Spatio-temporal PLC activation in parallel with intracellular Ca2+ wave propagation in mechanically stimulated single MDCK cells

Intracellular calcium ion transients evoked by cell poking independently of released autocrine ATP in Madin-Darby canine kidney cells

The mechanical stimulation induced by poking cells with a glass needle activates Piezo1 receptors and the adenosine triphosphate (ATP) autocrine pathway, thus increasing intracellular Ca2+ concentration. The differences between the increase in intracellular Ca2+ concentration induced by cell poking and by ATP-only stimulation have not been investigated. In this study, we investigated the Ca2+ signaling mechanism induced by autocrine ATP release during Madin-Darby Canine Kidney cell membrane deformation by cell poking. The results suggest that the pathways for supplying Ca2+ into the cytoplasm were not identical between cell poking and conventional ATP stimulation. The functions of the G protein-coupled receptor (GPCR) subunits (Gα $\alpha $ q, Gβ γ $\beta \gamma $ ), ATP-activated receptor and the upstream Ca2+ release signal from the intracellular endoplasmic reticulum Ca2+ store, were investigated. The results show that Gα $\alpha $ q plays a major role in the Ca2+ response evoked by ATP-only stimulation, while cell poking induces a Ca2+ response requiring the involvement of both Gα $\alpha $ q and Gβ γ $\beta \gamma $ units simultaneously. These results suggest that GPCR are not only activated by ATP-only stimulation or autocrine ATP release during Ca2+ signaling, but also activated by the mechanical effects of cell poking.

Genetic Loci in Phospholipase C-Like 1 (PLCL1) are Protective Factors for Allergic Rhinitis in Han Population of Northern Shaanxi, China

Background

Allergic rhinitis (AR) is a common allergic disease in otolaryngology. Its pathogenesis is still unclear. PLC1 plays a key role in calcium homeostasis and immune response, which is potentially related to AR. We aimed to explore the association between PLCL1 genetic loci and susceptibility to AR.

Methods

We recruited 1975 volunteers to perform an association analysis through SNPStats online software. False-positive report probability (FPRP) analysis was used to detect whether the positive findings were worth noting. Linkage disequilibrium and haplotype analysis were completed through Haploview and SNPStats. The influence of SNP-SNP interaction on AR susceptibility was evaluated through multifactor dimensionality reduction (MDR).

Results

The results showed that four genetic loci in PLCL1 (rs2139049, rs212164068, rs2228135, and rs6738825) are associated with AR susceptibility under multiple genetic models. Allele "A" of PLCL1-rs2139049 (OR = 0.85, p = 0.031) or of -rs212164068 (OR = 0.85, p = 0.030), and allele "G" of PLCL1-rs6738825 (OR = 0.84, p = 0.022) are significantly associated with reduced AR risk. PLCL1-rs2228135 is associated with an increased risk of AR in males or participants older than 43 years of age. FPRP analysis showed that most of positive results are noteworthy findings. Three loci model composed of rs2139049, rs2164068, and rs2228135 is the best model for predicting AR risk (p = 0.0022). In addition, the haplotype "G_rs2139049A_rs6738825A_rs2164068A_rs2228135" (OR = 0.50, p = 0.033) can reduce the AR risk.

Conclusion

Allele "A" of PLCL1-rs2139049, allele "A" of -rs212164068, and allele "G" of PLCL1-rs6738825 are protective factors of AR in Han population from northern Shaanxi, China.

Low-energy shock waves evoke intracellular Ca2+ increases independently of sonoporation

Low-energy shock waves (LESWs) accelerate the healing of a broad range of tissue injuries, including angiogenesis and bone fractures. In cells, LESW irradiations enhance gene expression and protein synthesis. One probable mechanism underlying the enhancements is mechanosensing. Shock waves also can induce sonoporation. Thus, sonoporation is another probable mechanism underlying the enhancements. It remains elusive whether LESWs require sonoporation to evoke cellular responses. An intracellular Ca²⁺ increase was evoked with LESW irradiations in endothelial cells. The minimum acoustic energy required for sufficient evocation was 1.7 μJ/mm². With the same acoustic energy, sonoporation, by which calcein and propidium iodide would become permeated, was not observed. It was found that intracellular Ca²⁺ increases evoked by LESW irradiations do not require sonoporation. In the intracellular Ca²⁺ increase, actin cytoskeletons and stretch-activated Ca²⁺ channels were involved; however, microtubules were not. In addition, with Ca²⁺ influx through the Ca²⁺ channels, the Ca²⁺ release through the PLC-IP₃-IP₃R cascade contributed to the intracellular Ca²⁺ increase. These results demonstrate that LESW irradiations can evoke cellular responses independently of sonoporation. Rather, LESW irradiations evoke cellular responses through mechanosensing.

Three-dimensional model of intracellular and intercellular Ca2+ waves propagation in endothelial cells

Intracellular and intercellular Ca²⁺ waves play key roles in cellular functions, and focal stimulation triggers Ca²⁺ wave propagation from stimulation points to neighboring cells, involving localized metabolism reactions and specific diffusion processes. Among these, inositol 1,4,5-trisphosphate (IP₃) is produced at membranes and diffuses into the cytoplasm to release Ca²⁺ from endoplasmic reticulum (ER). In this study, we developed a three-dimensional (3D) simulation model for intercellular and intracellular Ca²⁺ waves in endothelial cells (ECs). 3D model of 2 cells was reconstructed from confocal microscopic images and was connected via gap junctions. Cells have membrane and cytoplasm domains, and metabolic reactions were divided into each domain. Finally, the intracellular and intercellular Ca²⁺ wave propagations were induced using microscopic stimulation and were compared between numerical simulations and experiments. The experiments showed that initial sharp increases in intracellular Ca²⁺ occurred approximately 0.3 s after application of stimuli. In addition, Ca²⁺ wave speeds remained constant in cells, with intracellular and intercellular speeds of approximately 35 and 15 μm/s, respectively. Simulations indicated initial increases in Ca²⁺ concentrations at points of stimulation, and these were then propagated across stimulated and neighboring cells. In particular, initial rapid increases in intracellular Ca²⁺ were delayed and subsequent intracellular and intercellular Ca²⁺ wave speeds were approximately 25 and 12 μm/s, respectively. Simulation results were in agreement with those from cell culture experiments, indicating the utility of our 3D model for investigations of intracellular and intercellular messaging in ECs.

Involvement of plasma membrane Ca2+ channels, IP3 receptors, and ryanodine receptors in the generation of spontaneous rhythmic contractions of the cricket lateral oviduct

In the present study, the isolated cricket (Gryllus bimaculatus) lateral oviduct exhibited spontaneous rhythmic contractions (SRCs) with a frequency of 0.29±0.009 Hz (n=43) and an amplitude of 14.6±1.25 mg (n=29). SRCs completely disappeared following removal of extracellular Ca2+ using a solution containing 5mM EGTA. Application of the non-specific Ca2+ channel blockers Co2+, Ni2+, and Cd2+ also decreased both the frequency and amplitude of SRCs in dose-dependent manners, suggesting that Ca2+ entry through plasma membrane Ca2+ channels is essential for the generation of SRCs. Application of ryanodine (30 μM), which depletes intracellular Ca2+ by locking ryanodine receptor (RyR)-Ca2+ channels in an open state, gradually reduced the frequency and amplitude of SRCs. A RyR antagonist, tetracaine, reduced both the frequency and amplitude of SRCs, whereas a RyR activator, caffeine, increased the frequency of SRCs with a subsequent increase in basal tonus, indicating that RyRs are essential for generating SRCs. To further investigate the involvement of phospholipase C (PLC) and inositol 1,4,5-trisphosphate receptors (IP3Rs) in SRCs, we examined the effect of a PLC inhibitor, U73122, and an IP3R antagonist, 2-aminoethoxydiphenyl borate (2-APB), on SRCs. Separately, U73122 (10 μM) and 2-APB (30-50 μM) both significantly reduced the amplitude of SRCs with little effect on their frequency, further indicating that the PLC/IP3R signaling pathway is fundamental to the modulation of the amplitude of SRCs. A hypotonic-induced increase in the frequency and amplitude of SRCs and a hypertonic-induced decrease in the frequency and amplitude of SRCs indicated that mechanical stretch of the lateral oviduct is involved in the generation of SRCs. The sarcoplasmic reticulum Ca2+-pump ATPase inhibitors thapsigargin and cyclopiazonic acid impaired or suppressed the relaxation phase of SRCs. Taken together, the present results indicate that Ca2+ influx through plasma membrane Ca2+ channels and Ca2+ release from RyRs play an essential role in pacing SRCs and that Ca2+ release from IP3Rs may play a role in modulating the amplitude of SRCs, probably via activation of PLC.

Cx43-hemichannel function and regulation in physiology and pathophysiology: insights from the bovine corneal endothelial cell system and beyond

Intercellular communication in primary bovine corneal endothelial cells (BCECs) is mainly driven by the release of extracellular ATP through Cx43 hemichannels. Studying the characteristics of Ca²⁺-wave propagation in BCECs, an important form of intercellular communication, in response to physiological signaling events has led to the discovery of important insights in the functional properties and regulation of native Cx43 hemichannels. Together with ectopic expression models for Cx43 hemichannels and truncated/mutated Cx43 versions, it became very clear that loop/tail interactions play a key role in controlling the activity of Cx43 hemichannels. Interestingly, the negative regulation of Cx43 hemichannels by enhanced actin/myosin contractility seems to impinge upon loss of these loop/tail interactions essential for opening Cx43 hemichannels. Finally, these molecular insights have spurred the development of novel peptide tools that can selectively inhibit Cx43 hemichannels, but neither Cx43 gap junctions nor hemichannels formed by other Cx isoforms. These tools now set the stage to hunt for novel physiological functions for Cx43 hemichannels in primary cells and tissues and to tackle disease conditions associated with excessive, pathological Cx43-hemichannel openings.