Function of L-Type Calcium Channel Microdomain in Human Myocytes from Hearts with Ischemic versus Dilated Cardiomyopathies

Abstract

Introduction: Recently we have revealed how the imbalance of L-type calcium channels (LTCC) at the cell membrane could lead to arrhythmia in the whole heart, in a rat model of myocardial infarction as well as in a group of patients with dilated cardiomyopathy (DCM). In this study, we conduct a more extensive comparison of myocytes from hearts with ischemic (ICM) versus DCM. Also, the LTCC function is assessed in myocytes from patients with Left Ventricular Assistance Device (LVAD). Methods: Cardiomyocytes were isolated from ventricular tissue of donor normal hearts and hearts of patients with DCM or ICM with and without LVAD. LTCC current was recorded in distinct cellular compartments: T-tubules (TT) and the areas between them or “crests”, using super-resolution scanning patch-clamp technique. Cell size and T-tubules density were measured with confocal microscopy under Di-8-ANEPPS staining. Results: Cardiomyocytes from failing hearts develop a hypertrophic phenotype, more severe in DCM than in ICM patients, which is partially reversed with LVAD. In addition, these cells have less Z-grooves, lower TT density and a significantly increased LTCC density in the crest microdomains. Functionally, LTCCs open probability revealed to be abnormally high in failing patients. These pro-arrhythmic LTCCs, as it has been proposed in relation with the AP prolongation, are, interestingly, in the crests of DCM and in the TT of ICM myocytes. Inhibitor analysis showed that hyperphosphorylation of LTCC occurs via calmodulin-dependent kinase II in DCM and via protein kinase A in ICM. Implantation of LVAD was found to reduce the LTCC activity independently of the disease. Conclusion: These findings suggest that both ICM and DCM myocytes contain pro-arrhythmic hyper-active LTCCs but their increased activity occurs as the result of two different phosphorylation pathways targeting different microdomains.