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However , many if not all connexin isoforms also form functional hemichannels ( i . e . , the precursors of complete channels ) that mediate the rapid exchange of ions , second messengers and metabolites between the cell interior and the interstitial space .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None