Characterization and localization of P2 receptors in rat submandibular gland acinar and duct cells

[Ca2+](i) and the Cl- current were measured in isolated submandibular gland acinar and duct cells to characterize and localize the purinergic receptors expressed in these cells. In both cell types 2'-3'-benzoylbenzoyl (Bz)-ATP and ATP increased [Ca2+](i) mainly by activation of Ca2+ influx, UTP had only minimal effect on [Ca2+](i) at concentrations between 0.1 and 1 mM. However, a whole cell current recording showed that all nucleotides effectively activated Cl- currents. Inhibition of signal transduction through G proteins by guanyl-5'-beta-thiophosphate revealed that the effect of ATP on Cl- current was mediated in part by activation of a G protein-coupled and in part by a G protein-independent receptor. BzATP activated exclusively the G protein-independent portion, whereas UTP activated only the G protein-dependent portion of the Cl- current, Measurement of [Ca2+](i) in the microperfused duct showed that ATP stimulated a [Ca2+](i) increase when applied to the luminal or the basolateral sides. BzATP increased [Ca2+](i) only when applied to the luminal side, whereas UTP at 100 mu M increased [Ca2+](i) only when applied to the basolateral side. The combined results suggest that duct and possibly acinar cells express P(2)z receptors in the luminal and P(2)u receptors in the basolateral membrane.