Phagocytosis in Tetrahymena thermophila: naloxone-reversible inhibition by opiates.
1. Nanomolar concentrations of opiates inhibit phagocytosis in the ciliated protozoan Tetrahymena thermophila. 2. Naloxone and naltrexone counteract the effect of the opiate agonists tested. 3. The dose-response curves are U-shaped, with no detectable effect at low or high concentrations. 4. An increase in extracellular calcium and dopamine counteract the inhibition caused by metenkephalin. 5. The recognition mechanism for opiates in Tetrahymena cannot be classified as belonging to any of the mammalian opiate receptor subtypes and is perhaps a primitive receptor.
De Jesus
S
S
Biology Department, University of Puerto Rico, Rio Piedras 00931.
Renaud
F L
FL
D000818:Animals; D009270:Naloxone / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D010587:Phagocytosis / Q000187:drug effects*; D013768:Tetrahymena / Q000187:drug effects* / Q000502:physiology
D009294:Narcotics; D009270:Naloxone