Ca2+ release from sarcoplasmic reticulum of skinned fast- and slow-twitch muscle fibers

Neuromuscular junction instability and altered intracellular calcium handling as early determinants of force loss during unloading in humans

Key points

Few days of unloading are sufficient to induce a decline of skeletal muscle mass and function; notably, contractile force is lost at a faster rate than muscle mass.

The reasons behind this disproportionate loss of muscle force are still poorly understood.

We provide strong evidence of two mechanisms only hypothesized until now for the rapid muscle force loss in only 10 days of bed rest.

Our results show that an initial neuromuscular junction instability, accompanied by alterations in the innervation status and impairment of single fibre sarcoplasmic reticulum function contribute to the loss of contractile force in front of a preserved myofibrillar function and central activation capacity.

Early onset of neuromuscular junction instability and impairment in calcium dynamics involved in excitation–contraction coupling are proposed as eligible determinants to the greater decline in muscle force than in muscle size during unloading.

Abstract

Unloading induces rapid skeletal muscle atrophy and functional decline. Importantly, force is lost at a much higher rate than muscle mass. We aimed to investigate the early determinants of the disproportionate loss of force compared to that of muscle mass in response to unloading. Ten young participants underwent 10 days of bed rest (BR). At baseline (BR0) and at 10 days (BR10), quadriceps femoris (QF) volume (VOL) and isometric maximum voluntary contraction (MVC) were assessed. At BR0 and BR10 blood samples and biopsies of vastus lateralis (VL) muscle were collected. Neuromuscular junction (NMJ) stability and myofibre innervation status were assessed, together with single fibre mechanical properties and sarcoplasmic reticulum (SR) calcium handling. From BR0 to BR10, QFVOL and MVC decreased by 5.2% (P = 0.003) and 14.3% (P < 0.001), respectively. Initial and partial denervation was detected from increased neural cell adhesion molecule (NCAM)‐positive myofibres at BR10 compared with BR0 (+3.4%, P = 0.016). NMJ instability was further inferred from increased C‐terminal agrin fragment concentration in serum (+19.2% at BR10, P = 0.031). Fast fibre cross‐sectional area (CSA) showed a trend to decrease by 15% (P = 0.055) at BR10, while single fibre maximal tension (force/CSA) was unchanged. However, at BR10 SR Ca²⁺ release in response to caffeine decreased by 35.1% (P < 0.002) and 30.2% (P < 0.001) in fast and slow fibres, respectively, pointing to an impaired excitation–contraction coupling. These findings support the view that the early onset of NMJ instability and impairment in SR function are eligible mechanisms contributing to the greater decline in muscle force than in muscle size during unloading.

Few days of unloading are sufficient to induce a decline of skeletal muscle mass and function; notably, contractile force is lost at a faster rate than muscle mass.

The reasons behind this disproportionate loss of muscle force are still poorly understood.

We provide strong evidence of two mechanisms only hypothesized until now for the rapid muscle force loss in only 10 days of bed rest.

Our results show that an initial neuromuscular junction instability, accompanied by alterations in the innervation status and impairment of single fibre sarcoplasmic reticulum function contribute to the loss of contractile force in front of a preserved myofibrillar function and central activation capacity.

Early onset of neuromuscular junction instability and impairment in calcium dynamics involved in excitation–contraction coupling are proposed as eligible determinants to the greater decline in muscle force than in muscle size during unloading.

Metabolic immunomodulation of macrophage functional plasticity in nonhealing wounds

PURPOSE OF REVIEW

Despite modern advances in medicine, nonhealing wounds are the number one cause of nontraumatic, lower-limb amputation. Nonhealing wounds are characterized by a healing process stalled between inflammation and tissue remodel/repair, a stage characterized by a shift in macrophage functional phenotype. Characterization of diversity in macrophage functional phenotype in wounds and metabolic contributions to macrophage polarization are discussed.

RECENT FINDINGS

Macrophage functional diversity in phenotype has recently evolved from duality (classically activated, pro-inflammatory M1 and alternatively activated, anti-inflammatory M2) to include an additional four alternately activated subphenotypes (M2a, M2b, M2c and M2d). Metabolic pathway utilization shifts characterize macrophage polarization with resulting metabolic and immune outcomes impacting host-pathogen interactions during wound healing.

SUMMARY

Recognition of the key role macrophage diversity plays in wound healing, along with better characterization of diverse macrophage phenotypes, will inform our understanding of pathogenicity in wound healing. Comprehensive profiling of the metabolism regulating macrophage polarization and host-pathogen interaction creates opportunity of discovery for innovative new diagnostics and therapeutics for treating nonhealing wounds.

Bi-allelic expression of the RyR1 p.A4329D mutation decreases muscle strength in slow-twitch muscles in mice

Mutations in the ryanodine receptor 1 (RYR1) gene are associated with several human congenital myopathies, including the dominantly inherited central core disease and exercise-induced rhabdomyolysis, and the more severe recessive phenotypes, including multiminicore disease, centronuclear myopathy, and congenital fiber type disproportion. Within the latter group, those carrying a hypomorphic mutation in one allele and a missense mutation in the other are the most severely affected. Because of nonsense-mediated decay, most hypomorphic alleles are not expressed, resulting in homozygous expression of the missense mutation allele. This should result in 50% reduced expression of the ryanodine receptor in skeletal muscle, but its observed content is even lower. To study in more detail the biochemistry and pathophysiology of recessive RYR1 myopathies, here we investigated a mouse model we recently generated by analyzing the effect of bi-allelic versus mono-allelic expression of the RyR1 p.A4329D mutation. Our results revealed that the expression of two alleles carrying the same mutation or of one allele with the mutation in combination with a hypomorphic allele does not result in functionally equal outcomes and impacts skeletal muscles differently. In particular, the bi-allelic RyR1 p.A4329D mutation caused a milder phenotype than its mono-allelic expression, leading to changes in the biochemical properties and physiological function only of slow-twitch muscles and largely sparing fast-twitch muscles. In summary, bi-allelic expression of the RyR1 p.A4329D mutation phenotypically differs from mono-allelic expression of this mutation in a compound heterozygous carrier.

Functional Applications of Polyarginine-Hyaluronic Acid-Based Electrostatic Complexes

Background: Electrostatic complexes of poly (l-Arginine) (pArg) and hyaluronic acid (HA) have been investigated for their functional applications to supply free or polymeric form of l-Arginine (Arg) to target cells. As a vital amino acid, Arg plays significant role in multitude of pathophysiological processes ranging from wound healing to cancer. However, serum arginase expression and toxicity of Arg at cellular level renders exogenous delivery of this amino acid a challenging task. We showed that polyarginine-hyaluronic acid ionic nanocomplexes (pArg-HA iNCs) could be an effective way to deliver Arg to target cell populations. Materials and Methods: These electrostatic complexes were prepared by mixing HA (average m.w. of 200 kDa) with pArg (m.w. 5-15 kDa; Sigma) in aqueous solutions and purifying over glycerol. Nanocomplexes were characterized for their particle size, surface charge, capacity to release l-Arg, and intracellular uptake of complexes. Results: Synthesized nanocomplexes showed hydrodynamic diameter ranging from 140-306 nm depending on the content of pArg or HA within the formulation. With surface charge (ζ-potential) of -29 mV, the nanocomplexes showed pH-dependent release of Arg. At pH 7.4, pArg-HA iNCs released 30% of the total Arg-content, while at pH 5.0, 60% of Arg was released after 24 h. These electrostatically stabilized complexes were found to promote growth of human dermal fibroblasts (HDF) in wound-healing assay and increased nitric oxide (NO) activity in these cells in a time-dependent manner. Nanocomplexes also showed cellular uptake and enhanced dose-dependent toxicity against two pancreatic cancer cell lines, i.e. MIA PaCa-2 and Panc-1. Interestingly, the cytotoxic effect was synergized upon pre-treatment of the cells with a frontline chemotherapeutic agent, gemcitabine (GEM), and was not observed when the cells were treated with Arg alone. Conclusion: As such, this communication shows the prospect of pArg-HA iNC electrostatic nanocomplexes to interact and interfere with intracellular Arg metabolic machinery conducive to rescuing different pathological conditions.

Caffeine as a tool to investigate sarcoplasmic reticulum and intracellular calcium dynamics in human skeletal muscles

Caffeine is worldwide used for its power to increase cognitive and physical performance. The ergogenic effects of caffeine, however, do not depend on a direct action on muscles. Actually, the actions of caffeine on skeletal muscles, take place at millimolar concentrations which are far above the micromolar level reached after a regular consumption of coffee or similar drinks, and close to a lethal concentration. At millimolar concentrations caffeine exerts a powerful effect on sarcoplasmic reticulum (SR) activating the release of calcium via ryanodine receptors and, possibly, inhibiting calcium reuptake. For this reason caffeine has become a valuable tool for studying SR function and for diagnostics of SR related muscle disorders. This review aims to briefly describe the effects and the mechanism of action of caffeine on sarcoplasmic reticulum and to focus on its use to study intracellular calcium dynamics in human muscle fibers in physiological and pathological conditions.

Targeting metabolism to regulate immune responses in autoimmunity and cancer

Metabolic programming is emerging as a critical mechanism to alter immune cell activation, differentiation and function. Targeting metabolism does not completely suppress or activate the immune system but selectively regulates immune responses. The different metabolic requirements of the diverse cells that constitute an immune response provide a unique opportunity to separate effector functions from regulatory functions. Likewise, cells can be metabolically reprogrammed to promote either their short-term effector functions or long-term memory capacity. Studies in the growing field of immunometabolism support a paradigm of 'cellular selectivity based on demand', in which generic inhibitors of ubiquitous metabolic processes selectively affect cells with the greatest metabolic demand and have few effects on other cells of the body. Targeting metabolism, rather than particular cell types or cytokines, in metabolically demanding processes such as autoimmunity, graft rejection, cancer and uncontrolled inflammation could lead to successful strategies in controlling the pathogenesis of these complex disorders.

Back to Stir It Up: Erectile Dysfunction in an Evolutionary, Developmental, and Clinical Perspective

In this review, we analyze erectile dysfunction (ED) in the context of sexual selection. We highlight that ED is a specific human male characteristic linked to the loss of the baculum or penile bone and results from a range of physical and psychological factors. We discuss evolutionary interpretations that consider dysfunctional penile erection as an honest signal of a low-quality male. We further emphasize the importance of considering psychosocial context and early attachment dynamics for understanding the etiology of some types of ED. Finally, we suggest that the integration of developmental factors for understanding the emergence of this sexual disorder is instrumental for the calibration of more effective therapies.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter I - Foreword

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the "Giovanni Salviati Memorial", was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni "will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do". Since Giovanni's friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract approval of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality, international journals. This was true in the past, continues to be true in the present and will be true in the future. All 2018SpPMD Abstracts are indexed at the end of the Chapter IV.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter III - Abstracts of March 16, 2018

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the “Giovanni Salviati Memorial”, was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni “will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do”. Since Giovanni’s friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract approval of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality, international journals. The abstracts of the March 16, 2018 Padua Muscle Day are listed in this chapter III. All 2018SpPMD Abstracts are indexed at the end of the Chapter IV.

Identification and characterization of three novel mutations in the CASQ1 gene in four patients with tubular aggregate myopathy

Here, we report the identification of three novel missense mutations in the calsequestrin-1 (CASQ1) gene in four patients with tubular aggregate myopathy. These CASQ1 mutations affect conserved amino acids in position 44 (p.(Asp44Asn)), 103 (p.(Gly103Asp)), and 385 (p.(Ile385Thr)). Functional studies, based on turbidity and dynamic light scattering measurements at increasing Ca²⁺ concentrations, showed a reduced Ca²⁺ -dependent aggregation for the CASQ1 protein containing p.Asp44Asn and p.Gly103Asp mutations and a slight increase in Ca²⁺ -dependent aggregation for the p.Ile385Thr. Accordingly, limited trypsin proteolysis assay showed that p.Asp44Asn and p.Gly103Asp were more susceptible to trypsin cleavage in the presence of Ca²⁺ in comparison with WT and p.Ile385Thr. Analysis of single muscle fibers of a patient carrying the p.Gly103Asp mutation showed a significant reduction in response to caffeine stimulation, compared with normal control fibers. Expression of CASQ1 mutations in eukaryotic cells revealed a reduced ability of all these CASQ1 mutants to store Ca²⁺ and a reduced inhibitory effect of p.Ile385Thr and p.Asp44Asn on store operated Ca²⁺ entry. These results widen the spectrum of skeletal muscle diseases associated with CASQ1 and indicate that these mutations affect properties critical for correct Ca²⁺ handling in skeletal muscle fibers.

A guide to immunometabolism for immunologists

In recent years a substantial number of findings have been made in the area of immunometabolism, by which we mean the changes in intracellular metabolic pathways in immune cells that alter their function. Here, we provide a brief refresher course on six of the major metabolic pathways involved (specifically, glycolysis, the tricarboxylic acid (TCA) cycle, the pentose phosphate pathway, fatty acid oxidation, fatty acid synthesis and amino acid metabolism), giving specific examples of how precise changes in the metabolites of these pathways shape the immune cell response. What is emerging is a complex interplay between metabolic reprogramming and immunity, which is providing an extra dimension to our understanding of the immune system in health and disease.

Macrophage peroxisome proliferator-activated receptor γ deficiency delays skin wound healing through impairing apoptotic cell clearance in mice

Skin wound macrophages are key regulators of skin repair and their dysfunction causes chronic, non-healing skin wounds. Peroxisome proliferator-activated receptor gamma (PPARγ) regulates pleiotropic functions of macrophages, but its contribution in skin wound healing is poorly defined. We observed that macrophage PPARγ expression was upregulated during skin wound healing. Furthermore, macrophage PPARγ deficiency (PPARγ-knock out (KO)) mice exhibited impaired skin wound healing with reduced collagen deposition, angiogenesis and granulation formation. The tumor necrosis factor alpha (TNF-α) expression in wounds of PPARγ-KO mice was significantly increased and local restoration of TNF-α reversed the healing deficit in PPARγ-KO mice. Wound macrophages produced higher levels of TNF-α in PPARγ-KO mice compared with control. In vitro, the higher production of TNF-α by PPARγ-KO macrophages was associated with impaired apoptotic cell clearance. Correspondingly, increased apoptotic cell accumulation was found in skin wound of PPARγ-KO mice. Mechanically, peritoneal and skin wound macrophages expressed lower levels of various phagocytosis-related molecules. In addition, PPARγ agonist accelerated wound healing and reduced local TNF-α expression and wound apoptotic cells accumulation in wild type but not PPARγ-KO mice. Therefore, PPARγ has a pivotal role in controlling wound macrophage clearance of apoptotic cells to ensure efficient skin wound healing, suggesting a potential new therapeutic target for skin wound healing.

A mutation in the CASQ1 gene causes a vacuolar myopathy with accumulation of sarcoplasmic reticulum protein aggregates

A missense mutation in the calsequestrin-1 gene (CASQ1) was found in a group of patients with a myopathy characterized by weakness, fatigue, and the presence of large vacuoles containing characteristic inclusions resulting from the aggregation of sarcoplasmic reticulum (SR) proteins. The mutation affects a conserved aspartic acid in position 244 (p.Asp244Gly) located in one of the high-affinity Ca(2+) -binding sites of CASQ1 and alters the kinetics of Ca(2+) release in muscle fibers. Expression of the mutated CASQ1 protein in COS-7 cells showed a markedly reduced ability in forming elongated polymers, whereas both in cultured myotubes and in in vivo mouse fibers induced the formation of electron-dense SR vacuoles containing aggregates of the mutant CASQ1 protein that resemble those observed in muscle biopsies of patients. Altogether, these results support the view that a single missense mutation in the CASQ1 gene causes the formation of abnormal SR vacuoles containing aggregates of CASQ1, and other SR proteins, results in altered Ca(2+) release in skeletal muscle fibers, and, hence, is responsible for the clinical phenotype observed in these patients.

An official American Thoracic Society/European Respiratory Society statement: update on limb muscle dysfunction in chronic obstructive pulmonary disease

BACKGROUND

Limb muscle dysfunction is prevalent in chronic obstructive pulmonary disease (COPD) and it has important clinical implications, such as reduced exercise tolerance, quality of life, and even survival. Since the previous American Thoracic Society/European Respiratory Society (ATS/ERS) statement on limb muscle dysfunction, important progress has been made on the characterization of this problem and on our understanding of its pathophysiology and clinical implications.

PURPOSE

The purpose of this document is to update the 1999 ATS/ERS statement on limb muscle dysfunction in COPD.

METHODS

An interdisciplinary committee of experts from the ATS and ERS Pulmonary Rehabilitation and Clinical Problems assemblies determined that the scope of this document should be limited to limb muscles. Committee members conducted focused reviews of the literature on several topics. A librarian also performed a literature search. An ATS methodologist provided advice to the committee, ensuring that the methodological approach was consistent with ATS standards.

RESULTS

We identified important advances in our understanding of the extent and nature of the structural alterations in limb muscles in patients with COPD. Since the last update, landmark studies were published on the mechanisms of development of limb muscle dysfunction in COPD and on the treatment of this condition. We now have a better understanding of the clinical implications of limb muscle dysfunction. Although exercise training is the most potent intervention to address this condition, other therapies, such as neuromuscular electrical stimulation, are emerging. Assessment of limb muscle function can identify patients who are at increased risk of poor clinical outcomes, such as exercise intolerance and premature mortality.

CONCLUSIONS

Limb muscle dysfunction is a key systemic consequence of COPD. However, there are still important gaps in our knowledge about the mechanisms of development of this problem. Strategies for early detection and specific treatments for this condition are also needed.

Effects of male silkworm pupa powder on the erectile dysfunction by chronic ethanol consumption in rats

Erectile dysfunction (ED) is a highly prevalent disorder that affects millions of men worldwide. ED is now considered an early manifestation of atherosclerosis, and consequently, a precursor of systemic vascular disease. This study was designed to investigate the effects of male silkworm pupa powder (SWP) on the levels of nitric oxide synthase (NOS) expression, nitrite, and glutathione (GSH); lipid peroxidation; libido; and erectile response of the corpus cavernosum of the rat penis. We induced ED in the study animals by oral administration of 20% ethanol over 8 weeks. The SWP-treated male rats were divided into 3 groups that were orally administered 200, 400, and 800 mg/kg. The libido of the SWP-administered male rats was higher than that of the ethanol control group. In addition, the erectile response of the corpus cavernosum was restored in males on SWP administration, to a level similar to that of the normal group without ED. The testosterone concentration did not increase significantly. The lipid peroxidation in the corpus cavernosum of the male rats administered SWP decreased significantly. In contrast, compared to the ethanol group, SWP-administered male rats showed increased GSH levels in the corpus cavernosum. The level of nitrite and NOS expression in the corpus cavernosum of SWP-administered male rats increased significantly. These results indicated that SWP effectively restored ethanol-induced ED in male rats.

The promise of inhibition of smooth muscle tone as a treatment for erectile dysfunction: where are we now?

Ten years ago, the inhibition of Rho kinase by intracavernosal injection of Y-27632 was found to induce an erectile response. This effect did not require activation of nitric oxide-mediated signaling, introducing a novel target pathway for the treatment of erectile dysfunction (ED), with potential added benefit in cases where nitric oxide bioavailability is attenuated (and thus phosphodiesterase type 5 (PDE5) inhibitors are less efficacious). Rho-kinase antagonists are currently being developed and tested for a wide range of potential uses. The inhibition of this calcium-sensitizing pathway results in blood vessel relaxation. It is also possible that blockade of additional smooth muscle contractile signaling mechanisms may have the same effect. In this review, we conducted an extensive search of pertinent literature using PUBMED. We have outlined the various pathways involved in the maintenance of penile smooth muscle tone and discussed the current potential benefit for the pharmacological inhibition of these targets for the treatment of ED.

Fiber Types in Mammalian Skeletal Muscles

Mammalian skeletal muscle comprises different fiber types, whose identity is first established during embryonic development by intrinsic myogenic control mechanisms and is later modulated by neural and hormonal factors. The relative proportion of the different fiber types varies strikingly between species, and in humans shows significant variability between individuals. Myosin heavy chain isoforms, whose complete inventory and expression pattern are now available, provide a useful marker for fiber types, both for the four major forms present in trunk and limb muscles and the minor forms present in head and neck muscles. However, muscle fiber diversity involves all functional muscle cell compartments, including membrane excitation, excitation-contraction coupling, contractile machinery, cytoskeleton scaffold, and energy supply systems. Variations within each compartment are limited by the need of matching fiber type properties between different compartments. Nerve activity is a major control mechanism of the fiber type profile, and multiple signaling pathways are implicated in activity-dependent changes of muscle fibers. The characterization of these pathways is raising increasing interest in clinical medicine, given the potentially beneficial effects of muscle fiber type switching in the prevention and treatment of metabolic diseases.

Gene therapy as future treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is a major men's health problem. Although the high success rate of treating ED by phosphodiesterase 5 (PDE5) inhibitors has been reported, there are a significant number of ED patients who do not respond to currently available treatment modalities.

AREAS COVERED IN THIS REVIEW

To elucidate the current status of gene therapy applications for ED, gene therapy approaches for ED treatment are reviewed.

WHAT THE READER WILL GAIN

Gene therapy strategies that can enhance nitric oxide (NO) production or NO-mediated signaling pathways, growth factor-mediated nerve regeneration or K(+) channel activity in the smooth muscle could be promising approaches for the treatment of ED. Although the majority of gene therapy studies are still in the preclinical phase, the first clinical trial using non-viral gene transfer of Ca(2+)-activated, large-conductance K(+) channels into the corpus cavernosum of ED patients showed positive results.

TAKE HOME MESSAGE

Gene therapy represents an exciting future treatment option for ED, especially for people with severe ED unresponsive to current first-line therapies such as PDE5 inhibitors although the long-term safety of both viral and non-viral gene therapies should be established.

Improved function of diabetic wound-site macrophages and accelerated wound closure in response to oral supplementation of a fermented papaya preparation

Carica papaya Linn is widely known as a medicinal fruit. We sought to study a standardized fermented papaya preparation (FPP) for its effects on wound healing in adult obese diabetic (db/db) mice. FPP blunted the gain in blood glucose and improved the lipid profile after 8 weeks of oral supplementation. However, FPP did not influence weight gain during the supplementation period. FPP (0.2 g/kg body weight) supplementation for 8 weeks before wounding was effective in correcting wound closure. Studies on viable macrophages isolated from the wound site demonstrated that FPP supplementation improved respiratory-burst function as well as inducible NO production. Reactive oxygen species support numerous aspects of wound healing; NO availability in diabetic wounds is known to be compromised. Diabetic mice supplemented with FPP showed a higher abundance of CD68 as well as CD31 at the wound site, suggesting effective recruitment of monocytes and an improved proangiogenic response. This work provides the first evidence that diabetic-wound outcomes may benefit from FPP supplementation by specifically influencing the response of wound-site macrophages and the subsequent angiogenic response. Given that FPP has a long track record of safe human consumption, testing of the beneficial effects of FPP on diabetic wound-related outcomes in a clinical setting is warranted.

Characterization of nitrergic function in monkey penile erection in vivo and in vitro

The nitrergic nerve appears to have a major role in the neuronal regulation of penile erection. Cholinergic innervation has been shown histochemically in penile cavernous tissues, but its functional role is not well understood. This study was aimed at examining the functional properties of the nitrergic nerve and the possible involvement of cholinergic function in the regulation of monkey penile erection in vivo and in vitro. In anesthetized Japanese monkeys, electrical stimulation of the cavernous nerve caused a frequency-dependent increase in intracavernous pressure and penile erection, and atropine enhanced the pressure response. Intravenous injections of N(G)-nitro-L-arginine (L-NA) markedly inhibited the stimulation-induced pressure increase and the erectile response, and L-arginine partially restored the pressure response. In some monkeys, the intracavernous pressure increase caused by nerve stimulation was reversed by treatment with L-NA; however, L-arginine restored the pressor response. In addition, hexamethonium suppressed the pressure increase that resulted from the nerve stimulation. In corpus cavernosum isolated from monkeys, transmural electrical stimulation elicited frequency-dependent relaxation. The relaxation was attenuated by physostigmine, and was potentiated by atropine. Relaxation was markedly inhibited by treatment with L-NA. It appears that nitric oxide (NO) released from inhibitory nerves, even at low frequencies, has a pivotal role in the initiation and maintenance of intracavernous pressure increase and penile erection in monkeys. Prejunctional muscarinic receptors in nitrergic nerves are expected to participate in the impairment of NO release. Nitrergic nerves responsible for penile erection may originate from ganglia close to the corpus cavernosum.

Isoform switching in myofibrillar and excitation-contraction coupling proteins contributes to diminished contractile function in regenerating rat soleus muscle

Postnatal development of skeletal muscle occurs through the progressive transformation of diverse biochemical, metabolic, morphological, and functional characteristics from the embryonic to the adult phenotype. Since muscle regeneration recapitulates postnatal development of muscle fiber, it offers an appropriate experimental model to investigate the existing relationships between diverse muscle functions and the expression of key protein isoforms, particularly at the single-fiber level. This study was carried out in regenerating soleus muscle 14 days after injury. At this intermediate stage, the regenerating muscle exhibited a recovery of mass greater than its force generation capacity. The lower specific tension of regenerating muscle suggested intrinsic defective excitation-contraction coupling and/or contractility processes. The presence of developmental isoforms of both the voltage-gated Ca2+channel (α1C) and of ryanodine receptor 3, paralleled by an abnormal caffeine contracture development, confirms the immature excitation-contraction coupling of the regenerating muscle. The defective Ca2+handling could also be confirmed by the lower sarcoplasmic reticulum caffeine sensitivity of regenerating single fibers. Also, regenerating single fibers revealed a lower maximal specific tension, which was associated with the residual presence of embryonic myosin heavy chains. Moreover, the fibers showed a reduced Ca2+sensitivity of myofibrillar proteins, particularly those simultaneously expressing the slow and fast isoforms of troponin C. The present results indicate that the expression of developmental proteins determines the incomplete functional recovery of regenerating soleus.

Pathophysiology and treatment of diabetic erectile dysfunction

The pathophysiology of diabetes is multifactorial and no single etiology is at the forefront. The proposed mechanisms of erectile dysfunction (ED) in diabetic patients includes elevated advanced glycation end-products (AGEs) and increased levels of oxygen free radicals, impaired nitric oxide (NO) synthesis, increased endothelin B receptor binding sites and ultrastructural changes, upregulated RhoA/Rho-kinase pathway, NO-dependent selective nitrergic nerve degeneration and impaired cyclic guanosine monophosphate (cGMP)-dependent kinase-1 (PKG-1). The treatment of diabetic ED is multimodal. Treatment of the underlying hyperglycemia and comorbidities is of utmost importance to prevent or halt the progression of the disease. The peripherally acting oral phosphodiesterase type 5 (PDE5) inhibitors are the mainstay of oral medical treatment of ED in diabetics. Vacuum erection devices are an additional treatment as a non-invasive treatment option. Local administration of vasoactive medication via urethral suppository or intracorporal injection can be effective with minimal side-effects. Patients with irreversible damage of the erectile mechanism are candidates for penile implantation. Future strategies in the evolution of the treatment of ED are aimed at correcting or treating the underlying mechanisms of ED. With an appropriate vector, researchers have been able to transfect diabetic animals with agents such as neurotrophic factors and nitric oxide synthase (NOS). Further studies in gene therapy are needed to fully ascertain its safety and utility in humans.

Effects of ethanol on intracorporeal structures of the rat

OBJECTIVE

Previous studies demonstrated that acute in vitro exposure of corpus cavernosal tissue to ethanol decreased its response to field stimulation and pharmacological stimulation. In the present study we investigated the effects of chronic ethanol consumption on the ultrastructure of cavernosal smooth muscle cells, elastic fibres and collagen content.

MATERIAL AND METHODS

Fourteen adult wistar rats were divided into a control group (n = 7, fed a standard diet and tap water) and an alcoholic group (n = 7, fed a standard diet and 5% (v/v) ethanol in drinking water and by increasing the ethanol concentration for every week, at the end of 6th week 30% (v/v) ethanol concentration was attained. Same dose was given until 12th week. At the end of 12th week blood samples were obtained and the ethanol concentrations were determined. The cavernosal tissues were obtained and immunohistochemical examinations were performed.

RESULTS

Immunohistochemical analysis revealed that chronic ethanol exposure markedly decreased the content of smooth muscle cells, elastic fibres and collagen type 4.

CONCLUSION

Our findings suggest that in this animal model chronic ethanol exposure decreases the percentage of staining for smooth muscle actin, elastin, and collagen type 4 which are the key structures fundamental for erection.

RyR isoforms and fibre type-specific expression of proteins controlling intracellular calcium concentration in skeletal muscles

Muscle fibres which shorten with high maximum shortening velocity also exhibit fast kinetics of contraction, i.e. short values of time to peak tension and time to half relaxation. This short review aims to discuss the molecular basis of such correlation, to reach, based on the available literature, an answer to the question whether there is a correlation in expression of proteins determining shortening velocity, myosin isoforms in the first place, and proteins controlling cytosolic calcium concentration and its variations at rest or during contraction. Although the isoforms of RyR, the sarcoplasmic calcium release channels, do not show a tightly coordinated expression with myosin isoforms, other proteins involved in controlling intracellular calcium do. This is likely sufficient to guarantee the correlation between maximum shortening velocity and speed of isometric contraction.

Caffeine Use in Sports, Pharmacokinetics in Man, and Cellular Mechanisms of Action

Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.

Effect of sildenafil on the isolated rat aortic rings

Sildenafil, a highly selective inhibitor of PDE 5, is effective in the treatment of erectile dysfunction. Penile erection involves relaxation of smooth muscle of corpus cavernosum and its associated arterioles. The objective of this study was to investigate the effect of sildenafil on nitric oxide/cyclic guanosine monophosphate (NO/cGMP)-dependent relaxation of rat aortic rings. The contribution of sildenafil to the vasorelaxation of rat aortic rings was also investigated. Sildenafil produced significant potentiation of acetylcholine (ACh, 2 x 10(-6) m)-induced relaxation at concentration > or =1 x 10(-8) m. Addition of sildenafil (1 x 10(-7) m) to aortic rings failed to alter the effect of N(G)-nitro-L-arginine (l-NNA, 3 x 10(-5) m) or methylene blue (MB, 3 x 10(-5) m) on ACh response. Similarly, sildenafil (1 x 10(-7) m) augmented significantly the vasorelaxation induced by sodium nitroprusside over the range of 1 x 10(-9)-1 x 10(-8) m. When added to phenylephrine (3 x 10(-6) m)-precontracted rat aortic rings, sildenafil (1 x 10(-9)-1 x 10(-4) m) induced concentration-dependent relaxation reaching a maximum of 96.48 +/- 1.44%. These relaxations were not significantly attenuated by previous incubation with L-NNA (3 x 10(-5) m) or MB (3 x 10(-5) m). Denudation did not significantly affect the vasorelaxant effect of sildenafil. Sildenafil may act in the rat aortic rings through the amplification of NO/cGMP pathway. It may augment both basal endothelial NO function and exogenous NO-dependent vasodilatation. However, sildenafil may act by a mechanism independent of NO/cGMP pathway and this mechanism contributes to its smooth muscle relaxant effect.

MACROPHAGE ARGINASE REGULATION BY CCAAT/ENHANCER-BINDING PROTEIN ??

Arginase activity is expressed by macrophages in healing wounds and other sites of inflammation and has been shown to modulate the synthesis of nitric oxide, polyamines, and collagen. The role of CCAAT/enhancer-binding protein beta (C/EBPbeta) in the regulation of macrophage arginase by different agonists was investigated using C/EBPbeta-/- and +/+ macrophage cell lines. 8-Bromo-cyclic adenosine monophosphate (8-Br-cAMP, 0.5 mM), recombinant murine interleukin 4 (rmIL-4, 20 U/mL), Escherichia coli lipopolysaccharide (100 ng/mL), and hypoxia (1% O2) induced arginase activity in C/EBPbeta+/+ macrophages, where enzyme activity correlated with arginase I protein. Only rmIL-4 increased arginase activity in C/EBPbeta-/- cells. Arginase II protein was expressed constitutively in wild-type and C/EBPbeta-/- cell lines and was unaltered by 8-Br-cAMP or rmIL-4. rmIL-4-stimulated immortalized C/EBPbeta-/- macrophages demonstrated higher nuclear signal transducer and activator of transcription-6 (STAT6) and phospho-STAT6 content than their +/+ counterparts. Validating the biological relevance of findings with the cell lines, additional experiments examined wound fluids and peritoneal macrophages from C/EBPbeta-/- mice and demonstrated that both contained less arginase activity than those from wild-type controls. Wounds in C/EBPbeta-/- animals showed signs of delayed maturation, as manifested by the persistence of neutrophils in the inflammatory infiltrate. Peritoneal macrophages from C/EBPbeta+/+ animals responded to 8-Br-cAMP and rmIL-4 with increased arginase activity, whereas those from C/EBPbeta-/- mice did not respond to cAMP. Results demonstrate a key mechanistic role for C/EBPbeta in the modulation of macrophage arginase I expression in vivo and in vitro.

Altered expression of l-arginine metabolism pathway genes in chronic wounds in recessive dystrophic epidermolysis bullosa

Individuals with the severe, mutilating Hallopeau-Siemens form of recessive dystrophic epidermolysis bullosa (HS-RDEB) have trauma-induced blisters and skin erosions which often progress to wounds that are slow to heal. These chronic wounds cause considerable morbidity and there is an increased risk of squamous cell carcinoma arising in the wound margins. Currently, little is known about the keratinocyte cell biology in these wounds. Therefore, we compared the gene expression profiles of wound edge with nonwounded skin from two individuals with HS-RDEB. Trauma-induced wound sites had been present in both patients for more than 3 months. Hybridizations using DermArray gene expression filters showed relative differences in gene expression between wounded and unwounded skin. Notably, there was a fivefold increase in expression of arginase-1 (ARG1) in the chronic wound samples. Expression of seven other genes relevant to L-arginine metabolism also showed differences greater than twofold. L-arginine is known to have a critical role in the synthesis of nitric oxide as part of normal tissue repair. Although alterations in arginase isoenzymes have been detected previously in other chronic wounds (human and animal models), this is the first study to demonstrate differences in several components of the L-arginine metabolism pathway in chronic wounds, and the first to examine chronic wounds in HS-RDEB. The data show that the cascade of L-arginine metabolites is altered in HS-RDEB and the findings may provide new insight into the pathology of chronic wounds in this genodermatosis.

Comparative effects of sildenafil, phentolamine, yohimbine and l-arginine on the rabbit corpus cavernosum

Penile erection involves relaxation of smooth muscle of corpus cavernosum and associated arterioles. Sildenafil, a highly selective inhibitor of phosphodiesterase type 5, is effective in the treatment of erectile dysfunction. The aim of this study is to investigate the effect of sildenafil on smooth muscle of the rabbit corpus cavernosum (RCC) and to compare its effect with those of phentolamine, yohimbine and L-arginine. The effects of sildenafil, phentolamine, yohimbine and L-arginine were studied on the response of the RCC to electrical field stimulation (EFS) as well as on the phenylephrine (PE, 3 x 10(-6) M)-induced tone. EFS caused transient, frequency-dependent relaxation of the RCC that was inhibited by the nitric oxide synthase inhibitor NG-nitro-L-arginine (3 x 10(-5) M). Sildenafil (1 x 10(-9)-1 x 10(-6) M) and phentolamine (1 x 10(-9)-1 x 10(-6) M) enhanced the EFS-induced relaxation in a concentration-dependent manner with ED50 of 0.056 +/- 0.004 and 0.572 +/-0.035 microM at 8 Hz, respectively, yohimbine (3 x 10(-7)-3 x 10(-5) M) and L-arginine (3 x 10(-6)-3 x 10(-4) M) did not show significant effects (ED50 at 8 Hz = 35.84 +/-2.24 and 2.164 +/- 0.174 microM, respectively). Sildenafil (1 x 10(-9) and 1 x 10(-8) M) potentiated the EFS-induced relaxation caused by L-arginine (3 x 10(-5) m). Sildenafil, phentolamine, yohimbine and L-arginine reduced the PE-induced tone to different extents; the ED50 values were 0.81 +/- 0.097, 0.49 +/- 0.025 and 13.97 +/- 1.10 microM, respectively. Maximum concentration of L-arginine used failed to produce 50% relaxation (ED20 = 221.82 +/- 15.71 microM). The muscle relaxant effects of different combinations of sildenafil and L-arginine on PE-induced tone did not differ significantly from the sum of the individual effects. The results demonstrate that sildenafil, when compared to other drugs used in penile erection dysfunction, shows the highest potency on the nitrergic transmission in the RCC. On the other hand, phentolamine was found to possess the highest potency in inducing relaxation of RCC proving that its action is independent on the stimulated neurogenic system. In addition, the combination of less effective doses of sildenafil and L-arginine has a potential advantage on erectile functions. The importance of this combination remains to be solved clinically.

Oxygen and the regulation of gene expression in wounds

Work from Tom Hunt's laboratory first identified wound hypoxia as a potential regulator of the biology of cells participating in tissue repair. Current understanding of the role of oxygen in the regulation of gene expression begins to provide a mechanistic basis for the prediction that oxygen could be a fundamental regulator of wound healing made by the Hunt laboratory. The present article describes the experience of the authors' laboratory in defining the expression of two oxygen-regulated genes, those for the inducible form of nitric oxide synthase and for arginase I in experimental wounds. Observations made regarding these two genes are discussed in the context of the overall regulatory role of oxygen as a phenotypic modulator of inflammatory cells.

Arginine physiology and its implication for wound healing

Arginine is a basic amino acid that plays several pivotal roles in cellular physiology. Like any amino acid, it is involved with protein synthesis, but it is also intimately involved with cell signaling through the production of nitric oxide and cell proliferation through its metabolism to ornithine and the other polyamines. Because of these multiple functions, arginine is an essential substrate for wound healing processes. Numerous studies have shown that arginine supplementation can lead to normalization or improvement of healing. This article reviews the basic biochemistry and cell signaling within which arginine performs its functions. In particular, the requirement for this amino acid in tissue repair is highlighted.

Nandrolone decanoate treatment affects sarcoplasmic reticulum Ca(2+) ATPase function in skinned rat slow- and fast-twitch fibres

The effects of anabolic-androgenic steroid administration on the function of the sarcoplasmic reticulum (SR) pump were investigated in chemically skinned fibres from the extensor digitorum longus (EDL) and soleus muscles of sedentary rats. Twenty male rats were divided into two groups, one group received an intramuscular injection of nandrolone decanoate (15 mg x kg(-1)) weekly for 8 weeks, the second received similar weekly doses of vehicle (sterile peanut oil). Compared with control muscles, nandrolone decanoate treatment reduced SR Ca(2+) loading in EDL and soleus fibres by 49% and 29%, respectively. In control and treated muscles, the rate of Ca(2+) leakage depended on the quantity of Ca(2+) loaded. Furthermore, for similar SR Ca(2+) contents, the Ca(2+) leakage rate was not significantly modified by nandrolone decanoate treatment. Nandrolone decanoate treatment thus affects Ca (2+) uptake by the SR in a fibre-type dependent manner.

Caffeine-induced contracture in oesophageal striated muscle of normotensive and hypertensive rats

To elucidate whether properties of the sarcoplasmic reticulum are altered, not only in vascular smooth muscle, but also in visceral striated muscle of spontaneously hypertensive rats (SHR), caffeine-induced contractures in oesophageal striated muscle of Wistar Kyoto rats (WKY) and stroke-prone SHR (SHRSP) were compared. In both preparations, 30 mM caffeine induced a contracture with two components. The second component, which was diminished by extracellular Ca(2+) removal or Ni(2+) but not by verapamil, was much smaller in SHRSP. Both components and differences between WKY and SHRSP coincided with changes in intracellular Ca(2+). Although membrane potential was identical between these preparations, caffeine induced slight depolarization only in WKY preparations. Similar depolarization was observed with 10 mM K(+), which induced no contraction. It is suggested that the first and the second components of caffeine-induced contracture were induced by Ca(2+) released from sarcoplasmic reticulum and by Ca(2+) that entered through channels activated by sarcoplasmic reticulum Ca(2+) depletion, respectively. In SHRSP preparations, Ca(2+) from the latter pathway was clearly decreased, although this change is thought not to be related to the initiation of hypertension. These results suggest that Ca(2+) handling properties of cell membrane and sarcoplasmic reticulum are generally altered in muscles of SHRSP.

Endothelium-dependency of yohimbine-induced corpus cavernosum relaxation

Development and maintenance of penile erection requires the relaxation of the smooth muscle cells in the cavernous bodies and is essentially mediated by nitric oxide (NO). The penile flaccid state is conversely maintained by the alpha adrenergic neuroeffector system and by other vasoconstrictors, such as endothelin-1 (ET-1). In this study we examined the mechanisms involved in yohimbine-induced relaxation in human and rabbit corpora cavernosa (CC). We essentially found that yohimbine not only blocks contractions induced by adrenergic agonists, but also by non-adrenergic substances, such as ET-1. This effect was unrelated to antagonism at the level of ET receptors, because yohimbine did not affect ET-1-induced increase in intracellular calcium in isolated CC cells. Conversely, our data suggest that yohimbine counteracts ET-1-induced contractions by interfering with NO release from the endothelium. In fact, yohimbine-induced CC relaxation was inhibited by the mechanical removing of the endothelium and by blocking NO formation or signalling via guanylate cyclase and cGMP formation. Conversely, yohimbine activity was strongly increased by inhibiting cGMP degradation. In an experimental model of hypogonadism, performed on rabbits by chronic treatment with a long-lasting GnRH agonist, the relaxant yohimbine activity was also decreased, but completely restored by androgen supplementation. This effect was evident only in preparations in which the main source of NO was present (endothelium) or in which NO formation was not impaired by L-NAME. Our data indicate that the relaxant effect of yohimbine is both endothelium and androgen-dependent. This might justify the lack of efficacy of this drug in treatment of some form of organic erectile dysfunction.

Early changes of type 2B fibers after denervation of rat EDL skeletal muscle

Skeletal muscle type 2B fibers normally receive a moderate level of motoneuron discharge. As a consequence, we hypothesize that type 2B fiber properties should be less sensitive to the absence of the nerve. Therefore, we have investigated the response of sarcoplasmic reticulum and myofibrillar proteins of type 2B fibers isolated from rat extensor digitorum longus muscle after denervation (2 and 7 days). Single fibers were identified by SDS-PAGE of myosin heavy chain isoforms. Electrophysiological and isometric contractile properties of the whole muscle were also analyzed. The pCa-tension relationship of type 2B single fibers was shifted to the left at 2 days and to right at 7 days after denervation, with significant differences in the Hill coefficients and pCa threshold values in 2- vs. 7-day-denervated fibers. The sarcoplasmic reticulum Ca2+ uptake capacity and rate significantly decreased after 2 days of denervation, whereas both increased at 7 days. Caffeine sensitivity of sarcoplasmic reticulum Ca2+ release was transitory and markedly increased in 2-day-denervated fibers. Our results indicate that type 2B fiber functional properties are highly sensitive to the interruption of nerve supply. Moreover, most of 2-day-denervated changes were reverted at 7 days.

Intracavernous administration of SIN-1+VIP in an in vivo rabbit model for erectile function

In accordance with the data reporting the identification of nitric oxide synthase (NOS) and vasoactive intestinal polypeptide (VIP) positive nerve fibres in the trabecular meshwork of the corpus cavernosum, we suggest that nitric oxide (NO) and VIP may serve complementary physiological roles in penile erection. Therefore SIN-1 and VIP were administered alone and in combination in an in vivo rabbit model. All rabbits revealed basal pressure values of 5-8 cm H2O intracavernously. In the rabbits intracavernously (i.c.) injected with SIN-1 alone and VIP alone, no adequate erectile responses were observed. Whereas, in the group intracavernously injected with the combination of SIN-1+VIP, erectile responses with mean maximal intracavernous pressure (max. ICP) 52.8 (+/-13.2) cm H2O were noted. These pressure elevations do not statistically diverge (P>0.05) than the ones obtained in the control group administered i.c. injections of the combination of papaverine/phentolamine (mean max. ICP 51 (+/-14.73) cm H2O). Referring to our results, we conclude that the combined use of SIN-1+VIP could play an important role in the physiological treatment of erectile dysfunction.

Activation of the stem cell-derived tyrosine kinase/RON receptor tyrosine kinase by macrophage-stimulating protein results in the induction of arginase activity in murine peritoneal macrophages

Regulation of macrophage activities in response to inflammatory stimuli must be finely tuned to promote an effective immune response while, at the same time, preventing damage to the host. Our lab and others have previously shown that macrophage-stimulating protein (MSP), through activation of its receptor RON, negatively regulates NO production in response to IFN-gamma and LPS by inhibiting the expression of inducible NO synthase (iNOS). Furthermore, activated macrophages from mice harboring targeted mutations in RON produce increased levels of NO both in vitro and in vivo, rendering them more susceptible to LPS-induced endotoxic shock. In this study, we demonstrate that stimulation of murine peritoneal macrophages with MSP results in the RON-dependent up-regulation of arginase, an enzyme associated with alternative activation that competes with iNOS for the substrate L-arginine, the products of which are involved in cell proliferation and matrix synthesis. Expression of other genes associated with alternative activation, including scavenger receptor A and IL-1R antagonist, is also up-regulated in MSP-stimulated murine macrophages. Stimulation of cells with IFN-gamma and LPS blocks the ability of MSP to induce arginase activity. However, pretreatment of cells with MSP results in the up-regulation of arginase and inhibits their ability to produce NO in response to IFN-gamma and LPS, even in the presence of excess substrate, suggesting that the inhibition of NO by MSP occurs primarily through its ability to regulate iNOS expression.

Sarcoplasmic reticulum Ca(2+) content affects 4-CmC and caffeine contractures of rat skinned skeletal muscle fibers

This study investigated whether the sarcoplasmic reticulum Ca(2+) content of rat skeletal muscle fibers affected contractile responses obtained by an application of 4-chloro-m-cresol (4-CmC) and caffeine. Contractures were elicited on saponin-skinned fibers under different Ca(2+) loading conditions. The amplitude of 4-CmC and caffeine contractures of fast-twitch muscle fibers (edl, extensor digitorum longus) differed between the different loading conditions, and this is associated with a greater change in sensitivity to 4-CmC. When the sarcoplasmic reticulum was loaded with a low Ca(2+) concentration for a short period, the 4-CmC concentration providing half-maximal response was tenfold higher than with a larger sarcoplasmic reticulum Ca(2+) loading for a longer period, whereas for caffeine this concentration was only twofold higher in the same conditions. These findings indicate that 4-CmC contractile responses of edl muscle fibers are more dependent on luminal Ca(2+) activity than those of caffeine are. Thus 4-CmC would appear to be of greater interest than caffeine for the study of muscle contractile responses where variations in intracellular Ca(2+) activity exist.

Surgery induces human mononuclear cell arginase I expression

BACKGROUND

Arginase is a metabolic enzyme for the amino acid arginine that participates in the immune response to trauma. We hypothesize that surgical trauma induces arginase expression and activity in the human immune system.

METHODS

Peripheral mononuclear cell (MNC) arginase activity and expression and plasma nitric oxide metabolites and interleukin (IL)-10 were measured in patients undergoing elective general surgery. Twenty-two healthy volunteers served as a comparison population.

RESULTS

MNC arginase activity increased within 6 hours of surgery (p < 0.05) and coincided with increased arginase I protein expression. Plasma nitric oxide metabolites decreased significantly postoperatively (p < 0.05). Patients lacking an elevation in IL-10 failed to demonstrate increased MNC arginase activity.

CONCLUSION

Increased MNC arginase expression may contribute to postsurgical immune dysfunction by affecting arginine use and availability and nitric oxide metabolism in the immune system. Plasma IL-10 may play a role in regulating MNC arginase activity.

L-carnitine prevents increase in diastolic [CA2+] induced by doxorubicin in cardiac cells

Doxorubicin is a highly effective anticancer chemotherapeutic agent that produces a dose-dependent cardiomyopathy that limits its clinical usefulness. We investigated the acute effects of doxorubicin on diastolic free Ca2+ concentrations ([Ca2+]) and the cardioprotective action of L-carnitine in isolated cardiomyocytes loaded with fura-2/AM (acetoxymethyl ester). Exposure to 10(-6)-10(-4) M doxorubicin induced an elevation of diastolic calcium concentration ([Ca2+]) that was concentration dependent. Nitrendipine failed to prevent the doxorubicin-induced elevation of [Ca2+]. Incubation with L-carnitine (10(-8) to 10(-6) M) did not modify [Ca2+]. Pretreatment of cardiomyocytes with L-carnitine 10(-8)-10(-7) M did not prevent the doxorubicin effect on [Ca2+]. However, L-carnitine 10(-6) M fully inhibited the increase in [Ca2+] induced by this anthracycline derivative. These results indicate that acute exposure to doxorubicin impairs intracellular Ca2+ handling and that L-carnitine exerts a cardioprotective effect, in part by preventing the doxorubicin-induced increase in diastolic Ca2+ concentration.

Response to caffeine and ryanodine receptor isoforms in mouse skeletal muscles

The response to caffeine was studied in mouse muscles [diaphragm, soleus, and extensor digitorum longus (EDL)] with different ryanodine receptor isoform (RyR1, RyR3) composition and in single permeabilized muscle fibers dissected from diaphragm of wild-type (WT) and RyR3-deficient (RyR3-/-) mice at 1, 15, 30, and 60 postnatal days (PND). The caffeine response decreased during development, and, in adult mice, was greater in diaphragm, lower in EDL, and intermediate in soleus. This suggests a direct relation between response to caffeine and RyR3 expression. The lack of RyR3 reduced caffeine response in young, but not in adult mice, and did not abolish the age-dependent variation and the intermuscle differences. In diaphragm single fibers, the response to caffeine increased during development and was reduced in fibers lacking RyR3 both at 15 and 60 PND. A population of fibers highly responsive to caffeine was present in adult WT and disappeared in RyR3-/-. The results confirm the contribution of RyR3 to calcium release for contractile response and clarify the contribution of RyR3 to developmental changes and intermuscle differences.

Different Ca2+ releasing action of caffeine and depolarisation in skeletal muscle fibres of the rat

1. The relative abilities of caffeine and transverse tubular (T-) system depolarisation to induce Ca2+ release in mammalian skeletal muscle were compared in mechanically skinned fibres of the rat, in order to determine whether normal excitation-contraction (E-C) coupling is achieved by up-regulating the Ca2+-induced Ca2+ release process, as caffeine is known to do. 2. Caffeine triggered Ca2+ release in soleus (slow-twitch) fibres at much lower concentrations than in extensor digitorum longus (EDL) (fast-twitch) fibres when the sarcoplasmic reticulum (SR) of each type was loaded with Ca2+ at close to endogenous levels. The difference in caffeine sensitivity resulted at least in part from the SR being loaded endogenously at near maximal capacity in soleus fibres but at less than half of maximal capacity in EDL fibres. The caffeine sensitivity could be reversed by reversing the relative level of SR loading. 3. The ability of caffeine to induce Ca2+ release was markedly reduced by lowering the level of SR loading or by raising the free [Mg2+] from 1 to 3 mM. Caffeine, even at 30 mM, triggered little or no Ca2+ release in EDL fibres (a) at 1 mM (physiological) Mg2+ when the SR was loaded at two-thirds or less of the endogenous level, and (b) at 3 mM Mg2+ when the SR was loaded at close to the endogenous level. In contrast, depolarisation potently elicited Ca2+ release under these conditions in the same fibres. 4. The inability of 30 mM caffeine to induce Ca2+ release under certain conditions was not attributable to desensitisation or inactivation of the release channels, because there was no response even upon initial exposure to caffeine and depolarisation always remained able to trigger Ca2+ release. It instead appeared that caffeine was a relatively ineffectual stimulus in EDL fibres except under conditions where (a) the SR was heavily loaded, (b) the free [Mg2+] was low, or (c) a high [Cl-] was present. 5. These results show that the normal E-C coupling mechanism in mammalian skeletal muscle does not involve just enhancing Ca2+-induced Ca2+ release, and evidently requires the removal or bypassing of the inhibitory effect of Mg2+ on the Ca2+ release channels.

Characterization of RyR1-slow, a ryanodine receptor specific to slow-twitch skeletal muscle

Two distinct skeletal muscle ryanodine receptors (RyR1s) are expressed in a fiber type-specific manner in fish skeletal muscle (11). In this study, we compare [(3)H]ryanodine binding and single channel activity of RyR1-slow from fish slow-twitch skeletal muscle with RyR1-fast and RyR3 isolated from fast-twitch skeletal muscle. Scatchard plots indicate that RyR1-slow has a lower affinity for [(3)H]ryanodine when compared with RyR1-fast. In single channel recordings, RyR1-slow and RyR1-fast had similar slope conductances. However, the maximum open probability (P(o)) of RyR1-slow was threefold less than the maximum P(o) of RyR1-fast. Single channel studies also revealed the presence of two populations of RyRs in tuna fast-twitch muscle (RyR1-fast and RyR3). RyR3 had the highest P(o) of all the RyR channels and displayed less inhibition at millimolar Ca(2+). The addition of 5 mM Mg-ATP or 2.5 mM beta, gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) to the channels increased the P(o) and [(3)H]ryanodine binding of both RyR1s but also caused a shift in the Ca(2+) dependency curve of RyR1-slow such that Ca(2+)-dependent inactivation was attenuated. [(3)H]ryanodine binding data also showed that Mg(2+)-dependent inhibition of RyR1-slow was reduced in the presence of AMP-PCP. These results indicate differences in the physiological properties of RyRs in fish slow- and fast-twitch skeletal muscle, which may contribute to differences in the way intracellular Ca(2+) is regulated in these muscle types.