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991.
Na+-H+ exchange in rat and mouse renal brush-border membrane vesicles was studied by fluorescence quenching of the delta pH indicator, acridine orange. Brush-border membrane vesicles were isolated by a modified Mg/EGTA-precipitation method at low speed centrifugation (8000 X g). The enzymatic characteristics of these membrane vesicles were similar to those obtained by the original high-speed centrifugation method (Biber et al. (1981) Biochim. Biophys. Acta, 647, 169-176). The rates of Na+-H+ exchange in renal brush-border membrane vesicles from male and female rats were similar. Neither ovariectomy nor treatment of ovariectomized rats with estradiol or testosterone changed the activity of Na+-H+ exchanger. The rates of Na+-H+ exchange in the mouse were smaller than in the rat indicating the existence of species differences. Na+-H+ exchange in mouse renal brush-border membranes exhibit strong sex differences, the rates in the male being higher than in the female. Castration of male mice led to a decrease in Na+-H+ exchange to values found in females. Treatment of castrated mice with estradiol had no effect. In contrast, treatment with testosterone increased the rate of the exchanger by more than 100%. The effect of testosterone was restricted to the Vmax of the Na+-H+ exchanger, whereas the apparent Km for Na+ remained unchanged. Na+-dependent D-glucose transport in mouse renal luminal membranes exhibited also sex differences due to the potent stimulatory effect of testosterone. Therefore, Na+-H+ exchange and Na+-dependent D-glucose transport in the mouse kidney are under control of androgen hormones. This effect could be in close connection with the wellknown renotropic action of androgens in the mouse. 相似文献
992.
K Gawrisch D Stibenz A M?ps K Arnold W Linss K J Halbhuber 《Biochimica et biophysica acta》1986,856(3):443-447
31P-NMR spectra of phospholipids in membranes of erythrocyte microvesicles isolated from outdated blood units were recorded in the temperature range 5 to 55 degrees C. Within that range the lineshape is strongly influenced by an increasing rate of lateral diffusion of phospholipids. At 36 degrees C a diffusion constant, D, of (2 +/- 1) X 10(-12) m2/s was obtained. The diffusion rate is by a factor of 3 to 10 greater than in erythrocyte membranes measured by the photobleaching technique and is comparable with values obtained for several lipid model membranes. The differences in lateral diffusion rates are probably connected with the depletion of microvesicle membranes in membrane proteins. 相似文献
993.
994.
The experimental data of previous papers are considered as a basis for the hypothesis about intraneuronal system controlled by cyclic nucleotides and changing the membrane permeability upon creating the generatory potential. This system is suggested to be an extremal molecular regulator in which the price of action per single operation approximates the physical limit. The electro-mechanical intraneuronal system is capable of solving multidimensional physical problems by means of molecular "digital" hypersound holo-gram coded by DNA molecular text which is an image of functions of target search. 相似文献
995.
996.
Tetraphenylphosphonium is an indicator of negative membrane potential in Candida albicans 总被引:1,自引:0,他引:1
The characteristics of the uptake of lipophilic cations tetraphenylphosphonium (TPP+) into Candida albicans have been investigated to establish whether TPP+ can be used as a membrane potential probe for this yeast. A membrane potential (delta psi, negative inside) across the plasma membrane of C. albicans was indicated by the intracellular accumulation of TPP+. The steady-state distribution of TPP+ was reached within 60 min and varied according to the expected changes of delta psi. Agents known to depolarize membrane potential caused a rapid and complete efflux of accumulated TPP+. The initial influx of TPP+ was linear over a wide range of TPP+ concentrations (2.5-600 microM), indicating a non mediated uptake. Thus, TPP+ is a suitable delta psi probe for this yeast. 相似文献
997.
In a companion paper, the shapes of spectrin deficient mouse erythrocytes were described; in contrast to previous assumptions, spherules with tethered microvesicles rather than true "spherocytes" were found. Thence, spectrin deficient mouse erythrocytes are endowed with an excess of surface area for the given volume but the membrane is assuming a highly positive curvature. Observations during and after the action of enzymes cleaving the red cell surface charge (Neuraminidase, Trypsin, Chymotrypsin) showed that the previously positive membrane curvature, as well as the tendency of the membrane to flow into fingerlike protrusions was completely abolished. The erythrocytes of the spectrin deficient, desialylated mouse erythrocytes assumed a variety of shapes, often discocytic or even stomatocytic, i.e. their membrane presented with negative curvature. However, while these desialylated membranes could be easily deformed (elongated) by shear flow they did not recoil elastically into any definitive configuration after removal of the deforming forces. It is concluded from these observations that spectrin (acting on the inner interface between membrane and cytoplasm) and sialic acid residues (acting on the outer interface between membrane and plasma) exert antagonizing effects on membrane curvature and membrane bending elasticity. Sialic acid residues, strongly charged and situated on the outer side of the cell, produce positive membrane curvature; this observation can most readily be explained by assuming that this mechanical effect is caused by repulsive coulombic forces expanding the outer half of the bilayer. To explain the effect of the spectrin-complex in counteracting positive or in producing negative membrane curvature, a similar expansive coulombic force acting between the highly charged residues has been postulated. Thence, a model for explaining the overall elastic behaviour of the normal mammalian red cell is developed which is based on the assumption of elastic interactions of proteinacous membrane components coupled to the lipid bilayer of the membrane. 相似文献
998.
A new way of assessing the significance of intracellular signals that may regulate cellular proliferation, would be to analyze possible 'second messengers' when proliferation is slowed down, rather than stimulated. Therefore, we examined proliferating mononuclear blood cells from leukaemic patients which had been exposed to an inhibitory ox leucocyte extract. The extract decreased 3H-thymidine incorporation in leukaemic cells in short-term cultures. The inhibition was not cell-line specific, but was nevertheless non-toxic and not due to endotoxin. The K+ flux into the leukaemic cells was assessed with 86Rb+, a K+ analogue. An inverse relationship was found between 86Rb+ uptake and 3H-thymidine incorporation. The increased 86Rb+ influx was probably due to leakage or exchange mechanisms other than the Na+/K+ membrane pump, as suggested by ouabain inhibition experiments. However, the long lag time (greater than 45 min) between addition of inhibitor and a marked increase in 86Rb+ uptake does not support a role for the K+ flux as an early mediator of the inhibitory signal. 相似文献
999.
In cats under pentobarbital anaesthesia, intramotoneuronal administrations of 4-aminopyridine significantly prolong the falling phase of the antidromic action potential but have much less effect on the orthodromic action potential. 4-aminopyridine probably blocks the fast K channels involved in the repolarization of the membrane and indirectly activates ionic channels through enhancement of synaptic transmission, also suggested by the potentiation of excitatory postsynaptic potentials. In many cells, 4-aminopyridine depresses the amplitude and prolongs the time course of the after-hyperpolarization; therefore 4-aminopyridine may also partly block Ca2+-activated K+ channels. 相似文献
1000.
Chromosome condensation activity in the cytoplasm of anucleate and nucleate fragments of mouse oocytes 总被引:3,自引:0,他引:3
The activity of maturation promoting factor (MPF) which causes chromosome condensation and subsequent oocyte maturation was investigated in mouse oocytes using polyethylene-glycol-mediated cell fusion technique. Fully grown oocytes were bisected at germinal vesicle (GV) stage or shortly after germinal vesicle breakdown (GVBD) into anucleate and nucleate fragments. After 2-3 or 15-17 hr of culture these fragments were fused with interphase blastomeres from two-cell embryos. It was found that almost all the anucleate oocyte fragments cultured for a short term (2-3 hr), regardless of whether they were produced at GV stage or after GVBD, induced premature chromosome condensation in the blastomere nuclei, whereas only about 20% of those cultured for a long term (15-17 hr) could do so. On the other hand, the nucleate fragments always retain the cytoplasmic activity to induce chromosome condensation. Thus we suggested that the MPF initially could appear in mouse oocytes independently of the GV, that the mixing of GV material with the oocyte cytoplasm following GVBD had no effect on the activity of MPF in anucleate fragments, and that oocyte chromosomes or some components associated with them could play a significant role in maintaining the MPF activity. 相似文献