scholarly journals Hyperthyroidism increases the uncoupled ATPase activity and heat production by the sarcoplasmic reticulum Ca2+-ATPase

2003 ◽  
Vol 375 (3) ◽  
pp. 753-760 ◽  
Author(s):  
Ana Paula ARRUDA ◽  
Wagner S. da-SILVA ◽  
Denise P. CARVALHO ◽  
Leopoldo de MEIS
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Heat Production ◽  
Atp Hydrolysis ◽  
Fold Increase ◽  
Heat Sources ◽  
Muscle Type ◽  
Red Muscle

The sarcoplasmic reticulum Ca2+-ATPase is able to modulate the distribution of energy released during ATP hydrolysis, so that a portion of energy is used for Ca2+ transport (coupled ATPase activity) and a portion is converted into heat (uncoupled ATPase activity). In this report it is shown that T4 administration to rabbits promotes an increase in the rates of both the uncoupled ATPase activity and heat production in sarcoplasmic reticulum vesicles, and that the degree of activation varies depending on the muscle type used. In white muscles hyperthyroidism promotes a 0.8-fold increase of the uncoupled ATPase activity and in red muscle a 4-fold increase. The yield of vesicles from hyperthyroid muscles is 3–4-fold larger than that obtained from normal muscles; thus the rate of heat production by the Ca2+-ATPase expressed in terms of g of muscle in hyperthyroidism is increased by a factor of 3.6 in white muscles and 12.0 in red muscles. The data presented suggest that the Ca2+-ATPase uncoupled activity may represent one of the heat sources that contributes to the enhanced thermogenesis noted in hyperthyroidism.

Role of sarcoplasmic reticulum in loss of load-sensitive relaxation in pressure overload cardiac hypertrophy

1994 ◽  
Vol 266 (1) ◽  
pp. H68-H78 ◽  
Author(s):  
C. R. Cory ◽  
R. W. Grange ◽  
M. E. Houston
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Hypertrophy ◽  
Atpase Activity ◽  
Pressure Overload ◽  
Fold Increase ◽  
Left Ventricular ◽  
Isometric Tension ◽  
Tension Development ◽  
Sequestration Potential

The loss of load-sensitive relaxation observed in the pressure-overloaded heart may reflect a strategy of slowed cytosolic Ca2+ uptake to yield a prolongation of the active state of the muscle and a decrease in cellular energy expenditure. A decrease in the potential of the sarcoplasmic reticulum (SR) to resequester cytosolic Ca2+ during diastole could contribute to this attenuated load sensitivity. To test this hypothesis, both in vitro mechanical function of anterior papillary muscles and the SR Ca2+ sequestration potential of female guinea pig left ventricle were compared in cardiac hypertrophy (Hyp) and sham-operated (Sham) groups. Twenty-one days of pressure overload induced by coarctation of the suprarenal, subdiaphragmatic aorta resulted in a 36% increase in left ventricular mass in the Hyp. Peak isometric tension, the rate of isometric tension development, and the maximal rates of isometric and isotonic relaxation were significantly reduced in Hyp. Load-sensitive relaxation were significantly reduced in Hyp. Load-sensitive relaxation quantified by the ratio of a rapid loading to unloading force step in isotonically contracting papillary muscle was reduced 50% in Hyp muscles. Maximum activity of SR Ca(2+)-adenosinetriphosphatase (ATPase) measured under optimal conditions (37 degrees C; saturating Ca2+) was unaltered, but at low free Ca2+ concentrations (0.65 microM), it was decreased by 43% of the Sham response. Bivariate regression analysis revealed a significant (r = 0.84; P = 0.009) relationship between the decrease in SR Ca(2+)-ATPase activity and the loss of load-sensitive relaxation after aortic coarctation. Stimulation of the SR Ca(2+)-ATPase by the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase resulted in a 2.6-fold increase for Sham but only a 1.6-fold increase for Hyp. Semiquantitative Western blot radioimmunoassays revealed that the changes in SR Ca(2+)-ATPase activity were not due to decreases in the content of the Ca(2+)-ATPase protein or phospholamban. Our data directly implicate a role for decreased SR function in attenuated load sensitivity. A purposeful downregulation of SR Ca2+ uptake likely results from a qualitative rather than a quantitative change in the ATPase and possibly one of its key regulators, phospholamban.

scholarly journals Chemical modification of sarcoplasmic reticulum with methylbenzimidate. Stimulation of Ca2+ efflux

1987 ◽  
Vol 243 (1) ◽  
pp. 165-173 ◽  
Author(s):  
V Shoshan-Barmatz
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Chemical Modification ◽  
Atp Hydrolysis ◽  
Divalent Cations ◽  
Protein Factor ◽  
Time Period ◽  
Fold Stimulation ◽  
Stimulation Of

Treatment of sarcoplasmic reticulum membranes with 12 mM-methylbenzimidate (MBI) for 5 min, in the presence of 5 mM-ATP at pH 8.5, resulted in a 2-3-fold stimulation of ATP hydrolysis and over 90% inhibition of Ca2+ accumulation. This phenomenon was strictly dependent upon the presence of nucleotides with the following order of effectiveness: adenosine 5′-[beta, gamma-imido]triphosphate greater than or equal to ATP greater than UTP greater than ADP greater than AMP. Divalent cations such as Ca2+, Mg2+ and Mn2+, when present during the MBI treatment, prevented both the stimulation of ATPase activity and the inhibition of Ca2+ accumulation. Modification with MBI had no effect on E-P formation from ATP, ADP-ATP exchange, Ca2+ binding or ATP-Pi exchange catalysed by the membranes. Membranes modified with MBI in the presence of ATP and then passively loaded with Ca2+ released about 80% of their Ca2+ content within 3 s. Control membranes released only 3% of their Ca2+ during the same time period. MBI modification inhibited Ca2+ accumulation by proteoliposomes reconstituted with the partially purified ATPase but not with the purified ATPase fraction. These results suggest that MBI in the presence of ATP stimulates Ca2+ release by modifying a protein factor(s) other than the (Ca2+ + Mg2+)-ATPase.

Control of heat production by the Ca2+-ATPase of rabbit and trout sarcoplasmic reticulum

1998 ◽  
Vol 274 (6) ◽  
pp. C1738-C1744 ◽  
Author(s):  
Leopoldo De Meis
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Heat Production ◽  
Atp Hydrolysis ◽  
Rabbit Skeletal Muscle ◽  
Heparin Sodium ◽  
The Difference

The sarcoplasmic reticulum Ca2+-ATPase of rabbit skeletal muscle can convert the energy derived from a Ca2+ gradient into heat (L. de Meis, M. L. Bianconi, and V. A. Suzano. FEBS Lett. 406: 201–204, 1997). In this report, it is shown that this conversion varies depending on the temperature and on whether rabbit (endotherm) or trout (poikilotherm) sarcoplasmic reticulum vesicles are used. The gradient doubled the yield of heat produced during ATP hydrolysis and the calorimetric enthalpy of ATP hydrolysis (Δ H cal) value found with both rabbit and trout varied between −10 and −12 kcal/mol in leaky vesicles (no gradient) and between −20 and −22 kcal/mol with intact vesicles (gradient). For the rabbit, the difference of Δ H cal measured with and without gradient was detected in the range of 30–35°C and disappeared when the temperature was decreased below 30°C. For the trout, the difference was detected between 20 and 25°C and disappeared below 20°C. The effect of the gradient on the Δ H cal for ATP hydrolysis was modified by DMSO, trifluoperazine, and heparin sodium.

scholarly journals The Mechanism of the Action of Caffeine on Sarcoplasmic Reticulum

1968 ◽  
Vol 52 (5) ◽  
pp. 760-772 ◽  
Author(s):  
A. Weber
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Transport System ◽  
Turnover Rate ◽  
Atp Hydrolysis ◽  
Uptake System ◽  
Transport Atpase ◽  
Ca Uptake

Evidence is presented that caffeine does not act on the mitochondrial Ca uptake system and that its effect cannot be attributed to the accumulation of adenosine 3',5'-phosphate. Two distinct caffeine effects are described. At high ATP concentrations caffeine decreases the coupling between ATP hydrolysis and Ca inflow. It either inhibits inflow without any inhibition of the rate of ATP hydrolysis, or it stimulates the ATPase activity without stimulating Ca inflow. These high ATP concentrations (much higher than needed for the saturation of the transport ATPase) greatly reduce the control of the turnover rate of the transport system, by accumulated Ca. At low ATP concentrations when the transport system is under maximal control by accumulated Ca, caffeine inhibits the ATPase activity without affecting the rate of Ca inflow.

scholarly journals Correlation between Uncoupled ATP Hydrolysis and Heat Production by the Sarcoplasmic Reticulum Ca2+-ATPase

2001 ◽  
Vol 276 (46) ◽  
pp. 42793-42800 ◽  
Author(s):  
Marcelo Reis ◽  
Mariana Farage ◽  
Angela Cristina L. de Souza ◽  
Leopoldo de Meis
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Heat Production ◽  
Atp Hydrolysis

Evidence for active CO2 uptake by a CO2-ATPase in the acidophilic green alga Eremosphaera viridis

2001 ◽  
Vol 79 (11) ◽  
pp. 1274-1281
Author(s):  
Jason ST Deveau ◽  
Roger R Lew ◽  
Brian Colman
Keyword(s):  
Atpase Activity ◽  
Green Alga ◽  
Inorganic Carbon ◽  
Atp Hydrolysis ◽  
Dissolved Inorganic Carbon ◽  
Electrical Potential ◽  
Fold Increase ◽  
Co2 Uptake ◽  
Eremosphaera Viridis ◽  
A Value

We examined the mechanism(s) responsible for active uptake of dissolved inorganic carbon (DIC) during photosynthesis in the green alga Eremosphaera viridis De Bary. O2 electrode measurements of algal oxygen evolution and CO2 fluxes as a function of DIC availability indicate that E. viridis actively imports only CO2 during photosynthesis, and does not possess external carbonic anhydrase (CA). The K0.5[CO2] was 14.2 and 10.1 µM at pH 5.0 and 8.0, respectively. Both membrane potential and cellular resistance were measured under controlled conditions of [CO2] at either 2 or 15 µM. Active CO2 uptake was electrically silent, suggesting that CO2 uptake might be mediated by a CO2-ATPase. Comparison of ATPase activity in microsomal preparations at low (0 µM) and high (15 µM) [CO2] indicated a 1.25-fold increase in ATP hydrolysis in high [CO2]. The CO2-ATPase activity was inhibited by the broad-acting inhibitors diethylstilbestrol (DES) and N',N'-dicyclohexylcarbodiimide (DCCD) but unaffected by vanadate, fluoride, and nitrate. The K0.5[CO2] of the ATPase activity was 22.5 µM, a value very similar to the K0.5[CO2] for CO2 uptake by whole algal cells. These results suggest the existence of a CO2-ATPase as the major importer of DIC for photosynthesis in the microalga E. viridis.Key words: chlorophyte, CO2 transport, CO2-ATPase, photosynthesis, electrical potential, mass spectrometry.

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