Effects of morphine and (D-Ala, Met)-enkephalinamide on 45Ca-uptake to rat brain striatal slices

Effects of morphine and (D-Ala, Met)-enkephalinamide on 45Ca-uptake to rat striatal slices were examined. While morphine didn't give any effect on 45Ca-uptake to striatal slices in normal Krebs-Ringer solution, it inhibited K+ (40 mM)-stimulated 45Ca-uptake to slices. In high K+ medium, 45Ca-uptake was enhanced to 170% and this was reduced to 147 and 137% by 10(-5) and 10(-4) M morphine, respectively. Furthermore, the effect of morphine was antagonized by 10(-5) M naloxone. (D-Ala, Met)-enkephalinamide (10(-4) M) also inhibited K+-stimulated 45Ca-uptake to the slices to the same extent as was observed by morphine. K+-stimulated 45Ca-uptake to striatal slices obtained from chronically morphine administered rat (6 mg/kg, twice/day, 7 days) was not inhibited by morphine.