EFFECTS OF EXTRACELLULAR ATP ON CYTOSOLIC CA2-CELLS( CONCENTRATION AND SECRETORY RESPONSES IN RAT PAROTID ACINAR)

At concentrations > 50 mu M, extracellular ATP dose-dependently increa sed cytosolic Ca2+ concentration ([Ca2+](i)) via activation of P-2Z pu rinoceptors in rat parotid acinar cells. This increase in [Ca2+](i) is primarily due to entry of Ca2+ from the extracellular medium. Inosito l trisphosphate formation and Ca2+ release from intracellular Ca2+ sto res were slightly stimulated by ATP. These responses seem to result fr om the activation of a P-2 purinoceptor subtype different from P-2Z be cause the maximum responses were induced by much lower concentrations (< 0.25 mM) of ATP than those (> 1 mM) required to produce the maximum activation of Ca2+ entry. ATP did not stimulate amylase release, supp orting the view that an increase in [Ca2+](i) is not a sufficient stim ulus. In addition, ATP evoked a marked K+ release in the presence and absence of extracellular Ca2+, while in carbachol-stimulated cells, on ly a transient release of K+ was observed in the absence of extracellu lar Ca2+. The ATP-induced K+ release may be mediated by a mechanism in dependent of the opening of the Ca2+-sensitive K+ channels. (C) 1997 E lsevier Science Ltd.