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Returning to normal pH after acidosis, similar to reperfusion after ischemia, is prone to arrhythmias. The type and mechanisms of these arrhythmias have never been explored and were the aim of the present work. Langendorff-perfused rat/mice hearts and rat-isolated myocytes were subjected to respiratory acidosis and then returned to normal pH. Monophasic action potentials and left ventricular developed pressure were recorded. The removal of acidosis provoked ectopic beats that were blunted by 1 µM of the CaMKII inhibitor KN-93, 1 µM thapsigargin, to inhibit sarcoplasmic reticulum (SR) Ca2+ uptake, and 30 nM ryanodine or 45 µM dantrolene, to inhibit SR Ca2+ release and were not observed in a transgenic mouse model with inhibition of CaMKII targeted to the SR. Acidosis increased the phosphorylation of Thr17 site of phospholamban (PT-PLN) and SR Ca2+ load. Both effects were precluded by KN-93. The return to normal pH was associated with an increase in SR Ca2+ leak, when compared with that of control or with acidosis at the same SR Ca2+ content. Ca2+ leak occurred without changes in the phosphorylation of ryanodine receptors type 2 (RyR2) and was blunted by KN-93. Experiments in planar lipid bilayers confirmed the reversible inhibitory effect of acidosis on RyR2. Ectopic activity was triggered by membrane depolarizations (delayed afterdepolarizations), primarily occurring in epicardium and were prevented by KN-93. The results reveal that arrhythmias after acidosis are dependent on CaMKII activation and are associated with an increase in SR Ca2+ load, which appears to be mainly due to the increase in PT-PLN. [ABSTRACT FROM AUTHOR]

CLC-3, a member of the CLC family of chloride channels, mediates function in many cell types in the body. The multifunctional calcium-calmodulin-dependent protein kinase II (CaMKII) has been shown to activate recombinant CLC-3 stably expressed in tsA cells, a human embryonic kidney cell line derivative, and natively expressed channel protein in a human colonic tumour cell line T84. We examined the CaMKII-dependent regulation of CLC-3 in a smooth muscle cell model as well as in the human colonic tumour cell line, HT29, using whole-cell voltage clamp. In CLC-3-expressing cells, we observed the activation of a C1- conductance following intracellular introduction of the isolated autonomous CaMKII into the voltage-clamped cell via the patch pipette. The CaMKII-dependent C1- conductance was not observed following exposure of the cells to 1 µm autocamtide inhibitory peptide (AIP), a selective inhibitor of CaMKII. Arterial smooth muscle cells express a robust CaMKII-activated C1- conductance; however, CLC3-/- cells did not. The N-terminus of CLC-3, which contains a CaMKII consensus sequence, was phosphorylated by CaMKII in vitro, and mutation of the serine at position 109 (S109A) abolished the CaMKII-dependent C1- conductance, indicating that this residue is important in the gating of CLC-3 at the plasma membrane. [ABSTRACT FROM AUTHOR]