Influence of ATP on sarcoplasmic reticulum function of vascular smooth muscle

1982 ◽  
Vol 242 (3) ◽  
pp. C242-C249 ◽  
Author(s):  
G. D. Ford ◽  
M. L. Hess
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Vascular Smooth Muscle ◽  
Calcium Transport ◽  
Calcium Uptake ◽  
Specific Activity ◽  
Substrate Inhibition ◽  
Uptake Activity ◽  
Active Calcium ◽  
Active Preparation

A vesicular fraction isolated from bovine aorta and enriched in fragmented sarcoplasmic reticulum (FSR) exhibited active calcium transport and ATPase activity. By use of a hypotonic NaHCO3 extraction solution, an active preparation was isolated that retained activity for up to 4 days. A small but significant (P less than 0.05) Ca2+-stimulated, Mg2+-dependent ATPase associated with calcium transport was demonstrated with a specific activity of 0.33 mumol inorganic phosphate (Pi).mg-1.min-1. The basal Mg2+ ATPase demonstrated Michaelis-Menten kinetics [Km(Mg2+-ATP) = 0.44 +/- 0.01 X 10(-3) M; Vmax = 2.22 +/- 0.01 mumolPi.mg-1.min-1]. The Ca2+-stimulated, Mg2+-ATPase demonstrated apparent substrate inhibition (Ks approximately 10 mM) with no evidence for end-product (ADP) or excess added Ca2+ contributing to this inhibition. Oxalate-supported active calcium uptake velocities also exhibited quantitatively similar substrate inhibition. These results suggest that FSR from vascular smooth muscle contains either two enzymes or one enzyme with two isomeric forms, one of which is associated with the calcium uptake activity of this structure and the other of unknown function.

Competition between Oxalate and Phosphate during Active Calcium Accumulation by Sarcoplasmic Vesicles

1977 ◽  
Vol 32 (3-4) ◽  
pp. 281-287 ◽  
Author(s):  
Frank-Ulrich Beil ◽  
Dorothee von Chak ◽  
Wilhelm Hasselbach ◽  
Hans-Hermann Weber
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Binding ◽  
Calcium Transport ◽  
Calcium Uptake ◽  
Phosphate Uptake ◽  
Mutual Exclusion ◽  
Calcium Dependent ◽  
Uptake Activity ◽  
Active Calcium ◽  
Narrow Concentration Range

Abstract Sarcoplasmic Calcium Uptake, Oxalate and Phosphate Uptake, Oxalate-Phosphate Competition, Calcium Turnover 1. During ATP supported active calcium uptake oxalate as well as phosphate are accumulated with calcium. The uptake of calcium exceeds that of both anions by a small quantity - accounting for calcium binding to vesicular proteins and lipids. 2. From assay media containing phosphate and oxalate - nearly exclusively either oxalate or phosphate are taken up together with calcium by the sarcoplasmic reticulum vesicles. The mutual exclusion occurs in a very narrow concentration range of the anions. 3. In solutions containing phosphate and oxalate, calcium phosphate or calcium oxalate pre­ cipitates are formed according to their solubility properties. 4. When phosphate prevents oxalate from being taken up, calcium transport is inhibited. In­ hibition occurs, because the concentration of ionized calcium inside the vesicles rises approximately 100-fold when oxalate is replaced by phosphate. The activity of the calcium dependent ATPase parallels the calcium uptake activity. 5. It is excluded that the inhibition of calcium uptake produced by phosphate is caused by an enhanced permeability of the sarcoplasmic reticulum membranes for calcium in the presence of phosphate.

scholarly journals Effects of Hyperglycemia on Vascular Smooth Muscle Ca2+Signaling

2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Nahed El-Najjar ◽  
Rashmi P. Kulkarni ◽  
Nancy Nader ◽  
Rawad Hodeify ◽  
Khaled Machaca
Keyword(s):  
Insulin Resistance ◽  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Vascular Smooth Muscle ◽  
Complex Disease ◽  
Prolonged Exposure ◽  
In Vitro System ◽  
A7r5 Cells

Diabetes is a complex disease that is characterized with hyperglycemia, dyslipidemia, and insulin resistance. These pathologies are associated with significant cardiovascular implications that affect both the macro- and microvasculature. It is therefore important to understand the effects of various pathologies associated with diabetes on the vasculature. Here we directly test the effects of hyperglycemia on vascular smooth muscle (VSM) Ca2+signaling in an isolated in vitro system using the A7r5 rat aortic cell line as a model. We find that prolonged exposure of A7r5 cells to hyperglycemia (weeks) is associated with changes to Ca2+signaling, including most prominently an inhibition of the passive ER Ca2+leak and the sarcoplasmic reticulum Ca2+-ATPase (SERCA). To translate these findings to the in vivo condition, we used primary VSM cells from normal and diabetic subjects and find that only the inhibition of the ER Ca2+leaks replicates in cells from diabetic donors. These results show that prolonged hyperglycemia in isolation alters the Ca2+signaling machinery in VSM cells. However, these alterations are not readily translatable to the whole organism situation where alterations to the Ca2+signaling machinery are different.

scholarly journals Calcium Uptake Activity of Canine Myocardial Sarcoplasmic Reticulum in the Presence of Anesthetic Agents

1968 ◽  
Vol 23 (5) ◽  
pp. 597-604 ◽  
Author(s):  
RICHARD F. LAIN ◽  
MICHAEL L. HESS ◽  
EDWARD W. GERTZ ◽  
F. NORMAN BRIGGS
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Uptake ◽  
Anesthetic Agents ◽  
Uptake Activity

Functions of selected biochemical systems from the exercised-trained dog heart

1977 ◽  
Vol 42 (3) ◽  
pp. 426-431 ◽  
Author(s):  
L. A. Sordahl ◽  
G. K. Asimakis ◽  
R. T. Dowell ◽  
H. L. Stone
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Transport ◽  
Calcium Uptake ◽  
Atp Synthesis ◽  
Myocardial Cell ◽  
Ruthenium Red ◽  
Mitochondrial Membranes ◽  
Sedentary Control ◽  
Isolated Mitochondria ◽  
Biochemical Systems

Mitochondria and sarcoplasmic reticulum (SR) fractions were isolated from exercised-trained (E-T) and sedentary control dog hearts. Measurements of mitochondrial respiratory functions indicated no changes in energy-producing (ATP synthesis) capacity in mitochondria from E-T compared to control dog hearts. However, the ability of isolated mitochondria from E-T hearts to retain accumulated calcium was markedly decreased compared to controls. Inhibition of mitochondrial rates of calcium uptake with the inhibitor, ruthenium red, revealed fewer binding and/or transport sites in mitochondrial membranes from exercised-trained heart preparations. ATP-dependent binding (- oxalate) and uptake (+ oxalate) of calcium by SR preparations from E-T hearts were unchanged compared to controls. In contrast, significant differences in the rates of release of bound calcium were found in SR isolated from E-T hearts. Total myocardial protein, nucleic acids, and connective tissue levels were unchanged in E-T hearts compared to controls. The results suggest subtle changes are occurring in the energy-utilizing mechanism(s) involving calcium transport of the myocardial cell during exercise training. These changes may be related to alterations in the performance of the exercised-trained heart.

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