EXTRACELLULAR NUCLEOTIDES INCREASE CYTOSOLIC-FREE CALCIUM BY ACTIVATING P-2U-RECEPTORS IN SINGLE HUMAN GASTRIC MUCOUS CELLS

In single human gastric mucous cells extracellular ATP, ATP-gamma-S, A DP and UTP at micromolar concentrations caused a biphasic increase in [Ca2+](i). Consistent with a P-2u-receptor the rank-order of potency w as ATP greater than or equal to UTP > ATP-gamma-S > ADP, and cross-des ensitization of the Ca2+ responses occurred between ATP and UTP. The i nitial transient peak in [Ca2+](i) was resistent to extracellular Ca2 depletion which demonstrates mobilization of internal Ca2+, By contra st, 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 wit h thapsigargin. Thus, extracellular ATP and UTP activate a common P-2u -receptor most likely coupled to the Ca2+-phosphatidylinositol signall ing cascade. Extracellular nucleotides from various sources might be a n important factor in the regulation of human gastric mucous cells. (C ) 1995 Academic Press, Inc.