Microdomains of high calcium are not required for exocytosis in RBL-2H3 mucosal mast cells.
We have previously shown that store-associated microdomains of high Ca(2+) are not essential for exocytosis in RBL-2H3 mucosal mast cells. We have now examined whether Ca(2+) microdomains near the plasma membrane are required, by comparing the secretory responses seen when Ca(2+) influx was elicited by two very different mechanisms. In the first, antigen was used to activate the Ca(2+) release-activated Ca(2+) (CRAC) current (I(CRAC)) through CRAC channels. In the second, a Ca(2+) ionophore was used to transport Ca(2+) randomly across the plasma membrane. Since store depletion by Ca(2+) ionophore will also activate I(CRAC), different means of inhibiting I(CRAC) before ionophore addition were used. Ca(2+) 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 Ca(2+) occurs diffusely via the Ca(2+) ionophore, and at an average intracellular Ca(2)+ concentration that is no greater than that observed when Ca(2+) entry via CRAC channels triggers secretion. Our results suggest that microdomains of high Ca(2+) near the plasma membrane, or associated with mitochondria or Ca(2+) stores, are not required for secretion. Therefore, we conclude that modest global increases in intracellular Ca(2+) are sufficient for exocytosis in these nonexcitable cells.
Mahmoud
S F
SF
Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA.
Fewtrell
C
C
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D000941:Antigens / Q000276:immunology / Q000378:metabolism; D000968:Antimycin A / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000502:physiology*; D007093:Imidazoles / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology*; D007811:Lanthanum / Q000378:metabolism; D008407:Mast Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D009092:Mucous Membrane / Q000166:cytology / Q000502:physiology; D009840:Oligomycins / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000935:Antifungal Agents; D000941:Antigens; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007476:Ionophores; D009840:Oligomycins; D012701:Serotonin; D000001:Calcimycin; C048335:oligomycin B; D000968:Antimycin A; D019284:Thapsigargin; D007811:Lanthanum; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D011188:Potassium; D002118:Calcium