Role of cyclic amp dependent protein kinase in cannabinoid receptor modulation of potassium “A-current” in cultured rat hippocampal neurons

Abstract

Cannabinoid receptor agonists have been previously shown to enhance a potassium A-current (I A) in cultured rat hippocampal neurons. This effect has been further demonstrated to be dependent on G-protein linkage to adenylyl cyclase and levels of intracellular cyclic AMP (cAMP). The present study extends this analysis to the involvement of cAMP-dependent protein kinase (PKA) in this cascade. Specific activators and inhibitors of PKA were shown to have differential effects on the voltage dependence of I A. Specific activators of PKA produced a negative shift in voltage dependence of I A, whereas PKA inhibitors produced a positive shift in I A voltage dependence, the latter similar to that effected by the cannabinoid agonist WIN 55,212-2. Although the negative shift in I A induced by PKA stimulation could be reversed by PKA inhibitors, the positive shift produced by the PKA inhibitors alone was only 50–60% of the cannabinoid-produced shift in I A voltage dependence. This partial effect of PKA inhibition was confirmed by biochemical assays in the same cultured neurons that showed a similar 50–60% decrement in in vitro protein phosphorylation produced by PKA inhibitors. Results are discussed in terms of a diffusible second messenger linkage of the cannabinoid receptor to the A-current channel via the role of protein phosphorylation in modulation of I A.