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[Effects of long-term morphine exposure on the cAMP system and c-Fos phosphorylation in differentiated SH-SY5Y cells].

OBJECTIVE
To further understand the effects of long-term morphine exposure on the cAMP system and c-Fos phosphorylation in differentiated SH-SY5Y human neuroblastoma cells.


METHODS
Cellular changes of cAMP, PKA and c-Fos were detected by protein competitive conjunction, enzyme activity and isotope incorporation methods respectively.


RESULTS
(1) Long-term exposure (2 min-36 h) to morphine (100 mumol/L) could induce the biphasic changes in cAMP contents. Treament for 2 min to 1 h, morphine caused rapid and siginificant decrease of the cAMP level and then gradully recovered and apparently increased at 36 h. At that time, naloxone added to the incubation media caused an overshoot of cellular cAMP; (2) Long-term exposure to morphine could also induce the biphasic changes in cytosolic PKA activity. This is consistent with the changes of cAMP during the chronic treatment of cells with morphine. But no changes were observed in membrane PKA activity; (3) In morphine dependent-like cells decreased c-Fos phosphorylation level was observed. PKA inhibitor could significantly inhibit this change; (4) Concomitant administration of naloxone could block the changes in PKA activity and c-Fos phosphorylation described above.


CONCLUSIONS
The up-regulation of cAMP system in differentiated SH-SY5Y cells may be involved in the development of morphine dependent and in morphine dependent-like SH-SY5Y cells and PKA was suggested to regulate c-Fos dephosphorylation through activating phosphatase and then activate some genes transcription, which might be one of the important mechanism regardingas cellular adaptive responses underlying dependence to opioid drugs.