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Published online 16 April 2001. doi:10.1083/jcb.153.2.339
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© The Rockefeller University Press, 0021-9525/2001//339 $5.00
The Journal of Cell Biology, Volume 153, Number 2, , 2001 339-350

Original Article

Microdomains of High Calcium Are Not Required for Exocytosis in Rbl-2h3 Mucosal Mast Cells



Sahar F. Mahmouda and Clare Fewtrella

a Department of Molecular Medicine, Cornell University, Ithaca, New York 14853
Department of Molecular Medicine, Cornell University, C3-125 VMC, Ithaca, NY 14853.(607) 253-3659(607) 253-3870

cmf3{at}cornell.edu

We have previously shown that store-associated microdomains of high Ca2+ are not essential for exocytosis in RBL-2H3 mucosal mast cells. We have now examined whether Ca2+ microdomains near the plasma membrane are required, by comparing the secretory responses seen when Ca2+ influx was elicited by two very different mechanisms. In the first, antigen was used to activate the Ca2+ release–activated Ca2+ (CRAC) current (ICRAC) through CRAC channels. In the second, a Ca2+ ionophore was used to transport Ca2+ randomly across the plasma membrane. Since store depletion by Ca2+ ionophore will also activate ICRAC, different means of inhibiting ICRAC before ionophore addition were used. Ca2+ responses and secretion in individual cells were compared using simultaneous indo-1 microfluorometry and constant potential amperometry. Secretion still takes place when the increase in intracellular Ca2+ occurs diffusely via the Ca2+ ionophore, and at an average intracellular Ca2+ concentration that is no greater than that observed when Ca2+ entry via CRAC channels triggers secretion. Our results suggest that microdomains of high Ca2+ near the plasma membrane, or associated with mitochondria or Ca2+ stores, are not required for secretion. Therefore, we conclude that modest global increases in intracellular Ca2+ are sufficient for exocytosis in these nonexcitable cells.

Key Words: exocytosis • calcium signaling • mast cells • indo-1 • serotonin

© 2001 The Rockefeller University Press

Sahar Mahmoud's current address is Department of Neurobiology and Behavior, Cornell University, W 149 Mudd Hall, Ithaca, NY 14853.

Abbreviations used in this paper: [Ca2+]i, intracellular free ionized calcium concentration; CRAC, calcium release–activated Ca2+; ICRAC, Ca2+ release–activated Ca2+ current.


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