Velocity Of Calcium Waves Research Articles

Spatiotemporal cell junction assembly in human iPSC-CM models of arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disorder that causes life-threatening arrhythmias and myocardial dysfunction. Pathogenic variants in Plakophilin-2 (PKP2), a desmosome component within specialized cardiac cell junctions, cause the majority of ACM cases. However, the molecular mechanisms by which PKP2 variants induce disease phenotypes remain unclear. Here we built bioengineered platforms using genetically modified human induced pluripotent stem cell-derived cardiomyocytes to model the early spatiotemporal process of cardiomyocyte junction assembly invitro. Heterozygosity for truncating variant PKP2R413X reduced Wnt/β-catenin signaling, impaired myofibrillogenesis, delayed mechanical coupling, and reduced calcium wave velocity inengineered tissues. These abnormalities were ameliorated by SB216763, which activated Wnt/β-catenin signaling, improved cytoskeletalorganization, restored cell junction integrity in cell pairs, and improved calcium wave velocity in engineered tissues.Together, these findings highlight the therapeutic potential of modulating Wnt/β-catenin signaling in a human model of ACM.

Assessing the origin and velocity of Ca2+ waves in three-dimensional tissue: Insights from a mathematical model and confocal imaging in mouse pancreas tissue slices

Many tissues are gap-junction-coupled syncytia that support cell-to-cell communication via propagating calcium waves. This also holds true for pancreatic islets of Langerhans, where several thousand beta cells work in synchrony to ensure proper insulin secretion. Two emerging functional parameters of islet function are the location of wave initiator regions and the velocity of spreading calcium waves. High-frequency confocal laser-scanning imaging in tissue slices is one of the best available methods to determine these markers, but it is limited to two-dimensional cross-sections of an otherwise three-dimensional islet. Here we show how mathematical modeling can significantly improve this limitation. Firstly, we analytically determine the shape of velocity profiles of spherical excitation waves in the focal plane of a homogeneous three-dimensional space. Secondly, we introduce a mathematical model consisting of coupled excitable cells that considers cellular heterogeneities to approach more realistic conditions by means of numerical simulations. We demonstrate the effectiveness of our approach on experimentally recorded waves from an islet that was stimulated with 9 mM glucose. Furthermore, we show that calcium waves were primarily triggered by a specific region located 30 µm bellow the focal plane at the periphery of the islet. Additionally, we show that the velocity of the calcium wave was around 80 µm/s. We discuss the importance of our approach for the correct determination of the origin and velocity of calcium waves from experimental data, as well as the pitfalls that are due to improper procedural simplifications.

Regulation of calcium dynamics and propagation velocity by tissue microstructure in engineered strands of cardiac tissue.

Disruptions to cardiac tissue microstructure are common in diseased or injured myocardium and are known substrates for arrhythmias. However, we have a relatively coarse understanding of the relationships between myocardial tissue microstructure, propagation velocity and calcium cycling, due largely to the limitations of conventional experimental tools. To address this, we used microcontact printing to engineer strands of cardiac tissue with eight different widths, quantified several structural and functional parameters and established correlation coefficients. As strand width increased, actin alignment, nuclei density, sarcomere index and cell aspect ratio decreased with unique trends. The propagation velocity of calcium waves decreased and the rise time of calcium transients increased with increasing strand width. The decay time constant of calcium transients decreased and then slightly increased with increasing strand width. Based on correlation coefficients, actin alignment was the strongest predictor of propagation velocity and calcium transient rise time. Sarcomere index and cell aspect ratio were also strongly correlated with propagation velocity. Actin alignment, sarcomere index and cell aspect ratio were all weak predictors of the calcium transient decay time constant. We also measured the expression of several genes relevant to propagation and calcium cycling and found higher expression of the genes that encode for connexin 43 (Cx43) and a subunit of L-type calcium channels in thin strands compared to isotropic tissues. Together, these results suggest that thinner strands have higher values of propagation velocity and calcium transient rise time due to a combination of favorable tissue microstructure and enhanced expression of genes for Cx43 and L-type calcium channels. These data are important for defining how microstructural features regulate intercellular and intracellular calcium handling, which is needed to understand mechanisms of propagation in physiological situations and arrhythmogenesis in pathological situations.

Intercellular Ultrafast Calcium Wave Velocity and Propagation of Spontaneous Electrical Activity in A7r5 Cells at Physiological Temperature

Intercellular Ultrafast Calcium Wave Velocity and Propagation of Spontaneous Electrical Activity in A7r5 Cells at Physiological Temperature

Leptin and adiponectin have opposite effect on ciliary activity, calcium wave velocity and ovum transport velocity in the rat oviduct

Obesity (with high leptin and reduced adiponectin serum concentrations) correlates with reduced fertility. Embryos oviductal transport depends on coordinated ciliary activity and smooth muscle contractions, which are modulated by intracellular calcium levels. We hypothesize that leptin and adiponectin affect ciliary beat frequency and intracellular calcium homeostasis, changing the embryos transport velocity through the rat oviduct. Effect of different leptin or adiponectin concentrations (1, 10 and 100 ng/ml) over ciliary beat frecuency was tested on primary cultures of ciliated cells from the rat epithelium. We observe a transient decrease in ciliary beat frequency with leptin and increase with adiponectin. High leptin levels resulted in a reduction on propagation velocity of intracellular calcium wave produced after a mechanical stimulation in 24 hrs treated cell cultures, and adiponectin showed the opposite effect. We test in vivo effects in female rats, on day 1 of pregnancy, leptin or adiponectin (100 ng/ml) were injected in one side of ovarian bursa and vehicle in the contralateral side. On pregnancy day 5, leptin induces retention of the embryos in the oviduct, in other wise, adiponectin have no effects on embryonic transport all of the embryos were finding in uterus. These provide a possible explanation for the cellular effect of obesity on the reduced female fertility (ACT‐79 and CONICYT 24121342).

Propagation Mechanisms of Calcium Waves Arising During Arterial Vasomotion

Vasomotion consists in cyclic arterial diameter variations induced by synchronous contractions and relaxations of smooth muscle cells (SMCs) present in the arterial wall. These contractions have been shown to be due to an increase in the intracellular cytosolic calcium concentration. However, the arteries do not contract simultaneously on macroscopic distances and a propagation of the diameter variations can be observed. Our aim was to investigate this propagation. We stimulated endothelium denuded rat mesenteric arterial strips with the vasoconstrictor, phenylephrine (PE) to obtain vasomotion and observed that the contraction waves are linked to intercellular calcium waves through the SMCs. A velocity of about 100 μm/s was measured for the two kinds of waves which could propagate either from the distal to the proximal side of the artery or in the opposite direction. To investigate the calcium wave propagation mechanisms, we used a method allowing a PE stimulation of a small area of the strip. No calcium propagation could be induced by this local stimulation when the strip was in its resting state. However, if a low PE concentration was added to the whole strip, local PE stimulations induced calcium waves spreading over finite distances. The calcium wave velocity induced by local stimulation was identical to the velocity observed during vasomotion. This suggests that the propagation mechanisms are similar in the two cases. Using inhibitors of gap junctions and of voltage operated calcium channels, we showed that the locally induced calcium propagation likely depends on the propagation of the SMCs depolarization. Finally, from the experimental data gathered, it is possible to propose a model of the mechanisms underlying the propagation.

Intercellular calcium waves are associated with the propagation of vasomotion along arterial strips

Vasomotion consists of cyclic arterial diameter variations induced by synchronous contractions and relaxations of smooth muscle cells. However, the arteries do not contract simultaneously on macroscopic distances, and a propagation of the contraction can be observed. In the present study, our aim was to investigate this propagation. We stimulated endothelium-denuded rat mesenteric arterial strips with phenylephrine (PE) to obtain vasomotion and observed that the contraction waves are linked to intercellular calcium waves. A velocity of approximately 100 microm/s was measured for the two kinds of waves. To investigate the calcium wave propagation mechanisms, we used a method allowing a PE stimulation of a small area of the strip. No calcium propagation could be induced by this local stimulation when the strip was in its resting state. However, if a low PE concentration was added on the whole strip, local PE stimulations induced calcium waves, spreading over finite distances. The calcium wave velocity induced by local stimulation was identical to the velocity observed during vasomotion. This suggests that the propagation mechanisms are similar in the two cases. Using inhibitors of gap junctions and of voltage-operated calcium channels, we showed that the locally induced calcium propagation likely depends on the propagation of the smooth muscle cell depolarization. Finally, we proposed a model of the propagation mechanisms underlying these intercellular calcium waves.

The velocity of calcium waves is expected to depend non-monotoneously on the density of the calcium release units.

In this paper we develop a reaction-diffusion system describing the calcium dynamics in an agarose gel system with resuspended vesicles from the sarcoplasmic reticulum (SR vesicles). We focus on a simple model: compared with living cells (e.g. cardiac myocytes) an important property of the agarose gel system is the absence of the sarcolemma and the spatial separation of the calcium release units (CRUs). Our model includes the kinetics of ryanodine sensitive receptors (RyRs), the activity of the SERCA pumps and the diffusion of free calcium. We describe numerical simulations which show a biphasic relationship between the density of the CRUs and the propagation velocity of spreading waves. The non-monotony can be explained by changes in the amplitude of the local calcium concentration. We formulate implications for the in vitro system which could be verified in future experiments.

Inhibitors of SERCA and mitochondrial Ca-uniporter decrease velocity of calcium waves in rat cardiomyocytes.

Spontaneous calcium waves in isolated rat cardiomyocytes were investigated by confocal laser scanning microscopy using the fluorescent Ca(2+)-indicator fluo-4 AM. With increasing calcium overload propagation velocities reinforced. The calcium wavespeed was significantly diminished by drugs which interfere with the calcium uptake of both the sarcoplasmic reticulum (SR) and mitochondria, respectively. Stepwise addition of thapsigargin, a highly specific inhibitor of SERCA, decreased the wavespeed and allowed the determination of flux control coefficients which were found to be increasing from 0.15-0.75 in dependence on calcium overload. Kd was estimated to be between 0.4 and 0.6 nM TG. At 5 mM TG wavespeed was significantly reduced by almost 50%. Spontaneous calcium waves did not occur in bathing solutions with more than 20 nM thapsigargin. Calcium wave velocity was also reduced in the presence of the oxygen-bridged dinuclear ruthenium amine complex RU 360 which specifically blocks the mitochondrial Ca2+ uptake. The observed effects are likely due to a reduction of the ryanodine receptor's open probability. It is suggested that the intracellular Ca2+ signaling depends on both SR lumenal and cytosolic calcium concentration.

A New Approach to Study the Relationship between Calcium Waves and Diastolic (Ca2+)i in Heart Muscle Cells.

In the present study, changes in calcium waves with alternation of diastolic [Ca2+] i were investigated in a single common rat neonatal cultured heart muscle cell without changes in extracellular conditions. Heart muscle cells were loaded with fluo-3 by the “whole cell clamp” technique. Rapid chan ges in diastolic [Ca2+] i by variations in the membrane potential clarified the influences on calcium waves. When the membrane potential was held at 0 mV, inter wave basal [Ca2+] i were maintained at a high level. The membrane-holding potential was then momentarily altered to -80 mV and the basal [Ca2+] i registered a lower level within 1 sec. During these events, spontaneous calcium waves were analyzed by confocal laser scanning microscopy (X-t scanning mode). The frequency and velocity of calcium waves at 0 mV significantly increased compared with those at-80 mV. Moreover, these changes were more pronounced with increasing extracellular [Ca2+]. These results suggest that diastolic [Ca2+] i; directly influences calcium waves.