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: Dose - dependent bradycardia induced by verapamil was potentiated by LNa , LCa , and HCa .
### Output Text:
Dose - dependent bradycardia induced by <span class="chemical">verapamil</span> was potentiated by LNa , LCa , and HCa . 