A cDNA clone encoding skeletal muscle myosin light chain kinase (MLCK) was isolated from a rat skeletal muscle library using oligonucleotide probes. The total length of the rat skeletal muscle MLCK cDNA was 2823 base pairs with an open reading frame of 1830 base pairs. The deduced sequence of the 610-amino acid protein exhibited 96% amino acid identity to rabbit skeletal muscle MLCK in the carb...

The composition of skeletal muscle, in terms of the relative number of slow- and fast-twitch fibers, is tightly regulated to enable an organism to respond and adapt to changing physical demands. The phosphatase calcineurin and its downstream targets, transcription factors of the nuclear factor of activated T cells (NFAT) family, play a critical role in this process by promoting the formation of...

The resting membrane potential and intracellular potassium and sodium concentration of three guinea pig hind limb muscles were studied. These properties are related to the gross color, the speed of contraction, and the biochemically defined fiber type composing the muscle. The resting membrane potential and intracellular content were: white vastus (grossly white, fast-twitch glycolytic) -85.3 m...

The pyruvate dehydrogenase kinases (PDK1-4) regulate glucose oxidation through inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Immunoblot analysis with antibodies raised against recombinant PDK isoforms demonstrated changes in PDK isoform expression in response to experimental hyperthyroidism (100 microg/100 g body weight; 3 days) that was selective for fast-twitch vs sl...

During contractions, regulation of microvascular oxygen partial pressure (Pmv(O2)), which drives blood-myocyte O2 flux, is a function of skeletal muscle fiber type and oxidative capacity and can be altered by exercise training. The kinetics of Pmv(O2) during contractions in predominantly fast-twitch muscles evinces a more rapid fall to far lower levels compared with slow-twitch counterparts. Pe...

5'AMP-activated protein kinase (AMPK) has been suggested to be a key regulatory protein in exercise signaling of muscle glucose transport. To test this hypothesis, we investigated whether muscle glycogen levels affect AMPK activation and glucose transport stimulation similarly during contractions. Rats were preconditioned by a combination of swimming exercise and diet to obtain a glycogen-super...

Paralyzed skeletal muscle sometimes becomes faster and more fatigable after spinal cord injury (SCI) because of reduced activity. However, in some cases, pronounced muscle activity in the form of spasticity (hyperreflexia and hypertonus) occurs after long-term SCI. We hypothesized that this spastic activity may be associated with a reversal back to a slower, less fatigable muscle. In adult rats...

Certain enzymatic and structural features of myosin, purified from rat skeletal muscles representative of the fast twitch glycolytic (type IIb), the fast twitch oxidative (type IIa), and the slow twitch oxidative (type I) fiber, were determined and the results were compared with the measured contractile properties. Good correlation was found between the shortening velocities and Caz+-activated ...