Morphine

Standard of acetylfentanyl (hydrochloride), acrylfentanyl (hydrochloride), alfentanil (hydrochloride), butyrylfentanyl, carfentanyl, (±)-cis-3-methylfentanyl (hydrochloride), (±)-cis-3-methylthiofentanyl (hydrochloride), fentanyl (hydrochloride), furanylfentanyl (hydrochloride), α-methylfentanyl (hydrochloride), α-methylthiofentanyl (hydrochloride), β-hydroxyfentanyl (hydrochloride), ortho-fluorofentanyl (hydrochloride), ocfentanyl, para-fluorofentanyl (hydrochloride), remifentanyl (hydrochloride), sufentanyl, 4-ANPP, norfentanyl, butyrylfentanyl carboxy metabolite, despropionylpara-fluorofentanyl, (±)-trans-3-methyl norfentanyl, methoxyacetyl norfentanyl (hydrochloride), valerylfentanyl carboxy metabolite, morphine, methadone, EDDP, 6-MAM, codeine, MT-45, fentanyl-d5 (hydrochloride) and nordentanyl-d5 were purchased from Cayman Chemical (Ann Arbor, MI, USA) in form of methanolic solution at the concentration of 1 mg mL⁻¹. Working solutions were prepared at the concentration of 1 μg mL⁻¹ and stored at −20 °C. Water, methanol, acetonitrile and 2-propanol were obtained from Carlo Erba (Milano, Italia) while sodium carbonate, sodium bicarbonate and ammonium formate were purchased from Sigma-Aldrich (Milwaukee, WI, USA).

The cDNA for the β₂ adrenergic, GLP-1, MOR, NOP, and V₂ vasopressin receptors, and the cDNA for GRK2, was obtained from the cDNA Resource Center (Bloomsburg University, Bloomsburg, PA). In some experiments receptors modified to include the C-terminal tail of the V₂ vasopressin receptor were used. This involved substituting the last C-terminal residues with the last 29 C-terminal residues of the V₂ receptor (Oakley et al., 2000 (link)) (last 72 amino acids of the β₂ adrenoceptor, and the last 29 amino acids of the MOR, NOP and GLP-1 receptors). DAMGO, met-enkephalin, endomorphin-2, morphine, hydromorphone, oxymorphone, fentanyl, buprenorphine, vasopressin, N/OFQ and exendin-4 were all obtained from Cayman Chemical (Ann Arbor, MI). Isoproterenol was from Millipore Sigma.