IMP reamination to AMP in rat skeletal muscle fiber types.

Inosine 5'-monophosphate (IMP) reamination in skeletal muscle fiber sections of the rat hindlimb was studied. High IMP concentrations were established during ischemic contractions in each fiber section: 3.1, 2.

Purine nucleoside formation in rat skeletal muscle fiber types.

To determine the capacity for purine nucleotide degradation among skeletal muscle fiber types, we established energy-depleted conditions in muscles of the rat hindlimb by inducing muscle contraction during ischemia. After 5, 10, 15, or 20 min of ischemic contractions, representative muscle sections were freeze-clamped and analyzed for purine nucleotides, nucleosides, and bases. Fast-twitch muscle sections accumulated about fourfold more IMP than the slow-twitch red soleus muscle.

Morphologic and functional alterations in aging rat muscle.

To understand better the causes of reduced contractile force in aging skeletal muscle, we performed a physiologic and morphologic analysis of plantaris muscle in old rats. The peak twitch tension (Fmax) and rates of force development and relaxation were significantly lower in old (24 months old) rats than in young (six month old) rats. In teased muscle fiber preparations, there was a 5% reduction in the mean number of fibers in the aging plantaris muscle.

Muscle fiber composition and length-tension relationships in rats chronically exposed to alcohol.

Adult Fischer 344 rats were fed an alcohol diet (7-9 g/kg/day) for 12 weeks and were compared to pair-fed controls with regard to the contraction and fiber characteristics of the gastrocnemius and plantaris muscles of the leg. Muscles were isolated in situ with blood and nerve supplies intact. The muscles were stretched by 1 mm increments and were stimulated at each muscle length with a voltage (1 msec pulse) that had been observed to produce maximal twitch force at the initial muscle length.