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: Epithelial sodium channel ( ENaC ) subunit mRNA and protein expression in rats with puromycin aminonucleoside - induced nephrotic syndrome .
### Output Text:
Epithelial <span class="chemical">sodium</span> channel ( ENaC ) subunit mRNA and protein expression in rats with <span class="chemical">puromycin aminonucleoside</span> - induced nephrotic syndrome . 