Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study was to investigate the effects of calcium channel blockers on tertbutyl hydroperoxide (TBH) induced liver injury using isolated perfused rat hepatocytes. Rat hepatocytes were immobilized in agarose threads and perfused with Williams E medium. Hepatocyte injury was induced by the addition of tertbutyl hydroperoxide (1 mM) to the perfusion medium 30 min after the addition of either verapamil or diltiazim. Hepatocyte injury was observed by monitoring the functional and metabolic competence of hepatocytes or by ultrastructural morphological examination of hepatocytes. Verapamil (0.5 mM) reduced lactate dehydrogenase leakage in TBH-injured hepatocytes as compared to the controls (154+/-11% vs. 247+/-30%). Lipid peroxides production was reduced after verapamil pretreatment as compared to the controls and oxygen consumption was increased by pretreatment of hepatocytes with verapamil. Verapamil pretreatment increased the protein synthesis activity at both levels of granular endoplasmic reticulum and free polysomes in cytoplasm and decreased ATPase activity. Diltiazem was qualitatively effective as verapamil. It is concluded that in hepatocyte oxidative injury, calcium channel blockers exhibited hepatoprotective properties. The hepatoprotective effect of calcium channel blockers was accompanied by a decrease in ATPase activity, which may implicate a normalization of Ca2+i after TBH intoxication.
...
PMID:Evaluation of calcium channel blockers as potential hepatoprotective agents in oxidative stress injury of perfused hepatocytes. 1098 93

P-glycoprotein (P-gp) can transport a wide variety of cytotoxic compounds that have diverse structures. Therefore, the drug-binding domain of the human multidrug resistance P-gp likely consists of residues from multiple transmembrane (TM) segments. In this study, we completed cysteine-scanning mutagenesis of all the predicted TM segments of P-gp (TMs 1-5 and 7-10) and tested for inhibition by a thiol-reactive substrate (dibromobimane) to identify residues within the drug-binding domain. The activities of 189 mutants were analyzed. Verapamil-stimulated ATPase activities of seven mutants (Y118C and V125C (TM2), S222C (TM4), I306C (TM5), S766C (TM9), and I868C and G872C (TM10)) were inhibited by more than 50% by dibromobimane. The activities of mutants S222C (TM4), I306C (TM5), I868C (TM10), and G872C (TM10), but not that of mutants Y118C (TM2), V125C (TM2), and S776C (TM9), were protected from inhibition by dibromobimane by pretreatment with verapamil, vinblastine, or colchicine. These results and those from previous studies (Loo, T. W. and Clarke, D. M. (1997) J. Biol. Chem. 272, 31945-31948; Loo, T. W. and Clarke, D. M. (1999) J. Biol. Chem. 274, 35388-35392) indicate that the drug-binding domain of P-gp consists of residues in TMs 4, 5, 6, 10, 11, and 12.
...
PMID:Identification of residues within the drug-binding domain of the human multidrug resistance P-glycoprotein by cysteine-scanning mutagenesis and reaction with dibromobimane. 1101 59

Miltefosine (hexadecylphosphocholine) is used for topical treatment of breast cancers. It has been shown previously that a high percentage of breast carcinomas express MDR1 or MRP. We investigated the sensitivity of MDR1 -expressing cells to treatment with miltefosine. We show that cells overexpressing MDR1 (NCI/ADR-RES, KB-8-5, KB-C1, CCRF/VCR1000, CCRF/ADR5000) were less sensitive to miltefosine treatment when compared to the sensitive parental cell lines. HeLa cells transfected with MDR1 exhibited resistance to the compound, indicating that expression of this gene is sufficient to reduce the sensitivity to miltefosine. The resistance of MDR1-expressing cells to miltefosine was less pronounced than that to adriamycin or vinblastine. Expression of MDR2 did not correlate with the resistance to miltefosine. As shown by a fluorescence quenching assay using MIANS-labelled P-glycoprotein (PGP), miltefosine bound to PGP with a K(d)of approximately 7 microM and inhibited PGP-ATPase activity with an IC(50)of approximately 35 microM. Verapamil was not able to reverse the resistance to miltefosine. Concentrations of miltefosine up to approximately 60 microM stimulated, whereas higher concentrations inhibited the transport of [3H]-colchicine with an IC(50)of approximately 297 microM. Binding studies indicated that miltefosine seems to interact with the transmembrane domain and not the cytosolic nucleotide-binding domain of PGP. These data indicate that expression of MDR1 may reduce the response to miltefosine in patients and that this compound interacts with PGP in a manner different from a number of other substrates.
...
PMID:MDR1 causes resistance to the antitumour drug miltefosine. 1135 55

ABCG2 (also called MXR (3), BCRP (4), or ABCP (5) is a recently-identified ABC half-transporter, which causes multidrug resistance in cancer. Here we report that the expression of the ABCG2 protein in Sf9 insect cells resulted in a high-capacity, vanadate-sensitive ATPase activity in isolated membrane preparations. ABCG2 was expressed underglycosylated, and its ATPase activity was stimulated by daunorubicin, doxorubicin, mitoxantrone, prazosin and rhodamine 123, compounds known to be transported by this protein. ABCG2-ATPase was inhibited by low concentrations of Na-orthovanadate, N-ethylmaleimide and cyclosporin A. Verapamil had no effect, while Fumitremorgin C, reversing ABCG2-dependent cancer drug resistance, strongly inhibited this ATPase activity. The functional expression of ABCG2 in this heterologous system indicates that no additional partner protein is required for the activity of this multidrug transporter, probably working as a homodimer. We suggest that the Sf9 cell membrane ATPase system is an efficient tool for examining the interactions of ABCG2 with pharmacological agents.
...
PMID:Functional characterization of the human multidrug transporter, ABCG2, expressed in insect cells. 1143 80

Multidrug resistance mediated by the multidrug resistance-associated protein MRP1 is associated with decreased drug accumulation, which is in turn dependent on cellular glutathione. We have reported that verapamil, an inhibitor of drug transport, caused a decrease in cellular glutathione in CCRF-CEM/E1000 MRP1-overexpressing leukaemia cells (Biochem Pharmacol 55;1283--9, 1998). We now demonstrate that other inhibitors of MRP1-mediated drug transport (e.g. MK571, indomethacin, genistein, and nifedipine) deplete cellular glutathione in these leukaemia cells (>30% decrease; P < 0.01) while having no effect on the parental CCRF-CEM cells. However, treatment with etoposide or vincristine (at similar molar concentrations) caused a 20% decrease in glutathione. Verapamil-stimulated glutathione transport correlated with MRP1 expression in a series of drug-resistant cells, and glutathione was quantitatively recovered in the extracellular media. Further, verapamil-stimulated glutathione transport was rapid (50% decrease in 10 min), dose-dependent, and inhibited by vanadate, an inhibitor of ATPase activity, but not by sulphobromophthalein (BSP) or methionine, inhibitors of hepatic glutathione transporters. Incubation of CCRF-CEM/E1000 cells in 25 mM glutathione not only showed that verapamil-mediated efflux occurred against the concentration gradient, but also demonstrated the MRP1-mediated uptake of glutathione (P < 0.01 compared to the parental CCRF-CEM cells), which was not inhibited by vanadate. These results demonstrate that while MRP1 transports glutathione in the presence of inhibitors of drug transport, there is no convincing evidence for co-transport of glutathione with drug. They further demonstrate that MRP1 mediates the facilitated transport of glutathione into the MRP1-overexpressing CEM/E1000 cells, suggesting that MRP1 may play a major role in cellular glutathione homeostasis.
...
PMID:Verapamil-stimulated glutathione transport by the multidrug resistance-associated protein (MRP1) in leukaemia cells. 1144 50

Vasomotion, the phenomenon of vessel diameter oscillation, regulates blood flow and resistance. The main parameters implicated in vasomotion are particularly the membrane potential and the cytosolic free calcium in smooth muscle cells. In this study, these parameters were measured in rat perfused-pressurized mesenteric artery segments. The application of norepinephrine (NE) caused rhythmic diameter contractions and membrane potential oscillations (amplitude; 5.3 +/- 0.3 mV, frequency; 0.09 +/- 0.01 Hz). Verapamil (1 microM) abolished this vasomotion. During vasomotion, 10(-5) M ouabain (Na(+)-K(+) ATPase inhibitor) decreased the amplitude of the electrical oscillations but not their frequency (amplitude; 3.7 +/- 0.3 mV, frequency; 0.08 +/- 0.002 Hz). Although a high concentration of ouabain (10(-3) M) (which exhibits non-specific effects) abolished both electrical membrane potential oscillations and vasomotion, we conclude that the Na+-K+ ATPase could not be implicated in the generation of the membrane potential oscillations. We conclude that in rat perfused-pressurized mesenteric artery, the slow wave membrane type of potential oscillation by rhythmically gating voltage-dependent calcium channels, is responsible for the oscillation of intracellular calcium and thus vasomotion.
...
PMID:Role of membrane potential in vasomotion of isolated pressurized rat arteries. 1221 71

We used Daphnia magna bioassays to determine the LC(50) and the effects on the heart of the cardioactive drugs ouabain, verapamil, metaproterenol and metoprolol. Distinctions were made between the pharmacological and toxicological effects of these drugs and the adequacy of physicochemical characteristics of its habitat (reconstituted water). Video microscopy and digital image processing were used to study the pharmacological effects on the heart. D. magna exhibited the expected sensitivity to the reference toxicant sodium dodecyl sulfate with a LC(50) of 15.6+/-4.5 mg/l. All drugs were toxic with 48 h-LC(50) of 2.03 mg/l ouabain, 7.04 mg/l verapamil, 32.45 mg/l metaproterenol and 76.21 mg/l metoprolol. Ouabain was the most toxic and caused a positive concentration-dependent inotropic effect. Verapamil caused positive chronotropic and inotropic effects, while metaproterenol showed positive concentration-dependent chronotropic effects at high concentrations (10(-3) and 10(-4) M). Metoprolol induced a positive chronotropic effect at low concentrations (10(-8), 10(-7), 10(-6) M) and a negative chronotropic effect at high concentration (10(-4) M). Ouabain, metaproterenol and metoprolol in D. magna caused similar effects to those produced in mammals. In contrast, verapamil caused opposite effects. The results suggest the presence of Na(+), K(+)-ATPase receptors to verapamil and of non-specific adrenergic receptors in heart of D. magna.
...
PMID:The heart of Daphnia magna: effects of four cardioactive drugs. 1455 94

A multidrug resistant (MDR) cell line, derived from the human leukaemic cell K562 and selected for its resistance to Vincristine, was shown to be resistant to Thapsigargin (TG). A concentration of 50 nM TG was toxic to K562 cells whereas the MDR cell line, known as Lucena I cells, survived unaffected for up to seven days in culture. Similarly, no intracellular Ca2+ mobilization was observed in the MDR cell line treated with TG. This effect was not a result of TG extrusion by P glycoprotein (Pgp), as no mobilization was observed even in the presence of the Pgp inhibitors Verapamil (5 microM) and Cyclosporin A (0.16 microM). In the present study, both cell lines expressed comparable levels of Bcl-2 making it unlikely that Bcl-2 was involved in this process. Similarly, no overexpression of the endoplasmic reticulum Ca2+ ATPase (SERCA) could be detected in the MDR cell line and Ca2+ uptake by vesicles of the two cell types were equally sensitive to TG. These results confirm that MDR cells do not mobilize Ca2+ in the presence of TG but go against the possibility that this might be due to TG extrusion or to the overexpression of a resistant SERCA isoform.
...
PMID:Resistance to thapsigargin-induced intracellular calcium mobilization in a multidrug resistant tumour cell line. 1457 83

P-glycoprotein ATPase activity has been studied almost exclusively by measuring inorganic phosphate release from inside-out cellular vesicles. We have recently proposed a new method based on measurements of the extracellular acidification rate (ECAR) of living cells with a Cytosensor microphysiometer. This method allows for systematic investigation of the various factors influencing P-glycoprotein activation in living cells. Basal metabolic rates or ECARs of different MDR1-transfected cell lines were compared with those of the Mdr1a(-/-)1b(-/-) knockout, MRP1-transfected, and corresponding wild-type cell lines. Basal ECARs of all cells were on the order of 10(7) protons/cell/s, whereby those of genetically modified cells were on average (over all cell lines) slightly lower than those of wild-type cells. The expression level of P-glycoprotein in MDR1-transfected cells had no influence on basal ECARs. Verapamil-induced ECARs were specific for MDR1-transfected cells and increased with the expression level of P-glycoprotein. Moreover, ECARs were dependent on the metabolic state of the cell and were (2.8 +/- 1.2) x 10(6) and (8.0 +/- 1.5) x 10(6) protons/cell/s in glucose-deficient and glucose-fed NIH-MDR-G185 cells, respectively, after verapamil (10 muM) stimulation. The ECARs were practically identical to the rates of lactate extrusion and thus reflect the rates of ATP synthesis via glycolysis. Taking into account the number of P-glycoprotein molecules per cell, the rate of ATP hydrolysis in inside-out vesicles of the same cells was determined as (9.2 +/- 1.5) x 10(6) phosphates/cell/s, in good agreement with the rate of ATP synthesized in glucose-fed cells. The energy required for P-glycoprotein activation relative to the basal metabolic energy was twice as large in glucose-deficient as in glucose-fed cells, suggesting cellular protection by P-glycoprotein even under conditions of starvation.
...
PMID:The rate of P-glycoprotein activation depends on the metabolic state of the cell. 1554 55

The relationship between the expression level of putative drug resistance factors and sensitivity to anticancer drugs in human normal renal proximal tubule epithelial cells (RPTEC) and 3 kinds of renal cell carcinoma (RCC) cells, VMRC-RCW (RCW), OS-RC-2 (OS2), TUHR14TKB (14TKB), was examined. RPTEC exhibited high expression of P-glycoprotein (Pgp), gamma-glutamyl cysteine synthetase (gammaGCS) and cis-diamminedichloroplatinum (II) (CDDP) resistance-related gene 9 (CRR9), low expression of vacuolar ATPase (V-ATPase) and no expression of multidrug resistance-associated protein 1 (MRP1). 14TKB exhibited high expression of gammaGCS and CRR9, low expression of Pgp and V-ATPase, and no expression of MRP1. OS2 showed high expression of CRR9, low expression of Pgp, gammaGCS and MRP1, and no expression of V-ATPase. RCW exhibited high expression of Pgp, MRP1 and CRR9 and low expression of gammaGCS and V-ATPase. The level of expression of the resistance factors varied among the cells. GST activity and GST-pi expression level of each cell were correlated, and there were high levels in OS2 and RPTEC. When the cytotoxicity of anticancer drugs against each cell was measured at 96 h, the sensitivity to CDDP and Doxorubicin (DXR) in RPTEC and RCW was lower than that in the other cells. Sensitivity to DXR was enhanced by treatment with the Pgp inhibitor, Verapamil, in proportion to the Pgp expression level, and the sensitivity to CDDP was increased by the gammaGCS inhibitor, Buthionine sulfoximine, in proportion to the gammaGCS expression level (corresponding to GSH content). Although a significant increase in sensitivity to CDDP was not observed by treatment of RCC with the V-ATPase inhibitor, Bafilomycin, the sensitivity to DXR in Bafilomycin-treated cells increased about 2-fold. However, no relation between drug sensitivity and V-ATPase expression was observed. The features (such as degree of resistance) varied among the RCC cell lines manifesting many resistance factors or to the contrary, lacking or having lowered resistance factors in comparison with normal cells. Therefore, it is necessary in clinical cancer chemotherapy to determine and measure the level of expression of each resistance factor in respective tumor tissue.
...
PMID:Relationship between expression of drug-resistance factors and drug sensitivity in normal human renal proximal tubular epithelial cells in comparison with renal cell carcinoma. 1607 62


<< Previous 1 2 3 4 5 6 7 8 9 Next >>

---