To gain some insight into inotropic mechanisms, we compared the effects of several classes of inotropic interventions on the isometric twitch and force-velocity properties of isolated rabbit myocardium. Postextrasystolic potentiation was chosen as one of the interventions in the belief that its onset is so rapid that it would be unlikely to cause substantial chemical changes in the contractile ...

The activity of 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK), a negative regulator of cell size, is up-regulated with age in resting and overloaded fast-twitch skeletal muscle but not slow-twitch muscle. Here, we provide evidence to support the hypothesis that elevated AMPK activity plays a potentially important integrative role in the age-related atrophy and diminished capa...

We hypothesized that the occurrence of spontaneous Ca2+ release from the sarcoplasmic reticulum (SR), in diastole, might be a mechanism for the saturation of twitch potentiation common to a variety of inotropic perturbations that increase the total cell Ca. We used a videomicroscopic technique in single cardiac myocytes to quantify the amplitude of electrically stimulated twitches and to monito...

The twitch interpolation technique is commonly employed to assess the completeness of skeletal muscle activation during voluntary contractions. Early applications of twitch interpolation suggested that healthy human subjects could fully activate most of the skeletal muscles to which the technique had been applied. More recently, however, highly sensitive twitch interpolation has revealed that e...

Isometric twitch contractions have been studied in extensor hallucis brevis muscles of 32 healthy male subjects aged between 3 and 25 years. The maximum twitch tensions were found to increase gradually with age and then to undergo marked enhancement at puberty. After puberty little further change occurred. In the youngest children examined the twitch contraction times were already within the ad...

A qualitative histochemical assessment of glycogen loss in biopsies was made in bush-babies after running and jumping. Glycogen loss was related to the specific type of exercise. After running, glycogen loss was greatest in the slow-twitch oxidative fibre and depletion in the fast-twitch oxidative glycolytic fibres was similarly greater than in the fast-twitch glycolytic fibres. After jumping, ...

Ca(2+) entry during the action potential stimulates muscle contraction. During repetitive low frequency stimulation, skeletal muscle undergoes staircase potentiation (SP), a progressive increase in the peak twitch force induced by each successive stimulus. Multiple mechanisms, including myosin regulatory light chain phosphorylation, likely contribute to SP, a temperature-dependent process. Here...