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: Immunoblotting and immunohistochemistry revealed decreased expression of Na ( + ) / K ( + ) - ATPase , NHE3 , NBC1 , and AQP1 in the kidney of gentamicin - treated rats .
### Output Text:
Immunoblotting and immunohistochemistry revealed decreased expression of <span class="chemical">Na</span> ( + ) / <span class="chemical">K</span> ( + ) - ATPase , NHE3 , NBC1 , and AQP1 in the kidney of <span class="chemical">gentamicin</span> - treated rats . 