Dopaminergic tone regulates transient potassium current maximal conductance through a translational mechanism requiring D1Rs, cAMP/PKA, Erk and mTOR

Background: Dopamine (DA) can produce divergent effects at different time scales. DA has opposing immediate and long-term effects on the transient potassium current (I-A) within neurons of the pyloric network, in the Panulirus interruptus stomatogastric ganglion. The lateral pyloric neuron (LP) expresses type 1 DA receptors (D1Rs). A 10 min application of 5-100 mu M DA decreases LP I-A by producing a decrease in I-A maximal conductance (G(max)) and a depolarizing shift in I-A voltage dependence through a cAMP-Protein kinase A (PKA) dependent mechanism. Alternatively, a 1 hr application of DA (>= 5 nM) generates a persistent (measured 4 hr after DA washout) increase in I-A G(max) in the same neuron, through a mechanistic target of rapamycin (mTOR) dependent translational mechanism. We examined the dose, time and protein dependencies of the persistent DA effect. Results: We found that disrupting normal modulatory tone decreased LP I-A. Addition of 500 pM-5 nM DA to the saline for 1 hr prevented this decrease, and in the case of a 5 nM DA application, the effect was sustained for > 4 hrs after DA removal. To determine if increased cAMP mediated the persistent effect of 5nM DA, we applied the cAMP analog, 8-bromo-cAMP alone or with rapamycin for 1 hr, followed by wash and TEVC. 8-bromo-cAMP induced an increase in I-A G(max), which was blocked by rapamycin. Next we tested the roles of PKA and guanine exchange factor protein activated by cAMP (ePACs) in the DA-induced persistent change in I-A using the PKA specific antagonist Rp-cAMP and the ePAC specific agonist 8-pCPT-2'-O-Me-cAMP. The PKA antagonist blocked the DA induced increases in LP I-A G(max), whereas the ePAC agonist did not induce an increase in LP I-A G(max). Finally we tested whether extracellular signal regulated kinase (Erk) activity was necessary for the persistent effect by co-application of Erk antagonists PD98059 or U0126 with DA. Erk antagonism blocked the DA induced persistent increase in LP I-A. Conclusions: These data suggest that dopaminergic tone regulates ion channel density in a concentration and time dependent manner. The D1R-PKA axis, along with Erk and mTOR are necessary for the persistent increase in LP I-A induced by high affinity D1Rs.