Functional compartments in rat mast cells for cAMP and calcium on histamine release

The crosstalk between 3', 5'-cyclic adenosine monophosphate (cAMP), intrace llular calcium, and histamine release in rat mast cells using the stimulato ry effect of three different drugs, thapsigargin, sodium fluoride (NaF), an d compound 48/80 were studied. Each of these drugs induces histamine releas e by different mechanisms. The transducting pathways modulating cAMP and in tracellular calcium levels were modified by using, cholera toxin (CTX) whic h ADP-rybosylates Gs-protein, pertussis toxin (PTX) which ADP-rybosylates G i-protein, and okadaic acid (OA) which inhibits phosphatases 1 and 2a. Our results show that CTX increased cAMP levels and inhibited histamine release elicited by thapsigargin and compound 48/80. The inhibitory effect of CTX on histamine release was potentiated by OA in the presence of compound 48/8 0 but was decreased in the presence of thapsigargin. Calcium uptake was sti mulated by NaF and compound 48/80, The previous treatment with OA increased calcium uptake when combined with compound 48/80 but not with NaF. Treatme nt with NaF highly stimulated calcium uptake and cAMP levels only when comb ined with OA and CTX. These results suggest that the modulatory effect of i ntracellular calcium and cAMP on histamine release depend more on the cross talk of the activated signal transducting pathway than on the final level o f calcium or cAMP, further supporting the theory that rat mast cells are di vided into functionally distinct compartments. (C) 2000 Elsevier Science In c. All rights reserved.