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Evidence for receptor‐mediated calcium entry and refilling of intracellular calcium stores in FRTL‐5 rat thyroid cells

1992; Wiley; Volume: 150; Issue: 1 Linguagem: Inglês

10.1002/jcp.1041500113

1097-4652

Kid Törnquist,

Protein Kinase Regulation and GTPase Signaling

Abstract The aim of the present study was to investigate the relationship between agonist‐induced changes in intracellular free Ca 2+ ([Ca 2+ ] j ) and the refilling of intracellular Ca 2+ stores in Fura 2–loaded thyroid FRTL‐5 cells. Stimulating the cells with ATP induced a dose‐dependent increase in ([Ca 2+ ] j ). The ATP‐induced increase in [Ca 2+ ] j was dependent on both release of sequestered intracellular Ca 2+ as well as influx of extracellular Ca 2+ . Addition of Ni 2+ prior to ATP blunted the component of the ATP‐induced increase in [Ca 2+ ] j dependent on influx of Ca 2+ . In cells stimulated with ATP in a Ca 2+ ‐free buffer, readdition of Ca 2+ induced a rapid increase in [Ca 2+ ] j ; this increase was inhibited by Ni 2+ . In addition, the ATP‐induced influx of 45 Ca 2+ was blocked by Ni 2+ . Stimulating the cells with noradrenaline (NA) also induced release of sequestered Ca 2+ and an influx of extracellular Ca 2+ . When cells were stimulated first with NA, a subsequent addition of ATP induced a blunted increase in [Ca 2+ ] j . If the action of NA was terminated by addition of prazosin, and ATP was then added, the increase in [Ca 2+ ] j was restored to control levels. Addition of Ni 2+ prior to prazosin inhibited the restoration of the ATP response. In the presence of extracellular Mn 2+ , ATP stimulated quenching of Fura 2 fluorescence. The quenching was probably due to influx of Mn 2+ , as it was blocked by Ni 2+ . The results thus suggested that stimulating release of sequestered Ca 2+ in FRTL‐5 cells was followed by influx of extracellular Ca 2+ and rapid refilling of intracellular Ca 2+ stores.