Cholinergic regulation of epithelial sodium channels in rat alveolar type 2 epithelial cells

Abstract

We and others have shown that epithelial Na ϩ channels (ENaC) in alveolar type 2 (AT2) cells are activated by ␤2 agonists, steroid hormones, elevated oxygen tension, and by dopamine. Although acetylcholine receptors (AChRs) have been previously described in the lung, there are few reports of whether cholinergic agonists alter sodium transport in the alveolar epithelium. Therefore, we investigated how cholinergic receptors regulate ENaC activity in primary cultures of rat AT2 cells using cell-attached patchclamp recordings to assess ENaC activity. We found that the muscarinic agonists, carbachol (CCh) and oxotremorine, activated ENaC in a dose-dependent manner but that nicotine did not. CCh-induced activation of ENaC was blocked by atropine. Western blotting and immunohistochemistry suggested that muscarinic M2 and M3 receptors (mAChRs) but not nicotinic receptors were present in AT2 cells. Endogenous RhoA and GTP-RhoA increased in response to CCh and the increase was reduced by pretreatment with atropine. We showed that Y-27632, an inhibitor of Rho-associated protein kinase (ROCK), abolished endogenous ENaC activity and inhibited the activation of ENaC by CCh. We also showed that ROCK signaling was necessary for ENaC stability in 2F3 cells, a model for AT2 cells. Our results showed that muscarinic agonists activated ENaC in rat AT2 cells through M2 and/or M3 mAChRs probably via a RhoA/ROCK signaling pathway.

Respiratory Complications of Organophosphorus Nerve Agent and Insecticide Poisoning. Implications for Respiratory and Critical Care

“…In the biggest published autopsy case series of 85 patients with OP insecticide poisoning (treated with adequate doses of atropine: 12-24 mg every hour, up to 1 g/24 h), 75% of patients dying within 24 hours (n = 36) showed pulmonary interstitial edema, and 25% showed parenchymal hemorrhage (29). Bronchorrhea results from neuronal and nonneuronal cholinergic stimulation of the mucus glands, cilia, and cells producing periciliary fluid (30,31). Although atropine turns off excess fluid production, it does not increase the removal of fluid from the alveolus via the interstitial space and lymphatics (31).…”

“…Bronchorrhea results from neuronal and nonneuronal cholinergic stimulation of the mucus glands, cilia, and cells producing periciliary fluid (30,31). Although atropine turns off excess fluid production, it does not increase the removal of fluid from the alveolus via the interstitial space and lymphatics (31). Fluid removal therefore limits the rate of improvement in oxygenation after atropine therapy.…”

Preclinical anatomical, molecular, and functional imaging of the lung with multiple modalities

“…With conventional X-ray imaging, the rate of lung fluid clearance in freely breathing-anesthetized mice has been assessed in a model of aspiration pneumonia (62,143). In our studies, animals were X-ray imaged with acquisition periods of 120 s and X-ray density was quantified as an expression of lung fluid volume and normalized to the initial X-ray intensity (Io) as a function of change in lung fluid volume at any given time (I), where I-Io represents the difference in X-ray opacities (for example, before and after fluid clearance).…”

Chronic ethanol exposure alters the lung proteome and leads to mitochondrial dysfunction in alveolar type 2 cells

“…, where F(t) represents the amount of surface fluid in the lung at time t, K is the steady-state or peak amount of lung fluid, and ka is the rate of fluid absorption, the rates of secretion can be determined by dividing the peak fluid volume by the rate of absorption (K/ka) (50). Parameter estimation from curve fitting and statistical evaluations were done with SigmaPlot (San Rafael, CA).…”