Functional modifications of acid-sensing ion channels by ligand-gated chloride channels

Together, acid-sensing ion channels (ASICs) and epithelial sodium channels (ENaC) constitute the majority of voltage-independent sodium channels in mammals. ENaC is regulated by a chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR). Here we show that ASICs were reversibly inhibited by activation of GABA(A) receptors in murine hippocampal neurons. This inhibition of ASICs required opening of the chloride channels but occurred with both outward and inward GABA(A) receptor-mediated currents. Moreover, activation of the GABA(A) receptors modified the pharmacological features and kinetic properties of the ASIC currents, including the time course of activation, desensitization and deactivation. Modification of ASICs by open GABA(A) receptors was also observed in both nucleated patches and outside-out patches excised from hippocampal neurons. Interestingly, ASICs and GABA(A) receptors interacted to regulate synaptic plasticity in CA1 hippocampal slices. The activation of glycine receptors, which are similar to GABA(A) receptors, also modified ASICs in spinal neurons. We conclude that GABA(A) receptors and glycine receptors modify ASICs in neurons through mechanisms that require the opening of chloride channels.     

THIORIDAZINE (MELLARIL?) IN PSYCHIATRIC PATIENTS

Thioridazine (Mellaril®) was given to 104 psychiatric patients with a variety of illnesses, chiefly schizophrenic reactions. Of 14 patients treated in a double-blind study with successive one-month courses of drug or placebo, nine improved most on the drug and only one on placebo. These results, although limited, confirm a definite therapeutic action for this compound.Nine of 24 patients were significantly improved after treatment with thioridazine for an average of four months following previous treatwith other phenothiazine tranquilizers. Of ten patients treated intensively with thioridazine after they had not responded to other phenothiazine drugs, two were definitely improved and three were slightly improved. Twenty-eight of 56 patients treated from the outset with thioridazine were significantly improved after an average of six months. Most patients received from 100 to 400 mg. daily. These results were comparable to those obtained from other potent phenothiazine tranquilizers. The drug is particularly advantageous for a group of schizophrenic patients who are sometimes made worse by other phenothiazine derivatives or rauwolfia alkaloids. It should also be suitable for treating patients with psychoneuroses and chronic brain syndromes.Only minimal side reactions were observed, chiefly drowsiness, dizziness and nasal stuffiness. Weight gain occurred frequently during treatment.     

Isolation and characterization of rat cDNA clones for two distinct thyroid hormone receptors

Two distinct v-erbA-related cDNA clones representing the products of different genes were isolated from a rat liver cDNA library. The first, rc-erbA-alpha, was 82% identical to v-erbA and encoded a polypeptide with a calculated molecular mass of 45,000 daltons. This cDNA clone arises from the same gene product as a v-erbA-related cDNA isolated from rat brain by Thompson et al. (Thompson, C. C., Weinberger, C., Lebo, R., and Evans, R. (1987) Science 237, 1610-1614). The second cDNA clone, rc-erbA-beta, was 76% identical to v-erbA and encoded a polypeptide with a calculated molecular mass of 52,000 daltons. Both rc-erbA-alpha and rc-erbA-beta translational products bound 3,5,3'-triiodo-L-thyronine with affinities equal to each other (Kd approximately equal to 0.4 nM) and comparable to the nuclear thyroid hormone receptor extracted from rat liver. The relative affinities of a series of thyroid hormone analogs for both translational products were also identical. In various tissues and cell lines, the relative levels of rc-erbA-beta RNA, but not rc-erbA-alpha RNA, correlated with measurements of nuclear 3,5,3'-triiodo-L-thyronine binding sites. Based on this correlation, we suggest that rc-erbA-beta may encode the "classical" nuclear thyroid hormone receptor, whereas rc-erbA-alpha may encode an isoreceptor species with differing functional properties.     

Delayed-onset synergism between leukotriene B4 and prostaglandin E2 in human skin

The time-course of cutaneous inflammatory responses to LTB4 and PGE2 both alone and in combination has been studied in 10 healthy volunteers. LTB4 induced a transient wheal and flare response in some subjects, maximal at 15 minutes and succeeded by an erythematous, indurated lesion at 2-4 hours. PGE2 elicited a wheal and erythema response which resolved within 1-2 hours. Combination of LTB4 and PGE2 produced acute wheal and erythema responses which did not differ significantly from the summation of responses to the individual constituents of the mixture or from responses to a two-fold increase in the concentration of either component. Wheal and erythema responses persisted, however, with significant potentiation of responses 4 hours after injection. As both leukotrienes and prostaglandins are generated in acute allergic reactions, the effects of these mediators in combination could contribute to persisting and late-onset responses to allergen, in both the skin and lung. In particular, sustained responses to the combination of LTB4 and PGE2 might be important in the pathogenesis of inflammatory skin diseases such as psoriasis.     

A recombination event that redefines the Huntington disease region

We report both a recombination event that places the Huntington disease gene proximal to the marker D4S98 and an extended linkage-disequilibrium study that uses this marker and confirms the existence of disequilibrium between it and the HD locus. We also report the cloning of other sequences in the region around D4S98, including a new polymorphic marker R10 and conserved sequences that identify a gene in the region of interest.     

Social laughter is correlated with an elevated pain threshold

Although laughter forms an important part of human non-verbal communication, it has received rather less attention than it deserves in both the experimental and the observational literatures. Relaxed social (Duchenne) laughter is associated with feelings of wellbeing and heightened affect, a proximate explanation for which might be the release of endorphins. We tested this hypothesis in a series of six experimental studies in both the laboratory (watching videos) and naturalistic contexts (watching stage performances), using change in pain threshold as an assay for endorphin release. The results show that pain thresholds are significantly higher after laughter than in the control condition. This pain-tolerance effect is due to laughter itself and not simply due to a change in positive affect. We suggest that laughter, through an endorphin-mediated opiate effect, may play a crucial role in social bonding.     

Recruitment of doctors to non-standard grades in the NHS: analysis of job advertisements and survey of advertisers

Objectives To estimate the proportion of advertised non-consultant hospital posts that do not conform to nationally recognised terms and conditions of service and to investigate why these posts exist, who fills them, and what the doctors in such jobs do.Design Analysis of job advertisements and a cross sectional survey of advertisers.Setting Job advertisements in one of the leading UK publications listing hospital doctor vacancies (BMJ Careers).Results Nearly a quarter of non-consultant posts advertised in the two study periods (23% and 21%) were for non-standard grade posts. A questionnaire was sent to the medical staffing officer for each post. Of 430 questionnaires sent out 192 (45%) were returned. 98 trusts said they advertised non-standard grades because there was no more funding from the deanery for approved posts and 75 because service needs could not be met by doctors in training grades. In 132 posts (69%) the post holder would be required to do on-call work, and 50 advertisers (26%) required on-call duty for 1 in 5 or more frequently, which would conflict with the European Working Time Directive. 131 advertisers (68%) expected the posts to be filled by doctors from outside the European Economic Area.Conclusions Non-standard grade posts are mostly being created to meet service requirements when there is no more funding for standard training posts and are expected to be filled by doctors from overseas. Doctors in such posts can be more easily exploited and their careers hindered. The Department of Health''s annual census should include non-standard grade doctors.     

Methanol Emission from Leaves (Enzymatic Detection of Gas-Phase Methanol and Relation of Methanol Fluxes to Stomatal Conductance and Leaf Development)

We recently reported the detection of methanol emissions from leaves (R. MacDonald, R. Fall [1993] Atmos Environ 27A: 1709-1713). This could represent a substantial flux of methanol to the atmosphere. Leaf methanol production and emission have not been investigated in detail, in part because of difficulties in sampling and analyzing methanol. In this study we used an enzymatic method to convert methanol to a fluorescent product and verified that leaves from several species emit methanol. Methanol was emitted almost exclusively from the abaxial surfaces of hypostomatous leaves but from both surfaces of amphistomatous leaves, suggesting that methanol exits leaves via stomates. The role of stomatal conductance was verified in experiments in which stomates were induced to close, resulting in reduced methanol. Free methanol was detected in bean leaf extracts, ranging from 26.8 [mu]g g-1 fresh weight in young leaves to 10.0 [mu]g g-1 fresh weight in older leaves. Methanol emission was related to leaf development, generally declining with increasing leaf age after leaf expansion; this is consistent with volatilization from a cellular pool that declines in older leaves. It is possible that leaf emission could be a major source of methanol found in the atmosphere of forests.     

Intramuscular temperatures during exercise in the heat following pre-cooling and pre-heating

Pre-cooling improves heat tolerance and time to exhaustion in the heat. We tested the possibility that reduced tissue temperatures may explain this phenomenon, using three whole-body treatments: pre-cooling, thermoneutral (control) and pre-heating. Pre-cooling reduced muscle temperature (T_m) by 6.3 °C while pre-heating increased T_m 3.4 °C, relative to control. Despite this offset, T_m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond 40 min. Following pre-cooling, exercising oesophageal temperature (T_es) initially increased at 0.09 °C min⁻¹, being significantly faster than control (0.05 °C min⁻¹) and pre-heated conditions (0.03 °C min⁻¹). Pre-cooling lowered the sweat threshold and also resulted in a reduced cardiac frequency across the exercise-heat exposure. Our observations do not support the hypothesis that pre-cooling reduces T_m at the end of an exercise-heat exposure, thereby delaying the development of fatigue.     

Structural characterization of the rat carboxypeptidase A1 and B genes. Comparative analysis of the rat carboxypeptidase gene family

Nucleotide sequencing of a rat carboxypeptidase B (CPB) cDNA and direct sequencing of the CPB mRNA via primer extension on pancreatic polyadenylated RNA has yielded the complete amino acid sequence of rat CPB. The rat enzyme is synthesized as a precursor species containing a large amino-terminal fragment (108 amino acids) that contributes a putative signal sequence and an activation peptide. The mature form of rat CPB is homologous to bovine CPB (77% identity); the amino acids in bovine CPB which have been previously implicated in catalysis or ligand binding are invariant in the rat orthologue. The rat CPB cDNA was used as a probe for the isolation of the rat CPB gene. Detailed characterization of three overlapping rat genomic clones demonstrated that the coding region for the rat CPB precursor is sequestered in 11 exons which are dispersed throughout 34 kilobase pairs of genomic DNA. The nucleotide sequence of a large part of the gene has been determined including that of the exons, the exon/intron boundaries, and the 5' flanking region. We also report the partial nucleotide sequence of the rat CPA1 gene. Comparative analysis of the structural organization of the rat CPB, rat CPA1, and rat CPA2 genes (Gardell, S. J., Craik, C. S., Clauser, E., Goldsmith, E. J., Stewart, C.-B., Graf, M., and Rutter, W. J. (1988) J. Biol. Chem. 263, 17828-17836) reveals that, with one exception, the number, position, and sequence composition of the exons in these three carboxypeptidase genes are conserved in spite of considerable divergence with respect to the lengths of their corresponding intervening sequences. Conserved sequences in the 5' flanking regions of the rat CPA1, CPA2, CPB, and other pancreas-specific genes have been identified.