INHIBITORY-ACTION OF FATTY-ACIDS ON CALCIUM FLUXES IN THYROID FRTL-5 CELLS

In the present study, we wanted to investigate the action of fatty aci ds on agonist-evoked changes in intracellular free calcium ([Ca2+](i)) in thyroid FRTL-5 cells. Stimulating Fura 2 loaded cells with long ch ain unsaturated fatty acids increased [Ca2+](i) in a dose-dependent ma nner. This increase was in part dependent on extracellular calcium. Lo ng chain saturated fatty acids and short chain fatty acids had no effe cts on [Ca2+](i) per se. Pretreatment of the cells with long chain uns aturated fatty acids almost totally inhibited both the ATP- and thapsi gargin-evoked release of sequestered calcium and the entry of extracel lular calcium. Long chain saturated fatty acids also attenuated the AT P-evoked increase in [Ca2+](i), while short chain fatty acids had no e ffects on the ATP-evoked change in [Ca2+](i). The inhibitory effect of long chain unsaturated fatty acids on agonist-evoked changes in [Ca2](i) was not dependent on activation of protein kinase C, and was not due to an enhanced efflux of calcium. These fatty acids rapidly acidif ied the cytosol in the cells, which could, in part, explain the inhibi tory effect of the long chain unsaturated fatty acids on agonist-evoke d changes in [Ca2+](i). Addition of bovine serum albumin to the cells rapidly reversed the inhibitory effect of the fatty acids on [Ca2+](i) , and restored pH(i). Thus, fatty acids could be potential modulators of calcium signaling in FRTL-5 cells, possibly by modulating calcium e ntry at the level of the plasma membrane.