Chronic stimulation of mammalian muscle: changes in metabolite concentrations in individual fibers

Abstract

Single fibers were analyzed from rabbit fast-twitch tibialis anterior muscles freeze-clamped during continuous stimulation at 10 Hz for up to 8 wk. ATP declined after 1 wk to a stable level approximately 30% below controls. Phosphocreatine decreased earlier and to a greater extent (approximately 50%). Glycogen varied considerably among stimulated fibers and decreased on average approximately 75% by 8 wk. Glucose, lactate, citrate, and malate had changed little in the first 30 h and then increased four-, two-, four-, and sevenfold, respectively, over the next 5 wk. Glucose 6-phosphate showed the most unexpected behavior: with an overall upward trend, it descended to extremely low values (10% of control) after approximately 1 wk of stimulation. As long as high- and low-oxidative fibers were present, the former showed slightly higher levels of ATP, lactate, and malate; other metabolites did not differ in a consistent way. These unexpected observations, which differ strikingly from data for acute stimulation, shed light on adaptations that enable a chronically stimulated muscle to sustain a continuous high level of ATP utilization.

Adult fast myosin pattern and Ca 2+ -induced slow myosin pattern in primary skeletal muscle culture

“…A reduced intracellular phosphorylation potential and an elevated intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ), as they occur during sustained contractile activity, have been discussed as possible trigger events (2)(3)(4)(5). It was our aim to test whether an increase in [Ca 2ϩ ] i imposed on the muscle cell is indeed able to induce a fast-to-slow transition.…”

Postnatal development and plasticity of specialized muscle fiber characteristics in the hindlimb

“…Phenotypic variation among muscle fibers is based on qualitative and quantitative differences in expression of many genes that encode contractile proteins, enzymes of intermediary metabolism, and proteins serving other cellular functions [Baldwin et d.,tially from intrinsic developmental programs, adult skeletal muscle fibers retain the capability of responding to functional demands by varying their repertoire of expressed genes to alter their physiological, biochemical, and ultrastructural characteristics. Sustained changes in motor neuron activity, oxygen and nutrient supply, mechanical forces, or the hormonal milieu can modify specialized features of muscle fibers, a phenomenon termed "plasticity" [Baldwin et al, 1978;Kelly, 1978, 1981;Narusawa et al, 1987;Underwood and Williams, 1987;Henriksson et al, 1989;Condon et al, 1990;Williams and Neufer, 19961. Progress in identifying factors regulating the early stages of skeletal myogenesis has been impressive, but the molecular controls that govern fiber-type diversity remain unclear. We have focused attention on expression of the myoglobin gene as the starting point in efforts to gain a greater understanding of the molecular mechanisms of muscle specialization and plasticity.…”

Are Abnormalities in Sarcoplasmic Reticulum Calcium Cycling Properties Involved in Trapezius Myalgia?

“…With the exception of COX, all enzyme activities were assayed fluorometrically at 24-CY25-C according to previously published procedures. 15,16 The tissue was hand homogenized (0-CY4-C) in a phosphate buffer (pH 7.4) containing 5 mM mercaptoethanol, 0.5 mM EDTA, and 0.2% bovine serum albumin (BSA). Homogenates were diluted in 20 mM imidazole buffer with 0.2% BSA.…”