Cross-talk between protein kinase A and mitogen-activated protein kinases signalling in the adaptive changes observed during morphine withdrawal in the heart.

Our previous studies have shown that morphine withdrawal induced an increase in the expression of protein kinase (PK) A and mitogen-activated extracellular kinase (MAPK) pathways in the heart during morphine withdrawal. The purpose of the present study was to evaluate the interaction between PKA and extracellular signal-regulated kinase (ERK) signaling pathways mediating the cardiac adaptive changes observed after naloxone administration to morphine-dependent rats. Dependence on morphine was induced by a 7-day subcutaneous implantation of morphine pellets. Morphine withdrawal was precipitated on day 8 by an injection of naloxone (2 mg/kg). ERK1/2 and tyrosine hydroxylase (TH) phosphorylation was determined by quantitative blot immunolabeling using phosphorylation state-specific antibodies. Naloxone-induced morphine withdrawal activates ERK1/2 and phosphorylates TH at Ser31 in the right and left ventricle, with an increase in the mean arterial blood pressure and heart rate. When N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004), a PKA inhibitor, was infused, concomitantly with morphine, it diminished the expression of ERK1/2. In contrast, the infusion of calphostin C (a PKC inhibitor) did not modify the morphine withdrawal-induced activation of ERK1/2. The ability of morphine withdrawal to activate ERK that phosphorylates TH at Ser31 was reduced by HA-1004. The present findings demonstrate that the enhancement of ERK1/2 expression and the phosphorylation state of TH at Ser31 during morphine withdrawal are dependent on PKA and suggest cross-talk between PKA and ERK1/2 transduction pathway mediating morphine withdrawal-induced activation (phosphorylation) of TH.