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: This study addressed the potential role of calcium channel blockade in tricyclic antidepressant - induced hypotension .
### Output Text:
This study addressed the potential role of <span class="chemical">calcium</span> channel blockade in tricyclic antidepressant - induced hypotension . 