INFLUENCES OF COLCHICINE, VINBLASTINE AND CYTOCHALASIN ON THE RELEASE OF 5‐HYDROXYTRYPTAMINE FROM RAT BRAIN SYNAPTOSOMES

Abstract

Abstract— Rat brain synaptosomes preincubated with [ 3 H]5‐HT. were further incubated and the release of [ 3 H]5‐HT from the preparation was studied. The spontaneous release consisted of an initial rapid phase followed by slower release. Incubation with 60 mM‐KCl increased the release while 60 mw‐NaCl did not affect it. The effect of KG was abolished when NaCl was omitted from the medium. The potassium‐induced release was Ca 2+ ‐dependent while that induced by tyramine (10 −5 ‐10 −4 M) and the spontaneous release did not depend on Ca 2+ . Vinblastine (10 −5 –2.5 X 10 −4 M) caused an increase in the spontaneous release and an decrease in the potassium‐induced release, while it completely inhibited the release by tyramine at 2.5 X 10 −4 M. Colchicine (5 X 10 −5 –10 −3 M) and cytochalasin D (10 −5 , 10 −4 M) failed to produce any change in the release. Cytochalasin B (10 −5 , 10 −4 M) increased the spontaneous release and decreased the potassium‐induced release but it did not affect the release by tyramine. Colchicine (10 −3 M). vinblastine (10 −4 M) and cytochalasin B (10 −4 M) did not affect significantly Na + .K + ‐. Mg 2 ‐ and Ca 2+ ‐ATPase activities. These results suggest that none of microtubules. microfilaments and contractile protein participates in the mechanism of [ 3 H]5‐HT release from synaptosomes, in vitro.