Fasting increases plasma membrane fatty acid-binding protein (FABPPM) in red skeletal muscle

The present study was designed to investigate the presence of the fatty acid-binding protein (FABPPM) in the plasma membranes of skeletal muscles with different oxidative capacities for free fatty acid (FFA) oxidation during conditions of normal (fed) or increased (fasted) FFA utilization in the rat. Female Sprague-Dawley rats were either fed or fasted for 12, 24, or 48 h and, plasma membranes (PM) fractions from red and white skeletal muscles were isolated. Short-term fasting significantly decreased body weight by 11% and blood glucose concentration by 42% (6.6 ± 0.2-3.8 ± 0.4 mmol/l) and increased plasma FFA concentration by 5-fold (133 ± 14-793 ± 81 µmol/l). Immunoblotting of PM fractions showed that FABPPM protein content was 83 ± 18% higher in red than in white skeletal muscle and correlated with oxidative capacity as measured by succinate dehydrogenase activity (r = 0.78, p < 0.05). Short-term fasting significantly increased FABPPM protein content by 60 ± 8% in red skeletal muscle but no change was measured in white skeletal muscle. These results show that FABPPM protein content in skeletal muscle is related to oxidative potential and can be increased during a physiological condition known to be associated with an increase in FFA utilization, suggesting that cellular expression of FABPPM may play a role in the regulation of FFA metabolism in skeletal muscle. (Mol Cell Biochem 166: 153-158, 1997)     

Expression of subunits of the 19S complex and of the PA28 activator in rat skeletal muscle

A precise knowledge of the role of subunits of the 19S complex and the PA28 regulator, which associate with the 20S proteasome and regulate its peptidase activities, may contribute to design new therapeutic approaches for preventing muscle wasting in human diseases. The proteasome is mainly responsible for the muscle wasting of tumor-bearing and unweighted rats. The expression of some ATPase (MSS1, P45) and non ATPase (P112-L, P31) subunits of the 19S complex, and of the two subunits of the PA28 regulator, was studied in such atrophying muscles. The mRNA levels for all studied subunits increased in unweighted rats, and analysis of MSS1 mRNA distribution profile in polyribosomes showed that this subunit entered active translation. By contrast, only the mRNA levels for MSS1 increased in the muscles from cancer rats. Thus, gene expression of the proteasome regulatory subunits depends on a given catabolic state. Torbafylline, a xanthine derivative which inhibits tumor necrosis factor production, prevented the activation of protein breakdown and the increased expression of 20S proteasome subunits in cancer rats, without reducing the elevated MSS1 mRNA levels. Thus, the increased expression of MSS1 is regulated independently of 20S proteasome subunits, and did not result in accelerated proteolysis.     

Alterations in sarcomere structure, collagen organization, mitochondrial activity, and protein metabolism in the avian low score normal muscle weakness

Skeletal muscle fibers are surrounded by an extracellular matrix. The extracellular matrix is composed of glycoproteins, collagen, and proteoglycans. Proteoglycans have been suggested to play an important functional role in tissue differentiation. However, an understanding of how the extracellular matrix affects skeletal muscle development and function is largely unknown. In the avian genetic muscle weakness, low score normal (LSN), a late embryonic increase in the expression of decorin is followed by a subsequent increase in collagen crosslinking. The sarcomere organization, collagen fibril diameter and organization were investigated using transmission electron microscopy. Measurements were made at 20 days of embryonic development and 6 weeks posthatch. These studies showed changes in sarcomere organization and deterioration of muscle fibril structure in the LSN pectoral muscle. In vitro satellite cell cultures were developed and assayed for mitochondrial activity, and protein synthesis and degradation. In these analyses, mitochondrial activity from LSN satellite cells was significantly higher than those from normal pectoral muscle satellite cells. Protein synthesis rates between the normal and LSN satellite cell-derived myotubes were similar, but protein degradation rates were higher in the LSN cultures. Based on the reported functions of decorin as a regulator of cell proliferation and collagen fibril organization, it is possible that the late embryonic increase in decorin may be influencing the alterations in LSN sarcomere and collagen organization.     

Mesodermal Guidance of Pioneer Axon Growth

Pioneer axons in insect legs are experimentally accessible model systems for the molecular identification and cellular localization of guidance cues regulating the path of axon growth. A detailed study of the Fe2 pioneer axons in the legs of the cockroach was performed to examine the diversity of guidance mechanisms. A detailed microscopic analysis of the axons at various points in their trajectory indicates that the Fe2 axons grow on a mesodermal substratum which contains the cues guiding their growth along a stereotyped path. An identified pair of muscle pioneer cells (MPC) are likely to play an important role in enabling the Fe2 growth cones to respond to mesodermal guidance cues. The addition of heparan sulfate, heparitinase, and phosphatidylinositol-specific phospholipase C to the medium perturbs thein situpath of growth of the Fe2 axons and the location of the MPC in cultured embryos. This indicates a role for heparan sulfate proteoglycans and glycosylphosphatidylinositol-anchored proteins in axon guidance. When these results are compared to those of similar experiments performed on the well-characterized Ti1 axons, they indicate significant differences in the mechanisms that are used for axon guidance. The Fe2 neurons are a good model for elucidating the mechanisms used to guide axon growth on nonmuscle mesodermal substrates often encountered in the periphery of vertebrate embryos.     

肌肉营养因子

现已发现许多物质具有肌肉营养作用,这些物质称为肌肉营养因子。肌肉营养因子为运动神经元病和肌肉退行性病变的研究和治疗提供了新的手段。本文分别叙述了已知的各种肌肉营养因子的研究概况,并指出肌肉营养因子研究的方向和临床意义。     

自发性高血压大鼠血管平滑肌细胞的精氨酸转运和脂质体对转运的影响

本工作在培养的自发民生高血压大鼠和对照ＷＫＹ大鼠的主动脉平滑肌细胞上,观察细胞Ｌ－精氨酸转动转征,并观察脂质体作为Ｌ－Ａｒｇ载体对Ｌ－Ａｒｇ细胞转运的影响。     

5—羟色胺对肺动脉平滑肌细胞在缺氧条件下增殖的作用

本研究应用细胞培养、＾３Ｈ－ＴｄＲ掺入,核酸分子杂交、免疫组织化学染色技术,探讨无氧（０％Ｏ２＋９５％Ｎ２＋５％ＣＯ２）和／或低氧（２．５￣３％Ｏ２＋９２％Ｎ２＋５％ＣＯ２）对新生小牛肺动脉平滑肌细胞增殖和５－羟色胺转载体基因表达的影响。结果表明：无氧２４ｈ可刺激ＰＡＳＭ的ＤＮＡ合成,＾３Ｈ－ＴｄＲ的掺入增加（Ｐ〈０．０５）,加入５－羟色胺能非常显著地促进无氧ＰＡＳＭ增殖（Ｐ〈０．００１）,而对常     

Control of skeletal muscle fibres and adipose cells size in the flesh of rainbow trout

The distributions of the diameters of skeletal muscle fibres and adipocytes were studied in rainbow trout. The cellularity of perivisceral adipose tissues and subcutaneous ventral and dorsal adipose tissues were characterized more specifically. In these tissues, a population of small adipocytes was distinguishable from larger adipocytes. The same was observed in white muscle. The effects of extrinsic factors (dietary lipid in two different thermal conditions) and intrinsic factors (strains in two different saline conditions, growth hormone) on the long-term response of the cellularity of both muscle and adipose tissues were studied. The effects of thermal environment were tested on fish fed the same ration and the effects of saline environment on fish fed ad libitum. The mean size of white muscle fibres was relatively unaffected by the different treatments tested: genetic origin and dietary lipid in different environmental conditions. There were significant differences in growth rate due to genetic origin and saline environment. The possible involvement of hyperplasia in response to these different factors is discussed. Growth hormone supplementation enhanced the percentage of small diameter fibres indicating a role of this hormone in the control of muscle hyperplastic growth. The mean size of adipose cells was affected only slightly by the different treatments tested. An increase in adipose cell size with aging and lipid content was observed. The percentage of small adipocytes also increased with aging. Thus, it is proposed that the development of adipose tissues, and thus fat retention, both result from the recruitment of new adipocytes and from the increase in size of existing adipocytes. The hyperplastic process contributed significantly to the differences in fat retention due to different treatments tested (strains, thermal and saline environments). When partially substituting fish oils for corn oils in the diet, a large increase in the ventral adipose cell size was seen indicating a potential negative effect of n-6 fatty acids on cell proliferation. Growth hormone treatment, on the contrary, induced a decrease in the size of perivisceral adipocytes. Thus, diet and hormonal status affect adipose cells size through two different metabolic pathways: lipogenesis and lipolysis respectively.     

Sodium and Calcium Inward Currents in Freshly Dissociated Smooth Myocytes of Rat Uterus

Freshly dissociated myocytes from nonpregnant, pregnant, and postpartum rat uteri have been studied with the tight-seal patch-clamp method. The inward current contains both I_Na and I_Ca that are vastly different from those in tissue-cultured material. I_Na is abolished by Na⁺-free medium and by 1 μM tetrodotoxin. It first appears at ∼−40 mV, reaches maximum at 0 mV, and reverses at 84 mV. It activates with a voltage-dependent τ of 0.2 ms at 20 mV, and inactivates as a single exponential with a τ of 0.4 ms. Na⁺ conductance is half activated at −21.5 mV, and half inactivated at −59 mV. I_Na reactivates with a τ of 20 ms. I_Ca is abolished by Ca²⁺-free medium, Co²⁺ (5 mM), or nisoldipine (2 μM), and enhanced in 30 mM Ca²⁺, Ba²⁺, or BAY-K 8644. It first appears at ∼−30 mV and reaches maximum at +10 mV. It activates with a voltage-dependent τ of 1.5 ms at 20 mV, and inactivates in two exponential phases, with τ''s of 33 and 133 ms. Ca²⁺ conductance is half activated at −7.4 mV, and half inactivated at −34 mV. I_Ca reactivates with τ''s of 27 and 374 ms. I_Na and I_Ca are seen in myocytes from nonpregnant estrus uteri and throughout pregnancy, exhibiting complex changes. The ratio of densities of peak I_Na/I_Ca changes from 0.5 in the nonpregnant state to 1.6 at term. The enhanced role of I_Na, with faster kinetics, allows more frequent repetitive spike discharges to facilitate simultaneous excitation of the parturient uterus. In postpartum, both currents decrease markedly, with I_Na vanishing from most myocytes. Estrogen-enhanced genomic influences may account for the emergence of I_Na, and increased densities of I_Na and I_Ca as pregnancy progresses. Other influences may regulate varied channel expression at different stages of pregnancy.     

Histochemical and immunohistochemical studies on the origin of the blue marlin heater cell phenotype

The superior rectus muscle fibers of marlins, swordfish, sailfish and spearfish are modified for heat production at the expense of contractile ability. Although ‘heater cells’ are a muscle derivative (Bennett, 1971 and Block, 1991), the myoblast origin and developmental pathway of these thermogenic cells is unknown. To gain insight into heater cell origins, we characterized blue marlin superior rectus muscle and its heater tissue derivative with histochemical and immunological techniques. We specifically employed myosin ATPase and succinate dehydrogenase histochemical assays, and myosin heavy chain immunohistochemistry. Results revealed that marlin superior rectus muscles contain at least six distinct fiber types, and suggested the presence of both twitch and tonic fibers. Immunological results indicate that myosin is present within the thermogenic cells but not in myofibrillar lattices. The antibodies that recognized myosin in heater cells also labeled myosin in the twitch fibers of swimming muscle. In contrast, antibodies that labeled histologically defined tonic fibers did not label heater cells. These results suggest that heater cells and twitch fibers express the same myosin isoform, and establish a phenotypic connection between heater cells and twitch fibers. This conclusion is discussed in the context of the muscle-to-heater trajectory and the muscle fiber-type origin of heater cells.