Partial fast-to-slow conversion of regenerating rat fast-twitch muscle by chronic low-frequency stimulation.

Chronic low-frequency stimulation (CLFS) of rat fast-twitch muscles induces sequential transitions in myosin heavy chain (MHC) expression from MHCIIb --> MHCIId/x --> MHCIIa. However, the 'final' step of the fast-to-slow transition, i.e.

Deficiency in parvalbumin increases fatigue resistance in fast-twitch muscle and upregulates mitochondria.

The soluble Ca2+-binding protein parvalbumin (PV) is expressed at high levels in fast-twitch muscles of mice. Deficiency of PV in knockout mice (PV -/-) slows down the speed of twitch relaxation, while maximum force generated during tetanic contraction is unaltered. We observed that PV-deficient fast-twitch muscles were significantly more resistant to fatigue than were the wild type.

Effects of chronic low-frequency stimulation on Ca2+-regulatory membrane proteins in rabbit fast muscle.

Since chronic low-frequency stimulation of fast-twitch muscle fibers has a profound effect on all major functional elements of skeletal muscle, we analyzed the potential changes in the levels of Ca2+-regulatory membrane proteins during fast-to-slow transformation. In this study we show that, in addition to isoform-switching in myosin heavy chains, electrostimulation triggers a decline in fast isoforms and an increase in slow/cardiac isoforms of Ca2+-ATPase and calsequestrin. The levels of excitation-contraction coupling elements, such as the ryanodine receptor, the dihydropyridine receptor, triadin and sarcalumenin, decreased sharply following stimulation.

Identical responses of fast muscle to sustained activity by low-frequency stimulation in young and aging rats.

To investigate effects of sustained activity on major phenotypic properties, the left extensor digitorum longus muscle of young (15 wk) and aging (101 wk) male Brown Norway rats was subjected to 50 days of chronic low-frequency stimulation (CLFS; 10 Hz, 10 h/day). The contralateral muscle served as control. Changes in metabolic enzymes were analyzed by using glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase as reference enzymes of glycolysis and by using citrate synthase and 3-hydroxyacyl-CoA dehydrogenase as mitochondrial enzymes representative of aerobic-oxidative metabolism.

Energy-coupled transport across the outer membrane of Escherichia coli: ExbB binds ExbD and TonB in vitro, and leucine 132 in the periplasmic region and aspartate 25 in the transmembrane region are important for ExbD activity.

Ferric siderophores, vitamin B12, and group B colicins are taken up through the outer membranes of Escherichia coli cells by an energy-coupled process. Energy from the cytoplasmic membrane is transferred to the outer membrane with the aid of the Ton system, consisting of the proteins TonB, ExbB, and ExbD. In this paper we describe two point mutations which inactivate ExbD.