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: Western blot analysis revealed that AQP2 expression in medullary tissues was lowered after 3 and 5 days in WT mice ; however , AQP2 was unchanged in PKCa KO .
### Output Text:
Western blot analysis revealed that AQP2 expression in medullary tissues was lowered after 3 and 5 days in WT mice ; however , AQP2 was unchanged in PKCa KO . 