Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Ca2+ transport adenosine triphosphatase of sarcoplasmic reticulum was reconstituted in unilamellar liposomes prepared by reverse-phase evaporation. The size of the resulting proteoliposomes was similar to that of native sarcoplasmic reticulum vesicles, but their protein content was much lower, with a protein/lipid ratio (wt/wt) of 1:40-160, as compared with 1:1 in the native membrane. The proteoliposomes sustained adenosine triphosphate-dependent Ca2+ uptake at rates proportional to the protein content (1-2 mumol Ca2+/mg protein/min), reaching asymptotic levels corresponding to a lumenal calcium concentration of 10-20 mM. The low permeability of the proteoliposomes permitted direct demonstration of Ca2+/H+ countertransport and electrogenicity by parallel measurements in the same experimental system. Countertransport of one H+ per one Ca2+ was demonstrated, and inhibition of the Ca2+ pump by lumenal alkalinization was relieved by the H+ ionophore carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone. Consistent with the countertransport stoichiometry, net positive charge displacement was produced by Ca2+ transport, as revealed by a rapid oxonol VI absorption rise. The initial rise and the following steady-state level of oxonol absorption were highest when SO4(2-) was the prevalent anion and lowest in the presence of the lipophilic anion SCN-. The influence of anions was attributed to potential driven counterion compensation. The absorption rise was rapidly collapsed by addition of valinomycin in the presence of K+. Experimentation with Ca2+ and H+ ionophores was consistent with a primary role of Ca2+ and H+ in net charge displacement. The estimated value of the steady-state electrical potential observed under optimal conditions was approximately 50 mV and was accounted for by the estimated charge transfer associated with Ca2+ and H+ countertransport under the same conditions.
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PMID:H+ countertransport and electrogenicity of the sarcoplasmic reticulum Ca2+ pump in reconstituted proteoliposomes. 838 68

The mechanism of purine nucleobase transport in procyclic cells of the protozoan parasite Trypanosoma brucei brucei was investigated. Hypoxanthine uptake at 22 degrees C was rapid and saturable, exhibiting an apparent Km of 9.3 +/- 2.0 microM and a Vmax of 4.5 +/- 0.8 pmol x (10(7) cells)(-1) x s(-1). All the natural purine nucleobases tested (Ki 1.8-7.2 microM), as well as the purine analogues oxypurinol and allopurinol, inhibited hypoxanthine influx in a manner consistent with the presence of a single high-affinity carrier. Nucleosides and pyrimidine nucleobases had little or no effect on hypoxanthine influx. The uptake process was independent of extracellular sodium, but inhibited by ionophores inducing cytosolic acidification (carbonyl cyanide chlorophenylhydrazone, nigericin, valinomycin) or membrane depolarisation (gramicidin) as well as by the adenosine triphosphatase inhibitors N-ethylmaleimide and N,N'-dicyclohexylcarbodiimide. Using the fluorescent dyes bisoxonol and 2',7'-bis-(carboxyethyl)-5,6-carboxy-fluorescein to determine membrane potential and intracellular pH (pHi), the rate of hypoxanthine uptake was shown to be directly proportional to the protonmotive force. Similarly, under alkaline extracellular conditions hypoxanthine uptake was reversibly inhibited alongside a reduction in protonmotive force. In addition, hypoxanthine accelerated the rate of pH, recovery to pH 7 after base-loading with NH4Cl, indicative of a proton influx concurrent with hypoxanthine transport. Finally, after pretreatment of cells with N-ethylmaleimide, hypoxanthine induced a slow membrane depolarisation, demonstrating that hypoxanthine transport is electrogenic. These data show that hypoxanthine uptake in T. b. brucei procyclic cells is dependent on the protonmotive force, and are consistent with a nucleobase/H+-symporter model for this transporter.
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PMID:Hypoxanthine uptake through a purine-selective nucleobase transporter in Trypanosoma brucei brucei procyclic cells is driven by protonmotive force. 928 36

To study the mechanism of LH-releasing hormone (LHRH) pulse generation, the olfactory pit/placode and the migratory pathway of LHRH neurons from monkey embryos at embryonic age 35-37 were dissected out, under the microscope, and cultured on plastic coverslips coated with collagen in a defined medium for 2-5 weeks. First, we examined whether cultured neurons release the decapeptide into media. It was found that LHRH cells release LHRH in a pulsatile manner at approximately 50-min intervals. Further, LHRH release was stimulated by depolarization with high K+ and the Na+ channel opener, veratridine. However, whereas the Na+ channel blocker, tetrodotoxin suppressed the effects of veratridine, tetrodotoxin did not alter the effects of high K+. Subsequently, the role of extracellular and intracellular Ca2+ in LHRH release was examined. The results are summarized as follows: 1) exposing the cells to a low Ca2+ (20 nM) buffer solution suppressed LHRH release, whereas exposure to a normal Ca2+ solution (1.25 mM) maintained pulsatile LHRH release; 2) LHRH release from cultured LHRH cells was stimulated by the voltage-sensitive L-type Ca2+ channel agonist, Bay K 8644 (10 microM), whereas it was suppressed by the L-type Ca2+ channel blocker, nifedipine (1 microM), but not by the N-type channel blocker, omega-conotoxin GVIA (1 microM); 3) the intracellular Ca2+ stimulant, ryanodine (1 microM), stimulated LHRH release, whereas the intracellular Ca2+ transporting adenosine triphosphatase antagonist, thapsigargin (1 and 10 microM), did not yield consistent results; and 4) carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (1 microM), a mitochondrial Ca2+ mobilizer, stimulated LHRH release, whereas ruthenium red, a mitochondrial Ca2+ uptake inhibitor, did not induce consistent results. These results indicate that: 1) the presence of extracellular Ca2+ is essential for LHRH neurosecretion; 2) Ca2+ enters the cell via L-type channels but not N-type channels; and 3) mobilization of intracellular Ca2+ from inositol 1,4,5-triphosphate-sensitive stores, as well as mitochondrial stores, seem to contribute to LHRH release in these cells.
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PMID:Pulsatile release of luteinizing hormone-releasing hormone (LHRH) in cultured LHRH neurons derived from the embryonic olfactory placode of the rhesus monkey. 1006 21

A survey has been made of the properties of corn mitochondria in swelling and contraction. The mitochondria swell spontaneously in KCl but not in sucrose. Aged mitochondria will swell rapidly in sucrose if treated with citrate or EDTA. Swelling does not impair oxidative phosphorylation if bovine serum albumin is present.Contraction can be maintained or initiated with ATP + Mg or an oxidizable substrate, contraction being more rapid with the substrate. Magnesium is not required for substrate powered contraction. Contraction powered by ATP is accompanied by the release of phosphate. Oligomycin inhibits both ATP-powered contraction and the release of phosphate. However, it does not affect substrate-powered contraction. Substrate powered contraction is inhibited by electron-transport inhibitors. The uncoupler, carbonyl cyanide m-chlorophenyl hydrazone, accelerates swelling and inhibits both ATP-and substrate-powered contraction. However, the concentrations required are well in excess of those required to produce uncoupling and to accelerate adenosine triphosphatase; the concentrations required inhibit respiration in a phosphorylating medium.Phosphate is a very effective inhibitor of succinate-powered contraction. Neither oligomycin nor Mg affects the phosphate inhibition. Phosphate is less inhibitory with the ATP-powered contraction.The results are discussed in terms of a hypothesis that contraction is associated with a nonphosphorylated high energy intermediate of oxidative phosphorylation.
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PMID:Swelling and contraction of corn mitochondria. 1665 48

In primary sensory afferent neurons, Ca2+ plays a vital role in the regulation of cellular processes including receptor and synaptic plasticity, neurotransmitter and trophic factor release and gene regulation. Current understanding of the mechanisms underlying Ca2+ homeostasis of primary sensory afferent neurons is mostly derived from studies on dorsal root ganglia and nodose ganglia neuron cell bodies. Little is known about Ca2+ homeostasis in trigeminal ganglion neurons (TGNs). To determine what cellular processes contribute to electrically-evoked Ca2+ transients in TGNs, we probed Ca2+ regulatory mechanisms in TGN cell bodies from the ophthalmic division with a panel of pharmacological reagents. Ca2+ transients were evoked in fura-2 loaded TGNs by depolarizing the plasma membrane with brief (500 ms) puffs of 50 mM KCl. Cyclopiazonic acid (CPA; 5 microM), an inhibitor of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), significantly decreased the peak amplitude, and slowed the decay, of the KCl-evoked Ca2+ transients in TGNs. The mitochondrial protonophore, carbonyl cyanide 3-chloro-phenylhydrazone (CCCP; 5 microM) significantly increased the peak amplitude of KCl-evoked Ca2+ transients. These data demonstrate that Ca2+ stores do play a major role in Ca2+ homeostasis in TGN cell bodies. To determine the role of the sodium-calcium exchanger (NCX) in KCl-evoked Ca2+ transients in TGNs, we inhibited the exchanger with KB-R7943 (10 microM), or by replacing Na+ with Li+. NCX inhibition did not affect either the peak amplitude or the decay kinetics of the KCl-evoked Ca2+ transients. Therefore, the NCX does not play a significant role in removing cytosolic Ca2+ from TGNs. To test whether the plasma membrane calcium-ATPase (PMCA) contributes to Ca2+ extrusion, we inhibited its activity by a shift to alkaline pH (9.0). At pH 9.0, both the peak amplitude and decay time of the KCl-evoked Ca2+ transient were increased significantly. These data suggest that, in TGNs, the PMCA is the major mechanism for removing cytosolic Ca2+ following electrical activity.
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PMID:Calcium homeostasis in trigeminal ganglion cell bodies. 1704 58


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