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91.
Summary The Na+ requirement for active, electrogenic Cl– absorption byAmphiuma small intestine was studied by tracer techniques and double-barreled Cl–-sensitive microelectrodes. Addition of Cl– to a Cl–-free medium bathingin vitro intestinal segments produced a saturable (K
m
=5.4mm) increase in shortcircuit current (I
sc) which was inhibitable by 1mm SITS. The selectivity sequence for the anion-evoked current was Cl–=Br–>SCN–>NO
3
–
>F–=I–. Current evoked by Cl– reached a maximum with increasing medium Na concentration (K
m
=12.4mm). Addition of Na+, as Na gluconate (10mm), to mucosal and serosal Na+-free media stimulated the Cl– current and simultaneously increased the absorptive Cl– flux (J
ms
Cl
) and net flux (J
net
Cl
) without changing the secretory Cl– flux (J
sm
Cl
). Addition of Na+ only to the serosal fluid stimulatedJ
ms
Cl
much more than Na+ addition only to the mucosal fluid in paired tissues. Serosal DIDS (1mm) blocked the stimulation. Serosal 10mm Tris gluconate or choline gluconate failed to stimulateJ
ms
Cl
. Intracellular Cl– activity (a
Cl
i
) in villus epithelial cells was above electrochemical equilibrium indicating active Cl– uptake. Ouabain (1mm) eliminated Cl– accumulation and reduced the mucosal membrane potential
m
over 2 to 3 hr. In contrast, SITS had no effect on Cl– accumulation and hyperpolarized the mucosal membrane. Replacement of serosal Na+ with choline eliminated Cl– accumulation while replacement of mucosal Na+ had no effect. In conclusion by two independent methods active electrogenic Cl– absorption depends on serosal rather than mucosal Na+. It is concluded that Cl– enters the cell via a primary (rheogenic) transport mechanism. At the serosal membrane the Na+ gradient most likely energizes H+ export and regulates mucosal Cl– accumulation perhaps by influencing cell pH or HCO
3
–
concentration. 相似文献
92.
93.
94.
95.
Some properties of monolayers of (POPG) alone or of POPG in mixtures with (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm2·s?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m?1 in the presence of Na+, Ca2+ or low pH (2.0) in the subphase. (3) The presence of Ca2+ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na+ or Ca2+ in the subphase. 相似文献
96.
L G Hudson R Shaikh W A Toscano W F Greenlee 《Biochemical and biophysical research communications》1983,115(2):611-617
The responsiveness of 5 human squamous cell carcinoma (SCC) lines derived from tumors of the epidermis and tongue to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) was assessed by measuring the induction of the cytochrome P1-450-mediated monooxygenase activity, 7-ethoxycoumarin O-deethylase (ECOD). In 4 of the SCC lines the EC50 for this response was approximately 10(-9)M, whereas in one line the EC50 was 10(-10)M. In each of the less sensitive lines a concentration of 10(-10)M TCDD elicited less than 5% of the maximal enzyme activity. Specific binding of radiolabeled TCDD was detected in the cytosol fraction from all the SCC lines. The relative amount of receptor measured in each line correlated with maximally-induced ECOD activity. The data indicate that human cell lines derived from a target tissue for TCDD toxicity contain the TCDD receptor and show differential sensitivity to TCDD analogous to the murine strain differences in sensitivity regulated by the Ah locus. 相似文献
97.
The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime (“dwarfing” phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by O2 uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity. 相似文献
98.
Properties of a neutral allele model with intragenic recombination 总被引:35,自引:0,他引:35
R R Hudson 《Theoretical population biology》1983,23(2):183-201
An infinite-site neutral allele model with crossing-over possible at any of an infinite number of sites is studied. A formula for the variance of the number of segregating sites in a sample of gametes is obtained. An approximate expression for the expected homozygosity is also derived. Simulation results are presented to indicate the accuracy of the approximations. The results concerning the number of segregating sites and the expected homozygosity indicate that a two-locus model and the infinite-site model behave similarly for 4Nu less than or equal to 2 and r less than or equal to 5u, where N is the population size, u is the neutral mutation rate, and r is the recombination rate. Simulations of a two-locus model and a four-locus model were also carried out to determine the effect of intragenic recombination on the homozygosity test of Watterson (Genetics 85, 789-814; 88, 405-417) and on the number of unique alleles in a sample. The results indicate that for 4Nu less than or equal to 2 and r less than or equal to 10u, the effect of recombination is quite small. 相似文献
99.
Synthesis and characterization of two fluorescent sulfhydryl reagents 总被引:20,自引:0,他引:20
100.