(-)-STEPHOLIDINE ENHANCES K-INDUCED ACTIVATION OF SYNAPTOSOMAL TYROSINE 3-MONOOXYGENASE FROM RAT STRIATUM( DEPOLARIZATION)

AIM: To study the mechanism of K+ depolarization-induced activation of synaptosomal tyrosine 3-monooxygenase (TM) the effect of (-)-stepholi dine (SPD) on this activation. METHODS: The TM was assayed for DOPA by HPLC-ECD; the activities of Ca2+/calmodulin (CaM)-dependent protein k inase (PK II) and Ca2+/phosphoinositide-dependent protein. kinase (PKC ) were assayed using histidine as substrate, RESULTS: The incubation o f striatal synaptosomes in K+-riched (60 mmol . L(-1)) medium resulted in a marked activation of TM, PKC inhibitor polymyxin B (PMB) complet ely blocked the activation of K+ 60 mmol . L(-1) on TM, Selective D-2 receptor agonist quinpirole (QP), Ca2+ removal from incubation medium and CaM antagonist W7 failed to affect the activation, However, SPD en hanced the activation of K+ 60 mmol . L(-1) on TM, Meanwhile, the incu bation in K+ 60 mmol . L(-1) also activated PKC, Neither QP nor SPD af fected K+ depolarization-induced activation of PKC, CONCLUSION: The ac tivation of K+ depolarization on synaptosomal TM is enhanced by SPD an d this activation is mediated by PKC rather than by PK II.