CORRELATING CA2-2H3 MUCOSAL MAST-CELLS( RESPONSES AND SECRETION IN INDIVIDUAL RBL)

The role of Ca2+ in stimulus-response coupling in nonexcitable cells i s still not well understood. The Ca2+ responses of individual cells ar e extremely diverse, often displaying marked oscillations, and almost nothing is known about the specific features of these Ca2+ signals tha t are important for the functional response of a cell. Using the RBL-2 H3 mucosal mast cell as a model, we have studied the temporal relation ship between changes in intracellular Ca2+ and serotonin secretion at the single-cell level using simultaneous indo-1 photometry and constan t potential amperometry. Secretion in response to antigen never occurs until intracellular Ca2+ is elevated, nor is it seen during the first few oscillations in Ca2+, Exocytotic events tend to be clustered arou nd the peaks of oscillations, but excellent secretion is also seen in cells with sustained elevations in Ca2+. Ca2+ release from stores in t he absence of influx fails to elicit secretion, If refilling and conti nued release of Ca2+ from stores is prevented with thapsigargin, Ca2influx can still trigger secretion, suggesting that store-associated m icrodomains of Ca2+ are not required for exocytosis. Our findings demo nstrate the importance of an amplitude-encoded Ca2+ signal and Ca2+ in flux for stimulus-secretion coupling in these nonexcitable cells.