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Results for “Calcium-Transporting ATPases”

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At least 1,387 records · Page 77Linked to original sources
PubMed1990

[Changes in RBC Ca2(+)-ATPase activity and red-cell calcium concentration during dialysis in patients with uremia].

The changes of RBC Ca2(+)-ATPase activity and red cell calcium concentration during dialysis were observed in 19 patients with uremia. The results showed that in 12 patients treated by haemodialysis the RBC Ca2(+)-ATPase activity was lowered an average of 35 U than that in the controls (P less than 0.001); whereas red cell calcium was increased about 5 times (P less than 0.001). After a four-hour haemodialysis, the Ca2(+)-ATPase activity increased 20 U (P less than 0.05); and red cell calcium decreased 45 mumol/L cells (P less than 0.05). In 7 patients treated by CAPD the RBC Ca2(+)-ATPase activity was reduced to 60% of that in the controls (P less than 0.001); and red cell calcium was about 5 times as high as that in the controls (P less than 0.001). After one month of CAPD, the Ca2(+)-ATPase activity increased only 10 U (P greater than 0.05); but red cell calcium decreased 66 mumol/L cells (P less than 0.01).

Adult↗
PubMed1990

Inhibition of the calcium pump by human parathyroid hormone-(1-34) and human calcitonin in liver plasma membranes.

The effect of human parathyroid hormone-(1-34) (hPTH) and human calcitonin (hCT) on the activity of the Ca2(+)-extrusion pump in liver plasma membranes was studied. Both hormones were found to be potent inhibitors of Ca2+ transport and the related high-affinity (Ca2(+)-Mg2+)-ATPase activity, causing maximal inhibition of 25-30% at concentrations of 100 nM. Half-maximal inhibition was observed with 20 nM-hPTH and with 0.5 nM-hCT. By comparison, salmon calcitonin and intact bovine parathyroid hormone-(1-84) were inhibitory only at 10 microM. The effects of hCT and hPTH on the Ca2+ pump activity were not mimicked by cyclic AMP. Also, 10 microM of either hPTH-(1-34) or hCT did not alter the 45Ca2+ influx rate into isolated hepatocytes. We conclude that inhibition of Ca2+ efflux, rather than the stimulation of Ca2+ influx, may play a functional role in the control of hepatic calcium homeostasis by hPTH-(1-34) and hCT.

Biological Transport, Active↗
PubMed1990

Transporting of sodium and calcium cation in erythrocyte in patients with essential hypertension.

The sodium and calcium cation transport in erythrocyte and their influencing factors were studied in essential hypertensive (EH) patients. The result showed that plasma sodium pump inhibitor, endogenous digitalis-like compound (EDLC), rose in some patients and sodium pump was depressed in the others, but there were no parallel links between EDLC and sodium pump. The patients with normal sodium pump have mainly shown a decrease of their maximal CA++ pump activity and calmodulin (CaM) content in erythrocyte. It indicated that there might be different types of ion transporting defect in EH, and the abnormalities of these cation transports might be an important pathogenesis in EH.

Adult↗
PubMedDate not supplied

Effect of triiodo-L-thyronine treatment on Ca2+ sequestration in rat liver microsomes.

T3 administration to rats exerts quite different effects on enzyme activities associated to liver microsomal membranes such as G-6-Pase, Mg ATPase and Ca2(+)-dependent ATPase: in fact G-6-Pase activity is significantly enhanced, Mg ATPase is not affected whereas Ca2(+)-dependent ATPase is drastically inhibited. The T3 induced decrease in Ca2(+)-dependent ATPase activity is associated with a net reduction (to about 50% with respect to controls) of the Ca2+ sequestration in liver microsomal vesicles. The enhanced level of inorganic phosphate in the endoplasmic reticulum due to the stimulation of G-6-Pase activity does not significantly affect the uptake of calcium in microsomal vesicles. The decreased Ca2(+)-dependent ATPase activity is associated to an enhanced level of the enzyme in the phosphorylated form (E-P). This suggests that in liver preparations from T3 treated rats the turnover of ATP and cleavage of E-P is reduced, thus resulting in the accumulation of the phosphorylated intermediate. The accumulation of E-P is in agreement with the inhibition of the calcium sequestration since the active transport of this cation in microsomal membranes requires the hydrolysis of the E-P complex.

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↗
PubMed1979

[Studies of the presence of enzymes in various tissues of swine. 5. Studies of the activity and properties of adenosine triphosphatases in the pancreas].

Studies were conducted into the activities of magnesium-ATPase, sodium-potassium-ATPase, and HCO3-ATPase in homogenates of pancreas of 19 foetuses, with body weights between 340 g and 1,642 g, two piglets, with body weights of 9 kg and 10 kg, and four adult pigs. While general enzyme activity was low during foetal development, highest activies usually were recordable from HCO3-ATPase. High activities were recorded from both the piglets and adult pigs. The highest data, again, were recordable from HCO3-ATPase which is essential to the secretion of HCO3 ions. Maximum activity of magnesium-ATPase was based on an ATP-magnesium ratio of 1:1. HCO3-ATPase was best activated by 25 mM NaHCO3 and exhibited high stability to temperature. The activities of magnesium-ATPase and of HCO3-ATPase were inhibited by 10 mM of Rhodanid. Calcium-ATPase reached its maximum activity in response to 5 mM calcium concentration.

Adenosine Triphosphatases↗
PubMed1979

[Role of calcium in realization of nervous control during RNA synthesis in skeletal muscles].

The effects of Ca2+ on the RNA polymerase activity of the nuclei isolated from normal and denervated gastrocnemius muscles of the rabbit were studied. It was shown that 18 hrs after denervation the RNA synthesis in vitro, Ca2+ content and the Ca, Mg-ATPase activity of the nuclei are decreased. After addition of exogenous Ca2+ the incorporation of labelled UTP into the nuclei is stimulated in the denervated muscle and is inhibited in the control. Electrostimulation of the denervated muscle at the peripheral part of the sciatic nerve for 3 hrs increases both the RNA synthesis in the nuclei and the Ca2+ content, as well as the Ca, Mg-ATPase activity. Exogenous Ca2+ has an inhibitory effect on the nuclei of the stimulated muscle. The correlation established is indicative of participation of Ca2+ in the transmission of excitation in skeletal muscle sarcolemma to the processes occurring in nuclear structures.

Animals↗
PubMedDate not supplied

[The effect of catecholamines on the Ca2(+)-adenosinetriphosphatase of the sarcoplasmic reticulum in the skeletal muscles in chicken ontogeny].

It has been shown that the activity of Ca(2+)-ATPase increases during development. Epinephrine in vivo increases the activity of Ca(2+)-ATPase in chick skeletal muscles. The effect of hormone is lacking at embryonic stages of development and appears only before hatching. In the presence of exogenous protein kinase, cAMP also increases the activity of the enzyme, this effect being observed also in embryonic muscles. Lack of effect of epinephrine on Ca(2+)-ATPase in embryonic muscles is associated with non-reactivity of their adenylate cyclase to catecholamines. Ca(2+)-ATPase itself already at embryonic period is ready to react to cAMP. It is concluded that Ca(2+)-ATPase of sarcoplasmic reticulum is one of the sites of action of catecholamines on calcium metabolism in muscle cell and that this action is realized via the system adenylate cyclase-cAMP-protein kinase.

Animals↗
PubMed1990

Identification and characterization of high-affinity Ca2(+)-ATPase associated with axonal plasma membranes of dog mesenteric nerves.

The microsomal fraction isolated from dog mesenteric nerve fibres was found to contain ATPase activity stimulated by micromolar concentrations of Ca ions. Such a high-affinity Ca2(+)-ATPase (hereafter referred to as HA Ca-ATPase) followed a Michaelis-Menten kinetics with Km for Ca ions of 0.4 microM and Vmax = 12.5 +/- 2.4 mumol Pi.mg-1h-1. The examination of the subcellular origin of HA Ca-ATPase revealed that this enzyme is associated with axonal plasma membranes as documented by its co-purification with several plasma membrane marker enzymes and with tetrodotoxin-sensitive 3H-saxitoxin binding. The addition of exogenous magnesium ions (Mg) resulted in a non-competitive inhibition of HA Ca-ATPase with Ki = 0.5 mM. The reaction velocity of HA Ca-ATPase was also inhibited by other divalent ions with the order of potency Mg greater than Mn greater than Zn greater than or equal to Co greater than Ni. In contrast to low affinity (high Km) Mg- and Ca-ATPase, the HA Ca-ATPase was insensitive to the inhibition by sodium azide (10 mM) and sodium fluoride (10 mM). Similarly, the specific activity of HA Ca-ATPase was unaffected by vanadate (100 microM) and N-ethylmaleinimide (100 microM). It is concluded that axonal plasma membranes of dog mesenteric nerves contain HA Ca-ATPase which seems to be unrelated to calcium-transporting Mg-dependent, Ca-stimulated ATPase.

Animals↗