Endomorphin 2

There are some indications that biased μ-opioid ligands may diversely affect μ-opioid receptor (MOR) properties. Here, we used confocal fluorescence recovery after photobleaching (FRAP) to study the regulation by different MOR agonists of receptor movement within the plasma membrane of HEK293 cells stably expressing a functional yellow fluorescent protein (YFP)-tagged μ-opioid receptor (MOR-YFP). We found that the lateral mobility of MOR-YFP was increased by (D-Ala;2;,N-MePhe;4;,Gly;5;-ol)-enkephalin (DAMGO) and to a lesser extent also by morphine but decreased by endomorphin-2. Interestingly, cholesterol depletion strongly enhanced the ability of morphine to elevate receptor mobility but significantly reduced or even eliminated the effect of DAMGO and endomorphin-2, respectively. Moreover, the ability of DAMGO and endomorphin-2 to influence MOR-YFP movement was diminished by pertussis toxin treatment. The results obtained by agonist-stimulated [;35;S]GTPγS binding assays indicated that DAMGO exhibited higher efficacy than morphine and endomorphin-2 did and that the efficacy of DAMGO, contrary to the latter agonists, was enhanced by cholesterol depletion. Overall, our study provides clear evidence that biased MOR agonists diversely affect receptor mobility in plasma membranes as well as MOR/G protein coupling and that the regulatory effect of different ligands depends on the membrane cholesterol content.

Two highly selective mu-opioid receptor agonists, endomorphin-1 and endomorphin-2, have been identified and postulated to be endogenous ligands for mu-opioid receptors. Intrathecal (i.t.) administration of endomorphin-1 and endomorphin-2 at doses from 0.039 to 5 nmol dose-dependently produced antinociception with the paw-withdrawal test. The paw-withdrawal inhibition rapidly reached its peak at 1 min, rapidly declined and returned to the pre-injection levels in 20 min. The inhibition of the paw-withdrawal responses to endomorphin-1 and endomorphin-2 at a dose of 5 nmol observed at 1 and 5 min after injection was blocked by pretreatment with a non-selective opioid receptor antagonist naloxone (1 mg/kg, s.c.). The antinociceptive effect of endomorphin-2 was more sensitive to the mu (1)-opioid receptor antagonist, naloxonazine than that of endomorphin-1. The endomorphin-2-induced paw-withdrawal inhibition at both 1 and 5 min after injection was blocked by pretreatment with kappa-opioid receptor antagonist nor-binaltorphimine (10 mg/kg, s.c.) or the delta(2)-opioid receptor antagonist naltriben (0.6 mg/kg, s.c.) but not the delta(1)-opioid receptor antagonist 7-benzylidine naltrexone (BNTX) (0.

The endomorphin-1 (EM1) and endomorphin-2 (EM2) are endogenous opioid peptides, which modulate extensive bioactivities such as pain, cardiovascular responses, immunological responses and so on. The present study was undertaken to investigate the effects of EM1/EM2 on the primary cultured human umbilical vein endothelial cells (HUVECs) damaged by high glucose. PI AnnexinV-FITC detection was performed to evaluate the apoptosis rate. Levels of nitric oxide (NO) and nitric oxide synthase (NOS) activity were measured by the Griess reaction and the conversion of 3H-arginine to 3H-citrulline, respectively. Endothelin-1 (ET-1) was evaluated by the enzyme-linked immunosorbent assay (ELISA). Cell proliferation was determined by the MTT viability assay. mRNA expression of endothelial nitric oxide synthase (eNOS) and ET-1 were measured by real-time PCR. Our data showed that EM1/EM2 inhibited cell apoptosis. The high glucose induced increase in expression of NO, NOS and ET-1 were significantly attenuated by pretreatment with EM1/EM2 in a dose dependent manner. In addition, EM1/EM2 suppressed the mRNA eNOS and mRNA ET-1 expression in HUVECs under high glucose conditions. Naloxone, the nonselective opioid receptor antagonist, did not influence the mRNA eNOS expression when it was administrated on its own; but it could significantly antagonize the effects induced by EM1/EM2.