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: Recent data suggest that tricyclic antidepressants inhibit calcium influx in some tissues .
### Output Text:
Recent data suggest that tricyclic antidepressants inhibit <span class="chemical">calcium</span> influx in some tissues . 