sentence: The potency of TUG-891 , as well as that of the endogenous agonist aLa , was much lower at the endogenous FFAR4 of the colon cancer cell line HT29 with an EC of 4.4 µ M for TUG-891 and 33 µ M for aLa in the Ca release assay with different levels of receptor reserve being a possible underlying cause for this pronounced difference .