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Biomedical subjects

A F Bennett

Publications and source records attributed to A F Bennett.

71 records · Page 4Linked to original sources
PubMed1980

Histochemical, enzymatic, and contractile properties of skeletal muscle fibers in the lizard Dipsosaurus dorsalis.

Lizard skeletal muscle fiber types were investigated in the iliofibularis (IF) muscle of the desert iguana (Dipsosaurus dorsalis). Three fiber types were identified based on histochemical staining for myosin ATPase (mATPase), succinic dehydrogenase (SDH), and alphaglycerophosphate dehydrogenase (alphaGPDH) activity. The pale region of the IF contains exclusively fast-twitch-glycolytic (FG) fibers, which stain dark for mATPase and alphaGPDH, light SDH. The red region of the IF contains fast-twitch-oxidative-glycolytic (FOG) fibers, which stain dark for all three enzymes, and tonic fibers, which stain light for mATPase, dark for SDH, and moderate for alphaGPDH. Enzymatic activities of myofibrillar ATPase, citrate synthase, and alphaGPDH confirm these histochemical interpretations. Lizard FG and FOG fibers possess twitch contraction times and resistance to fatigue comparable to analogous fibers in mammals, but are one-half as oxidative and several times as glycolytic as analogous fibers in rats. Lizard tonic fibers demonstrate the acetylcholine sensitivity common to other vertebrate tonic fibers.

Adenosine Triphosphatases↗
PubMed1980

Histochemical determination of the fiber composition of locomotory muscles in a lizard, Dipsosaurus dorsalis.

A histochemical survey was done on the fiber composition of 12 different locomotory muscles in the lizard Dipsosaurus dorsalis. Three types of fibers were found in all muscles: (1) fast-twitch-glycolytic (FG); (2) fast-twitch-oxidative-glycolytic (FOG); and (3) tonic fibers. Virtually all locomotory muscles contain some tonic fibers. Most muscles have bulk white regions (containing mostly FG fibers) and distinct red, oxidative regions (with FOG and tonic fibers). These red regions are predominantly located around the joints in the hind limb muscles, and probably serve a postural and joint-stabilizing function. The predominance of FG fibers in the bulk white regions is well-correlated with the rapid, anaerobically supported predator escape behavior of D. dosalis.

Adenosine Triphosphatases↗
PubMed1979

Endothermy and activity in vertebrates.

Resting and maximal levels of oxygen consumption of endothermic vertebrates exceed those of ectotherms by an average of five- to tenfold. Endotherms have a much broader range of activity that can be sustained by this augmented aerobic metabolism. Ectotherms are more reliant upon, and limited by, anaerobic metabolism during activity. A principal factor in the evolution of endothermy was the increase in aerobic capacities to support sustained activity.

Adaptation, Biological↗
PubMedDate not supplied

Intrapopulation variation in ecological energetics of the garter snake Thamnophis sirtalis, with analysis of the precision of doubly labeled water measurements.

The evolution of energetics must begin with variation within populations in ecologically realized rates of energy acquisition and expenditure. We measured aspects of field energy budgets (including metabolic rates, feeding rates, and growth rates) in a large sample of free-living garter snakes (Thamnophis sirtalis) from a single temperate/mesic population in northwestern California during their summer active season. We then analyzed interindividual variation for correlations among variables and patterns attributable to body size and sex. Field metabolic rates (measured with use of doubly labeled water) scaled in direct proportion to body mass. These rates of field energy expenditure were higher (both in absolute terms and in relation to resting metabolic rates) than those previously measured in snakes and iguanian lizards and were similar to those reported for highly active, widely foraging scincomorphan lizards. Feeding rates (as indexed by water influx rates) and growth rates were correspondingly high compared to those of other squamate reptiles. We found considerable residual variation in all measured variables not attributable to body size. Effects of sex were detected for water influx and growth rates (females > males), but not for field metabolic rate. Individual field metabolic rate was apparently consistent (repeatable) over time, water influx rate was not, and individual growth rates were strongly negatively correlated over two sequential time periods. We were unable to detect convincing correlations between any individual measures of field energetics and any commonly measured, standard laboratory measurements of oxygen consumption (standard metabolic rate at two body temperatures and maximal oxygen consumption for exercise) made on the same individuals. However, body-size-independent field rates of energy expenditure, energy intake, and growth were strongly and positively intercorrelated among individuals. We attribute these patterns to an overriding effect of costs associated with digestion and growth on field energetics, such that individual snakes that were effective foragers achieved high feeding rates and, hence, high growth rates, but also incurred high costs of growth and digestion that largely determined field metabolic rate.

Animals↗