Acetylcholinesterase (AChE) mRNA levels are severalfold higher in fast rat muscles compared with slow. We hypothesized that AChE mRNA levels and AChE activity in the neuromuscular junction depend on a specific nerve-induced pattern of motor unit activation. Chronic low-frequency stimulation, mimicking the activation pattern in slow muscles, was applied to fast muscles in rats. Molecular forms o...

BACKGROUND We examined the time course of the functional alterations in two types of muscles following sciatic nerve crush in neonatal rats and the neuroprotective effect of Mg2+. METHODS The nerve crush was performed on the 2nd postnatal day. MgSO4*7H2O was administered daily for two weeks. Animals were examined for the contractile properties and for the number of motor units of extensor dig...

Recent evidence suggests aerobic exercise may help preserve soleus muscle mass during unloading. The purpose of this investigation was to examine the muscle-specific metabolic response to running as it relates to muscle growth. Mixed-muscle protein synthesis [fractional synthetic rate (FSR)] and gene expression (GE) were examined in the vastus lateralis (VL) and soleus (SOL) muscles from eight ...

We tested the hypothesis that the beta-myosin heavy chain (beta-MHC) 3'-untranslated region (UTR) mediates decreased protein expression after tenotomy of the rat soleus. We also tested the hypothesis that decreased protein expression is the result of RNA-protein interactions within the 3'-UTR. beta-MHC was chosen for study because of its critical role in the function of postural muscles such as...

Intrinsic muscle abnormalities affecting skeletal muscle are often reported during chronic heart failure (CHF). Because myosin is the molecular motor of force generation, we sought to determine whether its dysfunction contributes to skeletal muscle weakness in CHF and, if so, to identify the underlying causative factors. Severe CHF was induced in rats by aortic stenosis. In diaphragm and soleus...

Aging diminishes myogenic tone in arterioles from skeletal muscle. Recent evidence indicates that both large-conductance Ca2+-activated (BKCa) and voltage-dependent (KV) K+ channels mediate negative feedback control of the myogenic response. Thus we tested the hypothesis that aging increases the contributions of KV and BKCa channels to myogenic regulation of vascular tone. Because myogenic resp...

The calf muscles, compared with the thigh, are less responsive to resistance exercise in ambulatory and bed-rested individuals, apparently due to muscle-specific differences in protein metabolism. We chose to evaluate the efficacy of using amino acids to elevate protein synthesis in the soleus, because amino acids have been shown to have a potent anabolic effect in the vastus lateralis. Mixed m...

INTRODUCTION The soleus H-reflex is dynamically modulated during walking. However, modulation of the gastrocnemii H-reflexes has not been studied systematically. METHODS The medial and lateral gastrocnemii (MG and LG) and soleus H-reflexes were measured during standing and walking in humans. RESULTS Maximum H-reflex amplitude was significantly smaller in MG (mean 1.1 mV) or LG (1.1 mV) than...

Nine days of hindlimb suspension resulted in atrophy (55%) and loss of protein (53%) in rat soleus muscle due to a marked elevation in protein breakdown (66%, P < 0.005). To define which proteolytic system(s) contributed to this increase, soleus muscles from unweighted rats were incubated in the presence of proteolytic inhibitors. An increase in lysosomal and Ca 2+-activated proteolysis (254%, ...

Exercise capacity and skeletal muscle blood flow during exercise are reduced with advancing age. This reduction in blood flow capacity may be related to increased reactivity of skeletal muscle resistance vessels to vasoconstrictor stimuli. The purpose of this study was to test the hypothesis that aging results in increased vasoconstrictor responses of skeletal muscle resistance arterioles. Firs...