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Results for “Calcium-Transporting ATPases”

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PubMed1985

Favism: disordered erythrocyte calcium homeostasis.

The biochemical events that take place during acute hemolysis of G6PD-deficient subjects in favism are far from being elucidated. Evidence is here reported for a constantly and heavily disordered calcium homeostasis in the erythrocytes from seven favic patients. The abnormality, ie, a significantly impaired calcium ATPase activity and a parallel marked increase of intracellular calcium levels, was characteristic of the acute hemolytic crisis although unrelated to the attendant reticulocytosis. Concomitantly, a remarkable decrease of intracellular potassium was also observed. The mean +/- SD Ca2+-ATPase activity in the favic patients was 20.8 +/- 7.8 mumol Pi/g Hb/h compared with 37.2 +/- 8.5 in the matched controls represented by 12 healthy G6PD-deficient subjects (P less than .001). The mean +/- SD intraerythrocytic calcium content was 288 +/- 158 mumol/L of erythrocytes in the favic patients as compared with 22.0 +/- 8.2 in the G6PD-deficient controls (P less than .001). The intraerythrocytic potassium content was 76.6 +/- 19.3 mmol/L of erythrocytes in the favic patients and 106.6 +/- 8.2 in the G6PD-deficient controls (P less than .001). In vitro incubation of normal and G6PD-deficient erythrocytes with divicine, a pyrimidine aglycone present in fava beans and strongly implicated in the pathogenesis of favism, reproduces most of these events, including drop of calcium ATPase, increased intracellular calcium, and leakage of erythrocyte potassium.

Acute Disease↗
PubMed1985

Inactivation of a Ca2+-induced Ca2+ release channel from skeletal muscle sarcoplasmic reticulum during active Ca2+ transport.

ATP-dependent Ca2+ uptake by subfractions of skeletal muscle sarcoplasmic reticulum (SR) was studied with the Ca2+ indicator dye, antipyrylazo III. Ca2+ uptake by heavy SR showed two phases, a slow uptake phase and a fast uptake phase. By contrast, Ca2+ uptake by light SR exhibited a monophasic time course. In both fractions a steady state of Ca2+ uptake was observed when the concentration of free Ca2+ outside the vesicles was reduced to less than 0.1 microM. In the steady state, the addition of 5 microM Ca2+ to the external medium triggered rapid Ca2+ release from heavy SR but not from light SR, indicating that the heavy fraction contains a Ca2+-induced Ca2+ release channel. During Ca2+ uptake, heavy SR showed a constant Ca2+-dependent ATPase activity (1 mumol/mg protein X min) which was about 150 times higher than the rate of Ca2+ uptake in the slow uptake phase. Ruthenium red, an inhibitor of Ca2+-induced Ca2+ release, enhanced the rate of Ca2+ uptake during the slow phase without affecting Ca2+-dependent ATPase activity. Adenine nucleotides, activators of Ca2+ release, reduced the Ca2+ uptake rate. These results suggest that the rate of Ca2+ accumulation by heavy SR is not proportional to ATPase activity during the slow uptake phase due to the activation of the channel for Ca2+-induced Ca2+ release. In addition, they suggest that the release channel is inactivated during the fast Ca2+ uptake phase.

Adenine Nucleotides↗
PubMed1985

[How the activity of membrane enzymes is regulated].

The pattern of dependence of catalytic function for a number of key membrane bound enzymes on the state and properties of their lipid environment is analysed in the review presented. Using hexokinase, cytochrome c-oxidase, transport ATPases and other membrane bound oligomeric systems it has been shown that phospholipid bilayer regulates the interaction of protein components of these ensembles in the bilayer. This feature of membrane structures regulates the substrate accessibility and affinity to the corresponding active centres, the formation and a life-time of the oligomeric associates (that is especially important for membrane channels), their stability and so on. As the microviscosity of membrane bilayer is strongly modified not only in the course of pathologic but also in the process of adaptive alterations as well as depending on the day time, season and as a result of action of biologically active substance on membrane, the regulation of the functional activity of membrane proteins by this factor is an effective mode for metabolic control.

Adenosine Triphosphatases↗
PubMed1986

Regulatory systems for the cytoplasmic calcium concentration in smooth muscle.

Changes of the intracellular Ca concentrations play a predominant though not unique role in the regulation of the force development of smooth muscle cells. Contraction is initiated by an influx of Ca2+ through the cell membrane or by the release of Ca2+ from intracellular storage sites. Ca influx occurs via voltage operated channels and receptor operated channels. The intracellular Ca release induced by agonists probably originates from the endoplasmic reticulum. The removal of Ca2+ from the cytoplasm occurs by extrusion across the plasmalemma and by reaccumulation in the endoplasmic reticulum. These active Ca2+ transport systems are catalysed by (Ca2+ +Mg2+) ATPases. Na-Ca exchange across the sarcolemma of smooth muscle is probably of minor importance since the (Ca2+ +Mg2+)ATPase activity of plasma membranes is higher than the activity of the Na+K+ ATPase, the ultimate energy source for Na+-dependent Ca2+ extrusion. The (Ca2+ +Mg2+)ATPase of the plasmalemma has a Mr of 130.000 and it is stimulated by calmodulin. It resembles the Ca2+ transport ATPase of erythrocyte membranes, including immunological cross-reactivity. The Ca2+ transport enzyme of the endoplasmic reticulum has a Mr of 100.000, is insensitive to calmodulin and resembles the Ca2+ pump of sarcoplasmic reticulum of skeletal muscle. However, antibodies against the Ca2+ pump of skeletal muscle do not cross react with the enzyme of smooth muscle. Subcellular fractionation of pig stomach smooth muscle indicates that in this tissue the large fraction of the (Ca2+ +Mg2+)ATPase activity is present in the plasma membrane while less activity is found in the endoplasmic reticulum.

Animals↗
PubMedDate not supplied

[Electric activity of fragmented sarcoplasmic reticulum associated with the organic phase-water interface].

Electric activity of fragmented sarcoplasmic reticulum (FSR) in the model system organic phase-water was investigated by dynamic capacity method. FSR induced Mg-ATP, Ca2+-dependent change of border volt-potential only when phospholipids were present in the organic phase. It is suggested that FSR electric activity at the interface lipid-water is conditioned by functioning Ca2+, Mg2+-ATPase.

Animals↗
PubMed1986

[The Ca pump and Ca ATPase in the erythrocytes of patients with hypertension: disorders detected in cytoskeletal membranes and in solubilized Ca ATPase].

A study of Ca-ATPase and Ca-pump activity of the erythrocyte membrane's inverted vesicles with different cytoskeletal protein status demonstrated that Ca-pump activity remained unchanged, and Ca-ATPase activity was increased by 20-40%, as compared to erythrocytes from the normotensive controls, in hypertensive patients in the absence of exogenous calmodulin. These differences are assumed to be due to disorders of erythrocyte membrane structure in primary hypertension resulting in less efficient Ca-pump operation in the inverted vesicles. In all types of membranes obtained from hypertensive patients' erythrocytes in conditions of iso-osmotic hemolysis, calmodulin-induced increment of peak Ca-ATPase and Ca-pump activity was 2 or 3 times as low as that of normotensive controls. These differences remained in evidence after the solubilization of membrane proteins with triton X-100. No differences in calmodulin influence on Ca-ATPase affinity to Ca2+ could be found. The membranes obtained in iso-osmotic conditions demonstrated no calmodulin effect on Ca-ATPase activity which is attributed to partial proteolysis of the enzyme's molecule.

Adult↗
PubMed1986

[New knowledge in the biochemistry and function of ion channels].

Newer realizations concerning the structure and the function of various forms of ion canals are described. The Na- and K-ion channels occur in a particularly great number in certain membrane regions of nerve cells and muscle fibres and cause the formation and distribution of bioelectric signals. In the K-ion channels various types with different function appear in single cell forms. The Ca-ion channels play a role in the regulation of the release of neurotransmitters and of peptide hormones from granules as well as in the contraction of the heart and skeletal musculature. The ion channels are constructed by various proteins, in certain sections they specifically bind certain toxins and medicaments. The acetyl choline receptor consists of 5 subunits and acts as ion channels for Na- and K-ions; this is opened for a short time after binding of 2 molecules of acetyl choline to the alpha-subunits. The properties of the channel proteins are influenced by phosphorylation.

Animals↗
PubMed1986

Binding of Ca2+ entry blockers to cardiac sarcolemmal membrane vesicles. Characterization of diltiazem-binding sites and their interaction with dihydropyridine and aralkylamine receptors.

Stereospecific saturable and reversible binding of d-cis-diltiazem has been demonstrated in cardiac sarcolemmal membrane vesicles. Analysis of binding by either equilibrium or kinetic techniques indicates the presence of a single class of benzothiazepine receptors which bind diltiazem with a KD of 80 nM at 25 degrees C. Benzothiazepine receptors copurify with other sarcolemmal marker activities and exist in a complex with distinct receptors for dihydropyridine and aralkylamine Ca2+ entry blockers in a 1:1:1 stoichiometry. Ligand binding to one receptor of this complex influences binding reactions at the other two sites in a manner that depends on ambient temperature. Binding of either dihydropyridine agonists or antagonists causes partial inhibition of diltiazem binding at 25 degrees C (Bmax effect), while most dihydropyridine antagonists stimulate and agonists inhibit diltiazem binding at 37 degrees C (both are KD effects). This temperature-dependent change in receptor coupling was confirmed by Scatchard analyses and study of diltiazem dissociation kinetics. Verapamil, interacting at the aralkylamine receptor, inhibits diltiazem binding equivalently at 25 and 37 degrees C (KD effects). In addition, both classes of dihydropyridines inhibit verapamil binding in a temperature-independent fashion, as does diltiazem (all are KD effects). Allosteric coupling between benzothiazepine and dihydropyridine receptors is manifested in cardiac muscle since the negative inotropic potency of diltiazem is increased by nitrendipine and decreased by 4-(O-trifluromethy(phenyl)-2,6-dimethyl-5-nitro-1,4-dihydropyridin e-3- carboxylic acid, methyl ester. These results suggest a model in which the Ca2+ entry blocker receptor complex undergoes a change between 25 and 37 degrees C so that at the latter temperature all sites are directly coupled. Allosteric coupling may have important consequences in vivo since it can be detected in functional assays of Ca2+ channel activity.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Calcium channel modulators and calcium channels.

In recent years calcium has become recognized as an important 'second messenger', in that an increase in free intracellular calcium ion concentration is involved in many aspects of cellular activation. In excitable cells such as smooth muscle or cardiac tissue an influx of extracellular calcium ions through voltage sensitive calcium channels plays a major role in increasing the cytoplasmic free calcium concentration. It is now known that the activity of these calcium channels may be inhibited or stimulated by a range of ions, toxins and drugs. This article outlines the biochemistry and pharmacology of these 'calcium modulators', and discusses their present and future role as both biological tools, and as potent and selective drugs.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Role of water in processes of energy transduction: Ca2+-transport ATPase and inorganic pyrophosphatase.

After the proposal of the chemiosmotic theory by Mitchell (1966, 1979) it has been recognized that different membrane-bound enzymes are able to use the energy derived from ionic gradients for the synthesis of ATP. These include the F1-ATPases of mitochondria and chloroplasts, the Ca2+-dependent ATPase of sarcoplasmic reticulum and the (Na+,K+)-ATPase of plasma membrane. In these systems the process of energy transduction is fully reversible. The enzyme can use the energy derived from the hydrolysis of ATP to build up a concentration gradient of ions across the membrane and, in the reverse process, use the energy derived from the gradient to synthesize ATP. Another interesting system in which these forms of energy are interconverted is found in photosynthetic bacteria. In chromatophores of Rhodospirillum rubrum there is a membrane-bound pyrophosphatase that, like the transport ATPases, catalyses the synthesis of pyrophosphate from Pi when a light-dependent proton gradient is formed across the chromatophore membrane. Like F1-ATPase, this enzyme is also able to generate an electrochemical potential gradient of protons at the expense of pyrophosphate hydrolysis. The mechanism by which the energy derived from a gradient is used by membrane-bound enzymes to catalyse the synthesis of high-energy phosphate compounds is still far from understood. Among the different enzymes studied, Ca2+-dependent ATPase is probably the system in which most is known about the mechanism of energy transduction. We now know of experimental conditions which allow us to move the different intermediary steps of the catalytic cycle of the enzyme in the direction of ATP synthesis. Thus, ATP synthesis can be attained after a single catalytic cycle in the absence of a transmembrane Ca2+ gradient. The net synthesis of ATP can be promoted by a variety of perturbations, including Ca2+, pH and water activity. These experiments indicate that during the catalytic cycle different forms of energy are interconverted by the Ca2+-dependent ATPase. The ultimate step of the cycle seems to be a change of water activity within the catalytic site of the ATPase. A common feature of all membrane-bound enzymes mentioned above is that during the catalytic cycle there are steps in which the hydrolysis of a phosphate compound (ATP, pyrophosphate or an acyl phosphate residue) is accompanied by only a small change in free energy. In conditions similar to those found in the cytosol, the hydrolysis of these phosphate compounds is accompanied by a much larger change in free energy.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1986

Effect of compound 48/80 and ruthenium red on the Ca2+-ATPase of sarcoplasmic reticulum.

The effects of the condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde (compound 48/80) and ruthenium red on the partial reactions of the catalytic cycle of the sarcoplasmic reticulum Ca2+-ATPase of skeletal muscle were studied. The ATPase activity and both Ca2+ and Sr2+ uptake were inhibited by compound 48/80 when oxalate was used as a precipitating agent. The degree of inhibition decreased when oxalate was replaced by orthophosphate as the precipitating anion. Both the fast Ca2+ efflux and the synthesis of ATP observed during reversal of the Ca2+ pump were inhibited by compound 48/80. Inhibition of the reversal of the Ca2+ pump was caused by a competition between compound 48/80 and orthophosphate for the phosphorylation site of the enzyme. The fast Ca2+ release promoted by arsenate was impaired by compound 48/80. Ruthenium red competes with Ca2+ for the high affinity binding site of the Ca2+-ATPase, but did not interfere with the binding of Ca2+ to the low affinity binding site of the enzyme. In presence of Ca2+ concentrations higher than 5 microM, ruthenium red in concentrations up to 200 microM had no effect on both ATPase activity and Ca2+ uptake. However, the fast Ca2+ efflux promoted by arsenate and the fast Ca2+ efflux coupled with the synthesis of ATP observed during the reversal of the Ca2+ pump were inhibited by ruthenium red, half-maximal inhibition being attained in presence of 10-20 microM ruthenium red. In contrast to the effect of compound 48/80, ruthenium red did not inhibit the phosphorylation of the enzyme by orthophosphate. The ATP in equilibrium with Pi exchange catalyzed by the Ca2+-ATPase in the absence of transmembrane Ca2+ gradient was also inhibited by ruthenium red.

Adenosine Triphosphate↗
PubMed1987

Rapid calcium release from cardiac sarcoplasmic reticulum vesicles is dependent on Ca2+ and is modulated by Mg2+, adenine nucleotide, and calmodulin.

A subpopulation of canine cardiac sarcoplasmic reticulum vesicles has been found to contain a "Ca2+ release channel" which mediates the release of intravesicular Ca2+ stores with rates sufficiently rapid to contribute to excitation-contraction coupling in cardiac muscle. 45Ca2+ release behavior of passively and actively loaded vesicles was determined by Millipore filtration and with the use of a rapid quench apparatus using the two Ca2+ channel inhibitors, Mg2+ and ruthenium red. At pH 7.0 and 5-20 microM external Ca2+, cardiac vesicles released half of their 45Ca2+ stores within 20 ms. Ca2+-induced Ca2+ release was inhibited by raising and lowering external Ca2+ concentration, by the addition of Mg2+, and by decreasing the pH. Calmodulin reduced the Ca2+-induced Ca2+ release rate 3-6-fold in a reaction that did not appear to involve a calmodulin-dependent protein kinase. Under various experimental conditions, ATP or the nonhydrolyzable ATP analog, adenosine 5'-(beta, gamma-methylene)triphosphate (AMP-PCP), and caffeine stimulated 45Ca2+ release 2-500-fold. Maximal release rates (t1/2 = 10 ms) were observed in media containing 10 microM Ca2+ and 5 mM AMP-PCP or 10 mM caffeine. An increased external Ca2+ concentration (greater than or equal to 1 mM) was required to optimize the 45Ca2+ efflux rate in the presence of 8 mM Mg2+ and 5 mM AMP-PCP. These results suggest that cardiac sarcoplasmic reticulum contains a ligand-gated Ca2+ channel which is activated by Ca2+, adenine nucleotide, and caffeine, and inhibited by Mg2+, H+, and calmodulin.

Adenine Nucleotides↗
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↗