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: It is also suggested that the blockade of K ( + ) - channels sensitive to these blockers is not sufficient to prevent morphine - induced hypoactivity whereas morphine - induced hyperactivity seems to be connected to both quinine - and 4 - aminopyridine - sensitive K ( + ) - channels .
### Output Text:
It is also suggested that the blockade of <span class="chemical">K</span> ( + ) - channels sensitive to these blockers is not sufficient to prevent <span class="chemical">morphine</span> - induced hypoactivity whereas <span class="chemical">morphine</span> - induced hyperactivity seems to be connected to both <span class="chemical">quinine</span> - and <span class="chemical">4 - aminopyridine</span> - sensitive <span class="chemical">K</span> ( + ) - channels . 