CaM kinase augments cardiac L-type Ca2+ current:: a cellular mechanism for long Q-T arrhythmias

Early afterdepolarizations (EAD) caused by L-type Ca2+ current (I-Ca,I-L) are thought to initiate long Q-T arrhythmias, but the role of intracellular Ca2+ in these arrhythmias is controversial. Rabbit ventricular myocytes were stimulated with a prolonged EAD-containing action potential-clamp waveform to investigate the role of Ca2+/calmodulin-dependent protein kinase II (CaM kinase) in I-Ca,I-L during repolarization. I-Ca,I-L was initially augmented, and augmentation was dependent on Ca2+ from the sarcoplasmic reticulum because the augmentation was prevented by ryanodine or thapsigargin. I-Ca,I-L augmentation was also dependent on CaM kinase, because it was prevented by dialysis with the inhibitor peptide AC3-I and reconstituted by exogenous constitutively active CaM kinase when Ba2+ was substituted for bath Ca2+. Ultrastructural studies confirmed that endogenous CaM kinase, L-type Ca2+ channels, and ryanodine receptors colocalized near T tubules. EAD induction was significantly reduced in current-clamped cells dialyzed with ACS-I (4/15) compared with cells dialyzed with an inactive control peptide (11/15, P = 0.013). These findings support the hypothesis that EADs are facilitated by CaM kinase.