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1.
Adam Eyre-Walker 《Journal of molecular evolution》1998,47(6):686-690
Parsimony is commonly used to infer the direction of substitution and mutation. However, it is known that parsimony is biased
when the base composition of the DNA sequence is skewed. Here I quantify this effect for several simple cases. The analysis
demonstrates that parsimony can be misleading even when levels of sequence divergence are as low as 10%; parsimony incorrectly
infers an excess of common to rare changes. Caution must therefore be excercised in the use of parsimony.
Received: 13 November 1997 / Accepted: 18 June 1998 相似文献
2.
Mitochondrial Genes Collectively Suggest the Paraphyly of Crustacea with Respect to Insecta 总被引:9,自引:0,他引:9
Erik García-Machado Malgorzata Pempera Nicole Dennebouy Mario Oliva-Suarez Jean-Claude Mounolou Monique Monnerot 《Journal of molecular evolution》1999,49(1):142-149
Complete sequences of seven protein coding genes from Penaeus notialis mitochondrial DNA were compared in base composition and codon usage with homologous genes from Artemia franciscana and four insects. The crustacean genes are significantly less A + T-rich than their counterpart in insects and the pattern
of codon usage (ratio of G + C-rich versus A + T-rich codon) is less biased. A phylogenetic analysis using amino acid sequences
of the seven corresponding polypeptides supports a sister-taxon status for mollusks–annelid and arthropods. Furthermore, a
distance matrix-based tree and two most-parsimonious trees both suggest that crustaceans are paraphyletic with respect to
insects. This is also supported by the inclusion of Panulirus argus COII (complete) and COI and COIII (partial) sequence data. From analysis of single and combined genes to infer phylogenies,
it is observed that obtained from single genes are not well supported in most topologies cases and notably differ from that
of the tree based on all seven genes.
Received: 25 August 1998 / Accepted: 8 March 1999 相似文献
3.
To study the evolution of mtDNA and the intergeneric relationships of New World Jays (Aves: Corvidae), we sequenced the entire
mitochondrial DNA control region (CR) from 21 species representing all genera of New World jays, an Old World jay, crows,
and a magpie. Using maximum likelihood methods, we found that both the transition/transversion ratio (κ) and among site rate
variation (α) were higher in flanking domains I and II than in the conserved central domain and that the frequency of indels
was highest in domain II. Estimates of κ and α were much more influenced by the density of taxon sampling than by alternative
optimal tree topologies. We implemented a successive approximation method incorporating these parameters into phylogenetic
analysis. In addition we compared our study in detail to a previous study using cytochrome b and morphology to examine the effect of taxon sampling, evolutionary rates of genes, and combined data on tree resolution.
We found that the particular weighting scheme used had no effect on tree topology and little effect on tree robustness. Taxon
sampling had a significant effect on tree robustness but little effect on the topology of the best tree. The CR data set differed
nonsignificantly from the tree derived from the cytochrome b/morphological data set primarily in the placement of the genus Gymnorhinus, which is near the base of the CR tree. However, contrary to conventional taxonomy, the CR data set suggested that blue and
black jays (Cyanocorax sensu lato) might be paraphyletic and that the brown jay Psilorhinus (=Cyanocorax) morio is the sister group to magpie jays (Calocitta), a phylogenetic hypothesis that is likely as parsimonious with regard to nonmolecular characters as monophyly of Cyanocorax. The CR tree also suggests that the common ancestor of NWJs was likely a cooperative breeder. Consistent with recent systematic
theory, our data suggest that DNA sequences with high substitution rates such as the CR may nonetheless be useful in reconstructing
relatively deep phylogenetic nodes in avian groups.
Received: 10 November 1999 / Accepted: 16 March 2000 相似文献
4.
Song-Kun Shyue Stéphane Boissinot Horacio Schneider Iracilda Sampaio Maria Paula Schneider C.R. Abee Lawrence Williams David Hewett-Emmett Harry G. Sperling Jill A. Cowing Kanwaljit S. Dulai David M. Hunt Wen-Hsiung Li 《Journal of molecular evolution》1998,46(6):697-702
Although most New World monkeys have only one X-linked photopigment locus, many species have three polymorphic alleles at
the locus. The three alleles in the squirrel monkey and capuchin have spectral peaks near 562, 550, and 535 nm, respectively,
and the three alleles in the marmoset and tamarin have spectral peaks near 562, 556, and 543 nm, respectively. To determine
the amino acids responsible for the spectral sensitivity differences among these pigment variants, we sequenced all exons
of the three alleles in each of these four species. From the deduced amino acid sequences and the spectral peak information
and from previous studies of the spectral tuning of X-linked pigments in humans and New World monkeys, we estimated that the
Ala → Ser, Ile → Phe, Gly → Ser, Phe → Tyr, and Ala → Tyr substitutions at residue positions 180, 229, 233, 277, and 285,
respectively, cause spectral shifts of about 5, −2, −1, 8, and 15 nm. On the other hand, the substitutions His → Tyr, Met
→ Val or Leu, and Ala → Tyr at positions 116, 275, and 276, respectively, have no discernible spectral tuning effect, though
residues 275 and 276 are inside the transmembrane domains. Many substitutions between Val and Ile or between Val and Ala have
occurred in the transmembrane domains among the New World monkey pigment variants but apparently have no effect on spectral
tuning. Our study suggests that, in addition to amino acid changes involving a hydroxyl group, large changes in residue size
can also cause a spectral shift in a visual pigment.
Received: 17 July 1997 / Accepted: 7 December 1997 相似文献
5.
Synonymous substitution rates in mitochondrial and nuclear genes of Drosophila were compared. To make accurate comparisons, we considered the following: (1) relative synonymous rates, which do not require
divergence time estimates, should be used; (2) methods estimating divergence should take into account base composition; (3)
only very closely related species should be used to avoid effects of saturation; (4) the heterogeneity of rates should be
examined. We modified the methods estimating synonymous substitution numbers to account for base composition bias. By using
these methods, we found that mitochondrial genes have 1.7–3.4 times higher synonymous substitution rates than the fastest
nuclear genes or 4.5–9.0 times higher rates than the average nuclear genes. The average rate of synonymous transversions was
2.7 (estimated from the melanogaster species subgroup) or 2.9 (estimated from the obscura group) times higher in mitochondrial genes than in nuclear genes. Synonymous transversions in mitochondrial genes occurred
at an approximately equivalent rate to those in the fastest nuclear genes. This last result is not consistent with the hypothesis
that the difference in turnover rates between mitochondrial and nuclear genomes is the major factor determining higher synonymous
substitution rates in mtDNA. We conclude that the difference in synonymous substitution rates is due to a combination of two
factors: a higher transitional mutation rate in mtDNA and constraints on nuclear genes due to selection for codon usage.
Received: 27 November 1996 / Accepted: 8 May 1997 相似文献
6.
McClellan DA 《Journal of molecular evolution》2000,51(3):185-193
The codon-degeneracy model (CDM) predicts relative frequencies of substitution for any set of homologous protein-coding DNA
sequences based on patterns of nucleotide degeneracy, codon composition, and the assumption of selective neutrality. However,
at present, the CDM is reliant on outside estimates of transition bias. A new method by which the power of the CDM can be
used to find a synonymous transition bias that is optimal for any given phylogenetic tree topology is presented. An example
is illustrated that utilizes optimized transition biases to generate CDM GF-scores for every possible phylogenetic tree for
pocket gophers of the genus Orthogeomys. The resulting distribution of CDM GF-scores is compared and contrasted with the results of maximum parsimony and maximum
likelihood methods. Although convergence on a single tree topology by the CDM and another method indicates greater support
for that particular tree, the value of CDM GF-score as the sole optimality criterion for phylogeny reconstruction remains
to be determined. It is clear, however, that the a priori estimation of an optimum transition bias from codon composition
has a direct application to differentiating between alternative trees.
Received: 13 October 1999 / Accepted: 28 April 2000 相似文献
7.
Dorothy E. Pumo Peter S. Finamore William R. Franek Carleton J. Phillips Sima Tarzami Darlene Balzarano 《Journal of molecular evolution》1998,47(6):709-717
The complete mitochondrial genome was obtained from a microchiropteran bat, Artibeus jamaicensis. The presumptive amino acid sequence for the protein-coding genes was compared with predicted amino acid sequences from several
representatives of other mammalian orders. Data were analyzed using maximum parsimony, maximum likelihood, and neighbor joining.
All analyses placed bats as the sister group of carnivores, perissodactyls, artiodactyls, and cetaceans (e.g., 100% bootstrap
value with both maximum parsimony and neighbor joining). The data strongly support a new hypothesis about the origin of bats,
specifically a bat/ferungulate grouping. None of the analyses supported the superorder Archonta (bats, flying lemurs, primates,
and tree shrews). Our hypothesis regarding the relationship of bats to other eutherian mammals is concordant with previous
molecular studies and contrasts with hypotheses based solely on morphological criteria and an incomplete fossil record. The
A. jamaicensis mitochondrial DNA control region has a complex pattern of tandem repeats that differs from previously reported chiropteran
control regions.
Received: 22 January 1998 / Accepted: 3 June 1998 相似文献
8.
This paper reports an intraorder study on the D-loop-containing region of the mitochondrial DNA in rodents. A complete multialignment
of this region is not feasible with the exception of some conserved regions. The comparative analysis of 25 complete rodent
sequences from 23 species plus one lagomorph has revealed that only the central domain (CD), a conserved region of about 80
bp in the extended termination-associated sequences (ETAS) domain, adjacent to the CD, the ETAS1, and conserved sequence block
(CSB) 1 blocks are present in all rodent species, whereas the presence of CSB2 and CSB3 is erratic within the order. We have
also found a conserved region of 90 bp located between tRNAPro and ETAS1 present in fat dormouse, squirrel, guinea pig, and
rabbit. Repeated sequences are present in both the ETAS and the CSB domain, but the repeats differ in length, copy number,
and base composition in different species. The potential use of the D-loop for evolutionary studies has been investigated;
the presence/absence of conserved blocks and/or repeated sequences cannot be used as a reliable phylogenetic marker, since
in some cases they may be shared by distantly related organisms but not by close ones, while in other ones a relationship
between tree topology and presence/absence of such motifs is observed. Better results can be obtained by the use of the CD,
which, however, due to its reduced size, when used for tracing a phylogenetic tree, shows some nodes with low statistical
support.
Received: 26 February 2001 / Accepted: 6 June 2001 相似文献
9.
Boron enters plant roots as undissociated boric acid (H3BO3). Significant differences in B uptake are frequently observed even when plants are grown under identical conditions. It has
been theorized that these differences reflect species differences in permeability coefficient of H3BO3 across plasma membrane. The permeability coefficient of boric acid however, has not been experimentally determined across
any artificial or plant membrane. In the experiments described here the permeability coefficient of boric acid in liposomes
made of phosphatidylcholine was 4.9 × 10−6 cm sec−1, which is in good agreement with the theoretical value. The permeability coefficient varied from 7 × 10−6 to 9.5 × 10−9 cm sec−1 with changes in sterols (cholesterol), the type of phospholipid head group, the length of the fatty acyl chain, and the pH
of the medium. In this study we also used Arabidopsis thaliana mutants which differ in lipid composition to study the effect of lipid composition on B uptake. The chs1-1 mutant which has lower proportion of sterols shows 30% higher B uptake compared with the wild type, while the act1-1 mutant which has an increased percentage of longer fatty acids, exhibited 35% lower uptake than the wild type. Lipid composition
changes in each of the remaining mutants influenced B uptake to various extents. These data suggest that lipid composition
of the plasma membrane can affect total B uptake.
Received: 15 October 1999/Revised: 11 February 2000 相似文献
10.
Phylogenetic relationships of annelids,molluscs, and arthropods evidenced from molecules and morphology 总被引:10,自引:0,他引:10
Chang Bae Kim Seung Yeo Moon Stuart R. Gelder Won Kim 《Journal of molecular evolution》1996,43(3):207-215
Annelids and arthropods have long been considered each other's closest relatives, as evidenced by similarities in their segmented
body plans. An alternative view, more recently advocated by investigators who have examined partial 18S ribosomal RNA data,
proposes that annelids, molluscs, and certain other minor phyla with trochophore larva stages share a more recent common ancestor
with one another than any do with arthropods. The two hypotheses are mutually exclusive in explaining spiralian relationships.
Cladistic analysis of morphological data does not reveal phylogentic relationships among major spiralian taxa but does suggest
monophyly for both the annelids and molluscs. Distance and maximum-likelihood analyses of 18S rRNA gene sequences from major
spiralian taxa suggest a sister relationship between annelids and molluscs and provide a clear resolution within the major
groups of the spiralians. The parsimonious tree based on molecular data, however, indicates a sister relationship of the Annelida
and Bivalvia, and an earlier divergence of the Gastropoda than the Annelida–Bivalvia clade. To test further hypotheses on
the phylogenetic relationships among annelids, molluscs, and arthropods, and the ingroup relationships within the major spiralian
taxa, we combine the molecular and morphological data sets and subject the combined data matrix to parsimony analysis. The
resulting tree suggests that the molluscs and annelids form a monophyletic lineage and unites the molluscan taxa to a monophyletic
group. Therefore, the result supports the Eutrochozoa hypothesis and the monophyly of molluscs, and indicates early acquisition
of segmented body plans in arthropods.
Received: 25 September 1995 / Accepted: 15 March 1996 相似文献
11.
Peek AS Gaut BS Feldman RA Barry JP Kochevar RE Lutz RA Vrijenhoek RC 《Journal of molecular evolution》2000,50(2):141-153
Nucleotide sequences at two mitochondrial genes from 57 individuals representing eight species of deep-sea clams (Vesicomyidae)
were examined for variation consistent with the neutral model of molecular evolution. One gene, cytochrome oxidase subunit
I (COI), deviated from the expectations of neutrality by containing an excess of intraspecific nonsynonymous polymorphism.
Additionally, one species, Calyptogena kilmeri, showed a significant excess of rare polymorphism specifically at the COI locus. In contrast, a second mitochondrial gene,
the large-subunit 16S ribosomal RNA gene (16S), showed little deviation from neutrality either between or within species.
Together, COI and 16S show no deviation from neutral expectations by the HKA test, produce congruent phylogenetic relationships
between species, and show correlated numbers of fixed differences between species and polymorphism within species. These patterns
of both neutral and nonneutral evolution within the mitochondrial genome are most consistent with a model where intraspecific
nonsynonymous polymorphism at COI is near neutrality. In addition to examining the forces of molecular evolution, we extend
hypotheses about interspecific relationships within this family for geographical locations previously unexamined by molecular
methods including habitats near the Middle Atlantic, the Aleutian Trench, and Costa Rica.
Received: 10 March 1999 / Accepted: 13 September 1999 相似文献
12.
Ballard JW 《Journal of molecular evolution》2000,51(1):64-75
The current study compares the nucleotide variation among 22 complete mitochondrial genomes of the three distinct Drosophila simulans haplotypes with intron 1 of the alcohol dehydrogenase-related locus. This is the first study to investigate the sequence variation of multiple complete mitochondrial genomes within distinct
mitochondrial haplotypes of a single species. Patterns of variation suggest distinct forces are influencing the evolution
of mitochondrial DNA (mtDNA) and autosomal DNA in D. simulans. First, there is little variation within each mtDNA haplotype but strong differentiation among them. In contrast, there is
no support for differentiation of the mitochondrial haplotypes at the autosomal locus. Second, there is a significant deficiency
of mitochondrial variation in each haplotype relative to the autosomal locus. Third, the ratio of nonsynonymous to synonymous
substitutions is not equal in all branches of the well-resolved phylogeny. There is an excess of nonsynonymous substitutions
relative to synonymous substitutions within each D. simulans haplotype. This result is similar to that previously observed within the mtDNA of distinct species. A single evolutionary
force may be causally linked to the observed patterns of mtDNA variation—a rickettsia-like microorganism, Wolbachia pipientis, which is known to directly influence mitochondrial evolution but have a less direct influence on autosomal loci.
Received: 16 September 1999 / Accepted: 14 March 2000 相似文献
13.
14.
To determine the origin and evolutionary significance of a recently discovered isoform of the estrogen receptor (ERβ), we
examined the phylogenetic relationship of ERβ to the well-known α isoform (ERα) and other steroid receptors. Our phylogenetic
analyses traced the origin of ERβ to a single duplication event at least 450 million years ago. Since this duplication, the
evolution of both ER isoforms has apparently been constrained such that 80% of the amino acid positions in the DNA binding
domain (DBD) and 53% of the ligand binding domain (LBD) have remained unchanged. Using the phylogenetic tree, we determined
the amount of evolutionary change that had occurred in two ER isoforms. The DBD and the LBD had lower rates of evolutionary
change compared to the NH2 terminal domain. However, even with strong selective constraints on the DBD and LBD, our phylogenetic analyses demonstrate
two clearly separate phylogenetic histories for ERα and ERβ dating back several hundred million years. The ancient duplication
of ER and the parallel evolution of the two ER isoforms suggest that, although ERα and ERβ share a substantial degree of sequence
identity, they play unique roles in vertebrate physiology and reproduction.
Received: 19 January 1999 / Accepted: 26 May 1999 相似文献
15.
Bocchetta M Gribaldo S Sanangelantoni A Cammarano P 《Journal of molecular evolution》2000,50(4):366-380
The phylogenetic placement of the Aquifex and Thermotoga lineages has been inferred from (i) the concatenated ribosomal proteins S10, L3, L4, L23, L2, S19, L22, and S3 encoded in
the S10 operon (833 aa positions); (ii) the joint sequences of the elongation factors Tu(1α) and G(2) coded by the str operon tuf and fus genes (733 aa positions); and (iii) the joint RNA polymerase β- and β′-type subunits encoded in the rpoBC operon (1130 aa positions). Phylogenies of r-protein and EF sequences support with moderate (r-proteins) to high statistical confidence (EFs) the placement of the two hyperthermophiles at the base of the bacterial clade
in agreement with phylogenies of rRNA sequences. In the more robust EF-based phylogenies, the branching of Aquifex and Thermotoga below the successive bacterial lineages is given at bootstrap proportions of 82% (maximum likelihood; ML) and 85% (maximum
parsimony; MP), in contrast to the trees inferred from the separate EF-Tu(1α) and EF-G(2) data sets, which lack both resolution
and statistical robustness. In the EF analysis MP outperforms ML in discriminating (at the 0.05 level) trees having A. pyrophilus and T. maritima as the most basal lineages from competing alternatives that have (i) mesophiles, or the Thermus genus, as the deepest bacterial radiation and (ii) a monophyletic A. pyrophilus–T. maritima cluster situated at the base of the bacterial clade. RNAP-based phylogenies are equivocal with respect to the Aquifex and Thermotoga placements. The two hyperthermophiles fall basal to all other bacterial phyla when potential artifacts contributed by the
compositionally biased and fast-evolving Mycoplasma genitalium and Mycoplasma pneumoniae sequences are eschewed. However, the branching order of the phyla is tenuously supported in ML trees inferred by the exhaustive
search method and is unresolved in ML trees inferred by the quartet puzzling algorithm. A rooting of the RNA polymerase-subunit
tree at the mycoplasma level seen in both the MP trees and the ML trees reconstructed with suboptimal amino acid substitution
models is not supported by the EF-based phylogenies which robustly affiliate mycoplasmas with low-G+C gram-positives and,
most probably, reflects a ``long branch attraction' artifact.
Received: 22 September 1999 / Accepted: 11 January 2000 相似文献
16.
Molecular Evolution of Cytochrome b of Subterranean Mole Rats, Spalax ehrenbergi Superspecies, in Israel 总被引:1,自引:0,他引:1
We describe the molecular evolution of cytochrome b of blind subterranean mole rats. We examined 12 individuals for nucleotide differences in the region of 402 base pairs of
mitochondrial cytochrome b. Each individual represents a different population from the entire ecological and speciational range of the four chromosomal
species in Israel (2n= 52, 54, 58, and 60) belonging to the Spalax ehrenbergi superspecies. Our results indicate the following. (i) There are seven first-position transitional differences, compared to
34 variable third positions, with no observed second-position substitutions. (ii) A maximum of four amino acids differences
occurs across the range. (iii) Within-species diversity increases southward. Only 1 autoapomorphic substitution characterizes
either 2n= 52 or 2n= 54, but 6–11 substitutions characterize 2n= 58, and 9–13 substitutions characterize 2n= 60. (iv) Both parsimony and maximum-likelihood trees suggest two monophyletic groups: (a) 2n= 52 and 54, and (b) 2n= 58 and 60, as identified earlier by other protein and DNA markers. (v) Mitochondrial cytochrome b heterogeneity is significantly correlated with climatic factors (rainfall) and biotic factors (body size and allozymes).
We hypothesize that two selective regimes direct cytochrome b evolution in the S. ehrenbergi superspecies: (i) purifying selection in the flooded, mesic, hypoxic northern range of 2n= 52 and 54 and (ii) diversifying selection in the climatically spatiotemporal, xeric, and variable southern range of 2n= 58 and 60. Thus, the molecular evolution of mitochondrial cytochrome b in S. ehrenbergi is explicable by opposite selective stresses across the range of S. ehrenbergi in Israel, associated with the ecological adaptive radiation of the complex.
Received: 23 October 1998 / Accepted: 2 May 1999 相似文献
17.
J. Robert Macey Allan Larson Natalia B. Ananjeva Theodore J. Papenfuss 《Journal of molecular evolution》1997,44(6):660-674
A phylogenetic tree for major lineages of iguanian lizards is estimated from 1,488 aligned base positions (858 informative)
of newly reported mitochondrial DNA sequences representing coding regions for eight tRNAs, ND2, and portions of ND1 and COI.
Two well-supported groups are defined, the Acrodonta and the Iguanidae (sensu lato). This phylogenetic hypothesis is used
to investigate evolutionary shifts in mitochondrial gene order, origin for light-strand replication, and secondary structure
of tRNACys. These three characters shift together on the branch leading to acrodont lizards. Plate tectonics and the fossil record indicate
that these characters changed in the Jurassic. We propose that changes to the secondary structure of tRNACys may destroy function of the origin for light-strand replication which, in turn, may facilitate shifts in gene order.
Received: 28 May 1996 / Accepted: 27 December 1996 相似文献
18.
Tominaga O Su ZH Kim CG Okamoto M Imura Y Osawa S 《Journal of molecular evolution》2000,50(6):541-549
Phylogenetic analyses based on the mitochondrial ND5 gene comparisons and the geohistory of the Japanese Islands suggest
that each Japanese species belonging to the subtribe Carabina has its own history for the establishment of its present habitat
in the Japanese Islands. It can be roughly classified into two categories: (1) species which were derived from the ancestry
that inhabited ancient Japan at the time of its split from the Eurasian Continent [ca. 15 million years ago (MYA)], followed
by diversification within the Japanese Islands; and (2) species which invaded Hokkaido from the Eurasian Continent through
land-bridges from Sakhalin and/or the Kuriles or from western Japan from the Korean Peninsula during the glacial era (<2 MYA).
Received: 28 September 1999 / Accepted: 25 February 2000 相似文献
19.
To identify conserved features in the rapidly diverging portions of a well-conserved locus, completely sequenced in Plasmodium falciparum and Plasmodium berghei, a computational method based on recurrence analysis was exploited. At the level of the genomic sequence, in both species,
introns and intergenic sequences—though subject to rapid diversification—do not drift without constraints, but rather coevolve,
in the sense that they maintain not only an AT-rich base composition, but also a consistent use of recurring (AT)
n
tracts. One of the two genes present in the conserved locus encodes a protein that exhibits blocks of high similarity to
the first enzyme in glutathione biosynthesis (γ-glutamylcysteine synthetase) but bears long low-complexity insertions, absent
in other organisms. From an analysis of the aminoacid sequence, different constraints appear to act on the borders and on
the central part of the insertions. Albeit maintaining a strong bias toward hydrophylic residues, central portions diverge
more rapidly than borders, through point mutation and differential presence of entire tracts.
Received: 20 September 1999 / Accepted: 9 February 2000 相似文献
20.
We hypothesized that inhibition and activation of basolateral to luminal chloride transport mechanisms were associated with
respective decreases and increases in basolateral to luminal water fluxes. The luminal to basolateral (J
W
L→B
) and basolateral to luminal (J
W
B→L
) water fluxes across ovine tracheal epithelia were measured simultaneously. The mean J
W
L→B
(6.5 μl/min/cm2) was larger than J
W
B→L
(6.1 μl/min/cm2). Furosemide reduced J
W
B→L
from 6.0 to 5.6 μl/min/cm2. Diphenylamine-2-carboxylate (DPC) reduced J
W
B→L
from 7.9 to 7.3 μl/min/cm2 and reduced the membrane potential difference by 38%. Furosemide together with DPC decreased J
W
L→B
by 30% and J
W
B→L
by 15%. Norepinephrine increased J
W
B→L
from 4.9 to 6.0 μl/min/cm2. Neuropeptide Y in the presence of norepinephrine decreased J
W
L→B
(6.4 to 5.2 μl/min/cm2) and returned J
W
B→L
to its baseline value. Vasopressin increased J
W
B→L
from 4.1 to 5.1 μl/min/cm2. Endothelin-1 induced a simultaneous increase in J
W
B→L
(7.0 to 7.7 μl/min/cm2) and decrease in J
W
L→B
(7.4 to 6.4 μl/min/cm2); and decreased the membrane resistance. These data indicate that in tracheal epithelia under homeostatic conditions J
W
B→L
has a ∼15% actively coupled component. Consistent with our hypothesis, inhibition and receptor-induced stimulation of chloride
effluxes were associated with decreases and increases in J
W
B→L
, respectively. However, as inhibition of transcellular chloride transport always decreased J
W
L→B
more than J
W
B→L
, reducing transepithelial chloride transport did not result in less water being transported into the airway lumen.
Received: 12 October 1999/Revised: 14 March 2000 相似文献