Effects of intracellular Ca²⁺ on V-ATPase-mediated surfactant secretion.

<p>(A, B) Overnight cultured type II cells were treated with 20 nM Bafilomycin A1 (Baf A1) in the presence or absence of the intracellular Ca²⁺-chelator, BAPTA-AM (50 µM) (Panel A) or the ER Ca²⁺-ATPase inhibitor, thapsigargin (TPG, 100 µM) (Panel B). Surfactant secretion was expressed as a percentage of total cellular [³H] PC secreted into medium. Data shown are means ± SE. *P<0.05 <i>v.s.</i> control; #P<0.05 <i>v.s.</i> Baf A1 (ANOVA/Newman-Keuls Multiple Comparison Tests, n = 3 independent cell preparations for Panel A and n = 4 independent cell preparations for Panel B). (C) Isolated lamellar bodies were loaded with ³⁵Ca²⁺. After treated with 20 nM Baf A1 for 10 min, ⁴⁵Ca retained in lamellar bodies was measured. *P<0.05 <i>v.s.</i> control (n = 4 lamellar body preparations). (D) Type II cells were incubated with 20 nM Baf A1 for 1 hr in Ca²⁺-free or 2 mM Ca²⁺ buffer and surfactant secretion was measured. *P<0.01 <i>v.s.</i> control (n = 3 independent cell preparations).