Maximal Uptakes Research Articles

Comparative assessment of experimental myocardial infarction with 99Tcm-hexakis-tbutyl-isonitrile (sestamibi), 111In-antimyosin and 201T1

The monocationic 99Tcm-hexakis-2-methoxy-2-methyl propyl isonitrile (99Tcm-sestamibi) is a myocardial perfusion marker with potential clinical value in the diagnosis of ischaemic heart disease. The kinetics of this compound in experimental myocardial infarction in rabbits was compared to the distributions of 111In-antimyosin Fab and 201Tl at 24 h of persistent left anterior descending (LAD) coronary artery occlusion. The maximum uptake of 111In-antimyosin in the infarct was as high as 0.34% injected dose per gram (i.d. g-1), whereas normal myocardial activity was only 0.045% i.d. g-1. Maximal 201Tl and 99Tcm-sestamibi uptakes in normal myocardium were 0.16 and 0.14% i.d. g-1, respectively. Because of their faster blood clearances, 99Tcm-sestamibi and 201Tl were able to delineate regions of radiotracer distribution defects early. 111In-antimyosin required a longer circulation time for in vivo infarct visualization because of slower blood clearance. The data also demonstrated that in persistent LAD occlusion infarction in rabbits, the inverse distribution of sestamibi and 201Tl relative to antimyosin localization (indicator of myocyte necrosis) is not significantly different (I/N sestamibi = 0.213 I/N(AM) + 115.7, r = 0.91, and I/N(201Tl) = 0.181 I/N(AM) + 114.4, r = 0.89).

Histochemical and enzymatic characteristics of skeletal muscle in master athletes

Many older athletes are capable of endurance performances equal to those of young runners who have higher maximal O2 uptakes (VO2max). To determine whether this is a result of differences in skeletal muscle characteristics, gastrocnemius muscle biopsy samples were obtained from eight master athletes [aged 63 +/- 6 (SD) yr] and eight young (aged 26 +/- 3 yr) runners. The young runners were matched with the master athletes for 10-km running performance and for their volume, pace, and type of training. Despite similar 10-km run times, VO2max was 11% lower (P less than 0.05) in the master athletes. Fiber type distribution did not differ between groups, with both groups having 60% type I and very few type IIb fibers. Succinate dehydrogenase and beta-hydroxyacyl-CoA dehydrogenase activities, however, were 31 and 24% higher in the master athletes compared with the matched young runners, whereas lactate dehydrogenase activity was 46% lower (all P less than 0.05). The capillary-to-fiber ratio was also greater in the master athletes; however, capillary density was similar in the two groups, because of the master athletes' 34% larger (P less than 0.05) type I fibers. These differences in skeletal muscle characteristics may explain the master athletes' ability to perform as well as some young runners despite having a lower VO2max.

Estimates of Na+-K+ pumping in intact canine iliac arteries.

Estimates of Na+ pumping capacity were made using Na+-loaded canine iliac arteries. Ouabain-sensitive uptake of 204Tl or 86Rb was used to measure near-maximal pump rates and [3H]ouabain binding to measure the number of pump sites. Compared with Rb+, Tl+ had the higher affinity for the pump and showed better signal-to-noise characteristics. Maximal uptakes were 0.545 mumol . g-1 . min-1 for Rb+ and 0.40 mumol . g-1 . min-1 for Tl+. Specific ouabain binding (Kd: 28.62 +/- 0.58 nM) was inhibited by external K+, Tl+, and Rb+ and a maximal binding of 51.6 pmol/g wet weight translated into 3.2 X 10(13) sites per gram wet weight. Using these values, the maximal values of K+ transported per pump site per minute lie between 7752 and 10562. If each activation of the pump moves 2K+, the turnover rates could lie between 3876 and 5281 per minute.

The pH dependence of the Ca2+, Mg2+-ATPase of sarcoplasmic reticulum: evidence that the Ca2+ translocator bears a doubly negative charge.

The pH dependence of the Ca2+, Mg2+-ATPase pump of rabbit skeletal sarcoplasmic reticulum has been analyzed. Active uptake progress curves of the free luminal Ca2+ concentrationvs. time were obtained by fluorometric readout. The average rates (evaluated att =2 sec) and steady-state maximal uptakes ([Ca2+] i were determined at variable external [Ca2+] o , set by a Ca2+/EGTA buffer. The average rates (t=2 sec) and the [Ca2+] i values showed the same dependence on [Ca2+] o and pH. At pH 7.0, a second-order dependence on [Ca2+] o was observed with aKm (equal to [Ca2+] i for half-maximal rate) of 7.3×10−8m. Both the average rate and the maximal internal Ca2+ level achieved had identicalKm values. The apparent affinity of the pump for Ca2+ (Kapp=1/Km) shows little pH dependence between pH values of 7.0 and 8.0. The apparent affinity drops markedly with decreasing pH below pH 7.0, showing a slope of 1.63 on a log (Kapp)vs. pH plot. This is interpreted as competition between 2H+ and Ca2+ for occupation of each of the two outwardly oriented translocators. The maximal values of average rate (t=2 sec) and [Ca2+] i , were analyzed at saturating [Ca2+] o values to giveVm and [Ca2+]i, max values as a function of pH. These two parameters showed identical pH dependence, with a pH optimum between 6.0 and 6.5. These results are explained both qualitatively and quantitatively by a preliminary model of the steady-state behavior of the pump. The model assumes that enzyme dephosphorylation and countertranslocation represent the rate-limiting step of the cycle and that all other steps are at equilibrium. According to the model, the enzyme has two translocator sites, each bearing a doubly negative charge at pH 7.0 and above. Occupation of both sites by Ca2+ is necessary for transport. Partial or full protonation of the negative charges on the outwardly oriented translocators destroys their capacity for Ca2+ transport. This process is responsible for the decrease in apparent translocator affinity with decreasing pH. A pK a of 7.2±0.3 was determined for the outwardly oriented translocator. Transport of 2 Ca2+ is followed by their release to the lumen. Return of the carrier requires the loading of a charge-stoichiometric amount of alkali cation and H+. The pH dependence ofVm and [Ca2+]i, max is explained by the dual effect of protonation to lower the apparent affinity of the inwardly oriented translocator for internal Ca2+ and to produce single and doubly protonated forms of the translocator capable of high rates of enzyme dephosphorylation and return. A pK a of 6.4±0.3 was determined for the inwardly oriented form. Computer analysis shows that the model is capable of predicting the pH dependence of theKm,Vm and [Ca2+]i, max values. The liminations of the model are evaluated. The structural and physiological significance of the findings is discussed.

Cardiac output during exercise in altitude natives at sea level and high altitude.

Cardiac output during exercise in altitude natives at sea level and high altitude.

Influence of developmental adaptation on aerobic capacity at high altitude.

Influence of developmental adaptation on aerobic capacity at high altitude.

Diffusing capacity of the lung in Caucasians native to 3,100 m.

ARTICLESDiffusing capacity of the lung in Caucasians native to 3,100 mA. C. DeGraff Jr, R. F. Grover, R. L. Johnson Jr, J. W. Hammond Jr, and J. M. MillerA. C. DeGraff Jr, R. F. Grover, R. L. Johnson Jr, J. W. Hammond Jr, and J. M. MillerPublished Online:01 Jul 1970https://doi.org/10.1152/jappl.1970.29.1.71MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByHuman genetic adaptation to high altitudes: Current status and future prospectsQuaternary International, Vol. 461Measuring high-altitude adaptationLorna G. Moore22 November 2017 | Journal of Applied Physiology, Vol. 123, No. 5Exercise Capacity and Selected Physiological Factors by Ancestry and Residential Altitude: Cross-Sectional Studies of 9–10-Year-Old Children in TibetHigh Altitude Medicine & Biology, Vol. 15, No. 2Improvement in lung diffusion by endothelin A receptor blockade at high altitudeClaire de Bisschop, Jean-Benoit Martinot, Gil Leurquin-Sterk, Vitalie Faoro, Hervé Guénard, and Robert Naeije1 January 2012 | Journal of Applied Physiology, Vol. 112, No. 1Alveolar diffusion-perfusion interactions during high-altitude residence in guinea pigsCuneyt Yilmaz, D. Merrill Dane, and Connie C. W. Hsia1 June 2007 | Journal of Applied Physiology, Vol. 102, No. 6Residence at 3,800-m altitude for 5 mo in growing dogs enhances lung diffusing capacity for oxygen that persists at least 2.5 yearsConnie C. W. Hsia, Robert L. Johnson, Paul McDonough, D. Merrill Dane, Myresa D. Hurst, Jennifer L. Fehmel, Harrieth E. Wagner, and Peter D. Wagner1 April 2007 | Journal of Applied Physiology, Vol. 102, No. 4Long-term enhancement of pulmonary gas exchange after high-altitude residence during maturationPaul McDonough, D. Merrill Dane, Connie C. W. Hsia, Cuneyt Yilmaz, and Robert L. Johnson1 February 2006 | Journal of Applied Physiology, Vol. 100, No. 2Upregulation of erythropoietin receptor during postnatal and postpneumonectomy lung growthDavid J. Foster, Orson W. Moe, and Connie C. W. Hsia1 December 2004 | American Journal of Physiology-Lung Cellular and Molecular Physiology, Vol. 287, No. 6Mechanisms and Limits of Induced Postnatal Lung GrowthAmerican Journal of Respiratory and Critical Care Medicine, Vol. 170, No. 3Effects of birthplace and individual genetic admixture on lung volume and exercise phenotypes of Peruvian Quechua7 July 2003 | American Journal of Physical Anthropology, Vol. 123, No. 4Recruitment of Lung Diffusing CapacityChest, Vol. 122, No. 5Pulmonary gas exchange and acid-base state at 5,260 m in high-altitude Bolivians and acclimatized lowlandersPeter D. Wagner, Mauricio Araoz, Robert Boushel, José A. L. Calbet, Birgitte Jessen, Göran Rådegran, Hilde Spielvogel, Hans Søndegaard, Harrieth Wagner, and Bengt Saltin1 April 2002 | Journal of Applied Physiology, Vol. 92, No. 4Invited Review: Pulmonary alveoli: formation, the “call for oxygen,” and other regulatorsDonald Massaro, and Gloria D. Massaro1 March 2002 | American Journal of Physiology-Lung Cellular and Molecular Physiology, Vol. 282, No. 3Chronic airway infection leads to angiogenesis in the pulmonary circulationNatalie Hopkins, Elaine Cadogan, Shay Giles, and Paul McLoughlin1 August 2001 | Journal of Applied Physiology, Vol. 91, No. 2Exercise performance of Tibetan and Han adolescents at altitudes of 3,417 and 4,300 mQiu-Hong Chen, Ri-Li Ge, Xiao-Zhen Wang, Hui-Xin Chen, Tian-Yi Wu, Toshio Kobayashi, and Kazuhiko Yoshimura1 August 1997 | Journal of Applied Physiology, Vol. 83, No. 2Greater maximal O2 uptakes and vital capacities in Tibetan than Han residents of LhasaRespiration Physiology, Vol. 79, No. 2Distribution of regional lung function during mild exercise in residents of 3100 mRespiration Physiology, Vol. 22, No. 3Diffusing capacity and over-all ventilation: Perfusion in asthmaThe American Journal of Medicine, Vol. 57, No. 5Effects of acute through life-long hypoxic exposure on exercise pulmonary gas exchangeRespiration Physiology, Vol. 13, No. 1 More from this issue > Volume 29Issue 1July 1970Pages 71-76 Copyright & PermissionsCopyright © 1970 the American Physiological Societyhttps://doi.org/10.1152/jappl.1970.29.1.71PubMed5425040History Published online 1 July 1970 Published in print 1 July 1970 Metrics