Predicting time to decompression illness during exercise at altitude, based on formation and growth of bubbles

For altitude decompressions, we hypothesized that reported onset times of limb decompression illness (DCI) pain symptoms follow a probability distribution related to total bubble volume [V(b.)(t)] as a function of time. Furthermore, we hypothesized that the probability of ever experiencing DCI during a decompression is associated with the cumulative volume of bubbles formed. To test these hypotheses, we first used our previously developed formation-and-growth model (Am J Physiol Regulatory Integrative Comp Physiol 279: R2304-R2316, 2000) to simulate Vb.(t) for 20 decompression profiles in which 334 human subjects performed moderate repetitive skeletal muscle exercise (827 kJ/h) in an altitude chamber. Using survival analysis, we determined that, for a controlled condition of exercise, the fraction of the subject population susceptible to DCI can be approximately expressed as a power function of the formation-and-growth model-predicted cumulative volume of bubbles throughout the altitude exposure. Furthermore, for this fraction, the probability density distribution of DCI onset times is approximately equal to the ratio of the time course of formation-and growth-modeled total bubble volume to the predicted cumulative volume.     

Behavioral components of high-fat diet hyperphagia: meal size and postprandial satiety

Previously, rats fed a high-fat liquid diet (HF) ad libitum consumed more kilocalories and had greater weight gain than rats fed a liquid high-carbohydrate diet (HC) of equivalent energy density (Warwick, Z. S., and H. P. Weingarten. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 269: R30-R37, 1995). The present series of experiments sought to clarify the behavioral expression of HF hyperphagia by comparing HF and HC with regard to meal size and magnitude of postingestive satiety effect. Meal size of HF was greater than HC at 2.3 kcal/ml and also when diets were formulated at 1.15 kcal/ml. In a preload-test meal paradigm, an orally consumed HF preload was less satiating than a calorically equivalent HC preload across a range of preload volumes and intermeal intervals. Sensory-specific satiety was ruled out as an explanation of the relatively greater intake of test meal after an HF preload meal; an intragastrically delivered HF preload was less satiating than intragastric HC. Furthermore, a fat (corn oil emulsion) preload was less satiating than a carbohydrate (sucrose) preload when an evaporated milk test meal was used. These findings indicate that hyperphagia on an HF diet is expressed in increased meal size and decreased intermeal interval.     

Effects of gluconeogenic precursor flux alterations on glycogen resynthesis after prolonged exercise

The importance of gluconeogenic substrates (i.e., lactate, glycerol, and alanine) in the glycogen resynthesis observed in fasting rats after exhausting submaximal exercise [R.D. Fell et al. Am. J. Physiol. 238 (Regulatory Integrative Comp. Physiol. 7): R328-R332, 1980] was examined in muscles and liver in response to pharmacological alterations of gluconeogenic precursor flux. The minor role of lactate for glycogen resynthesis after prolonged submaximal exercise was confirmed by the insignificant accumulation of lactate neither in muscles nor in plasma. When the rate of lipolysis is reduced either by beta-blockade or by nicotinic acid injection, the replenishment of muscle glycogen persisted, suggesting that glycerol released by triglycerides hydrolysis did not play an important role in glycogen resynthesis. On the other hand, when pyruvate oxidation is enhanced by dichloroacetate (DCA), thus reducing plasma levels of lactate and alanine, glycogen resynthesis was completely blocked in liver and partly in some but not all muscles. This failure in total inhibition of glycogen resynthesis associated with the significant reduction of the plasma alanine level could be attributed to the possible stimulation of gluconeogenesis from alanine by DCA (R.A. Harris and D.W. Crabb. Arch. Biochem. Biophys. 189: 364-371, 1978). The results could point out alanine as the major gluconeogenic substrate during recovery from exhaustive exercise in fasting conditions.     

20-hydroxyeicosatetraenoic acid (20-HETE): structural determinants for renal vasoconstriction

The effects of natural and synthetic eicosanoids on the diameter of rat interlobular arteries studied in vitro were compared to that of the potent, endogenous vasoconstrictor 20-HETE. Vasoconstrictor activity was optimum for chain lengths of 20-22 carbons with at least one olefin or epoxide between located between C(13)-C(15) and an oxygen substituent at C(20)-C(22). The presence of delta (Zou et al. Am. J. Physiol. 1996, 270, R228; Gebremedhin, D. et al. Am. J. Physiol. 1998, 507, 771)-, delta (Carroll et al. Am. J. Physiol. 1996, 271, R863; Vazquez et al. Life Sci. 1995, 56, 1455)-, or delta (Imig et al. Hypertension 2000, 35, 307; Lopez et al. Amer. J. Physiol. 2001, 281, F420)-olefins had no influence on the vasoconstrictor response whereas the introduction of a C(7)-thiomethylene enhanced potency. A sulfonamide or alcohol, but not a lactone, could replace the C(1)-carboxylate. These data were used to construct a putative binding domain map of the 20-HETE receptor consisting of: (i) a comparatively open, hydrophilic binding site accommodating the C(1)-functionality; (ii) a hydrophobic trough spanning the olefins; (iii) a shallow pocket containing a critical pi-pi binding site in the vicinity of the pi (Ito et al. Am. J. Physiol. 1998, 274, F395; Quigley, R.; Baum, M.; Reddy, K. M.; Griener, J. C.; Falck, J. R. Am. J. Physiol. 2000, 278, F949)-olefin; and (iv) an oxyphilic binding site proximate to the omega-terminus.     

Effects of spaceflight and thyroid deficiency on hindlimb development. I. Muscle mass and IGF-I expression.

Thyroid deficiency (TD) in neonatal rats causes reduced growth of skeletal muscle that is disproportionately greater than that for other tissues (G. R. Adams, S. A. McCue, M. Zeng, and K. M. Baldwin. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 276: R954-R961, 1999). TD depresses plasma insulin-like growth factor I (IGF-I) levels, suggesting a mechanism for this effect. We hypothesized that TD and exposure to spaceflight (SF) would interact to reduce skeletal muscle growth via a reduction in IGF-I levels. Neonatal rats were flown in space for 16 days. There was a similar, nonadditive reduction in the growth of the body ( approximately 50%) and muscle weight (fast muscles, approximately 60%) with either TD or SF. In the soleus muscle, either SF or TD alone resulted in growth reductions that were augmented by SF-TD interactions. There were strong correlations between 1) muscle mass and muscle IGF-I levels and 2) circulating IGF-I and body weight. These results indicate that either hypothyroidism or exposure to SF will limit the somatic and muscle-specific growth of neonatal rats. The impact of these perturbations on skeletal muscle growth is relatively greater than the effect on somatic growth. The mechanisms by which either TD or SF impact growth appear to have a common pathway involving the control of plasma and muscle IGF-I concentrations.     

Effect of heat stress on LPS-induced febrile response in D-galactosamine-sensitized rats

We have previously reported that heat conditioning augments lipopolysaccharide (LPS)-induced fever in rats, which is accompanied by an accumulation of heat shock protein (HSP) in the liver and the reduction of the plasma level of tumor necrosis factor (TNF-alpha) (Kluger MJ, Rudolph K, Soszynski D, Conn CA, Leon LR, Kozak W, Wallen ES, and Moseley PL. Am J Physiol Regulatory Integrative Comp Physiol 273: R858-R863, 1997). In the present study we have tested whether inhibition of protein synthesis in the liver can reduce the effect of this heat conditioning on the LPS-induced febrile response in the rat. D-galactosamine (D-gal) was used to selectively inhibit liver protein synthesis. D-gal (500 mg/kg) or PBS as control was administered intraperitoneally 1 h before heat stress. LPS (50 microg/kg ip) was injected 24 h post-heat exposure. Treatment with D-gal blunted the febrile response to LPS. Moreover, heat-conditioned rats treated first with D-gal and subsequently with LPS demonstrated a profound fall in core temperature 10--18 h post-LPS. A significant increase of serum TNF-alpha accompanied this effect of D-gal on fever. Heat-conditioned animals receiving D-gal showed an inhibition in inducible HSP-70 in the liver. These data support the role of hepatic function in modulating the febrile response to LPS.     

Unequal autonegative feedback by GH models the sexual dimorphism in GH secretory dynamics

Growth hormone (GH) secretion, controlled principally by a GH-releasing hormone (GHRH) and GH release-inhibiting hormone [somatostatin (SRIF)] displays vivid sexual dimorphism in many species. We hypothesized that relatively small differences within a dynamic core GH network driven by regulatory interactions among GH, GHRH, and SRIF explain the gender contrast. To investigate this notion, we implemented a minimal biomathematical model based on two coupled oscillators: time-delayed reciprocal interactions between GH and GHRH, which endow high-frequency (40-60 min) GH oscillations, and time-lagged bidirectional GH-SRIF interactions, which mediate low-frequency (occurring every 3.3 h) GH volleys. We show that this basic formulation, sufficient to explain GH dynamics in the male rat [Farhy LS, Straume M, Johnson ML, Kovatchev BP, and Veldhuis JD. Am J Physiol Regulatory Integrative Comp Physiol 281: R38-R51, 2001], emulates the female pattern of GH release, if autofeedback of GH on SRIF is relaxed. Relief of GH-stimulated SRIF release damps the slower volleylike oscillator, allowing emergence of the underlying high-frequency oscillations that are sustained by the GH-GHRH interactions. Concurrently, increasing variability of basal somatostatin outflow introduces quantifiable, sex-specific disorderliness of the release process typical of female GH dynamics. Accordingly, modulation of GH autofeedback on SRIF within the interactive GH-GHRH-SRIF ensemble and heightened basal SRIF variability are sufficient to transform the well-ordered, 3.3-h-interval, multiphasic, volleylike male GH pattern into a femalelike profile with irregular pulses of higher frequency.     

Thiol-dependent aminopeptidase (350,000 mol wt) as a marker of epidermal contamination in sweat

L-Leucine 2-naphthylamide (Leu-NA) hydrolytic activity is increased 20-fold in eccrine sweat collected by simple scraping (SS) compared with sweat collected over the white petrolatum (Vaseline) barrier (clean sweat, CS) [Am. J. Physiol. 250 (Regulatory Integrative Comp. Physiol. 19): R691-R698, 1986]. Sephadex G-200 chromatography of SS but not that of CS showed a single peak of Leu-NA hydrolytic activity (at pH 8) at 350,000 mol wt. An enzyme with similar molecular weight was eluted from tape-stripped stratum corneum and from stripped skin in situ. Anion-exchange FPLC of the 350,000 fractions yielded a single Leu-NA hydrolase peak at pH 8 (pool IV), which also showed hydrolytic activity for benzoyl-L-arginine-2-naphthylamide (BANA). Both Leu-NA and BANA hydrolytic activities of pool IV were thiol dependent, inhibited by heavy metals, and activated by ethylenediaminetetraacetic acid. The pool IV enzyme also hydrolyzed L-lysine- and L-arginine-2-naphthylamide. The most prominent BANA hydrolase activity was seen in both SS and CS at pH 5.0 at 33,000, which was not associated with Leu-NA hydrolytic activity. Diethylaminoethyl cellulose chromatography of the 33,000 fractions yielded three peaks of BANA hydrolytic activity in SS but only one in CS, suggesting that this thiol-dependent BANA hydrolyzing enzyme in CS may be of sweat gland origin. We conclude that the 350,000 thiol-dependent Leu-NA-hydrolyzing aminopeptidase is one of the most prominent epidermal contaminants and thus is a useful marker of epidermal contamination in sweat samples.     

Skeletal muscle energy metabolism during prolonged, fatiguing exercise.

A depletion of phosphocreatine (PCr), fall in the total adenine nucleotide pool (TAN = ATP + ADP + AMP), and increase in TAN degradation products inosine 5'-monophosphate (IMP) and hypoxanthine are observed at fatigue during prolonged exercise at 70% maximal O(2) uptake in untrained subjects [J. Baldwin, R. J. Snow, M. F. Carey, and M. A. Febbraio. Am. J. Physiol. 277 (Regulatory Integrative Comp. Physiol. 46): R295-R300, 1999]. The present study aimed to examine whether these metabolic changes are also prevalent when exercise is performed below the blood lactate threshold (LT). Six healthy, untrained humans exercised on a cycle ergometer to voluntary exhaustion at an intensity equivalent to 93 +/- 3% of LT ( approximately 65% peak O(2) uptake). Muscle biopsy samples were obtained at rest, at 10 min of exercise, approximately 40 min before fatigue (F-40 =143 +/- 13 min), and at fatigue (F = 186 +/- 31 min). Glycogen concentration progressively declined (P < 0.01) to very low levels at fatigue (28 +/- 6 mmol glucosyl U/kg dry wt). Despite this, PCr content was not different when F-40 was compared with F and was only reduced by 40% when F was compared with rest (52. 8 +/- 3.7 vs. 87.8 +/- 2.0 mmol/kg dry wt; P < 0.01). In addition, TAN concentration was not reduced, IMP did not increase significantly throughout exercise, and hypoxanthine was not detected in any muscle samples. A significant correlation (r = 0.95; P < 0. 05) was observed between exercise time and glycogen use, indicating that glycogen availability is a limiting factor during prolonged exercise below LT. However, because TAN was not reduced, PCr was not depleted, and no correlation was observed between glycogen content and IMP when glycogen stores were compromised, fatigue may be related to processes other than those involved in muscle high-energy phosphagen metabolism.     

Central oxytocin modulates exercise-induced tachycardia

We have shown that vasopressinergic projections to dorsal brain stem are activated during exercise and facilitate exercise tachycardia in both trained (T) and sedentary (S) rats (Dufloth DL, Morris M, and Michelini LC. Am J Physiol Regulatory Integrative Comp Physiol 273: R1271-R1282, 1997). In the present study, we investigated whether oxytocinergic projections to the nucleus of the solitary tract (NTS)-dorsal motor nucleus of the vagus (DMV) complex (NTS/DMV) are involved in the differential heart rate (HR) response to exercise in T and S rats. Arterial pressure (AP) and HR responses to dynamic exercise (0.4-1.4 km/h) were compared in S and T pretreated with vehicle (saline), oxytocin (OT; 20 pmol/200 nl) or OT-receptor antagonist (OT(ant); 20 pmol/200 nl) into the NTS/DMV. OT content in specific brain regions and plasma were measured in separate S and T groups at rest and immediately after exercise. Exercise increased OT content in dorsal (4.5-fold) and ventral brain stem (2.7-fold) and spinal cord (3.4-fold) only in T rats. No significant changes were observed in neurosecretory regions or medial eminence and posterior pituitary, but plasma levels of T rats were reduced immediately after exercise. Blockade of NTS/DMV OT receptors did not change basal mean AP (MAP) and HR or the MAP response to exercise. However, OT(ant) potentiated exercise-induced tachycardia (average increase of 26%) only in the T group. Pretreatment with exogenous OT in the NTS/DMV blunted the tachycardic response both in S and T rats without changing the MAP response. Administration of OT-receptor antagonist or OT into the fourth cerebral ventricle had no effect on the cardiovascular response to dynamic exercise. Taken together, the results suggest that oxytocinergic projections to the NTS/DMV are stimulated when T rats exercise and that OT released at this level acts on OT receptors to restrain exercise-induced tachycardia.     

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.     

Cryptobiosis: a new theoretical perspective

The tardigrade is a microscopic creature that under environmental stress conditions undergoes cryptobiosis [Feofilova, E.P., 2003. Deceleration of vital activity as a universal biochemical mechanism ensuring adaptation of microorganisms to stress factors: A review. Appl. Biochem. Microbiol. 39, 1-18; Nelson, D.R., 2002. Current status of the tardigrada: Evolution and ecology. Integrative Comp. Biol. 42, 652-659]-a temporary metabolic depression-which is considered to be a third state between life and death [Clegg, J.S., 2001. Cryptobiosis-a peculiar state of biological organization. Comp. Biochem. Physiol. Part B 128, 613-624]. In contrast with death, cryptobiosis is a reversible state, and as soon as environmental conditions change, the tardigrade "returns to life." Cryptobiosis in general, and among the tardigrade in particular, is a phenomenon poorly understood [Guppy, M., 2004. The biochemistry of metabolic depression: a history of perceptions. Comp. Biochem. Physiol. Part B 139, 435-442; Schill, R.O., et al., 2004. Stress gene (hsp70) sequences and quantitative expression in Milensium tardigradum (Tardigrade) during active and cryptobiotic stages. J. Exp. Biol. 207, 1607-1613; Watanabe, M., et al., 2002. Mechanisn allowing an insect to survive complete dehydration and extreme temperatures. J. Exp. Biol. 205, 2799-2802; Wright, J.C., 2001. Cryptobiosis 300 years on from van Leuwenhoek: what have we learned about tardigrades? Zool. Anz. 240, 563-582]. Moreover, the ability of the tardigrade to bootstrap itself and to return to life seems paradoxical like the legendary Baron von Munchausen who pulled himself out of the swamp by grabbing his own hair. Two theoretical obstacles prevent us from advancing our knowledge of cryptobiosis. First, we lack appropriate theoretical understanding of reversible processes of biological computation in living systems. Second, we lack appropriate theoretical understanding of bootstrapping in living systems. In this short opinion article, I would like to present the idea that although cryptobiosis is obscure from a certain point of view, it makes sense within a scientific perspective suggesting that "organization becomes cause in the matter" [Strohman, R.C., 2000. Organization becomes cause in the matter. Nat. Biotechnol. 18, 575-576]. I present Bateson's idea that organisms have a "recursive hierarchical" form of organization [Neuman, Y., 2004. Meaning making in the immune system. Perspect. Biol. Med. 48, 320-327; Neuman, Y., in press. A theory of meaning. Inform. Sci.] and suggest that this form of organization allows bootstrapping through reversible process of computation as discussed by theoretical physicists [Bennett, C.H., 1982. The thermodynamics of computation-a review. Int. J. Theoret. Phys. 1, 905-940; Landauer and Bennett, 1985].     

Alternative mRNA splice variants of the rat ClC-2 chloride channel gene are expressed in lung: genomic sequence and organization of ClC-2.

The ClC-2 epithelial cell chloride channel is a voltage-, tonicity- and pH-regulated member of the ClC super family. We have previously shown that rat lung ClC-2 (rClC-2) is down-regulated at birth, and molecular diversity is generated by alternative splicing [Murray et al. (1995) Am. J. Respir. Cell Mol. Biol. 12, 597-604; Murray et al. (1996) Am. J. Physiol. 271, L829-L837; Chu et al . (1996) Nucleic Acids Res. 24, 3453-3457]. To investigate other possible mRNA splice variations, we sequenced the entire rClC-2 gene and found that ClC-2Sa (formerly ClC-2S) results from the deletion of exon 20. The preceding intron 19 has an unusually high CT content and a rare AAG acceptor site. Because both features were also found in intron 13, we next tested the hypothesis that intron 13 would be involved in alternative splicing. As predicted, a second splice product, ClC-2Sb, was found by RT-PCR, but only in lung. When we compared the genomic maps of rClC-2 and human ClC-1 (hClC-1), striking similarities were found in each exon except for rClC-2 exon 20, which is absent in hClC-1. These observations suggest that ClC-1 and ClC-2 may have evolved by gene duplication, mutation and DNA rearrangement.     

Helical growth of stage-IVb sporangiophores of <Emphasis Type="Italic">Phycomyces blakesleeanus</Emphasis>: the relationship between rotation and elongation growth rates

An understanding of the relationship between the two components of helical growth (rotation rate and elongation rate) is fundamental to understanding the biophysical and molecular mechanism(s) of cell wall extension in algal cells, fungal cells, and plant stems and roots. Helical growth occurs throughout development of the sporangiophores of Phycomyces blakesleeanus. Previous studies within the growth zone of stage-IVb sporangiophores have reported conflicting conclusions. An implicit assumption in the previous studies [E.S. Castle (1937) J Cell Comp Physiol 9:477-489; R. Cohen and M. Delbruck (1958) J Cell Comp Physiol 52:361-388; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] was that the relationship between rotation rate and elongation rate was independent of the magnitude of the elongation rate. In the present study, for stage-IVb sporangiophores growing at a steady rate, it is shown that the ratio of rotation rate and elongation rate decreases as the elongation rate increases. Previously proposed biophysical and molecular mechanisms cannot account for the observed behavior. The previously postulated fibril-reorientation mechanism [J.K.E. Ortega and R.I. Gamow (1974) J Theor Biol 47:317-332; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] is modified to accommodate this new finding. Other experiments were conducted to determine how the ratio of rotation rate and elongation rate behaves during a pressure response (a transient decrease in elongation rate produced by a large step-up in turgor pressure using the pressure probe). Results of these experiments indicate that this ratio increases during the pressure response.     

Actin in the ciliated protozoan Climacostomum virens: purification by DNAse I affinity chromatography, electrophoretic characterization, and immunological analysis.

The anti-actin monoclonal antibody (mab) JLA20 (Lin: Proc. Natl. Acad. Sci. U.S.A. 78:2335-2339, 1981) labels a 43 kD protein on Western blots of Climacostomum cell extracts; this protein does not react with an anti-alpha-smooth muscle actin mab (Skalli et al.: J. Cell Biol. 103:2787-2796, 1986) nor with an anti-alpha-sarcomeric actin mab (Skalli et al.: Am. J. Pathol. 130:515-531, 1988). This protein binds to DNAse I and can be purified by DNAse I affinity chromatography. The affinity-purified actin also reacts with mab JLA20. Two-dimensional gel analysis reveals that Climacostomum actin focuses as three spots which are more basic than the mammalian actin isoforms. After addition of KCl, the affinity-purified actin polymerizes into filaments as shown by electron microscopy after negative staining.     

Molecular and functional characterization of a vasotocin-sensitive aquaporin water channel in quail kidney

Both mammals and birds can concentrate urine hyperosmotic to plasma via a countercurrent multiplier mechanism, although evolutionary lines leading to mammals and birds diverged at an early stage of tetrapod evolution. We reported earlier (Nishimura H, Koseki C, and Patel TB. Am J Physiol Regul Integr Comp Physiol 271: R1535-R1543, 1996) that arginine vasotocin (AVT; avian antidiuretic hormone) increases diffusional water permeability in the isolated, perfused medullary collecting duct (CD) of the quail kidney. In the present study, we have identified an aquaporin (AQP) 2 homolog water channel in the medullary cones of Japanese quail, Coturnix coturnix (qAQP2), by RT-PCR-based cloning techniques. A full-length cDNA contains an 822-bp open reading frame that encodes a 274-amino acid sequence with 75.5% identity to rat AQP2. The qAQP2 has six transmembrane domains, two asparagine-proline-alanine (NPA) sequences, and putative N-glycosylation (asparagine-124) and phosphorylation sites (serine-257) for cAMP-dependent protein kinase. qAQP2 is expressed in the membrane of Xenopus laevis oocytes and significantly increased its osmotic water permeability (P(f)), inhibitable (P < 0.01) by mercury chloride. qAQP2 mRNA (RT-PCR) was detected in the kidney; medullary mRNA levels were higher than cortical levels. qAQP2 protein that binds to rabbit anti-rat AQP2 antibody is present in the apical/subapical regions of both cortical and medullary CDs from normally hydrated quail, and the intensity of staining increased only in the medullary CDs after water deprivation or AVT treatment. The relative density of the approximately 29-kDa protein band detected by immunoblot from the medullary cones was modestly higher in water-deprived/AVT-treated quail. The results suggest that 1) medullary CDs of quail kidneys express a mercury-sensitive functioning qAQP2 water channel, and 2) qAQP2 is at least partly regulated by an AVT-dependent mechanism. This is the first clear identification of AQP2 homolog in nonmammalian vertebrates.     

Diminished muscle growth in the obese Zucker rat following overload is associated with hyperphosphorylation of AMPK and dsRNA-dependent protein kinase

Previous data have suggested that insulin-resistant skeletal muscle may exhibit a diminished ability to undergo hypertrophy and that this result may be mediated, at least in part, from decrements in mammalian target of rapamycin (mTOR) signaling (Katta A, Kundla S, Kakarla SK, Wu M, Fannin J, Paturi S, Liu H, Addagarla HS, Blough ER. Am J Physiol Regul Integr Comp Physiol 299: R1666-R1675, 2010). Herein, we attempt to extend these observations by determining if this attenuation in muscle growth is associated with alterations in AMP-activated protein kinase (AMPK) signaling, an upstream mediator of mTOR, and changes in the activation of dsRNA-dependent protein kinase (PKR), which functions as an inhibitor of protein synthesis and potential mediator of protein degradation. Compared with that observed in lean Zucker (LZ) rats, the phosphorylation of AMPKα at Thr172 was higher after 3 wk of overload in the insulin-resistant obese Zucker (OZ) soleus (P < 0.05). This change in AMPKα phosphorylation was accompanied by increases in the amount of phosphorylated PKR (Thr446), elevations in the PKR-dependent phosphorylation of eukaryotic initiation factor (eIF)-2α (Ser51), augmented p38 MAP kinase (Thr180/Tyr182) phosphorylation, and increases in the amount of protein ubiquitination (P < 0.05). Taken together, these results suggest that the diminished hypertrophic response we observe in the OZ rat may be mediated, at least in part, by the hyperactivation of AMPK- and PKR-related signaling.     

Effects of voluntary exercise and genetic selection for high activity levels on HSP72 expression in house mice.

We studied expression of heat shock protein 72 (HSP72) in female mice from four replicate lines that had been selectively bred for high voluntary wheel running (S) and from four random-bred control lines (C). Mice from generation 23 were sampled after 6 days of wheel access, and those from generation 14 were sampled after 8 wk of access to wheels either free to rotate or locked. Mice from S lines ran approximately 2.6 times as many revolutions per day as did those from C lines. Western blotting of tissues from generation 23 mice indicated that S mice had elevated HSP72 expression in triceps surae muscle, but levels in spleen, kidney, heart, and lung were similar in S and C mice. HSP72 expression in triceps surae from generation 14 mice was measured by ELISA and analyzed with a two-way analysis of covariance. The interaction between wheel type and line type (S vs. C) was statistically significant, and subsequent analyses indicated that S mice had significantly elevated HSP72 expression only when housed with free wheels. Mice with the previously described mini-muscle phenotype (Houle-Leroy P, Guderley H, Swallow JG, and Garland T Jr. Am J Physiol Regul Integr Comp Physiol 284: R433-R443, 2003) occurred in both generations and had elevated HSP72 expression in triceps surae. For the generation 23 sample, wheel running as a covariate had a significant negative association with HSP72 expression, and the effect of line type was still statistically significant. Therefore, the increased HSP72 expression of S mice is not a simple proximate effect of their increased wheel running.     

A nonlinear compartmental model of Sr metabolism. II. Its physiological relevance for Ca metabolism

We have studied the peculiarities of the nonlinear compartmental model for human Sr metabolism (Staub JF, Foos E, Courtin B, Jochemsen R, and Perault-Staub AM. Am J Physiol Regul Integr Comp Physiol 284: R819-R834, 2003), including its physiological reliability in the context of Sr-Ca similarity-dissimilarity. We found it to be relevant to Ca metabolism, except for discrimination against Sr relative to Ca at urinary and intestinal levels. The main findings are as follows: 1) the saturable part of intestinal absorption, shared by Sr and Ca, does not seem to be responsible for the discrimination of the transcellular pathway; 2) although there is little discrimination in bone, the physicochemical behaviors of Sr and Ca at the bone surface differ, at least quantitatively; and 3) Sr behaves as a "tracer" for Ca metabolic pathways and, under non-steady-state conditions, can also reveal self-regulatory processes. It is suggested that they depend on Ca2+ (cationic)-sensing receptors that are apparently more sensitive to Sr than to Ca. Acting on gastrointestinal and osteoblast lineage cells, these slow processes might contribute to adaptive, rather than homeostatic, regulation of Ca metabolism. Understanding these features could help clarify the pharmacological and therapeutic effects of oral Sr.     

Isolation, characterization, cDNA cloning and gene expression of an avian transthyretin. Implications for the evolution of structure and function of transthyretin in vertebrates.

A chicken liver cDNA library was constructed in bacteriophage lambda gt10. A full-length transthyretin cDNA clone was identified by screening with rat transthyretin cDNA and was sequenced. A three-dimensional model of chicken transthyretin was obtained by computer-graphics-based prediction from the derived amino acid sequence for chicken transthyretin and from the structure of human transthyretin determined by X-ray diffraction analysis [Blake, C.C.F., Geisow, M.J., Oatley, S.J., Rérat, B. & Rérat, C. (1978) J. Mol. Biol. 121, 339-356]. The similarity of the amino acid sequences of chicken and human transthyretins was 75% overall and 100% for the central channel containing the thyroxine-binding site. Also, the organization of the transthyretin gene into exons and introns and the tissue specificity of expression of the transthyretin gene were similar in chicken and mammals, despite an evolutionary distance of about 3 x 10(8) years from their common ancestor, the Cotylosaurus. By far the highest levels of transthyretin mRNA were found in choroid plexus. The data suggest a fundamental role for the cerebral expression of transthyretin in all vertebrates. It has been proposed that this role is the transport of thyroxine from the bloodstream to the brain [Schreiber, G., Aldred, A.R., Jaworowski, A., Nilsson, C., Achen, M.G. & Segal, M.B. (1990) Am. J. Physiol. 258, R338-R345].