils to an antigenic challenge. They also seem to enhance the efficacy of the Ca2+ signal.

Topics: Adenosine-5'-(N-ethylcarboxamide); Animals; Antigens; beta-N-Acetylhexosaminidases; Calcimycin; Calcium Signaling; Cell Polarity; Concanavalin A; Dinitrophenols; Dose-Response Relationship, Drug; Ionophores; Leukemia; Membrane Potentials; Radioisotopes; Rats; Receptors, IgE; Rubidium; Serum Albumin; Tumor Cells, Cultured