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: Quinine is known to block voltage - , calcium - and ATP - sensitive K ( + ) - channels while 4 - aminopyridine is known to block voltage - sensitive K ( + ) - channels .
### Output Text:
<span class="chemical">Quinine</span> is known to block voltage - , <span class="chemical">calcium</span> - and <span class="chemical">ATP</span> - sensitive <span class="chemical">K</span> ( + ) - channels while <span class="chemical">4 - aminopyridine</span> is known to block voltage - sensitive <span class="chemical">K</span> ( + ) - channels . 