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Results for “Calcium-Transporting ATPases”

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PubMed1979

Diamide inhibited (Ca++ + Mg++) and (Mg++) dependent ATPase in erythrocyte membranes: activity at different temperatures.

After inhibition of the monovalent cation dependent ATPase, a (Ca++ + Mg++) and a (Mg++) dependent ATPase activity can be detected. The inhibition due to diamide on the (Mg++) ATPase, assayed in the 12.5 degrees C - 30 degrees C temperature range, is almost complete. On the contrary the diamide induced inhibition of (Ca++ + Mg++) ATPase, in the same temperature range, is not complete and the residual activity increases with temperature. The reported data indicate that the ATPase activity induced by calcium is much less diamide-sensitive and -SH-dependent than that elicited by Mg++ alone.

Adenosine Triphosphatases↗
PubMed1979

[Effect of thermostable protein kinase modulator on Mg, Ca-ATPase from nervous tissue].

Isoelectric focusing of a purified fraction of thermostable modulator of 3',5'-AMP-dependent protein kinase revealed five individual proteins, the main protein having an isoelectric point of 4,05. The molecular weight of this protein as determined by gel filtration is 8000--9000. The protein with a pI of 4,05 binds Ca2+ and in contrast to the original modulator inhibits the endogenous 3',5'-AMP-dependent phosphorylation of synaptic membranes. An addition of the original modulator fraction to the microsomes isolated from nervous tissue increases the Mg, Ca-ATPase activity and absorption of 45Ca. Neither the protein with a pI of 4,05 nor other individual proteins affect the activity of transport ATPase. The activating effect is partly restored after mixing of all the five subfractions. It is assumed that these proteins are aggregated by Ca2+ and change the activity of ATPase or membrane 3',5'-AMP-dependent protein kinase depending on the concentration of calcium ions.

Animals↗
PubMedDate not supplied

[Participation of Mg2+ and Ca2+ ions and the corresponding ATPases in the mechanism of the presynaptic action of amisyl and arecoline].

Amisyle and arecoline were found to be antagonistic drugs in the effect on content of Mg2+ and Ca2+ and on activity of corresponding ATPases in synaptosomes isolated from rat brain. Amisyle promoted the incorporation of 45Ca into synaptosomes but arecoline inhibited the reaction. The appear to be responsible for liberation and maintaining of neurotransmitters in presinaptic stores.

Adenosine Triphosphatases↗
PubMed1979

Subcellular calcium localization and AT0-dependent Ca2+-uptake by smooth endoplasmic reticulum in an invertebrate photoreceptor cell. An ultrastrucutral, cytochemical and X-ray microanalytical study.

In Hirudo medicinalis an extensive and highly elaborate three dimensional network of smooth endoplasmic reticulum cisternae is found in very close structural relationship to the receptive (microvillar) membrane, as reported for many other invertebrates. A variant of the potassium pyroantimonate technique showed that these submicrovillar endoplasmic reticulum cisternae (SMC) and mitochondria are major intracellular calcium stores. Furthermore, using saponine-skinned photoreceptors for an in situ accumulation experiment, calcium oxalate precipitates in SMC demonstrate that this organelle is able to accumulate Ca2+ from a concentration of 2 x 10(-5) M, when ATP, Mg2+, and oxalate ions are present in the accumulation medium. This result provides direct evidence for the hypothesis that SMC may play a particularly important role in the regulation of intracellular ionized calcium in invertebrate photoreceptor cells. Morphological evidence supports this view.

Animals↗
PubMed1975

Histoenzymatic changes in the dog kidney in an experimentally induced crushing injury of the thorax.

The experiments were carried out on dogs. Experimental animals were subjected to the trauma of the thorax during operation. The localization and activity of succinic dehydrogenase, NADH2-tetrazole reductase, adenosine triphosphatase, alkaline and acid phosphates in the kidneys were examined. An increase of the activity of all the investigated enzymes takes place under the influence of the stress. On the basis of the investigations it can be supposed that the processes of oxygen phosphorylation and active transport are intensified. An increase of the activity of acid phosphates gives evidence of the intensity of phagocytosis and pinocytosis processes in the kidney.

Acid Phosphatase↗
PubMed1979

Calcium handling by cardiac sarcoplasmic reticulum.

Over the past ten years knowledge of the biochemistry of cardiac sarcoplasmic reticulum vesicles has been considerably extended. In almost all respects the Ca2+ pump of cardiac sarcoplasmic reticulum shows striking similarities to the Ca2+ pump of skeletal muscle sarcoplasmic reticulum. On the other hand, Ca2+ release mechanisms seem to be more complex in cardiac than in skeletal sarcoplasmic reticulum. Future research undoubtedly will involve characterizing the function of the many additional proteins present in cardiac sarcoplasmic reticulum, and determining possible roles for these proteins in regulating Ca2+ uptake and Ca2+ release by these membranes.

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↗