| مستخلص: |
Abstract: Objective: In chronic atrial fibrillation (cAF) the potassium current I K,ACh develops agonist-independent constitutive activity. We hypothesized that abnormal phosphorylation-dependent regulation underlies the constitutive I K,ACh activity. Methods: We used voltage-clamp technique and biochemical assays to study I K,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 μmol/L carbachol)-activated I K,ACh was smaller in pAF and cAF. In pAF the selective I K,ACh blocker tertiapin abolished the muscarinic receptor-activated I K,ACh but excluded agonist-independent constitutive I K,ACh activity. Blockade of type-2A phosphatase and the subsequent shift to increased muscarinic receptor phosphorylation (and inactivation) reduced muscarinic receptor-activated I K,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 I K,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 I K,ACh activity results from abnormal channel phosphorylation by PKC but not by PKG or CaMKII, whereas the additional muscarinic receptor-mediated I K,ACh activation occurs apparently without involvement of these kinases. In cAF, the higher protein level of PKCε but not PKCα, PKCβ1 or PKCδ is likely to contribute to the constitutive I K,ACh activity. Conclusions: The occurrence of constitutive I K,ACh activity in cAF results from abnormal PKC function, whereas the muscarinic receptor-mediated I K,ACh activation does not require the contribution of PKG, PKC or CaMKII. Selective drug targeting of constitutively active I K,ACh channels may be suitable to reduce the ability of AF to become sustained. [Copyright &y& Elsevier] |
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