Seasonal effects on water and osmotically-active ionic contents Na+, K+ & Cl– of skeletal muscles of the spiny-tailed lizard, Uromastix hardwickii (original) (raw)
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Indian journal of physiology and pharmacology
Effects of season (summer & winter) on electrical characteristics of skeletal muscle membranes of the spiny-tailed lizard, Abstract This study deals with the observation of changes with temperature variations of the seasons in the muscular electrical excitability in the reptile Uromastix hardwickii. Freshly captured adult animals of both the sexes were used in all the experiments, and the gastrocnemius (skeletal) muscles were dissected out. The muscle samples were digested with digestive fluid (pepsin & Hcl), stirred, settled and supernatant was removed, till whitish fluid having clear cells obtained for patch clamp recording of ionic currents and potentials. Resting membrane potentials and action potentials of reptilian cell membranes were measured in whole cell current mode. The glass microelectrodes, with a tip diameter 2-3 μm and tip resistance 5-6 MW (when filled with intracellular solution) were used in these experiments.
Seasonal acclimatisation of muscle metabolic enzymes in a reptile (Alligator mississippiensis)
Journal of Experimental Biology
The concept that reptiles regulate their body temperature by behavioural means, such as shuttling between sun and shade , has become widely accepted in vertebrate thermal physiology. Behavioural adjustments enable many diurnal species of reptile to maintain high and stable body temperatures in the face of fluctuations in environmental temperatures . The importance of body temperature regulation is seen to lie in maximising the rates of temperature-sensitive physiological functions . The rates of chemical reactions, including those catalysed by enzymes, are dependent on the energetic state of the compounds involved, which in turn is strongly influenced by temperature. The rates of most physiological processes are, therefore, a direct function of the temperature of the organism. Thermoregulation that includes high metabolic heat production combined with effective insulation often allows endotherms to maintain an elevated body temperature within a narrow range . The low metabolic rates of reptiles make metabolic heat production negligible, and regulation of body temperature is achieved by behavioural means such as microhabitat selection Reptiles living in heterogeneous thermal environments are often thought to show behavioural thermoregulation or to become inactive when environmental conditions prevent the achievement of preferred body temperatures. By contrast, thermally homogeneous environments preclude behavioural thermoregulation, and ectotherms inhabiting these environments (particularly fish in which branchial respiration requires body temperature to follow water temperature) modify their biochemical capacities in response to long-term seasonal temperature fluctuations. Reptiles may also be active at seasonally varying body temperatures and could, therefore, gain selective advantages from regulating biochemical capacities. Hence, we tested the hypothesis that a reptile (the American alligator Alligator mississippiensis) that experiences pronounced seasonal fluctuations in body temperature will show seasonal acclimatisation in the activity of its metabolic enzymes. We measured body temperatures of alligators in the wild in winter and summer (N=7 alligators in each season), and we collected muscle samples from wild alligators (N=31 in each season) for analysis of metabolic enzyme activity (lactate dehydrogenase, citrate synthase and cytochrome c oxidase). There were significant differences in mean daily body temperatures between winter (15.66±0.43°C; mean ± S.E.M.) and summer (29.34±0.21°C), and daily body temperatures fluctuated significantly more in winter compared with summer. Alligators compensated for lower winter temperatures by increasing enzyme activities, and the activities of cytochrome c oxidase and lactate dehydrogenase were significantly greater in winter compared with summer at all assay temperatures. The activity of citrate synthase was significantly greater in the winter samples at the winter body temperature (15°C) but not at the summer body temperature (30°C). The thermal sensitivity (Q 10) of mitochondrial enzymes decreased significantly in winter compared with in summer. The activity of mitochondrial enzymes was significantly greater in males than in females, but there were no differences between sexes for lactate dehydrogenase activity. The differences between sexes could be the result of the sex-specific seasonal demands for locomotor performance. Our data indicate that biochemical acclimatisation is important in thermoregulation of reptiles and that it is not sufficient to base conclusions about their thermoregulatory ability entirely on behavioural patterns.
Thermoregulatory consequences of salt loading in the lizard, Pogona vitticeps
Journal of Experimental Biology, 2015
Previous research has demonstrated that dehydration increases the threshold temperature for panting and decreases the thermal preference of lizards. Conversely, it is unknown whether thermoregulatory responses like shuttling and gaping are similarly influenced. Shuttling, as an active behavioural response, is considered one of the most effective thermoregulatory behaviours, while gaping has been proposed to be involved in preventing brain over-heating in lizards. In this study we examined the effect of salt loading, a proxy for increased plasma osmolality, on shuttling and gaping in Pogona vitticeps. Then, we determined the upper and lower escape ambient temperatures (UETa and LETa), the percentage of time spent gaping, the metabolic rate (V̇O2), the evaporative water loss (EWL) during gaping and non-gaping intervals and the evaporative effectiveness (EWL/V̇O2) of gaping. All experiments were performed under isotonic (154 mM) and hypertonic saline injections (625, 1250 or 2500 mM). ...
Journal of Thermal Biology, 2017
We investigated the ability of juvenile American alligators (Alligator mississippiensis) to acclimate to temperature with respect to growth rate. We hypothesized that alligators would acclimate to cold temperature by increasing the metabolic capacity of skeletal muscles and the heart. Additionally, we hypothesized that lipid membranes in the thigh muscle and liver would respond to low temperature, either to maintain fluidity (via increased unsaturation) or to maintain enzyme reaction rates (via increased docosahexaenoic acid). Alligators were assigned to one of 3 temperature regimes beginning at 9 mo of age: constant warm (30°C), constant cold (20°C), and daily cycling for 12 h at each temperature. Growth rate over the following 7 mo was highest in the cycling group, which we suggest occurred via high digestive function or feeding activity during warm periods and energy-saving during cold periods. The warm group also grew faster than the cold group. Heart and liver masses were proportional to body mass, while kidney was proportionately larger in the cold group compared to the warm animals. Whole-animal metabolic rate was higher in the warm and cycling groups compared to the cold group-even when controlling for body mass-when assayed at 30°C, but not at 20°C. Mitochondrial oxidative phosphorylation capacity in permeabilized fibers of thigh muscle and heart did not differ among treatments. Membrane fatty acid composition of the brain was largely unaffected by temperature treatment, but adjustments were made in the phospholipid headgroup composition that are consistent with homeoviscous adaptation. Thigh muscle cell membranes had elevated polyunsaturated fatty acids in the cold group relative to the cycling group, but this was not the case for thigh muscle mitochondrial membranes. Liver mitochondria from cold alligators had elevated docosahexaenoic acid, which might be important for maintenance of reaction rates of membrane-bound enzymes.
Metabolic aspects of ionic shifts in toad muscle
Biochimica et Biophysica Acta, 1962
Oxygen consumption, lactic acid coment and ionic levels have been estimated in toad sartorius muscle in varying ionic environments and under conditions of rnetabolic inhibition. Levels of lactic acid, Na + and K + in vivo, and after soaking the sartorius in normal Ringer's solution are compared. The effect of varying external levels of Na + has been determined. The oxygen consumption of the tissue is increased in high-sodium Ringer's solution,, with a maximum effect at approx, twice the normal level of Na +. Lactic acid production is increased continuously as the external Na + concentration is raised, and is also higher in half-sodium Ringer's solution. These effects have been correlated with the ion shifts, and a highly significant relationship betwc~.n lactic acid level and muscle Na + content has been iound. A regnlatory effect of Na + on a preferred metabolic pathway is postulated. A small series of metabolic inhibitors has been studied. Dinitrophenol and methylene blue caused greatly accelerated rates of oxygen uptake and of lactic acid production, while iodoacetic acid depressed both. Sodium azide increased the lactic acid content and caused an initial stimulation of respiration. All the inhibitors were alike in causing movements of Na + and K + down the concentration gradients. These data have been correlated with shifts in adenosine triphosphate and creatine phosphate published earlier 1.
Estimation of intracellular pH in muscle of fishes from different thermal environments
Journal of Thermal Biology, 1999
A technique based on homogenisation of rapidly frozen tissue was used to investigate the regulation of intracellular pH (pH i ) in freshwater and marine ®sh from diverse environmental temperatures. The following species were held at ambient temperatures of ca. 18C (Notothenia coriiceps; Antarctica), 58C (Pleuronectes platessa, Myoxocephalus scorpius; North Sea), and 268C (Oreochromis niloticus; African lakes). The eects of seasonal acclimatisation to 4, 11 and 188C were also examined in rainbow trout in the winter, autumn and summer, respectively. Extracellular (whole blood) pH (pH e ) did not follow the constant relative alkalinity relationship, where pH + =pOH À for any particular temperature, over a range of 1±268C (overall dpH e /dT=0.00920.002 U 8C À1 ; P < 0.001), apparently being regulated by ionic¯uxes and ventilation. Intracellular pH (pH i ) was also regulated independently of pN(=0.5 pK water) in all species of ®sh examined. The inverse relationship between pH i and environmental temperature gave an overall dpH i /dT of À0.01020.001 U 8C À1 (for both white and red muscle) and À0.004 2 0.003 U 8C À1 (cardiac muscle). However, between 1 and 118C dpH i /dT was much higher (P < 0.001), À0.02220.003 U 8C À1 (white muscle) and À0.02220.004 U 8C À1 (red muscle). The possible adaptive roles for these dierent acid±base responses to environmental temperature variation among tissues and species, and the potential diculties of estimating pH i , are discussed. #
ACIDBASE IMBALANCE IN LIZARDS DURING ACTIVITY AND RECOVERY
1982
SUMMARY 1. The effects of treadmill exercise on oxygen consumption (J^), carbon dioxide production (J^o,), arterial blood lactate concentration ((Lr)a), arterial blood pH and arterial gas tensions (PaO, and PaOOt) were measured in 3 species of lizards (Varanus salvator, V. exanthematicus, Iguana iguana) 2. Varanus salvator was exercised 45 min at an intensity which required 85% of its VOt mBX.
Comparative Biochemistry and Physiology Part A: Physiology, 1991
Eff&s of temperature on aspects of ionic regulation in kidney and gills of Rut&s rut&s and Saluelinus a$inus were studied by a variety of techniques. 2. In the kidney tissue of coid acclimated R. rut&s, the maximal number of binding sites per mg protein (Bmax) and the activity of Na+, K+-ATPase, as well as tissue respiration increased significantly, whereas in S. alpinus no changes in these variables were observed. On the other hand, 86Rb+ efllux from kidney tissue was unaffected by temperature in R. rutiius, whereas it was about 60% lower in S. alpinus acclimated and measured at YC, than in specimens acclimated and measured at 15°C. 3. In both species, the activity of gill Na+, K+-ATPase was 1.5. to 2-fold higher in cold-acclimated than in warm-acclimated fish although Bmax decreased in R. r&us, but remained constant in S. alpinus. 4, Problems of ionic regulation are discussed with regard to differences in temperature sensitivity of passive flows and primary active transport of ions in the t&sues of poikilothermic animals. ~TRODU~ON Temperature plays a decisive role in the ionic regulation of poikilothe~s, one of the main reasons
Seasonal plasma T4 titers in the hibernating lizard Cnemidophorus sexlineatus
General and Comparative Endocrinology, 1982
A total of 242 Cnemidophorus sexlineutus were collected in biweekly samples from east-central Alabama and west-central Georgia during the period May 1978 to September 1979. Blood, collected in the field, was returned to the lab and subjected to a radioimmunoassay for thyroxine (T4). Mean biweekly plasma T., titers (ranging from 1.0 to 4.2 &ml) were plotted against the collection date. Analysis of these data indicated the presence of a significant (P < 0.01) quadratic (curvilinear) response with lower titers during the summer months of activity and higher titers during other months, thus suggesting definite seasonal changes in plasma T4 titers. These seasonal fluctuations could not be definitively explained in terms of changes in temperature, reproductive condition, or fat stores. Rather, these abrupt seasonal changes in plasma T4 titers coincided best with the entry into and emergence from hibernation. Plasma T, titers of hibernating lizards were found to be significantly higher (P < 0.05) than those of active lizards.