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排序方式: 共有288条查询结果,搜索用时 15 毫秒
1.
Inhibition of dihydropyridine-sensitive calcium channels by the plant alkaloid ryanodine 总被引:4,自引:0,他引:4
At micromolar concentrations, ryanodine interacts with the dihydropyridine receptor of rabbit skeletal muscle transverse tubules. Ryanodine displaces specifically bound [3H]PN200-110 with an apparent inhibition constant of approx. 95 microM and inhibits dihydropyridine-sensitive calcium channels in the same preparation with an IC50 of approx. 45 microM. These concentrations of ryanodine are approximately three orders of magnitude higher than those required to saturate binding of the alkaloid to the ryanodine receptor of sarcoplasmic reticulum and to open the calcium release channel of sarcoplasmic reticulum (i.e. 20 nM (1988) J. Gen. Physiol. 92, 1-26). Thus at sufficiently high dose, ryanodine may affect SR as well as plasma membrane Ca permeabilities. 相似文献
2.
Insulation of the conduction pathway of muscle transverse tubule calcium channels from the surface charge of bilayer phospholipid 总被引:14,自引:9,他引:5
Functional calcium channels present in purified skeletal muscle transverse tubules were inserted into planar phospholipid bilayers composed of the neutral lipid phosphatidylethanolamine (PE), the negatively charged lipid phosphatidylserine (PS), and mixtures of both. The lengthening of the mean open time and stabilization of single channel fluctuations under constant holding potentials was accomplished by the use of the agonist Bay K8644. It was found that the barium current carried through the channel saturates as a function of the BaCl2 concentration at a maximum current of 0.6 pA (at a holding potential of 0 mV) and a half-saturation value of 40 mM. Under saturation, the slope conductance of the channel is 20 pS at voltages more negative than -50 mV and 13 pS at a holding potential of 0 mV. At barium concentrations above and below the half-saturation point, the open channel currents were independent of the bilayer mole fraction of PS from XPS = 0 (pure PE) to XPS = 1.0 (pure PS). It is shown that in the absence of barium, the calcium channel transports sodium or potassium ions (P Na/PK = 1.4) at saturating rates higher than those for barium alone. The sodium conductance in pure PE bilayers saturates as a function of NaCl concentration, following a curve that can be described as a rectangular hyperbola with a half-saturation value of 200 mM and a maximum conductance of 68 pS (slope conductance at a holding potential of 0 mV). In pure PS bilayers, the sodium conductance is about twice that measured in PE at concentrations below 100 mM NaCl. The maximum channel conductance at high ionic strength is unaffected by the lipid charge. This effect at low ionic strength was analyzed according to J. Bell and C. Miller (1984. Biophysical Journal. 45:279-287) and interpreted as if the conduction pathway of the calcium channel were separated from the bilayer lipid by approximately 20 A. This distance thereby effectively insulates the ion entry to the channel from the bulk of the bilayer lipid surface charge. Current vs. voltage curves measured in NaCl in pure PE and pure PS show that similarly small surface charge effects are present in both inward and outward currents. This suggests that the same conduction insulation is present at both ends of the calcium channel. 相似文献
3.
Effect of divalent cations on the assembly of neutral and charged phospholipid bilayers in patch-recording pipettes. 总被引:1,自引:1,他引:0 下载免费PDF全文
R Coronado 《Biophysical journal》1985,47(6):851-857
Monolayers of the negatively charged phospholipid phosphatidylserine (PS) and of the amphoteric phospholipid dioleoylphosphatidylethanolamine (DOPE) were used to assemble bilayers at the tip of patch-recording pipettes. PS bilayers, with seal resistances in the range of gigaohmns (gigaseals), could only be generated when millimolar concentration of divalent cations, Ca++, Mg++, or Ba++ were present in the pipette and bath solutions. In contrast, gigaseals of DOPE were independent of divalent ion concentration in the pH range where DOPE is predominantly neutral (pH 6.5) or positively charged (pH 1.5). At pH 10.0, when most DOPE molecules bear a net negative charge, gigaseals became divalent cation dependent, in a manner quantitatively similar to that of PS at neutral pH. The results indicate that divalent cations play an important role in stabilizing gigaseals of negatively charged lipid but are of no consequence in neutral or positively charged seals. 相似文献
4.
T J Connelly R E Hayek B F Rusy R Coronado 《Biochemical and biophysical research communications》1992,186(1):595-600
The effect of clinical concentrations of volatile anesthetics on ryanodine receptors of cardiac and skeletal muscle sarcoplasmic reticulum was evaluated using [3H]ryanodine binding. At 2 volume percent, halothane and enflurane stimulated binding to cardiac SR by 238% and 204%, respectively, while isoflurane had no effect. In contrast, halothane and enflurane had no effect on [3H]ryanodine binding to skeletal ryanodine receptors, while isoflurane produced a significant stimulation. These results suggest that volatile anesthetics interact in a site-specific manner with ryanodine receptors of cardiac or skeletal muscle to effect Ca2+ release-channel gating. 相似文献
5.
There is increasing evidence that Ca2+ release from sarcoplasmic reticulum (SR) of mammalian skeletal muscle is regulated or modified by several factors including
ionic composition of the myoplasm. We have studied the effect of Cl− on the release of Ca2+ from the SR of rabbit skeletal muscle in both skinned psoas fibers and in isolated terminal cisternae vesicles. Ca2+ release from the SR in skinned fibers was inferred from increases in isometric tension and the amount of release was assessed
by integrating the area under each tension transient. Ca2+ release from isolated SR was measured by rapid filtration of vesicles passively loaded with 45Ca2+. Ca2+ release from SR was stimulated in both preparations by exposure to a solution containing 191 mm choline-Cl, following pre-equilibration in Ca2+-loading solution that had propionate as the major anion. Controls using saponin (50 μg/ml), indicated that the release of
Ca2+ was due to direct action of Cl− on the SR rather than via depolarization of T-tubules. Procaine (10 mm) totally blocked Cl−- and caffeine-elicited tension transients recorded using loading and release solutions having ([Na+] + [K+]) × [Cl−] product of 6487.69 mm
2 and 12361.52 mm
2, respectively, and blocked 60% of Ca2+ release in isolated SR vesicles. Surprisingly, procaine had only a minor effect on tension transients elicited by Cl− and caffeine together. The data from both preparations suggests that Cl− induces a relatively small amount of Ca2+ release from the SR by activating receptors other than RYR-1. In addition, Cl− may increase the Ca2+ sensitivity of RYR-1, which would then allow the small initial release of Ca2+ to facilitate further release of Ca2+ from the SR by Ca2+-induced Ca2+ release.
Received: 6 February 1996/Revised: 17 July 1996 相似文献
6.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
7.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
8.
The significance of polyoxometalates in the field of molecular magnetism is discussed. We show that this kind of inorganic complexes provides remarkable examples for the study of the exchange interactions in clusters. On the other hand, we examine the possibility of using these metal oxide anions as magnetic components of molecular materials containing organic tetrathiafulvalenes as electron donor molecules. 相似文献
9.
C. Coronado B. Sánchez-Andújar A. J. Palomares 《World journal of microbiology & biotechnology》1996,12(2):127-136
The extracellular and surface polysaccharides produced by Rhizobium species constitute a composite macromolecular interface between the bacterial cell and its environment. Several of these polysaccharides are involved in the complex series of interactions leading to the establishment of an effective Rhizobium-legume symbiosis. Extracellular heteropolysaccharides (EPSs) are found in culture supernatants, while capsular polysaccharides adhere to the cell surface. Cyclic (1–2)--d glucan is a periplasmic oligosaccharide that has also been found in the culture supernatants of some strains. The lipopolysaccharides (LPSs), which form part of the outer membrane and contain the O-somatic antigens, comprise the other major group of extracellular polysaccharides. In this review we will describe the major Rhizobium extracellular structures and their role in symbiosis with leguminous plants.The authors are with the Departamento de Microbiologia y Parasitologia, Facultad de Farmacia. Universidad de Sevilla, 41012 Sevilla, Spain 相似文献
10.
Thermodynamic and kinetic studies of the gating behavior of a K+- selective channel from the sarcoplasmic reticulum membrane 总被引:4,自引:4,他引:0 下载免费PDF全文
A voltage-dependent, K+-selective ionic channel from sarcoplasmic reticulum of rabbit skeletal muscle has been studied in a planar phospholipid bilayer membrane. The purpose [corrected] of this work is to study the mechanism by which the channel undergoes transitions between its conducting and nonconducting states. Thermodynamic studies show that the "open" and "closed" states of the channel exist in a voltage-dependent equilibrium, and that the channel displays only a single open state; the channel conductance is 120 pmho in 0.1 M K+. The channel's gating process follows single exponential kinetics at all voltages tested, and the individual opening and closing rate constants are exponentially dependent on voltage. The individual rate constants may also be determined from a stochastic analysis of channel fluctuations among multiple conductance levels. Neither the thermodynamic nor the kinetic parameters of gating depend on the absolute concentration of channels in the bilayer. The results are taken as evidence that the channel gates by an unusually simple two-state conformational mechanism in which the equivalent of 1.1 net charges are moved across the membrane during the formation of the open channel. 相似文献