Abstract 10467: Distinct Distribution of Functional Calcium Channels Revealed by Super-resolution Scanning Patch-clamp in Adult Rat Atrial Cardiomyocytes
Background: Specific spatial distribution of L-type calcium channels (LTCCs) in ventricular myocytes is known to be crucial for EC coupling. However little is known about the spatial distribution of functional LTCCs in atria. Also the extent of the t-tubular (TT) network in atrial cardiomyocytes in comparison with the well-developed TT network in ventricle remains debatable.
Methods: Confocal microscopy and scanning ion conductance microscopy were used to characterize cell surface topography and TTs in isolated rat atrial myocytes. Ventricular myocytes were used as control cells as they have a well-studied TT system. Super-resolution scanning patch-clamp was applied to identify distribution of functional LTCCs in different subcellular domains. Spontaneous Ca2+ transient events were promoted by Ca2+ loading by 1 min of 4-Hz pacing and optically visualized by Ca2+-sensitive fluorescent dye Fluo-4 AM.
Results: About one half of the studied atrial myocytes had TTs, most of them located in the left atrium. Myocytes with TTs (density: 17.3±0.5%) and well-developed surface topography had a larger mean diameter (19.4±1.3μm) than cells with disorganized TTs (density: 12.7±0.5%, P=0.006) or absent TTs and non-structured areas on the surface (16.2±0.6μm, P=0.021, and 12.2±0.4μm, P<0.001). Functional atrial LTCCs were found in TTs openings and in the crest areas of the sarcolemma with similar frequency in contrast to ventricular cells where LTCCs were exclusively clustered in TTs. Atrial LTCCs recorded in TTs had the same open probability but higher amplitude at more negative voltages compared to LTCCs observed in the crest. Optical mapping revealed that atrial myocytes were more prone to have spontaneous Ca2+ sparks than ventricular myocytes (0.8±0.22 sparks/cell vs. 0.08±0.03 sparks/cell, P<0.001). Interestingly, wider atrial cells were also more disposed to have Ca2+ sparks (15.8±0.7 μm vs. 11.6±0.4, respectively) which could be linked to a more developed TTs network.
Conclusions: This study provides the first direct evidence of distinct distribution of functional LTCCs within the specific, subcellular compartments of atrial versus ventricular myocytes and offers new insights into the molecular mechanisms of unique atrial myocyte calcium cycling.
- © 2013 by American Heart Association, Inc.