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.

Low concentrations of A23187 increase calcium uptake by cardiac sarcoplasmic reticulum

1985 ◽  
Vol 249 (6) ◽  
pp. H1211-H1215
Author(s):  
J. J. Murray ◽  
A. V. Kuzmin ◽  
P. W. Reed ◽  
D. O. Levitsky
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Uptake ◽  
Atp Hydrolysis ◽  
Ionophore A23187 ◽  
Uptake System ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Calcium Dependent ◽  
Uptake Measurement

The divalent cation ionophore A23187 at a concentration of 1 nM produced an increased rate of oxalate-supported calcium uptake by isolated cardiac sarcoplasmic reticulum as determined by absorbance changes of the calcium-sensitive dye murexide. Addition of a higher concentration of A23187 (0.1 microM) produced a decreased rate of calcium uptake. Measurement of the time during which ATPase was activated by calcium addition also suggested an increased rate of calcium uptake in the presence of 1 nM A23187 and an inhibition of calcium uptake at a higher concentration of the ionophore (0.1 microM). Ca2+-stimulated ATPase activity and incorporation of 32Pi from [gamma-32P]ATP into sarcoplasmic reticular proteins were increased by A23187 at concentrations of 1 nM or greater. An increased coupling of calcium uptake to ATP hydrolysis was observed at 1 nM A23187, while concentrations of the ionophore greater than or equal to 10 nM produced a decreased coupling. Addition of an inhibitor of cyclic AMP-dependent protein kinase decreased the rate of calcium uptake, and this inhibition was reversed in a concentration-dependent manner by 0.01–1 nM A23187. These data suggest that A23187 can activate a mechanism involving the calcium-dependent phosphorylation of protein that may regulate the activity of the calcium uptake system of the sarcoplasmic reticulum. These observations appear to provide an explanation for some of the contractile effects of A23187 in intact cardiac muscle that suggest that treatment with the ionophore results in an increased sequestration of calcium from the cytoplasm.

scholarly journals The effect of calmodulin on the phosphoprotein intermediate of Mg2+-dependent Ca2+-stimulated adenosine triphosphatase in human erythrocyte membranes

1981 ◽  
Vol 194 (2) ◽  
pp. 481-486 ◽  
Author(s):  
D A Jeffery ◽  
B D Roufogalis ◽  
S Katz
Keyword(s):  
Steady State ◽  
Atpase Activity ◽  
Turnover Rate ◽  
Erythrocyte Membranes ◽  
Steady State Concentration ◽  
Transport Atpase ◽  
Dependent Atpase ◽  
Mgcl2 Concentration ◽  
Human Erythrocyte Membranes ◽  
State Concentration

The effect of calmodulin on the formation and decomposition of the Ca2+-dependent phosphoprotein intermediate of the (Mg2+ + Ca2+)-dependent ATPase in erythrocyte membranes was investigated. In the presence of 60 microM-Ca2+ and 25 microM-MgCl2, calmodulin (0.5-1.5 microgram) did not alter the steady-state concentration of the phosphoprotein, but increased its rate of decomposition. Higher calmodulin concentrations significantly decreased the steady-state concentration of phosphoprotein. Calmodulin (0.5-1.7 microgram) increased Ca2+-transport ATPase activity by increasing the turnover rate of its phosphoprotein intermediate. Increasing the MgCl2 concentration from 25 microM to 250 microM increased the (Mg2+ + Ca2+)-dependent ATPase activity, but decreased the concentration of the phosphoprotein intermediate. Similarly to calmodulin, MgCl2 increased the turnover rate of the Ca2+-transport ATPase complex (about 3-fold). At the higher MgCl2 concentration calmodulin did not further affect the decomposition of the phosphoprotein intermediate. It was concluded that both calmodulin and MgCl2 increase the turnover of the Ca2+-pump by enhancing the decomposition of the Ca2+-dependent phosphoprotein intermediate.

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.

scholarly journals AIF4-induced inhibition of the ATPase activity, the Ca2+-transport activity and the phosphoprotein-intermediate formation of plasma-membrane and endo(sarco)plasmic-reticulum Ca2+-transport ATPases in different tissues. Evidence for a tissue-dependent functional difference

1989 ◽  
Vol 261 (2) ◽  
pp. 655-660 ◽  
Author(s):  
L Missiaen ◽  
F Wuytack ◽  
H De Smedt ◽  
F Amant ◽  
R Casteels
Keyword(s):  
Smooth Muscle ◽  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Intermediate Formation ◽  
Functional Difference ◽  
Transport Activity ◽  
Fast Skeletal Muscle ◽  
Transport Atpase ◽  
Plasmic Reticulum

AIF4- inhibits the (Ca2+ + Mg2+)-ATPase activity of the plasma-membrane and the sarcoplasmic-reticulum Ca2+-transport ATPase [Missiaen, Wuytack, De Smedt, Vrolix & Casteels (1988) Biochem. J. 253, 827-833]. The aim of the present work was to investigate this inhibition further. We now report that AIF4- inhibits not only the (Ca2+ + Mg2+)-ATPase activity, but also the ATP-dependent 45Ca2+ transport, and the formation of the phosphoprotein intermediate by these pumps. Mg2+ potentiated the effect of AIF4-, whereas K+ had no such effect. The plasma-membrane Ca2+-transport ATPase from erythrocytes was 20 times less sensitive to inhibition by AIF4- as compared with the Ca2+-transport ATPase from smooth muscle. The endoplasmic-reticulum Ca2+-transport ATPase from smooth muscle was inhibited to a greater extent than the sarcoplasmic-reticulum Ca2+-transport ATPase of slow and fast skeletal muscle.

Tryptic Fragmentation of the Calcium Transport System in the Sarcoplasmic Reticulum

1973 ◽  
Vol 28 (3-4) ◽  
pp. 178-182 ◽  
Author(s):  
A. Migala ◽  
B. Agostini ◽  
W. Hasselbach
Keyword(s):  
Molecular Weight ◽  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Calcium Transport ◽  
Smooth Surface ◽  
Calcium Uptake ◽  
Surface Structures ◽  
Transport Atpase ◽  
Protein Fragments ◽  
Calcium Dependent

Two protein fragments with a molecular weight of 50-60 000 daltons are formed when the calcium transport ATPase of the SR is mildly digested with trypsin. The initial fragmentation of the ATPase does not interfere with calcium transport, calcium dependent ATPase activity and phosphoprotein formation. The decay of the initially formed protein fragments after prolonged tryptic digestion is accompanied by the decline of the rate of calcium uptake and the calcium concentrating ability while the activity of the calcium activated ATPase is reduced only moderately. The initial tryptic fragmentation does not give rise to any change in the morphological appearance in the SR membranes. After prolonged digestion brush border or smooth surface structures are observed depending on the agent used for negative staining.

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.

Localization of Atpase Activity in the Sarcoplasmic Reticulum of Myocardium

1976 ◽  
Vol 34 ◽  
pp. 84-85
Author(s):  
M. Ashraf ◽  
H. M. Jones ◽  
L. H. Livingston
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cell Membrane ◽  
Atpase Activity ◽  
Cell Membranes ◽  
Myocardial Cell ◽  
Cytochemical Localization ◽  
Transport Atpase ◽  
Biochemical Evidence ◽  
Functional Roles ◽  
Adenosine Triphosphatases

Transcellular exchange of various ions takes place via adenosine triphosphatases (ATPases) which are embedded in the cell and its organelle membranes. Due to heterogeneity in the functional roles of myocardial cell membranes, it is generally agreed that different kinds of ATPases exist in the cell. Biochemical evidence indicates that a major ATPase is involved with the Na+-K+ pump and is located in the myocardial cell membrane. Another ATPase, Ca transport ATPase, is localized in the sarcoplasmic reticulum. Little is presently known of the cytochemical localization and distribution of ATPases and their correlation with myocardial cell membranes. In this study an attempt was made to demonstrate the cytochemical distribution of Ca++ ATPase in the myocardium.

Sign in / Sign up

Export Citation Format

Share Document