Role Of Mechanosensitive Ion Channels Research Articles

Abstract B041: Investigating the impact of extracellular matrix stiffness on macrophage function and organoid growth in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDAC) has a 5-year survival rate of only 11%. Current treatments mostly target the cancer cells themselves and have not been able to significantly improve survival rates, meaning there is an urgent need for novel therapies. PDAC is unique among solid tumors because it exhibits extensive desmoplasia that is characterized by an abundance of extracellular matrix (ECM) components. In recent years, an increasing body of work has shown that cancer tissue is stiffer than normal tissue by a factor of 3 or more. This increase in ECM stiffness has been shown to play an important role in affecting cell-to-cell communication as well as cancer progression and chemoresistance . However, how ECM stiffness affects tumor-associated macrophages, an important component of the pancreatic tumor microenvironment (TME), is still understudied. Previous studies have demonstrated that macrophages are highly responsive to mechanical cues, with the mechanical environment influencing macrophage polarization and function in a context- and disease-dependent manner. Elucidating these potential changes in PDAC can provide us with insights on how stiffness affects therapeutic outcome. Healthy pancreatic tissue typically exhibits a storage modulus of approximately 0.5-1 kPa, whereas PDAC tissue can range from 4-10 kPa. To study macrophage responses to varying stiffness, we cultured RAW264.7 mouse macrophage cell lines on 2D substrates with stiffness levels of 0.2, 2, and 8 kPa. We observed that macrophages cultured on stiffer matrices exhibited a trend toward a pro-inflammatory phenotype, with increased expression of M1 markers such as iNOS, IL-1β, and IL-6, compared to those cultured on softer matrices. However, conditioned media from macrophages cultured on both soft and stiff substrates similarly reduced the size of PDAC organoids, indicating a lack of functional difference between these groups. These findings suggest the need for more sophisticated models that better replicate the PDAC TME to fully capture the complex cell-to-cell interactions that are not evident in 2D cultures. To address this limitation, we developed a 3D tri-culture tunable biomimetic mouse model comprising PDAC organoids, host-matched cancer-associated fibroblasts (CAFs), and macrophages. This novel model allows us to modulate the stiffness of the 3D co-culture system through the addition of collagen I and CAFs. Rheometry data confirmed that the stiff tri-culture model had a significantly higher storage modulus than the soft tri-culture model. Using qPCR, we investigated the role of mechanosensitive ion channels, specifically Transient Receptor Potential Vanilloid-type 4 (TRPV4) and Piezo1, in mediating macrophage mechanosensing in response to varying levels of matrix stiffness. This study highlights the importance of 3D models that can recapitulate biophysical cues of cancer and will allow us to better understand how macrophages respond to stiffness, which may give rise to new therapeutic targets and development of new treatments in the future. Citation Format: Bayan Mahgoub, Weikun Xiao, Eileen Fung, Shannon Mumenthaler, Reginald Hill. Investigating the impact of extracellular matrix stiffness on macrophage function and organoid growth in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr B041.

The Effects of Airflow on the Mechanosensitive Channels of Escherichia coli MG1655 and the Impact of Survival Mechanisms Triggered.

Understanding how bacteria respond to ventilated environments is a crucial concept, especially when considering accurate airflow modeling and detection limits. To properly design facilities for aseptic conditions, we must minimize the parameters for pathogenic bacteria to thrive. Identifying how pathogenic bacteria continue to survive, particularly due to their multi-drug resistance characteristics, is necessary for designing sterile environments and minimizing pathogen exposure. A conserved characteristic among bacterial organisms is their ability to maintain intracellular homeostasis for survival and growth in hostile environments. Mechanosensitive (MS) channels are one of the characteristics that guide this phenomenon. Interestingly, during extreme stress, bacteria will forgo favorable homeostasis to execute fast-acting survival strategies. Physiological sensors, such as MS channels, that trigger this survival mechanism are not clearly understood, leaving a gap in how bacteria translate physical stress to an intracellular response. In this paper, we study the role of mechanosensitive ion channels that are potentially triggered by aerosolization. We hypothesize that change in antimicrobial uptake is affected by aerosolization stress. Bacteria regulate their defense mechanisms against antimicrobials, which leads to varying susceptibility. Based on this information we hypothesize that aerosolization stress affects the antimicrobial resistance defense mechanisms of Escherichia coli (E. coli). We analyzed the culturability of knockout E. coli strains with different numbers of mechanosensitive channels and compared antibiotic susceptibility under stressed and unstressed airflow conditions. As a result of this study, we can identify how the defensive mechanisms of resistant bacteria are triggered for their survival in built environments. By changing ventilation airflow velocity and observing the change in antibiotic responses, we show how pathogenic bacteria respond to ventilated environments via mechanosensitive ion channels.

Membrane stretch due to hypoosmolality leads to the development of various pulmonary and cardiovascular diseases

High blood pressures over a long period of time can lead to the development of diseases such as congestive heart failure(CHF). Congestive heart failure also commonly leads to the development of conditions such as hyponatremia, a common electrolyte disorder which increases the body’s water levels, creating hypoosmotic conditions for cells; these hypoosmotic conditions cause cell swelling, which subsequently causes mechanical stress on the cells. In these hypoosmotic environments, specific mechanosensitive ion channels which are activated by these mechanical stresses on cells may play a critical role in the progression of conditions resulting from these hypoosmotic environments, such as pulmonary arterial hypertension (PAH) and CHF. This study aims to look at the connection between the effects of hypoosmotic conditions in cells on the pathogenesis of the development of chronic diseases such as PAH and CHF. Mechanical actions on specific mechanosensitive ion channels such as Piezo1 have already been shown to play a critical role in regulating intracellular Ca2+homeostasis, which play an important part in the regulation of the vascular tone in places such as the pulmonary arteries; mechanical stimulation from hypotonic environments such as those seen in hyponatremia lead to Piezo1-mediated increases of intracellular Ca2+, which are subsequently linked to the increased contraction and proliferation of pulmonary arterial endothelial cells(PAECs). The proliferation of PAECs contribute to the pathogenesis of diseases, such as pulmonary arterial hypertension(PAH) or CHF, which there is currently no cure for. Patch-clamp experiments were conducted to examine the activity of mechanosensitive cation currents; graphed results showed that the activity of mechanosensitive cation currents were significantly increased (p<0.05) in PAECs treated with a hypoosmotic solution when compared with PAECs treated in an isosmotic control solution. Digital fluorescence microscopy using fura-2 AM, a membrane-permeable Ca2+ sensitive fluorescent indicator, and a Nikon digital imaging fluorescent microscopy system was also used to measure intracellular Ca2+ concentration in PAECs; graphed data indicated that the change in intracellular calcium concentration in PAECs was significantly increased(p<0.05) when placed in a hypoosmotic solution, than when placed in an isosmotic solution. The collective data indicates that hypoosmotic conditions increase the activity of mechanosensitive ion channels, as well as intracellular Ca2+ levels, which may prove the role of mechanosensitive ion channels like Piezo1 and TRPC6 in the development of diseases such as PAH and CHF. This work is supported in part by the National Heart, Lung, and Blood Institute of the National Institutes of Health Grants HL135807 and HL146764. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Piezo1 Mechano-Activation Is Augmented by Resveratrol and Differs between Colorectal Cancer Cells of Primary and Metastatic Origin.

Cancer cells must survive aberrant fluid shear stress (FSS) in the circulation to metastasize. Herein, we investigate the role that FSS has on colorectal cancer cell apoptosis, proliferation, membrane damage, calcium influx, and therapeutic sensitization. We tested this using SW480 (primary tumor) and SW620 cells (lymph node metastasis) derived from the same patient. The cells were exposed to either shear pulses, modeling millisecond intervals of high FSS seen in regions of turbulent flow, or sustained shear to model average magnitudes experienced by circulating tumor cells. SW480 cells were significantly more sensitive to FSS-induced death than their metastatic counterparts. Shear pulses caused significant cell membrane damage, while constant shear decreased cell proliferation and increased the expression of CD133. To investigate the role of mechanosensitive ion channels, we treated cells with the Piezo1 agonist Yoda1, which increased intracellular calcium. Pretreatment with resveratrol further increased the calcium influx via the lipid-raft colocalization of Piezo1. However, minimal changes in apoptosis were observed due to calcium saturation, as predicted via a computational model of apoptosis. Furthermore, SW480 cells had increased levels of Piezo1, calcium influx, and TRAIL-mediated apoptosis compared to SW620 cells, highlighting differences in the mechano-activation of metastatic cells, which may be a necessary element for successful dissemination in vivo.

The role of mechanosensitive ion channels in the gastrointestinal tract.

Mechanosensation is essential for normal gastrointestinal (GI) function, and abnormalities in mechanosensation are associated with GI disorders. There are several mechanosensitive ion channels in the GI tract, namely transient receptor potential (TRP) channels, Piezo channels, two-pore domain potassium (K2p) channels, voltage-gated ion channels, large-conductance Ca2+-activated K+ (BKCa) channels, and the cystic fibrosis transmembrane conductance regulator (CFTR). These channels are located in many mechanosensitive intestinal cell types, namely enterochromaffin (EC) cells, interstitial cells of Cajal (ICCs), smooth muscle cells (SMCs), and intrinsic and extrinsic enteric neurons. In these cells, mechanosensitive ion channels can alter transmembrane ion currents in response to mechanical forces, through a process known as mechanoelectrical coupling. Furthermore, mechanosensitive ion channels are often associated with a variety of GI tract disorders, including irritable bowel syndrome (IBS) and GI tumors. Mechanosensitive ion channels could therefore provide a new perspective for the treatment of GI diseases. This review aims to highlight recent research advances regarding the function of mechanosensitive ion channels in the GI tract. Moreover, it outlines the potential role of mechanosensitive ion channels in related diseases, while describing the current understanding of interactions between the GI tract and mechanosensitive ion channels.

Piezo channels contribute to the regulation of myelination in Schwann cells.

Peripheral nerves and Schwann cells have to sustain constant mechanical constraints, caused by developmental growth as well as stretches associated with movements of the limbs and mechanical compressions from daily activities. In Schwann cells, signaling molecules sensitive to stiffness or stretch of the extracellular matrix, such as YAP/TAZ, have been shown to be critical for Schwann cell development and peripheral nerve regeneration. YAP/TAZ have also been suggested to contribute to tumorigenesis, neuropathic pain, and inherited disorders. Yet, the role of mechanosensitive ion channels in myelinating Schwann cells is vastly unexplored. Here we comprehensively assessed the expression of mechanosensitive ion channels in Schwann cells and identified that PIEZO1 and PIEZO2 are among the most abundant mechanosensitive ion channels expressed by Schwann cells. Using classic genetic ablation studies, we show that PIEZO1 is a transient inhibitor of radial and longitudinal myelination in Schwann cells. Contrastingly, we show that PIEZO2 may be required for myelin formation, as the absence of PIEZO2 in Schwann cells delays myelin formation. We found an epistatic relationship between PIEZO1 and PIEZO2, at both the morphological and molecular levels. Finally, we show that PIEZO1 channels affect the regulation of YAP/TAZ activation in Schwann cells. Overall, we present here the first demonstration that PIEZO1 and PIEZO2 contribute to mechanosensation in Schwann cells as well myelin development in the peripheral nervous system.

206 The Role of Mechanosensitive Ion Channels in Primary Open Angle Glaucoma

OBJECTIVES/GOALS: Intraocular pressure is the most significant risk factor for glaucoma. Mechanosensitive proteins may have a critical role in transducing mechanical stimuli that ultimately lead to death of retinal ganglion cells. Our goal is to use genetic and functional approaches to discover mechanosensitive ion channels that mediate the progression of glaucoma. METHODS/STUDY POPULATION: Association data, obtained using a logistic regression model that included age, gender and population substructure as co-variates, for 2,576 SNPs located in the PIEZO1 and PIEZO2 genomic regions were extracted from the NEIGHBORHOOD genome-wide association study results for primary open angle glaucoma (POAG) (3,853 cases and 33,480 controls) and the subset of cases with intraocular pressure (IOP) measurements > 21mmHg (high-tension, HTG) (1868 cases and 33,480 controls). Rare coding PIEZO1 and PIEZO2 variants were evaluated using logistic regression and SNP data from the Human Exome array in 2606 POAG cases and 2606 controls and the subset of 1868 HTG cases and 2606 controls. Immunohistochemistry was used to characterize the expression of Piezo1 and Piezo2 in mouse eye sections. RESULTS/ANTICIPATED RESULTS: Exome data analysis identified two protein-altering variants associated with lower glaucoma risk (P<0.05): a PIEZO1 missense allele (Arg1527His; OR= 0.18, P= 0.001) and a variant disrupting a splice donor site (c.1107+1G>C; OR=0.38, P= 0.02), that prematurely truncates the protein. Investigation of the NEIGHBORHOOD GWAS dataset identified nominal association with common PIEZO2 variants (minor allele frequency > 0.3) in POAG overall (top SNP rs264179, P= 0.008) and in the HTG subgroup (top SNP rs264160, P= 0.001). The associated PIEZO2 SNPs are significantly associated with gene expression in lymphocytes (P< 1x10-8) with the risk allele correlated with decreased gene expression. Piezo1 and Piezo2 are expressed in many ocular tissues in the mouse, including cornea, ciliary body and retina. DISCUSSION/SIGNIFICANCE: We identify rare, protein-altering PIEZO1 variants associated with lower glaucoma risk and show that Piezo1 and Piezo2 are broadly expressed in the eye. Common variants influencing PIEZO2 expression also show nominal association with POAG risk. Inhibition of Piezo1 or augmentation of Piezo2 could be novel therapeutic strategies for glaucoma.

The potential role of mechanosensitive ion channels in substrate stiffness-regulated Ca2+ response in chondrocytes

ABSTRACT Purpose The stiffness of the pericellular matrix (PCM) decreases in the most common degenerative joint disease, osteoarthritis (OA). This study was undertaken to explore the potential functional role of transient receptor potential vanilloid 4 (TRPV4), Piezo1, and Piezo2 in transducing different PCM stiffness in chondrocytes. Methods and Results Polydimethylsiloxane (PDMS) substrates with different stiffness (designated 197 kPa, 78 kPa, 54 kPa, or 2 kPa, respectively) were first prepared to simulate the decrease in stiffness of the PCM that chondrocytes encounter in osteoarthritic cartilage. Next, the TRPV4-, Piezo1-, or Piezo2-knockdown primary chondrocytes (designated TRPV4-KD, Piezo1-KD, or Piezo2-KD cells) were seeded onto these different PDMS substrates. Then, using a Ca2+-imaging system, substrate stiffness-regulated intracellular Ca2+ influx ([Ca2+] i ) in chondrocytes was examined to investigate the role of TRPV4, Piezo1, and Piezo2 in Ca2+ signaling in response to different stiffness. Results showed that the characteristics of intracellular [Ca2+] i in chondrocytes regulated by PDMS substrate exhibited stiffness-dependent differences. Additionally, stiffness-evoked [Ca2+] i changes were suppressed in TRPV4-KD, Piezo1-KD, or Piezo2-KD cells compared with control siRNA-treated cells, implying that any channel is fundamental for Ca2+ signaling induced by substrate stiffness. Furthermore, TRPV4-mediated Ca2+ signaling played a central role in the response of chondrocytes to 197 kPa and 78 kPa substrate, while Piezo1/2-mediated Ca2+ signaling played a central role in the response of chondrocytes to 54 kPa and 2 kPa substrate. Conclusions Collectively, these findings indicate that chondrocytes might perceive and distinguish the different PCM stiffness by using different mechanosensitive ion channels.

Stretching the Function of Innate Immune Cells.

The importance of innate immune cells to sense and respond to their physical environment is becoming increasingly recognized. Innate immune cells (e.g. macrophages and neutrophils) are able to receive mechanical signals through several mechanisms. In this review, we discuss the role of mechanosensitive ion channels, such as Piezo1 and transient receptor potential vanilloid 4 (TRPV4), and cell adhesion molecules, such as integrins, selectins, and cadherins in biology and human disease. Furthermore, we explain that these mechanical stimuli activate intracellular signaling pathways, such as MAPK (p38, JNK), YAP/TAZ, EDN1, NF-kB, and HIF-1α, to induce protein conformation changes and modulate gene expression to drive cellular function. Understanding the mechanisms by which immune cells interpret mechanosensitive information presents potential targets to treat human disease. Important areas of future study in this area include autoimmune, allergic, infectious, and malignant conditions.

Mechanosensitive ion channels contribute to mechanically evoked rapid leaflet movement in Mimosa pudica.

Mechanoperception, the ability to perceive and respond to mechanical stimuli, is a common and fundamental property of all forms of life. Vascular plants such as Mimosa pudica use this function to protect themselves against herbivory. The mechanical stimulus caused by a landing insect triggers a rapid closing of the leaflets that drives the potential pest away. While this thigmonastic movement is caused by ion fluxes accompanied by a rapid change of volume in the pulvini, the mechanism responsible for the detection of the mechanical stimulus remains poorly understood. Here, we examined the role of mechanosensitive ion channels in the first step of this evolutionarily conserved defense mechanism: the mechanically evoked closing of the leaflet. Our results demonstrate that the key site of mechanosensation in the Mimosa leaflets is the pulvinule, which expresses a stretch-activated chloride-permeable mechanosensitive ion channel. Blocking these channels partially prevents the closure of the leaflets following mechanical stimulation. These results demonstrate a direct relation between the activity of mechanosensitive ion channels and a central defense mechanism of M. pudica.

Biomechanical micromotion at the neural interface modulates intracellular membrane potentials in vivo

Objective. Respiration and vascular pulsation cause relative micromotion of brain tissue against stationary implants resulting in repetitive displacements of 2–4 µm (due to vascular pulsation) and 10–30 µm (due to breathing) in rats. However, the direct functional impact of such tissue micromotion on the cells at the neural interface remains unknown. This study aims to test the hypothesis that micromotion in brain tissue causes changes in membrane potentials (MPs) through the activation of mechanosensitive ion channels. Approach. Intracellular MPs were recorded from Aplysia ganglion cells (n = 8) and cortical cells (n = 15) in vivo in n = 7 adult rats. Cyclic stresses between 0.2 and 4 kPa repeated at 1 Hz were tested in Aplysia ganglion cells. For the in vivo experiments, 30 μM of gadolinium chloride (Gd3+), a non-selective blocker of mechanosensitive ion channels, was used to assess the role of such ion channels. Main results. In Aplysia ganglion cells, there were no MP changes for <1.5 kPa, and action potentials were observed at >3.1 kPa. Drug studies utilizing 5-HT showed an 80% reduction in firing frequency from controls. In in vivo experiments, periodic pulsations (1–10 mV) were observed in the MPs of cells that corresponded to breathing and heart-rate. In response to the addition of 30 µM Gd3+, we observed a significant reduction (0.5–3 mV) in the periodic pulsations in MP in all cortical cells across four different rats, suggesting the role of mechanosensitive ion channels in mediating MP fluctuations due to tissue micromotion at the neural interface. Significance. Under chronic conditions, the tissue at the interface stiffens due to scar tissue formation, which is expected to increase the likelihood of recruiting stretch-receptors due to tissue micromotion. It is speculated that such chronic sub-threshold pulsations in MPs might trigger the immune response at the neural interface.

Channelling the Force to Reprogram the Matrix: Mechanosensitive Ion Channels in Cardiac Fibroblasts.

Cardiac fibroblasts (CF) play a pivotal role in preserving myocardial function and integrity of the heart tissue after injury, but also contribute to future susceptibility to heart failure. CF sense changes to the cardiac environment through chemical and mechanical cues that trigger changes in cellular function. In recent years, mechanosensitive ion channels have been implicated as key modulators of a range of CF functions that are important to fibrotic cardiac remodelling, including cell proliferation, myofibroblast differentiation, extracellular matrix turnover and paracrine signalling. To date, seven mechanosensitive ion channels are known to be functional in CF: the cation non-selective channels TRPC6, TRPM7, TRPV1, TRPV4 and Piezo1, and the potassium-selective channels TREK-1 and KATP. This review will outline current knowledge of these mechanosensitive ion channels in CF, discuss evidence of the mechanosensitivity of each channel, and detail the role that each channel plays in cardiac remodelling. By better understanding the role of mechanosensitive ion channels in CF, it is hoped that therapies may be developed for reducing pathological cardiac remodelling.

Mechanotransduction in gastrointestinal smooth muscle cells: role of mechanosensitive ion channels.

Mechanosensation, the ability to properly sense mechanical stimuli and transduce them into physiologic responses, is an essential determinant of gastrointestinal (GI) function. Abnormalities in this process result in highly prevalent GI functional and motility disorders. In the GI tract, several cell types sense mechanical forces and transduce them into electrical signals, which elicit specific cellular responses. Some mechanosensitive cells like sensory neurons act as specialized mechanosensitive cells that detect forces and transduce signals into tissue-level physiological reactions. Nonspecialized mechanosensitive cells like smooth muscle cells (SMCs) adjust their function in response to forces. Mechanosensitive cells use various mechanoreceptors and mechanotransducers. Mechanoreceptors detect and convert force into electrical and biochemical signals, and mechanotransducers amplify and direct mechanoreceptor responses. Mechanoreceptors and mechanotransducers include ion channels, specialized cytoskeletal proteins, cell junction molecules, and G protein-coupled receptors. SMCs are particularly important due to their role as final effectors for motor function. Myogenic reflex-the ability of smooth muscle to contract in response to stretch rapidly-is a critical smooth muscle function. Such rapid mechanotransduction responses rely on mechano-gated and mechanosensitive ion channels, which alter their ion pores' opening in response to force, allowing fast electrical and Ca2+ responses. Although GI SMCs express a variety of such ion channels, their identities remain unknown. Recent advancements in electrophysiological, genetic, in vivo imaging, and multi-omic technologies broaden our understanding of how SMC mechano-gated and mechanosensitive ion channels regulate GI functions. This review discusses GI SMC mechanosensitivity's current developments with a particular emphasis on mechano-gated and mechanosensitive ion channels.

Role of Mechanosensitive Ion Channels in Focused Ultrasound Based Neuromodulation for Pain

Role of Mechanosensitive Ion Channels in Focused Ultrasound Based Neuromodulation for Pain

Role of mechanosensitive ion channels in the sensation of pain.

Our ability to sense mechanical cues from our environment depend on the capacity of molecular sensor capable of converting mechanical energy into biochemical or electrical signals. This process, termed mechanotransduction, relies on the activity of mechanosensitive ion channels (MSCs) that are expressed in most tissues, including cells of the inner and outer ear, sensory and sympathetic neurons, and vascular cells. However, the precise role these channels play in the physiology of the cells and organs, where they are expressed is not completely understood. In this review, we will explore some of the recent findings on the role of MSCs to our sense of mechanical pain.

Role of mechanosensitive ion channels in skeletal muscle regeneration

Role of mechanosensitive ion channels in skeletal muscle regeneration

029 - The role of mechanosensitive ion channels during zebrafish heart development and regeneration

029 - The role of mechanosensitive ion channels during zebrafish heart development and regeneration

The race to the nociceptor: mechanical versus temperature effects in thermal pain of dental neurons

The sensing of hot and cold stimuli by dental neurons differs in several fundamental ways. These sensations have been characterized quantitatively through the measured time course of neural discharge signals that result from hot or cold stimuli applied to the teeth of animal models. Although various hypotheses have been proposed to explain the underlying mechanism, the ability to test competing hypotheses against experimental recorded data using biophysical models has been hindered by limitations in our understanding of the specific ion channels involved in nociception of dental neurons. Here we apply recent advances in established biophysical models to test the competing hypotheses. We show that a sharp shooting pain sensation experienced shortly following cold stimulation cannot be attributed to the activation of thermosensitive ion channels, thereby falsifying the so-called neuronal hypothesis, which states that rapidly transduced sensations of coldness are related to thermosensitive ion channels. Our results support a central role of mechanosensitive ion channels and the associated hydrodynamic hypothesis. In addition to the hydrodynamic hypothesis, we also demonstrate that the long time delay of dental neuron responses after hot stimulation could be attributed to the neuronal hypothesis—that a relatively long time is required for the temperature around nociceptors to reach some threshold. The results are useful as a model of how multiphysical phenomena can be combined to provide mechanistic insight into different mechanisms underlying pain sensations.

Induction of Calcium Influx in Cortical Neural Networks by Nanomagnetic Forces.

Nanomagnetic force stimulation with ferromagnetic nanoparticles was found to trigger calcium influx in cortical neural networks without observable cytotoxicity. Stimulated neural networks showed an average of 20% increment in calcium fluorescence signals and a heightened frequency in calcium spiking. These effects were also confined spatially to areas with engineered high magnetic field gradients. Furthermore, blockage of N-type calcium channels inhibited the stimulatory effects of the nanomagnetic forces, suggesting the role of mechano-sensitive ion channels in mediating calcium influx.

Role of BKCain Stretch-Induced Relaxation of Colonic Smooth Muscle

Stretch-induced relaxation has not been clearly identified in gastrointestinal tract. The present study is to explore the role of large conductance calcium-activated potassium channels (BKCa) in stretch-induced relaxation of colon. The expression and currents of BKCa were detected and the basal muscle tone and contraction amplitude of colonic smooth muscle strips were measured. The expression of BKCa in colon is higher than other GI segments (P < 0.05). The density of BKCa currents was very high in colonic smooth muscle cells (SMCs). BKCa in rat colonic SMCs were sensitive to stretch. The relaxation response of colonic SM strips to stretch was attenuated by charybdotoxin (ChTX), a nonspecific BKCa blocker (P < 0.05). After blocking enteric nervous activities by tetrodotoxin (TTX), the stretch-induced relaxation did not change (P > 0.05). Still, ChTX and iberiotoxin (IbTX, a specific BKCa blocker) attenuated the relaxation of the colonic muscle strips enduring stretch (P < 0.05). These results suggest stretch-activation of BKCa in SMCs was involved in the stretch-induced relaxation of colon. Our study highlights the role of mechanosensitive ion channels in SMCs in colon motility regulation and their physiological and pathophysiological significance is worth further study.