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Pharmacological Characterization of an Opioid Receptor in the Ciliate Tetrahymena
Author(s) -
CHIESA RICARDO,
SILVA WALTER I.,
RENAUD FERNANDO L.
Publication year - 1993
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1993.tb04478.x
Subject(s) - tetrahymena , opioid , opioid receptor , agonist , (+) naloxone , receptor , biology , phagocytosis , pharmacology , morphine , δ opioid receptor , ciliate , competitive antagonist , microbiology and biotechnology , biochemistry , ecology
A pharmacological characterization has been performed of the opioid receptor involved in modulation of phagocytosis in the protozoan ciliate Tetrahymena. Studies on inhibition of phagocytosis by mammalian prototypic opioid agonists revealed that morphine and β‐endorphin have the highest intrinsic activity, whereas all the other opioids tested can only be considered partial agonists. However, morphine (a mu‐receptor agonist) is twice as potent as β‐endorphin (a delta‐receptor agonist). Furthermore, the sensitivity for the opioid antagonist naloxone, determined in the presence of morphine and β‐endorphin, is very similar to the sensitivity exhibited by mammalian tissues rich in mu‐opioid receptors. We suggest that the opioid receptor coupled to phagocytosis in Tetrahymena is mulike in some of its pharmacological characteristics and may serve as a model system for studies on opioid receptor function and evolution.