G-Protein β ₃ -Subunit 825T Allele Is Associated With Enhanced Human Atrial Inward Rectifier Potassium Currents

Abstract

We found an association between the Gbeta(3) 825T allele and amplitude of human atrial I(K1) and I(K,ACh). Increased background current density in TT carriers could shorten action potential duration and may be due to I(K,ACh) being constitutively active in this genotype.

Molecular Basis of Downregulation of G-Protein–Coupled Inward Rectifying K + Current ( I K,ACh ) in Chronic Human Atrial Fibrillation

“…4 and TWIK1), 15 we selected Kir2.1 because its abundance is suggested to be responsible for Ͼ80% of I K1 . 16 Because the changes in I K,ACh density in human chronic AF seem to be similar to those detected in association with the C825T polymorphism of the gene encoding for the G-protein ␤3 subunit, 17 we genotyped our patients to investigate whether chronic AF and the homozygous 825T allele gene variant are independent contributors to K ϩ current density. Finally, to examine the functional aspects of the observed current changes in chronic AF, we recorded APs in both single myocytes and trabeculae after pharmacological stimulation of I K,ACh with the muscarinic receptor agonist carbachol.…”

“…Atrial myocytes were isolated using our previous protocol 17 and were suspended in a storage solution consisting of (in mmol/L): KCl 20, KH 2 PO 4 10, glucose 10, K-glutamate 70, ␤-hydroxybutyrate 10, taurine 10, EGTA 10, and albumin 1 (pHϭ7.4). Cell yield of well-striated, rod-shaped myocytes was 17.5Ϯ1.6% (nϭ41).…”

“…The presented data were not corrected for the calculated liquid junction potential (Ϫ12 mV, software JPCalc). 17 The membrane currents were corrected for a linear leak conductance calculated from the reversal potential of I K,ACh . 17 Atrial APs were recorded in human right atrial myocytes with patch-electrodes (tip resistance 6 to 8 M⍀) filled with the following solution (in mmol/L): K-aspartate 100, NaCl 8, KCl 40, Mg-ATP 5, EGTA 5, CaCl 2 2, GTP-Tris 0.1, and HEPES 10 (pHϭ7.4); the bath solution contained (in mmol/L): NaCl 150, KCl 5.4, and MgCl 2 2 (otherwise as above).…”

Defective Cardiac Ryanodine Receptor Regulation During Atrial Fibrillation

“…13 As in ventricular RyR2, the atrial RyR2 macromolecular complex is composed of calstabin2, the catalytic subunit of PKA, the PKA regulatory subunit (RII), mAKAP, and the protein phosphatases PP1 and PP2A ( Figure 1A). When immunoprecipitated RyR2 was incubated with [ 32 P]ATP and PKA or cAMP, RyR2 was phosphorylated in a manner completely reversible by the specific PKA inhibitor PKI [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] (PKI), providing evidence that atrial RyR2 is substrate for PKA phosphorylation and that PKA is directly associated with the channel complex ( Figure 1B). Consistent with previous findings from ventricular myocardium demonstrating that PKA phosphorylation of RyR2 reduces the binding affinity of calstabin2, 13,15,22 PKA phosphorylation of atrial RyR2 specifically reduced the amount of calstabin2 in the RyR2 macromolecular complex as determined by coimmunoprecipitation in a manner completely inhibited by PKI ( Figure 1C).…”

“…RA appendage tissue was obtained at the time of cardiac surgery as described previously 18 from patients with chronic AF (Ͼ6 months; nϭ10), and patients in sinus rhythm (nϭ10).…”