Molecular and electrophysiological differences in the L-type Ca2+ channel of the atrium and ventricle of rat hearts

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 alpha 2 delta-2 (Cacna2d2) was more abundantly expressed in the atrium (similar to 5-fold) than in the ventricle. In contrast, alpha 1c (Cacna1c) (Cav 1.2) mRNA was significantly less abundant in the atrium. The level of the alpha 1c (Cacna1c) (Cav 1.2) protein was decreased (similar to 0.5-fold) and that of alpha 2 delta-1 (Cacna2d1) was increased (similar to 2-fold) in the atrium compared with the ventricle. Although the peak ICa,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.