DOWN-REGULATION OR LONG-TERM INHIBITION OF PROTEIN-KINASE-C (PKC) REDUCES NORADRENALINE RELEASE EVOKED VIA EITHER PKC-DEPENDENT OR PKC-INDEPENDENT PATHWAYS IN HUMAN SH-SY5Y NEUROBLASTOMA-CELLS

Long-term (8-48 h) treatment of SH-SY5Y neuroblastoma cells with phorb ol-12,13-dibutyrate (PDBu; 100 nM) promotes the downregulation of prot ein kinase C (PKC) subtypes alpha and epsilon and reduces by up to 60% noradrenaline (NA) release evoked via both PKC-dependent (M(3)-muscar inic receptor activation) and PKC-independent (depolarization) pathway s, over similar time courses. A similar effect on release is observed following long-term (16-48 h) incubation with the PKC inhibitor Po 31- 7549 (10 mu M), even after removal of the inhibitor, indicating a mech anism which is not rapidly reversible. Evidence is presented which sug gests that long-term treatment with PDBu does not (1) affect calcium e ntry, (2) modulate levels of proteins important in the secretory mecha nism dr (3) reduce the number of secretory vesicles. Thus, the decreas e in NA release in SH-SY5Y cells following down-regulation of PKC appe ars to be the result of a sustained reduction in PKC activity acting o n a component of the secretory pathway not involved in the regulation of calcium entry or vesicle number. Copyright (C) 1996 Elsevier Scienc e ireland Ltd.