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: After recovery of blood pressure to control values , the extrusion of Na + from cardiac cells was normalized , as revealed by restoration of the ( Na , K ) - ATPase activity .
### Output Text:
After recovery of blood pressure to control values , the extrusion of <span class="chemical">Na</span> + from cardiac cells was normalized , as revealed by restoration of the ( <span class="chemical">Na</span> , <span class="chemical">K</span> ) - ATPase activity . 