Background In patients with acute respiratory failure, gas exchange is impaired due to the accumulation of fluid in the lung airspaces. This life-threatening syndrome is treated with mechanical ventilation, which is adjusted to maintain gas exchange, but can be associated with the accumulation of carbon dioxide in the lung. Carbon dioxide (CO2) is a by-product of cellular energy utilization and its elimination is affected via alveolar epithelial cells. Signaling pathways sensitive to changes in CO2 levels were described in plants and neuronal mammalian cells. However, it has not been fully elucidated whether non-neuronal cells sense and respond to CO2. The Na,K-ATPase consumes ~40% of the cellular metabolism to maintain cell homeostasis. Our study examines the effects of increased pCO2 on the epithelial Na,K-ATPase a major contributor to alveolar fluid reabsorption which is a marker of alveolar epithelial function. Principal Findings We found that short-term increases in pCO2 impaired alveolar fluid reabsorption in rats. Also, we provide evidence that non-excitable, alveolar epithelial cells sense and respond to high levels of CO2, independently of extracellular and intracellular pH, by inhibiting Na,K-ATPase function, via activation of PKCζ which phosphorylates the Na,K-ATPase, causing it to endocytose from the plasma membrane into intracellular pools. Conclusions Our data suggest that alveolar epithelial cells, through which CO2 is eliminated in mammals, are highly sensitive to hypercapnia. Elevated CO2 levels impair alveolar epithelial function, independently of pH, which is relevant in patients with lung diseases and altered alveolar gas exchange.
References
[1]
Avery WG, Samet P, Sackner MA (1970) The acidosis of pulmonary edema. Am J Med 48: 320–4.
Amato MB, Barbas CS, Medeiros DM, Magaldi RB, Schettino GP, et al. (1998) Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med 338: 347–54.
[4]
The Acute Respiratory Distress Syndrome Network (2000) Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 342: 1301–8.
[5]
Laffey JG, Kavanagh BP (1999) Carbon dioxide and the critically ill–too little of a good thing? Lancet 354: 1283–6.
[6]
Laffey JG, Honan D, Hopkins N, Hyvelin JM, Boylan JF, et al. (2004) Hypercapnic acidosis attenuates endotoxin-induced acute lung injury. Am J Respir Crit Care Med 169: 46–56.
[7]
Lang JD, Figueroa M, Sanders KD, Aslan M, Liu Y, et al. (2005) Hypercapnia via reduced rate and tidal volume contributes to lipopolysaccharide-induced lung injury. Am J Respir Crit Care Med 171: 147–57.
[8]
Vertrees RA, Nason R, Hold MD, Leeth AM, Schmalstieg FC, et al. (2004) Smoke/burn injury-induced respiratory failure elicits apoptosis in ovine lungs and cultured lung cells, ameliorated with arteriovenous CO2 removal. Chest 125: 1472–82.
[9]
Pfeiffer B, Hachenberg T, Wendt M, Marshall B (2002) Mechanical ventilation with permissive hypercapnia increases intrapulmonary shunt in septic and nonseptic patients with acute respiratory distress syndrome. Crit Care Med 30: 285–9.
[10]
Lang JD Jr., Chumley P, Eiserich JP, Estevez A, Bamberg T, et al. (2000) Hypercapnia induces injury to alveolar epithelial cells via a nitric oxide-dependent pathway. Am J Physiol Lung Cell Mol Physiol 279: L994–1002.
[11]
Cherniack NS, Longobardo GS (1970) Oxygen and carbon dioxide gas stores of the body. Physiol Rev 50: 196–243.
[12]
Hashimoto M, Negi J, Young J, Israelsson M, Schroeder JI, et al. (2006) Arabidopsis HT1 kinase controls stomatal movements in response to CO(2). Nat Cell Biol 8: 391–7.
[13]
Jones WD, Cayirlioglu P, Kadow IG, Vosshall LB (2007) Two chemosensory receptors together mediate carbon dioxide detection in Drosophila. Nature 445: 86–90.
[14]
Hu J, Zhong C, Ding C, Chi Q, Walz A, et al. (2007) Detection of Near-Atmospheric Concentrations of CO2 by an Olfactory Subsystem in the Mouse. Science 317: 953–7.
[15]
Putnam RW, Filosa JA, Ritucci NA (2004) Cellular mechanisms involved in CO(2) and acid signaling in chemosensitive neurons. Am J Physiol Cell Physiol 287: C1493–526.
[16]
Wang X, Wu J, Li L, Chen F, Wang R, et al. (2003) Hypercapnic acidosis activates KATP channels in vascular smooth muscles. Circ Res 92: 1225–32.
[17]
Zhou Y, Zhao J, Bouyer P, Boron WF (2005) Evidence from renal proximal tubules that HCO3- and solute reabsorption are acutely regulated not by pH but by basolateral HCO3- and CO2. Proc Natl Acad Sci U S A 102: 3875–80.
[18]
Rutschman DH, Olivera W, Sznajder JI (1993) Active transport and passive liquid movement in isolated perfused rat lungs. J Appl Physiol 75: 1574–80.
[19]
Saumon G, Basset G (1993) Electrolyte and fluid transport across the mature alveolar epithelium. J Appl Physiol 74: 1–15.
[20]
Dada LA, Sznajder JI (2003) Mechanisms of pulmonary edema clearance during acute hypoxemic respiratory failure: role of the Na,K-ATPase. Crit Care Med 31: S248–52.
[21]
Skou JC (1998) Nobel Lecture. The identification of the sodium pump. Biosci Rep 18: 155–69.
[22]
Comellas AP, Dada LA, Lecuona E, Pesce LM, Chandel NS, et al. (2006) Hypoxia-mediated degradation of Na,K-ATPase via mitochondrial reactive oxygen species and the ubiquitin-conjugating system. Circ Res 98: 1314–22.
[23]
Chen J, Lecuona E, Briva A, Welch LC, Sznajder JI (2007) Carbonic Anhydrase II and Alveolar Fluid Reabsorption During Hypercapnia. 2007-0121OC.
[24]
Mutlu GM, Sznajder JI (2005) Mechanisms of pulmonary edema clearance. Am J Physiol Lung Cell Mol Physiol 289: L685–95.
[25]
Matthay MA, Folkesson HG, Clerici C (2002) Lung epithelial fluid transport and the resolution of pulmonary edema. Physiol Rev 82: 569–600.
[26]
Ware LB, Matthay MA (2000) The acute respiratory distress syndrome. N Engl J Med 342: 1334–49.
[27]
Sibley DR, Benovic JL, Caron MG, Lefkowitz RJ (1987) Regulation of transmembrane signaling by receptor phosphorylation. Cell 48: 913–22.
[28]
Dada LA, Chandel NS, Ridge KM, Pedemonte C, Bertorello AM, et al. (2003) Hypoxia-induced endocytosis of Na,K-ATPase in alveolar epithelial cells is mediated by mitochondrial reactive oxygen species and PKC-zeta. J Clin Invest 111: 1057–64.
[29]
Connors AF Jr., Dawson NV, Thomas C, Harrell FE, Desbiens N Jr., et al. (1996) Outcomes following acute exacerbation of severe chronic obstructive lung disease. The SUPPORT investigators (Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments). Am J Respir Crit Care Med 154: 959–67.
[30]
Kregenow DA, Swenson ER (2002) The lung and carbon dioxide: implications for permissive and therapeutic hypercapnia. Eur Respir J 20: 6–11.
[31]
Ware LB, Matthay MA (2001) Alveolar fluid clearance is impaired in the majority of patients with acute lung injury and the acute respiratory distress syndrome. Am J Respir Crit Care Med 163: 1376–83.
[32]
Efendiev R, Bertorello AM, Pedemonte CH (1999) PKC-beta and PKC-zeta mediate opposing effects on proximal tubule Na+,K+-ATPase activity. FEBS Lett 456: 45–8.
[33]
Feschenko MS, Sweadner KJ (1997) Phosphorylation of Na,K-ATPase by protein kinase C at Ser18 occurs in intact cells but does not result in direct inhibition of ATP hydrolysis. J Biol Chem 272: 17726–33.
[34]
Litvan J, Briva A, Wilson MS, Budinger GR, Sznajder JI, et al. (2006) beta-Adrenergic Receptor Stimulation and Adenoviral Overexpression of Superoxide Dismutase Prevent the Hypoxia-mediated Decrease in Na,K-ATPase and Alveolar Fluid Reabsorption. J Biol Chem 281: 19892–8.
[35]
Dumasius V, Sznajder JI, Azzam ZS, Boja J, Mutlu GM, et al. (2001) beta(2)-adrenergic receptor overexpression increases alveolar fluid clearance and responsiveness to endogenous catecholamines in rats. Circ Res 89: 907–14.
[36]
Ridge KM, Dada L, Lecuona E, Bertorello AM, Katz AI, et al. (2002) Dopamine-induced exocytosis of Na,K-ATPase is dependent on activation of protein kinase C-epsilon and -delta. Mol Biol Cell 13: 1381–9.
[37]
Bertorello AM, Hopfield JF, Aperia A, Greengard P (1990) Inhibition by dopamine of (Na(+)+K+)ATPase activity in neostriatal neurons through D1 and D2 dopamine receptor synergism. Nature 347: 386–8.
[38]
Bradford M (1976) A rapid and sensitive method for the quantitation of microgram quantities of proteins utilizing the principle of protein-dye binding. Anal. Biochem. 72: 248–254.
[39]
Ridge KM, Rutschman DH, Factor P, Katz AI, Bertorello AM, et al. (1997) Differential expression of Na-K-ATPase isoforms in rat alveolar epithelial cells. Am J Physiol 273: L246–55.
[40]
Lecuona E, Dada LA, Sun H, Butti ML, Zhou G, et al. (2006) Na,K-ATPase {alpha}1-subunit dephosphorylation by protein phosphatase 2A is necessary for its recruitment to the plasma membrane. Faseb J 20: 2618–20.
[41]
Garcia A, Cereghini S, Sontag E (2000) Protein phosphatase 2A and phosphatidylinositol 3-kinase regulate the activity of Sp1-responsive promoters. J Biol Chem 275: 9385–9.
[42]
Laemmli UK (1970) Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature 227: 680–5.
[43]
Batlle DC, Godinich M, LaPointe MS, Munoz E, Carone F, et al. (1991) Extracellular Na+ dependency of free cytosolic Ca2+ regulation in aortic vascular smooth muscle cells. Am J Physiol 261: C845–56.
[44]
Ridge KM, Olivera WG, Saldias F, Azzam Z, Horowitz S, et al. (2003) Alveolar type 1 cells express the alpha2 Na,K-ATPase, which contributes to lung liquid clearance. Circ Res 92: 453–60.
[45]
Chibalin AV, Ogimoto G, Pedemonte CH, Pressley TA, Katz AI, et al. (1999) Dopamine-induced endocytosis of Na+,K+-ATPase is initiated by phosphorylation of Ser-18 in the rat alpha subunit and Is responsible for the decreased activity in epithelial cells. J Biol Chem 274: 1920–7.
