Double Drop-Off Droplet Digital PCR: A Novel, Versatile Tool for Mutation Screening and Residual Disease Monitoring in Acute Myeloid Leukemia Using Cellular or Cell-Free DNA

In acute myeloid leukemia (AML), somatic gene mutations are important prognostic markers and increasingly constitute therapeutic targets. Therefore, robust, sensitive, and fast diagnostic assays are needed. Current techniques for mutation screening and quantification, including next-generation sequencing and quantitative PCR, each have weaknesses that leave a need for novel diagnostic tools. We established double drop-off digital droplet PCR (DDO-ddPCR) assays for gene mutations in NPM1, IDH2, and NRAS, which can detect and quantify diverse alterations at two nearby hotspot regions present in these genes. These assays can be used for mutation screening as well as quantification and sequential monitoring. The assays were validated against next-generation sequencing and existing ddPCR assays and achieved high concordance with an overall sensitivity comparable to conventional digital PCR. In addition, the feasibility of detecting and monitoring genetic alterations in peripheral blood cell-free DNA (cfDNA) of patients with AML by DDO-ddPCR was studied. cfDNA analysis was found to have similar sensitivity compared to quantitative PCR-based analysis of peripheral blood. Finally, the cfDNA-based digital PCR in several clinical scenarios was found to be useful in long-term monitoring of target-specific therapy, early response assessment during induction chemotherapy, and identification of mutations in patients with extramedullary disease. Thus, DDO-ddPCR-based cfDNA analysis may complement existing genetic tools for diagnosis and disease monitoring in AML.

A fluorescence in situ hybridization-based screen allows rapid detection of adverse cytogenetic alterations in patients with acute myeloid leukemia

In adult acute myeloid leukemia (AML), the karyotype of the leukemic cell is among the strongest prognostic factors. The Medical Research Council (MRC) and the European LeukemiaNet (ELN) classifications distinguish between favorable, intermediate and adverse cytogenetic risk patients who differ in their treatment response and overall survival. Conventional cytogenetic analyses are a mandatory component of AML diagnostics but they are time-consuming; therefore, therapeutic decisions in elderly patients are often delayed. We investigated whether a screening approach using a panel of seven fluorescence in situ hybridization (FISH) probes would allow rapid identification of adverse chromosomal changes. In a cohort of 334 AML patients, our targeted FISH screening approach identified 80% of adverse risk AML patients with a specificity of 99%. Incorporating FISH screening into diagnostic workup has the potential to accelerate risk stratification and treatment selection, particularly in older patients. This approach may allow therapeutic decisions more quickly, which benefits both patients and physicians and might save costs.

Detection of cross-sex chimerism in the common marmoset monkey (Callithrix jacchus) in interphase cells using fluorescence in situ hybridisation probes specific for the marmoset X and Y chromosomes

Chimerism associated with placental sharing in marmosets has been traditionally analysed using conventional chromosome staining on metaphase spreads or polymerase chain reaction. However, the former technique requires the presence of proliferating cells, whereas the latter may be associated with possible blood cell contamination. Therefore, we aimed to develop a single-cell analysis technique for sexing marmoset cells. We applied fluorescent in situ hybridisation (FISH) to cell nuclei using differentially labelled X and Y chromosome-specific probes. Herein we present the validation of this method in metaphase cells from a marmoset lymphoblastoid cell line, as well as application of the method for evaluation of cross-sex chimerism in interphase blood lymphocytes and haematopoietic bone marrow cells from marmosets of same- and mixed-sex litters. The results show conclusively that haematopoietic cells of bone marrow and leucocytes from blood are cross-sex chimeric when the litter is mixed sex. In addition, single samples of liver and spleen cell suspensions from one individual were tested. Cross-sex chimerism was observed in the spleen but not in liver cells. We conclude that FISH is the method of choice to identify cross-sex chimerism, especially when combined with morphological identification of nuclei of different cell types, which will allow a targeted tissue-specific analysis.

Increased chromosome 16 disomy rates in human spermatozoa and recurrent spontaneous abortions

OBJECTIVE

To investigate if unexplained recurrent spontaneous abortions (RSA) are associated with increased rates of aneuploidy in spermatozoa of RSA partners ("RSA-men").

DESIGN

Case-control study.

SETTING

Academic research center.

PATIENT(S)

Patients enrolled at the Hormone and Fertility Center and controls at the Department of Urology (LMU-Munich).

INTERVENTION(S)

Sperm samples of 11 partners of unexplained RSA cases evaluated for elevated diploidy and disomy levels of chromosomes 1-22, X, and Y by multicolor sperm fluorescence in situ hybridization (FISH).

MAIN OUTCOME MEASURE(S)

Aneuploidy rates obtained in RSA-men compared with controls from the literature and internally; an increase of the aneuploidy rate was considered statistically significant, when it differed ≥ 2 standard deviations from the mean baseline level in controls.

RESULT(S)

Our sperm FISH data on RSA men showed increased disomy rates for at least three chromosomes in more than 60% of patients but no statistically significant increase of the overall mean sperm disomy or diploidy rate. In particular, meiotic errors involving chromosome 16 contributed to increased sperm disomy in more than 60% of our patients.

CONCLUSION(S)

These data suggest that among paternal meiotic errors nondisjunction of chromosome 16 might have similar relative influence on fetal aneuploidy compared with maternal chromosome 16 disomy.

Distinct nuclear orientation patterns for mouse chromosome 11 in normal B lymphocytes

Background

Characterizing the nuclear orientation of chromosomes in the three-dimensional (3D) nucleus by multicolor banding (mBANDing) is a new approach towards understanding nuclear organization of chromosome territories. An mBANDing paint is composed of multiple overlapping subchromosomal probes that represent different regions of a single chromosome. In this study, we used it for the analysis of chromosome orientation in 3D interphase nuclei. We determined whether the nuclear orientation of the two chromosome 11 homologs was random or preferential, and if it was conserved between diploid mouse Pre B lymphocytes of BALB/c origin and primary B lymphocytes of congenic [T38HxBALB/c]N wild-type mice. The chromosome orientation was assessed visually and through a semi-automated quantitative analysis of the radial and angular orientation patterns observed in both B cell types.

Results

Our data indicate that there are different preferential patterns of chromosome 11 orientation, which are not significantly different between both mouse cell types (p > 0.05). In the most common case for both cell types, both copies of chromosome 11 were oriented in parallel with the nuclear border. The second most common pattern in both types of B lymphocytes was with one homolog of chromosome 11 positioned with its telomeric end towards the nuclear center and with its centromeric end towards the periphery, while the other chromosome 11 was found parallel with the nuclear border. In addition to these two most common orientations present in approximately 50% of nuclei from each cell type, other orientations were observed at lower frequencies.

Conclusions

We conclude that there are probabilistic, non-random orientation patterns for mouse chromosome 11 in the mouse B lymphocytes we investigated (p < 0.0001).

Chromosome evolution in new world monkeys (Platyrrhini)

During the last decades, New World monkey (NWM, Platyrrhini, Anthropoideae) comparative cytogenetics has shed light on many fundamental aspects of genome organisation and evolution in this fascinating, but also highly endangered group of neotropical primates. In this review, we first provide an overview about the evolutionary origin of the inferred ancestral NWM karyotype of 2n = 54 chromosomes and about the lineage-specific chromosome rearrangements resulting in the highly divergent karyotypes of extant NWM species, ranging from 2n = 16 in a titi monkey to 2n = 62 in a woolly monkey. Next, we discuss the available data on the chromosome phylogeny of NWM in the context of recent molecular phylogenetic analyses. In the last part, we highlight some recent research on the molecular mechanisms responsible for the large-scale evolutionary genomic changes in platyrrhine monkeys.

Multicolor 3D fluorescence in situ hybridization for imaging interphase chromosomes

Fluorescence in situ hybridization (FISH) of specific DNA probes has become a widely used technique mostly for chromosome analysis and for studies of the chromosomal location of specific DNA segments in metaphase preparations as well as in interphase nuclei. FISH on 3D-preserved nuclei (3D-FISH) in combination with 3D-microscopy and image reconstruction is an efficient tool to analyze the spatial arrangement of targeted DNA sequences in the nucleus. Recent developments of a "new generation" of confocal microscopes that allow the distinct visualization of at least five different fluorochromes within one experiment opened the way for multicolor 3D-FISH experiments. Thus, numerous differently labeled nuclear targets can be delineated simultaneously and their spatial interrelationships can be analyzed on the level of individual nuclei.In this chapter, we provide protocols for the preparation of complex DNA-probe sets suitable for 3D-FISH with up to six different fluorochromes, for 3D-FISH on cultured mammalian cells (growing in suspension or adherently) as well as on tissue sections, and for 3D immuno-FISH.In comparison with FISH on metaphase chromosomes and conventional interphase cytogenetics, FISH on 3D-preserved nuclei requires special demands with regard to probe quality, fixation, and pretreatment steps of cells in order to achieve the two goals, namely the best possible preservation of the nuclear structure and at the same time an efficient probe accessibility.

Chromosome phylogeny of the subfamily Pitheciinae (Platyrrhini, Primates) by classic cytogenetics and chromosome painting

BACKGROUND

The New World monkey (Platyrrhini) subfamily Pitheciinae is represented by the genera Pithecia, Chiropotes and Cacajao. In this work we studied the karyotypes of Pithecia irrorata (2n = 48) and Cacajao calvus rubicundus (2n = 45 in males and 2n = 46 in females) by G- and C-banding, NOR staining and chromosome painting using human and Saguinus oedipus whole chromosome probes. The karyotypes of both species were compared with each other and with Chiropotes utahicki (2n = 54) from the literature.

RESULTS

Our results show that members of the Pitheciinae have conserved several chromosome forms found in the inferred ancestral Platyrrhini karyotype (associations of human homologous segments 3a/21, 5/7a, 2b/16b, 8a/18, 14/15a and 10a/16a). Further, the monophyly of this subfamily is supported by three chromosomal synapomorphies (2a/10b, an acrocentric 15/14 and an acrocentric human 19 homolog). In addition, each species presents several autapomorphies. From this data set we established a chromosomal phylogeny of Pitheciinae, resulting in a single most parsimonious tree.

CONCLUSIONS

In our chromosomal phylogeny, the genus Pithecia occurred in a more basal position close to the inferred ancestor of Platyrrhini, while C. c. rubicundus and C. utahicki are closely related and are linked by exclusive synapomorphies.

Replication-timing-correlated spatial chromatin arrangements in cancer and in primate interphase nuclei

Using published high-resolution data on S-phase replication timing, we determined the three-dimensional (3D) nuclear arrangement of 33 very-early-replicating and 31 very-late-replicating loci. We analyzed diploid human, non-human primate and rearranged tumor cells by 3D fluorescence in situ hybridization with the aim of investigating the impact of chromosomal structural changes on the nuclear organization of these loci. Overall, their topology was found to be largely conserved between cell types, species and in tumor cells. Early-replicating loci were localized in the nuclear interior, whereas late-replicating loci showed a broader distribution with a higher preference for the periphery than for late-BrdU-incorporation foci. However, differences in the spatial arrangement of early and late loci of chromosome 2, as compared with those from chromosome 5, 7 and 17, argue against replication timing as a major driving force for the 3D radial genome organization in human lymphoblastoid cell nuclei. Instead, genomic properties, and local gene density in particular, were identified as the decisive parameters. Further detailed comparisons of chromosome 7 loci in primate and tumor cells suggest that the inversions analyzed influence nuclear topology to a greater extent than the translocations, thus pointing to geometrical constraints in the 3D conformation of a chromosome territory.

Preparation of Complex DNA Probe Sets for 3D FISH with up to Six Different Fluorochromes

INTRODUCTIONDNA probes for fluorescence in situ hybridization (FISH) can be generated and labeled by various methods. This protocol describes the conjugation of dUTPs with haptens or fluorochromes, as well as the generation and labeling of DNA probes using those modified dUTPs. Sources of probe DNA include genomic DNA, DNA from flow-sorted chromosomes, bacterial artificial chromosomes (BACs), and cosmids. DNA amplification and labeling procedures involving degenerate oligonucleotide-primed PCR (DOP-PCR) and multiple displacement amplification (MDA) are provided. Advice is given for setting up complex probe pools, such as those containing large pools of BAC probes. Also included is a method for probe precipitation and preparation of a hybridization mix ready to be used for 3D fluorescence in situ hybridization (FISH) experiments.

Evolutionary genomic remodelling of the human 4q subtelomere (4q35.2)

BACKGROUND

In order to obtain insights into the functionality of the human 4q35.2 domain harbouring the facioscapulohumeral muscular dystrophy (FSHD) locus, we investigated in African apes genomic and chromatin organisations, and the nuclear topology of orthologous regions.

RESULTS

A basic block consisting of short D4Z4 arrays (10-15 repeats), 4q35.2 specific sequences, and approximately 35 kb of interspersed repeats from different LINE subfamilies was repeated at least twice in the gorilla 4qter. This genomic organisation has undergone evolutionary remodelling, leading to the single representation of both the D4Z4 array and LINE block in chimpanzee, and the loss of the LINE block in humans. The genomic remodelling has had an impact on 4qter chromatin organisation, but not its interphase nuclear topology. In comparison with humans, African apes show very low or undetectable levels of FRG1 and FRG2 histone 4 acetylation and gene transcription, although histone deacetylase inhibition restores gene transcription to levels comparable with those of human cells, thus indicating that the 4qter region is capable of acquiring a more open chromatin structure. Conversely, as in humans, the 4qter region in African apes has a very peripheral nuclear localisation.

CONCLUSION

The 4q subtelomere has undergone substantial genomic changes during evolution that have had an impact on chromatin condensation and the region's transcriptional regulation. Consequently, the 4qter genes in African apes and humans seem to be subjected to a different strategy of regulation in which LINE and D4Z4 sequences may play a pivotal role. However, the effect of peripheral nuclear anchoring of 4qter on these regulation mechanisms is still unclear. The observed differences in the regulation of 4qter gene expression between African apes and humans suggest that the human 4q35.2 locus has acquired a novel functional relevance.

Evolutionarily conserved, cell type and species-specific higher order chromatin arrangements in interphase nuclei of primates

Several studies demonstrated a gene-density-correlated radial organization of chromosome territories (CTs) in spherically shaped nuclei of human lymphocytes or lymphoblastoid cells, while CT arrangements in flat-ellipsoidal nuclei of human fibroblasts are affected by both gene density and chromosome size. In the present study, we performed fluorescence in situ hybridization (FISH) experiments to three-dimensionally preserved nuclei (3D-FISH) from human and nonhuman primate cultured lymphoblastoid cells and fibroblasts. We investigated apes, Old, and New World monkeys showing either evolutionarily conserved karyotypes, multiple translocations, fusions, or serial fissions. Our goal was to test whether cell type specific differences of higher order chromatin arrangements are evolutionarily conserved in different primate lineages. Whole genome painting experiments and further detailed analyses of individual chromosomes indicate a gene-density-correlated higher order organization of chromatin in lymphoblastoid cell nuclei of all studied primate species, despite evolutionary chromosome reshuffling. In contrast, in primate fibroblast nuclei evolutionary translocations, fissions and fusions resulted in positional shifts of orthologous chromosome segments, thus arguing against a functional role of chromosome size-dependent spatial chromatin arrangements and for geometrical constraints in flat-ellipsoidal fibroblast nuclei. Notably, in both cell types, regions of rearranged chromosomes with distinct differences in gene density showed polarized arrangements with the more gene-dense segment oriented towards the nuclear interior. Our results indicate that nonrandom breakage and rejoining of preferentially gene-dense chromosomes or chromosome segments may have occurred during evolution.

Inter- and intra-specific gene-density-correlated radial chromosome territory arrangements are conserved in Old World monkeys

Recently it has been shown that the gene-density correlated radial distribution of human 18 and 19 homologous chromosome territories (CTs) is conserved in higher primates in spite of chromosomal rearrangements that occurred during evolution. However, these observations were limited to apes and New World monkey species. In order to provide further evidence for the evolutionary conservation of gene-density-correlated CT arrangements, we extended our previous study to Old World monkeys. They comprise the remaining species group to be analyzed in order to obtain a comprehensive overview of the nuclear topology of human 18 and 19 homologous CTs in higher primates. In the present study we investigated four lymphoblastoid cell lines from three species of Old World monkeys by three-dimensional fluorescence in situ hybridization (3D-FISH): two individuals of Japanese macaque (Macaca fuscata), crab-eating macaque (Macaca fascicularis), and an interspecies hybrid individual between African green monkey (Cercopithecus aethiops) and Patas monkey (Erythrocebus patas). Our data demonstrate that gene-poor human 18 homologous CTs are located preferentially close to the nuclear periphery, whereas gene-dense human 19 homologous CTs are oriented towards the nuclear center in all cell lines analyzed. The gene-density-correlated positioning of human 18 and 19 homologous CTs is evolutionarily conserved throughout all major higher primate lineages, despite chromosomal inversions, fusions, fissions or reciprocal translocations that occurred in the course of evolution in these species. This remarkable preservation of a gene-density-correlated chromatin arrangement gives further support for a functionally relevant higher-order chromatin architecture.

Phylogenetic inferences of Atelinae (Platyrrhini) based on multi-directional chromosome painting in Brachyteles arachnoides, Ateles paniscus paniscus and Ateles b. marginatus

We performed multi-directional chromosome painting in a comparative cytogenetic study of the three Atelinae species Brachyteles arachnoides, Ateles paniscus paniscus and Ateles belzebuth marginatus, in order to reconstruct phylogenetic relationships within this Platyrrhini subfamily. Comparative chromosome maps between these species were established by multi-color fluorescence in situ hybridization (FISH) employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. The three species included in this study and four previously analyzed species from all four Atelinae genera were subjected to a phylogenetic analysis on the basis of a data matrix comprised of 82 discrete chromosome characters. The results confirmed that Atelinae represent a monophyletic clade with a putative ancestral karyotype of 2n = 62 chromosomes. Phylogenetic analysis revealed an evolutionary branching sequence [Alouatta [Brachyteles [Lagothrix and Ateles]]] in Atelinae and [Ateles belzebuth marginatus [Ateles paniscus paniscus [Ateles belzebuth hybridus and Ateles geoffroyi]]] in genus Ateles. The chromosomal data support a re-evaluation of the taxonomic status of Ateles b. hybridus.

The evolutionary history of human chromosome 7

We report on a comparative molecular cytogenetic and in silico study on evolutionary changes in human chromosome 7 homologs in all major primate lineages. The ancestral mammalian homologs comprise two chromosomes (7a and 7b/16p) and are conserved in carnivores. The subchromosomal organization of the ancestral primate segment 7a shared by a lemur and higher Old World monkeys is the result of a paracentric inversion. The ancestral higher primate chromosome form was then derived by a fission of 7b/16p, followed by a centric fusion of 7a/7b as observed in the orangutan. In hominoids two further inversions with four distinct breakpoints were described in detail: the pericentric inversion in the human/African ape ancestor and the paracentric inversion in the common ancestor of human and chimpanzee. FISH analysis employing BAC probes confined the 7p22.1 breakpoint of the pericentric inversion to 6.8 Mb on the human reference sequence map and the 7q22.1 breakpoint to 97.1 Mb. For the paracentric inversion the breakpoints were found in 7q11.23 between 76.1 and 76.3 Mb and in 7q22.1 at 101.9 Mb. All four breakpoints were flanked by large segmental duplications. Hybridization patterns of breakpoint-flanking BACs and the distribution of duplicons suggest their presence before the origin of both inversions. We propose a scenario by which segmental duplications may have been the cause rather than the result of these chromosome rearrangements.

Multi-directional chromosome painting maps homologies between species belonging to three genera of New World monkeys and humans

We mapped chromosomal homologies in two species of Chiropotes (Pitheciini, Saki Monkeys) and one species of Aotus (Aotinae, Owl Monkey) by multi-directional chromosome painting. Human chromosome probes were hybridized to Chiropotes utahicki, C. israelita and Aotus nancymae metaphases. Wooly Monkey chromosome paints were also hybridized to Owl Monkey metaphases. We established Owl Monkey chromosome paint probes by flow sorting and reciprocally hybridized them to human chromosomes. The karyotypes of the Bearded Saki Monkeys studied here are close to the hypothesized ancestral platyrrhine karytoype, while that of the Owl Monkey appears to be highly derived. The A. nancymae karyotype is highly shuffled and only three human syntenic groups were found conserved coexisting with 17 derived human homologous associations. A minimum of 14 fissions and 13 fusions would be required to derive the A. nancymae karyotype from that of the ancestral New World primate karyotype. An inversion between homologs to segments of human 10 and 16 suggests a link between Callicebus and Chiropotes, while the syntenic association of 10/11 found in Aotus and Callicebus suggests a link between these two genera. Future molecular cytogenetic work will be needed to determine whether these rearrangements represent synapomorphic chromosomal traits.

Investigation of marmoset hybrids (Cebuella pygmaea × Callithrix jacchus) and related Callitrichinae (Platyrrhini) by cross-species chromosome painting and comparative genomic hybridization

We report on the cytogenetics of twin offspring from an interspecies cross in marmosets (Callitrichinae, Platyrrhini), resulting from a pairing between a female Common marmoset (Callithrix jacchus, 2n = 46) and a male Pygmy marmoset (Cebuella pygmaea, 2n = 44). We analyzed their karyotypes by multi-directional chromosome painting employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. Both hybrid individuals had a karyotype with a diploid chromosome number of 2n = 45. As a complementary tool, interspecies comparative genomic hybridization (iCGH) was performed in order to screen for genomic imbalances between the hybrids and their parental species, and between Callithrix argentata and S. oedipus, respectively. These genomic imbalances were confined to centromeric and telomeric heterochromatin, while euchromatic chromosome regions appeared balanced in all species investigated. When comparing marmosets and tamarins, sequence divergence of centromeric heterochromatin was already clearly noticeable. In the C. argentata and C. pygmaea genomes numerous subtelomeric regions were affected by amplification of different repetitive sequences. Cross-species FISH with a microdissection-derived C. pygmaea repetitive probe revealed species specificity of this repetitive sequence at the molecular cytogenetic level of resolution.

Chromosomal anchoring of linkage groups and identification of wing size QTL using markers and FISH probes derived from microdissected chromosomes in Nasonia (Pteromalidae: Hymenoptera)

Nasonia vitripennis is a small parasitic hymenopteran with a 50-year history of genetic work including linkage mapping with mutant and molecular markers. For the first time we are now able to anchor linkage groups to specific chromosomes. Two linkage maps based on a hybrid cross (N. vitripennis x N. longicornis) were constructed using STS, RAPD and microsatellite markers, where 17 of the linked STS markers were developed from single microdissected banded chromosomes. Based on these microdissections we anchored all linkage groups to the five chromosomes of N. vitripennis. We also verified the chromosomal specificity of the microdissection through in situ hybridization and linkage analyses. This information and technique will allow us in the future to locate genes or QTL detected in different mapping populations efficiently and fast on homologous chromosomes or even chromosomal regions. To test this approach we asked whether QTL responsible for the wing size in two different hybrid crosses (N. vitripennis x N. longicornis and N. vitripennis x N.giraulti) map to the same location. One QTL with a major effect was found to map to the centromere region of chromosome 3 in both crosses. This could indicate that indeed the same gene/s is involved in the reduction of wing in N. vitripennis and N. longicornis.

Chromosomal studies in Callicebus donacophilus pallescens, with classic and molecular cytogenetic approaches: multicolour FISH using human and Saguinus oedipus painting probes

This paper presents the karyotype of Callicebus donacophilus pallescens for the first time. The analysis included G-, C-, NOR-banding techniques and FISH with chromosome painting probes from Saguinus oedipus and Homo sapiens. The results were compared with the karyotypes of Callicebus moloch donacophilus and C. moloch previously published. These three karyotypes display the same diploid number (2n = 50) but diverge about the number of biarmed and acrocentric chromosomes. The acrocentrics 14 and 15 from C. m. donacophilus and C. moloch have undergone an in-tandem fusion originating a large acrocentric (pair 10) in C. d. pallescens. The major submetacentric pair (pair 1) from C. d. donacophilus and C. moloch have undergone fission originating two acrocentric pairs in C. d. pallescens (pairs 15 and 22). Herein was evidence that, in spite of the high interspecific variation among Callicebus, most of the chromosomes remained conserved.

The phylogeny of howler monkeys (Alouatta, Platyrrhini): reconstruction by multicolor cross-species chromosome painting

We performed multidirectional chromosome painting in a comparative cytogenetic study of the three howler monkey species Alouatta fusca, A. caraya and A. seniculus macconnelli (Atelinae, Platyrrhini) in order to reconstruct phylogenetic relationships within this genus. Comparative genome maps between these species were established by multicolor fluorescence in-situ hybridization (FISH) employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. The three species included in this study and previously analyzed howler monkey species were subjected to a phylogenetic analysis on the basis of a data matrix comprised of 98 discrete molecular cytogenetic characters. The results revealed that howler monkeys represent the genus with the most extensive karyotype diversity within Platyrrhini so far analyzed with high levels of intraspecific chromosomal variability. Two different multiple sex chromosome systems were identified. The phylogenetic analysis indicated that Alouatta is a monophyletic clade which can be derived from a proposed ancestral Atelinae karyotype of 2n = 62 chromosomes by a chromosome fusion, a fission, a Y-autosomal translocation and a pericentric inversion. Following these suggestions, the genus Alouatta can be divided into two distinct species groups: the first includes A. caraya and A. belzebul, the second A. s. macconnelli, A. sara, A. s. arctoidea and A. fusca.

Towards unlimited colors for fluorescence in-situ hybridization (FISH)

We describe a FISH protocol that allows rehybridization of complex DNA probes up to four times to the same specimen. This strategy, which we termed ReFISH, opens a wide range of new applications to conventional band pass filter epifluorescence microscopy. These include M-FISH karyotyping and cross-species color banding that emulate multiplex probe sets labeled with up to 12 fluorochromes in sequential hybridizations to the same specimen. We designed a human 24-color karyotyping probe set in combination with a 29-color cross-species color banding probe set using gibbon painting probes. Applying the ReFISH principle, 53 painting probes on individual metaphases were discriminated. This allowed simultaneous screening for inter- and intrachromosomal rearrangements on normal human diploid cells, a HeLa derived cell line, and highly rearranged gibbon chromosomes. Furthermore, the present ReFISH experiments successfully combine 24-color FISH with laser scanning confocal microscopy to study the 3D organization of all 46 human chromosome territories in individual interphase cell nuclei.

Molecular cytogenetic characterization of the EBV-producing cell line B95-8 (Saguinus oedipus, Platyrrhini) by chromosome sorting and painting

The cell line B95-8 releases Epstein-Barr virus (EBV) with high titres of transforming activity and is widely used as a model in cancer research and virology. There are, however, controversial reports about the species of origin, cell line stability and karyotype. To address these questions, B95-8 chromosomes were analysed by chromosome sorting and painting by multicolour fluorescence in-situ hybridization. Reciprocal painting was performed between B95-8, 'wildtype' New World monkey and human chromosomes. Saguinus oedipus was revealed as the species of origin. A further five cell-line-specific marker chromosomes, resulting from translocations, deletions and an insertion were found. Although human chromosome 6 or 13 homologues were always involved in these rearrangements, co-hybridization of an EBV-specific DNA probe did not reveal site-specific hybridization to marker chromosomes or at translocation breakpoints. The multicolour probe set described here will be of special value for further evolutionary studies in New World monkeys.

Molecular cytotaxonomy of New World monkeys (Platyrrhini) - comparative analysis of five species by multi-color chromosome painting gives evidence for a classification of Callimico goeldii within the family of Callitrichidae

Chromosome rearrangements are considered as "rare genomic changes" and can provide useful markers and even landmarks for reconstructing phylogenies complementary to DNA sequence data and bio-morphological comparisons. Here, we applied multi-directional chromosome painting to reconstruct the chromosome phylogeny and evolutionary relationships among the New World monkey (Platyrrhini) species Callithrix argentata, Cebuella pygmaea, Saguinus oedipus, Callithrix jacchus and Callimico goeldii. The results clarified several aspects of New Wold monkey phylogeny. In particular the phylogenetic position of C. goeldii was elucidated, which has been controversially discussed and variously classified in the family Callitrichidae, in the family Cebidae or in its own family Callimiconidae. Comparative genome maps were established by multi-color fluorescence in situ hybridization (FISH) with human, S. oedipus and Lagothrix lagothricha chromosome- specific DNA probes. From these data we reconstructed the putative ancestral karyotype of all Callitrichidae. Various derived chromosomal syntenies are shared by all five species and cytogenetically define Callitrichidae - including Callimico goeldii -- as a distinctive group within the Platyrrhini. C. pygmaea and C. argentata share identical chromosomal syntenies from which S. oedipus and C. jacchus differ by single independent translocations. A common derived chromosomal change links Callimico with the marmosets to the exclusion of the tamarins, however, it has further diverged from an ancestral marmoset karyotype by at least four apomorphic rearrangements. Saimiri sciureus, representing the Cebinae, exclusively shares a derived syntenic association with all Callithrichidae, defining the genus Saimiri as a sister group.

Evolutionary conservation of chromosome territory arrangements in cell nuclei from higher primates

We demonstrate that the nuclear topological arrangement of chromosome territories (CTs) has been conserved during primate evolution over a period of about 30 million years. Recent evidence shows that the positioning of chromatin in human lymphocyte nuclei is correlated with gene density. For example, human chromosome 19 territories, which contain mainly gene-dense and early replicating chromatin, are located toward the nuclear center, whereas chromosome 18 territories, which consist mainly of gene-poor and later replicating chromatin, is located close to the nuclear border. In this study, we subjected seven different primate species to comparative analysis of the radial distribution pattern of human chromosome 18- and 19-homologous chromatin by three-dimensional fluorescence in situ hybridization. Our data demonstrate that gene-density-correlated radial chromatin arrangements were conserved during higher-primate genome evolution, irrespective of the major karyotypic rearrangements that occurred in different phylogenetic lineages. The evolutionarily conserved positioning of homologous chromosomes or chromosome segments in related species supports evidence for a functionally relevant higher-order chromatin arrangement that is correlated with gene-density.

Involvement of phospholipase D in store-operated calcium influx in vascular smooth muscle cells

In non-excitable cells, sustained intracellular Ca2+ increase critically depends on influx of extracellular Ca2+. Such Ca2+ influx is thought to occur by a 'store-operated' mechanism, i.e. the signal for Ca2+ entry is believed to result from the initial release of Ca2+ from inositol 1,4,5-trisphosphate-sensitive intracellular stores. Here we show that the depletion of cellular Ca2+ stores by thapsigargin or bradykinin is functionally linked to a phosphoinositide-specific phospholipase D (PLD) activity in cultured vascular smooth muscle cells (VSMC), and that phosphatidic acid formed via PLD enhances sustained calcium entry in this cell type. These results suggest a regulatory role for PLD in store-operated Ca2+ entry in VSMC.

Fluorescence in situ hybridization (FISH) maps chromosomal homologies between the dusky titi and squirrel monkey

The Platyrrhini are one of the most karyologically derived groups of primates and the evolution of their karyotypes is far from understood. The identification of the origin and direction of chromosome rearrangements will contribute to a better understanding of New World monkey phylogeny, taxonomy, and evolution. We mapped homology and identified translocations in the chromosomes of the dusky titi monkey (Callicebus moloch, 2n = 50) and the squirrel monkey (Saimiri sciureus, 2n = 44) by fluorescence in situ hybridization (FISH) of human chromosome paints. The hybridization results established chromosomal homologies between these New World primates, humans, other primates, and more distantly related mammalian species and show that both species have highly rearranged karyotypes. The total number of hybridization signals was 37 in C. moloch and 40 in S. sciureus, which is in the range of most comparisons of human chromosomes with phylogenetically more distant species outside of the primate order. Parsimony analyses of outgroup painting patterns allowed us to propose an ancestral karyotype for New World monkeys consisting of 2n = 56 with homologs to the following human chromosomes or chromosome segments: 1b; 1c; 2a; 2b; 3a; 3b; 3/21; 4; 5; 6; 7; 8a; 8/18; 9; 10a; 10/16; 11; 12; 13; 14/15; 15a; 16a; 17; 19; 20; 22; X; Y. Associations 8/18 and 10/16 are derived ancestral associations for all Platyrrhini. A 2/16 association found in S. sciureus and C. moloch was also seen in Ateles geoffroyi and Cebus capucinus; a 5/7 association in S. sciureus was present in A. geoffroyi, C. capucinus, and Alouatta belzebul. Other associations seen in the dusky titi monkey or the squirrel monkey are probably automorphisms. Comparison with chromosome phylogenies based on R-banding [Dutrillaux et al., 1986] showed that there were many errors in assigning homology with human chromosomes. The chromosomal phylogeny of New World monkeys based on banding patterns is in need of revision using modern molecular methods.

Thapsigargin-insensitive calcium pools in vascular smooth muscle cells

Since sarcoplasmic Ca2+-ATPase may play an important role for the regulation of cytosolic free calcium concentration ([Ca2+]i) and may be altered in primary hypertension, the effects of thapsigargin and bradykinin on intracellular calcium pools in cultured vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats of the Münster strain (SHR) and normotensive Wistar-Kyoto (WKY) rats were investigated. VSMC were cultured on glass cover slips and [Ca2+]i was measured using the fluorescent dye fura2. To exclude transplasmamembrane calcium influx all experiments were performed in a calcium free medium. Thapsigargin, a selective inhibitor of the sarcoplasmic Ca2+-ATPase, and bradykinin, that is known to induce inositol trisphosphate release, dose dependently caused an increase of [Ca2+]i by emptying intracellular Ca2+ stores. The peak increase of [Ca2+]i after addition of saturation doses of thapsigargin (1 micromol/L) was not significantly different in the two strains (SHR: 69 +/- 11 nmol/L, n=24; WKY: 58 +/- 12 nmol/L, n=20; mean +/- SEM). When 10 micromol/L bradykinin was added after depletion of the thapsigargin-sensitive pools, still a release of [Ca2+]i could be observed. The bradykinin-induced [Ca2+]i increase was similar in the absence and presence of thapsigargin in VSMC from SHR (62 +/- 12 nmol/L, n=20; vs 52 +/- 18 nmol/L, n=22). In contrast, in the VSMC from WKY a significant reduction of the bradykinin induced [Ca2+]i-increase could be observed after the depletion of the thapsigargin sensitive calcium pools (70 +/- 8 nmol/L, n=21, vs. 33 +/- 7, n=20; p<0.002). It is concluded that bradykinin releases calcium from a pool that is not refilled by the common, thapsigargin-sensitive Ca2+-ATPase. In contrast to VSMC from normotensive WKY, in VSMC from spontaneously hypertensive rats thapsigargin and bradykinin sensitive pools may be regulated separately.

Low concentrations of ouabain increase cytosolic free calcium concentration in rat vascular smooth muscle cells

1. Low ouabain concentrations in the nanomolar range significantly increased cytosolic free calcium concentration. 2. The ouabain-induced cytosolic free calcium concentration increase was due to transplasmamembrane calcium influx, which could be prevented in the absence of extracellular calcium or by addition of the calcium channel blocker nifedipine. 3. The amount of stored cellular Ca2+, as determined by the thapsigargin-induced cytosolic free calcium concentration increase, was also enhanced by 1 nmol/l ouabain. 4. It is concluded that low ouabain concentrations affect intracellular cytosolic free calcium concentration homoeostasis.

Transforming growth factor beta 1 modulates angiotensin II-induced calcium influx in vascular smooth muscle

The modulatory effects of transforming growth factor beta 1 (TGF beta 1) on the angiotensin II (Ang II)-induced increase in cytosolic free calcium concentration ([Ca2+]i) were investigated in vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). [Ca2+]i in VSMC was measured using the fluorescent dye fura-2. When TGF beta 1 was applied 30s prior to Ang II, the Ang II-induced [Ca2+]i increase was significantly enhanced in VSMC from SHR (P < 0.05 compared to control), whereas after the preincubation with TGF beta 1 for 30 min, the Ang II-induced [Ca2+]i increase was significantly reduced in VSMC from both strains. Using the manganese-quenching technique, it was confirmed that short-term exposure to TGF beta 1 enhanced the Ang II-induced trans-plasma-membrane calcium influx in SHR. The inhibition of protein kinase C by calphostin C abolished the stimulatory effect of TGF beta 1 on the Ang II-induced [Ca2+]i increase. It is concluded that TGF beta 1 modulates the Ang II-induced calcium handling in VSMC.

Effect of Na,K-ATPase inhibition on cytosolic free calcium ions in vascular smooth muscle cells of spontaneously hypertensive and normotensive rats

OBJECTIVE

To investigate the role of Na(+)-Ca2+ exchange in the regulation of cytosolic free Ca2+ and the pathogenesis of primary hypertension.

METHOD

Cytosolic free Ca2+ ([Ca2+]i) in cultured vascular smooth muscle cells from normotensive and spontaneously hypertensive rats of the Münster strain was measured using the fluorescent dye fura-2 after inhibition of Na+,K+ATPase by ouabain and after addition of angiotensin II.

RESULTS

[Ca2+]i showed a rapid increase together with a depolarization of membrane potential as measured by merocyanine 540. The ouabain-induced increase in [Ca2+]i was blocked in Ca(2+)-free medium and by nifedipine, but incubation with the inhibitor of the Na(+)-Ca2+ exchange, NiCl2, did not diminish the effect of ouabain. Likewise, in Na(+)-free medium the response to ouabain was not suppressed. The angiotensin II-induced changes in [Ca2+]i were diminished in Ca(2+)-free medium and by nifedipine, but enhanced by NiCl2.

CONCLUSION

The increase in [Ca2+]i after Na+,K+ ATPase inhibition is not due to a modulation of Na(+)-Ca2+ exchange, but to a Ca2+ influx through Ca2+ channels. Changes in Na(+)-Ca2+ exchange caused by Na+,K+ ATPase inhibition may not play an important role in vascular smooth muscle cells of spontaneously hypertensive rats.

Mechanism of the action of angiotensin-converting enzyme inhibitors on agonist-induced Ca2+ influx

To evaluate the direct effects of the angiotensin-converting enzyme (ACE) inhibitors, captopril, enalaprilat, enalapril (a prodrug without therapeutically significant ACE inhibitory effect) and ramiprilat, on cellular calcium metabolism, the cytosolic free calcium concentration was measured in cultured rat vascular smooth muscle cells using the fluorescent dye, fura-2. Preincubation with captopril, enalaprilat, enalapril, or ramiprilat for 40 min significantly reduced the angiotensin II-induced transplasma membrane calcium influx but did not influence the angiotension II-induced calcium release from internal stores. Captopril and ramiprilat also inhibited arginine vasopressin, but not the thapsigargin-, norepinephrine-, or the BayK 8644-induced changes in cytosolic calcium. Phorbol 12-myristate 13-acetate pretreatment for 30 s caused an increase in the angiotensin II-induced rise in cytosolic calcium. Although both captopril and verapamil reduced responses to angiotensin II to similar extents, only verapamil blocked the ability of phorbol 12-myristate 13-acetate to enhance responses to angiotensin II. It is concluded that ACE inhibitors modulate the effects of some but not all agonist-induced transplasma membrane calcium influx.

Effect of inhibition of sarcoplasmic Ca(2+)-ATPase on vasoconstriction and cytosolic Ca2+ in aortic smooth muscle from spontaneously hypertensive and normotensive rats

To evaluate the influence of the sarcoplasmic Ca(2+)-ATPase, isometric vasoconstrictions of aortic strips from spontaneously hypertensive rats from the Münster strain (SHR) and normotensive Wistar-Kyoto rats (WKY) were measured after inhibition of Ca(2+)-ATPase by thapsigargin. Inhibition of Ca(2+)-ATPase by thapsigargin caused a biphasic contractile response of the aorta in both SHR and WKY (maximum increase of tension: 1.7 +/- 0.3 x 10(-3) Newton and 2.1 +/- 0.3 x 10(-3) Newton, respectively; mean +/- SE). The second peak of the contractile response was abolished in the absence of external calcium or by inhibition of transplasmamembrane calcium influx by nifedipine, indicating that the second peak occurs as a consequence of calcium influx from the extracellular space. The initial peak of the contractile response after thapsigargin administration was abolished in the presence of an intracellular calcium antagonist, 8-(diethylamino-)-octyl-3,4,5-trimethoxybenzoate (TMB-8), indicating that the initial response was due to calcium release from intracellular stores. Measurements using the fluorescent dye fura2 showed that thapsigargin increased the cytosolic free calcium concentration ([Ca2+]i) in SHR by 72.6 +/- 7.3 nmol/l (n = 34) and in WKY by 53.3 +/- 6.6 nmol/l (n = 39), showing no significant differences between the two strains. The inhibition of Ca(2+)-ATPase increases [Ca2+]i and causes vasoconstriction. The vasoconstriction produced by thapsigargin is not significantly different between SHR and WKY.

Reduced cytosolic free sodium concentration in vascular smooth muscle cells from spontaneously hypertensive rats

1. Cytosolic free sodium concentration and sodium transport systems were measured in intact cultured vascular smooth muscle cells from spontaneously hypertensive rats of the Münster strain and from normotensive Wistar-Kyoto rats using the sodium-sensitive fluorescent dye sodium-binding benzofuran isophthalate. 2. Resting cytosolic free sodium concentration was significantly lower in vascular smooth muscle cells from spontaneously hypertensive rats than from Wistar-Kyoto rats (10.2 +/- 1.5 mmol/l, n = 26, versus 19.4 +/- 2.5 mmol/l, n = 20, P < 0.01). 3. Inhibition of Na+, K(+)-ATPase by ouabain caused a dose-dependent increase in cytosolic free sodium concentration in spontaneously hypertensive rats and Wistar-Kyoto rats. 4. Activation of Na(+)-Ca2+ exchange by ionomycin increased cytosolic free sodium concentration in both strains. However, the ionomycin-induced increase in cytosolic free sodium concentrations was significantly higher in vascular smooth muscle cells from spontaneously hypertensive rats than from Wistar-Kyoto rats (220 +/- 35% of the resting cytosolic free sodium concentration versus 148 +/- 27%; P < 0.05). The ionomycin-induced increase in cytosolic free sodium concentration was prevented in the absence of external sodium or by inhibition of Na(+)-Ca2+ exchange by NiCl2. 5. Activation of Na(+)-H+ exchange by intracellular acidification of vascular smooth muscle cells with propionic acid increased cytosolic free sodium concentration in each strain (19.6 +/- 5.7 versus 16.3 +/- 3.2 mmol/l). 6. It is concluded that concepts concerning the role of cytosolic free sodium concentration in the pathogenesis of primary hypertension need to be reinvestigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Different calcium storage pools in vascular smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats

OBJECTIVE

To evaluate whether the distribution of intracellular free calcium may be impaired in primary hypertension.

DESIGN

Cytosolic free calcium and stored calcium were investigated in cultured vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

The concentrations of intracellular and stored calcium were investigated in cultured vascular smooth muscle cells from spontaneously hypertensive rats aged 6 months from the Münster strain (SHR) and from age-matched normotensive Wistar-Kyoto (WKY) rats. Vascular smooth muscle cells were grown on coverslips, and fluorescence measurements of the intracellular calcium concentration were performed using fura-2. The different effects of thapsigargin, a selective Ca-ATPase inhibitor, and of angiotensin II (Ang II) on the calcium storage pools were investigated.

RESULTS

In the absence of external calcium thapsigargin produced a dose-dependent transient increase in the concentration of intracellular calcium in vascular smooth muscle cells. The thapsigargin-induced maximum peak increase in the concentration of intracellular calcium was not significantly different in SHR and WKY rats. After depletion of the thapsigargin-sensitive calcium pools the addition of 100 nmol/l Ang II produced a rise in the concentration of intracellular calcium in vascular smooth muscle cells from SHR and WKY rats. Using vascular smooth muscle cells from the SHR the Ang II-induced increase in the concentration of intracellular calcium was not significantly different in the presence and absence of thapsigargin, indicating that the calcium pools depleted by thapsigargin and Ang II do not overlap significantly in vascular smooth muscle cells from SHR. In contrast, in the WKY rats the response to Ang II was significantly diminished after depletion of the thapsigargin-sensitive pool. When Ang II and thapsigargin were administered in the reverse order, i.e. Ang II before thapsigargin, the thapsigargin response was diminished in the WKY rats but not in the SHR.

CONCLUSION

SHR differ from WKY rats in having vascular smooth muscle cells that contain thapsigargin-sensitive calcium storage pools that are distinct from the Ang II-sensitive calcium pools.

Role of Na(+)-Ca2+ exchange in agonist-induced changes in cytosolic Ca2+ in vascular smooth muscle cells

Changes in cytosolic free calcium concentration ([Ca2+]i) induced by angiotensin II (ANG II), arginine vasopressin (AVP), angiotensin III (ANG III), norepinephrine (NE), or thapsigargin were investigated after inhibition of the Na(+)-Ca2+ exchange in vascular smooth muscle cells (VSMC) from Wistar-Kyoto rats by use of the fluorescent dye technique. The ANG II-induced peak [Ca2+]i increase was significantly enhanced after inhibition of Na(+)-Ca2+ exchange by NiCl2 or 1,3-dimethyl-2-thiourea (DMTU): control, 99 +/- 9 (SE) nM (n = 64); NiCl2, 181 +/- 23 nM (n = 23; P < 0.01); DMTU, 182 +/- 35 nM (n = 10; P < 0.05). In the absence of external calcium, the inhibition of the Na(+)-Ca2+ exchange by NiCl2 also enhanced the ANG II-induced [Ca2+]i increase. Inhibition of Na(+)-Ca2+ exchange by removal of external sodium, which was replaced by choline, augmented the ANG II-induced [Ca2+]i increase to 174 +/- 26 nM (n = 11; P < 0.05 compared with control). The inhibition of the protein kinase C activity by isoquinoline-sulfonyl-O-2-methylpiperazine blocked the enhancing effect of NiCl2 on ANG II-induced [Ca2+]i increase. The inhibition of the Na(+)-Ca2+ exchange did not enhance the increase in [Ca2+]i induced by ANG III, NE, or thapsigargin. The AVP-induced changes in [Ca2+]i were not significantly different in the presence or absence of NiCl2. It is concluded that the recovery of resting [Ca2+]i after stimulation by ANG II is mediated by calcium efflux via the Na(+)-Ca2+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of captopril on vasoconstriction and Ca2+ fluxes in aortic smooth muscle

The effects of captopril on the response of cytosolic free Ca2+ concentration in cultured vascular smooth muscle cells of aortas from Wistar-Kyoto and spontaneously hypertensive rats to angiotensin II (Ang II) and bradykinin were studied using fura 2. Incubation with captopril for longer than 10 minutes caused a decreased response of cytosolic free Ca2+ to Ang II and bradykinin. Maximal effects of captopril were observed after a 40-minute incubation. The inhibitory effect of captopril was abolished in Ca(2+)-free medium, suggesting that captopril acts by blocking Ca2+ influx. Similar effects were observed with enalaprilat. Isometric contraction of aortic strips induced by Ang II in normotensive rats was reduced from 6.5 +/- 2.5 to 1.8 +/- 0.6 mN by a 40-minute incubation with 1 mumol/L captopril (P = .016). Enalaprilat similarly decreased the Ang II-induced contraction. Besides the inhibition of the angiotensin converting enzyme, direct effects of Ang II converting enzyme inhibitors on vascular contraction and Ca2+ influx in vascular smooth muscle cells may be of therapeutic relevance.

Concentration-dependent effects of insulin on Ca2+ influx in vascular smooth muscle cells of normotensive and spontaneously hypertensive rats

1. The effect of insulin on cytosolic free Ca2+ concentration was measured using fura-2 in vascular smooth muscle cells of normotensive and spontaneously hypertensive rats. 2. In both strains, insulin increased cytosolic free Ca2+ concentration in a concentration range between 10(-6) and 10(-3) units/ml. The maximum increase in cytosolic free Ca2+ concentration was observed with 10(-5) units/ml insulin (107 +/- 25 and 82 +/- 27 nmol/l in spontaneously hypertensive rats and normotensive rats, respectively). 3. The effect of insulin was dependent on extracellular Ca2+ and was enhanced by stimulation of protein kinase C. 4. Thus insulin appears to induce a Ca2+ influx in vascular smooth muscle cells only over a certain range of concentrations. No significant difference in the response to insulin of cells from normotensive and hypertensive rats was observed.

Effect of cytokines on cytosolic-free calcium in human platelets from essential hypertensives

The different effects of cytokines on cytosolic-free calcium concentration ([Ca2+]i) and intracellular stored calcium were investigated in platelets from 35 essential hypertensive patients (HT) and 45 age- and sex-matched normotensive control subjects (NT). Erythropoietin (EPO) and interleukin 2 significantly increased platelet [Ca2+]i, whereas platelet-derived growth factor, and fibroblast growth factor had no significant effect on [Ca2+]i. The EPO-induced rise of [Ca2+]i was significantly higher in HT compared to NT (15.2 +/- 4.3 nmol/L v 1.3 +/- 1.7 nmol/L, P < .01). Preincubation with EPO significantly increased calcium in intracellular stores in platelets from HT and NT. Inhibition of protein kinase C significantly enhanced EPO-induced rise of stored calcium. It is concluded that an increased response of HT to EPO may be associated with essential hypertension.

Erythropoietin increases cytosolic free calcium concentration in vascular smooth muscle cells

OBJECTIVES

The underlying pathophysiological mechanism leading to raised blood pressure after treatment with erythropoietin is a point of much discussion. Direct vasopressor effects of erythropoietin have been shown recently. The aim was to determine whether erythropoietin effects cytosolic free calcium concentration ([Ca2+]i in vascular smooth muscle cells.

METHODS

The effect of erythropoietin on ([Ca2+]i was measured with the fluorescent dye fura2 in cultured vascular smooth muscle cells from Wistar Kyoto rats.

RESULTS

Mean resting [Ca2+]i was 90.8(SEM 5.6) nM (n = 32). Addition of erythropoietin at concentrations of 100 U.ml-1 and 250 U.ml-1 increased [Ca2+]i to 112.3(5.0) nM (n = 23, p < 0.05) and 128.4(4.0) nM (n = 10, p < 0.01), respectively. Preincubation with erythropoietin caused a dose dependent increase in angiotensin II induced changes of [Ca2+]i in vascular smooth muscle cells.

CONCLUSIONS

One mechanism of erythropoietin induced hypertension may be an increase in [Ca2+]i in vascular smooth muscle cells.

Angiotensin II responses after protein kinase C activation in vascular smooth muscle cells of spontaneously hypertensive rats

To examine the interaction of protein kinase C (PKC) with agonist-induced calcium fluxes in hypertension, cytosolic free calcium ([Ca2+]i) was measured in vascular smooth muscle cells (vSMC) of normotensive and spontaneously hypertensive rats (SHR) after incubation with phorbol,-12 myristate,-13 acetate (PMA) and application of angiotensin II (AII). To distinguish between calcium influx through voltage-dependent calcium channels and calcium mobilization from intracellular stores, the calcium agonist BayK 8644 was used. Resting [Ca2+]i was 108.0 +/- 10.6 nM (mean +/- SEM, n = 25) in normotensive and 102.0 +/- 11.4 nM (n = 21) in hypertensive cells. After pretreatment with PMA 10(-7) M for 60 min, resting [Ca2+]i of normotensive vSMC increased to 145.0 +/- 13.8 nM (n = 17) while the resting level of the hypertensive cells decreased to 68.0 +/- 2.4 nM (n = 14, p < 0.05 as compared with normotensive cells) in hypertensive vSMC. Maximum increase in [Ca2+]i induced with 10 M AII for normotensive and hypertensive vSMC was similar: 230.5 +/- 34.4 nM (n = 14) and 212.5 +/- 26.7 nM (n = 17). After pretreatment with PMA 10(-7) M, the maximum increase in [Ca2+]i induced by AII in hypertensive cells was limited to 108.0 +/- 6.2 nM (p < 0.05 as compared with normotensive cells), whereas the increase in [Ca2+]i in normotensive vSMC remained the same as before: 211.5 +/- 23.4 nM. After administration of 10(-5) M BayK 8644, [Ca2+]i increased by 54.3 +/- 12.2 nM (n = 4) and 43.4 +/- 17.4 nM (n = 5) in normotensive and hypertensive vSMC, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of protein kinase C activation on intracellular Ca2+ distribution in vascular smooth muscle cells of spontaneously hypertensive rats

Protein kinase C is known to influence contraction in vascular smooth muscle cells by Ca(2+)-dependent and Ca(2+)-independent mechanisms. In the present study, the effect of protein kinase C activation by phorbol 12-myristate 13-acetate on resting cytosolic free Ca2+ and on cellular Ca2+ pools was assessed in cultured rat aortic muscle cells using fura 2. Cellular Ca2+ pools were evaluated with the selective inhibitor of the sarcoplasmic Ca2+ ATPase, thapsigargin. In normotensive vascular smooth muscle cells, protein kinase C activation caused a redistribution of Ca2+ from the thapsigargin-sensitive pool into the cytoplasm, whereas, in hypertensive cells, no significant effect of protein kinase C activity on cellular Ca2+ distribution was found. It is concluded that protein kinase C modulates the amount of Ca2+ stored in the thapsigargin-sensitive calcium stores. In hypertensive cells, the regulation of Ca2+ pools by protein kinase C is disturbed.