In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Immunoelectron microscopy further revealed an increased labeling of alpha - ENaC in the apical plasma membrane of cortical collecting duct principal cells of PAN - treated rats , indicating enhanced apical targeting of alpha - ENaC subunits .
### Output Text:
Immunoelectron microscopy further revealed an increased labeling of alpha - ENaC in the apical plasma membrane of cortical collecting duct principal cells of <span class="chemical">PAN</span> - treated rats , indicating enhanced apical targeting of alpha - ENaC subunits . 