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Mancarella S, Yue Y, Karnabi E, Qu Y, El-Sherif N, Boutjdir M. Impaired Ca[sup2+] homeostasis is associated with atrial fibrillation in the α1D L-type Ca[sup2+] channel KU mouse. Am J Physiol Heart Circ Physiol 295: H2017-H2024, 2008. First published September 12, 2008; doi: 10.1152/ajpheart.00537.2008.-The novel α1D Ca[sup2+] channel together with α1D Ca[sup2+] channel contribute to the L-type Ca[sup2+] current (I[subCa-L]) in the mouse supraventricular tissue. However, its functional role in the heart is just emerging. We used the α1D gene knockout (KO) mouse to investigate the electrophysiological features, the relative contribution of the α1D Ca[sup2+] channel to the global I[subCa-L], the intracellular Ca[sup2+] transient, the Ca[sup2+] handling by the sarcoplasmic reticulum (SR), and the inducibility of atrial fibrillation (AF). In vivo and ex vivo ECG recordings from α1D KO mice demonstrated significant sinus bradycardia, atrioventricular block, and vulnerability to AF. The wild-type mice showed no ECG abnormalities and no AF. Patch-clamp recordings from isolated α1D KO atrial myocytes revealed a significant reduction of I[subCa-L] (24.5%; P < 0.05). However, there were no changes in other currents such as I[subNa], I[subCa-T], I[subK], If, and I[subf] and no changes in α[subIC] mRNA levels of α1D KO atria. Fura 2-loaded atrial myocytes showed reduced intracellular Ca[sup2+] transient (-40%; P < 0.05) and rapid caffeine application caused a 17% reduction of the SR Ca[sup2+] content (P < 0.05) and a 28% reduction (P < 0.05) of fractional SR Ca[sup2+] release in α1D KO atria. In conclusion, genetic deletion of α1D Ca[sup2+] channel in mice results in atrial electrocardiographic abnormalities and AF vulnerability. The electrical abnormalities in the α1D KO mice were associated with a decrease in the total I[subCa-L] density, a reduction in intracellular Ca[sup2+] transient, and impaired intracellular Ca[sup2+] handling. These findings provide new insights into the mechanism leading to atrial electrical dysfunction in the α1D KO mice. [ABSTRACT FROM AUTHOR]

Objectives: Ischemic preconditioning (PC) reduces myocardial infarction by a mechanism that involves opening of mitochondrial ATP-dependent potassium channels (mKATP), reactive oxygen species (ROS), and possibly activation of p38 mitogen-activated protein kinase (p38 MAPK). The actual order of these steps, however, is a matter of current debate. This study examined whether protection afforded by menadione, which protects by causing mitochondria to produce ROS, requires mKATP opening. In addition, we tested whether protection from anisomycin, a p38 MAPK activator, is dependent on ROS production. Methods and Results: Isolated, buffer-perfused rat hearts were pretreated with menadione, and infarction was assessed after 30 min of regional ischemia and 120 min of reperfusion. Menadione reduced infarction in a dose-dependent manner with an EC50 of 270 nM. Menadione’s infarct-limiting effect was insensitive to 200 μM 5-hydroxydecanoate (5HD), an mKATP channel blocker, whereas protection by diazoxide and PC were blocked by 5HD. Anisomycin caused hearts to resist infarction and this protective effect was abrogated by SB203580, a p38 MAPK inhibitor, and 2-mercaptopropionylglycine (MPG), a free radical scavenger. Conclusions: These results indicate that mKATP opening occurs upstream of mitochondrial ROS generation in the protective pathway. Furthermore, protection afforded by anisomycin was p38 MAPK- and ROS-dependent. [Copyright &y& Elsevier]

The novel alpha1D Ca2+ channel together with alpha1C Ca2+ channel contribute to the L-type Ca2+ current (I(Ca-L)) in the mouse supraventricular tissue. However, its functional role in the heart is just emerging. We used the alpha1D gene knockout (KO) mouse to investigate the electrophysiological features, the relative contribution of the alpha1D Ca2+ channel to the global I(Ca-L), the intracellular Ca2+ transient, the Ca2+ handling by the sarcoplasmic reticulum (SR), and the inducibility of atrial fibrillation (AF). In vivo and ex vivo ECG recordings from alpha1D KO mice demonstrated significant sinus bradycardia, atrioventricular block, and vulnerability to AF. The wild-type mice showed no ECG abnormalities and no AF. Patch-clamp recordings from isolated alpha1D KO atrial myocytes revealed a significant reduction of I(Ca-L) (24.5%; P < 0.05). However, there were no changes in other currents such as I(Na), I(Ca-T), I(K), I(f), and I(to) and no changes in alpha1C mRNA levels of alpha1D KO atria. Fura 2-loaded atrial myocytes showed reduced intracellular Ca2+ transient (approximately 40%; P < 0.05) and rapid caffeine application caused a 17% reduction of the SR Ca2+ content (P < 0.05) and a 28% reduction (P < 0.05) of fractional SR Ca2+ release in alpha1D KO atria. In conclusion, genetic deletion of alpha1D Ca2+ channel in mice results in atrial electrocardiographic abnormalities and AF vulnerability. The electrical abnormalities in the alpha1D KO mice were associated with a decrease in the total I(Ca-L) density, a reduction in intracellular Ca2+ transient, and impaired intracellular Ca2+ handling. These findings provide new insights into the mechanism leading to atrial electrical dysfunction in the alpha1D KO mice.

Alpha1D L-type Ca channel was assumed to be of neuroendocrine origin only; however, alpha1D L-type Ca channel knockout mice exhibit sinus bradycardia and atrioventricular block, indicating a distinct role of alpha1D in the heart. The presence and distribution of alpha1D Ca channel in the heart and its regulation by protein kinase A (PKA) are just emerging. Our objective was to examine the localization of alpha1D L-type Ca channel in rabbit and rat hearts and its modulation by PKA. Here, we show the exclusive presence of alpha1D Ca channel transcript in the sinoatrial node, atrioventricular node, and atria but not in the ventricle by RT-PCR and the expression of alpha1D Ca channel protein in atrial myocytes' sarcolemma by indirect immunostaining and Western blot. There is no significant difference in the expression level of alpha1D Ca channel in the left versus right atrium. Superfusion of membrane-permeable 8-bromo-cAMP resulted in a significant increase of the peak current density of alpha1D Ca current expressed in tsA201 cells. This increase was inhibited by the PKA inhibitor (PKI). Application of 8-bromo-cAMP also readily phosphorylated the alpha1D Ca channel protein. The results are first to demonstrate that PKA phosphorylation of L-type Ca channel alpha1D-subunit resulted in an increase of the alpha1D Ca channel activity. Together with the observation that alpha1D Ca channel is exclusively present in the sinoatrial node and atria, the findings suggest that alpha1D Ca channel plays a unique role in the sinoatrial tissue and is a target for sympathetic control of heart rhythm.

Objectives: Ischemic preconditioning (PC) reduces myocardial infarction by a mechanism that involves opening of mitochondrial ATP-dependent potassium channels (mK(ATP)), reactive oxygen species (ROS), and possibly activation of p38 mitogen-activated protein kinase (p38 MAPK). The actual order of these steps, however, is a matter of current debate. This study examined whether protection afforded by menadione, which protects by causing mitochondria to produce ROS, requires mK(ATP) opening. In addition, we tested whether protection from anisomycin, a p38 MAPK activator, is dependent on ROS production., Methods and Results: Isolated, buffer-perfused rat hearts were pretreated with menadione, and infarction was assessed after 30 min of regional ischemia and 120 min of reperfusion. Menadione reduced infarction in a dose-dependent manner with an EC(50) of 270 nM. Menadione's infarct-limiting effect was insensitive to 200 microM 5-hydroxydecanoate (5HD), an mK(ATP) channel blocker, whereas protection by diazoxide and PC were blocked by 5HD. Anisomycin caused hearts to resist infarction and this protective effect was abrogated by SB203580, a p38 MAPK inhibitor, and 2-mercaptopropionylglycine (MPG), a free radical scavenger., Conclusions: These results indicate that mK(ATP) opening occurs upstream of mitochondrial ROS generation in the protective pathway. Furthermore, protection afforded by anisomycin was p38 MAPK- and ROS-dependent.