Opioids suppress basal and nicotine-induced catecholamine secretion via a stabilizing effect on actin filaments

Catecholamine secretion and actin filament disassembly are closely coupled in chromaffin cells. Opioid suppression of catecholamine secretion is fast and transient, both characteristics of actin filament involvement. The aim of the present work was to test the hypothesis that opioids suppress catecholamine secretion via an inhibitory effect on actin filament disassembly. For this purpose we used the PC12 rat pheochromocytoma cell line. Norepinephrine and dopamine were measured by enzyme-linked immunosorbent assay or RIA. Polymerized actin was measured by rhodamine-phalloidin and visualized by confocal laser scanning microscopy. Opioids suppressed basal catecholamine secretion. The onset of this effect was fast and transient, peaking at 2 min, and was reversible by opioid antagonists. Synchronously, opioids suppressed actin filament disassembly; this was also reversible by opioid antagonists. Cytochalasin B prevented the inhibitory effect of opioids on catecholamine secretion. In addition, opioids suppressed the stimulatory effect of nicotine on catecholamine secretion and actin depolymerization. Changes in actin cytoskeleton in neuron-like PC12 cells make them resistant to both effects of opioids, i.e. on catecholamine secretion and actin disassembly. In conclusion, our data suggest that the suppressive effect of opioids on basal and nicotine-induced catecholamine secretion may result from an opioid-provoked stabilization of cortical actin. It also appears that basal catecholamine secretion is associated with opioid-sensitive machinery regulating the continuous formation of short-lived areas of cortical actin filament disassembly.