Gamma-ray-induced cell killing and chromosome abnormalities in the bone marrow of p53-deficient mice

Resistance to the lethal effects of ionizing radiation has been demonstrated in a wide variety of cell types with defects in the p53 gene (thymocytes, splenic B and T cells, in vitro hemopoietic colony-forming cells and intestinal cells of the mouse, embryo cells of the rat, and human Burkitt's lymphoma cells). In contrast, Slichenmeyer et al. (Cancer Res. 53, 4164-4167, 1993) found no evidence of resistance in fibroblasts derived from p53 null mice. The aim of our study was to compare the radiation response of hemopoietic colony-forming cells (in vitro CFC) and of fibroblastoid colony-forming cells or units (CFU-F) within the same tissue (marrow) in p53 null mice (-/-), heterozygotes (+/-) and wild-type animals (+/+). We have also tested the hypothesis that, in proliferating cells, radiation-induced cell killing is mediated through chromosome damage by examining the relationship between these end points in hemopoietic cells of the three mouse types. Both in vitro CFC and CFU-F of -/- mice were resistant to cell killing compared with +/+ and +/- mice whose cellular sensitivities were indistinguishable. The resistance was characterized by a broader "shoulder" on the cell survival curve, i.e. a higher extrapolation number but similar D0 values using the multitarget model or a lower alpha coefficient using the linear-quadratic model. The frequency of chromosomally abnormal marrow cells after irradiation was similar for the three genotypes. However, marrow cells with aberrations carried more aberrations in -/- mice than in +/+ or +/- mice such that the total number of aberrations per 100 cells was higher in -/- mice. Since there were no differences in the yields of aberrations between genotypes in spleen lymphocytes or in CFU-F (both noncycling at the time of irradiation) and less mitotic inhibition in -/- marrow cells than in +/+ or +/- cells, the chromosomal radiosensitivity of -/- marrow hemopoietic cells might be related to reduced cell cycle delay allowing insufficient time for repair, but other explanations have been considered. We postulate that the radiation resistance of both hemopoietic CFC and CFU-F in -/- mice is a consequence of the failure of DNA/chromosome damage to trigger apoptosis or permanent cell cycle arrest to the same extent as in the +/+ or +/- mice: hence the lack of correlation between chromosome damage and cell death in the three mouse types.

PTH/PTHrP receptor is temporally regulated during osteoblast differentiation and is associated with collagen synthesis

The temporal sequence of PTH/PTHrP receptor mRNA, binding, biologic activity, and its dependence on matrix synthesis was determined using MC3T3-E1 preosteoblast-like cells and primary rat calvarial cells in vitro. Osteoblastic cells were induced to differentiate and form mineralized nodules with the addition of ascorbic acid and beta-glycerophosphate, and samples were collected from 0-26 days of culture. DNA levels as determined by fluorometric analysis increased 12- and 17-fold during the collection period for both MC3T3-E1 and primary calvarial cells respectively. Steady state mRNA levels for the PTH/PTHrP receptor as determined by northern blot analysis, were initially low for both cell types, peaked at day 4 and 5 for MC3T3-E1 and primary calvarial cells respectively, and declined thereafter. Competition binding curves were performed during differentiation using 125I-PTHrP. The numbers of receptors per microgram DNA were greatest at days 3 and 5 for MC3T3-E1 and primary calvarial cells respectively. The biologic activity of the receptor was evaluated by stimulating the cells with 10 nM PTHrP and determining cAMP levels via a binding protein assay. The PTHrP-stimulated cAMP levels increased 5-fold to peak values at day 5 for MC3T3-E1! cells and 6-fold to peak values at day 4 for the primary calvarial cells. Ascorbic acid was required for maximal development of a PTH-dependent cAMP response since ascorbic acid-treated MC3T3-E1 cells had twice the PTH-stimulated cAMP levels as non-treated cells. When the collagen synthesis inhibitor 3,4-dehydroproline was administered to MC3T3-E1 cultures prior to differentiation, there was a subsequent diminution of the PTH/PTHrP receptor mRNA gene expression and numbers of receptors per cell; however, if administered after the initiation of matrix synthesis there was no reduction in PTH/PTHrP receptor mRNA. These findings indicate that the PTH/PTHrP receptor is associated temporally at the level of mRNA, protein, and biologic activity, with a differentiating, matrix-producing osteoblastic cell in vitro.

Growth factor induction of cytosolic protein tyrosine kinase activity in human haemopoietic progenitor cells isolated by flow cytometry

We employed a highly sensitive method to assay protein tyrosine kinase activity in extracts of subpopulations of CD34+ bone marrow progenitor cells isolated by fluorescence activated cell sorting in an attempt to better define how growth-factor induction of enzymatic activity relates to progenitor cell maturation. FACS analysis confirmed that, under the conditions employed, essentially all of the CD34+ cells in adult human marrow that lacked the CD38 antigen were devoid of the myeloid maturation marker CD33 as well as the lineage antigens: CD10, 13, 14, 15, 16, 19, 71 and glycophorin A. A variable portion (50-90%) of these CD34+, CD38- progenitor cells expressed HLA-DR. CD34+, CD38- cells that did not express HLA-DR were found to lack detectable levels of either membrane or cytosolic tyrosine kinase activity. HLA-DR+ progenitor cells that lacked CD38 possessed elevated levels of cytosolic tyrosine kinase activity but only low levels of plasma membrane activity. In contrast, CD34+ cells that expressed CD38 (and HLA-DR) possessed high levels of membrane-associated tyrosine kinase activity. A cocktail of haemopoietic growth factors that included IL-3, IL-6 and stem cell factor effectively induced tyrosine kinase activity in CD34+, CD38-, HLA-DR- progenitor cells. Growth factor induction of tyrosine kinase activity in these cells was not inhibited by actinomycin D or cyclohexamide. Most of the tyrosine kinase activity induced by these growth factors was recovered from the cytosolic fraction of disrupted cells. Thus, induction of cytosolic tyrosine kinase activity is an early event in the response of uncommitted haemopoietic cells to haemopoietic growth factors. Subsequent activation of membrane tyrosine kinases may initiate key transduction processes as these cells begin to differentiate.

Identification and functional role of beta-adrenergic receptor subtypes in primate and rodent: in vivo versus isolated myocytes

We determined the relationship between the beta 1- and beta 2-adrenergic receptor subtypes in isolated myocytes and their physiological responsiveness in chronically instrumented conscious baboons and rats. In conscious baboons, isoproterenol (ISO) (0.02 microgram/kg) increased left ventricular (LV) dP/dt by 89 +/- 6.7% from 2898 +/- 370 mmHg/s and only by 13 +/- 3.3% from 2491 +/- 146 mmHg/s after beta 1-adrenergic receptor blockade, indicating that the predominant physiological response was mediated by beta 1-adrenergic receptors. Decreases in mean arterial pressure (-11 +/- 0.5 mmHg v -16 +/- 4.6 mmHg) and coronary vascular resistance (-3.1 +/- 0.4 v -3.6 +/- 0.4 mmHg/ml/min) induced by ISO were not different before and after beta 1-blockade, indicating that beta 2-adrenergic receptors were not blocked. In conscious rats, ISO (0.4 microgram/kg) increased LV dP/dt by 50 +/- 4.9% from 13252 +/- 2002 mmHg/s and only by 10 +/- 3.9% from 10793 +/- 1364 mmHg/s after beta 1-adrenergic receptor blockade: whereas decreases in mean arterial pressure induced by ISO were not different before and after beta 1-blockade (-19 +/- 2.4 mmHg v -16 +/- 2.2 mmHg), i.e. very consistent with the physiological responses in baboons. In vitro studies of isolated myocytes, using radioligand binding with 125I-cyanopindolol (125I-cyp) and the subtype beta 1-selective antagonist betaxolol and the beta 2-selective antagonist ICI 118551 indicated that the beta 1/beta 2 ratio of rat myocytes was 92/8: whereas baboon myocytes were more equally distributed (59/41). Thus, in both species the preponderance of effects of ISO on ventricular function was beta 1-adrenergic receptor mediated, which is consistent with the beta 1/beta 2 ratio in rat myocytes but not in baboon myocytes, where a significant fraction of beta 2-adrenergic receptors does not appear to exert an effect on conctractility in vivo.

Messenger functions of phosphatidic acid

Under physiological conditions, phosphatidic acid (PA) is an anionic phospholipid with moderate biological reactivity. Some of its biological effects can be attributed to lyso-PA and diacylglycerol generated by the action of cellular hydrolases. However, it is clear that the parent compound exhibits biological activities of its own. Early studies implicated PA in the transport of Ca++ across plasma membranes as well as in the mobilization of intracellular stored calcium. Both responses may be induced as a consequence of other cellular processes activated by PA, as opposed to being directly mediated by the lipid. PA may be involved in the activation of certain functions confined to specialized groupings of cells, such as the neutrophil superoxide-generating enzyme or actin polymerization. Recent studies implicate PA as an activator of intracellular protein kinases, and a PA-dependent superfamily of kinases involved in cellular signalling has been hypothesized. Deployed on the outer surface of the plasma membrane, PA potentially provides a method of communication between cells in direct contact. This review will explore the known functions of PA as an intracellular mediator and extracellular messenger of biological activities and address ways in which these functions are potentially regulated by cellular enzymes which hydrolyse the phospholipid.

[Fetal erythroblasts from maternal blood for prenatal genetic diagnosis]

OBJECTIVE

To study fetal erythroblasts (FE) from maternal peripheral blood for the diagnosis of fetal aneuploidies.

METHODS

FE expressing the glycophorin A(GPA) were isolated from 13 pregnant women with male fetus (8-14 w) by fluorescence-activated cell sorting(FACS), FE were identified by oligonucleotide primed in situ labelling (PRINS) with Y centromeric satellite DNA primer. The concentration of pregnancy-associated plasma protein A (PAPP-A) was measured by enzyme-labelled immunosorbent assay (ELISA) in serum samples of 41 normal pregnant women (8-14 w). In 5 pregnant women suspicious of fetal Down's syndrome (10-13 w) the serum and FE were examined by PAPP-A, GPA/FACS and PRINS with 21 chromosome centrometric primer.

RESULTS

Detection of flow sorted FE from 13 pregnant women by Y primer showed 14.5% of GPA positive signal. There was no difference in serum level of PAPP-A between 5 pregnant women and 41 normal controls, and all GPA positive cell nuclei of the 5 cases displayed two signals with 21 chromosome.

CONCLUSION

Measurement of fetal erythroblasts from maternal blood for the diagnosis of genetic fetal aneuploidies is a promising non-invasive, rapid and reliable technique.

Applications of the normal-incidence rotating-sample ellipsometer to high- and low-spatial-frequency gratings

The normal-incidence rotating-sample ellipsometer is an instrument that can be used to characterize grating surfaces from the measured ratio ρof complex reflection coefficients r(y)/r(x) of light polarized perpendicular and parallel to the grating groove direction. Experimental results at different wavelengths for different gratings with spatial frequencies from 150 to 5880 grooves/mm are presented. The groove depth of the 5880-grooves/mm gold-coated grating can be estimated from the measured ρ and rigorous grating theory.

The leucine-responsive regulatory protein (Lrp) from Escherichia coli. Stoichiometry and minimal requirements for binding to DNA

Lrp (Leucine-responsive regulatory protein) regulates the expression of a number of operons in Escherichia coli. A recent study of DNA sequences recognized by Lrp established the consensus as a 15-bp sequence, YAGHAWATTWTDCTR (Y = C/T, H = "not G," W = A/T, D ="not C," R = A/G) (Cui, Y., Wang, Q., Stormo, G. D., and Calvo, J. M. (1995) J. Bacteriol. 177, 4872-4880). Here we report the stoichiometry of Lrp binding (an Lrp dimer binds to a single binding site) and studies that define the minimal length of DNA required for binding. A double-stranded 15 mer having a sequence that closely matches the consensus does not show measurable binding to Lrp. One or two base pairs of DNA flanking each end are not sufficient for binding, but constructs having 3-5 additional base pairs (21 mer) show relatively strong binding. Single-stranded flanking DNA also contributes to strong binding. The extent of the contribution to binding is dependent upon whether the single strand is on the left or right of the double-stranded region and whether the polarity of the single-stranded DNA is 5' to 3' or 3' to 5'.

In vivo microdialysis study on changes in septal dynorphin and beta-endorphin activities in active and hibernating Columbian ground squirrels

State-dependent changes in extracellular concentration of endogenous opioids in the septum of Columbian ground squirrels were examined in the hibernating and euthermic states using in vivo microdialysis. The order of estimated extracellular concentration was found to be: hibernating > interbout euthermia > non-hibernating euthermia for dynorphin A and interbout euthermia > hibernating > non-hibernating euthermia for beta-endorphin. The apparent turnover rates of dynorphin A during hibernation was 15 times greater than that during euthermic non-hibernation phase and that of beta-endorphin was 8-fold greater. These results demonstrate that subfamilies of endogenous opioids may vary differentially in their activities at different stages of an annual hibernation cycle and may reflect their different roles in the regulation of hibernation.

Overstretching B-DNA: the elastic response of individual double-stranded and single-stranded DNA molecules

Single molecules of double-stranded DNA (dsDNA) were stretched with force-measuring laser tweezers. Under a longitudinal stress of approximately 65 piconewtons (pN), dsDNA molecules in aqueous buffer undergo a highly cooperative transition into a stable form with 5.8 angstroms rise per base pair, that is, 70% longer than B form dsDNA. When the stress was relaxed below 65 pN, the molecules rapidly and reversibly contracted to their normal contour lengths. This transition was affected by changes in the ionic strength of the medium and the water activity or by cross-linking of the two strands of dsDNA. Individual molecules of single-stranded DNA were also stretched giving a persistence length of 7.5 angstroms and a stretch modulus of 800 pN. The overstretched form may play a significant role in the energetics of DNA recombination.

[The role of thoracoscopy in the diagnosis and treatment of lung cancer]

Using video-assisted thoracoscopic techniques in 32 lung cancer patients over the past 3 years, we have performed a vriety of procedures previously accomplished by "open" techniques. This group of patients included stage I (7 patients), stage II-IIIa (10), stage IV (15). Our procedures include wedge resections of lung tumor using endoscopic mechnical stapling devicesin 7 patients; pulmonary lobectomy in 7; lung cancer staging in 7; pleural biopsies and pleurodesis in 11. There were no mortality and no serious complications associated with the procedure. Our experience indicates on expanded role of thoracoscopy in the diagnosis and treatment of lung cancer.

[A study on complicated chromosome translocation by fluorescence in situ hybridization (FISH) of G-banded chromosomes]

An experimental method of fluorescence in situ hybridization (FISH) with conventionally G-band chromosomes was developed to analyze the complex chromosome rearrangements of patients. In order to obtain optimal results of both G-banding and fluorescence signals, it was essential that G-banded chromosomes were fixed with formaldehyde prior to fluorescence in situ hybridization. The karyotype of a patient with spontaneous abortion might be described as 46, XX, t(1; 5; 12) (1pter-->1q25 : : 12q24-->12qter; 5qter-->5p11 : : 1q25-->1qter; 12pter-->12q24 : : 5p11-->5pter) by the analysis of conventional cytogenetics. However, her karyotype should be identified as 46, XX, t(1; 5; 12) (1pter-->1q23 : : 12q22-->12qter; 5qter-->5p11 : : 1q25-->1qter; 12pter-->12q22 : : 1q23-->1q25 : : 5p11-->5pter) with this newly established method. This investigation indicates that this technique described above is a powerful tool to detect complex chromosome rearrangements of patients.

Cytosolic inactivation of translocated neutrophil plasma membrane protein tyrosine phosphatase

Phosphotyrosine phosphatases (PTPases) regulate cellular metabolic activation by reversing the effects of tyrosine kinases activated earlier in intracellular signaling pathways. We coupled fluorescence-activated cell sorter analysis using anti-CD45 monoclonal antibody with direct measurements of enzyme activity in resolved subcellular fractions to define mechanisms that potentially regulate the availability and activity of CD45-PTPase on neutrophil plasma membranes. Neutrophils in freshly obtained blood as well as neutrophils freshly isolated from blood were found to possess detectable levels of plasma membrane CD45 as assessed by immunofluorescence. However, plasma membranes from these cells were essentially devoid of PTPase catalytic activity, which was largely confined to the specific granules. Granulocyte-macrophage colony-stimulating factor (GM-CSF) upregulated both the catalytic and antigenic components of CD45-PTPase on the plasma membrane of these cells. Upregulation was associated with a shift in the particulate subcellular PTPase catalytic activity from the specific granule fraction to the plasma membrane fraction. The tyrosine kinase inhibitor genistein abrogated GM-CSF-promoted upregulation of plasma membrane CD45 PTPase but did not prevent the GM-CSF-dependent decrease in specific granule catalytic activity. Anti-CD45 antibody immunoprecipitated PTPase activity from both specific granules of resting cells and plasma membranes of GM-CSF-treated cells. However, antiphosphotyrosine immunoprecipitated only activity that had translocated to the plasma membrane, suggesting a role for CD45 phosphorylation in translocation. Western analysis confirmed the tyrosine phosphorylation of CD45 in plasma membranes of GM-CSF-treated neutrophils. Preincubation of plasma membranes of GM-CSF-stimulated neutrophils with cytosol from resting cells resulted in a time- and temperature-dependent loss in membrane PTPase as a consequence of the effects of a cytosolic inactivator. Cytosol obtained from stimulated neutrophils possessed substantially reduced levels of this PTPase inactivator. We conclude that activity of the catalytic component of membrane PTPase in circulating neutrophils is regulated by a cytosolic inactivator. Upon stimulation, intact CD45 PTPase is incorporated into the plasma membrane by a process that requires tyrosine phosphorylation. As a result of inhibition of the cytosolic inactivator, the translocated PTPase expresses full activity, thereby amplifying the potential regulatory influence of the enzyme on the cells' functional response.

State-dependent changes of brain endogenous opioids in mammalian hibernation

Endogenous opioids belonging to three opioid families were measured in different states of the hibernation cycle in brain of the Columbian ground squirrels. Using high-performance liquid chromatography-EC detection, the hypothalamic and septal concentrations of met-enkephalin were found to be significantly higher (p < 0.05) in the hibernating state than that in the nonhibernating state. In contrast, met-enkephalin content in the medulla decreased significantly during hibernation. Leuenkephalin content was only increased in the hypothalamus of hibernating animals. Using radioimmunoassay, dynorphin A-like immunoreactivity was observed to increase in the claustrum and striatum, whereas beta-endorphin-like peptides showed a significant increase in the hypothalamus during hibernation. It is evident that the changes in endogenous opioids in brain during hibernation are state dependent, type specific and region specific. These specific alterations of various endogenous opioids may imply their different roles in hibernation.

Sixteen-beam grating-based division-of-amplitude photopolarimeter

A 16-beam grating-based division-of-amplitude photopolarimeter that employs a transmission grating and a linear photodiode detector array has been developed and tested. The transmission grating splits the incident light beam into 16 orders with essentially uniform intensity distribution. Linear polarizers are placed in fanned-out azimuth orientations in different orders, and a quarter-wave retarder is inserted in one order. After calibration, the photopolarimeter makes time-resolved measurements of all the Stokes parameters of the incident light with a precision of 0.001. The calibration and testing of the system at 632.8 nm are presented.

[Scavenging effects of daphnetin and its Cu, Zn complexes on superoxide radical]

The scavenging effects of daphnetin (D) and its Cu, Zn complexes on superoxide radical (O2-.) generated through the photooxidation of riboflavin were studied with human red blood cells (RBC) and RBC membrane as experimental material. The Cu ( II ) complex showed the highest activity. SOD, D and its Cu ( II ), Zn ( II ) complexes were found to have inhibitory effect on the production of lipid peroxide in the membrane, SOD being the best among them.

[Application of serology and 14C-urea breath test to monitoring of the effect of anti-Helicobacter pylori chemotheraphy]

In order to evaluate the value of serology and 14C-urea breath test in monitoring the effect of anti-Helicobacter pylori chemotherapy, at the first stage of this study, endoscopy, 14C-urea breath test and serology (H. pylori IgG antibody measured by ELISA) were performed in 42 of patients before the onset of anti-H pylori chemotherapy and at 1, 3, 6 and 12 months after termination of the treatment. On analyzing the change of the results of breath test and serology during the one year follow-up period in these patients, "above the cutoff value" in breath test and "reduction of A value less than 15% when comparing with pretreatment" in serology were made as the H. pylori positive criteria for monitoring therapeutic effectiveness on H. pylori. At the second stage of this study, total of another 63 of patients were studied to test the accuracy of the monitoring criteria. The results showed that the sensitivity of breath test was all 100.0% and specificity 95.5% and 100.0% respectively at 6 and 12 month after termination of treatment, the sensitivity of serology was all 100.0% and specificity was 50.0% and 83.3% respectively. A scheme for monitoring the effect of anti-H. pylori chemotherapy by combination of 14C-urea breath test and serology is proposed based on this study.

Aberrant progenitors common to megakaryocytic and myeloid cells in a Down's infant with transient abnormal myelopoiesis

Phenotypic characteristics of blasts were studied in a Down's infant with transient abnormal myelopoiesis (TAM). Two major subpopulations were identified: (1) CD33+CD42b+ cells with platelet peroxidase activity, the commitment of which to megakaryocytic lineage was supported by an increased expression of GATA-1 mRNA; (2) CD33+CD34+CD7+CD4+ cells with immature ultrastructure, which could be either immature megakaryocytic or myeloid cells with aberrant differentiation. Mixed colonies containing megakaryocytes and monocyte/macrophages in the peripheral blood suggested the presence of progenitors common to these subpopulations. These results may indicate that subpopulations of blasts with phenotypic diversity could be derived from aberrant common progenitors to megakaryocytic and myeloid lineages in this patient.

Mineralization of bone-like extracellular matrix in the absence of functional osteoblasts

When grown in medium containing ascorbic acid and beta-glycerol phosphate, mouse MC3T3-E1 cells express an osteoblast phenotype and produce a highly mineralized extracellular matrix. The purpose of this study was to independently examine the role of the collagenous matrix and functional osteoblasts on the mineralization process. Cultures with and without an extensive collagenous matrix were prepared by growing MC3T3-E1 cells in the presence and absence of ascorbic acid. Matrix-rich cultures mineralized at much lower calcium phosphate ion products than nonmatrix cultures. At higher ion products, spontaneous precipitation in the medium and cell layers of nonmatrix cultures were observed. In contrast, mineral in matrix-rich cultures was still exclusively associated with collagen fibrils and not with ectopic sites in the cell layer or medium. To examine the effect of cell viability on matrix mineralization, cells were grown 8 or 16 days in the presence of ascorbic acid, then killed and incubated in a mineralizing medium. Significant mineralization was not observed in the collagenous matrix of 8-day killed cultures or age-matched controls. At 16 days mineral was associated with collagen fibrils at specific foci in the matrix of both viable and killed cultures. This observation is consistent with the concept that collagenous matrices must undergo a maturation process before they can support a mineral induction and growth. It further shows that osteoblast-like cells are not required for mineralization of mature matrices, but are required for matrix maturation.

Effects of isoprenaline on delayed rectifier potassium current in isolated guinea pig ventricular myocytes

AIM

To study the effects of isoprenaline (Iso) on the delayed rectifier potassium current (Ik) in isolated guinea pig ventricular myocytes.

METHODS

Single cells were isolated from guinea pig ventricle. Ik was studied under voltage clamp conditions.

RESULTS

When Ik was activated by depolarizing pulses to +40 mV of increasing duration (40-300 ms), Iso 1 mumol . L-1 caused an enhancement in Ik which was larger for longer pulses (150-300 ms). This was also seen when the intracellular calcium was buffered by 1,2-bis(2-aminophenoxy) ethane-N, N, N1, N1-tetraacetic acid (BAPTA). Intracellular application of BAPTA caused a decrease in Ik activated by longer pulses.

CONCLUSION

There were two components of Ik, one of which was modulated by Iso and intracellular Ca2+.

[Quantitative determination of ursolic acid in folium Ilicis cornutae (gouguye) gathered in different and periods]

The content of ursolic acid in Folium Ilicis Cornutae (Gouguye) gathered in different periods from Yongfeng county of Jiangxi province was determined by TLCS method. The result shows that the content appears to be low in samples gathered in April, but about the same in samples of February, June, August, October and December.

Cardiac channel gating charge movements: recovery from inactivation

The nonlinear charge movements which occur during membrane depolarization of cardiac ventricular myocytes (QON) have been previously identified and separated, by kinetic and steady-state criteria, into constituent components arising from the gating of Na channels and Ca channels. In contrast, the nature and time course of the OFF charge movements (QOFF), which follow membrane repolarization have not been as clearly established. In order to address this question cardiac QOFF was studied using small-diameter, 17-day-old embryonic chick ventricular myocytes that can be rapidly and uniformly voltage-clamped. The application of brief (5.4 ms) depolarizing steps were employed to produce Na channel inactivation but little Ca channel inactivation. Following the return of the membrane potential to -100 mV QOFF, measured as the gating current termed IgOFF, displayed two kinetic components. Double exponential fits to IgOFF yielded time constants of a few tenths of a millisecond for the fast component (IgOFFfast) and of 1-2 ms for the slower component (IgOFFslow). The time course and voltage dependence for the slower component suggested that it might be linked to the inactivation, and the recovery from inactivation, of Na channels. In order to identify these kinetic components double-pulse protocols were employed in which the duration of the prepulse and the interval separating the prepulse and test pulse were varied. The time course for the decay of IgOFFslow following a brief inactivating prepulse was similar to the time course for the recovery of the Na channel QON (QNaRecov). Both IgOFFslow and QNaRecov preceded the recovery of the Na channel (ionic) current. The recovery from inactivation of both the Na current and QNa displayed a similar voltage dependence. These experiments have helped to identify the two components of cardiac IgOFF and, therefore, will facilitate the interpretation of further biophysical and pharmacological studies concerning cardiac Na channel and Ca channel gating charge movements.

Identification of a global repressor gene, rsmA, of Erwinia carotovora subsp. carotovora that controls extracellular enzymes, N-(3-oxohexanoyl)-L-homoserine lactone, and pathogenicity in soft-rotting Erwinia spp

The production of extracellular enzymes such as pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt) is activated by the cell density (quorum)-sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone (HSL); plant signals; and aep genes during postexponential growth of Erwinia carotovora subsp. carotovora 71. Studies with mutants of E. carotovora subsp. carotovora 71 derepressed in exoenzyme production led to the identification of a negative regulator gene, rsmA (rsm, repressor of secondary metabolites). Nucleotide sequencing, transcript assays, and protein analysis established that a 183-bp open reading frame encodes the 6.8-kDa RsmA. rsmA has extensive homology with the csrA gene of Escherichia coli, which specifies a negative regulator of carbon storage. Moreover, the suppression of glycogen synthesis in E. coli by rsmA indicates that the Erwinia gene is functionally similar to csrA. Southern hybridizations revealed the presence of rsmA homologs in soft-rotting and non-soft-rotting Erwinia spp. and in other enterobacteria such as Enterobacter aerogenes, E. coli, Salmonella typhimurium, Shigella flexneri, Serratia marcescens, and Yersinia pseudotuberculosis. rsmA suppresses production of Pel, Peh, Cel, and Prt, plant pathogenicity, and synthesis of HSL in E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, E. carotovora subsp. carotovora, and E. chrysanthemi. In the E. carotovora subsp. carotovora 71, rsmA reduces the levels of transcripts of hslI, a luxI homolog required for HSL biosynthesis. This specific effect and the previous finding that HSL is required for extracellular enzyme production and pathogenicity in soft-rotting Erwinia spp. support the hypothesis that rsmA controls these traits by modulating the levels of the cell density (quorum)-sensing signal.