Schöfl C, Rössig L, Pötter E, von zur Mühlen A, Brabant G
Department of Clinical Endocrinology, Medizinische Hochschule Hannover, Germany.
Biochem Biophys Res Commun. 1995 Aug 24;213(3):928-34. doi: 10.1006/bbrc.1995.2218.
In single human thyrocytes extracellular ATP, ATP-gamma-S, ADP and UTP caused a concentration-dependent biphasic increase in [Ca2+]i. Consistent with a P2u-receptor the rank-order of potency was ATP = UTP > ATP-gamma-S > ADP, and cross-desensitization of the Ca2+ responses occurred between ATP and UTP. The initial transient peak in [Ca2+]i was resistant to extracellular Ca2+ depletion which demonstrates mobilisation of internal Ca2+ by IP3 whose formation was rapidly enhanced by ATP and UTP. By contrast, the sustained plateau phase required influx of external Ca2+. Ca2+ influx occurs most likely through a capacitative Ca2+ entry mechanism, which was shown to exist in these cells by experiments performed with thapsigargin. Thus, low micromolar concentrations of extracellular ATP and UTP activate a common P2u-receptor coupled to the C(a2+)-phosphatidylinositol signalling cascade in human thyrocytes. This indicates that extracellular nucleotides from various sources might play an important role in human thyroid physiology.
