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.     

Day-night variations in blood and intracellular pH in a lizard,Dipsosaurus dorsalis

Blood pH, PCO2 and PO2 of Dipsosaurus dorsalis were measured during the day and at night. Lizards at constant body temperature (25, 37 degrees C) and lizards experiencing diurnal changes in body temperature similar to those in nature were studied. In lizards at constant body temperatures, blood pH was about 0.1 unit less and blood PCO2 was 4-7 Torr higher at night compared to day. Similar patterns were seen in lizards on natural thermal cycles. Intracellular pH (pHi) of skeletal muscle, esophagus and liver was about 0.2 units lower at night than day but myocardial pHi was unchanged. Reduction in breathing frequency, and thus a relative hypercapnia from hypoventilation was consistent with the nocturnal acidification of the blood and intracellular compartments. Nocturnal acidification (CO2 retention) corresponds to periods of minimum metabolism. The possible impacts of diurnal shifts in hydrogen ion concentration on energy metabolism and metabolic regulation are discussed.     

Distribution of fiber types in locomotory muscles of dogs

The distribution of Type I and Type II fibers, as determined from histochemical estimation of myofibrillar ATPase activity, was studied within and among the locomotory muscles of the forelimb, trunk, and hindlimb of three mongrel dogs. All Type II fibers had high oxidative capacities as estimated from the histochemical assay for reduced nicotinamide adenine dinucleotide tetrazolium reductase, so they were not further divided into subpopulations. Furthermore, Type I and Type II fibers had similar oxidative potentials as indicated by both histochemistry and biochemistry. Type I fiber populations ranged between 14% and 100% in the muscles sampled. The highest percentages of Type I fibers were found in deep muscles of physiological extensor groups in the arm and thigh that serve to resist gravity (antigravity muscles) when the dog is in the quadrupedal standing position. More superficial muscles in these same groups had fewer Type I fibers. The patterns of Type I fiber distribution among muscles in the antigravity groups of the forearm and leg were the opposite of those in the arm and thigh, with the more superficial muscles of the distal limb segments having more Type I fibers than the deeper muscles. In all limb segments, muscle groups that do not serve to resist gravity did not show as much intermuscular variation. Type I fiber populations in these muscles did not exceed 50%. A stratification of fiber types also existed within muscles, both in extensor and flexor groups, with the deeper portions of the muscles having more Type I fibers than the more superficial portions.     

Capillarization,mitochondrial densities,oxygen diffusion distances and innervation of red and white muscle of the lizard Dipsosaurus dorsalis

Summary The white and red regions of the iliofibularis muscle of the lizard Dipsosaurus dorsalis were analyzed using histologic and morphometric analysis. These regions are composed of fast glycolytic (FG) and both fast oxidative, glycolytic (FOG) and tonic fibers, respectively. Endplate morphology and number of endplates per fiber were estimated from fibers from both areas. Capillary volume densities of the red and white regions were quantified from transverse sections. Mitochondrial volume of fibers from the red and white regions were estimated from electron micrographs.All fibers from the white region of the iliofibularis possessed a single, well defined endplate, as did most red region fibers. The remaining red fibers (28±5%) possessed an average of 14.7±3 endplates each, distributed along the entire length of the fiber at intervals of approximately 1124 m.Red fibers possessed twice the mitochondrial volume of white fibers (7.6±0.4%, red; 3.8±0.3%, white). Mitochondria were distributed uniformly through the fibers from both regions. Capillary anisotropy was low ( = 1.018) in both regions. Capillary densities of the red region (629±35 mm^-2) were much greater than those of the corresponding White region (73±8 mm^-2).The data indicate that capillary densities, mitochondrial volumes and theoretical diffusion distances correlate well with the oxidative capacity of lizard muscle fibers. Tonic fibrs of this species appear oxidative and therefore metabolically capable of functioning during locomotion. The similar mitochondrial volumes and capillary densities of reptilian and mammalian muscles suggest that the greater oxidative capacity of mammalian muscle is due in part to possession of more oxidatively active mitochondria rather than to possession of more mitochondria per se.     

Reptilian skeletal muscle: contractile properties of identified, single fast-twitch and slow fibers from the lizard Dipsosaurus dorsalis

Contractile properties and innervation patterns were determined in identified single fibers from the iliofibularis muscle of the desert iguana, Dipsosaurus dorsalis. Single fibers from both the red and white regions of the iliofibularis muscle were dissected along their length under oil and a portion was mounted on transducers for determination of maximum isometric tension (Po) and unloaded shortening velocity (Vmax) using the slack test method. Fibers were chemically skinned and activated by high Ca++. The remaining portion of the muscle fiber was mounted on a glass slide and histochemically treated to demonstrate myosin ATPase activity. Fibers studied functionally could therefore be classified as fast or slow according to their myosin ATPase activity, and they could also be classified metabolically according to the region of the muscle from which they were dissected. Fast-twitch glycolytic (FG) fibers from the white region and fast-twitch oxidative, glycolytic (FOG) and slow fibers from the red region had shortening velocities at 25 degrees C of 7.5, 4.4, and 1.5 l X s-1, respectively. Po did not differ in the three fiber types, averaging 279 kN X m-2. In a second experiment, 10 microns sections were examined every 30 microns through the proximal-most 7.5 mm of the iliofibularis muscle for motor endplates. Sections were stained to demonstrate regions of acetylcholinesterase activity. Fibers with visible endplates were classified in serial sections by histochemical treatment for myosin ATPase and succinic dehydrogenase. All slow fibers examined (n = 22) exhibited multiple endplates, averaging one every 725 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Salt and water balance in the desert iguana,Dipsosaurus dorsalis

Summary Adult desert iguanas were either injected IM with aldosterone or lizard physiological saline (Ringers). These pairs according to group were left intact, adrenalectomized, or sham-adrenalectomized. Some groups of operated lizards were loaded IP with either NaCl or KCl. Aldosterone markedly reduced sodium output by the nasal salt gland during these experiments whereas Ringers did not. Nasal and urine K output of those lizards treated with aldosterone did not differ from that of their respective controls. The K/Na ratio of both the nasal fluid and urine increased only in the aldosterone treated lizards. The effect of aldosterone on the wet weight, dry weight, or proportion of water in the urine, or on precise changes of sodium and potassium levels therein was obscured by the complex traumatic effects of experimentation on the formation and voiding of urine.Bilateral adrenalectomy markedly elevated nasal sodium output in the controls. Adrenalectomized lizards treated with aldosterone, however, reduced nasal sodium output even if loaded with NaCl. The pattern of nasal K excretion resembled those of the controls.This study was supported in part by grant GB-3010 from the U.S. National Science Foundation.     

Histochemical determination of muscle fiber types in locomotor muscles of anuran amphibians.

1. A histochemical study using myosin ATPase, succinate dehydrogenase and alpha-glycerophosphate dehydrogenase reactions and a morphometric analysis with image analyser, was carried out in sartorius and gastrocnemius muscles of two anuran species, Rana perezi and Bufo calamita, that show different locomotor activities. 2. Four types of muscle fiber were found. There were interspecific variations in their proportions, with a predominance of oxidative muscle fibers in Bufo calamita. 3. These results agree with those obtained previously for the metabolic profile of several tissues from both species and point to a clear metabolic basis for the differences in locomotor activities between these two species.     

Patterns of olfactory projections in the desert iguana,Dipsosaurus dorsalis

The neural organization of the olfactory system in the desert iguana, Dipsosaurus dorsalis, has been investigated by using the Fink-Heimer technique to trace the efferents of the main and accessory olfactory bulbs, and Golgi preparations to determine the spatial relations between olfactory afferents and neurons in the primary olfactory centers. The accessory olfactory bulb projects to the ipsilateral nucleus sphericus via the accessory olfactory tract. The main olfactory bulb projects to the ipsilateral telen-cephalon via four tracts. The medial olfactory tract projects to the rostral continuation of medial cortex and to the septum. The intermediate olfactory tract projects to the olfactory tubercle and retrobulbar formation. The lateral olfactory tract projects to the rostral part of lateral cortex. The intermediate and lateral olfactory tracts also merge caudally to form the stria medullaris, which crosses the midline in the habenular commissure and distributes fibers to the contralateral hemisphere via two tracts. The lateral corticohabenular tract terminates in the contralateral lateral cortex. The anterior olfactohabenular tract terminates in the contralateral olfactory tubercle, retrobulbar formation and septum. The relation of olfactory afferents to neurons in the medial cortex, lateral cortex, nucleus sphericus, and septum corresponds to a pattern of organization that is typical of many olfactorecipient structures. Such structures are trilaminar, with neurons whose somata are situated in the intermediate layer (layer 2) sending spine-laden dendrites into an outer, molecular layer (layer 1). Olfactory afferents intersect the distal segments of these dendrites. By contrast, other olfactorecipient structures in Dipsoaurus deviate from the familiar pattern. Olfactory afferents intersect somata lying in layer 2 of the retrobulbar formation. Olfactory afferents include some fibers which course perpendicularly to the surface of the olfactory tubercle and extend deep to layer 2.     

Capillarity and fiber types in locomotory muscles of wild common coots,Fulica atra

Six locomotory muscles of wild common coots, Fulica atra, were analyzed histochemically. Capillarity and fiber-type distributions were correlated to the functional implications and physiological needs of each muscle. Leg muscles exhibit three unevenly distributed fiber types, a pattern that reflects the great variety of terrestrial and aquatic locomotory performances that coots are able to develop. Aerobic zones are presumably recruited during steady swimming and diving, while regions with anaerobic characteristics may be used for bursts of activity such as sprint swimming or during take off, when coots run along the water's surface. Fiber types and capillarization in wing muscles have a marked oxidative trend. High wing beat frequencies, short and broad wings, and the long distance migrations that these birds perform indicate that the presence of high numbers of oxidative fibers and the well developed capillary supply are needed for enhanced oxygen uptake. The pectoralis muscle, except in its deep part, has exclusively fast oxidative fibers with a very high staining intensity for succinate dehydrogenase assay as compared to the same fiber type of other muscles. Its predominant role in flapping flight justifies these characteristics that are typical of fibers with high aerobic metabolism. The deep part of the pectoralis muscle presents a low proportion of an unusual slow anaerobic fiber type. These fibers could play a role during feeding dives when the bird presses the air out of the feathers by tightening the wings against the body. A linear relationship between capillary and fiber densities in all coot muscles studied reflects an adjustment between fiber diameter and vascularization in order to obtain the oxygen for mitochondrial supply. This strategy seems a suitable way to cope with the rigid aerobic constraints that flying and diving impose upon the coot's physiology. J. Morphol. 237:147–164, 1998. © 1998 Wiley-Liss, Inc.