Does the autoantibody immunodominant region on thyroid peroxidase include amino acid residues 742-771?

Identification of the thyroid peroxidase (TPO) amino acid residues that comprise the autoantibody immunodominant region is an important goal that has proven difficult because of the conformational nature of the epitopes involved. Recent data suggest that the immunodominant region has been located. Thus, by autoantibody recognition of tryptic fragments of native TPO, as well as of conformational portions of TPO expressed as cell-free translates, the autoantibody immunodominant region appears to include amino acid residues 742-771, near the C terminus of the ectodomain. To evaluate this deduction, we expressed as cell-free translates the full TPO ectodomain, as well as TPO truncated after residues 741 and 771. The epitopic integrity of these molecules was first confirmed by immunoprecipitation by patient sera containing TPO autoantibodies. However, autoantibody recognition could involve a minority of TPO autoantibodies with the individual sera, not fulfilling the strict criteria for immunodominance. In order to obtain definitive data, we performed immunoprecipitations on these TPO variants with four recombinant human monoclonal autoantibodies that define the immunodominant region. All four monoclonal autoantibodies immunoprecipitated TPO 1-741 to the same extent as they did TPO 1-771 and the full TPO ectodomain, indicating that the immunodominant region comprises (at least in large part) amino acid residues upstream of residue 741.

Clinical characteristics of transmitted transfusion virus infection in children

Clinical characteristics of transmitted transfusion virus (TTV) infection and its pathogenicity in children were evaluated. Serum TTV DNA from 118 children (mean age: 7.8 +/- 2.8 years) was detected by nested PCR. The product of PCR was cloned and sequenced. The positive rate for serum TTV-DNA in 20 healthy children, 9 cases of acute hepatitis, 51 cases of chronic hepatitis, 24 cases of nephritis or nephrotic syndrome and 14 cases of hypoplastic anemia or acute leukemia was 20%, 11%, 29%, 42% and 21% respectively, but there was no significant difference in TTV-DNA frequency among them (P > 0.05). Of the 16 patients receiving immunosuppressive agent for a long time, 7 (44%) were positive for TTV-DNA, and of the 17 cases not receiving immunosuppressive agent, 5 (29%) were positive with the difference being not significant (P > 0.05). Essential characteristics were pathogen-carrier or asymptomatic infection in children with TTV infection. Long-term employment of immunosuppressive agent did not increase the incidence in TTV infection. There was still high prevalence in TTV infection in healthy children not receiving blood product, suggesting the possibility of non hematogenous transmitted transfusion in TTV transmission.

Paternal inheritance of chloroplast DNA in interspecific hybrids in the genus Larrea (Zygophyllaceae)

The mode of chloroplast DNA (cpDNA) inheritance was investigated in the genus Larrea (Zygophyllaceae) by polymerase chain reaction (PCR) amplification of cpDNA fragments using three pairs of chloroplast universal primers. A total of 20 F(1)s from interspecific crosses among five different taxa in the section Bifolium was examined. Twelve F(1)s were from six crosses between L. cuneifolia (4x) and L. divaricata (2x) (Peru or Argentina) or L. tridentata (2x or 4x). Eight F(1)s were from two sets of reciprocal crosses between L. divaricata (2x) (Argentina) and L. tridentata (2x). Length polymorphism was observed in all three regions of cpDNA that separated L. cuneifolia parents from L. divaricata and L. tridentata parents and in one of the three cpDNA regions that differentiated L. divaricata (Argentina) parents from L. tridentata (2x) parents. In each case, it was the paternal cpDNA marker that appeared in the F(1) individuals. This was further confirmed by restriction fragment length polymorphism (RFLP) analysis of the amplified cpDNA fragments. Larrea may be the fifth genus reported in angiosperms with a paternal bias in cpDNA transmission. Possible mechanisms that may result in paternal cpDNA inheritance were briefly reviewed. Based on the observed uniparental paternal inheritance of cpDNA, restriction analysis of the three cpDNA regions and previous cytogenetic studies, L. divaricata was probably the maternal progenitor of L. cuneifolia.

Enhanced calcium transients in glial cells in neonatal cerebellar cultures derived from S100B null mice

S100B is the major low-affinity Ca(2+)-binding protein in astrocytes. In order to study the role of S100B in the maintenance of Ca(2+) homeostasis, we generated S100B null mice by a targeted inactivation of the S100B gene. Absence of S100B expression was demonstrated by Northern and Western blotting for S100B mRNA and protein, respectively, and immunoperoxidase staining of sections of various brain regions. S100B null mice were viable, fertile, and exhibited no overt behavioral abnormalities up to 12 months of age. On the basis of light microscopy and immunohistochemical staining, there were no discernable alterations in the distribution and morphology of astrocytes or neurons in sections of adult brains of these mice. Astrocytes in cerebellar cultures derived from 6-day-old S100B null mice exhibited enhanced Ca(2+) transients in response to treatment with KCl or caffeine. On the other hand, granule neurons, in the same cultures, exhibited normal Ca(2+) transients in response to treatment with KCl, caffeine, or N-methyl-d-aspartate. These results demonstrate a specific decrease in Ca(2+)-handling capacity in astrocytes derived from S100B null mice and suggest that S100B plays a role in the maintenance of Ca(2+) homeostasis in astrocytes.

Long-term blockade of the expression of cocaine sensitization by ondansetron, a 5-HT(3) receptor antagonist

Intermittent cocaine administration induces sensitization (reverse tolerance) to its behavioral effects. The mechanism(s) mediating sensitization is not clear, however, previous research has implicated 5-HT(3) receptors in the expression of sensitization. The present experiment evaluated the ability of the 5-HT(3) receptor antagonist, ondansetron, administered during withdrawal from chronic intermittent cocaine administration, to block the expression of sensitization. Rats were pretreated for 14 days by daily subcutaneous injections of either 40 mg/kg cocaine or 0.9% saline. During the first 5 days of withdrawal from this pretreatment regimen, all rats received a daily subcutaneous injection of 0-1.0 mg/kg ondansetron. On days 7, 14 or 28 of withdrawal from the cocaine pretreatment, the rats received a 15.0-mg/kg cocaine challenge. Ambulatory behavior was automatically recorded for 60 min. Ondansetron had no significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron blocked the expression of sensitization at all withdrawal times. We thus report that it is possible to permanently block the expression of sensitization once it has developed by administering a 5-HT(3) receptor antagonist.

DNA methylator and mismatch repair phenotypes are not mutually exclusive in colorectal cancer cell lines

A potential link between DNA repair and de novo methylation of exogenous sequences in colorectal cancer cell lines suggested that cells deficient in mismatch repair (MMR-) had an increased ability to silence the introduced virus promoter by DNA methylation due to the presence of a methylator phenotype (MET+) (Lengauer et al., 1997a). We explored this relationship in more detail and found that although there was a clear difference in the abilities of MMR+ cells to express the viral promoter compared to their MMR- counterparts, this difference was not consistently explained by levels of methylation in the viral promoter. Furthermore, we were unable to distinguish differences between the levels of methylation of six endogenous known CpG islands or 100 random DNA fragments containing CCGG sites within the cells. No consistent differences between the abilities of the cells to methylate the CpG island in exon 2 of the p16 gene were observed after transient demethylation by 5-aza-2'-deoxycytidine nor in the levels of expression of three human methyltransferase enzymes. Our results do not therefore support the existence of mutually exclusive DNA methylation (MET) and DNA repair (MMR) phenotypes. Oncogene (2000) 19, 943 - 952.

Distinct roles of synaptic and extrasynaptic NMDA receptors in excitotoxicity

Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of (45)Ca(2+) evoked by applying exogenous NMDA or L-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased (45)Ca(2+) accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.

[High-level expression of Mycobacterium tuberculosis 16,000 antigen in E. coli]

OBJECTIVE

To gain the recombinant protein antigen 16,000 of Mycobacterium tuberculosis highly expressed in E. coli and study its immunological characteristics.

METHODS

DNA fragments code for the protein were obtained by PCR, then cloned into the pET plasmid vector to gain recombinant E. coli. Cells were cultured and induced to produce recombinant protein, whose molecular size and present form were analyzed by SDS-PAGE, and its immunological characteristics were analyzed by Western-blotting and ELISA technology.

RESULTS

The clone was analyzed at the nucleotide lever and shown the same DNA sequence coding for natural 16,000 protein. Analyzed by SDS-PAGE and Western-blotting, it was found to produce immunoreactive proteins with mobilities very similar to those of the 16,000 protein antigen, and the recombinant protein amounted to 40% of total cell proteins. ELISA results indicated that the purified recombinant protein could distinguish sera from tuberculosis patients with anti-PPD antibody and those from tuberculin positive contacts.

CONCLUSIONS

Recombinant 16,000 protein antigen highly expressed in the form of solution in E. coli was gained and this antigen was located in cell plasma. This recombinant protein showed specific immunogenicity.

Blockade of glutamate receptors and barbiturate anesthesia: increased sensitivity to pentobarbital-induced anesthesia despite reduced inhibition of AMPA receptors in GluR2 null mutant mice

BACKGROUND

Barbiturates enhance gamma-aminobutyric acid type A (GABA(A)) receptor function and also inhibit the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of glutamate receptor. The relative contribution of these actions to the behavioral properties of barbiturates is not certain. Because AMPA receptor complexes that lack the GluR2 subunit are relatively insensitive to pentobarbital inhibition, GluR2 null mutant mice provide a novel tool to investigate the importance of AMPA receptor inhibition to the anesthetic effects of barbiturates.

METHODS

GluR2 null allele (-/-), heterozygous (+/-), and wild-type (+/+) mice were injected with pentobarbital (30 and 35 mg/kg intraperitoneally). Sensitivity to anesthetics was assessed by measuring the latency to loss of righting reflex, sleep time, and the loss of corneal, pineal, and toe-pinch withdrawal reflexes. In addition, patch-clamp recordings of acutely dissociated CA1 hippocampal pyramidal neurons from (-/-) and (+/+) mice were undertaken to investigate the effects of barbiturates on kainate-activated AMPA receptors and GABA-activated GABA(A) receptors.

RESULTS

Behavioral tests indicate that sensitivity to pentobarbital was increased in (-/-) mice. In contrast, AMPA receptors from (-/-) neurons were less sensitive to inhibition by pentobarbital (concentrations that produced 50% of the maximal inhibition [IC50], 301 vs. 51 microM), thiopental (IC50, 153 vs. 34 microM), and phenobarbital (IC50, 930 vs. 205 microM) compared with wild-type controls, respectively. In addition, the potency of kainate was greater in (-/-) neurons, whereas no differences were observed for the potentiation of GABA(A) receptors by pentobarbital.

CONCLUSIONS

The GluR2 null mutant mice were more sensitive to pentobarbital anesthesia despite a reduced sensitivity of GluR2-deficient AMPA receptors to barbiturate blockade. Our results indicate that the inhibition of AMPA receptors does not correlate with the anesthetic effects of barbiturates in this animal model. We postulate that the increase in the sensitivity to anesthetics results from a global suppression of excitatory neurotransmission in GluR2-deficient mice.

The effects of continuous cocaine dose on the induction of behavioral tolerance and dopamine autoreceptor function

The current experiment evaluated the dose-dependent nature of the induction of behavioral tolerance, and changes in dopamine autoreceptor function, by continuously administering different doses of cocaine. For all experiments, rats were exposed to a 14-day pretreatment regimen involving the continuous administration of either 0, 5, 10, 20, or 40 mg/kg/day cocaine. All subjects were then withdrawn from the pretreatment regimen for 7 days. The subjects were placed in activity monitors, and ambulation measured. In experiment 1, the subjects were challenged with 0.0, 7.5, or 15.0 mg/kg i.p. cocaine on day 7 of withdrawal from the continuous cocaine administration regimen. The results indicated that all continuous cocaine doses induced significant tolerance to the 15.0 mg/kg cocaine challenge, relative to the control group. Furthermore, the 5.0 mg/kg/day group exhibited significantly less tolerance than the 40.0 mg/kg/day group. In experiment 2, the subjects were challenged with 0.0, 0.063, or 0.125 mg/kg quinpirole. The results indicated that the 0.063-mg/kg quinpirole challenge inhibited activity, while the 0.125 mg/kg quinpirole challenge enhanced behavior. The results further suggested that the inhibition of behavior was greater in the cocaine-pretreated subjects than in the saline control group. In experiment 3, the subjects were challenged with the same doses of quinpirole in combination with 15 mg/kg i.p. cocaine. The low quinpirole challenge dose inhibited cocaine-induced hyperactivity, while the higher challenge dose enhanced cocaine-induced hyperactivity. The results suggest that the induction of tolerance by continuous cocaine administration is dose-dependent. Continuous cocaine administration did induce dopamine autoreceptor supersensitivity. However, different continuous cocaine doses did not induce differential degrees of dopamine autoreceptor supersensitivity.

Specific coupling of NMDA receptor activation to nitric oxide neurotoxicity by PSD-95 protein

The efficiency with which N-methyl-D-aspartate receptors (NMDARs) trigger intracellular signaling pathways governs neuronal plasticity, development, senescence, and disease. In cultured cortical neurons, suppressing the expression of the NMDAR scaffolding protein PSD-95 (postsynaptic density-95) selectively attenuated excitotoxicity triggered via NMDARs, but not by other glutamate or calcium ion (Ca2+) channels. NMDAR function was unaffected, because receptor expression, NMDA currents, and 45Ca2+ loading were unchanged. Suppressing PSD-95 blocked Ca2+-activated nitric oxide production by NMDARs selectively, without affecting neuronal nitric oxide synthase expression or function. Thus, PSD-95 is required for efficient coupling of NMDAR activity to nitric oxide toxicity, and imparts specificity to excitotoxic Ca2+ signaling.

Alteration of Na+ currents in dorsal root ganglion neurons from rats with a painful neuropathy

Increased excitability of primary sensory neurons may be important for the generation of neuropathic pain from nerve injury. The currents underlying the action potentials of these neurons are largely carried by Na+, and changes in Na+ currents have been postulated to contribute to this increased excitability. Using patch clamp in whole-cell mode, we recorded Na+ currents from DRG neurons freshly isolated from rats with a chronic constriction injury (CCI), an animal model of neuropathic pain. We found significant changes in Na+ currents after CCI when cell size and Na+ channel properties were used to segregate DRG neurons. Most changes were concentrated in small neurons (< or = 25 microm diameter) and in the slow TTX-resistant current that is predominant in these cells. CCI produced two principal changes in these cells: it shifted the voltage-dependence of activation of the TTX-resistant current to more negative potentials and it reduced the average density of this current. The decrease in density appears to be primarily due to the decrease in the number of small neurons expressing this current. The net result is a change in both activation and steady-state inactivation properties of the total Na+ current to more negative potentials without a significant change in the density of total Na+ current. The change in activation properties of the TTX-resistant Na+ current are similar to those produced by some hyperalgesic autacoids, and may contribute to the increase in primary afferent excitability and hyperalgesia that occurs after this lesion.

[The 38,000 protein of Mycobacterium tuberculosis is overexpressed in Escherichia coli]

OBJECTIVE

To obtain recombinant 38,000 protein in large quantities and to study its immunologic characteristics by stable expression of the gene encoding for 38,000 antigen of Mycobacterium tuberculosis in E. coli.

METHODS

Expression plasmid was constructed with DNA recombinant technique. Positive clones were screened using double digestion and polymerase chain reaction. Recombinant plasmid was transformed into E. coli. Then E. coli carrying recombinant plasmid were induced. The expression of 38,000 antigen was identified by SDS-polyacrylamid gel electrophoresis (PAGE) and immunoblotting. Stained gel was scanned to detect expression level of recombinant antigen.

RESULTS

Gel stained with coomassie blue G-250 showed that the induced E. coli carrying recombinant plasmid can produce 38,000 protein at high level. Gel scan showed that 38,000 antigen expression in E. coli was about 36% - 40% of total cellular protein. The recombinant 38,000 antigen existed mostly in inclusion bodies. The recombinant antigen can react with antibodies: serum of pulmonary tuberculosis patients and the goats immuned with Mycobacterium tuberculosis.

CONCLUSIONS

Constructed recombinant E. coli can overproduce 38,000 antigen of Mycobacterium tuberculosis. Inclusion bodies are easy to purify and can protect the recombinant antigen from protease, on the other hand, it has not biological activity unless the denatured protein is accurately folded.

Withdrawal from continuous cocaine administration: time dependent changes in accumbens 5-HT3 receptor function and behavioral tolerance

We have previously reported that continuous cocaine administration functionally down regulates 5-HT3 receptors in the nucleus accumbens. The current experiments evaluated the duration of behavioral tolerance to cocaine and whether the duration of behavioral tolerance and 5-HT3 receptor down-regulation co-varied. Rats were withdrawn from a pretreatment regimen (40 mg/kg/per day cocaine or 0.9% saline for 14 days) for 1, 7 or 14 days. The rats were either sacrificed, and slices from the nucleus accumbens obtained, or were exposed to behavioral rating procedures. The results indicated that continuous cocaine administration significantly attenuated the ability of mCPBG to facilitate K+ -stimulated DA release on days 1 and 7, but not day 14, of withdrawal. Furthermore, continuous cocaine administration induced behavioral tolerance to a cocaine challenge on days 1 and 7, but not day 14, of withdrawal. These results suggest that continuous cocaine administration functionally down-regulates 5-HT3 receptors in the nucleus accumbens, and this functional down-regulation co-varies with the behavioral tolerance induced by continuous cocaine administration. Hence, a functional down-regulation of accumbens 5-HT3 receptors may represent a partial mechanism for the tolerance following continuous cocaine administration.

[A fluorometric method for the determination of norepinephrine in tissue]

This paper reported the determination of norepinephrine (NE) by spectrofluorometry in tissue. The linear relationship between the flecoroscence intensity and the content of NE was in the range of 10-100 ng (lambdaex/lambdaem = 410 nm/505 nm). The rate of recovery is 91.68%-96.64% and RSD (n = 10) is 6.1%. This method is simple, rapid and sensitive.

Blockade of accumbens 5-HT3 receptor down-regulation by ondansetron administered during continuous cocaine administration

The present experiment examined whether ondansetron, co-administered with continuous cocaine, would block the down regulation of accumbens 5-HT3 receptors. Rats were exposed to a 14-day pretreatment regimen that involved the continuous infusion of 40 mg kg(-1) day(-1) cocaine or 0.9% saline via a subcutaneously implanted osmotic minipump. In addition to the continuous cocaine or saline administration, all subjects received daily subcutaneous (s.c.) injections of either vehicle or 0.1 mg kg(-1) ondansetron for the entire 14-day pretreatment regimen. The rats were then withdrawn from this pretreatment regimen for seven days, and slices from the nucleus accumbens obtained. The slices were perfused with 25 mM K+ in the absence and presence of 0, 12.5, 25, or 50 microM m-Chlorophenyl-biguanide HCl (mCPBG). The efflux samples were assayed for dopamine content by high pressure liquid chromatography (HPLC) with electrochemical detection. Continuous cocaine administration significantly attenuated the ability of mCPBG to facilitate K+-induce dopamine overflow compared to saline control rats. In addition, the rats that received ondansetron and cocaine during the 14-day pretreatment period, the ability of mCPBG to enhance K+ stimulated dopamine release was not significantly different from the saline control subjects. For all groups except the cocaine alone group, the effects of mCPBG on K+ stimulated dopamine release were Ca2+ dependent, suggesting that these effects are receptor mediated. These results suggest that continuous cocaine administration functionally down-regulates 5-HT3 receptors in the nucleus accumbens, and that this down-regulation can be blocked by chronic ondansetron administration. Hence, a functional down regulation of accumbens 5-HT3 receptors represents a significant contribution to the tolerance induced by continuous cocaine administration.

Local anesthetics inhibit the G protein-mediated modulation of K+ and Ca++ currents in anterior pituitary cells

The effects of local anesthetics (LAs) on G protein-mediated responses of voltage-dependent K+ (I(K)) and Ca++ currents in rat anterior pituitary tumor (GH3) cells were analyzed by using a whole-cell voltage clamp. Extracellular lidocaine inhibited I(K) with an IC50 of 1.9 mM, comparable to 2.6 mM for I(Ba) but 10 times higher than the IC50 for I(Na) (0.17 mM). Low concentrations of lidocaine (30-100 microM), which had no direct effect on basal I(K), attenuated both the stimulatory and inhibitory modulation of K+ channels by thyrotropin-releasing hormone (TRH). Both modulations had an IC50 approximately 40 microM independent of [TRH]. Intracellular QX314 (100 microM), a quaternary, charged form of lidocaine, also significantly attenuated the TRH effects; however, external QX314 and the neutral LA benzocaine (100 microM) did not. Lidocaine (</=100 microM) inhibited the TRH-induced increase in [Ca++] but failed to block either the GTP-gamma-S-induced increase in I(K), the activation of I(K) by directly elevated [Ca++] (ca. 3 x 10(-7) M), or the phorbol-12,13-dibutyrate-induced inhibition of Ca++-activated I(K). Agonist binding assays revealed that none of the these LAs affected TRH receptor binding. Similar to its effect on TRH modulation of I(K), lidocaine (100 microM) attenuated the inhibition of Ca++ channels in GH3 cells by somatostatin (1 microM). These results suggest that lidocaine's action occurs between agonist binding and G protein activation. Such inhibition of G protein pathways may be an important component of the general action of LAs acting at spinal sites, or for i.v. therapeutics or during cardiotoxic episodes.

Inverse halftoning using wavelets

This work introduces a new approach to inverse halftoning using nonorthogonal wavelets. The distinct features of this wavelet-based approach are: 1) edge information in the highpass wavelet images of a halftone image is extracted and used to assist inverse halftoning, 2) cross-scale correlations in the multiscale wavelet decomposition are used for removing background halftoning noise while preserving important edges in the wavelet lowpass image, and 3) experiments show that our simple wavelet-based approach outperforms the best results obtained from inverse halftoning methods published in the literature, which are iterative in nature.

Inhibition by local anesthetics of Ca2+ channels in rat anterior pituitary cells

The characteristics of local anesthetic inhibition of voltage-dependent Ca2+ channels in a rat pituitary clonal cell line were investigated by whole-cell voltage clamp and compared with inhibition by the dihydropyridine Ca2+ channel antagonist, nicardipine. With extracellular Ba2+ (10 mM) as the current carrier, depolarization above -40 mV evoked a slowly inactivating I(Ba). Extracellularly applied lidocaine inhibited I(Ba) without changing the activation threshold, the voltage of peak current, or the reversal potential. Inhibition was greater at a holding potential of -60 mV (IC50 = 1.2 mM) than at -80 mV (IC50 = 2.6 mM). This depolarization-induced potentiation in I(Ba) inhibition developed over 0.1-10 s after membrane depolarization began. Nicardipine also dose-dependently inhibited I(Ba) with an IC50 = 90 nM (at a holding potential = -80 mV). Both lidocaine and nicardipine shifted the I(Ba) steady-state inactivation (availability) curves to the left. Double-pulse protocols revealed that lidocaine (1 mM) accelerated the depolarization-induced inhibition (inactivation) of I(Ba) over the rate in drug-free solutions, but had no effect on the hyperpolarization-induced removal of channel inactivation. Nicardipine also accelerated the depolarization-induced inactivation of I(Ba) but, in addition, it slowed the hyperpolarization-induced inactivation removal. The relative inhibitory action of lidocaine in suppressing I(Ba) was unchanged in the presence of nicardipine. These results suggest that lidocaine has a direct action on membrane Ca2+ channels, similar to the voltage-dependent action of dihydropyridine, but acting at a separate and independent site.

Methylation dynamics, epigenetic fidelity and X chromosome structure

DNA methylation of the X chromosome is reviewed and discussed, with emphasis on the partial methylation seen in the mouse X-linked Pgk1 promoter region. A new study of partial methylation is presented in which the methylation of CpG site H3 in the mouse Igf2 upstream region was quantitatively measured during growth of subcloned cells in tissue culture. Before subcloning the average methylation level was 50%. After subcloning, methylation was highly variable in early stage clones. With continued passage, clones initially having high methylation lost methylation, whereas clones initially having low methylation gained methylation. By about the 25th generation, all clones had returned to a steady-state methylation level of 50%. These findings are discussed in the context of epigenetic mechanisms and epigenetic fidelity. Interpretation of the results is made according to a model that assumes stochastic methylation and demethylation, with rate parameters influenced by local chromatin structure. A second type of study is reported in which we have measured chromatin accessibility differences between the active X chromosome (Xa) and the inactive X chromosome (Xi). We found that Xa/Xi differences in accessibility to DNase I are surprisingly labile. Relatively infrequent DNA nicks rapidly eliminate differential accessibility.

[Spectrofluorometric determination of corticosterone in plasma and tissue]

Corticosterone is one of the adrenal hormones. This paper reported the determination of corticosterone in plasma and tissue of small mammals with spectrofluorometry. The linear relationship between the fluorescence intensity and the concentration of corticosterone is over the range of 0.01-0.24 microg/mL (lambdaex = 470nm, lambdaem = 525nm). The average rate of standard recovery is 96.0% and RSD (n = 10) is 4.2%. This method is simple, rapid and sensitive.

Blockade of the expression of sensitization and tolerance by ondansetron, a 5-HT3 receptor antagonist, administered during withdrawal from intermittent and continuous cocaine

The present experiment evaluated the ability of the 5-HT3 antagonist, ondansetron, administered during withdrawal from chronic cocaine administration, to block the expression of sensitization and tolerance induced by the intermittent or continuous administration of cocaine, respectively. Rats were pretreated with 40 mg/kg/per day cocaine for 14 days by either s.c. injections or osmotic minipumps, or 0.9% saline, administered via osmotic minipump. During the first 5 days of withdrawal from this pretreatment regimen, all rats received a daily s.c. injection of 0-1.0 mg/kg ondansetron. On day seven of withdrawal from the cocaine pretreatment (2 days after the final ondansetron injection) all subjects received a 15.0 mg/kg i.p. cocaine challenge. Their behavior was then rated according to the Ellinwood and Balster (1974) scale for 60 min. The results indicated that daily injections of ondansetron, on days 1-5 of withdrawal from the pretreatment regimen, had no significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron, on days 1-5 of withdrawal from intermittent cocaine administration, significantly blocked the expression of sensitization. In the continuous cocaine group, ondansetron injections, on days 1-5 of withdrawal from continuous cocaine administration, also blocked the expression of behavioral tolerance. The results therefore indicate that changes in 5-HT3 receptor function are associated with the expression of tolerance and sensitization, respectively.

Differential replication timing of X-linked genes measured by a novel method using single-nucleotide primer extension

The ratio of two differentially replicating alleles is not constant during S phase. Using this fact, we have developed a method for determining allele-specific replication timing for alleles differing by at least a single base pair. Unsynchronized cells in tissue culture are first sorted into fractions based on DNA content as a measure of position in S phase. DNA is purified from each fraction and used for PCR with primers that bracket the allelic difference, amplifying both alleles. The ratio of alleles in the amplified product is then determined by a single nucleotide primer extension (SNuPE) assay, modified as described [Singer-Sam,J. and Riggs,A.D. (1993) Methods Enzymol., 225, 344-351]. We report here use of this SNuPE-based method to analyze replication timing of two X-linked genes, Pgk-1 and Xist, as well as the autosomal gene Gabra-6. We have found that the two alleles of the Gabra-6 gene replicate synchronously, as expected; similarly, the active allele of the Pgk-1 gene on the active X chromosome (Xa) replicates early relative to the silent allele on the inactive X chromosome (Xi). In contrast, the expressed allele of the Xist gene, which is on the Xi, replicates late relative to the silent allele on the Xa.

Wavelet packet image coding using space-frequency quantization

We extend our previous work on space-frequency quantization (SFQ) for image coding from wavelet transforms to the more general wavelet packet transforms. The resulting wavelet packet coder offers a universal transform coding framework within the constraints of filterbank structures by allowing joint transform and quantizer design without assuming a priori statistics of the input image. In other words, the new coder adaptively chooses the representation to suit the image and the quantization to suit the representation. Experimental results show that, for some image classes, our new coder gives excellent coding performance.

Simple one-step procedure for the separation of apolipoproteins A1 and A2 by high-performance liquid chromatography

A simple assay method for apolipoproteins apo A1 and apo A2 by HPLC is introduced. The simple one-step method is based on fractionation of apo A1 and apo A2 from other serum proteins which are precipitated at 100 degrees C and removed by centrifugation. The apo A1 and apo A2 which remain in solution can be recovered and resolved by size-exclusion chromatography without ultracentrifugation and delipidation by an organic solvent. This makes sample preparation easier. The recoveries of apo A1 and apo A2 were 104.26% and 101.04%; the precision (C.V.%) of apo A1 and apo A2 was 0.88 and 1.63 respectively.

First Report of Papaya Leaf Curl Disease in Pakistan

Papaya plants with virus-disease-like symptoms were observed in back yards and commercial groves in Multan, Pakistan. Leaves of the diseased plants displayed downward curling and thickened, dark green veins. Leaf-like enations grew from the base of the diseased leaves. These symptoms are similar to those of cotton leaf curl disease. In addition, diseased papayas were stunted and distorted. Leaf extracts from 3 diseased and 2 healthy papayas were tested in enzyme-linked immunosorbent assay against antibodies to geminiviruses. SCRI-52 and SCRI-60, two monoclonal antibodies to Indian cassava mosaic virus (2), reacted positively (more than 7× healthy background) with the diseased samples but not with the healthy ones. Total nucleic acids from the papaya samples were used as templates in polymerase chain reaction with primers F500 and R1800 (1), which are capable of amplifying a region of DNA A component of the whitefly-transmitted geminiviruses. A DNA fragment of approximately 1.4 kb was amplified from the nucleic acids of the diseased but not the healthy papayas. Under high stringency conditions (1), cloned DNA A fragments of both cotton leaf curl virus and cotton leaf crumple virus cross-hybridized with the amplified DNA fragment, but the hybridization signals were much weaker than those of the homologous hybridization. This is the first report of the papaya leaf curl disease in Pakistan. These data demonstrated that a geminivirus may be the causative agent of this papaya disease. We are currently determining the relationship between the geminivirus infecting papaya and cotton leaf curl virus. References: (1) A. Nadeem et al. Mol. Plant Pathol. (On-line: /1997/0612nadeem). (2) M. M. Swanson et al. Ann. Appl. Biol. 211:285, 1992.

Extracellular calcium sensed by a novel cation channel in hippocampal neurons

Extracellular concentrations of Ca2+ change rapidly and transiently in the brain during excitatory synaptic activity. To test whether such changes in Ca2+ can play a signaling role we examined the effects of rapidly lowering Ca2+ on the excitability of acutely isolated CA1 and cultured hippocampal neurons. Reducing Ca2+ excited and depolarized neurons by activating a previously undescribed nonselective cation channel. This channel had a single-channel conductance of 36 pS, and its frequency of opening was inversely proportional to the concentration of Ca2+. The inhibition of gating of this channel was sensitive to ionic strength but independent of membrane potential. The ability of this channel to sense Ca2+ provides a novel mechanism whereby neurons can respond to alterations in the extracellular concentration of this key signaling ion.

COBRA: a sensitive and quantitative DNA methylation assay

We report here on a quantitative technique called COBRA to determine DNA methylation levels at specific gene loci in small amounts of genomic DNA. Restriction enzyme digestion is used to reveal methylation-dependent sequence differences in PCR products of sodium bisulfite-treated DNA as described previously. We show that methylation levels in the original DNA sample are represented by the relative amounts of digested and undigested PCR product in a linearly quantitative fashion across a wide spectrum of DNA methylation levels. In addition, we show that this technique can be reliably applied to DNA obtained from microdissected paraffin-embedded tissue samples. COBRA thus combines the powerful features of ease of use, quantitative accuracy, and compatibility with paraffin sections.

Cyclic nucleotides regulate the activity of L-type calcium channels in smooth muscle cells from rat portal vein

In order to advance our previous findings that the macroscopic slow Ca2+ currents of vascular smooth muscle (VSM) cells are regulated by cyclic nucleotides, the effects of cAMP and cGMP on the activity of single slow (L-type) Ca2+ channels were investigated using cell-attached patch clamp (22-25 degrees C). Freshly isolated VSM cells were obtained from adult male rat portal vein. For the single-channel recordings, the pipette was filled with a solution containing 90 mM Ba2+ and 1 microM Bay-K-8644 solution, and the bath contained 140 mM KCl to "zero" the membrane potential. Depolarizing pulses to 0 mV, from a holding potential (HP) of -80 mV, elicited inward unitary currents. The activity of these channels was completely blocked by superfusion of 10 microM nifedipine. Extracellular perfusion of the single cells with membrane-permeable cGMP and cAMP analogs (8Br-cGMP and 8Br-cAMP) at 1 mM caused a slight inhibition, but higher doses (3 mM), clearly showed an inhibitory effect on the single-channel activity. cAMP (100 microM) stimulated one out of five patches tested, and 100 microM cGMP showed no effect in three patches tested. Compared with control, both cyclic nucleotides at 3 mM decreased the ensemble-averaged currents by 26.7 +/- 4.1% and 37.3 +/- 2.1%, respectively. Unit amplitude and slope conductance were not changed. The normal conductance of the Ca2+ channel was 20.8 +/- 0.04 pS (n = 9), and the conductances in the presence of cAMP (n = 5) and cGMP (n = 6) were 19.3 +/- 0.04 and 20.5 +/- 0.05 pS, respectively. Single-channel kinetic analysis showed that cAMP did not affect the mean open-time, and cGMP slightly decreased the mean open-time. However, both cAMP and cGMP increased the mean closed-time. In addition, cAMP decreased the open probability (NPo) by a factor of 1.7, from 0.26 +/- 0.04 to 0.15 +/- 0.03 (P < 0.05, Student's t-test) and cGMP decreased NPo by a factor of 2.5, from 0.24 +/- 0.08 to 0.10 +/- 0.02 (P < 0.05). H-7, a non-specific protein kinase inhibitor, prevented the inhibitory effects of both cAMP and cGMP on the activity of single Ca2+ channels in rat portal vein cells. The results demonstrate that both cAMP and cGMP inhibit L-type Ca2+ channel activities in VSM cells from rat portal vein. This inhibition may be mediated by the cAMP and cGMP-dependent protein kinase phosphorylation of the L-type Ca2+ channels (or an associated regulatory protein).

Blockade of cocaine sensitization and tolerance by the co-administration of ondansetron, a 5-HT3 receptor antagonist, and cocaine

The present experiment evaluated the ability of the 5-HT3 antagonist, ondansetron, administered during chronic cocaine administration, to block the development of sensitization and tolerance induced by the intermittent or continuous administration of cocaine, respectively. Rats were pretreated with 40 mg/kg per day cocaine for 14 days by either SC injections or osmotic minipumps, or 0.9% saline, administered by SC injection. During this chronic (cocaine) treatment, all rats received a daily SC injection of 0-1.0 mg/kg ondansetron. The rats were then withdrawn from the pretreatment regimen for 7 days. On day 7 of withdrawal from the cocaine pretreatment all subjects received a 15.0 mg/kg IP cocaine challenge, and their behavior was then rated according to the modified Ellinwood and Balster scale for 60 min. The results indicated that daily injections of ondansetron had no consistent or significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron with cocaine significantly blocked the development of sensitization with an inverted U-shape dose-response curve. In the continuous cocaine group ondansetron injections also attenuated the development of behavioral tolerance. The results therefore indicate that 5-HT3 receptor stimulation during continuous and intermittent cocaine administration is an important link in the development of behavioral tolerance and sensitization.

Genome organization and gene expression of saguaro cactus carmovirus

The complete sequence of the single-stranded, (+)-sense RNA genome of saguaro cactus carmovirus (SCV) has been determined. The 3879 nucleotide genome contains five open reading frames (ORFs). The 5'-proximal ORF encodes a 26 kDa protein (p26) and terminates with an amber codon which is readthrough into an in-frame p57 ORF to generate an 86 kDa fusion protein (p86). Two small, centrally located ORFs encode a 6 kDa protein (p6) and a 9 kDa protein (p9), respectively. The 3'-proximal ORF encodes a 37 kDa (p37) capsid protein (CP). Analysis of the nucleotide and predicted amino acid sequences supports the classification of SCV in the genus Carmovirus in the family Tombusviridae. All predicted SCV proteins are expressed in an in vitro translation system. SCV p26 and the readthrough fusion protein p86 are synthesized from the genomic RNA while p6, p9 and p37 CP ORFs at the 3' half of the genome are expressed from two subgenomic (sg) RNAs. The 5' termini of both sg RNAs have been mapped. The large 1614 nucleotide sg RNA contains the p6 and p9 ORFs as the first and the second ORFs respectively from its 5' end. It directs the synthesis of abundant p6 but a small amount of p9. While a synthetic transcript with the p9 ORF at the 5' end is a more efficient messenger for p9, no corresponding sg RNA has been identified in vivo. The smaller 1396 nucleotide sg RNA contains only the p37 ORF and directs the synthesis of SCV CP.

Space-frequency quantization for wavelet image coding

A new class of image coding algorithms coupling standard scalar quantization of frequency coefficients with tree-structured quantization (related to spatial structures) has attracted wide attention because its good performance appears to confirm the promised efficiencies of hierarchical representation. This paper addresses the problem of how spatial quantization modes and standard scalar quantization can be applied in a jointly optimal fashion in an image coder. We consider zerotree quantization (zeroing out tree-structured sets of wavelet coefficients) and the simplest form of scalar quantization (a single common uniform scalar quantizer applied to all nonzeroed coefficients), and we formalize the problem of optimizing their joint application. We develop an image coding algorithm for solving the resulting optimization problem. Despite the basic form of the two quantizers considered, the resulting algorithm demonstrates coding performance that is competitive, often outperforming the very best coding algorithms in the literature.

Joint space-frequency segmentation using balanced wavelet packet trees for least-cost image representation

We examine the question of how to choose a space varying filterbank tree representation that minimizes some additive cost function for an image. The idea is that for a particular cost function, e.g., energy compaction or quantization distortion, some tree structures perform better than others. While the wavelet tree represents a good choice for many signals, it is generally outperformed by the best tree from the library of wavelet packet frequency-selective trees. The double-tree library of bases performs better still, by allowing different wavelet packet trees over all binary spatial segments of the image. We build on this foundation and present efficient new pruning algorithms for both one- and two-dimensional (1-D and 2-D) trees that will find the best basis from a library that is many times larger than the library of the single-tree or double-tree algorithms. The augmentation of the library of bases overcomes the constrained nature of the spatial variation in the double-tree bases, and is a significant enhancement in practice. Use of these algorithms to select the least-cost expansion for images with a rate-distortion cost function gives a very effective signal adaptive compression scheme. This scheme is universal in the sense that, without assuming a model for the signal or making use of training data, it performs very well over a large class of signal types. In experiments it achieves compression rates that are competitive with the best training-based schemes.

Enhanced LTP in mice deficient in the AMPA receptor GluR2

AMPA receptors (AMPARs) are not thought to be involved in the induction of long-term potentiation (LTP), but may be involved in its expression via second messenger pathways. However, one subunit of the AMPARs, GluR2, is also known to control Ca2+ influx. To test whether GluR2 plays any role in the induction of LTP, we generated mice that lacked this subunit. In GluR2 mutants, LTP in the CA1 region of hippocampal slices was markedly enhanced (2-fold) and nonsaturating, whereas neuronal excitability and paired-pulse facilitation were normal. The 9-fold increase in Ca2+ permeability, in response to kainate application, suggests one possible mechanism for enhanced LTP. Mutant mice exhibited increased mortality, and those surviving showed reduced exploration and impaired motor coordination. These results suggest an important role for GluR2 in regulating synaptic plasticity and behavior.

Platelet-derived growth factor induces a long-term inhibition of N-methyl-D-aspartate receptor function

Platelet-derived growth factor (PDGF) is a multifunctional protein that plays important roles in many tissues, including the mammalian central nervous system. PDGF and PDGF receptors (PDGFRs) are expressed in virtually every region of the central nervous system where they are involved in the development, survival, growth, and differentiation of both neuronal and glial cells. We now report that a brief activation of PDGFRs produced a long-lasting inhibition of N-methyl-D-aspartate (NMDA)-dependent excitatory postsynaptic currents in CA1 pyramidal neurons in rat hippocampal slices. PDGF also inhibited NMDA receptors (NMDA-Rs) in cultured hippocampal neurons by a mechanism that involves a decrease in single channel open probability. Non-NMDA receptor function was not affected by PDGF in hippocampal neurons. Experiments with mutant PDGFRs and chelation of intracellular Ca2+ in Xenopus oocytes indicate that this inhibition depends on a phospholipase C-gamma-induced elevation of intracellular Ca2+ levels. The PDGF-induced inhibition of NMDA-Rs is produced by a mechanism different than the well characterized phenomenon of Ca2+-dependent NMDA-R run down because the effect of PDGF was blocked by the phosphatase inhibitor, calyculin A, and was not affected by the microtubule polymerizing agent, phalloidin. Because elevations of PDGF levels are associated with neurological trauma or disease, we propose that PDGF can exert neuroprotective effects by inhibiting NMDA-R-dependent excitotoxicity.

Adaptive transforms for image coding using spatially varying wavelet packets

We introduce a novel, adaptive image representation using spatially varying wavelet packets (WPs), Our adaptive representation uses the fast double-tree algorithm introduced previously (Herley et al., 1993) to optimize an operational rate-distortion (R-D) cost function, as is appropriate for the lossy image compression framework. This involves jointly determining which filter bank tree (WP frequency decomposition) to use, and when to change the filter bank tree (spatial segmentation). For optimality, the spatial and frequency segmentations must be done jointly, not sequentially. Due to computational complexity constraints, we consider quadtree spatial segmentations and binary WP frequency decompositions (corresponding to two-channel filter banks) for application to image coding. We present results verifying the usefulness and versatility of this adaptive representation for image coding using both a first-order entropy rate-measure-based coder as well as a powerful space-frequency quantization-based (SPQ-based) wavelet coder introduced by Xiong et al. (1993).

ATP-Dependent inhibition of Ca2+-activated K+ channels in vascular smooth muscle cells by neuropeptide Y

Neuropeptide Y(NPY) inhibits Ca2+-activated K+ channels reversibly in vascular smooth muscle cells from the rat tail artery. NPY (200 microM) had no effect in the absence of intracellular adenosine 5'-triphosphate (ATP) and when the metabolic poison cyanide-M-chlorophenyl hydrozone (10 microM) was included in the intracellular pipette solution. NPY was also not effective when ATP was substituted by the non-hydrolysable ATP analogue adenosine 5'-[beta gamma-methylene]-triphosphate (AMP-PCP). NPY inhibited Ca2+-activated K+ channel activity when ATP was replaced by adenosine 5'-O-(3-thiotriphosphate) (ATP [gamma-S]) and the inhibition was not readily reversed upon washing. Protein kinase inhibitor (1 microM), a specific inhibitor of adenosine 3', 5'-cyclic monophosphate-dependent protein kinase, had no significant effect on the inhibitory action of NPY. The effect of NPY on single-channel activity was inhibited by the tyrosine kinase inhibitor genistein (10 microM) but not by daidzein, an inactive analogue of genistein. These observations suggest that the inhibition by NPY of Ca2+-activated K+ channels is mediated by ATP-dependent phosphorylation. The inhibitory effect of NPY was antagonized by the tyrosine kinase inhibitor genistein.

Ca2+ currents in human colonic smooth muscle cells

Voltage-gated Ca2+ currents were investigated in single smooth muscle cells freshly isolated from the circular layer of the human colon (ascending and descending portions) using the whole cell voltage-clamp technique. Tissue samples were obtained at the time of therapeutic surgery. In physiological salt solution (containing 2 mM Ca2+), an inward current was observed when the cell membrane was depolarized in the presence of tetrodotoxin. This current disappeared when Ca2+ was removed from the bath solution and was inhibited when Ca2+ channel blockers were applied, indicating that the inward current was a Ca2+ current (ICa). Changing the holding potential (HP) from -100 mV to more positive potentials (e.g., -60 and -40 mV) markedly decreased the amplitude of ICa. The voltage dependence of steady-state activation and inactivation was represented by Boltzmann distributions; there was a substantial amount of overlap (window current) between -60 and -10 mV. A fast-inactivating ICa component followed by a slow-inactivating ICa component was observed in some cells from both ascending and descending colons. The fast ICa component was observed only when cells were held at -80 or -100 mV, and had a more negative threshold potential (-70 to -60 mV). This component was sensitive to low concentrations of Ni2+ (30 microM) but was resistant to nifedipine (10-20 microM). In contrast, the slow (sustained) ICa component was observed at all HPs (-40 to -100 mV) and had a more positive threshold potential (about -40 mV). This component was insensitive to low concentration of Ni2+ but was sensitive to nifedipine and BAY K 8644.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for accurate determination of terminal sequences of viral genomic RNA

A combination of ligation-anchored PCR and anchored cDNA cloning techniques were used to clone the termini of the saguaro cactus virus (SCV) RNA genome. The terminal sequences of the viral genome were subsequently determined from the clones. The 5' terminus was cloned by ligation-anchored PCR, whereas the 3' terminus was obtained by a technique we term anchored cDNA cloning. In anchored cDNA cloning, an anchor oligonucleotide was prepared by phosphorylation at the 5' end, followed by addition of a dideoxynucleotide at the 3' end to block the free hydroxyl group. The 5' end of the anchor was subsequently ligated to the 3' end of SCV RNA. The anchor-ligated, chimerical viral RNA was then reverse-transcribed into cDNA using a primer complementary to the anchor. The cDNA containing the complete 3'-terminal sequence was converted into ds-cDNA, cloned, and sequenced. Two restriction sites, one within the viral sequence and one within the primer sequence, were used to facilitate cloning. The combination of these techniques proved to be an easy and accurate way to determine the terminal sequences of SCV RNA genome and should be applicable to any other RNA molecules with unknown terminal sequences.

Potassium currents in rat colonic smooth muscle cells and changes during development and aging

In a previous study on freshly isolated single smooth muscle cells from the circular layer of the rat distal colon, we reported that the L-type Ca2+ current density increased during development and gradually declined with further aging [ZI Xiong, N Sperelakis, N Noffsinger, C Fenoglio-Preiser (1993) Am J Physiol 265: C617-C625]. Since K+ current plays a key role in controlling excitability of the cells and hence the motility of the colon, in the present study the voltage-gated K+ channel currents, (IK) were investigated using the whole-cell voltage-clamp technique in colonic myocytes from rats of different ages. A Ca(2+)-sensitive K+ current [IK(Ca)] and two kinds of Ca(2+)-insensitive outward K+ currents were identified and characterized. IK(Ca) was recorded at potentials more positive than -40 mV in Ca(2+)-containing bath solution, and was blocked by Ca2+ channel antagonists and tetraethylammonium ion (TEA+). After removing Ca2+ from the bath solution and using a high ethylenebis(oxonitrilo)tetraacetate (EGTA, 4 mM) concentration in the pipette, two types of Ca(2+)-insensitive IK were recorded. The first and faster component was usually activated at potentials more positive than -50 mV, and was more sensitive to 4-aminopyridine (4-AP). In contrast, the second and slower (delayed) component was activated at potentials more positive than -30 mV, and was more sensitive to TEA. The total density of the Ca(2+)-insensitive IK component decreased dramatically during the neonatal period: from 32.2 +/- 3.2 pA/pF in 3-day-old rats to 17.8 +/- 2.6 pA/pF in 40-day-old rats; there was no further decline during aging (up to 480 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of Ca(2+)-activated K+ channel activity by tyrosine kinase inhibitors in vascular smooth muscle cell

The effects of the tyrosine kinase inhibitors genistein, lavendustin A, and tyrphostin A25 on Ca(2+)-activated K+ channel activities in freshly isolated single vascular smooth muscle cells from the rat tail artery were studied by patch clamp recording technique. Genistein (5-50 microM) and lavendustin A (10 microM) increased whole-cell Ca(2+)-activated K+ channel currents. Increase in single channel activities by genistein and lavendustin A was also observed in excised inside-out patches. Diadzein (15 microM), an inactive analogue of genistein, did not alter channel activities. Tyrphostin A25 (10 nM), which had no significant effect on whole-cell currents in concentrations up to 50 microM, increased the open probability of the channels by 841% in inside-out patches. No potentiation of whole-cell and single channel activities by genistein was observed when ATP was omitted from the intracellular solutions. These observations suggest that tyrosine kinase modulates Ca(2+)-activated K+ channel activities in vascular smooth muscle cells.

Regulation of L-type calcium channels of vascular smooth muscle cells

Vascular tone is regulated by a variety of neurotransmitters, vasoactive hormones and autacoids, and vasoactive drugs. These actions are mediated, at least in part, by actions on the membrane ion channels, exerted either directly or indirectly. In this article, we described evidence that four different protein kinase systems (PK-A, PK-G, PK-C, and Ca2+/CaM-PK) act on and modulate the L-type Ca2+ slow channels in VSM cells and other types of cells. In cardiac muscle, both cAMP/PK-A and cGMP/PK-G have opposing effects. cAMP/PK-A stimulating and cGMP/PK-G inhibiting. In VSM, both cyclic nucleotides and their related kinases act in the same direction, namely both inhibit ICa(L). In skeletal muscle, both cAMP and cGMP also act in the same direction on ICa(L), but to stimulate. Ca2+ channel phosphorylation may be an important mechanism for the cyclic nucleotide-dependent actions of some vasodilators. In cardiac muscle, in addition to the slower indirect pathway--exerted via cAMP/PK-A--there is a faster more-direct pathway for ICa(L) stimulation by the beta-adrenergic receptor. This latter pathway involves direct modulation of the channel activity by the alpha subunit of the Gs-protein (Gs alpha). The two pathways (direct and indirect) are also present in VSM cells, although the indirect pathway produces inhibition of ICa(L)). PK-C and calmodulin-PK also may play roles in regulation of the L-type Ca2+ channels in smooth muscle cells, possibly mediated by phosphorylation of some regulatory-type of protein. Thus, it appears that the L-type Ca2+ slow channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of factors intrinsic and extrinsic to the cell (Figs 9, 14).

Neuropeptide Y inhibits Ca(2+)-activated K+ channels in vascular smooth muscle cells from the rat tail artery

The effects of neuropeptide Y (NPY) on the Ca(2+)-activated K+ channel in smooth muscle cells from the rat tail artery were studied by whole-cell and single-channel patch-clamp recording techniques. In the presence of nifedipine (1 microM), whole-cell outward currents through Ca(2+)-activated K+ channels were inhibited by NPY in a dose-dependent manner from 20 to 200 nM. A maximum inhibition to about 48% of the control current could be achieved. Recordings from outside-out patches showed that the open probability of Ca(2+)-activated K+ channels were similarly inhibited by NPY. At 200 nM NPY, the open probability was reduced to about 36% of the control value. NPY did not affect the open times or current amplitude, but increased significantly the short (from 0.49 to 0.58 ms) and long (from 441 to 728 ms) closed times. Inhibition of Ca(2+)-activated K+ channels by NPY may contribute to its excitatory action on vascular smooth muscle cells.

Regulation of slow calcium channels of myocardial cells and vascular smooth muscle cells by cyclic nucleotides and phosphorylation

The slow Ca2+ channels (L-type) of the heart are stimulated by cAMP. Elevation of cAMP produces a very rapid increase in number of slow channels available for voltage activation during excitation. The probability of a Ca2+ channel opening and the mean open time of the channel are increased. Therefore, any agent that increases the cAMP level of the myocardial cell will tend to potentiate ICa, Ca2+ influx, and contraction. The action of cAMP is mediated by PK-A and phosphorylation of the slow Ca2+ channel protein or an associated regulatory protein (stimulatory type). The myocardial slow Ca2+ channels are also regulated by cGMP, in a manner that is opposite or antagonistic to that of cAMP. We have demonstrated this at both the macroscopic level (whole-cell voltage clamp) and the single-channel level. The effect of cGMP is mediated by PK-G and phosphorylation of a protein, as for example, a regulatory protein (inhibitory-type) associated with the Ca2+ channel. Introduction of PK-G intracellularly causes a relatively rapid inhibition of ICa(L) in both chick and rat heart cells. Such inhibition occurs for both the basal and stimulated ICa(L). In addition, the cGMP/PK-G system was reported to stimulate a phosphatase that dephosphorylates the Ca2+ channel. In addition to the slower indirect pathway--exerted via cAMP/PK-A--there is a faster more-direct pathway for ICa(L) stimulation by the beta-adrenergic receptor. This latter pathway involves direct modulation of the channel activity by the alpha subunit (alpha s*) of the Gs-protein. In vascular smooth muscle cells the two pathways (direct and indirect) also appear to be present, although the indirect pathway produces inhibition of ICa(L). PK-C and calmodulin-PK also may play roles in regulation of the myocardial slow Ca2+ channels. Both of these protein kinases stimulate the activity of these channels. Thus, it appears that the slow Ca2+ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of factors intrinsic and extrinsic to the cell, and thereby control can be exercised over the force of contraction of the heart.

Regulation of L-type calcium channels by cyclic nucleotides and phosphorylation in smooth muscle cells from rabbit portal vein

In a previous study, we demonstrated that a high concentration (> or = 1 microM) of isoproterenol (ISO) produced a dual effect on L-type Ca2+ current (ICa(L)) in vascular smooth muscle (VSM) cells from the portal vein: an initial stimulatory action followed by a sustained inhibition. The first stimulatory phase was fast (presumably more direct) and may reflect G-protein gating of the Ca2+ channels. The second inhibitory phase was slower (presumably more indirect) and may be mediated by the adenylate cyclase/cAMP pathway. In order to define further the mechanism for the ISO inhibition of ICa(L), the effects of cyclic nucleotides and their related protein kinases were examined in freshly isolated single smooth muscle cells from the rabbit portal vein using the whole-cell voltage clamp technique. To isolate ICa(L), the pipette solution contained high Cs+ (to block K+ outward current), and the bath contained physiological salt solution. Upon extracellular application of membrane-permeable cAMP and cGMP analogs (8-Br-cAMP and 8-Br-cGMP, 3 mM), ICa(L) was significantly inhibited by 27.9 +/- 5.0 and 33.5 +/- 4.8%, respectively. Forskolin (100 microM) also depressed ICa(L). The protein kinase inhibitor, H-7, prevented the inhibitory effects of both cyclic nucleotides and forskolin. In addition, intracellular application (via the patch pipettes) of cAMP-dependent protein kinase (PK-A, catalytic subunit; 1.76 microM) and cGMP-dependent protein kinase (PK-G, 50 nM, pre-activated by 10 microM cGMP) significantly inhibited the peak amplitude of ICa(L) by 45.5 +/- 10 and 43.2 +/- 6.2%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)