Carbon Monoxide Rapidly Impairs Alveolar Fluid Clearance by Inhibiting Epithelial Sodium Channels

Abstract

Carbon monoxide (CO) is currently being evaluated as a therapeutic modality in the treatment of patients with acute lung injury and acute respiratory distress syndrome. No study has assessed the effects of CO on transepithelial ion transport and alveolar fluid reabsorption, two key aspects of alveolocapillary barrier function that are perturbed in acute lung injury/acute respiratory distress syndrome. Both CO gas (250 ppm) and CO donated by the CO donor, CO-releasing molecule (CORM)-3 (100 microM in epithelial lining fluid), applied to healthy, isolated, ventilated, and perfused rabbit lungs, significantly blocked (22)Na(+) clearance from the alveolar compartment, and blocked alveolar fluid reabsorption after fluid challenge. Apical application of two CO donors, CORM-3 or CORM-A1 (100 microM), irreversibly inhibited amiloride-sensitive short-circuit currents in H441 human bronchiolar epithelial cells and primary rat alveolar type II cells by up to 40%. Using a nystatin permabilization approach, the CO effect was localized to amiloride-sensitive channels on the apical surface. This effect was abolished by hemoglobin, a scavenger of CO, and was not observed when inactive forms of CO donors were employed. The effects of CO were not blocked by 8-bromoguanosine-3',5'-cyclic guanosine monophosphate, soluble guanylate cyclase inhibitors (methylene blue and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), or inhibitors of trafficking events (phalloidin oleate, MG-132, and brefeldin A), but the amiloride affinity of H441 cells was reduced after CO exposure. These data indicate that CO rapidly inhibits sodium absorption across the airway epithelium by cyclic guanosine monophosphate- and trafficking-independent mechanisms, which may rely on critical histidine residues in amiloride-sensitive channels or associated regulatory proteins on the apical surface of lung epithelial cells.

Carbon Monoxide (CO) Is a Novel Inhibitor of Connexin Hemichannels

“…Application of 100 M CORM-2 once the currents stabilized caused inhibition of Cx46 HCs (Fig. 1A) with a time constant () of 29 s. This concentration of CORM-2 has been previously used in studies on other ion channels (27)(28)(29)(30). To study the voltage dependence of the CORM-2 inhibition, oocytes were exposed to 100 M CORM-2 for 3 min (to ensure a maximal effect) and HC currents were recorded using a protocol wherein oocytes were held at Ϫ60 mV and then exposed for 15 s to voltages ranging from Ϫ60 to ϩ60 mV in 10 mV steps.…”

“…Because Cx46 is a phosphoprotein, an involvement of guanylyl cyclase and PKG in the effect of CORM-2 is possible. However, pre-incubation for 45 min with 2 M KT5823 (a specific PKG inhibitor) or 50 M ODQ (1H- [1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one, a specific guanylyl cyclase inhibitor) (27,28) did not affect the current inhibition induced by 100 M CORM-2 (Fig. 5A).…”

Regulation of Colonic Ion Transport by Gasotransmitters

“…35) Another interaction known with ion channels is the cGMP-independent inhibition of Na ϩ channels in alveolar epithelium, which may be caused by a modification of histidine residues in the ion channels (or regulators of them) as concluded from experiments with diethyl pyrocarbonate, a histidine-modifying agent. 38) In the gut wall, enteric neurones, the key players in the regulation of intestinal functions, express the enzymes for CO production such as heme oxygenase II. 39,40) Both heme oxygenase I and heme oxygenase II are expressed in the rat colon as observed immunohistochemically and by reverse transcription-polymerase chain reaction (RT-PCR).…”

Heme oxygenase-1 promotes migration and β-epithelial Na+ channel expression in cytotrophoblasts and ischemic placentas

“…While there is limited evidence in the literature related to the role of HO-1 in regulating ␤-ENaC expression, a recent study by Wang et al (28) found that heme (the substrate for HO) inhibits, while carbon monoxide (HO metabolite) stimulates, ENaC activity in renal epithelial cells. However, another study demonstrated that CO has the capacity to inhibit amiloride-sensitive channels in airway epithelial cells (3). These studies do not specify the ENaC subunit affected by the treatments; therefore, it is still unclear whether HO-1 has the capacity to increase expression and activity of all the ENaC subunits.…”