Characterization of platelet-activating factor-induced cytosolic calcium mobilization in human eosinophils.
BACKGROUND
Activated eosinophils play an important role in the pathogenesis of bronchial asthma and other allergic diseases, and platelet-activating factor (PAF) is a potent activator of eosinophils.


OBJECTIVE
To characterize the cytosolic Ca2+ ([Ca2+]i) mobilization in human eosinophils in response to PAF.


METHODS
[Ca2+]i responses to PAF were examined in human eosinophils using a microscopic fura-2 fluorescence-ratio imaging system.


RESULTS
PAF caused a significant and dose-dependent increase in (Ca2+)i, which consisted of an initial rapid rise followed by a sustained elevation. This PAF-induced (Ca2+)i rise was inhibited by WEB 2086, a specific PAF receptor antagonist. The addition of 5 mM EGTA or 1 mM Ni2+ to a nominally Ca2+-free solution did not appreciably reduce the initial rise but significantly inhibited the sustained rise. The application of a protein kinase C inhibitor, Ro31-8220, augmented the sustained increase by PAF. Thapsigargin, a microsomal Ca2+ ATPase inhibitor, induced no appreciable change in a nominally Ca2+-free solution but induced a marked increase in (Ca2+)i when changed to a Ca2+-containing solution.


CONCLUSIONS
The initial rapid rise and the following sustained rise in (Ca2+)i by PAF depends on Ca2+ release from the intracellular Ca2+ stores and Ca2+ influx, respectively, which are regulated by protein kinase C in human eosinophils. Furthermore, the so called Ca2+-capacitative entry is possibly involved in the Ca2+ influx from the extracellular solution in human eosinophils.
Oshiro
T
T
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai 980-8574, Japan.
Kakuta
Y
Y
Shimura
S
S
Nara
M
M
Shirato
K
K
D020013:Calcium Signaling / Q000187:drug effects / Q000276:immunology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004533:Egtazic Acid; D004804:Eosinophils / Q000187:drug effects / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D010972:Platelet Activating Factor / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology
D010972:Platelet Activating Factor; D004533:Egtazic Acid; D019284:Thapsigargin; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases