Nanoscale architecture and dynamics of Ca _V 1.3 channel clusters in cardiac myocytes revealed by single channel nanoscopy

The clustering of L-type calcium channels for functional regulation of intracellular calcium signaling remains poorly understood. Here we applied super-resolution imaging to study Ca _V 1.3 channel clusters in human iPSC-derived atrial cardiomyocytes (hiPSC-aCM) to analyze subcellular localization, dimensions, architecture, and dynamics, which were largely unexplored previously. STimulated Emission Depletion (STED) imaging characterized the localization and structure of Ca _V 1.3 channel clusters in living cardiomyocytes. DNA Points Accumulation for Imaging in Nanoscale Topography (DNA-PAINT) achieved true molecular resolution, revealing an irregular channel distribution with substantial spacing. Single Particle Tracking (SPT) showed that channels co-diffuse in confined and stationary membrane nanodomains. The cytosolic C-terminal tail of Ca _V 1.3 by itself was found sufficient for cluster formation. In conclusion, our LTCC clustering studies demonstrate that Ca _V 1.3 channel clusters consist of mobile individual channels inside defined membrane nanodomains, in contrast to previous models of dense channel packing.