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: During activation with Na + , the Vmax remained unchanged , however the K ( Na ) increased by 50 % , indicating a profound decrease in the affinity of the Na + - binding site in NO - deficient rats .
### Output Text:
During activation with <span class="chemical">Na</span> + , the Vmax remained unchanged , however the <span class="chemical">K</span> ( <span class="chemical">Na</span> ) increased by 50 % , indicating a profound decrease in the affinity of the <span class="chemical">Na</span> + - binding site in <span class="chemical">NO</span> - deficient rats . 