Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Calcium-Transporting ATPases”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources
PubMed1991

A possible role for the dimer ribbon state of scallop sarcoplasmic reticulum. Dimmer ribbons are associated with stabilization of the Ca(2+)-free Ca-ATPase.

The Ca-ATPase activity of membranous scallop sarcoplasmic reticulum was found to be unstable when the Ca(2+)-binding sites on the Ca-ATPase were unoccupied. The decay in activity could be slowed or halted by inclusion in the preincubation medium of Na+, K+, nucleotides, ethylene glycol, or high concentrations of choline chloride. Stabilization of the Ca(2+)-free Ca-ATPase by Na+ and K+ showed a markedly different concentration dependence to that seen with activation of the Ca(2+)-activated ATPase activity by the two ions. Examination in the electron microscope of scallop membranes negatively stained in the presence of EGTA under conditions where the enzyme had been stabilized against lack of Ca2+ always showed vesicles containing dimer ribbon structures, whereas unstabilized membranes did not show dimer ribbons. There was an association between the effectiveness of a medium in stabilizing the enzyme in the presence of EGTA and the extent and quality of the dimer arrays seen in the microscope. Comparison of the range of Ca2+ concentration over which the Ca(2+)-binding sites on the scallop Ca-ATPase titrated with the range over which the dimer ribbon structural state was lost indicated that the Ca(2+)-binding sites on the Ca-ATPase must be empty for dimer ribbon formation to occur. Previous studies (Franzini-Armstrong, C., Ferguson, D. G., Castellani, L., and Kenney, L. J. (1987) Ann. N. Y. Acad. Sci. 483, 44-56) have found that the Ca-ATPase molecules in scallop adductor muscle freeze-fractured after fixation under relaxing conditions are arranged in dimer ribbons. Thus, the association of stabilization of the Ca(2+)-free Ca-ATPase with the presence of dimer ribbons implies that one function of the dimer state may be to stabilize the scallop enzyme in situ, when the Ca2+ concentration in the sarcoplasm is low and the muscle is relaxed.

Adenine Nucleotides↗
PubMed1991

Dissociation of purified erythrocyte Ca(2+)-ATPase by hydrostatic pressure.

Subunit interactions in the Ca(2+)-ATPase from erythrocyte plasma membranes were investigated through a combination of fluorescence spectroscopy and high-pressure techniques. Application of hydrostatic pressure in the range of 1 bar to 2.4 kbar promoted full dissociation of the ATPase, as revealed by spectral shifts of the intrinsic fluorescence emission and by changes in the fluorescence polarization of dansyl-conjugated ATPase. Pressure dissociation of the ATPase displayed a dependence on protein concentration compatible with dissociation of a dimer. Calculated from pressure-dissociation curves, the standard volume change dV0 for the association of subunits was 43-50 ml/mol and K0, the dissociation constant at atmospheric pressure, was 6-9 x 10(-8) M. Addition of Ca2+ stabilized the dimeric ATPase structure against pressure dissociation, whereas addition of vanadate facilitated dissociation by pressure. These results suggest that intersubunit interactions depend on the equilibrium between the two major conformational states E1 and E2 of the ATPase. Addition of calmodulin in the presence of Ca2+ had no additional effect when compared to that observed in the presence of Ca2+ alone. This finding is interpreted in terms of the mechanism of calmodulin activation of ATPase catalysis.

Calcium↗
PubMedDate not supplied

[Catalytic and transport cycle of sarcoplasmic reticulum Ca(2+)-ATPase].

Recent information on mechanisms of ATP hydrolysis and relevant transport of calcium ions by the membrane-bound Ca(2+)-ATP-ase of the sarcoplasmic reticulum is summarized. Stages of the catalytic and transport cycles of the Ca(2+)-ATP-ase and conformational states of the enzyme are considered in detail.

Adenosine Triphosphate↗
PubMed1991

[Biologist's view on diastolic dysfunction].

Modern biology provides satisfactory explanations for the abnormalities of the different phases of relaxation and diastole. Ventricular filling depends on three factors: active relaxation; the only factor is the concentration of ATP which has to re-increase. This requires elimination of the cytoplasmic calcium which activates ATP-ase by the Ca2+ ATPase of the sarcoplasmic reticulum and the Na+/Ca2+ pump. In hypertrophy, the concentration of the first and the activity of the second are decreased; passive wall compliance, which depends on the quantity and quality of parietal collagen. This factor is partially regulated in the myocardium by the concentration of aldosterone and angiotensin II; atrial contraction, which depends on the size of the atria and their isomyosine content. This changes in atrial overload to a slow form of myosine, one of the mechanisms of adaptation.

Calcium↗
PubMed1991

Drug action of thapsigargin on the Ca2+ pump protein of sarcoplasmic reticulum.

Thapsigargin is found to be a potent inhibitor of the intracellular Ca2+ pump proteins from skeletal muscle sarcoplasmic reticulum (SR), cardiac SR, and brain microsomes. For skeletal muscle SR, the molar ratio of thapsigargin to Ca2+ pump protein for complete inhibition (MRc) of the Ca2+ loading rate, Ca(2+)-dependent ATPase activity, and formation of phosphorylated intermediate (EP) was approximately 1. When the Ca2+ pump protein of low affinity to Ca2+ (E2 state) was pretreated with thapsigargin, ATP and Ca2+ binding to the Ca2+ pump protein was completely inhibited. In the presence of Ca2+ (E1 state), Ca2+ pump protein was protected from inactivation by thapsigargin with respect to Ca2+ binding and EP formation. The MRc for brain microsomes, which mediate Ca2+ uptake into intracellular (inositol 1,4,5-trisphosphate-releasable) Ca2+ pools, is likewise stoichiometric. Approximately 30% of Ca2+ loading activity of brain microsomes was insensitive to thapsigargin, indicating the presence of other Ca2+ pumping system(s). The MRc for heart is 3.8, indicating that the Ca2+ pump of cardiac SR is less sensitive to thapsigargin. Phosphorylation of cardiac SR with protein kinase A increased the sensitivity to thapsigargin to MRc of 2.8. In summary, we find that: 1) thapsigargin is the most effective inhibitor of the Ca2+ pump protein of intracellular membranes (SR and endoplasmic reticulum); 2) its primary inhibitory action appears to inactivate the E2 form of the enzyme preferentially; 3) cardiac SR shows lesser sensitivity to thapsigargin than skeletal muscle SR and brain microsomes; protein kinase A treatment of cardiac SR enhances the sensitivity to the drug.

Adenosine Triphosphate↗
PubMed1991

Halothane inhibits agonist-induced inositol phosphate and Ca2+ signaling in A7r5 cultured vascular smooth muscle cells.

Halothane, an anesthetic with marked depressant effects on the circulation, was studied for its ability to inhibit inositol phosphate and Ca2+ signaling evoked by the vasoactive hormone arginine vasopressin (AVP) and Ca2+ responses elicited by platelet-derived growth factor and by thapsigargin in cultured A7r5 vascular smooth muscle cells. Changes in apparent [Ca2+]i were measured using the indicator indo-1 and flow cytometry, whereas inositol phosphate levels were determined using myo-[3H]inositol and column chromatography. Preincubation with clinically relevant concentrations of halothane resulted in dose-dependent depression of [Ca2+]i responses evoked on stimulation with AVP. Halothane (2.0%) inhibited the increases in [Ca2+]i by 34-45%. In cells incubated in Ca(2+)-free medium plus 0.5 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, the halothane effect was more marked, with 1.5% halothane inhibiting the responses by approximately 53-61%. However, when Ca2+ influx was stimulated by addition of 5 mM Ca2+ in the continued presence of the agonist, the [Ca2+]i response was inhibited by only 15%, suggesting that release of Ca2+ rather than Ca2+ influx is more sensitive to inhibition by the anesthetic. The effects of halothane on Ca2+ homeostasis are not explained solely by anesthetic-induced depletion of Ca2+ from intracellular stores, because the anesthetic inhibited increases in [Ca2+]i elicited by thapsigargin in cells suspended in Ca(2+)-free medium by only 31%. Halothane inhibited inositol phosphate formation elicited by AVP, suggesting an additional means by which the anesthetic may alter agonist-induced Ca2+ responses. The current results also demonstrate that halothane actions are not specific solely to responses evoked by AVP, which acts via a guanine nucleotide-binding protein-linked signaling pathway, but include responses stimulated by platelet-derived growth factor, an agonist that elevates [Ca2+]i via receptor-latent tyrosine kinase activity. The current results demonstrate that, in vascular smooth muscle cells, halothane alters Ca2+ homeostasis, an action that may underlie the in vivo vasodilator effects of the anesthetic.

Animals↗
PubMed1991

Regulation of sarcoplasmic reticulum protein phosphorylation by localized cyclic GMP-dependent protein kinase in vascular smooth muscle cells.

The role of cGMP-dependent protein kinase in the regulation of intracellular Ca2+ levels in vascular smooth muscle cells was examined by studying the effects of cGMP on the phosphorylation of the Ca(2+)-ATPase regulatory protein phospholamban. Cultured rat aortic smooth muscle cells incubated with atrial natriuretic peptide II or sodium nitroprusside responded with increased phosphorylation of the 6000-Da subunit of phospholamban. The identity of phospholamban was confirmed using immunoprecipitation methods. Phosphorylation was associated with an increase in the activation of membrane-associated ATPase by Ca2+. These results indicated that at least one site of action of cGMP in smooth muscle cells is the sarcoplasmic reticulum, where phosphorylation of proteins regulating Ca2+ fluxes occurs. Studies using confocal laser scanning microscopy to define the cellular distribution of cGMP-dependent protein kinase suggested that the enzyme was localized to the same cellular region(s) as was phospholamban. Phosphorylation of proteins by cGMP in broken cell fractions from rabbit aorta was also performed. Phospholamban and other proteins were phosphorylated in the presence of cGMP but not cAMP, suggesting that only cGMP-dependent protein kinase was associated with smooth muscle membrane fractions containing phospholamban. These results suggest that one mechanism of action of cGMP in the reduction of intracellular Ca2+ is the activation of sarcoplasmic reticulum Ca(2+)-ATPase via phosphorylation of phospholamban. The data also support the concept that compartmentalization of protein kinases with substrates in the intact cell is an important factor involved in protein phosphorylation.

Animals↗
PubMed1977

Ca2+-activated ATPase of rat liver plasma membrane.

Rat liver plasma membranes hydrolyze ATP in the presence of Ca2+. The rate of hydrolysis is different when Mg2+ions are present in the incubation system. Several parameters differentiate Ca2+-ATPase from Mg2+-ATPase: a) the Km of ATP hydrolysis for Ca2+ (2.25 x 10(-4) M) is lower than for Mg2+ (2.14 x 10(-3) M); b) the shape of the activation curve is hyperbolic in the presence of Ca2+ and sigmoid in the presence of Mg2+; c) Mg2+-ATPase shows two different values of activation energy while Ca2+-ATPase presents only a single value; d) Ca2+-ATPase is inhibited, while Mg2+-ATPase is unaffected by cyclic AMP. Ca2+-ATPase is localized on the plasma membrane and is not inhibited by cysteine. It does not hydrolyze substrates different from nucleotides triphosphate, such as glucose-1-phosphate or alpha-glycero-phosphate. The enzyme is probably related to a mechanism of calcium transport.

Adenosine Triphosphate↗
PubMed1977

Studies on adenosine triphosphatase activity of rat cardiac myosin in isoproterenol-induced cardiac hypertrophy.

Ca2+- and K+ -activated ATPase activity of cardiac myosin from normal and hypertrophied rat hearts was investigated. Cardiac hypertrophy was induced by isoproterenol treatment. A nearly 40% increase in heart mass was seen after seven consecutive days of isoproterenol injection (5 mg/kg) as determined by either heart weight expressed as per cent of body weight or by dry heart weight and total protein content. The measurement of ATP hydrolysis revealed that cardiac myosin from isoproterenol-treated rats had a significant decrease (P less than 0.01) in Ca2+-activated ATPase activity at low ionic strength (0.05 M KCl) in the presence of 5 and 10 mM Ca2+. In contrast, in a high ionic strength medium (0.50 M KCl) the K+- and Ca2+-activated ATPase activity of myosin prepared from hypertrophied myocardium remained unchanged. Comparative analysis of protein present in the light chains of myosin showed no alteration in the proportion of LC1 to LC2 in the myosin from hypertrophied hearts, however, a decrease in the absorption of myosin in the u.v. region was observed. On the basis of our results one can hypothesize that there may be some conformational change in the myosin molecule from hypertrophied myocardium, thereby modifying both Ca2+-sensitivity and ATPase activity at a low KCl concentration.

Animals↗
PubMed1979

Toxic substances and cell membrane function.

The exposed location and functional importance of cell membranes make them particularly susceptible to the toxic effects of many chemicals. The likelihood of such effects has been appreciated for many years. However, the recent advent of new techniques has greatly increased our understanding of the complexities of membrane structure and function. These data make it quite clear that the interaction of toxic compounds with either the protein or the lipid component of cell membranes may substantially alter membrane function. This paper summarizes the current concepts of membrane structure and function and discusses the techniques currently in use to study cell membranes. Several examples are presented in which xenobiotics significantly alter membrane function. These include effects of heavy metals on passive ion permeability, impairment of osmoregulation and calcium transport by organochlorine pesticides, inhibition of the transport of neurotransmitter metabolites by phenoxyacetic acid herbicides in choroid plexus, and reduction in intestinal nutrient transport by heavy metals. Hence the study of the interactions of foreign compounds with membrane function may enhance our understanding of mechanisms both of toxicity and of basic membrane function.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1979

Nerve cell calcium as a messenger for opiate and endorphin actions.

The studies outlined in this chapter provide convincing evidence for the role of calcium in pharmacological and biochemical actions of opiates on the central nervous system. The ability of the synaptosomes to accumulate excess calcium during narcotic exposure represents a singular major example of cellular adaptation at the level of the membrane. These findings together with the possibility that CDR and calcium may mediate a number of processes involving neurotransmitter activity provide many avenues for the future study of opiates and other central nervous system depressants.

Animals↗
PubMed1979

Na,K-ATPase in excitation-contraction coupling of vascular smooth muscle from cattle.

Lowering the extracellular K+ content from 6 to 0.6 mM causes a rise, and elevation from 6 to 8.5 mM a fall of 45Ca++ efflux from the vascular smooth muscle cells of the arteria carotis communis of cattle. In contrast, a level of 17 mM K+ has no influence. Removal of extracellular calcium does not block these effects. 10(-4) M ouabain also induces a rise in Ca++ efflux, additional potassium reduction then being without effect; 10(-9) M ouabain is of no influence. The 45Ca++ efflux kinetics correlates with the activity of the isolated Na,K-ATPase. Tonus increases of the vascular strips by 10(-4) M ouabain and potassium deficiency cannot be blocked by 4 mM lanthanum or removal of extracellular calcium. Unlike sodium, potassium stimulates the active Ca++ binding and the activity of the Ca-ATPase of the microsomal fraction. The ative Ca++ binding of the mitochondria is stimulated by both ions. It is postulated that the activity of the plasma membrane Na,K-pump is able to regulate the tonus of big arteries through alteration of Ca++ storage processes.

Animals↗
PubMed1979

[Biochemical mechanisms for the effect of alcohol on the brain].

This paper reviews and discusses basic knowledge of biochemical mechanisms of action of ethanol upon the central nervous system, the emphasis being on effects upon cerebral membrane structures and processes as well as mechanisms of chemical synaptic transmission. Results of detailed studies into material and steric changes in membranes, ion-dependent adenosine triphosphatases, variations in ion balance, effects upon cyclic nucleotides, influences on special transmitter systems, and mechanisms of formation of morphine-analogous condensation products are presented. In addition, open questions are derived and formulated in problem complexes.

Acetaldehyde↗