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61.
The plasma membrane Ca2+ ATPase in erythrocytes is vital for the maintenance of intracellular Ca2+ levels. Since the cytoplasmic Ca2+ concentration is elevated in older erythrocytes, the properties of the Ca2+ transport ATPase were examined during cell aging using inside-out vesicles (IOVs) prepared from density-separated, young (less dense, Ey) and old (more dense, Eo) rat and human erythrocytes. The transport of Ca2+ and the coupled hydrolysis of ATP were measured using radiolabeled substrates. The calmodulin-independent Ca2+ transport activity (Ey, 38.8 vs. Eo, 23.3 nmols/min/mg IOV protein) and the Ca2+ dependent ATP phosphohydrolase activity (Ey, 53.5 vs. Eo, 48.8 nmols/min/mg protein) were greater in IOVs prepared from younger (less dense) rat erythrocytes. The calmodulin-independent Ca2+ transport activity in IOVs from human erythrocytes was 12.9 nmols/min/mg IOV protein for Ey and 10.7 nmols/min/mg IOV protein for Eo. Inside-out vesicles from older (more dense) cells exhibited a lower pumping efficiency as determined by the calculated stoichiometry, molecule of Ca2+ transported per molecule of ATP hydrolyzed (rat: Ey, 0.74 vs. Eo, 0.49; human: Ey, 1.22 vs. Eo, 0.77). The enzymatic activity of rat and human Ey IOVs was labile. The Ca2+ transport activity in Ey but not Eo IOVs rapidly declined during cold storage (4°C). The decrease in Ca2+ transport activity during aging may accentuate the age-related decline in several erythrocytic properties.Abbreviations IOV
Inside-Out Vesicles
- Ey
Erythrocytes enriched with young (less dense) cells
- Eo
Erythrocytes enriched with old (more dense) cells
- ACEase
Acetylcholinesterase 相似文献
62.
63.
Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment 总被引:5,自引:0,他引:5
Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method. 相似文献
64.
When acutely transferred to diluted seawater (SW), Procephalothrix spiralis and Clitellio arenarius regulate water content (g H2O/g solute free dry wt = s.f.d.w.) via loss of Na and Cl (µmoles/g.s.f.d.w.). The present study extends these observations to a greater range of salinities and determines the effects of long-term, stepwise acclimation to diluted seawaters. Final exposure to a given experimental seawater (70, 50, 30, 15%) was 48 hours. Osmolality (mOsm/kg H2O) and Na, K, and Cl ion concentrations (mEq/l) were determined in total tissue water and in the extracellular fluid of C. arenarius. Extracellular volume was determined as the 14C-polyethylene glycol space. Both species behaved as hyperosmotic conformers in diluted seawaters. However, reduction of the osmotic gradient between worm and medium occurred in P. spiralis, but not C. arenarius, in 30 and 15% SW. In both species, osmolality and Na, Cl, and K concentrations in total tissue water decreased with increased dilution of the SW. Water content increased with dilution of the medium but was lower than that which would be predicted based on approximation of the van't Hoff relation. This indicated the occurrence of regulatory volume decrease (RVD). In P. spiralis, in 70 or 50% SW, RVD was accompanied by loss of Na and Cl contents. However, in 30 or 15% SW, Na and Cl contents increased and in worms in 15% SW K content decreased. The latter movements of Na, Cl and K are indicative of cellular hysteresis and were associated with decreased viability, indicating the lower limits of regulatory ability in this species. In comparison, RVD in C. arenarius occurred in all diluted seawaters and was accompanied by loss of Na and Cl contents. In C. arenarius, evidence for reduced viability was absent. Removal of the supra- and subesophageal ganglia of C. arenarius resulted in retention of water, Na and Cl (g H2O or µmoles/g s.f.d.w.) in worms acclimated to 70% SW. Removal of the cerebral ganglia and cephalic glands of P. spiralis did not significantly influence regulation of water content. 相似文献
65.
Hideto Kuwayama 《生物化学与生物物理学报:生物膜》1988,940(2)
The effect of membrane potential on the activity of the ATP-dependent Ca2+ pump of isolated canine ventricular sarcolemmal vesicles were investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K+, and the initial rates of Ca2+ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca2+ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K+ channel blocker, tetraethylammonium ion or Ba2+. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca2+ pump is suggested from the increase of Ca2+ uptake by negative potential induced by valinomycin. 相似文献
66.
The components of magnesium efflux in squid axons have been studied under internal dialysis and voltage clamp conditions. The present report rules out the existence of an ATP-dependent, Na0- and Mg0-independent Mg2+ efflux (ATP-dependent Mg2+ pump) leaving the Mg2+---Na+ exchange system as the only mechanism for Mg2+ extrusion. The main features of the Mg2+ efflux are: (1) The efflux is completely dependent on ATP. (2) The efflux can be activated either by external Na+ (forward Mg2+---Na+ exchange) or external Mg2+ (Mg2+---Mg2+ exchange). (3) The mobility of the Mg2+ exchanger in the Na0+-loaded form is greater than that in the Mg2+-loaded one. (4) In variance with the Na+---Ca2+ exchange mechanism, Mg2+---Mg2+ exchange is not activated by external monovalent cations. (5) ATPγS replaces ATP in activating Mg2+---Na+ exchange suggesting that a phosphorylation/dephosphorylation process regulates this transport mechanism. 相似文献
67.
Myocardial sodium-pump activity was examined from ouabain-sensitive 86Rb+ uptake using myocytes isolated from guinea-pig heart. Either sodium loading or the sodium ionophore, monensin, increased 86Rb+ uptake by over 400%, indicating that the amount of Na+ available to the pump is the primary determinant of its activity, and that the sodium pump has a substantial reserve capacity in quiescent myocytes. Moreover, the degree of the above stimulation is markedly higher than corresponding values reported with multicellular preparations, suggesting that diffusion barriers make it impossible to observe the capacity of the sodium pump in the latter preparations. Removal of extracellular Ca2+ increased ouabain-sensitive 86Rb+ uptake, probably by enhancing turnover of the sodium pump rather than increasing availability of Na+ to the pump. 相似文献
68.
Birgit Rose Toshihiko Yada Werner R. Loewenstein 《The Journal of membrane biology》1986,94(2):129-142
Summary The viralsrc gene downregulates junctional communication, closing cell-to-cell membrane channels presumably by way of the phosphoinositide signal route. We show that TMB-8 [8-N, N-(diethylamino) octyl-3,4,5-trimethoxybenzoate] counteracts this downregulation in cells transformed by temperature-sensitive mutant Rous sarcoma virus: TMB-8 (36–72 m) raises junctional permeability when applied during activity ofsrc protein kinase, i.e., at steady permissive temperature; and TMB-8 inhibits the fall of junctional permeability, when the activity ofsrc protein kinase gets turned on. TMB-8 also (reversibly) inhibits the growth of the cells at permissive temperature and reverses the morphological changes associated with transformation. The morphological reversal lags several hours behind the junctional-permeability reversal. Communication recovers within a few minutes when the activity of thesrc protein kinase is turned off (in absence of TMB-8). Sodium orthovanadate (20 m) prevents this recovery, but it has no major effect on junctional permeability on its own. We discuss possible modes of action of these agents on critical stages of the signal route, related to intracellular Ca2+ and protein kinase C. 相似文献
69.
Summary Na–K–Cl cotransport stoichiometry and affinities for Na, K and Cl were determined in flounder intestine. Measurement of simultaneous NaCl and RbCl influxes resulted in ratios of 2.2 for Cl/Na and 1.8 for Cl/Rb. The effect of Na and Rb on Rb influx showed first order kinetics withK
1/2 values of 5 and 4.5mm and Hill coefficients of 0.9 and 1.2, respectively. The effect of Cl on rubidium influx showed a sigmoidal relationship withK
1/2 of 20mm and a Hill coefficient of 2.0. The effects of variations in Na and Cl concentration on short-circuit current (I
sc) were also determined. TheK
1/2 for Na was 7mm with a Hill coefficient of 0.9 and theK
1/2 for Cl was 46mm with a Hill coefficient of 1.9. Based on the simultaneous influx measurements, a cotransport stoichiometry of 1Na1K2Cl is concluded. The Hill coefficients for Cl suggest a high degree of cooperativity between Cl binding sites. Measurements of the ratio of net Na and Cl transepithelial fluxes under short-circuit conditions (using a low Na Ringer solution to minimize the passive Na flux) indicate that the Cl/Na flux ratio is approximately 21. Therefore Na recycling from serosa to mucosa does not significantly contribute to theI
sc. Addition of serosal ouabain (100 m) inhibited Rb influx, indicating that Na–K–Cl cotransport is inhibited by ouabain. This finding suggests that a feedback mechanism exists between the Na–K-ATPase on the basolateral membrane and the apical Na–K–2Cl cotransporter. 相似文献
70.
Summary The E1 subgroup (E1, A, Ib, etc.) of antibacterial toxins called colicins are known to form voltage-dependent channels in planar lipid bilayers. The genes for colicins E1, A and Ib have been cloned and sequenced, making these channels interesting models for the widespread phenomenon of voltage dependence in cellular channels. In this paper we investigate ion selectivity and channel size—properties relevant to model building. Our major finding is that the colicin E1 channel is large, having a diameter ofat least 8 Å at its narrowest point. We established this from measurements of reversal potentials for gradients formed by salts of large cations or large anions. In so doing, we exploited the fact that the colicin channel is permeable to both cations and anions, and its relative selectivity to them is a functions and anions, and its relative selectivity to them is a function of pH. The channel is anion selective (Cl– over K+) in neutral membranes, and the degree of selectivity is highly dependent on pH. In negatively charged membranes, it becomes cation selective at pH's higher than about 5. Experiments with pH gradients cross the membrane suggest that titratable groups both within the channel lumen and near the channel ends affect the selectivity. Individual E1 channels have more than one open conductance state, all displaying comparable ion selectivity. Colicins A and Ib also exhibit pH-dependent ion selectivity, and appear to have even larger lumens than E1. 相似文献