Nicotinic receptors on rat alveolar macrophages dampen ATP- induced increase in cytosolic calcium concentration

Background: Nicotinic acetylcholine receptors (nAChR) have been identified on a variety of cells of the immune system and are generally considered to trigger anti-inflammatory events. In the present study, we determine the nAChR inventory of rat alveolar macrophages (AM), and investigate the cellular events evoked by stimulation with nicotine. Methods: Rat AM were isolated freshly by bronchoalveolar lavage. The expression of nAChR subunits was analyzed by RT-PCR, immunohistochemistry, and Western blotting. To evaluate function of nAChR subunits, electrophysiological recordings and measurements of intracellular calcium concentration ([Ca2+](i)) were conducted. Results: Positive RT-PCR results were obtained for nAChR subunits alpha 3, alpha 5, alpha 9, alpha 10, beta 1, and beta 2, with most stable expression being noted for subunits alpha 9, alpha 10, beta 1, and beta 2. Notably, mRNA coding for subunit alpha 7 which is proposed to convey the nicotinic anti-inflammatory response of macrophages from other sources than the lung was not detected. RT-PCR data were supported by immunohistochemistry on AM isolated by lavage, as well as in lung tissue sections and by Western blotting. Neither whole-cell patch clamp recordings nor measurements of [Ca2+](i) revealed changes in membrane current in response to ACh and in [Ca2+](i) in response to nicotine, respectively. However, nicotine (100 mu M), given 2 min prior to ATP, significantly reduced the ATP-induced rise in [Ca2+](i) by 30%. This effect was blocked by a-bungarotoxin and did not depend on the presence of extracellular calcium. Conclusions: Rat AM are equipped with modulatory nAChR with properties distinct from ionotropic nAChR mediating synaptic transmission in the nervous system. Their stimulation with nicotine dampens ATP-induced Ca2+-release from intracellular stores. Thus, the present study identifies the first acute receptor-mediated nicotinic effect on AM with anti-inflammatory potential.