EFFECTS OF ARACHIDONIC ACID ON BINDING PROPERTIES OF OPIOID RECEPTORS

APAYDIN, Serpil

M.S.in Biochemistry
Supervisor: Assoc. Prof. Dr. Huseyin Avni Oktem
September, 1997, 62 pages

In this study, effect of arachidonic acid (AA) and lysophosphatidic acid (LPA) on [3H]Naloxone specific binding to rat brain membrane opioid receptors was investigated. This effect was characterized with respect to receptor binding parameters (KD and Bmax) and receptor type (m and d). Computer analysis of homolog displacement data revealed that, AA caused a decrease in the Bmax values of receptor binding at 1.5 mmol/mg protein. Under similar conditions KD values are not affected. Furthermore, it was observed that antagonist configuration of opioid receptors were more susceptible to AA inhibition. By blockage experiments, inhibitory effect of AA was studied individually at m and d sites. AA, inhibited opioid receptor binding in a dose-dependent manner, with IC50's of 1.5 and 1.8 mmol/mg protein in the presence and in the absence of Na+, respectively. IC50 values of AA at m site were 1.6 and 1.9 mmol/mg protein in the presence and absence of Na+, while at d site this value was below 0.5 mmol/mg protein in both case, indicating a more effective blockage at d site. In our experimental system, LPA at physiological concentration (100-400 nM) was observed to be capable of modulating opioid receptor binding. LPA at 100 nM concentration stimulated while 200 and 400 nM concentrations inhibited receptor binding by 37 and 52%, respectively. Our data suggest a possible antagonistic cross talking mechanism between opioid and LPA signal transduction system.

Keywords: Rat brain membrane, Opioid receptors, Naloxone, AA, LPA