P_2Y‐purinoceptor regulation of surfactant secretion from rat isolated alveolar type II cells is associated with mobilization of intracellular calcium

Abstract

1 The effect of methylene, thio, and imido substituted analogues of adenosine 5'-triphosphate (ATP) on surfactant phospholipid secretion and calcium mobilization in rat isolated alveolar Type II cells was studied. 2 ATP was the most potent secretagogue of adenine nucleotides studied. The rank order of agonist potency for [3H]-phosphatidylcholine secretion was ATP > adenosine 5'-O-(3-thiotriphosphate) (,S-ATP) > P, 'y-imido adenosine 5'-triphosphate (AMPPNP) > P, y-methylene adenosine 5'-triphosphate (f, 7-CH2-ATP) > a, P-methylene adenosine 5'-triphosphate (a, P-CH2-ATP). The respective EC5os were 10-6M, 2 x 10-6M, 2 x 10-M, 5 x 10-5M, and >2.5 x 10-4 M. 3 Exogenous ATP also induced a rapid mobilization ofintracellular calcium monitored by changes in Fura 2 fluorescence. The rank order of agonist potency for calcium mobilization was similar to the rank order ofagonist potency for surfactant secretion: ATP = yS-ATP> AMPPNP> a, P-CH2-ATP. 4 There was no effect of EGTA on ATP-induced calcium mobilization, consistent with the hypothesis that exogenous ATP induces release of calcium from intracellular stores.5 These data are consistent with a P21-purinoceptor regulating surfactant secretion from isolated Type II cells via mobilization of intracellular calcium, since: (a) non-hydrolyzed analogues of ATP are potent secretagogues, (b) P, -y-CH2-ATP was a more potent secretagogue than a, P-CH2-ATP and (c) the rank orders of agonist potency for calcium mobilization and phospholipid secretion were the same.

Calcium mobilization and response recovery following P2‐purinoceptor stimulation of rat isolated alveolar type II cells

“…We found a similar EC50 for intracellular Ca2 + mobilization and surfactant phospholipid secretion. This is consistent with the findings of Rice & Singleton (1987) where the order of potency among methylene, thio and imido substituted ATP analogues was similar for phospholipid release and Ca2+ mobilization in cultured Type II cells. These findings suggest Ca2 + mobilization is associated with ATP-stimulated surfactant phospholipid release.…”

“…IP3 acts on nonmitochondrial stores to release Ca2 + (Dubyak, 1986), and elevation of intracellular Ca2+ is associated with secretion in many cell types including pancreatic islet cells and alveolar Type II cells (Zawalich et al, 1983;Dobbs et al, 1986b). P2-purinoceptor stimulation of Type II alveolar cells leads to an elevation of intracellular Ca2+ in association with surfactant phospholipid release (Rice & Singleton, 1987). Further work with Type II cells demonstrated rapid densensitization of the Ca2'-response upon restimulation with ATP (Dorn & Rice, 1988).…”

Effect of Oxygen Exposure on ATP Content of Rat Bronchoalveolar Lavage

“…Lactate dehydrogenase levels were determined on lavage fluid utilizing previously described methods (5).…”

“…In contrast, Ward and Roberts (9) reported decreased synthesis and secretion of DSPC by lung slices obtained from newborn rabbits exposed to 95% oxygen for 48 h. Thus, hyperoxia causes a significant perturbation of surfactant homeostasis. As ATP is a potent stimulus for surfactant phospholipid secretion in vitro (5,6) and hyperoxia has also been reported to modulate surfactant phospholipid secretion (7,8), we tested whether changes in bronchoalveolar lavage ATP content are associated with hyperoxia-induced changes in DSPC secretion by measuring bronchoalveolar lavage ATP and disaturated phosphatidylcholine content in rats exposed to varying inspired oxygen concentrations.…”

Increases in intracellular calcium via activation of an endogenous P2‐purinoceptor in cultured CHO‐K1 cells

“…In general, the rank order of potency at P2x is x,,-methylene ATP (o,j-MeATP) > P,y-methylene ATP > ATP = ADP > 2-methylthio ATP (2-MeSATP) and at P2Y, 2-MeSATP > ATP = ADP > ax,-MeATP > P,y-methylene ATP. The extracellular effects of ATP and its related agonists have been thoroughly investigated in cultured cell lines (Hallam & Pearson, 1986;Phaneuf et al, 1987;Rice & Singleton, 1987;Ehrlich et al, 1988;Cowen et al, 1990;Kastritsis et al, 1992;Koike et al, 1992;Sato et al, 1992) and current classification suggests the existence of at least three additional subtypes of P2-purinoceptors (see TIPS Receptor Nomenclature supplement, 1993). These include a receptor found primarily on platelets (P2T; Gordon, 1986) and one responsible for permeabilisation of mast cells (P2z; Cockroft & Gomperts, 1980).…”