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: In vitro perfusion of bepridil in the life - support medium for isolated sino - atrial tissue from rabbit heart , caused a reduction in action potential ( AP ) spike frequency ( recorded by KCl microelectrodes ) starting at doses of 5 X 10 ( - 6 ) M .
### Output Text:
In vitro perfusion of <span class="chemical">bepridil</span> in the life - support medium for isolated sino - atrial tissue from rabbit heart , caused a reduction in action potential ( AP ) spike frequency ( recorded by <span class="chemical">KCl</span> microelectrodes ) starting at doses of 5 X 10 ( - 6 ) M . 