CALCIUM INFLUX IS REQUIRED FOR TANNIN-MEDIATED ARACHIDONIC-ACID RELEASE FROM ALVEOLAR MACROPHAGES

The role of Ca2+ was investigated in the response of alveolar macropha ges to cotton tannin, an agent implicated in the lung disease byssinos is in textile mill workers. A physiological concentration of extracell ular Ca2+ was found to be required for tannin-mediated release of radi olabeled arachidonic acid (AA). Flow cytometry using indo 1 indicated that tannin caused a rapid and dose-dependent Ca2+ increase in macroph ages that also required extracellular Ca2+. Ethylene glycol-bis(beta-a minoethyl ether)N,N,N',N'- tetraacetic acid virtually abolished the Ca 2+ influx mediated by tannin but had little effect on intracellular Ca 2+ release induced by thapsigargin, N-formylmethionyl-leucylphenylalan ine, or thimerosal. A mechanism for extracellular Ca2+ influx was demo nstrated by rapid Mn2+ quenching of indo 1 by tannin. Verapamil inhibi ted tannin-mediated Ca2+ influx and AA release, but the effective conc entration was 100 mu M. 1,2-Bis(2-aminophenoxy) ethane-N,N,N',N'-tetra acetic acid chelated all Ca2+ in the cells and effectively abolished t he tannin response. Exposure to tannin was not associated with cytotox icity, as judged by Cr-51 release. The data suggest that tannin induce s Ca2+ influx in alveolar macrophages, which represents an important p rerequisite for a cell-signaling pathway resulting in the accumulation of free AA.