Antigen and carbachol mobilize calcium by similar mechanisms in a transfected mast cell line (RBL-2H3 cells) that expresses ml muscarinic receptors.
Because of unresolved questions about the mechanism of Ag-stimulated Ca2+ influx, Ca2+ mobilization in response to carbachol and Ag was compared in transfected rat basophilic RBL-2H3(ml) cells that expressed both Fc epsilon and ml muscarinic receptors. Although the stimulants activated phospholipase C via different coupling mechanisms, a G protein for carbachol or a tyrosine kinase for Ag, they released Ca2+ from the same intracellular pool and used the same or very similar mechanisms for influx of Ca2+ as indicated by the similar patterns of inhibition of uptake of 45Ca2+ by various cations. With both stimulants, influx and sustained increases in free cytosolic Ca2+ ([Ca2+]i) were associated with relatively small increases in inositol 1,4,5-trisphosphate (IP3). Blockade of Ca2+ influx resulted in rapid decline in [Ca2+]i to basal levels; resumption of influx caused a substantial "spike" in [Ca2+]i before [Ca2+]i reequilibrated at the same former steady-state levels but without perturbing levels of IP3. Thus, the refilling and discharge of Ca2+ from IP3-sensitive stores might occur synchronously on resumption of influx, or asynchronously during sustained influx and elevation of [Ca2+]i. Together, the results suggested that influx of Ca2+ in response to stimulation via Fc epsilon receptors occurred through a pathway, analogous to that observed with other types of stimulants, in which Ca2+ influx follows emptying of intracellular Ca2+ stores by IP3. Also, secretion was highly dependent on this IP3-dependent pathway.
Choi
O H
OH
Laboratory of Chemical Pharmacology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
Lee
J H
JH
Kassessinoff
T
T
Cunha-Melo
J R
JR
Jones
S V
SV
Beaven
M A
MA
D000818:Animals; D000941:Antigens / Q000276:immunology*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017455:Receptors, IgE / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology*; D014162:Transfection
D000941:Antigens; D017455:Receptors, IgE; D011976:Receptors, Muscarinic; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D002118:Calcium