Inhibition of Ca²⁺ influx by surfactant in NR8383 alveolar macrophages

Abstract.

Objective:

Pulmonary surfactants reduce alveolar surface tension and alter inflammatory cell function. We studied the effects of surfactant preparations on Ca²⁺ influx regulated by protein kinase C (PKC) and mitogen-activated protein kinases (MAPK) and cytokine secretion in the alveolar macrophage (AM) cell line NR8383.

Methods:

Fura-2-loaded AMs were stimulated with zymosan (200 μg/ml), 1,2-dioctanoyl-sn-glycerol (DOG, 20 μM) or C₆-ceramide (C₆C, 10 μM) in the presence of exogenous surfactants (beractant, calfactant or colfosceril) or surfactant phospholipid (dipalmitoyl phosphatidylcholine, DPPC), at 250 μg/ml phospholipid and changes in cytosolic free Ca ²⁺ (Δ[Ca²⁺]_i) and cytokines were measured.

Results:

Zymosan-induced Δ[Ca²⁺]_i (117 ± 5 nM) at 3 min was reduced (p <0.001) by beractant (50 ± 6 nM), colfosceril (61 ± 2 nM), calfactant (46 ± 5 nM), and DPPC (52 ± 5 nM). Beractant inhibited the Δ[Ca²⁺]_i by PKC stimulation with DOG and all preparations reduced the MAPK-induced Ca²⁺ influx by C₆C. Beractant and Ca²⁺ channel blocker SKF 96365 (10 μM) together abolished the zymosan-stimulated Δ[Ca²⁺]_i. Zymosan-stimulated TNF-α and IL-1β secretion was also inhibited by surfactant pretreatment.

Conclusions:

These results indicate that exogenous surfactant inhibits Ca²⁺ influx and cytokine secretion in zymosan-stimulated AMs. This anti-inflammatory activity may be through an interaction with downstream signaling elements or Ca²⁺ channels.