Smooth muscle relaxation after contraction is thought to reflect “latch-like” slow cycling bridge formation and deformation. However, how actin-myosin interaction contributes to the transfer from fast-cycling cross bridges to slow-cycling bridges is still unclear. The thiadiazinone compound EMD57033 is known to bind to an allosteric pocket in the myosin motor domain and to increase basal and actin-activated myosin ATPase activity and contractile force in striated muscles. Therefore, we investigated whether EMD57033 affected the relaxation process after Ca²⁺ removal by affecting slow cycling bridge formation and/or deformation in β-escin skinned (cell membrane-permeabilized) carotid artery and taenia cecum from guinea pigs. EMD57033 at ≥30 µM decreased the force decay during relaxation in both the skinned carotid artery and taenia cecum, irrespective of the presence of ATP. A kinetic analysis in the present study indicated that EMD57033 significantly prolonged τslow-detach, a time constant of detachment of the slow cycling bridge, in both the skinned carotid artery and taenia cecum, irrespective of the presence of nucleoside triphosphates (ATP or ITP). Further studies are necessary to elucidate how EMD57033 modulates the smooth muscle myosin (SMM) structure, SMM activity, and thick filament organization, affecting slow cycling bridge formation and deformation, although EMD57033 might change slow cycling bridge formation, resulting in both cycling rate modulation and an increase in the affinity of SMM to actin.

A number of factors have been recently associated with the development of disorders of gut-brain interaction (DGBI), including genetic predisposition, early-life environment, intestinal microbiota, infection, microinflammation, and increased mucosal permeability. In addition, impaired gastrointestinal motility is important not only as a cause of DGBI but also as a consequent final phenotype. Gastrointestinal motor measurements are the predominant method for the assessment of and therapeutic intervention into motor abnormalities. As such, these measurements should be considered for DGBI patients who do not respond to first-line approaches such as behavioral therapy, dietary modifications, and pharmacotherapy. This comprehensive review focuses on the functional changes in the upper gastrointestinal tract caused by DGBI and describes ongoing attempts to develop imaging modalities to assess these dysfunctions in the esophageal and gastric regions. Recent advances in imaging techniques could help elucidate the pathophysiology of DGBI, with exciting potential for research and clinical practice.

Distal gastrectomy is the most frequently performed procedure for gastric cancer. Gastric emptying after distal gastrectomy is generally considered to be accelerated due to resection of the antrum, pylorus, and duodenal bulb. Food residue, however, is frequently observed in the gastric remnant in patients after distal gastrectomy at the time of endoscopy after routine overnight fasting. This observation suggests delayed gastric emptying and conflicts with the general understanding of accelerated gastric emptying after distal gastrectomy. We searched for reports that evaluated the separate gastric emptying of liquids and solids with scintigraphy after distal gastrectomy in humans and also addressed the physiologic changes in gastric emptying after distal gastrectomy. Most all reports showed that gastric emptying of liquids after distal gastrectomy was accelerated compared to healthy controls, especially immediately after feeding. In contrast, some gastric emptying of solids was accelerated early after the meal ingestion, but thereafter emptying of solids remaining in the stomach was delayed beginning about 60 min after the meal in patients after distal gastrectomy. This delayed solid gastric emptying after distal gastrectomy was considered associated with food residue in the remnant stomach. We conclude that gastric emptying after distal gastrectomy was accelerated for liquids and solids soon after the meal ingestion but delayed for solids later than 60 min after the meal ingestion.

Histamine is a well-known mediator of bronchoconstriction. Despite the widespread use of histamine as a tool to study the bronchial smooth muscle function, the precise mechanism by which it causes calcium mobilization in bronchial smooth muscle cells remains unclear. Therefore, the current study aimed to investigate the mechanism of action of histamine in calcium mobilization in cultured human bronchial smooth muscle cells. A series of in vitro calcium imaging experiments have shown that histamine increases intracellular calcium levels in a concentration-dependent manner. The half maximum concentration of cytosolic Ca²⁺ peak was 3.00 ± 0.25 µM of histamine. Histamine was able to mobilize calcium from intracellular stores, even in the absence of extracellular calcium. These histamine-induced calcium elevations were completely blocked by the H₁ receptor antagonist chlorpheniramine (1 µM). Histamine-induced calcium elevation was also completely inhibited by the phospholipase C (PLC) inhibitor U73122 (1 µM) and inositol 1,4,5-trisphosphate (InsP₃) receptor inhibitor caffeine (20 mM). Cyanide p-(trifluoromethoxy)phenylhydrazone (1 µM) and oligomycin (1 µg/ml) effectively attenuated histamine-induced calcium release from intracellular stores. In the presence of histamine, cytosolic calcium elevation induced by reperfusion of 1.28 mM extracellular calcium after the depletion of stores was significantly inhibited by FCCP and oligomycin, unlike in the presence of thapsigargin. Based on the above results, we can conclude that histamine activates the intracellular PLC/InP₃ pathway through the H₁ receptor, which in turn activates the InP₃ receptor present in intracellular stores to mobilize calcium in human bronchial smooth muscle cells. In addition, the mitochondria appear to be involved in the release of calcium from intracellular stores. These results provide insights into the mechanisms underlying histamine-induced calcium mobilization for bronchoconstriction under pathophysiological conditions.

Aging is linked to a gradual decline in the gastric motor function, contributing to reduced food intake, and its association with frailty and sarcopenia. A key cellular change in the gastric neuromuscular apparatus is the loss of interstitial cells of Cajal (ICC), pacemaker cells of the gut. The ICC function as pacemakers that generate electrical slow waves and mediate enteric neurotransmission, playing a critical role in gastric motility. Aging-related ICC depletion leads to impaired gastric compliance and reduced slow wave activity, which contributes to early satiety and reduced food intake. Recent studies have elucidated the molecular and epigenetic mechanisms underlying aging-related ICC decline, highlighting the roles of ICC stem/precursor cells (ICC-SCs), transformation-related protein 53 (TRP53), extracellular signal-regulated kinase (ERK), and insulin-like growth factor 1 (IGF1) pathways, and epigenetic regulation mediated by the histone methyltransferase enhancer of zeste 2 (EZH2). By synthesizing the current findings, this review aims to provide a comprehensive understanding of the mechanisms driving ICC decline and to explore potential therapeutic strategies for preserving gastric motility in aging populations. Future research should aim to translate these discoveries into clinical applications to improve the gastric motor function and overall health in the aging population. Identifying effective interventions targeting ICC maintenance may ultimately help to alleviate age-related gastric motor dysfunction and its associated health burdens, including frailty, malnutrition, and impaired quality of life.

The relationship between gut microbiota and intestinal motility is crucial for maintaining gastrointestinal health. Intestinal motility refers to the coordinated movements of the digestive tract, essential for effective digestion, nutrient absorption, and timely waste elimination. Recent studies have demonstrated that microbiota play a crucial role not only in the maturation of intestinal motility but also in the ongoing maintenance of established motility patterns. Disruptions in motility can lead to various disorders, such as chronic constipation, irritable bowel syndrome, and chronic idiopathic pseudo-obstruction. Gut microbiota significantly influence intestinal motility through mechanisms like bile acid metabolism and the production of short-chain fatty acids. In patients with diarrhea-predominant irritable bowel syndrome, elevated primary-to-secondary bile acid ratios suggest a complex interaction between gut bacteria and bile acids that can enhance motility via receptors like TGR5. Additionally, the role of interstitial cells of Cajal in facilitating non-neuronal contractions has revolutionized our understanding of motility regulation, highlighting both neural and non-neural factors. Various therapeutic approaches, including prebiotics, probiotics, and fecal microbiota transplantation, have been explored to improve intestinal motility, although their effectiveness has been limited. Advancements in gene-related research and innovative diagnostic methods are vital for a deeper understanding of how the gut microbiome regulates motility. This review synthesizes current knowledge on the interplay between gut microbiota and intestinal motility, emphasizing the need for interdisciplinary research to develop effective treatments targeting gut microbiota for gastrointestinal disorders. By unraveling these complex interactions, we can pave the way for novel therapeutic strategies that enhance intestinal health and improve the quality of life for those affected by motility-related disorders.

Smooth muscle research is at the forefront of translational science, bridging the gap between basic molecular discoveries and clinical applications. The symposium “Muscle and Pathology/Health: Frontiers of Translational Research” at the 66th Annual Meeting of Japan Society of Smooth Muscle Research showcased recent advances in this field. The presentations highlighted diverse topics, including molecular targeting in malignant hyperthermia, the therapeutic potential of probiotics in inflammatory bowel disease, sex differences in pulmonary hypertension and the impact of dietary components on vascular health. These studies underscore the importance of precision therapies, personalized medicine and functional foods in understanding and managing diseases. As technological innovations continue to drive research, the symposium provided insight into future directions, such as developing targeted molecular therapies, leveraging probiotics for systemic effects, expanding sex-based studies, and industrializing outcomes of basic science. The findings presented offer promising avenues for new treatment strategies that could revolutionize smooth muscle-related healthcare, emphasizing the potential for improved patient outcomes through translational research.

Thermoregulation is essential for maintaining homeostasis in mammals under various environmental conditions. Impairment of this function can result in severe conditions, such as fever, heat stroke, and malignant hyperthermia (MH). In this review, we will focus on the role of the type 1 ryanodine receptor (RYR1), a Ca²⁺ release channel that is crucial for excitation-contraction coupling in skeletal muscles. Mutations in RYR1 are associated with muscle disorders, including MH, which is characterized by dysregulated Ca²⁺-induced Ca²⁺ release (CICR). Recent advances from genetically engineered mouse models of MH have provided new insights into the pathophysiological mechanisms underlying anesthetic- and heat-induced episodes, and revealed a heat-induced Ca²⁺ release (HICR) mechanism mediated by RYR1. Experimental evidences demonstrate that anesthetics induce simultaneous increases in cellular temperature and cytosolic Ca²⁺ concentration. Therefore, this review proposes that an increase in cellular temperature triggers further Ca²⁺ release via HICR, establishing a positive feedback loop that sustains excessive heat production during MH crises.

Inflammatory bowel disease (IBD) is a term that describes disorders involving long-standing inflammation of tissues in the digestive tract. The onset and exacerbation of IBD is linked to multiple factors, including genetic and immunological influences, diet, and gut bacteria. Additionally, it is associated with a high risk of cancer. Research shows that the longer a person is breastfed, the lower their risk of developing IBD, highlighting the impact of human breast milk components on intestinal bacteria. Human breast milk contains many bioactive components, such as lactoferrin and milk oligosaccharides, are known to be effective in preventing and treating IBD. Probiotics are defined as live microorganisms that provide beneficial effects on the host by altering the balance of indigenous intestinal bacteria. While probiotics, such as lactic acid bacteria and bifidobacteria, have been clinically applied in IBD treatment, there are currently no reports on the application of human breast milk-derived probiotics for this purpose. We clarified the preventive and therapeutic effects of human breast milk-derived probiotics on IBD, as well as the underlying mechanisms. This review highlights the importance of breastfeeding to prevent IBD, and focuses on the therapeutic effects of human breast milk-derived probiotics in IBD. These bioactive compounds in human breast milk are instrumental in establishing a beneficial gut microbiota and promoting proper immune system maturation during early life.

Pulmonary arterial hypertension (PAH) is a rare and fatal cardiovascular disease characterized by pulmonary vascular remodeling, leading to a progressive increase in pulmonary vascular resistance and pulmonary arterial pressure (PAP). Elevated PAP induces right ventricular hypertrophy and eventually progresses to right heart failure. Pulmonary vascular remodeling is primarily caused by the excessive proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) in the medial layer. This is mediated by the binding of growth factors to their specific receptor tyrosine kinases. To date, several growth factors, including epidermal growth factor, fibroblast growth factor, insulin-like growth factor, platelet-derived growth factor (PDGF), transforming growth factor-β, and vascular endothelial growth factor, have been implicated in the development of PAH. Our previous studies have demonstrated that the upregulated expression of Ca²⁺-sensing receptors in PASMCs contributes to the development of PAH. This upregulation was induced by increased PDGF levels in PASMCs from PAH patients. Therefore, imatinib (a tyrosine kinase inhibitor including PDGF receptors) and corosolic acid (with inhibitory effects of PDGF signaling) suppressed the excessive proliferation and migration of PASMCs from PAH patients. These treatments also ameliorated pulmonary vascular remodeling in pulmonary hypertensive rats. This review focuses on the pathological roles of growth factors, especially PDGF, in the pathogenesis and progression of PAH.

In Japan, there is an approximate 10 year gap between average life expectancy and healthy life expectancy, which represents a decade characterized by poor health. To shorten this period and promote healthy aging, we searched for food ingredients that promote vascular health. Focusing on nitric oxide (NO) released by vascular endothelial cells, we first established an evaluation method to measure the NO production capacity of the vascular endothelium in real-time. This helped identify Sakurajima-radish (Raphanus sativus cv. Sakurajima Daikon), which promotes NO production in vascular endothelial cells. The ability of Sakurajima-radish to induce NO production was observed in both the edible part of the enlarged root and the leaves to an equal extent. We identified the active component, trigonelline, and found that Sakurajima-radish contains much higher amounts of trigonelline than other natural products. There was no statistically significant difference in trigonelline content among the varieties of Sakurajima-radish distributed across Kagoshima Prefecture, nor was there any significant difference among the production areas within Kagoshima Prefecture, including outlying islands. The trigonelline content of Sakurajima-radish remained relatively stable across most cooking methods. A clinical study involving healthy individuals showed that Sakurajima-radish consumption (170 g/day for 10 days) caused a significant increase in flow-mediated dilation and blood trigonelline levels. This article elucidates the potential of Sakurajima-radish as a functional food that can be stored, cooked, and eaten in various forms with significant health benefits contributing to improved vascular function.

Laparoscopic distal gastrectomy with Billroth I reconstruction (LDGBI) is a standard procedure for early-stage gastric cancer. Although both Delta-shaped (Delta) and circular stapler (CS) techniques are commonly used for anastomosis, their long-term effects on remnant gastric motility and postoperative quality of life (QOL) remain insufficiently defined. This retrospective study analyzed 43 patients who underwent LDGBI at least one year prior, divided into CS (n=22) and Delta (n=21) groups. Gastric emptying was evaluated using the ¹³C-acetate breath test, focusing on residual reservoir capacity (RR5) and half-emptying time (T1/2). Postgastrectomy symptoms and living status were assessed via structured questionnaires. The Delta group demonstrated significantly lower RR5 (40.5% vs. 56.1%, P=0.033) and shorter T1/2 (4.8 vs. 8.5 min, P=0.033), indicating diminished reservoir function and accelerated gastric emptying. These alterations correlated with a higher incidence of early dumping abdominal symptoms (66.7% vs. 27.3%, P=0.015), as well as trends toward increased early dumping general symptoms and greater body weight loss. The Delta method is associated with enhanced gastric emptying and more frequent postgastrectomy symptoms, likely due to a wider anastomotic stoma. Tailoring the stoma size or selecting alternative reconstruction methods based on remnant gastric volume may help mitigate adverse outcomes and improve patients’ quality of life following LDGBI.