Evidence for receptor-mediated calcium entry and refilling of intracellular calcium stores in FRTL-5 rat thyroid cells.
The aim of the present study was to investigate the relationship between agonist-induced changes in intracellular free Ca2+ ([Ca2+]i) and the refilling of intracellular Ca2+ stores in Fura 2-loaded thyroid FRTL-5 cells. Stimulating the cells with ATP induced a dose-dependent increase in ([Ca2+]i). The ATP-induced increase in [Ca2+]i was dependent on both release of sequestered intracellular Ca2+ as well as influx of extracellular Ca2+. Addition of Ni2+ prior to ATP blunted the component of the ATP-induced increase in [Ca2+]i dependent on influx of Ca2+. In cells stimulated with ATP in a Ca(2+)-free buffer, readdition of Ca2+ induced a rapid increase in [Ca2+]i; this increase was inhibited by Ni2+. In addition, the ATP-induced influx of 45Ca2+ was blocked by Ni2+. Stimulating the cells with noradrenaline (NA) also induced release of sequestered Ca2+ and an influx of extracellular Ca2+. When cells were stimulated first with NA, a subsequent addition of ATP induced a blunted increase in [Ca2+]i. If the action of NA was terminated by addition of prazosin, and ATP was then added, the increase in [Ca2+]i was restored to control levels. Addition of Ni2+ prior to prazosin inhibited the restoration of the ATP response. In the presence of extracellular Mn2+, ATP stimulated quenching of Fura 2 fluorescence. The quenching was probably due to influx of Mn2+, as it was blocked by Ni2+. The results thus suggested that stimulating release of sequestered Ca2+ in FRTL-5 cells was followed by influx of extracellular Ca2+ and rapid refilling of intracellular Ca2+ stores.
Törnquist
K
K
Endocrine Research Laboratory, University of Helsinki, Minerva Foundation Institute for Medical Research, Finland.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D009532:Nickel / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*
D011956:Receptors, Cell Surface; D015759:Ionomycin; D009532:Nickel; D000255:Adenosine Triphosphate; D002118:Calcium