ml138ML138 (CID 44601470) is a hhly selective agonist at kappa opioid receptors (KOR) that potently activate G protein coupling but weakly interact with β arrestin2.To record a 12-lead ECG with an FE238 Octal Bio amp or ML138 Octal Bio amp the following items are required in addition to the LabChart software, PowerLab, and amplifier:. MLAC29