Using Physician-Level Emergency Department Utilization Reports to Address Avoidable Visits by Patients Managed by Pediatric Specialists

OBJECTIVES

Emergency department (ED) utilization is a major driver of cost. Specialist physicians have an important role in addressing ED utilization, especially at tertiary medical centers that treat highly specialized patients. We analyzed if reporting of ED utilization to pediatric specialist physicians can decrease ED visits.

METHODS

Physicians within pediatric neurology, hematology and oncology, infectious diseases, and pulmonary divisions received their ED use reports. By using control charts, we examined if this intervention decreased the rate of ED utilization.

RESULTS

Overall, for the 4 divisions, specialty-related ED utilization decreased significantly during all hours, weekdays, and office hours. This was in the setting of ED utilization increasing for all diagnoses ED visits. Pediatric ED volume did not change during the study period.

CONCLUSIONS

Physician-level reporting of ED utilization was associated with a reduction in ED use by patients managed by our pediatric specialists.

Immunoglobulin A Dysgammaglobulinemia Is Associated with Pediatric-Onset Obsessive-Compulsive Disorder

Background: Inflammation and immune dysregulation have been implicated in the pathogenesis of pediatric-onset obsessive-compulsive disorder (OCD) and tic disorders such as Tourette syndrome (TS). Though few replicated studies have identified markers of immune dysfunction in this population, preliminary studies suggest that serum immunoglobulin A (IgA) concentrations may be abnormal in these children with these disorders. Methods: This observational retrospective cohort study, conducted using electronic health records (EHRs), identified 206 children with pediatric-onset OCD and 1024 adults diagnosed with OCD who also had testing for serum levels of IgA. IgA deficiency and serum IgA levels in pediatric OCD were compared with IgA levels from children diagnosed with autism spectrum disorders (ASD; n = 524), tic disorders (n = 157), attention-deficit/hyperactivity disorder (ADHD; n = 534), anxiety disorders (n = 1206), and celiac disease, a condition associated with IgA deficiency (n = 624). Results: Compared with ASD and anxiety disorder cohorts, the pediatric OCD cohort displayed a significantly higher likelihood of IgA deficiency (OR = 1.93; 95% CI = 1.18-3.16, and OR = 1.98; 95% CI = 1.28-3.06, respectively), though no difference was observed between pediatric OCD and TS cohorts. Furthermore, the pediatric OCD cohort displayed similar rates of IgA deficiency and serum IgA levels when compared with the celiac disease cohort. The pediatric OCD cohort also displayed the highest percentage of IgA deficiency (15%,) when compared with TS (14%), celiac disease (14%), ADHD (13%), ASD (8%), and anxiety disorder (8%) cohorts. When segregated by sex, boys with OCD displayed a significantly higher likelihood of IgA deficiency when compared with all comparison cohorts except for celiac disease and tic disorders; no significant difference in IgA deficiency was observed between female cohorts. Pediatric OCD subjects also displayed significantly lower adjusted serum IgA levels than the ASD and anxiety disorder cohorts. Adults with OCD were also significantly less likely than children with OCD to display IgA deficiency (OR = 2.71; 95% CI = 1.71-4.28). When compared with children with celiac disease, no significant difference in IgA levels or rates of IgA deficiency were observed in the pediatric OCD cohort. Conclusions: We provide further evidence of IgA abnormalities in pediatric-onset OCD. These results require further investigation to determine if these abnormalities impact the clinical course of OCD in children.

Clinical Management of Pediatric Acute-Onset Neuropsychiatric Syndrome: Part II-Use of Immunomodulatory Therapies

Introduction: Pediatric Acute-onset Neuropsychiatric Syndrome (PANS) is a clinically heterogeneous disorder with a number of different etiologies and disease mechanisms. Inflammatory and postinfectious autoimmune presentations of PANS occur frequently, with some clinical series documenting immune abnormalities in 75%-80% of patients. Thus, comprehensive treatment protocols must include immunological interventions, but their use should be reserved only for PANS cases in which the symptoms represent underlying neuroinflammation or postinfectious autoimmunity, as seen in the PANDAS subgroup (Pediatric Autoimmune Neuropsychiatric Disorders associated with Streptococcal infections). Methods: The PANS Research Consortium (PRC) immunomodulatory task force is comprised of immunologists, rheumatologists, neurologists, infectious disease experts, general pediatricians, psychiatrists, nurse practitioners, and basic scientists with expertise in neuroimmunology and PANS-related animal models. Preliminary treatment guidelines were created in the Spring of 2014 at the National Institute of Health and refined over the ensuing 2 years over conference calls and a shared web-based document. Seven pediatric mental health practitioners, with expertise in diagnosing and monitoring patients with PANS, were consulted to create categories in disease severity and critically review final recommendations. All authors played a role in creating these guidelines. The views of all authors were incorporated and all authors gave final approval of these guidelines. Results: Separate guidelines were created for the use of immunomodulatory therapies in PANS patients with (1) mild, (2) moderate-to-severe, and (3) extreme/life-threatening severity. For mildly impairing PANS, the most appropriate therapy may be "tincture of time" combined with cognitive behavioral therapy and other supportive therapies. If symptoms persist, nonsteroidal anti-inflammatory drugs and/or short oral corticosteroid bursts are recommended. For moderate-to-severe PANS, oral or intravenous corticosteroids may be sufficient. However, intravenous immunoglobulin (IVIG) is often the preferred treatment for these patients by most PRC members. For more severe or chronic presentations, prolonged corticosteroid courses (with taper) or repeated high-dose corticosteroids may be indicated. For PANS with extreme and life-threatening impairment, therapeutic plasma exchange is the first-line therapy given either alone or in combination with IVIG, high-dose intravenous corticosteroids, and/or rituximab. Conclusions: These recommendations will help guide the use of anti-inflammatory and immunomodulatory therapy in the treatment of PANS.

Clinical evaluation of youth with pediatric acute-onset neuropsychiatric syndrome (PANS): recommendations from the 2013 PANS Consensus Conference

On May 23 and 24, 2013, the First PANS Consensus Conference was convened at Stanford University, calling together a geographically diverse group of clinicians and researchers from complementary fields of pediatrics: General and developmental pediatrics, infectious diseases, immunology, rheumatology, neurology, and child psychiatry. Participants were academicians with clinical and research interests in pediatric autoimmune neuropsychiatric disorder associated with streptococcus (PANDAS) in youth, and the larger category of pediatric acute-onset neuropsychiatric syndrome (PANS). The goals were to clarify the diagnostic boundaries of PANS, to develop systematic strategies for evaluation of suspected PANS cases, and to set forth the most urgently needed studies in this field. Presented here is a consensus statement proposing recommendations for the diagnostic evaluation of youth presenting with PANS.

Effects of simple aromatic compounds and flavonoids on Ca2+ fluxes in rat pituitary GH(4)C(1) cells

The biological activity of phenolic compounds from plants is well documented in vitro, but little is known about the possible effect of simple aromatic compounds and flavonoids on voltage-operated Ca2+ channels (VOCCs). In pituitary cells, several intracellular pathways may regulate the activity of VOCCs. In this study, we investigated the effect of nine phenylpropanes and metanes, and 20 flavonoids on high K(+)-induced 45Ca2+ entry in clonal rat pituitary GH(4)C(1) cells. At the highest dose tested (20 microg/ml), flavone (a flavone) inhibited 45Ca2+ entry by 63.5%, naringenin (a flavanone) by 56.3% and genistein (an isoflavone) by 54.6%. The phenylmetane derivative octyl gallate was the most potent compound tested, with an IC(50) value of 15.0 microg/ml. The IC(50) value for the reference compound verapamil hydrochloride was 3.0 microg/ml. In sharp contrast to the above, the flavonols quercetin and morin potentiated 45Ca2+ entry. At 20 microg/ml, quercetin increased 45Ca2+ entry by 54.1% and morin by 48.0%. Quercetin increased the cellular cAMP content in a concentration-dependent manner. H 89, an inhibitor of protein kinase A, inhibited the effect of quercetin on 45Ca2+ entry. The results thus suggest that the effect of quercetin is the result of a protein kinase A-mediated activation of VOCCs. Quercetin induced a rapid and marked increase in both the transient (143.1+/-4.2%) and delayed (198.8+/-10.0%) Ca2+ currents, measured by the whole cell patch clamp technique. The onset of the inhibitory effect of octyl gallate was slow, but resulted in an almost complete inhibition of both Ca2+ currents.

A founder mutation of the potassium channel KCNQ1 in long QT syndrome: implications for estimation of disease prevalence and molecular diagnostics

OBJECTIVES

We took advantage of the genetic isolate of Finns to characterize a common long QT syndrome (LQTS) mutation, and to estimate the prevalence of LQTS.

BACKGROUND

The LQTS is caused by mutations in different ion channel genes, which vary in their molecular nature from family to family.

METHODS

The potassium channel gene KCNQ1 was sequenced in two unrelated Finnish patients with Jervell and Lange-Nielsen syndrome (JLNS), followed by genotyping of 114 LQTS probands and their available family members. The functional properties of the mutation were studied using a whole-cell patch-damp technique.

RESULTS

We identified a novel missense mutation (G589D or KCNQ1-Fin) in the C-terminus of the KCNQ1 subunit. The voltage threshold of activation for the KCNQ1-Fin channel was markedly increased compared to the wild-type channel. This mutation was present in homozygous form in two siblings with JLNS, and in heterozygous form in 34 of 114 probands with Romano-Ward syndrome (RWS) and 282 family members. The mean (+/- SD) rate-corrected QT intervals of the heterozygous subjects (n = 316) and noncarriers (n = 423) were 460 +/- 40 ms and 410 +/- 20 ms (p < 0.001), respectively.

CONCLUSIONS

A single missense mutation of the KCNQ1 gene accounts for 30% of Finnish cases with LQTS, and it may be associated with both the RWS and JLNS phenotypes of the syndrome. The relative enrichment of this mutation most likely represents a founder gene effect. These circumstances provide an excellent opportunity to examine how genetic and nongenetic factors modify the LQTS phenotype.

Homozygosity for a HERG potassium channel mutation causes a severe form of long QT syndrome: identification of an apparent founder mutation in the Finns

OBJECTIVES

We studied the clinical characteristics and molecular background underlying a severe phenotype of long QT syndrome (LQTS).

BACKGROUND

Mutations of cardiac ion channel genes cause LQTS, manifesting as increased risk of ventricular tachycardia and sudden death.

METHODS

We studied two siblings showing prolonged QT intervals corrected for heart rate (QTc), their asymptomatic parents with only marginally prolonged QTc intervals and their family members. The potassium channel gene HERG was screened for mutations by deoxyribonucleic acid sequencing, and the electrophysiologic consequences of the mutation were studied in vitro using the whole-cell patch-clamp technique.

RESULTS

A novel missense mutation (L552S) in the HERG channel, present in the homozygous state in the affected siblings and in the heterozygous state in their parents, as well as in 38 additional subjects from six LQTS families, was identified. One of the homozygous siblings had 2:1 atrioventricular block immediately after birth, and died at the age of four years after experiencing unexplained hypoglycemia. The other sibling had an episode of torsade de pointes at the age of two years. The mean QTc interval differed significantly (p < 0.001) between heterozygous symptomatic mutation carriers (500 +/- 59 ms), asymptomatic mutation carriers (452 +/- 34 ms) and noncarriers (412 +/- 23 ms). When expressed in vitro, the HERG-L552S formed functional channels with increased activation and deactivation rates.

CONCLUSIONS

Our data demonstrate that homozygosity for a HERG mutation can cause a severe cardiac repolarization disorder without other phenotypic abnormalities. Absence of functional HERG channels appears to be one cause for intrauterine and neonatal bradycardia and 2:1 atrioventricular block.

GABA(A) and GABA(C) receptors have contrasting effects on excitability in superior colliculus

We have recently found that GABA(C) receptor subunit transcripts are expressed in the superficial layers of rat superior colliculus (SC). In the present study we used immunocytochemistry to demonstrate the presence of GABA(C) receptors in rat SC at protein level. We also investigated in acute rat brain slices the effect of GABA(A) and GABA(C) receptor agonists and antagonists on stimulus-evoked extracellular field potentials in SC. Electrical stimulation of the SC optic layer induced a biphasic, early and late, potential in the adjacent superficial layer. The late component was completely inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione or CoCl(2), indicating that it was generated by postsynaptic activation. Muscimol, a potent GABA(A) and GABA(C) receptor agonist, strongly attenuated this postsynaptic potential at concentrations >10 microM. In contrast, the GABA(C) receptor agonist cis-aminocrotonic acid, as well as muscimol at lower concentrations (0.1-1 microM) increased the postsynaptic potential. This increase was blocked by (1,2,5, 6-tetrahydropyridine-4-yl)methylphosphinic acid, a novel competitive antagonist of GABA(C) receptors. Our findings demonstrate the presence of functional GABA(C) receptors in SC and suggest a disinhibitory role of these receptors in SC neuronal circuitry.

Tumor necrosis factor-alpha, sphingomyelinase, and ceramide inhibit store-operated calcium entry in thyroid FRTL-5 cells

Tumor necrosis factor alpha (TNF-alpha) is a potent inhibitor of proliferation in several cell types, including thyroid FRTL-5 cells. As intracellular free calcium ([Ca2+]i) is a major signal in activating proliferation, we investigated the effect of TNF-alpha on calcium fluxes in FRTL-5 cells. TNF-alpha per se did not modulate resting [Ca2+]i. However, preincubation (10 min) of the cells with 1-100 ng/ml TNF-alpha decreased the thapsigargin (Tg)-evoked store-operated calcium entry in a concentration-dependent manner. TNF-alpha did not inhibit the mobilization of sequestered calcium. To investigate whether the effect of TNF-alpha on calcium entry was mediated via the sphingomyelinase pathway, the cells were pretreated with sphingomyelinase (SMase) prior to stimulation with Tg. SMase inhibited the Tg-evoked calcium entry in a concentration-dependent manner. Furthermore, an inhibition of calcium entry was obtained after preincubation of the cells with the membrane-permeable C2-ceramide and C6-ceramide analogues. The inactive ceramides dihydro-C2 and dihydro-C6 showed only marginal effects. Neither SMase, C2-ceramide, nor C6-ceramide affected the release of sequestered calcium. C2- and C6-ceramide also decreased the ATP-evoked calcium entry, without affecting the release of sequestered calcium. The effect of TNF-alpha and SMase was inhibited by the kinase inhibitor staurosporin and by the protein kinase C (PKC) inhibitor calphostin C but not by down-regulation of PKC. However, we were unable to measure a significant activation of PKC using TNF-alpha or C6-ceramide. The effect of TNF-alpha was not mediated via activation of either c-Jun N-terminal kinase or p38 kinase. We were unable to detect an increase in the ceramide (or sphingosine) content of the cells after stimulation with TNF-alpha for up to 30 min. Thus, one mechanism of action of TNF-alpha, SMase, and ceramide on thyroid FRTL-5 cells is to inhibit calcium entry.

Retarded growth and deficits in the enteric and parasympathetic nervous system in mice lacking GFR alpha2, a functional neurturin receptor

Glial cell line-derived neurotrophic factor (GDNF) and a related protein, neurturin (NTN), require a GPI-linked coreceptor, either GFR alpha1 or GFR alpha2, for signaling via the transmembrane Ret tyrosine kinase. We show that mice lacking functional GFR alpha2 coreceptor (Gfra2-/-) are viable and fertile but have dry eyes and grow poorly after weaning, presumably due to malnutrition. While the sympathetic innervation appeared normal, the parasympathetic cholinergic innervation was almost absent in the lacrimal and salivary glands and severely reduced in the small bowel. Neurite outgrowth and trophic effects of NTN at low concentrations were lacking in Gfra2-/- trigeminal neurons in vitro, whereas responses to GDNF were similar between the genotypes. Thus, GFR alpha2 is a physiological NTN receptor, essential for the development of specific postganglionic parasympathetic neurons.

Sphingosine inhibits voltage-operated calcium channels in GH4C1 cells

In the present study we investigated the mechanism of inhibitory action of sphingosine (SP) on voltage-activated calcium channels (VOCCs) in pituitary GH4C1 cells. Using the patch-clamp technique in the whole-cell mode, we show that SP inhibits Ba2+ currents (IBa) when 0.1 mM BAPTA is included in the patch pipette. However, when the BAPTA concentration was raised to 1-10 mM, SP was without a significant effect. The effect of SP was apparently not mediated via a kinase, as it was not inhibited by staurosporine. By using the double-pulse protocol (to release possible functional inhibition of the VOCCs by G proteins), we observed that G proteins apparently evoked very little functional inhibition of the VOCCs. Furthermore, including GDPbetaS (guanyl-5'-yl thiophosphate) in the patch pipette did not alter the inhibitory effect of SP on the Ba2+ current, suggesting that SP did not modulate the VOCCs via a G protein-dependent pathway. Single-channel experiments with SP in the pipette, and experiments with excised outside-out patches, suggested that SP directly inhibited VOCCs. The main mechanism of action was a dose-dependent prolongation of the closed time of the channels. The results thus show that SP is a potent inhibitor of VOCCs in GH4C1 cells, and that calcium may be a cofactor in this inhibition.

Distribution of GABA receptor rho subunit transcripts in the rat brain

The gamma-aminobutyric acid (GABA) receptor rho subunits recently cloned from rat and human retina are thought to form GABA receptor channels belonging to a pharmacologically distinct receptor class, termed GABA(C). In this work we have examined the distribution of rho1, rho2 and rho3 subunits, and found expression of all three transcripts in several regions of the rat nervous system. In situ hybridization revealed expression of rho2 in the adult rat retina and some other parts of the visual pathways. A high local rho2 expression was seen in the superficial grey layer of the superior colliculus, and in the dorsal lateral geniculate nucleus. Expression was also detected in the 6th layer of visual cortex and in the CA1 pyramidal cell layer of hippocampus. With reverse transcriptase-polymerase chain reaction, expression of rho1 was mainly seen in the adult rat retina and dorsal root ganglia, as well as, at a significantly lower level, in the superior colliculus, hippocampus, brain stem, thalamus, postnatal day 8 (P8) superior colliculus and P8 hippocampus. Expression pattern of rho3 mRNA was clearly different from that of rho1 and rho2, being strongest in the hippocampus, and significantly lower in the retina, dorsal root ganglia and cortex. No rho3 expression was observed in adult or P8 superior colliculus or in P8 hippocampus. The present results clearly demonstrate that expression of GABA receptor rho subunits is not restricted to the retina, but significant expression can also be detected in many other brain regions, especially in those belonging to the visual pathways. The expression pattern of the rho subunits may be helpful in solving the functional significance of the receptors formed from these subunits.

Regulated stimulation of epithelial cell DNA synthesis by fibroblast-derived mediators

Interactions of interstitial fibroblasts with nearby epithelial cells are thought to play a role in lung growth and development. The present studies support this premise. Medium conditioned by second-passage lung fibroblasts (FCM) stimulated both DNA synthesis and accumulation in low-density (2 x 10(4)/cm2) cultures of type II alveolar epithelial cells. FCM effects did not require serum; they were time- and dose dependent, with half-maximal FCM activity at 1:8 dilution. A maximal response to FCM required 30 h of exposure. FCM activity was reduced in medium from fibroblasts treated with dexamethasone, suggesting physiological regulation. Type II cells subjected to cyclic mechanical stress demonstrated an increased response to FCM compared with static cultures. FCM activity did not appear to be accounted for by hepatocyte growth factor, keratinocyte growth factor, acidic fibroblast growth factor, or fibronectin. These results suggest that early passage lung fibroblasts release, by regulated pathways, one or more factors that stimulate DNA synthesis by type II cells. Sensitivity to FCM appears to be elevated in type II cell cultures subjected to cyclic mechanical stress.

E1A-induced immortalization of rat type II alveolar epithelial cells

Using a retroviral vector expressing the adenoviral 12S E1A gene product the authors have immortalized rat type II alveolar epithelial cells. For a period of time, the immortalized cells retain many of the ultrastructural characteristics of type II cells in situ, including the presence of lamellar bodies. By 250 days in culture, however, neither lamellar bodies, SP-A, nor a phospholipid profile characteristic of surfactant were present. The cell bind the lectin Maclura pomifera and stably express cytokeratins and the E1A gene product. The cell line also has a diploid karyotype, exhibits contact inhibition of growth, and does not grow in soft agar. E1A-immortalized cell lines should prove useful as models for study of certain aspects of type II alveolar epithelial cell function.

The rho 1 GABA receptor cloned from rat retina is down-modulated by protons

We have cloned and sequenced the full-length cDNA of the rat GABA (gamma-aminobutyric acid) rho 1 receptor subunit. The deduced amino acid sequence (474 amino acids) of the rat rho 1 receptor is 95% homologous to the previously cloned human rho 1 receptor. The rho 1 cDNA includes a 5' 129 bp and a 3' 2.6 kb untranslated region, which contains a sequence homologous to the human medium reiteration frequency repetitive sequence, MER18. The rat rho 1 receptor shows 45-50% similarity to the GABAA receptor beta subunits. This similarity is among the highest between all GABAA receptor subunit classes, giving no support at the molecular level to the classification of the rho subunits to a novel GABAC receptor class. The rat rho 1 cDNA formed functional GABA receptors insensitive to bicuculline, but sensitive to blockade by picrotoxin, when transiently expressed in the human embryonic kidney cell line HEK 293. We studied the sensitivity of the rho 1-mediated GABA current to variations in extracellular pH (pH0), and found that these receptors are strongly down-modulated by H+ ions. A decrease in pH0 from 7.4 to 6.4 decreased the GABA current by 51 +/- 8%, whereas an increase in pH0 from 7.4 to 8.4 increased the current by 77 +/- 8%. In view of the up-regulatory effect of protons on the GABA current observed in a number of preparations, the rho 1 receptors may contain a novel down-regulatory binding site for protons characteristic to these receptors.

Proton modulation of functionally distinct GABAA receptors in acutely isolated pyramidal neurons of rat hippocampus

We have studied the effect of extracellular pH (pHo) on the GABAA receptor-mediated chloride conductance in acutely isolated pyramidal neurons from area CA1 of the rat hippocampus under whole-cell voltage clamp in bicarbonate-free solutions. The conductance evoked by saturating or near-saturating concentrations (200-1000 microM) of GABA showed a marked sensitivity to variations of pHo around 7.4. A decrease in pHo between 8.4 and 6.4 increased the GABAA receptor-mediated chloride conductance by about two-fold per pH unit. In contrast, when evoked by a low agonist concentration (1-10 microM) the conductance showed an equally marked decrease upon a decrease in pHo. The half-time for desensitization of the conductance induced by 500 microM GABA was around 900 ms at pHo 6.4 and 7.4, but decreased to 650 ms at pHo 8.4. A fall in pHo decreased the amount of desensitization of the conductance evoked by a 5 s application of 5 microM, but not of 500 microM, GABA. The concentration-response relationship of the GABA-induced conductance showed a local plateau between 50 and 100 microM of GABA, which was particularly evident at high pHo. Assuming two receptor populations with a high and a low affinity for GABA, the effect of H+ on the GABAA receptors could be explained as an increase in the EC50 of the high affinity receptor, and an apparently non-competitive potentiation of both the high and the low affinity receptors. The GABAA receptor-mediated conductance was markedly inhibited by 20-50 microM Zn2+. In addition, Zn2+ reverted the down-modulation by H+ observed at low GABA concentrations to up-modulation. Diazepam (1-10 microM) had only a marginal effect on the GABA-gated conductance. Taken together, the results suggest the coexistence in individual hippocampal neurons of two distinct GABAA receptor populations having differential sensitivities to H+. In the light of the inhibitory action of Zn2+ and the virtual absence of an effect of diazepam it is probable that a significant fraction of the GABAA receptors lack the gamma 2 subunit. The observation that an elevated pH has a strong suppressing effect on the conductance evoked by high concentrations of GABA may at least partly explain why an extracellular alkalosis leads to neuronal hyperexcitability.

Sphingosine derivatives inhibit depolarization-evoked calcium entry in rat GH4C1 cells

Several investigations have suggested that sphingosine (SP) derivatives are potent inhibitors of protein kinase C. In GH4C1 cells, protein kinase C is a potent modulator of voltage-operated calcium channels (VOCCs). The aim of the present study was to investigate whether SP derivatives could modify calcium entry via VOCCs. Using fura-2-loaded cells and 45Ca2+ flux studies, we show that several SPs potently and rapidly inhibit depolarization-evoked calcium entry in a dose-dependent manner. The effect was not due to an enhanced efflux of calcium from the cells, as the depolarization-evoked entry of Ba2+ was inhibited by the SPs. A similar inhibition was observed with 1,2-dioctanoylglycerol, an activator of sphingomyelinase in GH3 cells. Phorbol myristate acetate and 1-oleyl-2-acetylglycerol had only a modest inhibitory effect. Furthermore, whole cell patch-clamp experiments showed that sphingosinephosphorylcholine (SPC) potently attenuated calcium entry via VOCCs. In experiments using cells grown on coverslips, we found that the inhibitory effect of SPC on calcium entry was reversible. The addition of sphingomyelinase or hexanoyl ceramide, a cell-permeable ceramide, only modestly inhibited the depolarization-evoked entry of calcium, whereas arachidonic acid and phosphatidic acid had no effect. The SP metabolite sphingosine-1-phosphate had no effect on the entry of calcium. The results suggest that the effects of the SPs were probably not the result of a conversion to ceramide or of the production of other lipid second messengers. In cells with down-regulated protein kinase C, SPC, SP, and 1,2-dioctanoylglycerol inhibited depolarization-evoked calcium entry, suggesting that the inhibition was independent of an action mediated via protein kinase C. The SPs per se did not induce any changes in intracellular free calcium, and they did not inhibit the TRH-evoked release of sequestered calcium in the cells. However, TRH-evoked calcium entry was inhibited. The results suggest that SPs are potential regulators of calcium entry mediated by VOCCs in GH4C1 cells.

The role of bicarbonate in GABAA receptor-mediated IPSPs of rat neocortical neurones

1. The ionic mechanism underlying the fast, GABAA receptor-mediated inhibitory postsynaptic potential (IPSPA) was examined in rat neocortical neurones using intracellular recording techniques. Synaptic responses were evoked by orthodromic stimulation applied to the subcortical white matter or to the pial surface. All experiments were carried out at a constant extracellular Cl- concentration. 2. The resting membrane potential was -76.2 +/- 1.0 mV (mean +/- S.E.M., n = 32) and in most cells IPSPA was depolarizing. The reversal potential of IPSPA (EIPSP-A) was -70.2 +/- 0.9 mV (n = 32) and that of a more slowly developing hyperpolarizing response (IPSPB) was -91.4 +/- 1.3 mV (n = 28). 3. An examination of the temporal relationships between excitatory postsynaptic potentials (EPSPs) and IPSPAs in different cells suggested that, despite partial overlap of these responses, EPSPs had little influence on the measured values of EIPSP-A. 4. Application of 20 mM trimethylamine (TriMA), a membrane-permeant weak base which is expected to produce a rise in pHi (and hence in intracellular HCO3-), induced a reversible positive shift in EIPSP-A of up to +9.0 mV (mean + 4.2 mV) at an extracellular pH (pHo) of 7.4. In some experiments, the shift in reversal potential was associated with a change in the polarity of IPSPA from hyperpolarizing to depolarizing. 5. Application of 20 mM lactate (a membrane-permeant weak acid which is expected to produce a fall in pHi and hence in intracellular HCO3-) at pHo 7.0 produced a hyperpolarizing shift in EIPS-A of up to -7.5 mV (mean -5.6 mV). In some experiments, exposure to lactate changed the polarity of IPSPA from depolarizing to hyperpolarizing. 6. Changes in pHo from 7.4 to 7.0 reduced the effect of TriMA and augmented that of lactate on EIPSP-A, as could be expected on the basis of the pHo-dependent change in the fraction of membrane permeable non-charged weak base or acid. 7. Under control conditions, a change in pHo from 7.4 to 7.0 produced a slight positive shift (< +2 mV) in EIPSP-A. In the presence of TriMA, a similar change in pHo gave rise to a negative shift (-1.8 to -2.7 mV). 8. The results obtained indicate that HCO3- ions contribute significantly to the IPSPA, thereby making EIPSP-A more positive than the Cl- equilibrium potential.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of extracellular and intracellular pH on GABA-gated chloride conductance in crayfish muscle fibres

The effect of intracellular and extracellular pH on GABA-gated Cl- conductance was studied using H(+)-selective microelectrodes and a three-microelectrode voltage clamp in crayfish leg opener muscle fibres in bicarbonate-free solutions. Experimental variation of intracellular pH in the range 6.4-8.0 did not affect the GABA-gated conductance. In contrast to this, the GABA-gated conductance was sensitive to changes in external pH. Raising the external pH from 7.4 to 8.4 decreased the GABA-gated peak conductance observed immediately following application of GABA by 30%, and a change from 7.4 to 6.4 produced an increase of 26%. The effect of extracellular pH on the GABA-gated peak conductance was approximately linear in the pH range 6.4-8.9. A slight decrease in the slope of the pH-conductance relationship was evident in the pH range 5.4-6.4. The desensitization of the GABA-gated conductance was also affected by external pH. At pH 6.9 the conductance produced by 1 mM GABA showed a desensitization of about 15%, and at pH 8.9 this value was 34%. Raising the external pH in the presence of GABA decreased the GABA-gated peak conductance and increased the fractional desensitization, while lowering the external pH produced opposite effects, and was capable of repriming the conductance from a desensitized state to the non-desensitized state. The above results show that the GABA-gated conductance is sensitive to changes in external pH in the physiological range, and suggest that pH-dependent changes in the postsynaptic efficacy of GABA-mediated inhibition may contribute to H+ modulation of neuronal excitability.

GABA-gated anion channels in intact crayfish opener muscle fibres and stretch-receptor neurons are neither activated nor desensitized by glutamate

The influence of glutamate on the GABA-activated Cl- conductance was studied in the slowly adapting stretch-receptor neuron and dactylopodite opener muscle fibre of the crayfish (Astacus astacus) using a two-microelectrode and a three-microelectrode voltage clamp, respectively. Glutamate (0.5-1.0 mM) had no effect on the GABA-activated conductance in either preparation. This indicates that the availability of the inhibitory channels for activation of GABA is not influenced by glutamate. The present results are in sharp contrast to those obtained by Franke et al. (J Comp Physiol A 159:591-609, 1986) in experiments on excised membrane patches, which suggested that glutamate is capable of both activating and desensitizing inhibitory postsynaptic channels in the crayfish opener muscle fibre.

Inward current caused by sodium-dependent uptake of GABA in the crayfish stretch receptor neurone

A two-microelectrode current-voltage clamp and Cl(-)-selective microelectrodes were used to examine the effects of gamma-aminobutyric acid (GABA) on membrane potential, current and intracellular Cl- activity (aiCl) in the crayfish stretch receptor neurone. All experimental solutions were CO2-HCO3- free. 2. GABA (500 microM) produced a mono- or biphasic depolarization (amplitude < or = 10 mV), often with a prominent initial depolarizing component followed by a transient shift to a more negative level. In some neurones, an additional depolarizing phase was seen upon washout of GABA. Receptor desensitization, being absent, played no role in the multiphasic actions of GABA. 3. The pronounced increase in membrane conductance evoked by GABA (500 microM) was associated with an increase in aiCl which indicates that the depolarizing action was not due to a current carried by Cl- ions. 4. The currents activated by GABA under voltage clamp conditions were inwardly directed when recorded at the level of the resting membrane potential, and they often revealed a biphasic character. The reversal potential of peak currents activated by pulses of 500 microM-GABA (EGABA) was 9-12 mV more positive than the reversal potential of the simultaneously measured net Cl- flux (ECl). ECl was 2-7 mV more negative than the resting membrane potential. 5. EGABA (measured using pulses of 500 microM-GABA) was about 10 mV more positive than the reversal potential of the current activated by 500 microM-muscimol, a GABA agonist that is a poor substrate of the Na(+)-dependent GABA uptake system. 6. In the absence of Na+, the depolarization and inward current caused by 500 microM-GABA were converted to a hyperpolarization and to an outward current. Muscimol produced an immediate outward current both in the presence and absence of Na+. 7. Following block of the inhibitory channels by picrotoxin (100-200 microM), the depolarizing effect of 500 microM-GABA was enhanced and the transient hyperpolarizing shifts were abolished. 8. In the presence of picrotoxin, GABA (> or = 2 microM) produced a concentration-dependent monophasic inward current which had a reversal potential of +30 to +60 mV. This current was inhibited in the absence of Na+ and by the GABA uptake blocker, nipecotic acid. Unlike the channel-mediated current, the picrotoxin-insensitive current was activated without delay also at low (2-10 microM) concentrations of GABA.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of gamma-aminobutyric acid on intracellular pH in the crayfish stretch-receptor neurone

The effect of gamma-aminobutyric acid (GABA) on intracellular pH (pHi) was examined in the crayfish stretch-receptor neurone using H(+)-selective microelectrodes and a two-microelectrode voltage clamp. In the presence of 30 mmol l-1 HCO3- (pH 7.4), application of GABA (0.5 mmol l-1) produced a mean fall in pHi of 0.26 units. The initial rate of fall of pHi was attributable to a net influx of acid equivalents of 6.3 mmol l-1 min-1. In the nominal absence of HCO3-, GABA had little effect on pHi. The HCO3(−)-dependent acidosis caused by GABA was inhibited by picrotoxin (0.1 mmol l-1) but not by depletion of extracellular and intracellular Cl-. Acetazolamide (0.1 mmol l-1) decreased the rate of fall of pHi caused by a step increase in CO2 partial pressure as well as by GABA, which indicates that the neurone contains carbonic anhydrase. In the presence of both Cl- and HCO3-, the reversal potential of the GABA-activated current was more positive than under nominally HCO3(−)-free conditions. In line with this, GABA induced a marked HCO3(−)-dependent depolarization, and this depolarizing action was enhanced in the absence of Cl- so as to lead to triggering of action potentials. All these observations support the conclusion that the GABA-induced fall in pHi is due to a net efflux of HCO3- through the inhibitory anion channels.

Postsynaptic fall in intracellular pH and increase in surface pH caused by efflux of formate and acetate anions through GABA-gated channels in crayfish muscle fibres

H(+)-selective microelectrodes and a two- or three-microelectrode voltage clamp were used to examine the influence of weak-acid, carboxylate anions on the actions of GABA on postsynaptic intracellular pH, surface pH and on membrane potential in fibres of the crayfish leg opener muscle. Substitution of 30 mM Cl- by formate or acetate promoted a GABA-induced decrease in intracellular pH, which was coupled to an increase in surface pH and to a depolarization. Such effects were not seen in the presence of an equivalent amount of lactate, methanesulphonate or glucuronate. Both the GABA-induced depolarization and the fall in internal pH promoted by formate and acetate were blocked by picrotoxin, and the fall in pH was reversibly inhibited by a K(+)-induced depolarization. The rate of the fall in intracellular pH produced by GABA (0.2 mM) was about 0.02 pH units/min in the presence of formate and 0.03 pH units/min in the presence of acetate. Under steady-state conditions, both 30 mM formate and acetate (but not lactate) induced a positive shift in the reversal potential of GABA-activated current, which was accounted for by a relative permeability vs Cl- of formate and acetate of 0.5 and 0.15, respectively. The conductance sequence of the anions was identical to the permeability sequence, i.e. Cl- greater than formate greater than acetate greater than lactate approximately equal to 0. This sequence is strictly correlated to the Stokes diameter of the anions. The relative permeabilities of the anions indicate that the effective diameter of the GABA-gated channel is about 0.5 nm. The fact that the GABA-induced acidosis was slower in the presence of formate than in the presence of acetate suggests that, in the former case, the rate-limiting step in the fall in internal pH is the entry of non-dissociated formic acid. All the above results are consistent with a scheme where GABA induces a channel-mediated efflux of permeant weak-acid anions, which gives rise to an inward (depolarizing) current and to an intracellular acidosis. A comparison of the permeability properties of crayfish and vertebrate GABA-gated channels suggests that effects similar to those seen in this work are likely to occur in mammalian and other vertebrate neurons in the presence of permeant weak-acid anions.

Influence of GABA-gated bicarbonate conductance on potential, current and intracellular chloride in crayfish muscle fibres

1. The effects of gamma-aminobutyric acid (GABA) on membrane potential and conductance as well as on the intracellular Cl- activity (aiCl) and intracellular pH (pHi) were studied in crayfish muscle fibres using a three-microelectrode voltage clamp and ion-selective microelectrodes. In the presence of CO2-HCO3-, the intracellular HCO3- activity (aiHCO3) was estimated from pHi. 2. In a nominally HCO3(-)-free solution, a near-saturating concentration of GABA (0.2 mM) produced a marked increase in membrane conductance but little change in potential. In a solution containing 30 mM-HCO3- (equilibrated with 5% CO2 + 95% air; pH 7.4), the GABA-induced increase in conductance was associated with a depolarization of about 15 mV, with an increase in aiCl and with a decrease in aiHCO3. All these effects were blocked by picrotoxin (PTX). The depolarizing action of GABA was augmented following depletion of extracellular and intracellular Cl-. 3. The GABA-induced increase in aiCl which took place in the presence of HCO3- was blocked by clamping the membrane potential at its resting level. This indicates that the increase in aiCl was due to passive redistribution of Cl-. In both the presence and absence of HCO3-, the GABA-activated transmembrane flux of Cl- showed reversal at the level of the resting potential, which indicates that under steady-state conditions the Cl- equilibrium potential (ECl) is identical to the resting potential. 4. In a Cl(-)-free, 30 mM-HCO3(-)-containing solution, 0.5 mM-GABA produced a PTX-sensitive increase in conductance which amounted to 15% of the conductance activated in the presence of Cl-. In the absence of both Cl- and HCO3-, the respective figure was 2.8%. Assuming constant-field conditions, the conductance data yielded a permeability ratio PHCO3/PCl of 0.42 for the GABA-activated channels. 5. In a Cl(-)-containing, HCO3(-)-free solution, the reversal potential of the GABA-activated current (EGABA) was, by about 1 mV, less negative than the resting membrane potential (RP). In a solution containing Cl- and 30 mM-HCO3-, EGABA-RP was 12 mV. Simultaneous measurements of EGABA, aiCl and aiHCO3 (pHi) gave a PHCO3/PCl value of 0.33. 6. In a Cl(-)-free, HCO3(-)-containing solution EGABA was close to the HCO3- equilibrium potential (EHCO3) and an experimental acidosis which produced a negative shift in EHCO3 was associated with a similar shift in EGABA.(ABSTRACT TRUNCATED AT 400 WORDS)

The in vivo and in vitro effects of interleukin-1 and tumor necrosis factor on murine cytomegalovirus infection

The effects of tumor necrosis factor (TNF) and interleukin-1 (IL-1) on infection with murine cytomegalovirus (MCMV) were investigated in vitro and in vivo. The addition of each of these cytokines (at 1 ng/ml) to tissue culture monolayers 24 hr prior to MCMV challenge produced a reproducible decrease in vital titer (from 1 x 10(8) pfu to approximately 4 x 10(6) pfu for both cytokines). There was no further increase in this effect when a 10 or 100 ng/ml of each of these cytokines was employed. Despite these in vitro effects, the pretreatment of suckling, weanling, or adult mice with 80 or 400 ng of TNF or IL-1 alone, or 80 ng of each cytokine together, had no effect on the survival of mice following MCMV. Similarly, neither of these cytokines adversely influenced the protective effects of hyperimmune anti-MCMV antiserum; that is, they did not attenuate the protection conferred by the antiserum nor affect the protective effects of subtherapeutic doses of the antiserum. We conclude that despite promising antiviral effects against MCMV in vitro, these agents do not result in a useful therapeutic effect in vivo. Moreover, despite the ability of IL-1 to induce ACTH and corticosterone in mice, IL-1 treatment did not increase the mortality to CMV.