EFFECTS OF PURINE NUCLEOTIDES AND NUCLEOSIDE ON CYTOSOLIC CALCIUM LEVELS IN RAT TRACHEAL SMOOTH-MUSCLE CELLS

Extracellular adenosine triphosphate (ATP) has a range of effects on a wide variety of cells through the activation of specific purinoceptor s. The aim of this study was to establish whether P-2 purinoceptors ar e present on airway smooth muscle cells, Experiments were conducted on cultured rat tracheal smooth-muscle cells (first through third passag e). Intracellular Ca2+ ([Ca2+](i)) was measured using Fura-2 and dual- excitation wavelength microfluorometry. The effects of ATP adenosine d iphosphate (ADP), uridine triphosphate (UTP), and adenosine (ADO) were measured in concentrations from 10(-6) to 10(-3) M. At a concentratio n of 10(-4) M, the peak [Ca2+](i) was 502 +/- 92 nM for ATP and 543 +/ - 76 nM for UTP (mean +/- standard error of the mean). ADO had no sign ificant effect on Ca2+ release. Peak [Ca2+](i) induced by ATP was not dependent on extracellular Ca! but was blocked by U-73122, an inhibito r of phospholipase C. Pretreatment with adenosine deaminase and desens itization with alpha beta-MeATP had no effect on ATP-induced Ca2+ rele ase. The effects of ATP (10(-4) M) on peak [Ca2+](i) were potentiated by the presence of ADO 10(-5) M (969 +/- 257 nM; P < 0.05). The presen ce of XAC, a blocker of A(1) and A(2) ADO receptors did not prevent th is effect. In the presence of XAC, ADO 10(-6) M potentiated the effect s of ATP (peak [Ca2+](i): 1,300 +/- 229 nM). The addition of 1433U83, a blocker of A(3) ADO receptors, blocked the synergistic effect of ADO 10(-6) M on ATP. These data show that P-2 purinoceptors, most likely of the P-2U subtype, are present on airway smooth muscle cells and tha t the newly discovered A(3) ADO receptor appears to be also present.