Relaxation of the smooth muscle cells in the cavernosal arterioles and sinuses results in increased blood flow into the penis, raising corpus cavernosum pressure to culminate in penile erection. Nitric oxide, released from non-adrenergic/non-cholinergic nerves, is considered the principle stimulator of cavernosal smooth muscle relaxation, however, the inhibition of vasoconstrictors (that is, norepinephrine and endothelin-1, refs. 5-9) cannot be ignored as a potential regulator of penile erection. The calcium-sensitizing rho-A/Rho-kinase pathway may play a synergistic role in cavernosal vasoconstriction to maintain penile flaccidity. Rho-kinase is known to inhibit myosin light chain phosphatase, and to directly phosphorylate myosin light-chain (in solution), altogether resulting in a net increase in activated myosin and the promotion of cellular contraction. Although Rho-kinase protein and mRNA have been detected in cavernosal tissue, the role of Rho-kinase in the regulation of cavernosal tone is unknown. Using pharmacologic antagonism (Y-27632, ref. 13, 18), we examined the role of Rho-kinase in cavernosal tone, based on the hypothesis that antagonism of Rho-kinase results in increased corpus cavernosum pressure, initiating the erectile response independently of nitric oxide. Our finding, that Rho-kinase antagonism stimulates rat penile erection independently of nitric oxide, introduces a potential alternate avenue for the treatment of erectile dysfunction.
Nitrovasodilators such as nitroglycerine, via production of nitric oxide and an increase in [cGMP], can induce arterial smooth muscle relaxation without proportional reduction in myosin light chain (MLC) phosphorylation or myoplasmic [Ca2+]. These findings suggest that regulatory systems, other than MLC phosphorylation and Ca2+, partially mediate nitroglycerine‐induced relaxation. In swine carotid artery, we found that a membrane‐permeant cGMP analogue induced relaxation without MLC dephosphorylation, suggesting that cGMP mediated the relaxation. Nitroglycerine‐induced relaxation was associated with a reduction in O2 consumption, suggesting that the interaction between phosphorylated myosin and the thin filament was inhibited. Nitroglycerine‐induced relaxation was associated with a 10‐fold increase in the phosphorylation of a protein on Ser16. We identified this protein as heat shock protein 20 (HSP20), a member of a family of proteins known to bind to thin filaments. When homogenates of nitroglycerine‐relaxed tissues were centrifuged at 6000 g, phosphorylated HSP20 preferentially sedimented in the pellet, suggesting that phosphorylation of HSP20 may increase its affinity for the thin filament. We noted that a domain of HSP20 is partially homologous to the ‘minimum inhibitory sequence’ of skeletal troponin I. The peptide HSP20110‐121, which contains this domain, bound to actin‐containing filaments only in the presence of tropomyosin, a characteristic of troponin I. High concentrations of HSP20110‐121 abolished Ca2+‐activated force in skinned swine carotid artery. HSP20110‐121 also partially decreased actin‐activated myosin S1 ATPase activity. These data suggest that cGMP‐mediated phosphorylation of HSP20 on Ser16 may have a role in smooth muscle relaxation without MLC dephosphorylation. HSP20 contains an actin‐binding sequence at amino acid residues 110–121 that inhibited force production in skinned carotid artery. We hypothesize that phosphorylation of HSP20 regulates force independent of MLC phosphorylation via binding of HSP20 to thin filaments and inhibition of cross‐bridge cycling.
The purpose of this study is to test predicted form-function relationships between cranial suture complexity and masticatory muscle mass and biomechanics in a mouse model. Specifically, to test the hypothesis that increased masticatory muscle mass increases sagittal suture complexity, we measured the fractal dimension (FD), temporalis mass, and temporalis bite force in myostatin-deficient (GDF8(-/-)) mice and wild-type CD-1 mice (all male, 6 months old). Myostatin is a negative regulator of muscle mass, and myostatin-deficient mice show a marked increase in muscle mass compared to normal mice. We predicted that increased sagittal suture complexity would decrease suture stiffness. The data presented here demonstrate that increased suture complexity (measured as FD) was observed in a hypermuscular mouse model (GDF8(-/-)) with significantly increased temporalis muscle mass and bite forces. Hypermuscular mice were also found to possess suture connective tissue that was less stiff (i.e., underwent more displacement before failure occurred) when loaded in tension. By decreasing stiffness, suture complexity apparently helps to dissipate mechanical loads within the cranium that are related to chewing. These results suggest that cranial suture connective tissue locally adapts to functional demands of the biomechanical suture environment. As such, cranial sutures provide a novel model for studies in connective tissue mechanotransduction.
BackgroundMulti-walled carbon nanotubes (MWCNTs) are widely used in many disciplines due to their unique physical and chemical properties. Therefore, some concerns about the possible human health and environmental impacts of manufactured MWCNTs are rising. We hypothesized that instillation of MWCNTs impairs pulmonary function in C57BL/6 mice due to development of lung inflammation and fibrosis.MethodsMWCNTs were administered to C57BL/6 mice by oropharyngeal aspiration (1, 2, and 4 mg/kg) and we assessed lung inflammation and fibrosis by inflammatory cell infiltration, collagen content, and histological assessment. Pulmonary function was assessed using a FlexiVent system and levels of Ccl3, Ccl11, Mmp13 and IL-33 were measured by RT-PCR and ELISA.ResultsMice administered MWCNTs exhibited increased inflammatory cell infiltration, collagen deposition and granuloma formation in lung tissue, which correlated with impaired pulmonary function as assessed by increased resistance, tissue damping, and decreased lung compliance. Pulmonary exposure to MWCNTs induced an inflammatory signature marked by cytokine (IL-33), chemokine (Ccl3 and Ccl11), and protease production (Mmp13) that promoted the inflammatory and fibrotic changes observed within the lung.ConclusionsThese results further highlight the potential adverse health effects that may occur following MWCNT exposure and therefore we suggest these materials may pose a significant risk leading to impaired lung function following environmental and occupational exposures.
Introduction The combination of the independent risk factors for erectile dysfunction, obesity, hypertension, and diabetes are manifested collectively in a condition known as metabolic syndrome X. However, the exact mechanism(s) by which the combination of these factors contributes to erectile dysfunction have yet to be elucidated. Aim We hypothesized that protein kinase C (PKC) and Rho-kinase enhanced vascular tone and thus contributed to erectile dysfunction in this condition. Methods Erectile function was evaluated by recording voltage-dependent increases in intracavernosal pressure following stimulation of the cavernosal nerve in 16- to 20-week-old lean and obese-diabetic Zucker rats. Cavernosal tissue contractile and relaxation responses were evaluated in vitro when contracted with phenylephrine, endothelin-1 and relaxed by Rho-kinase, PKC inhibitors or sodium nitroprusside. Additionally, cavernosal tissue Rho-kinase, protein kinase, and nitric oxide synthase isoform expression were evaluated by Western blot. Results The voltage-dependent erectile responses were suppressed by >30% in the obese-diabetic Zucker rat. The maximal stress generated by cavernosal tissue from the obese-diabetic was significantly greater than the lean response by greater than 0.8 mN/mm2 for both phenylephrine and endothelin stimulation. The PKC inhibitor, chelerythrine, inhibited more than 30% of the phenylephrine-induced and 70% of the endothelin-1-induced contractions. Rho-kinase inhibition, with either Y-27632 or HA-1077, revealed impaired relaxations of nearly 30% in tissue from obese-diabetic animals. Western blot analysis revealed increased protein expression of PKC α and δ and Rho-kinase α and β but no loss for endothelial or neuronal nitric oxide synthase. Conclusion In this rodent model both PKC and Rho-kinase signaling elements may contribute to an enhanced vasoconstriction state of the penile smooth muscle that was differentially dependent on the agonist used. The enhanced vasoconstrictive state of the tissue could contribute to the reduced voltage-dependent erectile response in the obese-diabetic Zucker rat.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.