In vivo volumetric imaging of microcirculation within human skin under psoriatic conditions using optical microangiography

BACKGROUND AND OBJECTIVE

There is a growing body of evidence suggesting that vascular abnormalities may play crucial role in several dermatologic diseases, such as psoriasis, port wine stain, and skin cancer. To improve our understanding of vascular involvement in these skin conditions, there is a need for a non-invasive imaging modality capable of assessing 3D microcirculations within skin tissue beds in vivo. This study aims to demonstrate whether ultra-high sensitive optical microangiography (UHS-OMAG) is feasible to visualize skin microcirculations in 3D and to quantify microvascular vessel density under normal and psoriatic conditions in vivo.

STUDY DESIGN/MATERIAL AND METHODS

An UHS-OMAG system operating at 1,310 nm wavelength was used for in vivo imaging of microcirculation in human skin. The system has a spatial resolution of ∼10 µm × 20 µm (axial × lateral), running at 280 fps to acquire 3D imaging dataset to represent morphology and capillary level microvascular blood perfusion within the scanned skin tissue volume. The sensitivity of the system to the blood flow is as low as ∼4 µm/second. With this system, we performed the imaging experiments on the skin of a volunteer with stable plaque-type psoriasis. The microcirculation and structural information of normal and diseased skins were compared both qualitatively and quantitatively.

RESULTS

The UHS-OMAG is capable of differentiating the microcirculation within the normal skins from that in the psoriatic skins. The 3D optical images show that the blood vessel elongation and the dense network in the psoriatic lesion skin, the appearance of which is not observed within the normal skin. Based on the results obtained from one subject, the statistical analyses show that higher blood vessel density presented within the psoriasis lesion skin than that of the normal skin.

CONCLUSIONS

UHS-OMAG can be a valuable tool for imaging skin microcirculations non-invasively with high-speed and high-sensitivity, and therefore may have a useful role in future clinical diagnosis and treatment of dermatologic diseases such as psoriasis in human subjects.

In vivo volumetric imaging of microcirculation within human skin under psoriatic conditions using optical microangiography

BACKGROUND AND OBJECTIVE

There is a growing body of evidence suggesting that vascular abnormalities may play crucial role in several dermatologic diseases, such as psoriasis, port wine stain, and skin cancer. To improve our understanding of vascular involvement in these skin conditions, there is a need for a non-invasive imaging modality capable of assessing 3D microcirculations within skin tissue beds in vivo. This study aims to demonstrate whether ultra-high sensitive optical microangiography (UHS-OMAG) is feasible to visualize skin microcirculations in 3D and to quantify microvascular vessel density under normal and psoriatic conditions in vivo.

STUDY DESIGN/MATERIAL AND METHODS

An UHS-OMAG system operating at 1,310 nm wavelength was used for in vivo imaging of microcirculation in human skin. The system has a spatial resolution of ∼10 µm × 20 µm (axial × lateral), running at 280 fps to acquire 3D imaging dataset to represent morphology and capillary level microvascular blood perfusion within the scanned skin tissue volume. The sensitivity of the system to the blood flow is as low as ∼4 µm/second. With this system, we performed the imaging experiments on the skin of a volunteer with stable plaque-type psoriasis. The microcirculation and structural information of normal and diseased skins were compared both qualitatively and quantitatively.

RESULTS

The UHS-OMAG is capable of differentiating the microcirculation within the normal skins from that in the psoriatic skins. The 3D optical images show that the blood vessel elongation and the dense network in the psoriatic lesion skin, the appearance of which is not observed within the normal skin. Based on the results obtained from one subject, the statistical analyses show that higher blood vessel density presented within the psoriasis lesion skin than that of the normal skin.

CONCLUSIONS

UHS-OMAG can be a valuable tool for imaging skin microcirculations non-invasively with high-speed and high-sensitivity, and therefore may have a useful role in future clinical diagnosis and treatment of dermatologic diseases such as psoriasis in human subjects.

CvhSlicer: an interactive cross-sectional anatomy navigation system based on high-resolution Chinese visible human data

We introduce the design and implementation of an interactive system for the navigation of cross-sectional anatomy based on Chinese Visible Human (CVH) data, named CvhSlicer. This system is featured in real-time computation and rendering of high-resolution anatomical images on standard personal computers (PCs) equipped with commodity Graphics Processing Units (GPUs). In order to load the whole-body dataset into the memory of a common PC, several processing steps are first applied to compress the huge CVH data. Thereafter, an adaptive CPU-GPU balancing scheme is performed to dynamically distribute rendering tasks among CPU and GPU based on parameters of computing resources. Experimental results demonstrate that our system can achieve real-time performance and has great potential to be used in anatomy education.

Abstract P2-09-21: Effect of MDR1 Gene Polymorphisms and Haplotypes on Taxanes-Based Chemotherapy Responses in Chinese Han Patients with Breast Cancer

Background: In recent years, taxanes play an important role in chemotherapy of breast cancer patients, and its response rate is about 50%. Taxanes is primarily metabolized by CYP450 in liver microsome, and it also is a substrate for P-glycoprotein (the coded product of MDR1 gene). The interindividual heterogeneity in drug-metabolizing enzymes and transporters has contributed to the variability on anti-cancer efficacy of taxanes in breast cancer patients. Several studies showed that the pharmacokinetics of taxanes was influenced by the MDR1 polymorphisms. The aim of this study is to investigate the relationship between MDR1 gene polymorphisms and taxanes-based chemotherapy responses, and provides useful information for clinical personalized medicine and prognostic judgment.

Material and Methods: Genotyping of MDR1 variants was determined in the blood samples from 142 Chinese Han patients with breast cancer, by PCR-RFLP. The association of the gene polymorphisms of MDR1 C1236T at exon 12, G2677T/A at exon 21 and C3435T at exon 26 with chemotherapy responses was analyzed on the 63 patients, who received taxanes-based neoadjuvant chemotherapy [56 cases with TA (taxanes and anthracycline), 7 cases with TAC (C: cyclophosphamide)] and had the intact treatment follow-up information.

Results: In the 142 breast cancer patients, the frequencies of C1236T, G2677T, G2677A and C3435T variant alleles was 70.7%,52.1%,2.5% and 46.5%, respectively, and the frequency of 3435T allele was significantly higher in comparison with that in healthy subjects (34.7%). In the 63 patients with neoadjuvant chemotherapy, the overall clinical response rate (CR+PR) to chemotherapy was 66.7%. 3435TT genotype was showed to be related to taxanes-based chemotherapy, and its efficient rate was 23.1%, significantly lower than that of patients carrying C allele (73.5%; x2 = 9.125, P=0.003). The 3 SNPs were in linkage disequilibrium, and the 4 haplotypes TTT, TGC, CGC and TTC were 90.6 % of all. The patients who carrying 2677G-3435C haplotype showed better response to chemotherapy compared with those with the other haplotypes combined (72.1% vs 40.0%;x2=9.125, P=0.003). The response rate of the patients with 2677T-3435T haplotype or 1236T-3435T haplotype (54.3% or 54.9%) were lower than that of the patients harboring the other haplotypes (82.4% or 91.7%;x2=4.128 and x2=4.118, P =0.042 for both) respectively, and the efficient rate of the patients with 1236T-2677T-3435T (54.3%) were also lower than that of the patients with other haplotypes combined (82.4%;x2=4.128, P=0.042).

Conclusion: C1236T, G2677T/A and C3435T of MDR1 gene were polymorphic with different frequency in breast cancer patients. The analyses of MDR1 C3435T genotype and its haplotypes with C1236T or G2677T/A are valuable for predicting the taxanes-based chemotherapy responses in breast cancer patients, which deserve the further study.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-09-21.

Ultrahigh sensitive optical microangiography for in vivo imaging of microcirculations within human skin tissue beds

In this paper, we demonstrate for the first time that the detailed cutaneous blood flow at capillary level within dermis of human skin can be imaged by optical micro-angiography (OMAG) technique. A novel scanning protocol, i.e. fast B scan mode is used to achieve the capillary flow imaging. We employ a 1310nm system to scan the skin tissue at an imaging rate of 300 frames per second, which requires only ~5 sec to complete one 3D imaging of capillary blood flow within skin. The technique is sensitive enough to image the very slow blood flows at ~4 microm/sec. The promising results show a great potential of OMAG's role in the diagnosis, treatment and management of human skin diseases.

Study on environmental estrogen pollution in Yangtze River (Nanjing section) by an in vivo bioassay

Estrogenic activities and main causative fractions in three representative sections of Yangtze River (Nanjing section) were determined. The results showed that significant vitellogenin (VTG) and 17beta-estradiol (E(2)) induction and gonad atrophy were observed. Estradiol equivalents of actual water samples from Jiangxinzhou section, Sanchahe section and Daqiao section were 0.3651, 0.1301 and 0.5060 ng L(-1), respectively. Polar contaminants were responsible for the estrogenic activities in Jiangxinzhou section and Daqiao section while mid-polar and nonpolar contaminants resulted in majority of the estrogenic activity in Sanchahe section. To Jiangxinzhou section, Sanchahe section and Daqiao section, good positive correlations between VTG and E(2) (the correlation coefficients were 0.737, 0.690 and 0.817, respectively) and good inverse correlations between VTG and gonado-somatic index (GSI; the correlation coefficients were -0.838, -0.540 and -0.794, respectively) were obtained, whereas the correlations between E(2) and GSI were relatively poor (the correlation coefficients were only -0.557, -0.620 and -0.509, respectively).

Active biomonitoring of complex pollution in Taihu Lake with Carassius auratus

Carassius auratus bred in clean water were selected to conduct active biomonitoring (ABM) exposures in Meiliang and Gong bays in the northern polluted area of Taihu Lake. The biotransformation enzymes 7-ethoxyresorufin-O-deethylase (EROD) and glutathione S-transferase (GST), antioxidant enzymes glutathione peroxidase (GP(X)), reduced glutathione (GSH) content and superoxide dismutase (SOD) and lipoperoxidation (as TBARS) in liver were determined as biomarkers during the field exposure period. At the same time, the contents of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and heavy metals in the surface sediments of biomonitoring sites were measured. The total PAH concentrations ranged from 248.8 to 375.9microgkg(-1) dry weight, PCB from 1.26 to 2.41microgkg(-1), OCP from 0.15 to 2.06microgkg(-1), and heavy metal from 126.3 to 210.0mgkg(-1). The results indicate that complex pollution by persistent organic pollutants and heavy metals is present in the northern end of Taihu Lake and the in situ exposed organisms were stressed. Moreover, Meilaing Bay is a more stressful place to fish living there. The integrated biomarker response (IBR) was calculated by combining different biomarkers to single value, which can be used to describe the toxically-induced stress level of populations in different areas. Pollutant concentrations were displayed as star plots and compared to IBR star plots. There was a visual correlation between the PCB gradient and the OCP gradient measured in the sediments and the IBR variation.

Studies on protective effects of human paraoxonases 1 and 3 on atherosclerosis in apolipoprotein E knockout mice

Paraoxonase (PON) possesses antiatherogenic potentials, but the distinct functions of PON members in alleviating atherosclerosis are not yet clear. This study aimed to evaluate the protective effects of hPON1 and hPON3 against atherosclerosis, and thereby exploring their synergistic mechanism in atherosclerosis development. We generated the recombinant adenovirus AdPON1 and AdPON3, which were capable of expressing hPON1 and hPON3. After AdPON1 and AdPON3 were injected intravenously into 5-week-old apolipoprotein E knockout mice, abundant hPON1 and hPON3 mRNA expression levels were detected. However, increase in serum lactonase activity was detected only in AdPON1-treated mice. Serum antioxidation and anti-inflammation capabilities in AdPON1-treated mice, reflected by malondialdehyde, total antioxidant capability and tumor necrosis factor-alpha levels, were greatly enhanced, whereas those in AdPON3-treated mice were not significantly affected. Nevertheless, histological analysis revealed that adenovirus-mediated expression of hPON1, hPON3 or both of them reduced atherosclerotic plaque area to a similar extent. Although no synergistic mechanism was detected in reducing arterial lesion size, hPON1 and hPON3 showed synergistic effects on promoting macrophage cholesterol efflux. In conclusion, hPON1 and hPON3 exhibited similar potentials in reducing arterial lesion size, but they exerted antiatherogenic effects in distinct ways.

Flux regulation of cardiac ryanodine receptor channels

The cardiac type 2 ryanodine receptor (RYR2) is activated by Ca²⁺-induced Ca²⁺ release (CICR). The inherent positive feedback of CICR is well controlled in cells, but the nature of this control is debated. Here, we explore how the Ca²⁺ flux (lumen-to-cytosol) carried by an open RYR2 channel influences its own cytosolic Ca²⁺ regulatory sites as well as those on a neighboring channel. Both flux-dependent activation and inhibition of single channels were detected when there were super-physiological Ca²⁺ fluxes (>3 pA). Single-channel results indicate a pore inhibition site distance of 1.2 ± 0.16 nm and that the activation site on an open channel is shielded/protected from its own flux. Our results indicate that the Ca²⁺ flux mediated by an open RYR2 channel in cells (∼0.5 pA) is too small to substantially regulate (activate or inhibit) the channel carrying it, even though it is sufficient to activate a neighboring RYR2 channel.

Ryanodine receptor luminal Ca2+ regulation: swapping calsequestrin and channel isoforms

Sarcoplasmic reticulum (SR) Ca(2+) release in striated muscle is mediated by a multiprotein complex that includes the ryanodine receptor (RyR) Ca(2+) channel and the intra-SR Ca(2+) buffering protein calsequestrin (CSQ). Besides its buffering role, CSQ is thought to regulate RyR channel function. Here, CSQ-dependent luminal Ca(2+) regulation of skeletal (RyR1) and cardiac (RyR2) channels is explored. Skeletal (CSQ1) or cardiac (CSQ2) calsequestrin were systematically added to the luminal side of single RyR1 or RyR2 channels. The luminal Ca(2+) dependence of open probability (Po) over the physiologically relevant range (0.05-1 mM Ca(2+)) was defined for each of the four RyR/CSQ isoform pairings. We found that the luminal Ca(2+) sensitivity of single RyR2 channels was substantial when either CSQ isoform was present. In contrast, no significant luminal Ca(2+) sensitivity of single RyR1 channels was detected in the presence of either CSQ isoform. We conclude that CSQ-dependent luminal Ca(2+) regulation of single RyR2 channels lacks CSQ isoform specificity, and that CSQ-dependent luminal Ca(2+) regulation in skeletal muscle likely plays a relatively minor (if any) role in regulating the RyR1 channel activity, indicating that the chief role of CSQ1 in this tissue is as an intra-SR Ca(2+) buffer.

Syphilis co-infection does not affect HIV disease progression

HIV and syphilis are often seen as co-infections since they share a common mode of transmission. During episodes of syphilis, CD4 counts transiently decrease and HIV viral loads increase; however, the effect of syphilis co-infection on HIV disease progression (time to AIDS or death) is unclear. We analysed prospectively collected information on 2239 persons with estimated dates of HIV seroconversion (205 [9.2%] with confirmed syphilis and 66 [2.9%] with probable syphilis) in order to determine the effect of syphilis co-infection on HIV disease progression. In multivariate models censored at highly active antiretroviral therapy (HAART) initiation or last visit, adjusting for CD4 count, age, race, gender, and hepatitis B and C status, syphilis (confirmed + probable) was not associated with increased hazard of AIDS or death (hazard ratio 0.99, 95% CI 0.73-1.33). Treating HAART as a time-varying covariate or limiting the analysis to only confirmed syphilis cases did not significantly alter the results. Despite transient changes in CD4 counts and viral loads, syphilis does not appear to affect HIV disease progression.

Distribution of vasoactive intestinal peptide and substance P messenger ribonucleic acid in intestinal nerve of Remak of chicken

The intestinal nerve of Remak (INR) is unique to birds. The exact distributions and secretions of the peptide transmitters in the INR that innervate the intestine, and the patterns of their projections to the nerve plexus of the intestinal wall, are still unclear. In the present study, the distributions of chicken vasoactive intestinal peptide (VIP) mRNA and substance P (SP) mRNA in the chicken INR were demonstrated by means of in situ hybridization histochemistry, using sense and antisense digoxigenin-labeled RNA probes. The in situ hybridization histochemistry results suggested that VIP mRNA-positive neurons were mainly distributed in ganglions, whereas some of the INR fibers were weakly positive. The proportion of VIP mRNA-positive cells among total neurons was 75% in the juxta-jejunoileum portion and 87% in the juxta-rectal portion of the INR. Most SP mRNA-positive cells were sporadically distributed in layers or small groups within the ganglions, as well as in nerve trunks between ganglions. Moreover, the proportion of positive cells among total neurons was 83% in the juxta-jejunoileum portion and 98% in the juxta-rectal portion of the INR, which suggests that both VIP and SP mRNA are coexpressed in the chicken INR. Our results provide an approach to further study of the locations of VIP and SP in nerve tissue.

Semiparametric analysis for recurrent event data with time-dependent covariates and informative censoring

Recurrent event data analyses are usually conducted under the assumption that the censoring time is independent of the recurrent event process. In many applications the censoring time can be informative about the underlying recurrent event process, especially in situations where a correlated failure event could potentially terminate the observation of recurrent events. In this article, we consider a semiparametric model of recurrent event data that allows correlations between censoring times and recurrent event process via frailty. This flexible framework incorporates both time-dependent and time-independent covariates in the formulation, while leaving the distributions of frailty and censoring times unspecified. We propose a novel semiparametric inference procedure that depends on neither the frailty nor the censoring time distribution. Large sample properties of the regression parameter estimates and the estimated baseline cumulative intensity functions are studied. Numerical studies demonstrate that the proposed methodology performs well for realistic sample sizes. An analysis of hospitalization data for patients in an AIDS cohort study is presented to illustrate the proposed method.

Oxytocin receptor expressed on the smooth muscle mediates the excitatory effect of oxytocin on gastric motility in rats

The aim of this study was to localize oxytocin receptor (OTR) in the stomach and to investigate the effect of OT on gastric motility in rats. Western blot and immunohistochemistry methods were used to localize OTR in stomach. The motility of stomach was recorded in vivo (recording of the intragastric pressure), in vitro (recording of the contraction of muscle strips) and on isolated smooth muscle cells. OTR was expressed on cells of both circular and longitudinal muscle of stomach. Systemic administration of OT induced an early transient decrease and a subsequent increase on intragastric pressure. Devazepide (1 mg kg(-1), i.v.), a cholecystokinin-1 (CCK(1)) receptor antagonist, completely abolished the transient response but did not influence the subsequent one. OT (10(-9)-10(-6) mol L(-1)) dose-dependently increased the contraction of the muscle strips of gastric body, antrum, and pyloric sphincter, and decreased the average cell length of isolated smooth muscle cells. Tetrodotoxin and atropine did not influence the effect of OT on muscle strips. Pretreatment with atosiban, an OTR antagonist, inhibited the spontaneous contraction of muscle strips and abolished the excitatory effect of OT on the muscle strips and the isolated cells. These results suggest that the OTR is expressed on the smooth muscle of the stomach and mediates excitatory effect of OT on gastric motility.

Cluster characterization of mouse embryonic stem cell-derived pluripotent embryoid bodies in four distinct developmental stages

The formation of embryoid bodies (EBs) is the principal step in the differentiation of embryonic stem (ES) cells. In this study, the morphological characteristics and gene expression patterns of EBs related to the sequential stages of embryonic development were well defined in four distinct developmental groups over 112 days of culture: early-stage EBs groups (1-7 days of differentiation), mid-stage EBs groups (9-15 days of differentiation), maturing EBs groups (17-45 days of differentiation) and matured EBs groups (50 days of differentiation). We first determined definite histological location of apoptosis within EBs and the sequential expression of molecular markers representing stem cells (Oct4, SSEA-1, Sox-2 and AKP), germ cells (Fragilis, Dazl, c-kit, StellaR, Mvh and Stra8), ectoderm (Neurod, Nestin and Neurofilament), mesoderm (Gata-1, Flk-1 and Hbb) and endoderm (AFP and Transthyretin). Our results revealed that developing EBs possess either pluripotent stem cell or germ cell states and that three-dimensional aggregates of EBs initiate mES cell differentiation during prolonged culture in vitro. Therefore, we suggest that this EB system to some extent recapitulates the early developmental processes occurring in vivo.

Upregulation of PIP3-dependent Rac exchanger 1 (P-Rex1) promotes prostate cancer metastasis

Excessive activation of G-protein coupled receptor (GPCR) and receptor tyrosine kinase (RTK) pathways has been linked to prostate cancer metastasis. Rac activation by guanine-nucleotide exchange factors (GEFs) plays an important role in directional cell migration, a critical step of tumor metastasis cascades. We found that upregulation of P-Rex1, a Rac-selective GEF synergistically activated by Gβγ freed during GPCR signaling and PIP3 generated during either RTK or GPCR signaling, strongly correlates with metastatic phenotypes in both prostate cancer cell lines and human prostate cancer specimens. Silencing endogenous P-Rex1 in metastatic prostate cancer PC-3 cells selectively inhibited Rac activity and reduced cell migration and invasion in response to ligands of both epidermal growth factor receptor and G-protein coupled CXC chemokine receptor 4. Conversely, expression of recombinant P-Rex1, but not its “GEF-dead” mutant, in non-metastatic prostate cancer CWR22Rv1 cells increased cell migration and invasion via Rac-dependent lamellipodia formation. More importantly, using a mouse xenograft model, we demonstrated that expression of P-Rex1, but not its mutant, induced lymph node metastasis of CWR22Rv1 cells without an effect on primary tumor growth. Thus, by functioning as a coincidence detector of chemotactic signals from both GPCRs and RTKs, P-Rex1-dependent activation of Rac promotes prostate cancer metastasis.

Trifluoperazine: a rynodine receptor agonist

Trifluoperazine (TFP), a phenothiazine, is a commonly used antipsychotic drug whose therapeutic effects are attributed to its central anti-adrenergic and anti-dopaminergic actions. However, TFP is also a calmodulin (CaM) antagonist and alters the Ca(2+) binding properties of calsequestrin (CSQ). The CaM and CSQ proteins are known modulators of sarcoplasmic reticulum (SR) Ca(2+) release in ventricular myocytes. We explored TFP actions on cardiac SR Ca(2+) release in cells and single type-2 ryanodine receptor (RyR2) channel activity in bilayers. In intact and permeabilized ventricular myocytes, TFP produced an initial activation of RyR2-mediated SR Ca(2+) release and over time depleted SR Ca(2+) content. At the single channel level, TFP or nortryptiline (NRT; a tricyclic antidepressant also known to modify CSQ Ca(2+) binding) increased the open probability (Po) of CSQ-free channels with an EC(50) of 5.2 microM or 8.9 microM (respectively). This Po increase was due to elevated open event frequency at low drug concentrations while longer mean open events sustained Po at higher drug concentrations. Activation of RyR2 by TFP occurred in the presence or absence of CaM. TFP may also inhibit SR Ca uptake as well as increase RyR2 opening. Our results suggest TFP and NRT can alter RyR2 function by interacting with the channel protein directly, independent of its actions on CSQ or CaM. This direct action may contribute to the clinical adverse cardiac side effects associated with these drugs.

Liposome-mediated transfer can improve the efficacy of islet labeling with superparamagnetic iron oxide

An in vivo method for islet visualization using magnetic resonance imaging (MRI), using superparamagnetic iron oxide (SPIO), has been described. Herein we have developed a protocol that uses cationic liposomes to increase the efficiency of islet cell labeling by SPIO in vitro. Fresh islet cells were incubated in RPMI-1640 medium, to which had been added a range of concentrations of ferucarbotran, a SPIO contrast agent. At each SPIO concentration, duplicate samples were incubated with versus without addition of cationic liposomes. We measured intracellular iron concentration, cell viability, and insulin-release function after labeling. We observed that the amount of iron bound to islet cells increased as the concentration of added SPIO increased. The presence of liposomes increased labeling efficiency at each SPIO concentration. In vitro MRI confirmed the effect of liposomes to improve labeling efficiency of islet cells by SPIO.

Tricyclic antidepressant amitriptyline alters sarcoplasmic reticulum calcium handling in ventricular myocytes

Tricyclic antidepressants such as amitriptyline (AMT) have been reported to have adverse side effects on cardiac performance. AMT effects on Ca handling in ventricular myocytes, however, are not well understood. Therefore, we investigated AMT action on sarcoplasmic reticulum (SR) Ca release in ventricular myocytes, ryanodine receptor (RyR) activity, and Ca uptake by SR microsomes. In permeabilized myocytes, AMT transiently increased free luminal Ca concentration ([Ca]) followed by marked depletion. AMT (10 microM) caused a rapid and a transient increase of Ca spark frequency, followed by a significant suppression of spark activity. The latter was associated with a decrease of Ca spark amplitude and SR Ca load to 87 and 60%, respectively. AMT (10 microM) completely abolished propagation of spontaneous Ca waves. Higher concentrations of AMT (0.1-1 mM) evoked SR Ca release reminiscent of the effect of caffeine (20 mM) and caused almost complete depletion of SR Ca content. Studies on single calsequestrin-free RyR channels revealed that AMT increased the mean open time and open probability (Po) in a dose-dependent fashion (dissociation constant = 4.2 microM). High concentrations of AMT (> 25 microM) evoked frequent long openings with Po reaching very high levels (> 0.70). In studies with cardiac SR microsomes, AMT slowed the rate of ATP-dependent Ca uptake. We conclude that AMT affects SR Ca handling in ventricular myocytes by multiple mechanisms, including direct stimulation of RyRs and inhibition of SR Ca uptake. These effects could contribute to AMT cardiotoxicity.

A map of the class III region of the sheep major histocompatibilty complex

Background

The central, or class III, region of the major histocompatibility complex (MHC) is an important gene rich sub-region of the MHC of mammals and contains many loci implicated in disease processes and potential productivity traits. As a prelude to identifying MHC loci associated with productivity traits in sheep, we have used BAC and cosmid libraries of genomic DNA to generate a physical map of the sheep MHC class III region. This map will facilitate association studies and provide insights into the distribution of recombination events in this chromosomal segment.

Results

Twenty eight sheep genes were identified in 10 BAC clones which spanned approximately 700 kbp of a chromosomal region adjacent to the class I region of the sheep MHC and which therefore covers most, if not all, of the class III of the sheep MHC. The relative positions of 17 of these genes was established as well as two additional groups of genes for which the intragroup order was not known. Cosmid mapping permitted a more detailed mapping of the complement genes present in the class III and showed a local inversion (relative to humans) of one pair of the duplicated complement C4 and CYP21 loci. A panel of 26 single nucleotide polymorphisms (SNPs) was identified in 10 loci, covering ≈600 kbp of the mapped region.

Conclusion

This report provides a physical map covering ≈700 kbp of the class III of the sheep MHC together with a SNP panel which will facilitate disease and productivity association studies. The presence of a local inversion (relative to humans) of one pair of the duplicated C4 and CYP21 loci and a previously described dinucleotide tandem repeat locus (BfMs) has been located within an intron of the SK12VL gene.

Luminal Ca2+ regulation of single cardiac ryanodine receptors: insights provided by calsequestrin and its mutants

The luminal Ca2+ regulation of cardiac ryanodine receptor (RyR2) was explored at the single channel level. The luminal Ca2+ and Mg2+ sensitivity of single CSQ2-stripped and CSQ2-associated RyR2 channels was defined. Action of wild-type CSQ2 and of two mutant CSQ2s (R33Q and L167H) was also compared. Two luminal Ca2+ regulatory mechanism(s) were identified. One is a RyR2-resident mechanism that is CSQ2 independent and does not distinguish between luminal Ca2+ and Mg2+. This mechanism modulates the maximal efficacy of cytosolic Ca2+ activation. The second luminal Ca2+ regulatory mechanism is CSQ2 dependent and distinguishes between luminal Ca2+ and Mg2+. It does not depend on CSQ2 oligomerization or CSQ2 monomer Ca2+ binding affinity. The key Ca2+-sensitive step in this mechanism may be the Ca2+-dependent CSQ2 interaction with triadin. The CSQ2-dependent mechanism alters the cytosolic Ca2+ sensitivity of the channel. The R33Q CSQ2 mutant can participate in luminal RyR2 Ca2+ regulation but less effectively than wild-type (WT) CSQ2. CSQ2-L167H does not participate in luminal RyR2 Ca2+ regulation. The disparate actions of these two catecholaminergic polymorphic ventricular tachycardia (CPVT)–linked mutants implies that either alteration or elimination of CSQ2-dependent luminal RyR2 regulation can generate the CPVT phenotype. We propose that the RyR2-resident, CSQ2-independent luminal Ca2+ mechanism may assure that all channels respond robustly to large (>5 μM) local cytosolic Ca2+ stimuli, whereas the CSQ2-dependent mechanism may help close RyR2 channels after luminal Ca2+ falls below ∼0.5 mM.