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: The loss of beta2 resulted in negative shifts in the voltage dependence of inactivation as well as significant decreases in sodium current density in acutely dissociated hippocampal neurons .
### Output Text:
The loss of beta2 resulted in negative shifts in the voltage dependence of inactivation as well as significant decreases in <span class="chemical">sodium</span> current density in acutely dissociated hippocampal neurons . 