Molecular and Electrophysiological Differences in the L-Type Ca²⁺ Channel of the Atrium and Ventricle of Rat Hearts

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Background Many pathological conditions induce electrical remodeling, possibly through intracellular Ca²⁺ overload, but the currently available L-type Ca²⁺ channel blockers may be detrimental because of their global negative inotropic effects. Methods and Results To determine whether the L-type Ca²⁺ channel is identical throughout the heart, the distribution of the mRNAs and proteins comprising the L-type Ca²⁺ channel and its electrophysiological properties were analyzed in rat atria and ventricles. The mRNA of α₂δ-2 (Cacna2d2) was more abundantly expressed in the atrium (~5-fold) than in the ventricle. In contrast, α_1C (Cacna1c) (Cav1.2) mRNA was significantly less abundant in the atrium. The level of the α_1C (Cacna1c) (Cav1.2) protein was decreased (~0.5-fold) and that of α₂ δ-1 (Cacna2d1) was increased (~2-fold) in the atrium compared with the ventricle. Although the peak I_Ca,L density showed no significant differences, voltage dependence of inactivation and activation of the current showed a more depolarized shift in the atrium than in the ventricle. Conclusion These results indicate that in the rat heart the L-type Ca²⁺ channel differs between the atrium and ventricle with regard to gene expression and electrophysiological properties. (Circ J 2006; 70: 610 - 614)