DUAL EFFECTS OF OPIOIDS ON TRANSMITTER RELEASE, INTRACELLULAR CALCIUM AND CALCIUM-UPTAKE IN SK-N-SH CELL-LINE

The effect of opiates on KCl-induced neurotransmitter release (preloaded [H-3] norepinephrine), intracellular calcium level (fura 2) and calcium influx (Ca-45(++) uptake) was measured in the human neuroblastoma SK-N-SH. Opiates exerted either inhibition or augmentation of transmitter release, both effects were blocked by naloxone. Similarly, opiates either reduced or potentiated KCl-induced elevation in cytosolic [Ca++], with neighboring cells responding oppositely. The stimulatory effect of opiates on cytosolic calcium was dependent on the presence of extracellular calcium ions. Opiates stimulated calcium uptake by SK-N-SH cells. This stimulation was blocked by naloxone but was not prevented by pretreating the cells with pertusis toxin.