Nonselective Cation Channels Maintain Alveolar Fluid Clearance After Exposure to Toxins from Respiratory Pathogens Restricted; Files & ToC

Galarza Paez, Lilian (Spring 2022)

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Normal gas exchange in the alveoli is facilitated by a thin fluid layer. This layer is carefully regulated by two ion channels: highly selective cation channels (HSC/ENaC) and nonselective cation channels (NSC). Previous research found that both channels contribute about equally to alveolar fluid clearance (AFC). Since the molecular composition of NSC is a recent discovery, not much is known about NSC’s response to various respiratory pathogens. NSC are composed of an alpha-ENaC subunit and at least one acid-sensing ion channel 1a (ASIC1a) subunit. Our study aims are to understand how NSC contribute to alveolar epithelial permeability and how the lungs respond to toxins from respiratory pathogens. We hypothesize that AFC will be lower in the absence of ASIC1a (ASIC1 KO) when exposed to toxins from respiratory pathogens: Lipopolysaccharide (LPS) from E. coli and Pneumolysin (PLY) from P. pneumoniae. Additionally, we hypothesize that ASIC1 KO animals will have increased baseline alveolar epithelial permeability. All animal protocols were approved by Emory’s IACUC.

We introduced pathogen toxins via intratracheal instillation or intraperitoneal injections to ASIC1 KO (KO) and wildtype (WT) mouse models. We determined AFC through changes in the concentrations of Evans Blue (EB) or Fluorescein isothiocyanate–dextran (FITC-dextran) in instillates. Permeability of capillaries and alveolar epithelium were investigated by looking at dye accumulation in pulmonary tissue. Concentrations were determined using spectrophotometry. Our findings suggest that LPS and PLY inhibit all HSC-related AFC leaving only NSC-associated AFC. The AFC of LPS and PLY treated KO animals is lower than AFC for LPS treated WT animals. Neither HSC nor NSC are fully functioning or contributing to AFC in toxin treated groups. Observations on permeability are preliminary but suggest fluid accumulation in the interstitium for the ASIC1 KO group. 

Collectively, these results suggest that the regulation of the alveolar fluid layer is dependent on the function of NSC especially after exposure to toxins. HSC and NSC appear to contribute to alveolar permeability and pulmonary capillary integrity but more research is needed. Our findings can help guide treatment for alveolar flooding caused by toxins from different respiratory pathogens by elucidating their mechanism of action. 

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