Electron tomography unravels new insights into fiber cell wall nanostructure; exploring 3D macromolecular biopolymeric nano-architecture of spruce fiber secondary walls.

Lignocellulose biomass has a tremendous potential as renewable biomaterials for fostering the "bio-based society" and circular bioeconomy paradigm. It requires efficient use and breakdown of fiber cell walls containing mainly cellulose, hemicellulose and lignin biopolymers. Despite their great importance, there is an extensive debate on the true structure of fiber walls and knowledge on the macromolecular nano-organization is limited and remains elusive in 3D. We employed dual-axis electron tomography that allows visualization of previously unseen 3D macromolecular organization/biopolymeric nano-architecture of the secondary S2 layer of Norway spruce fiber wall. Unprecedented 3D nano-structural details with novel insights into cellulose microfibrils (~ 2 nm diameter), macrofibrils, nano-pore network and cell wall chemistry (volume %) across the S2 were explored and quantified including simulation of structure related permeability. Matrix polymer association with cellulose varied between microfibrils and macrofibrils with lignin directly associated with MFs. Simulated bio-nano-mechanical properties revealed stress distribution within the S2 and showed similar properties between the idealized 3D model and the native S2 (actual tomogram). Present work has great potential for significant advancements in lignocellulose research on nano-scale understanding of cell wall assembly/disassembly processes leading to more efficient industrial processes of functionalization, valorization and target modification technologies.

Pacing-induced heterogeneities in intracellular Ca2+ signaling, cardiac alternans, and ventricular arrhythmias in intact rat heart.

Optical mapping studies have suggested that intracellular Ca2+ and T-wave alternans are linked through underlying alternations in Ca2+ cycling-inducing oscillations in action potential duration through Ca2+-sensitive conductances. However, these studies cannot measure single-cell behavior; therefore, the Ca2+ cycling heterogeneities within microscopic ventricular regions are unknown. The goal of this study was to measure cellular activity in intact myocardium during rapid pacing and arrhythmias. We used single-photon laser-scanning confocal microscopy to measure Ca2+ signaling in individual myocytes of intact rat myocardium during rapid pacing and during pacing-induced ventricular arrhythmias. At low rates, all myocytes demonstrate Ca2+ alternans that is synchronized but whose magnitude varies depending on recovery kinetics of Ca2+ cycling for each individual myocyte. As rate increases, some cells reverse alternans phase, giving a dyssynchronous activation pattern, even in adjoining myocytes. Increased pacing rate also induces subcellular alternans where Ca2+ alternates out of phase with different regions within the same cell. These forms of heterogeneous Ca2+ signaling also occurred during pacing-induced ventricular tachycardia. Our results demonstrate highly nonuniform Ca2+ signaling among and within individual myocytes in intact heart during rapid pacing and arrhythmias. Thus, certain pathophysiological conditions that alter Ca2+ cycling kinetics, such as heart failure, might promote ventricular arrhythmias by exaggerating these cellular heterogeneities in Ca2+ signaling.