THE CALMODULIN ANTAGONIST W-7 DEPLETES INTRACELLULAR CALCIUM STORES IN FRTL-5 THYROID-CELLS

Incubating Fura 2 loaded thyroid FRTL-5 cells with the calmodulin inhibitor W-7 decreased the ATP-evoked increase in intracellular free calcium. In addition, pretreatment of the cells with W-7 decreased both the thapsigargin-evoked release of sequestered calcium and the entry of extracellular calcium. Studies with 45Ca2+ showed that W-7 decreased the amount of sequestered calcium in the cells. Furthermore, after stimulating with ATP, the ability to sequester calcium was decreased in cells treated with W-7 compared with control cells. The results suggest that calmodulin is necessary for the signal-transduction system in FRTL-5' cells, and may be especially important in maintaining functional intracellular calcium stores in the cells. © 1993 Academic Press, Inc.