Direct Evidence for Microdomain-Specific Localization and Remodeling of Functional L-Type Calcium Channels in Rat and Human Atrial Myocytes
Background—Distinct subpopulations of L-type calcium channels (LTCCs) with different functional properties exist in cardiomyocytes. Disruption of cellular structure may affect LTCC in a microdomain-specific manner and contribute to the pathophysiology of cardiac diseases, especially in cells lacking organized T-tubules such as atrial myocytes (AMs).
Methods and Results—Isolated rat and human AMs were characterized by scanning ion conductance, confocal, and electron microscopy. Half of AMs possessed T-tubules and structured topography, proportional to cell width. Bigger proportion of myocytes in the left atrium had organized T-tubules and topography than in the right atrium. Super-resolution scanning patch-clamp showed LTCCs distribute equally in T-tubules (T-LTCCs) and crest areas of the sarcolemma (C-LTCCs), whereas in ventricular myocytes (VMs) LTCCs primarily cluster in T-tubules. Rat, but not human, T-LTCCs had open probability similar to C-LTCCs, but exhibited ~40% greater current. Optical mapping of Ca2+ transients revealed that rat AMs presented ~3-fold as many spontaneous Ca2+ release events as VMs. Occurrence of C-LTCCs and spontaneous Ca2+ transients were eliminated by either a caveolae-targeted LTCC antagonist or disrupting caveolae with methyl-β-cyclodextrin, with an associated ~30% whole-cell ICa,L reduction. Heart failure (HF, 16-weeks post-MI) in rats resulted in a T-tubule degradation (by ~40%) and significant elevation of spontaneous Ca2+ release events. While not affecting LTCC occurrence, HF led to ~25% decrease in T-LTCC amplitude.
Conclusions—We provide the first direct evidence for the existence of two distinct subpopulations of functional LTCCs in rat and human AMs, with their biophysical properties modulated in HF in a microdomain-specific manner.
- scanning ion conductance microscopy
- chronic heart failure
- calcium channel
- atrial myocyte
- calcium signaling
- Received June 28, 2015.
- Revision received September 24, 2015.
- Accepted October 2, 2015.
Circulation is published on behalf of the American Heart Association, Inc., by Wolters Kluwer. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits use, distribution, and reproduction in any medium, provided that the original work is properly cited.