Mast cell activation involves plasma membrane potential- and thapsigargin-sensitive intracellular calcium pools.
The regulation and role of the intracellular Ca2+ pools were studied in rat peritoneal mast cells. Cytosolic free calcium concentration ([Ca2+]i) was monitored in fura-2 loaded mast cells. In the presence of Ca2+ and K+, compound 48/80 induced a biphasic increase in [Ca2+]i composed of a fast transient phase and an apparent sustained phase. The sustained phase was partially inhibited by the addition of Mn2+. DTPA, a cell-impermeant chelator of Mn2+, reversed this inhibition, suggesting that a quenching of fura-2 fluorescence occurs in the extracellular medium. In the absence of extracellular Ca2+, the transient phase, but not the sustained one, could be preserved, provided that mast cells were depolarized. The transient phase was completely abolished by thapsigargin, a microsomal Ca(2+)-ATPase inhibitor. Maximum histamine release induced by either compound 48/80 or antigen was obtained in the absence of added Ca2+ only when mast cells were depolarized. These histamine releases were inhibited by low doses (< 30 nM) of thapsigargin. Thapsigargin at higher doses induced histamine release which was unaffected by changing the plasma membrane potential, but was completely dependent on extracellular Ca2+, showing that a Ca2+ influx is required for thapsigargin-induced exocytosis. Together, these results suggest that the mobilization of Ca2+ from thapsigargin sensitive-intracellular pools induced by compound 48/80 or antigen is sufficient to trigger histamine release. The modulation of these pools by the plasma membrane potential suggest their localization is close to the plasma membrane.
Kassel
O
O
Inserm U425, Université Louis Pasteur, Illkirch, France.
Amrani
Y
Y
Landry
Y
Y
Bronner
C
C
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects; D016257:Fura-2; D006636:Histamine Release / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D004369:Pentetic Acid / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D019284:Thapsigargin / Q000494:pharmacology*; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D003189:p-Methoxy-N-methylphenethylamine; D008345:Manganese; D019284:Thapsigargin; D004369:Pentetic Acid; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium; D016257:Fura-2