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: There is also a clinical suggestion that acute L - type Ca ( 2 ) channel blockade can promote AF , consistent with an AF promoting effect of Ca ( 2 + ) channel inhibition .
### Output Text:
There is also a clinical suggestion that acute L - type <span class="chemical">Ca</span> ( 2 ) channel blockade can promote AF , consistent with an AF promoting effect of <span class="chemical">Ca</span> ( 2 + ) channel inhibition . 