Validation of FLIPR membrane potential dye for high throughput screening of potassium channel modulators

A fluorescence-based assay using the FLIPR Membrane Potential Assay Kit (FMP) was evaluated for functional characterization and high throughput screening (HTS) of potassium channel (ATP-sensitive K+ channel; K(ATP)) modulators. The FMP dye permits a more sensitive evaluation of changes in membrane potential with a more rapid response time relative to DiBAC4(3). The time course of responses is comparable to ligand-evoked activation of the channel measured by patch-clamp studies. The pharmacological profile of the K+ channel evaluated by using reference K(ATP) channel openers is in good agreement with that derived previously by DiBAC4(3)-based FLIPR assays. Improved sensitivity of responses together with the diminished susceptibility to artifacts such as those evoked by fluorescent compounds or quenching agents makes the FMP dye an alternative choice for HTS screening of potassium channel modulators.

Lack of age-associated LFA-1 up-regulation and impaired ICAM-1 binding in lymphocytes from patients with Down syndrome

To investigate the role of LFA-1 in the immune defects in DS patients, we analysed lymphocytes from DS patients in LFA-1 expression and LFA-1 mediated cell adhesion. DS patients less than 2 years of age expressed a higher level of LFA-1 when compared with age-matched controls. The difference in LFA-1 expression was much less significant in older DS patients when compared with age-matched children. Although older children (2-15-year-old groups) without DS tend to increase their expression of lymphocyte LFA-1 when compared with younger normal children (0-2 years old), DS patients showed no age-associated increase in lymphocyte LFA-1 expression. Two-colour analysis with CD4/CD8 and LFA-1 in patients and controls showed that proportions of CD4 + lymphocytes were comparable in DS patients and controls, while the proportion of CD8 + lymphocytes was higher in older DS patients. Expression levels of LFA-1 on both CD4 + and CD8 + lymphocytes in younger DS patients were higher when compared with age-matched controls and close to the expression levels in the older DS group. Proportions of memory lymphocytes expressing the CD45RO isoform were higher in both younger and older DS patients when compared with age-matched control groups. Noticeably, the LFA-1 expression levels on CD45RO lymphocytes from younger DS patients were higher than the levels of the controls and declined in the older DS group. We tested lymphocytes (EBV transformed B cells, resting and anti-CD3 stimulated T cells) for cellular adhesion to recombinant ICAM-1 and found that lymphocytes from DS patients were less adhesive, even though their beta2 integrin expression was comparable with that of normal controls. These results suggest that more generalized pathological processes, such as early senescence of the immune system or ineffective lymphocyte activation, and subsequent integrin dysfunction may underlie the immune defects in DS patients.

Allergen-induced bronchial inflammation is associated with decreased levels of surfactant proteins A and D in a murine model of asthma

BACKGROUND

Increasing evidence suggests that pulmonary surfactant protein A (SP-A) and D (SP-D) participate in the lung defence against pathogens. However, the role of surfactant proteins in the pathogenesis of allergen-induced airway inflammation has not been elucidated. In this study we examined the levels and distributions of SP-A and SP-D in a dust mite (Dermatophagoides pteronyssinus, Der p) allergen-induced murine model of asthma.

METHODS

The concentration of SP-A and SP-D in the bronchoalveolar lavage fluid (BALF) and the distribution of surfactant proteins in the lung were assayed by ELISA and immunohistochemistry methods, respectively. The effect of surfactant proteins on allergen-induced pulmonary lymphocyte proliferation was also studied.

RESULTS

We demonstrated that there were marked reductions of SP-A and SP-D levels in the BALF of Der p-sensitized BALB/c mice at 48-72 h after allergen challenge (AC). Both purified SP-A and SP-D were able to suppress, in a dose dependent manner, Der p-stimulated intrapulmonary lymphocyte proliferation of naïve mice with saline or allergen challenge, or of Der p-sensitized mice with saline challenge. On the contrary, this suppressive effect was mild (< 9%) on lymphocytes from sensitized mice after AC.

CONCLUSION

These results indicated the involvement of pulmonary surfactant proteins in the allergic bronchial inflammation of sensitized mice.

Mutation analysis in the family of a Taiwanese boy with with epidermolysis bullosa simplex dowling-meara

Epidermolysis bullosa simplex (EBS) is a group of hereditary bullous diseases characterized by intraepidermal blistering due to mechanical stress-induced degeneration of basal keratinocytes. The major subtypes of EBS, including EBS Dowling-Meara (EBS-DM), are caused by mutations of the basal keratin genes, keratin 5 (KRT5) or keratin 14 (KRT14). Here, we describe the first reported pedigree of EBS-DM in Taiwan. The proband was a 5-day-old newborn, who presented with numerous blisters of various sizes, some of which were hemorrhagic, as well as erosions on the extremities and hard palate since birth. Biopsy of a new vesicle showed subepidermal and basal cleavage with infiltration of eosinophils and neutrophils. Electron microscopy revealed cytolysis of basal cells and clumping of tonofilaments forming thick bundles and peculiar electron-dense round or oval basket-weave bodies. These features are characteristic of EBS-DM. The proband's mother had also suffered from a similar blistering disorder since birth, with gradual appearance of mottled pigmentation on the trunk, diffuse irregular or linear palmoplantar hyperkeratosis, and nail dystrophy. Mutation analysis revealed a heterozygous point mutation (R125C) in helix 1A of keratin 14 in the proband and his mother. The detection of this pathogenic point mutation enables future prenatal diagnosis in this family.

Functional implication of spare ATP-sensitive K(+) channels in bladder smooth muscle cells

ATP-sensitive K(+) (K(ATP)) channels play important roles in the regulation of excitability in urinary bladder smooth muscle cells. Patch-clamp studies revealed that the current density was about 9-fold higher in the pig bladder smooth muscle cells, compared with guinea pig, although the rank order of potencies for suppression of electrical field-stimulated contraction of bladder strips by K(ATP) channel openers (KCOs) showed a nearly 1:1 correlation between pig and guinea pig. To investigate the existence of spare K(ATP) channels, P1075-evoked current and membrane potential responses were studied in bladder smooth muscle cells. During a 10-min exposure to P1075 (10 microM), K(ATP) currents ran down by approximately 30.5%, whereas membrane hyperpolarization remained constant. P1075 evoked membrane hyperpolarization with an EC(50) value of 0.20 +/- 0.02 microM, comparable to that required for smooth muscle relaxation (EC(50) = 0.11 +/- 0.01 microM). However, these potencies are 6-fold higher than those required for current activation (EC(50) = 0.73 +/- 0.4 microM). These findings demonstrate that the reduction in membrane excitability by KCOs is associated with membrane hyperpolarization, and that a low amount of K(ATP) channel opening is sufficient to suppress bladder smooth muscle contraction.

Potassium channels: molecular defects, diseases, and therapeutic opportunities

Potassium channels play important roles in vital cellular signaling processes in both excitable and nonexcitable cells. Over 50 human genes encoding various K(+) channels have been cloned during the past decade, and precise biophysical properties, subunit stoichiometry, channel assembly, and modulation by second messenger and ligands have been elucidated to a large extent. Recent advances in genetic linkage analysis have greatly facilitated the identification of many disease-producing loci, and naturally occurring mutations in various K(+) channels have been identified in diseases such as long-QT syndromes, episodic ataxia/myokymia, familial convulsions, hearing and vestibular diseases, Bartter's syndrome, and familial persistent hyperinsulinemic hypoglycemia of infancy. In addition, changes in K(+) channel function have been associated with cardiac hypertrophy and failure, apoptosis and oncogenesis, and various neurodegenerative and neuromuscular disorders. This review aims to 1) provide an understanding of K(+) channel function at the molecular level in the context of disease processes and 2) discuss the progress, hurdles, challenges, and opportunities in the exploitation of K(+) channels as therapeutic targets by pharmacological and emerging genetic approaches.

Molecular characterization of human SUR2-containing K(ATP) channels

The distribution of human sulfonylurea receptor-2 (SUR2)-containing K(ATP) channels was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR). mRNA for SUR2B was detected in a variety of tissues including brain, skeletal, cardiac and smooth muscle, whereas SUR2A message was restricted to cardiac and skeletal muscle. An additional splice variant of SUR2 that lacked exon 17 was also identified by RT-PCR in tissues expressing both SUR2A and SUR2B or SUR2B alone. Quantification of RNA for SUR2 exon 17+ and SUR2 exon 17- splice variants using real-time Taqman PCR indicated differential levels of expression in brain, kidney, skeletal muscle, heart and small intestine. Interestingly, the SUR2 exon 17+ variant is the major species expressed in all tissues examined in this study. Each of the SUR2 splice variants transiently expressed with the inward rectifier Kir 6.2 formed functional K(ATP) channels in HEK 293 cells as assessed either by changes in DiBAC(4)(3) fluorescence responses or glyburide-sensitive whole cell currents. Collectively, our findings demonstrate that various SUR2 splice variants have distinct expression patterns and can form functional K(ATP) channels.

Chronic granulomatous disease: a case report

Chronic granulomatous disease (CGD) is a rare inherited disorder caused by defects in the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex of phagocytic leukocytes. The leukocytes of the CGD patients cannot produce adequate amount of superoxide and other oxygen metabolites which are toxic to microorganisms. As a result, the phagocytes fail to kill the ingested microorganisms, especially those with catalase activity. Typically, CGD patients suffer from recurrent pyogenic infections starting from the first year of life. We report a young boy who had experienced recurrent perianal abscess, osteomyelitis and bacterial enterocolitis. Flow cytometric analysis revealed defects in the neutrophil respiratory burst pathway and defined the carrier state of his mother and younger sister. He received antimicrobial prophylaxis at our out-patient clinics and remained well at present. We try to make clinical physician keep in mind the diagnosis of CGD by presenting this typical case. In the meantime, we review the recent literature regarding the advances in diagnosis and management of CGD.

Pharmacology of human sulphonylurea receptor SUR1 and inward rectifier K(+) channel Kir6.2 combination expressed in HEK-293 cells

1. The pharmacological properties of K(ATP) channels generated by stable co-expression of the sulphonylurea receptor SUR1 and the inwardly rectifying K(+) channel Kir6.2 were characterized in HEK-293 cells. 2. [(3)H]-Glyburide (glibenclamide) bound to transfected cells with a B(max) value of 18.5 pmol mg(-1) protein and with a K(D) value of 0.7 nM. Specific binding was displaced by a series of sulphonylurea analogues with rank order potencies consistent with those observed in pancreatic RINm5F insulinoma and in the brain. 3. Functional activity of K(ATP) channels was assessed by whole cell patch clamp, cation efflux and membrane potential measurements. Whole cell currents were detected in transfected cells upon depletion of internal ATP or by exposure to 500 microM diazoxide. The currents showed weak inward rectification and were sensitive to inhibition by glyburide (IC(50)=0.92 nM). 4. Metabolic inhibition by 2-deoxyglucose and oligomycin treatment triggered (86)Rb(+) efflux from transfected cells that was sensitive to inhibition by glyburide (IC(50)=3.6 nM). 5. Diazoxide, but not levcromakalim, evoked concentration-dependen decreases in DiBAC(4)(3) fluorescence responses with an EC(50) value of 14.1 microM which were attenuated by the addition of glyburide. Diazoxide-evoked responses were inhibited by various sulphonylurea analogues with rank order potencies that correlated well with their binding affinities. 6. In summary, results from ligand binding and functional assays demonstrate that the pharmacological properties of SUR1 and Kir6.2 channels co-expressed in HEK-293 cells resemble those typical of native K(ATP) channels described in pancreatic and neuronal tissues.

Decreased sodium and increased transient outward potassium currents in iron-loaded cardiac myocytes. Implications for the arrhythmogenesis of human siderotic heart disease

BACKGROUND

Patients with chronic iron overload may develop a cardiomyopathy manifested by ventricular arrhythmias and heart failure. We hypothesized that iron-loaded cardiomyocytes may have abnormal excitability.

METHODS AND RESULTS

We examined a new model of human iron overload, the Mongolian gerbil given repeated injections of iron dextran. In ventricular myocytes, we measured iron concentration and distribution, action potential, sodium and potassium currents, and sodium channel protein. We showed for the first time that (1) the iron content of gerbil ventricular cardiomyocytes was increased to amounts similar to those of patients with iron-induced cardiomyopathy; (2) the overshoot and duration of the cardiac action potential decreased; (3) sodium current was reduced, steady-state inactivation was enhanced, and single-channel currents were unchanged; and (4) transient outward potassium current was increased, but inwardly rectifying potassium current was unchanged. Neonatal rat cardiomyocytes incubated with iron for 1 to 3 days showed similar changes, and levels of cardiac sodium channel proteins were unchanged.

CONCLUSIONS

Abnormal excitability and heterogeneous cardiac iron deposition may cause the arrhythmogenesis of human siderotic heart disease.

Lymphocyte adhesion to epithelia and endothelia mediated by the lymphocyte endothelial-epithelial cell adhesion molecule glycoprotein

Upon encountering the relevant vascular bed, lymphocytes attach to endothelial adhesion molecules, transmigrate out of circulation, and localize within tissues. Lymphocytes may then be retained at microanatomic sites, as in tissues, or they may continue to migrate to the lymphatics and recirculate in the blood. Lymphocytes also interact transiently, but with high avidity, with target cells or APC that are infected with microbes or have taken up exogenous foreign Ags. This array of adhesive capabilities is mediated by the selective expression of lymphocyte adhesion molecules. Here, we developed the 6F10 mAb, which recognizes a cell surface glycoprotein designated lymphocyte endothelial-epithelial cell adhesion molecule (LEEP-CAM), that is distinct in biochemical characteristics and distribution of expression from other molecules known to play a role in lymphocyte adhesion. LEEP-CAM is expressed on particular epithelia, including the suprabasal region of the epidermis, the basal layer of bronchial and breast epithelia, and throughout the tonsillar and vaginal epithelia. Yet, it is absent from intestinal and renal epithelia. Interestingly, it is expressed also on vascular endothelium, especially high endothelial venules (HEV) in lymphoid organs, such as tonsil and appendix. The anti-LEEP-CAM mAb specifically blocked T and B lymphocyte adhesion to monolayers of epithelial cells and to vascular endothelial cells in static cell-to-cell binding assays by approximately 40-60% when compared with control mAbs. These data suggest a role for this newly identified molecule in lymphocyte binding to endothelium, as well as adhesive interactions within selected epithelia.

Characterization of the ATP-sensitive potassium channels (KATP) expressed in guinea pig bladder smooth muscle cells

ATP-sensitive K+ (KATP) channels play an important role in the regulation of smooth muscle membrane potential. To investigate the properties of KATP channels in guinea pig urinary bladder smooth muscle cells, fluorescence-based assays were carried out with the membrane potential-sensitive probe bis-(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC4(3)]. The prototypical channel openers, including pinacidil, (-)-cromakalim, and diazoxide, elicited concentration-dependent decreases in membrane potential that were attenuated by glyburide. Similar responses were evoked by a reduction in intracellular ATP levels by metabolic inhibition. The observed rank order potency (EC50) for evoking membrane potential changes by potassium channel openers, P1075 (53 nM) approximately Bay X 9228 > (-)-cromakalim approximately ZD6169 approximately pinacidil > Bay X 9227 approximately ZM244085 > diazoxide (59 microM), showed a good correlation with that of bladder smooth muscle relaxation, as assessed by isolated tissue bath studies. The maximal efficacies of (-)-cromakalim, pinacidil, Bay X 9228, and ZD6169 were comparable with the response achieved by the reference activator P1075. Whole cell currents in bladder smooth muscle cells were increased in both inward and outward directions by P1075 and were reversed by glyburide to control levels. The molecular composition assessed by reverse transcriptase-polymerase chain reaction analysis using subunit-specific primers revealed the presence of mRNA for inward rectifying potassium channel (KIR6.2) and sulfonylurea receptors (SUR)2B and SUR1. The subunit profile together with pharmacological properties suggests that the KATP channel in bladder smooth muscle cells could be composed of SUR2B associated with a single inward rectifier, KIR6.2. In summary, these studies have characterized the pharmacological profile using fluorescent imaging plate reader-based membrane potential techniques and provide evidence for the molecular identity of KATP channels expressed in guinea pig bladder smooth muscle cells.

Membrane anchoring of calnexin facilitates its interaction with its targets

Calnexin, a chaperone that resides in the endoplasmic reticulum, participates in the quality control function of this compartment. Many glycoproteins in the process of folding associate transiently with this chaperone via interactions involving the recognition of their mono-glucosylated glycans. Some misfolded proteins which are retained in the endoplasmic reticulum exhibit prolonged association with calnexin. We have examined whether the transmembrane and cytoplasmic domains of calnexin influence the association of this chaperone with its targets. Interactions of wild type and truncated calnexin with a glycoprotein that is retained in the endoplasmic reticulum (the lymphocyte tyrosine kinase, Ltk), with membrane IgM heavy chains, and with the MHC class I heavy chain protein were investigated. A soluble calnexin molecule lacking the transmembrane domain and cytoplasmic tail does not associate with any of these proteins. When a heterologous transmembrane domain is fused to the lumenal portion of calnexin, this membrane-bound protein can bind Ltk, IgM heavy chains, and MHC class I heavy chain proteins. These results suggest that calnexin must be membrane-anchored in order to recognize its substrates.

Inhibitory effect of pulmonary surfactant proteins A and D on allergen-induced lymphocyte proliferation and histamine release in children with asthma

The role of pulmonary surfactant proteins in the pathogenesis of airway inflammation and the impact on asthma has not been elucidated. This study was designed to examine the effect of surfactant proteins A (SP-A) and D (SP-D) on phytohemagglutinin- (PHA) and mite allergen Dermatophagoides pteronyssinus (Der p)-induced histamine release and the proliferation of peripheral blood mononuclear cells (PBMC) in children with asthma in stable condition (n = 21), asthmatic children during acute attacks (n = 9), and age-matched control subjects (n = 7). The results show that SP-A and SP-D were able to reduce the incorporation of [3H]thymidine into PBMC in a dose-dependent manner. In addition to the intact, native SP-A and SP-D proteins, a recombinant peptide composed of the neck and carbohydrate recognition domain (CRD) of SP-D [SP-D(N/CRD)] was also found to have the same suppressive effect on lymphocyte proliferation. This effect was abolished by the presence of 100 mM mannose (for SP-A) or maltose (for SP-D) in the culture medium, which suggested that the CRD regions of SP-A and SP-D may interact with the carbohydrate structures on the surface molecules of lymphocytes. The inhibitory effects of surfactant proteins on PHA- and Der p-stimulated lymphocyte responses were observed in stable asthmatic children and age-matched control subjects, while only a mild suppression (< 25%) was seen in activated lymphocytes derived from asthmatic children with acute attacks. SP-A and SP-D were also found to inhibit allergen-induced histamine release, in a dose-dependent manner, in the diluted whole blood of asthmatic children. We conclude that both SP-A and SP-D can inhibit histamine release in the early phase of allergen provocation and suppress lymphocyte proliferation in the late phase of bronchial inflammation, the two essential steps in the development of asthmatic symptoms. It appears that SP-A and SP-D may be protective against the pathogenesis of asthma.

Inactivation of Kv2.1 potassium channels

We report here several unusual features of inactivation of the rat Kv2.1 delayed rectifier potassium channel, expressed in Xenopus oocytes. The voltage dependence of inactivation was U-shaped, with maximum inactivation near 0 mV. During a maintained depolarization, development of inactivation was slow and only weakly voltage dependent (tau = 4 s at 0 mV; tau = 7 s at +80 mV). However, recovery from inactivation was strongly voltage dependent (e-fold for 20 mV) and could be rapid (tau = 0.27 s at -140 mV). Kv2.1 showed cumulative inactivation, where inactivation built up during a train of brief depolarizations. A single maintained depolarization produced more steady-state inactivation than a train of pulses, but there could actually be more inactivation with the repeated pulses during the first few seconds. We term this phenomenon "excessive cumulative inactivation." These results can be explained by an allosteric model, in which inactivation is favored by activation of voltage sensors, but the open state of the channel is resistant to inactivation.

Contribution of the NH2 terminus of Kv2.1 to channel activation

Opening and closing of voltage-operated channels requires the interaction of diverse structural elements. One approach to the identification of channel domains that participate in gating is to locate the sites of action of modifiers. Covalent reaction of Kv2.1 channels with the neutral, sulfhydryl-specific methylmethanethiosulfonate (MMTS) caused a slowing of channel gating with a predominant effect on the kinetics of activation. These effects were also obtained after intracellular, but not extracellular, application of a charged MMTS analog. Single channel analysis revealed that MMTS acted primarily by prolonging the latency to first opening without substantially affecting gating transitions after the channel first opens and until it inactivates. To localize the channel cysteine(s) with which MMTS reacts, we generated NH2- and COOH-terminal deletion mutants and a construct in which all three cysteines in transmembrane regions were substituted. Only the NH2-terminal deletion construct gave rise to currents that activated slowly and displayed MMTS-insensitive kinetics. These results show that the NH2-terminal tail of Kv2.1 participates in transitions leading to activation through interactions involving reduced cysteine(s) that can be modulated from the cytoplasmic phase.

Role of transmembrane segment S5 on gating of voltage-dependent K+ channels

The cytoplasmic half of S5 (5'S5) has been identified as part of the inner mouth of the pore based on evidence that mutations in this region greatly alter single channel conductance, 4-aminopyridine (4-AP) block and the rate of channel closing upon repolarization (deactivation). The latter effect, suggestive of a role for 5'S5 in channel gating was investigated in the present study. The biophysical properties of chimeric channels, in which the 5'S5 regions were exchanged between two host channels (Kv2.1 and Kv3.1) that differ in 4-AP sensitivity and deactivation rate, were examined in a Xenopus oocyte expression system. Exchange of 5'S5 between Kv2.1 and Kv3.1 confers steady-state voltage dependence of activation and rates of channel deactivation similar to those of the donor channel. The involvement of voltage-dependent gating was confirmed by the observation that exchanging the 5'S5 segment of Kv2.1 with that of Kv3.1 confers a change from slow to fast deactivation kinetics by accelerating the decay of off-gating charge movement. We suggest that a conformational change that extends from the voltage-sensor in S4 to the region of the pore lined by S5 regulates the stability of the open state. Therefore, the cytoplasmic end of S5, in addition to forming part of the conduction pathway near the inner mouth of the pore, also participates in the conformational rearrangements associated with late steps in channel activation and early steps in deactivation.

Multiple residues specify external tetraethylammonium blockade in voltage-gated potassium channels

We have mapped residues in the carboxyl half of the P region of a voltage-gated K+ channel that influence external tetraethylammonium (TEA) block. Fifteen amino acids were substituted with cysteine and expressed in oocytes from monomeric or heterodimeric cRNAs. From a total of six mutant channels with altered TEA sensitivity, three were susceptible to modification by extracellularly applied charged methanethiosulfonates (MTSX). Another residue did not affect TEA block but was protected from MTSX by TEA. MTSX modification of position Y380C, thought to form the TEA binding site, affected TEA affinity only moderately, and this effect could be reversed by additional charge transfer from an oppositely charged MTSX analog. The results show that TEA block is modulated from multiple sites, including residues located deep in the pore and that several side chains besides that of Y380 are exposed at the TEA receptor.

Functional role of a conserved aspartate in the external mouth of voltage-gated potassium channels

Mutation of the glycines in a conserved Gly-Tyr-Gly-Asp sequence in the P-region of voltage-gated K channels has identified determinants of Na/K selectivity. But the function of the negatively charged Asp is not known because mutations at this position are not tolerated, owing to the fourfold replication of mutations in a tetrameric channel. We have successfully mutated Asp378-->Thr in a tandem dimer Kv2.1 construct to yield a twofold neutralization of charge at this site. When expressed in Xenopus oocytes, the mutated channels showed markedly altered ion conduction and blockade. Potassium conduction in the inward direction was selectively reduced, so that the instantaneous current-voltage relationship obtained in isotonic KCl became strongly outwardly rectifying. The relative permeability to Na+, PNa/PK, increased from 0.02 to 0.10 without changing the ion selectivity sequence K > Rb >> Cs >> Na. The IC50 for block by external tetraethylammonium (TEA) increased more than 100-fold without affecting block by internal TEA. We conclude that Asp378 is an essential part of a potassium ion binding site associated with the Na/K selectivity filter at the external mouth of the pore.

K+ pore structure revealed by reporter cysteines at inner and outer surfaces

The structure of the carboxyl half of the pore-forming region of Kv2.1 was studied by replacing each of 15 consecutive residues between positions 383 and 369 with a reporter cysteine residue. Extracellular application of charged, membrane-impermeant methanethiosulfonates irreversibly modified currents at four cysteine-substituted positions, K382, Y380, I379, and D378. Intracellular exposure to methanethiosulfonate ethyltrimethylammonium revealed another set of reactive mutants (V374, T373, T372, and T370). Our results indicate that positions 378 and 374 are exposed at outer and inner mouths of the channel, respectively, and immersed in the aqueous phase. In contrast to present topological models, the 383-369 region appears to span the pore mainly as a nonperiodic structure.

Mutational analysis of ion conduction and drug binding sites in the inner mouth of voltage-gated K+ channels

Pore properties that distinguish two cloned, voltage-gated K+ channels, Kv2.1 and Kv3.1, include single-channel conductance, block by external and internal tetraethylammonium, and block by 4-aminopyridine. To define the inner mouth of voltage-gated K+ channels, segmental exchanges and point mutations of nonconserved residues were used. Transplanting the cytoplasmic half of either transmembrane segments S5 or S6 from Kv3.1 into Kv2.1 reduced sensitivity to block by internal tetraethylammonium, increased sensitivity to 4-aminopyridine, and reduced single-channel conductance. In S6, changes in single-channel conductance and internal tetraethylammonium sensitivity were associated with point mutations V400T and L403 M, respectively. Although individual residues in both S5 and S6 were found to affect 4-aminopyridine blockade, the most effective change was L327F in S5. Thus, both S5 and S6 contribute to the inner mouth of the pore but different residues regulate ion conduction and blockade by internal tetraethylammonium and 4-aminopyridine.

Segmental exchanges define 4-aminopyridine binding and the inner mouth of K+ pores

4-Aminopyridine (4AP) blocks the intracellular mouth of voltage-gated K+ channels. We identified critical regions for 4AP binding with chimeric channels in which segments of a low affinity clone (Kv2.1, IC50 = 18 mM) were replaced with those of a high affinity clone (Kv3.1, IC50 = 0.1 mM). 4AP sensitivity was not transferred with the S5-S6 linker (pore or P region). Instead, a chimera of the cytoplasmic half of S6 increased block 20-fold, without affecting gating. A double chimera of the cytoplasmic halves of S5 and S6 fully transferred 4AP sensitivity. Because 4AP block was inhibited by tetrapentylammonium, we conclude that determinants of 4AP binding lie in the S6 segment that forms the cytoplasmic vestibule of the pore and that this site may overlap a quaternary ammonium site.

Cromakalim effects of acetylcholine-induced changes in cytosolic calcium and tension in swine trachealis

The effects of cromakalim, an ATP-sensitive K+ channel activator, on changes in cytosolic calcium concentration [( Ca++]i) and tension induced by acetylcholine (ACh; 0.1-10 microM) were examined in swine tracheal smooth muscle. Cromakalim (10 microM) hyperpolarized muscle cells by approximately 18 mV from -58 mV (resting membrane potential) to -76 mV. Cromakalim relaxed muscle contractions evoked by ACh at a concentration of 0.1 microM, but not at higher concentrations. Measurement of [Ca++]i using Fura-2 demonstrated that except at 0.1 microM ACh, cromakalim did not alter peak increases in [Ca++]i. At 0.1 microM ACh, the peak transient was decreased, but not eliminated. Cromakalim reduced steady-state increases in [Ca++]i at ACh less than or equal to 1 microM, but not 10 microM ACh. Tension was similarly affected. These data suggest that ACh-induced increases in steady-state [Ca++]i and tension are inhibited by cromakalim-induced hyperpolarization. The initial ACh-induced transient increase in [Ca++]i is not greatly altered. Cromakalim did not alter the transient peak tension and [Ca++]i relationship. The relationship between steady-state [Ca++]i/tension (EC50 = 321 nM) obtained for control, cromakalim inhibition and after glibenclamide reversal of cromakalim inhibition falls to the left of the peak transient [Ca++]i/tension relationship (EC50 = 587 nM). Thus, the Ca++ sensitivity of the contractile proteins during steady-state stimulation by ACh was increased from that at rest. We conclude that electromechanical coupling is important in ACh-induced contraction at concentrations less than 1 microM. Pharmacomechanical coupling with little or no sensitivity to changes in potential is important at higher ACh concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Giant nevocellular nevi with rickets and brainstem tumor

A boy, 9 years, 8 months of age, with hairy pigmented nevi over the trunk, upper extremities, and face with bone deformities characteristic of rickets was admitted because of general weakness and poor appetite for 3 weeks. Repeated examinations demonstrated marked brainstem dysfunction; a brainstem tumor was visualized by computed tomography. The patient died 14 days after admission despite supportive treatment. The relationship between giant intradermal nevocellular nevi and brain tumor is discussed.

Concentration-dependence of acetylcholine-induced changes in calcium and tension in swine trachealis

Acetylcholine (ACh)-induced increases in intracellular calcium concentration ([Ca++]i) and tension were measured simultaneously in swine tracheal smooth muscle strips loaded with the calcium-sensitive fluorescent dye Fura-2. ACh at concentrations greater than or equal to 3 x 10(-8) M induced concentration-dependent increases in tension which reached a maximum at 10(-4) M. Increases in [Ca++]i occurred at all [ACh] tested (10(-8) to 10(-4) M). After addition of ACh at concentrations greater than 3 x 10(-7) M, [Ca++]i increased rapidly to a concentration dependent-peak then declined to a concentration-independent steady state approximately 250 nM above the resting [Ca++]i of 257 +/- 12 nM. There was a steep relationship (slope factor greater than 3) between the peak tension and the peak [Ca++]i reached at each [ACh]. The rate of decline of [Ca++]i to the steady state at [ACh] greater than 73 x 10(-7) M was well correlated with the peak [Ca++]i reached. We conclude that the peak increase in calcium induced by ACh sets the level of tension to be attained and the rate of decline of the transient increase in [Ca++]i. The steady-state [Ca++]i is sufficient for maintenance of tension.

Dubin-Johnson syndrome presenting with neonatal cholestasis

We report a case of Dubin-Johnson syndrome presenting with neonatal cholestasis. Liver histology was studied during the neonatal period and at 6 years of age. Distinct brownish pigment granules in hepatocytes were noted. This case confirms that Dubin-Johnson syndrome is a cause of neonatal cholestasis.

Charcot-Marie-Tooth disease: a case presenting with hyperreflexia

We report a 10-year-old girl with progressive weakness of lower extremities, feet deformity, and sensory impairment on both feet for 3 years. Absent ankle tendon reflex, exaggerated knee jerk and prolonged nerve conduction velocity were noted by physical and electrophysiological examination. Nerve and muscle biopsy showed demyelination and neurogenic changes respectively and supported the diagnosis of Charcot-Marie-Tooth disease, type I. The point that the diagnosis of Charcot-Marie-Tooth disease remains possible even in the absence of family history and the typical clinical picture is stressed. Complete electrophysiological study and tissue diagnosis are required for early diagnosis, early rehabilitation and reconstructive surgery.

Late onset hemorrhagic cystitis after allogeneic bone marrow transplantation

Three patients with acute myeloblastic leukemia, thalassemia major and aplastic anemia experienced hemorrhagic cystitis on the 23rd, 35th and 36th day respectively after allogeneic bone marrow transplantation. The conditioning regimens before transplantation comprised cyclophosphamide with or without busulfan and total lymphoid irradiation. The hematuria lasted from 5 to 45 days and then subsided after treatment. Multiple factors including the toxicity of chemotherapeutic agents, viral infection and graft-versus-host reactions may contribute to late onset hemorrhagic cystitis after allogeneic bone marrow transplantation. Adequate treatment to minimize urothelial damage from chemotherapy, screening for viral infection and controlling graft-versus-host disease are mandatory in decreasing the complication of late-onset hemorrhagic cystitis after bone marrow transplantation.

Measurement of testosterone in seminal plasma, saliva and serum by solid-phase enzymeimmunoassay

When testosterone concentrations in serum, saliva and seminal plasma were measured with a solid-phase enzymeimmunoassay in which antitestosterone antibody was bound to CNBr-Sepharose-4B, we found the ratios of testosterone in saliva and seminal plasma to that in serum were 2.5 +/- 0.2% and 5.19 +/- 0.42%. Testosterone level in saliva could be an index of free serum testosterone. In addition, we found a correlation between sperm motility and testosterone level in seminal plasma when sperm motility was measured with a transmembrane migration method. This enzymeimmunoassay could be applied to clinical studies of testosterone.

The spermicidal potency of Coca-Cola and Pepsi-Cola

The inhibitory effect of Old Coke, caffeine-free New Coke, New Coke, Diet Coke and Pepsi-Cola on human sperm motility was studied with a trans-membrane migration method. None of them could decrease sperm motility to less than 70% of control within one hour. A previous study which claimed a marked variation of spermicidal potencies among different formulations of Coca-Cola could not be confirmed. Even if cola has a spermicidal effect, its potency is relatively weak as compared with other well-known spermicidal agents.

Effect of phosphatidylcholine, lysophosphatidylcholine, arachidonic acid and docosahexaenoic acid on the motility of human sperm

Lysophosphatidylcholine, arachidonic acid and docosahexaenoic acid were found to have a concentration-dependent inhibitory effect on the motility of human sperm, whilst phosphatidylcholine had no effect. Seminal plasma attenuated the sperm-immobilizing potencies of these lipids. Because all of the three inhibitors of motility are hydrolytic products of phosphatidylcholine, and the catalytic enzyme, phospholipase A2, is known to be calcium dependent, it is suggested that calcium might inhibit sperm motility by activating phospholipase A2 which in turn releases lysophosphatidylcholine and free fatty acids.

Detection of antibodies to HTLV-III by ELISA in AIDS risk groups in Taiwan: a preliminary report

A total of 2321 serum samples were collected from a variety of AIDS risk groups. The samples were tested for anti-HTLV-III using ELISA. Low prevalences of seropositivity were detected in the high-risk groups. Among 120 homosexuals/bisexuals, one seropositive suffering from full-blown AIDS was an American traveler. Another native homosexual who yielded a high ELISA reading was a "possible" AIDS. Three hemophiliacs with strongly positive reactions received injections of a U.S.-produced factor VIII; all are asymptomatic currently. A patient with hairy cell leukemia had a markedly elevated ELISA reading. Another patient with syphilis also had a markedly high reading, despite having no other known risk factor. Among the low-risk groups a patient who had suffered from oral candidiasis for eight years had no risk factor, yet he yielded repeatedly high ELISA readings. Another patient with a weak positive reaction was a symptomless blood donor. This preliminary study concludes that Taiwan is several years behind the U.S. and is at present not an endemic area for AIDS. To achieve successful AIDS control in the future, however, the homosexuals in Taiwan should change their sexual behavior now. Since many initially weakly-reactive samples became negative on repeated testing it appears that non-specific or false positive ELISA reactions occur frequently. Accordingly when ELISA is used for diagnostic purposes, additional confirming tests are mandatory.