Calcium influx is required for tannin-mediated arachidonic acid release from alveolar macrophages.
The role of Ca2+ was investigated in the response of alveolar macrophages to cotton tannin, an agent implicated in the lung disease byssinosis in textile mill workers. A physiological concentration of extracellular Ca2+ was found to be required for tannin-mediated release of radiolabeled arachidonic acid (AA). Flow cytometry using indo 1 indicated that tannin caused a rapid and dose-dependent Ca2+ increase in macrophages that also required extracellular Ca2+. Ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid virtually abolished the Ca2+ influx mediated by tannin but had little effect on intracellular Ca2+ release induced by thapsigargin, N-formylmethionyl-leucylphenylalanine, or thimerosal. A mechanism for extracellular Ca2+ influx was demonstrated by rapid Mn2+ quenching of indo 1 by tannin. Verapamil inhibited tannin-mediated Ca2+ influx and AA release, but the effective concentration was 100 microM. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid chelated all Ca2+ in the cells and effectively abolished the tannin response. Exposure to tannin was not associated with cytotoxicity, as judged by 51Cr release. The data suggest that tannin induces Ca2+ influx in alveolar macrophages, which represents an important prerequisite for a cell-signaling pathway resulting in the accumulation of free AA.
Thoracic Diseases Research Unit, Mayo Clinic and Foundation, Rochester, Minnesota 55905.
P J
PJ
Bates
N V
NV
Ralston
Z
Z
Vuk-Pavlović
M S
MS
Rohrbach
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002857:Chromium / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D047348:Hydrolyzable Tannins / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D009994:Osmolar Concentration; D011817:Rabbits
D002121:Calcium Channel Blockers; D047348:Hydrolyzable Tannins; D002857:Chromium; D016718:Arachidonic Acid; D008345:Manganese; D002118:Calcium