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

Abstract

1 The effect of adenosine 5'-triphosphate (ATP) on surfactant phospholipid secretion, calcium mobilization, and the time course for recovery of the response system was studied in isolated alveolar Type II cells of the rat. 2 ATP (10 M) stimulated a biphasic intracellular Ca2+ transient monitored by changes in Fura-2 fluorescence, from a basal level of 126 ± 9nm, to a rapid peak of 391 + nm, followed by a prolonged plateau 26 + 4nM above baseline (mean ± s.e.mean, n = 26).3 ATP-stimulated surfactant phospholipid secretion and peak Ca2+ levels had similar EC50 s(1 x 10-6M), and were unaffected by chelation of extracellular Ca2". However, the prolonged plateau phase was abolished by chelation of extracellular Ca2 . 4 There was a 15min refractory period before full recovery of the Ca2+-response to ATP. Recovery was dependent on extracellular Ca2 , was accelerated by removing extracellular agonist and was prolonged following stimulation with the poorly hydrolyzed ATP analogue, ATP-y-S. 5 While the Type II cell was capable of multiple ATP-induced Ca2 + transients following recovery, no additional surfactant phospholipid was released with sequential stimulation. 6 These findings suggest initial exposure of Type II cells to ATP mobilizes intracellular Ca2+, stimulates phospholipid secretion and rapidly desensitizes the cell to further stimulation by ATP. Recovery of the ATP-induced Ca2+-response depends on presence of extracellular Ca2 + and removal of agonist.

The effects of Bay K 8644 and nifedipine on the responses of rat urinary bladder to electrical field stimulation, β,γ‐methylene ATP and acetylcholine

“…In the dog mesenteric artery, nifedipine can selectively inhibit the purinergic component of the contractions evoked by sympathetic nerve stimulation (Omote et al, 1989), and in snail neurones nanomolar concentrations of extracellular ATP can activate membrane calcium channels (Yatani et al, 1982). Also, P2-purinoceptor-mediated calcium mobilization across the cell membrane has been observed in rat isolated alveolar type II cells (Dorn et al, 1989), murine thymocytes (El-Moatassim et al, 1989), human promyelocyteic cell line HL60 (Nonotte et al, 1989), Ehrlich ascites tumour cells (Dubyak & De Young, 1985), pancreatic i-cells (Gylfe & Hellman, 1987) and rat parotid acinar cells (McMillian et al, 1987).…”

“…It has been observed that ATP can affect the ionic permeability of the plasma membrane of many cell types (Kolb & Wakelam, 1983;Marchenko et al, 1987;Inoue, 1990). Among the ions, calcium may be of importance in mediating the action of ATP (Yatani et al, 1982;Dorn et al, 1989;Nonotte et al, 1989), and in guinea-pig and rat urinary bladder the contractions induced by ATP have been demonstrated to be dependent on extracellular calcium (Iacovou et al, 1988;Bhat et al, 1989). Nifedipine, a 1,4-dihydropyridine, blocks calcium channels and can preferentially inhibit the non-cholinergic component of motor transmission in rat urinary bladder (Iravani et al, 1988).…”

A Fluorescent Microplate Assay for Exocytosis in Alveolar Type II Cells

“…[18][19][20][21][22] Substantial direct and indirect evidence indicates that Ca 2+ is a major 2nd messenger to trigger intracellular fusion events and to integrate a number of different stimuli into a common cellular response. [23][24][25][26][27][28][29][30][31] In addition, more recent data indicate that the postfusion phase is an important determinant of the secretory time scale. 4 This is evidenced by the fact that surfactant phospholipids accumulate in cell supernatants for much longer periods than compared to the rapid rundown of LB-PM fusion events within the cells.…”

Sharing signals: connecting lung epithelial cells with gap junction channels

“…The existence of calcium-regulated pathways for surfactant secretion stems from a large body of pharmacological evidence obtained from primary type II cells in culture. Increases in intracellular calcium increase surfactant secretion either by a direct effect on the secretory machinery (70,75,109,117,242,316) or through a protein kinase C-dependent pathway (44,108,224,229,286), or both. Stimulation of surfactant secretion by endothelin-1 also shows both a calcium-and protein kinase C-dependent component (244).…”