Plasma Membrane ATPase Activity Research Articles

The role of polyamines in the regulation of the plasma membrane and the tonoplast proton pumps under salt stress

Polyamine content (PAs) often changes in response to abiotic stresses. It was shown that the accumulation of PAs decreased in roots treated for 24 h with 200 mM NaCl. The role of polyamines (putrescine – PUT, spermidine – SPD and spermine – SPM) in the modification of the plasma membrane(PM) H +-ATPase (EC 3.6.3.6) and the vacuolar(V) H +-ATPase (EC 3.6.3.14) activities in cucumber roots treated with NaCl was investigated. 24 h treatment of seedlings with 50 μM PUT, SPD or SPM lowered the activities of proton pumps in both membranes. The decreased H +-ATPase activity in plasma membranes isolated from the PA-treated roots was positively correlated with a lower level of PM-H +-ATPase CsHA3 transcript. However, transcript levels of PM-H +-ATPase CsHA2 and V-ATPase subunit A and c in roots treated with 50 μM PAs were similar to those in the control. Additionally, treatment of plants with salt markedly increased the activity of the PM- and V-H +-ATPases. However, exposure of plants to 20% PEG had no effect on these activities. These data suggest that, under salt stress conditions, the increase in H +-ATPase activities is caused mainly by the ionic component of salt stress. It seems that the main role of the PAs in the 24 h salt-treated cucumber plants could be a result of their cationic character. The PA levels decreased when concentration of Na + increased, so action of PAs contributes to ionic equilibrium. Moreover, the decrease in the concentration of polyamines, which inhibit the PM-H +-ATPase and the V-H +-ATPase, at least under the studied conditions, seems to be beneficial. Thus, plants can increase salinity tolerance by modifying the biosynthesis of polyamines.

Kidney Damage in Rats Bearing an Adrenocorticotropin and Prolactin Secreting Tumor

The effect of chronic high plasma corticosteroids' concentration upon renal function was studied in rats bearing a transplantable pituitary mammotropic tumor which produces large quantities of ACTH and prolactin (MtTF4S). Kidney splanchnomegaly and degenerative changes of renal cortex, particularly in proximal tubules, as well as cytolysis and appearance of vacuoles were noticed in tumor bearing rats. (Na+ + K+)-ATPase activity in renal plasma membranes decreased 67% in rats with a tumor secreting ACTH and prolactin, and 64% in rats with a tumor secreting growth hormone and prolactin when compared with controls. After adrenalectomy of MtTF4S rats, kidney weight as well as plasma concentrations of urea, sodium, chloride and phosphate ions were normalized indicating the involvement of adrenal glands in the development of disturbances in renal function.

Intracellular pH Homeostasis Plays a Role in the Tolerance of Debaryomyces hansenii and Candida zeylanoides to Acidified Nitrite

The effects of acidified-nitrite stress on the growth initiation and intracellular pH (pH(i)) of individual cells of Debaryomyces hansenii and Candida zeylanoides were investigated. Our results show that 200 microg/ml of nitrite caused pronounced growth inhibition and intracellular acidification of D. hansenii at an external pH (pH(ex)) value of 4.5 but did not at pH(ex) 5.5. These results indicate that nitrous acid as such plays an important role in the antifungal effect of acidified nitrite. Furthermore, both yeast species experienced severe growth inhibition and a pH(i) decrease at pH(ex) 4.5, suggesting that at least some of the antifungal effects of acidified nitrite may be due to intracellular acidification. For C. zeylanoides, this phenomenon could be explained in part by the uncoupling effect of energy generation from growth. Debaryomyces hansenii was more tolerant to acidified nitrite at pH(ex) 5.5 than C. zeylanoides, as determined by the rate of growth initiation. In combination with the fact that D. hansenii was able to maintain pH(i) homeostasis at pH(ex) 5.5 but C. zeylanoides was not, our results suggest that the ability to maintain pH(i) homeostasis plays a role in the acidified-nitrite tolerance of D. hansenii and C. zeylanoides. Possible mechanisms underlying the different abilities of the two yeast species to maintain their pH(i) homeostasis during acidified-nitrite stress, comprising the intracellular buffer capacity and the plasma membrane ATPase activity, were investigated, but none of these mechanisms could explain the difference.

Shoot Apex Demand Determines Assimilate and Nutrients Partitioning and Nutrient‐uptake Rate in Tobacco Plants

Abstract Our previous experiment revealed that apex‐removed plants have larger root systems but a lower K+‐uptake rates than intact tobacco plants. Since the apex is not only a center of growth and metabolism, but also an important place of auxin synthesis and export, the aims of this study were to distinguish whether the apex demand or auxin synthesized in the apex regulates assimilate and nutrients partitioning within plant, and to explain the reason for the lower K+‐uptake rate of the apex‐removed plant. In comparison with the control plant, covering the shoot apex with a black transparent plastic bag reduced net increases in dry matter and nutrients; however, the distribution of the dry matter and nutrients between shoot and roots and nutrient‐uptake rates were not changed. Removal of the shoot apex shifted the dry mass and nutrients distributions to roots, and reduced the rate of nutrient uptake. Application of 1‐naphthylacetic acid (NAA) could partly replace the role of the removed apex, stimulated assimilate and nutrient deposition into the treated tissue, and enhanced the reduced plasma membrane ATPase activity of roots to the control level. However, treatment of the apex‐removed plants with NAA could not rescue the reduced nutrient uptake rate and the shifted assimilates and nutrients partitioning caused by excision of the apex. Higher nutrient uptake rate of the intact plants could not be explained by root growth parameters, such as total root surface area and number of root tips. The results from the present study indicate that strong apex demand determined assimilates and nutrients partitioning and nutrient‐uptake rate in tobacco (Nicotiana tabacum) plants.

Ethanol tolerance and the variation of plasma membrane composition of yeast floc populations with different size distribution

The ethanol tolerance of a self-flocculating yeast strain SPSC01 was investigated in an oxygen-limited fed-batch bioreactor. Employing Focused Beam Reflectance Measurement (FBRM) on-line monitoring system, four yeast floc populations with the average size ranging from 100 to 400 μm were obtained. It was found that ethanol tolerance increased with the increasing floc size in the 100, 200, and 300 μm floc populations, while increasing the average floc size further to 400 μm resulted in lower ethanol tolerance. Examination of the membrane composition of different floc populations revealed that the plasma membrane composition of the floc populations was significantly different in the contents of ergosterol, phosphatidylinositol, as well as phospholipid palmitoleic acid. What's more, the plasma membrane of more ethanol tolerant floc population was less permeable when subjected to 15% (v/v) ethanol shock treatment, and the plasma membrane ATPase activities were higher in the floc populations with higher ethanol tolerance. These results indicate that the average size distribution of the floc populations exerted great influence on the physiological status of yeast cells during the ethanol production process, leading to the changes in plasma membrane composition that contributed to improved ethanol tolerance in self-flocculating yeast SPSC01.

Magnesium lithospermate B possesses inhibitory activity on Na+,K+-ATPase and neuroprotective effects against ischemic stroke

To examine if magnesium lithospermate B (MLB) extracted from Danshen, the dried roots of Salvia miltiorrhiza, may act as an active component responsible for the cardiac therapeutic effect of this traditional Chinese herb via the same molecular mechanism triggered by cardiac glycosides, such as ouabain and digoxin. Moreover, we wanted to test if MLB may provide neuroprotection against ischemic stroke as observed for cardiac glycosides. Similarity in the chemical structure and molecular configuration between MLB and ouabain was analyzed. The inhibition potency of MLB and ouabain on Na( +),K( +) -ATPase activity of a commercial product, as well as in purified membrane fractions from rat brain and heart tissues, was examined and compared. Neuroprotective effect of MLB against ischemic stroke was also evaluated using a cortical brain slice-based assay model. Dose-dependent inhibition on the commercial Na( +),K( +)-ATPase equivalent to that for ouabain was observed for MLB of approximately half dosage by weight. This relative potency of ouabain and MLB was also observed for their inhibition on Na( +),K( +)-ATPase activity of plasma membrane purified from rat tissues, although these 2 inhibitors exhibited somewhat lower competence in these crude extracts. In ischemic gerbil brains, post-treatment with MLB significantly reduced the infarct size, visualized by 2,3,5-triphenyltetrazolium chloride staining, by approximately 55% when compared with the control group. These results evidently suggest that the cardiac therapeutic effect of Danshen should be at least partly attributed to the effective inhibition of Na( +),K( +)-ATPase by MLB, and that MLB provides anti-ischemic neuroprotection in gerbils subjected to focal ischemia and reperfusion.

Glucose controls multiple processes inSaccharomyces cerevisiaethrough diverse combinations of signaling pathways

We have studied how the lack of glucose sensors in the plasma membrane, or of the enzymes Hxk1, Hxk2, Glk1, which catalyze the first intracellular step in glucose metabolism, affect the different responses of Saccharomyces cerevisiae to glucose. Lack of the G-protein-coupled receptor Gpr1 or of Snf3/Rgt2 did not affect glucose repression of different genes or activation by glucose of plasma membrane ATPase, whereas lack of Gpr1 decreased, in an additive manner with lack of Mth1, the degradation of fructose 1,6-bisphosphatase that takes place in the presence of glucose. In an hxk1 hxk2 glk1 strain, unable to phosphorylate glucose, all of these responses to the sugar were suppressed or strongly reduced. In the absence of Hxk2 (or Hxk1 and Hxk2), glucose repression of SUC2, GAL1 and GDH2 was relieved, but that of FBP1 and ICL1 was maintained. Hxk1 or Hxk2 were needed for activation of plasma membrane ATPase but not for degradation of FbPase.

Synaptic Plasma Membrane Na+, K+-ATPase Activity is Significantly Reduced by the α-Keto Acids Accumulating in Maple Syrup Urine Disease in Rat Cerebral Cortex

The objective of the present study was to investigate the in vitro effects of the branched-chain alpha-keto acids accumulating in maple syrup urine disease, namely L-2-ketoisocaproic acid, L-2-keto-3-methylvaleric acid and L-2-ketoisovaleric acid on Na(+), K(+)-ATPase activity in synaptic plasma membranes from cerebral cortex of 35-day-old rats. All keto acids significantly inhibited Na(+), K(+)-ATPase activity at concentrations similar (1 mM) or even lower (0.5 mM) than those found in blood and cerebrospinal fluid of maple syrup urine disease patients. We also tested the effects of alanine on this enzyme activity. Alanine per se did not alter Na(+), K(+)-ATPase activity, but totally prevented the branched-chain alpha-keto acids-induced Na(+), K(+)-ATPase inhibition, indicating that alanine and the keto acids may possibly bind to the same site on the enzyme. We also observed that the branched-chain amino acids leucine, isoleucine and valine also inhibited Na(+) K(+)-ATPase activity to a similar degree as that of the branched-chain alpha-keto acids and that alanine was able to fully prevent these effects. Considering that Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings may be involved in the pathophysiology of the neurological dysfunction of maple syrup urine disease.

Membrane potential governs lateral segregation of plasma membrane proteins and lipids in yeast

The plasma membrane potential is mainly considered as the driving force for ion and nutrient translocation. Using the yeast Saccharomyces cerevisiae as a model organism, we have discovered a novel role of the membrane potential in the organization of the plasma membrane. Within the yeast plasma membrane, two non-overlapping sub-compartments can be visualized. The first one, represented by a network-like structure, is occupied by the proton ATPase, Pma1, and the second one, forming 300-nm patches, houses a number of proton symporters (Can1, Fur4, Tat2 and HUP1) and Sur7, a component of the recently described eisosomes. Evidence is presented that sterols, the main lipid constituent of the plasma membrane, also accumulate within the patchy compartment. It is documented that this compartmentation is highly dependent on the energization of the membrane. Plasma membrane depolarization causes reversible dispersion of the H(+)-symporters, not however of the Sur7 protein. Mitochondrial mutants, affected in plasma membrane energization, show a significantly lower degree of membrane protein segregation. In accordance with these observations, depolarized membranes also considerably change their physical properties (detergent sensitivity).

Effect of Drugs from the Class of Cardiac on the Na+, K+-ATPase Activity

The effect of drugs from the class of cardiac (methyldigoxin, verapamil, propranolol), antiepileptic (carbamazepine), sedative (diazepam) and antihistaminic (promethazine) drugs on Na+, K+-ATPase activity of plasma membranes in rat brain synaptosomes was studied. Methyldigoxin in concentration of 0.1 mmol L-1 inhibits enzyme activity by 80%. Verapamil, propranolol and promethazine in concentrations of 20, 20 and 2 mmol L-1, respectively, inhibit entirely this ATPase activity. Carbamazepine and diazepam in concentrations of 0.02-60 mmol L-1 have no effect on the activity of this enzyme. According to drugs concentrations that inhibit 50% of enzyme activity (IC50), the potency order of drugs was: methyldigoxin ≫ promethazine > verapamil ≥ propranolol. From inhibition of commercially available purified Na+, K+-ATPase isolated from porcine cerebral cortex in the presence of chosen drugs, as well as from the kinetic studies on synaptosomal plasma membranes, we may concluded that the drugs inhibit enzyme activity, in partly by acting directly on the enzyme protein. Propranolol, verapamil and promethazine inhibitions were in an uncompetitive manner. The results suggest that these three drugs may contribute to neurological dysfunction and point out to the necessity to take into consideration the side effects of the investigated drugs during the treatment of various pathological conditions.

Oxidative stress and septic shock: metabolic aspects of oxygen-derived free radicals generated in the liver during endotoxemia

This review describes the role of oxidative stress caused by endotoxin challenge in sepsis or septic shock symptoms. We observed that endotoxin injection resulted in lipid peroxide formation and membrane damage (near 60-150 kDa) in the livers of experimental animals, causing decreased levels of scavengers or quenchers of free radicals. The administration of alpha-tocopherol completely prevented injury to the liver plasma membrane caused by endotoxin, and suggested that lipid peroxidation by free radicals might occur in a tissue ischemic state, probably by disseminated intravascular coagulation (DIC), in endotoxemia. In mice, depression of Ca(2+)-ATPase activity in the liver plasma membrane may contribute to the membrane damage caused by endotoxin, and the increase of [Ca(2+)](i) in the liver cytoplasm may partially explain the oxidative stress that occurs in endotoxemia. It seems that endotoxin-induced free radical formation is regulated by Ca(2+) mobilization. Moreover, we have suggested that the oxidative stress caused by endotoxin may be due, at least in part, to the changes in endogenous zinc or selenium regulation during endotoxemia. Interestingly, the extent of TNF-alpha-induced oxidative stress may be the result of a synergism between TNF-alpha and gut-derived endotoxin. It is likely that bacterial or endotoxin translocation plays a significant role in TNF-alpha-induced septic shock. On the other hand, although nitric oxide (NO) has been implicated in the pathogenesis of vascular hyporesponsiveness and hypotension in septic shock in our experimental model, it is unlikely that NO plays a significant role in liver injury caused by free radical generation in endotoxemia.

Modification of plasma membrane and vacuolar H +-ATPases in response to NaCL and ABA

The role of ABA in the modification of membrane proton pump activity in cucumber roots which had been stressed for 24h with 200 mmol/dm(3) NaCl was investigated. It was shown that treatment of plants with salt distinctly increased the activity of the plasma membrane H(+)-ATPase (EC 3.6.3.6) as well as of the vacuolar H(+)-ATPase (EC 3.6.3.14). In roots treated with NaCl, an increase of ABA level was observed. Moreover, 24-h treatment of seedlings with 50 micro mol/dm(3) ABA increased the activity of proton pumps in both membranes. However, when ABA was added to the reaction medium, no changes in ATPase activities were observed. The increased H(+)-ATPase activity in plasma membranes isolated from the ABA-treated roots was positively correlated with a higher level of PM-H(+)-ATPase transcript. These data have provided evidence that under salt stress conditions, the role of ABA action due to salinity on the induction of the PM-H(+)-ATPase could be at the level of gene expression.

In vitro responses of rat alveolar macrophages to particle suspensions and water-soluble components of dust storm PM 2.5

A study was conducted to investigate the in vitro toxicities of dust storm particulate matter with an aerodynamic diameter ⩽ 2.5 μm (PM 2.5) on rat alveolar macrophages (AM). This was based on the ambient PM 2.5 collected in March 2004 from Baotou city, Inner Mongolia Autonomous Region, China. The particles were classified as normal (from sunshiny and clean days) and dust storm samples according to the dust storm classification, and the local weather and air quality monitoring data. The cell viability, levels of cellular thiobarbituric acid-reactive species (TBARS), glutathione (GSH), and cytosolic free calcium ions (Ca 2+), and the plasma membrane ATPase activities and membrane lipid fluidity were determined 4 h following the in vitro treatment of AM with differing dosages of the collected samples. Results revealed that dust storm PM 2.5 and their water-soluble fractions at high dosages generated oxidant stress on AM, induced leakage of lactate dehydrogenase (LDH), significantly decreased activities of plasma membrane Na +K +-ATPase, increased intracellular Ca 2+ levels, and led to significant alterations in membrane lipid fluidity, finally resulting in cytotoxicity. A two-way ANOVA showed that there was no significant difference in the above indices measured between the normal and dust storm PM 2.5, suggesting the deleterious effects of ambient PM 2.5 from Baotou city were based on the dose used rather than the type of particles. But due to a higher concentration of airborne PM 2.5 mass concentration in dust storm days than that in normal days, it concluded that during dust storm episodes, a much more serious effect on AM was imminent.

Effect of exogenous silicon (Si) on H +-ATPase activity, phospholipids and fluidity of plasma membrane in leaves of salt-stressed barley ( Hordeum vulgare L.)

Silicon (Si) is generally considered a beneficial element for the growth of higher plants, especially for those grown under stressed environments. Recently, the mitigating role of Si in salt stress has received worldwide attention. However, its mechanisms involved remain poorly understood. We studied the effects of Si on plasma membrane fluidity, phospholipids and H +-ATPase activity and reduced glutathione (GSH) concentration with two contrasting barley cultivars differing in their salt tolerance. The results showed that plasma membrane H +-ATPase activity decreased in leaves of plants treated with 120 mM NaCl, and this decrease was more obvious in salt-sensitive cultivar (Kepin No. 7) than in salt-tolerant cultivar (Jian 4). Under NaCl stress, plasma membrane fluidity decreased, and the ratio of phospholipids to proteins in plasma membrane vesicles increased. GSH concentration decreased in leaves of plants exposed to 120 mM NaCl in salt-sensitive cultivar (but not in salt-tolerant cultivar). Inclusion of 1.0 mM Si to the salt treatment increased plasma membrane H +-ATPase activity in both cultivars as compared with the plants treated with 120 mM NaCl only. The addition of Si to salt treatment was also found to recover membrane fluidity to control (neither NaCl nor Si added) level, and decrease the ratio of phospholipids to protein. Furthermore, GSH concentration in leaves of salt-treated plants was increased by addition of Si. It is suggested that Si maintain the optimal membrane fluidity and increase GSH concentration, which contributes to reducing oxidative damage to enzymes induced by active oxygen species and enhances plasma membrane H +-ATPase activity under NaCl stress.

Na +, K + ATPase activity is markedly reduced by cis-4-decenoic acid in synaptic plasma membranes from cerebral cortex of rats

We have previously demonstrated that octanoic (OA) and decanoic acids (DA) inhibit Na +, K + ATPase activity in synaptic plasma membranes from rat brain. The objective of the present study was to investigate the in vitro effects of the other metabolites that accumulate in tissues of medium-chain acyl-CoA dehydrogenase (MCAD)-deficient patients, namely cis-4-decenoic acid (cDA), octanoylcarnitine (OC), hexanoylcarnitine (HC), hexanoylglycine (HG), phenylpropionylglycine (PPG) and suberoylglycine (SG), on Na +, K + ATPase activity in synaptic plasma membrane from cerebral cortex of 30-day-old rats. cDA, the pathognomonic compound found in this disorder, provoked the strongest inhibition on this enzyme activity at concentrations as low as 0.25 mM, whereas OC inhibited this activity at 1.0 mM and higher concentrations in a dose-dependent manner. In contrast, HC, HG, PPG and SG did not affect Na +, K + ATPase activity. Furthermore, pre-treatment of cortical homogenates with the antioxidant enzymes catalase plus superoxide dismutase totally prevented cDA-induced Na +, K + ATPase inhibition. We also provided evidence that cDA, as well as OA and DA, caused lipid peroxidation, which may explain, at least in part, the inhibitory properties of these compounds towards Na +, K + ATPase. Considering that Na +, K + ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings, especially those regarding to the marked inhibitory effect of cDA, may be involved in the pathophysiology of the neurological dysfunction of MCAD-deficient patients.

Effects of Metal Ions on Plasma Membrane Mg2+‐ATPase in Rat Uterus and Ovaries

The in vitro effects of cadmium and mercury were investigated on the Mg(2+)-ATPase activity of plasma membranes from the rat ovary and uterus. ATP hydrolyzing activities were significant and dose-dependent-inhibited in both plasma membrane preparations by both metals. According to the IC(50) and apparent K(i), Cd(2+) was most potent in the ovary, while Hg(2+) was most potent in the uterus. In ovaries and uterus, Cd(2+) inhibits competitively, while Hg(2+) inhibits noncompetitively in both organs. The observed inhibition was a consequence of direct action of the chosen metal ions on the enzyme protein and by decreasing ATP hydrolysis, Hg(2+) and Cd(2+) may affect mammalian fertility.

Effect of ultrasonic exposure on Ca 2+-ATPase activity in plasma membrane from Aloe arborescens callus cells

We investigated the effect of ultrasound on plasma membrane (PM) Ca 2+-ATPase activity of Aloe arborescens callus cells in solid culture. The calluses were exposed by a 20 kHz digital sonifier at the powers of 2 and 10 W from the effective exposure times of 2–10 s. PM Ca 2+-ATPase activity was almost significantly higher at 2 W both in continuous wave and 10% duty cycle than that of the control (no ultrasound) at effective exposure times of 5 and 10 s. However, its activity decreased at 10 W in continuous wave exposure. It is possible that the PM Ca 2+-ATPase configuration or structure may be partly damaged by high-energy ultrasound at 10 W. Our results showed that low-energy ultrasound exposure was a useful physical field to stimulate A. arborescens callus cells to adapt environmental stress through PM Ca 2+-ATPase activity increase.

Effects of different cultivation temperatures on plasma membrane ATPase activity and lipid composition of sugar beet roots

Sugar beet seedlings ( Beta vulgaris L. cv. Monohill) were cultivated for 3 weeks at different root and shoot temperatures and the plasma membranes (PM) from roots were purified by aqueous two-phase partitioning and analyzed for lipid composition and ATPase activities. Lipid analyses, undertaken immediately after PM purification from the roots, showed that a low root zone temperature (10 °C) decreased the ratio between the major lipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE). A low temperature in the root environment increased the mol% of PE and decreased the mol% of phosphatidic acid (PA), independent on the shoot growth temperature. A low temperature also decreased the mol% of linoleic acid (18:2) and increased mol% of linolenic acid (18:3) in the analyzed lipid classes, especially in PC and PE. The ratio between acyl chain lipids and protein generally increased in PM from roots grown at 10 °C, compared with higher temperature. The changes in lipid composition correlated with changes in ATPase activities, detected as hydrolyses of MgATP. The kinetic parameters, K m and V of the PM H +ATPase in roots increased at a low cultivation temperature, independent on shoot temperature. Moreover, Arrhenius analyses showed that the transition temperature was independent of both root or shoot growth temperature at 10–24 °C, whereas the activation energy of the ATPase was dependent on the growth temperature of the root, and independent on shoot temperature. Thus, acclimation processes can take place in roots, irrespective of the shoot temperature.

ATPase activity of purified plasma membranes and digestive vacuoles from Plasmodium falciparum

The ATPase activity of the human malaria parasite, Plasmodium falciparum was investigated using two experimental systems, (i) digestive vacuoles, and (ii) purified plasma membranes isolated from a chloroquine-sensitive and a chloroquine-resistant strain. No correlation between the level of ATPase activity and chloroquine sensitivity could be detected. In both systems, the ATPase activity of the chloroquine-resistant and -sensitive strain was decreased in the presence of the P-glycoprotein inhibitor vanadate. Susceptibility to inhibition by vanadate together with the lack of effect of ouabain implies a P-type ATPase activity in the plasma membrane. Furthermore, the inhibition of Fac8 ATPase activity by oligomycin both in the digestive vacuoles and the plasma membranes would be consistent with higher levels of Pgh1 in Fac8. Our data are consistent with the presence of a V-type H +-ATPase in the parasite food vacuole. Bafilomycin A1 and N-ethylmaleimide decreased the vacuolar ATPase activity in both chloroquine-resistant and -sensitive strains. Interestingly, a 30% decrease was observed between the ATPase activity of plasma membranes isolated from Fac8 and D10 in the presence of bafilomycin A1, suggesting the presence of a V-type ATPase in D10 plasma membrane that is underexpressed or altered in the plasma membrane of the chloroquine-resistant Fac8. The chemosensitisers tested had no effect on the ATPase activity of chloroquine-resistant P. falciparum in both systems suggesting that their activity is not mediated through an ATP-dependent mechanism. No effect was observed on the vacuolar ATPase activity in the presence of the antimalarials tested indicating that an ATP-dependent transport has not been activated.

Effects of dp-B on ATPase activity of insect plasma membrane

Inhibition of ATPase from aphid plasma membrane, sarcoplasmic reticulum (SR), and brain synaptosomal plasma membrane of locust, by 1,5-diphenyl-2-penten-1-one (dp-B), was studied. Results demonstrated that dp-B exhibited the similar effects on ATPase found in the three membranes amongst which the plasma membrane Ca 2+–Mg 2+-ATPase is the primary target. The effects of dp-B on Ca 2+–Mg 2+-ATPase activity were bi-directional: the enzyme enhanced hydrolyzation when dp-B or Ca 2+ concentrations were low but inhibited significantly when at high concentrations. The inhibition of Ca 2+–Mg 2+-ATPase by dp-B from brain synaptosomal plasma membrane of insect is higher than that from other organizational plasma membranes of the insect. Dp-B inhibiting Ca 2+- and CaM-requiring ATPase activity may be an important mechanism by which the insect gets poisoned (for example aphid).