Chronic atrial fibrillation is associated with constitutive IK,ACh activity resulting from abnormal PKC function, whereas muscarinic receptor-mediated activation does not require PKC.
Observational (n=105)
What are the phosphorylation-dependent mechanisms underlying constitutive IK,ACh channel activity in chronic atrial fibrillation?
Constitutive IK,ACh channel activity in chronic atrial fibrillation is driven by abnormal PKC-dependent phosphorylation, suggesting constitutively active IK,ACh channels as potential therapeutic targets for sustained AF.
OBJECTIVE: In chronic atrial fibrillation (cAF) the potassium current IK,ACh develops agonist-independent constitutive activity. We hypothesized that abnormal phosphorylation-dependent regulation underlies the constitutive IK,ACh activity. METHODS: We used voltage-clamp technique and biochemical assays to study IK,ACh regulation in atrial appendages from 61 sinus rhythm (SR), 11 paroxysmal AF (pAF), and 33 cAF patients. RESULTS: Compared to SR basal current was higher in cAF only, whereas the muscarinic receptor (2 micromol/L carbachol)-activated IK,ACh was smaller in pAF and cAF. In pAF the selective IK,ACh blocker tertiapin abolished the muscarinic receptor-activated IK,ACh but excluded agonist-independent constitutive IK,ACh activity. Blockade of type-2A phosphatase and the subsequent shift to increased muscarinic receptor phosphorylation (and inactivation) reduced muscarinic receptor-activated IK,ACh in SR but not in cAF, pointing to an impaired function of G-protein-coupled receptor kinase. Using subtype-selective kinase inhibitors we found that in SR the muscarinic receptor-activated IK,ACh requires phosphorylation by protein kinase G (PKG), protein kinase C (PKC), and calmodulin-dependent protein kinase II (CaMKII), but not by protein kinase A (PKA). In cAF, constitutive IK,ACh activity results from abnormal channel phosphorylation by PKC but not by PKG or CaMKII, whereas the additional muscarinic receptor-mediated IK,ACh activation occurs apparently without involvement of these kinases. In cAF, the higher protein level of PKCepsilon but not PKCalpha, PKCbeta1 or PKCdelta is likely to contribute to the constitutive IK,ACh activity. CONCLUSIONS: The occurrence of constitutive IK,ACh activity in cAF results from abnormal PKC function, whereas the muscarinic receptor-mediated IK,ACh activation does not require the contribution of PKG, PKC or CaMKII. Selective drug targeting of constitutively active IK,ACh channels may be suitable to reduce the ability of AF to become sustained.
Voigt et al. (Tue,) conducted a observational in Chronic atrial fibrillation (n=105). Chronic atrial fibrillation vs. Sinus rhythm was evaluated on IK,ACh channel constitutive activity and regulation. Chronic atrial fibrillation is associated with constitutive IK,ACh activity resulting from abnormal PKC function, whereas muscarinic receptor-mediated activation does not require PKC.
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