Maternal heat stress reduces body and organ growth in calves: Relationship to immune status

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In utero heat stress reduces growth relative to calves born to cooled dams.

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Immune organ growth is further compromised beyond whole body growth.

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Jejunal enterocyte apoptosis is accelerated at birth after in utero heat stress.

Late-gestation heat stress of dairy cows reduces fetal growth and influences postnatal performance and immune status of the offspring. Our first objective was to evaluate the effect of in utero heat stress on overall fetal and organ growth, particularly organs associated with immune function. The second objective was to examine the cellular mechanism of altered passive immunity in neonatal bull calves after in utero heat stress. Specifically, we examined the rate of apoptosis of intestinal cells early in life, as it is associated with gut closure. Dams were dried off approximately 45 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT) or cooling (CL). During the dry period all cows were housed under shade in a freestall barn, where the pen for CL cows was equipped with active cooling, including water soakers and fans, whereas the pen for HT cows had no soakers or fans. Using rectal temperature and respiration rate as indicators, heat stress was severe. Average rectal temperature in HT cows was 39.3°C compared with 39.0°C in CL cows, and HT cows had a respiration rate of 66.7 breaths/min compared with 43.2 breaths/min for CL cows. Bull calves (n = 30) were immediately separated from their dams at birth, weighed, and then killed before colostrum feeding (n = 5/treatment; d 0) or at 1 or 2 d of age following colostrum feeding (n = 5/treatment per day). After slaughter, the small intestine was removed and weighed, and samples from the jejunum were fixed for immunohistochemistry. Birth weight of bulls from HT dams was 1.1 kg lower than that of bulls from CL dams. Thymus, spleen, and heart weights of HT bulls were lower relative to those of CL bulls, whereas liver weight of HT bulls tended to be lower relative to that of CL bulls. Jejunal cell apoptosis decreased with age in both HT and CL calves after birth, mirroring gut closure. However, in utero heat stress increased the apoptotic rate in the jejunum, particularly at birth. We conclude that the chronic exposure to heat strain of HT compared with CL dams in late gestation significantly affected fetal growth and immune tissue development, which may be associated with reduced immune function in early life. Also, late-gestation heat stress increased calves' intestinal apoptosis in the first 2 d of life, which might explain the decreased IgG uptake and limited passive immune competence observed in previous studies.

Effect of late-gestation heat stress in nulliparous heifers on postnatal growth, passive transfer of immunoglobulin G, and thermoregulation of their calves

Youngstock such as nulliparous pregnant dairy heifers are not typically considered for active cooling, as they are thought to be more heat tolerant than mature cows. Recently, the benefits of heat stress abatement in pregnant heifers were studied, but the effect of in utero hyperthermia on the calf is still unknown. Herein, we aimed to investigate the effects of late-gestation heat stress in nulliparous heifers on the growth, immune, and thermoregulatory responses of their calves. Pregnant nulliparous dams were randomly selected for either active cooling (CL; fans and soakers; n = 15) or heat stress (HT; n = 16) 60 d before expected calving. After birth, respiration rate, rectal temperature, skin temperature, and sweating rate were obtained from their heifer calves at 24 h and on d 14, 28, 42, and 56. Blood samples and body weights were both collected for measurement of total protein and hematocrit and calculation of average daily gains, respectively. Gestation length was shorter in HT heifers (272 vs. 276 ± 1.28 d) relative to CL heifers. Birth weights, weaning weights, body weights up to d 56, and average daily gain from birth to weaning were not different between in utero HT (IUHT; n = 13) and in utero CL (IUCL; n = 12) calves. Apparent efficiency of absorption of immunoglobulin G tended to be lower in IUHT calves (26.3 vs. 42.7 ± 9.0%), and serum IgG concentrations from birth to d 56 were significantly lower in IUHT calves relative to IUCL calves (22.0 vs. 32.4 ± 4.47 g/L). Postnatal respiration rate, rectal temperature, sweating rate, total protein, and hematocrit were not different between in utero treatments. There was a tendency for IUHT calves to have lower skin temperature at 24 h (34.9 vs. 36.9 ± 1.05°C), and skin temperature tended to be elevated in IUHT calves at d 56 (29.6 vs. 27.9 ± 1.05°C). In summary, the lack of heat stress abatement during late gestation reduces gestation length of nulliparous heifers. Additionally, providing active cooling to nulliparous heifers during the prepartum period confers immune benefits to their offspring, although it does not translate to growth improvements.

When do dry cows get heat stressed? Correlations of rectal temperature, respiration rate, and performance

Previous studies have documented the negative effects of heat stress during the dry period on dairy cow performance during the next lactation, but an easy method to assess heat stress for dry cow management is lacking. In an effort to determine a threshold for heat stress based on the physiological response of respiration rate, an easily measured variable, an analysis including data collected from 6 different studies (n = 144 cows) was performed to summarize the correlations among rectal temperature (RT) and respiration rate (RR) during the dry period, milk production during the first 8 wk of lactation (MK), calf birth weight (CW), body weight at calving (BW), gestation length (GL), and dry matter intake (DMI) pre- and postpartum. Studies were conducted in Florida during the summer, and dry cows were assigned to 2 treatments: heat stress (only shade; HT, n = 75 cows) and cooling (shade, fans, and soakers; CL, n = 69 cows). Average RT (0.3°C) and RR [26 breaths per min (bpm)] of HT cows increased compared with CL. In addition, the CL group produced more milk (2.8 kg/d) during the first 8 wk of the subsequent lactation relative to HT. Correlation analysis indicated that RR of HT was negatively correlated with MK and GL. Within HT, RT was also negatively correlated with MK and GL and tended to be negatively correlated with CW. In addition to being negatively correlated with RT and RR, HT MK was positively correlated with CW, GL, and DMI postpartum. In CL, no correlations were observed for RR, but RT was positively correlated with BW, and MK was positively correlated with DMI postpartum and tended to be positively correlated with GL. Moreover, the overall RT was 39.1 ± 0.48°C and RR was 61 ± 19.5 bpm, which indicates that RR over 61 bpm is an indicator of heat stress in cows during the dry period and can be easily assessed at the cow level. In summary, the more heat load a cow carries in the dry period, the greater the negative effects are on subsequent milk production, which may suggest a threshold for the effects of heat stress. Also, variation among cows within the HT group indicates that cows with longer gestation length have heavier calves, eat more postpartum, and produce more milk, but not as much as CL cows.

P2X7 receptor-Pannexin1 complex: pharmacology and signaling

Pannexin 1 (Panx1), an ortholog to invertebrate innexin gap junctions, has recently been proposed to be the pore induced by P2X(7) receptor (P2X(7)R) activation. We explored the pharmacological action of compounds known to block gap junctions on Panx1 channels activated by the P2X(7)R and the mechanisms involved in the interaction between these two proteins. Whole cell recordings revealed distinct P2X(7)R and Panx1 currents in response to agonists. Activation of Panx1 currents following P2X(7)R stimulation or by membrane depolarization was blocked by Panx1 small-interfering RNA (siRNA) and with mefloquine > carbenoxolone > flufenamic acid. Incubation of cells with KN-62, a P2X(7)R antagonist, prevented current activation by 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP). Membrane permeabilization to dye induced by BzATP was also prevented by Panx1 siRNA and by carbenoxolone and mefloquine. Membrane permeant (TAT-P2X(7)) peptides, provided evidence that the Src homology 3 death domain of the COOH-terminus of the P2X(7)R is involved in the initial steps of the signal transduction events leading to Panx1 activation and that a Src tyrosine kinase is likely involved in this process. Competition assays indicated that 20 microM TAT-P2X(7) peptide caused 50% reduction in Src binding to the P2X(7)R complex. Src tyrosine phosphorylation following BzATP stimulation was reduced by KN-62, TAT-P2X(7) peptide, and by the Src tyrosine inhibitor PP2 and these compounds prevented both large-conductance Panx1 currents and membrane permeabilization. These results together with the lack Panx1 tyrosine phosphorylation in response to P2X(7)R stimulation indicate the involvement of an additional molecule in the tyrosine kinase signal transduction pathway mediating Panx1 activation through the P2X(7)R.

Localization of the pannexin1 protein at postsynaptic sites in the cerebral cortex and hippocampus

Pannexins (Panx) constitute a new family of gap junction type proteins. Functional expression in paired Xenopus oocytes indicated that pannexins are capable of forming communicating junctions but also proved to be active in forming of unopposed hemichannels. In the vertebrate brain pannexins have been found in neurons. However, the subcellular cerebral localization of pannexin proteins which could gain first clues on their putative function is essentially unknown. Here we demonstrate by light and electron microscopical immunohistochemistry that Panx1 reveals postsynaptic localization in rodent hippocampal and cortical principal neurons accumulating at postsynaptic densities. The postsynaptic localization was corroborated by co-localization of Panx1 with postsynaptic density protein 95 (PSD-95), a prominent postsynaptic scaffolding protein, in hippocampal neurons expressing tagged versions of these proteins. The asymmetric synaptic distribution of Panx1 suggests that it may function in neurons as non-junctional channels (pannexons) at postsynaptic sites and comprises a novel component of the postsynaptic protein complex.

Pediatric Oncology Group (POG) studies of acute myeloid leukemia (AML): a review of four consecutive childhood AML trials conducted between 1981 and 2000

From 1981 to 2000, a total of 1823 children with acute myeloid leukemia (AML) enrolled on four consecutive Pediatric Oncology Group (POG) clinical trials. POG 8101 demonstrated that the induction rate associated with the 3+7+7 combination of daunorubicin, Ara-C, and 6-thioguanine (DAT) was greater than that associated with an induction regimen used to treat acute lymphoblastic leukemia (82 vs 61%; P=0.02). Designed as a pilot study to determine the feasibility of administration of noncross-resistant drug pairs and later modified to assess the effect of dose intensification of Ara-C during the second induction course, POG 8498 confirmed the high initial rate of response to DAT (84.2%) and showed that dose intensification of Ara-C during the second induction course resulted in a trend toward higher event-free survival (EFS) estimates than did standard-dose DAT (2+5) during the second induction course (5 year EFS estimates, 22 vs 27%; P=0.33). Age <2 years and leukocyte count <100 000/mm3 emerged as significantly good prognostic factors. The most significant observation made in the POG 8498 study was the markedly superior outcome of children with Down's syndrome who were treated on the high-dose Ara-C regimen. POG 8821 compared the efficacy of autologous bone marrow transplantation (BMT) with that of intensive consolidation chemotherapy. Intent-to-treat analysis revealed similar 5-year EFS estimates for the group that underwent autologous BMT (36+/-4.7%) and for the group that received only intensive chemotherapy (35+/-4.5%) (P=0.25). There was a high rate of treatment-related mortality in the autologous transplantation group. The study demonstrated superior results of allogeneic BMT for patients with histocompatible related donors (5-year EFS estimate 63+/-5.4%) and of children with Down's syndrome (5-year EFS estimate, 66+/-8.6%). The POG 9421 AML study evaluated high-dose Ara-C as part of the first induction course and the use of the multidrug resistance modulator cyclosporine. Preliminary results showed that patients receiving both high-dose Ara-C for remission induction and the MDR modulator for consolidation had a superior outcome (5-year EFS estimate, 42+/-8.2%) than did patients receiving other treatment; however, the difference was not statistically significant. These four studies demonstrate the importance of dose intensification of Ara-C in the treatment of childhood AML; cytogenetics as the single most prognostic factor and the unique curability of AML in children with Down's syndrome.

Phase I trial of intrathecal liposomal cytarabine in children with neoplastic meningitis

PURPOSE

We performed a phase I trial of intrathecal (IT) liposomal cytarabine (DepoCyt; Enzon Pharmaceuticals, Piscataway, NJ and SkyePharma Inc, San Diego, CA) to determine the maximum-tolerated dose, the dose-limiting toxicities, and the plasma and CSF pharmacokinetics of IT lipsomal cytarabine in children >/= 3 years of age with advanced meningeal malignancies.

PATIENTS AND METHODS

Eighteen assessable patients received IT liposomal cytarabine through either an indwelling ventricular access device or via lumbar puncture. Liposomal cytarabine was given once every 2 weeks during induction, once every 4 weeks during consolidation, and once every 8 weeks during the maintenance phase of treatment. The initial dose was 25 mg, with subsequent escalations to 35 and 50 mg. CSF pharmacokinetic samples were obtained in a subset of patients.

RESULTS

Arachnoiditis, characterized by fever, headache, nausea, vomiting, and back pain was noted in the first two patients at the 25 mg dose level. Therefore, subsequent patients were treated with dexamethasone, beginning the day of liposomal cytarabine administration and continuing for 5 days. Headache (grade 3) was dose limiting in two of eight patients enrolled at the 50 mg dose level. Eight of the 14 patients assessable for response demonstrated evidence of benefit manifest as prolonged disease stabilization or response.

CONCLUSION

The maximum-tolerated dose and recommended phase II dose of liposomal cytarabine in patients between the ages of 3 and 21 years is 35 mg, administered with dexamethasone (0.15 mg/kg/dose, twice a day for 5 days). A phase II trial of IT liposomal cytarabine in children with CNS leukemia in second or higher relapse is in development.

Practice parameter: evaluation of children and adolescents with recurrent headaches: report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society

OBJECTIVE

The Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society develop practice parameters as strategies for patient management based on analysis of evidence. For this parameter, the authors reviewed available evidence on the evaluation of the child with recurrent headaches and made recommendations based on this evidence.

METHODS

Relevant literature was reviewed, abstracted, and classified. Recommendations were based on a four-tiered scheme of evidence classification.

RESULTS

There is inadequate documentation in the literature to support any recommendation as to the appropriateness of routine laboratory studies or performance of lumbar puncture. EEG is not recommended in the routine evaluation, as it is unlikely to define or determine an etiology or distinguish migraine from other types of headaches. In those children undergoing evaluation for recurrent headache found to have a paroxysmal EEG, the risk for future seizures is negligible; therefore, further investigation for epilepsy or treatments aimed at preventing future seizures is not indicated. Obtaining a neuroimaging study on a routine basis is not indicated in children with recurrent headaches and a normal neurologic examination. Neuroimaging should be considered in children with an abnormal neurologic examination or other physical findings that suggest CNS disease. Variables that predicted the presence of a space-occupying lesion included 1) headache of less than 1-month duration; 2) absence of family history of migraine; 3) abnormal neurologic findings on examination; 4) gait abnormalities; and 5) occurrence of seizures.

CONCLUSIONS

Recurrent headaches occur commonly in children and are diagnosed on a clinical basis rather than by any testing. The routine use of any diagnostic studies is not indicated when the clinical history has no associated risk factors and the child's examination is normal.

Modified cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone therapy for posttransplantation lymphoproliferative disease in pediatric patients undergoing solid organ transplantation

PURPOSE

The authors report the use of a cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone (CHOP)-based chemotherapy regimen in treating six children with posttransplantation lymphoproliferative disorder (PTLD) that developed after solid organ transplantation.

MATERIALS AND METHODS

The chemotherapy regimen consisted of a 29-day induction with CHOP and then as many as 15 cycles of maintenance therapy using methotrexate and cytarabine alternating with vincristine, adriamycin, mercaptopurine, and prednisone.

RESULTS

All patients attained remission. One patient died of sepsis while in remission. Four of the five remaining patients have been followed-up in remission for as long as 8 years without losing the graft. One of the patients experienced relapse after completing therapy and subsequently died with disease.

CONCLUSIONS

The authors conclude that pediatric patients with PTLD after solid organ transplantation that fails conservative management can be treated successfully with CHOP-based chemotherapy.

Relaxation of myometrium by calcitonin gene-related peptide is independent of nitric oxide synthase activity in mouse uterus

Calcitonin gene-related peptide (CGRP) inhibits myometrial contractile activity. However, the responsiveness of the mouse myometrium to CGRP is dependent on the hormonal and gestational stage. The inhibitory effect of CGRP in the myometrium is prominent during gestation and declines at parturition. The present study was undertaken to examine if nitric oxide (NO) production by nitric oxide synthase (NOS) isoforms mediates the inhibitory action of CGRP on uterine contractions as has been suggested earlier. Transgenic mice deficient in either of the three major NOS isoforms: endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) were used. Isometric force measurements on myometrial strips obtained from NOS-deficient mice were carried out and the inhibitory capacity of CGRP was monitored. CGRP inhibited KCl-induced contractions of the myometrial strips obtained from eNOS(-/-), iNOS(-/-), and nNOS(-/-) mice with equal efficiency as in wild-type animals. Additionally, NOS protein expression in the mouse uterus during gestation and during the estrous cycle was examined by means of Western immunoblot analysis. No correlation between NOS expression and inhibitory activity of CGRP was evident. The results suggest that the inhibitory action of CGRP in the mouse uterus is independent of the activity of these NOS isoforms.

Sensitivity of myometrium to CGRP varies during mouse estrous cycle and in response to progesterone

Calcitonin gene-related peptide (CGRP) inhibits contractions of the myometrium. Isometric force measurements on myometrial strips were carried out to monitor the inhibitory capacity of CGRP in the myometrium during the estrous cycle and in response to estrogen and progesterone in ovariectomized mice. CGRP inhibition of KCl-induced contractions was lowest at estrus and significantly increased during metestrus and diestrus. Progesterone treatment of ovariectomized mice resulted in a significant increase in the responsiveness of the myometrium to CGRP. Expression of CGRP-receptor component protein (CGRP-RCP), a marker of CGRP-receptor expression, was quantitated by Western and Northern blot analyses. The levels of inhibition exerted by CGRP during the various stages of the estrous cycle and in response to steroid hormone treatment correlated with the protein levels of CGRP-RCP. The mRNA levels did not change significantly during the estrous cycle or in response to hormone treatment, indicating that the regulation of CGRP-RCP protein does not occur at the transcriptional level. CGRP had an inhibitory effect both when applied before the stimulus for contraction and when applied during a sustained contracture induced by KCl. This suggests that CGRP-induced generation of second messengers can influence late events in electro-/chemomechanical coupling and/or the contractile machinery directly.

Lagrangian-based methods for finding MAP solutions for MRF models

Finding maximum a posteriori (MAP) solutions from noisy images based on a prior Markov random field (MRF) model is a huge computational task. In this paper, we transform the computational problem into an integer linear programming (ILP) problem. We explore the use of Lagrange relaxation (LR) methods for solving the MAP problem. In particular, three different algorithms based on LR are presented. All the methods are competitive alternatives to the commonly used simulation-based algorithms based on Markov Chain Monte Carlo techniques. In all the examples (including both simulated and real images) that have been tested, the best method essentially finds a MAP solution in a small number of iterations. In addition, LR methods provide lower and upper bounds for the posterior, which makes it possible to evaluate the quality of solutions and to construct a stopping criterion for the algorithm. Although additive Gaussian noise models have been applied, any additive noise model fits into the framework.

Exchange of conductance and gating properties between gap junction hemichannels

Gap junction channels span the membranes of two adjacent cells and allow the gated transit of molecules as large as second messengers from cell to cell. The structure of the gap junction channel pore is not resolved. For identification of pore determinants we used a chimera of two connexins, cx46 and cx32E(1)43, that form membrane channels with distinct unit conductances and channel kinetics. Exchange of the first transmembrane segment (M1) between these connexins resulted in a chimera that exhibited most of the channel properties of the M1 donor, including single channel conductance, channel kinetics, and the preference to dwell at a subconductance level. The M1 segment thus appears to be an important determinant of conductance and gating properties of connexin channels.

A multi-institutional retrospective study of intracranial ependymoma in children: identification of risk factors

PURPOSE

The goal of this multi-institutional retrospective study of children with intracranial ependymoma was to identify risk factors associated with unfavorable overall survival (OS) and event-free survival (EFS).

PATIENTS AND METHODS

Clinical data, including demographics, tumor location, spread, histology, details of surgery, radiation treatment, and chemotherapy were collected. Clinical characteristics and univariate and multivariate analyses of risk factors for OS and EFS are presented.

RESULTS

Eleven U.S. institutions contributed 83 patients treated from 1987 to 1991. The OS at 5 and 7 years was 57% and 46%, and EFS at 5 and 7 years was 42% and 33%. Patients 3 years of age or younger differed from the older group by more common infratentorial location, less common gross total resection (GTR), and postoperative use of chemotherapy rather than radiation. This younger group of patients had worse survival (P < 0.01) than the older age group. Other than young age, less than GTR and World Health Organization (WHO) II grade 3 histology were significant adverse risk factors for EFS in univariate and multivariate analyses. OS shared the same adverse risk factors except for histology in multivariate analysis, which was only of borderline significance (P = 0.05). Progression at the original tumor location, present in 89% of patients, was the major pattern of tumor recurrence. Adjuvant chemotherapy in the group older than 3 years or craniospinal radiation in M0 patients did not significantly change EFS.

CONCLUSIONS

Adverse outcome in childhood intracranial ependymoma is related to age (3 years or younger), histology (grade 3), and degree of surgical resection (less than GTR). New approaches, particularly for local tumor control in younger patients, are needed to improve survival.

Gating of cx46 gap junction hemichannels by calcium and voltage

Connexin 46 (cx46), when expressed in Xenopus oocytes, not only forms typical gap junction channels between paired cells but also forms open gap junction hemichannels in the plasma membrane of single cells. The gap junction hemichannels share properties with complete gap junction channels in terms of permeability and gating. Here we characterize the gate that closes hemichannels in response to increased calcium concentration with whole-cell and single-channel records. The channels close within a narrow range of extracellular calcium concentrations (1-2 mM) which includes the calcium concentration prevailing in the primary site of cx46 expression, the lens. The effect of calcium on the channels is determined by voltage. A cysteine mutant of cx46, cx46L35C, was used to determine the localization of the gate. Experimental evidence suggests that position 35 is pore lining. The localization protocol tests the accessibility of position 35 for thiol reagents applied extra- or intracellularly to the channel closed by calcium. Channel closure by calcium excluded the thiol reagent from the outside but not from the inside. Consequently, the gate results in a regional closure of the pore and it is located extracellular to the position 35 of cx46. The present data also suggest that the cx46 gap junction hemichannel may exert a physiological function in the lens. Considering the association of calcium with cataract formation, it is feasible that misregulation of cx46 gap junction hemichannels could be a cause for cataract.

Localization of a voltage gate in connexin46 gap junction hemichannels

Cysteine replacement mutagenesis has identified positions in the first transmembrane domain of connexins as contributors to the pore lining of gap junction hemichannels (Zhou et al. 1997. Biophys. J. 72:1946-1953). Oocytes expressing a mutant cx46 with a cysteine in position 35 exhibited a membrane conductance sensitive to the thiol reagent maleimidobutyryl biocytin (MBB). MBB irreversibly reduced the single-channel conductance by 80%. This reactive cysteine was used to probe the localization of a voltage gate that closes cx46 gap junction hemichannels at negative potentials. MBB was applied to the closed channel either from outside (whole cell) or from inside (excised membrane patches). After washout of the thiol reagent the channels were tested at potentials at which the channels open. After extracellular application of MBB to intact oocytes, the membrane conductance was unaffected. In contrast, channels treated with intracellular MBB were blocked. Thus the cysteine in position 35 of cx46 is accessible from inside but not from the outside while the channel is closed. These results suggest that the voltage gate, which may be identical to the "loop gate" (Trexler et al. 1996. Proc. Natl. Acad. Sci. USA. 93:5836-5841), is located extracellular to the 35 position. The voltage gate results in regional closure of the pore rather than closure along the entire pore length.

[How can primary health care influence patients' alcohol drinking habits. "Simple intervention" results in a new therapeutic perspective]

A review of findings in randomised trials with at least one-year follow-up suggests that primary care physicians can intervene briefly and successfully for patients manifesting symptoms of excessive drinking but no serious dependence. The risk level can be assessed by summing the preceding week's intake of spirits, wine and beer in standard measures and then convert it into grams of pure alcohol. Denial is minimised by using a non-judgmental lifestyle approach, and defining problems in terms of lifestyle habits and its consequences. Nervous problems, hypertension and dyspepsia are the most common diagnoses in the target group. Measurement of biochemical markers can be used, the serum gamma-glutamyl transpeptidase (GGT) level being still the most useful. Questionnaires are of limited value as they are associated with high false-positive rates. To motivate patients to reduce alcohol consumption, an intervention strategy with feedback is proposed, mainly based on the monitoring of symptoms and clinical findings including biochemical markers, and a self-help pamphlet is recommended. It is emphasised that the goal should be realistic to the patient, and that controlled drinking is an acceptable goal even in cases of mild dependence.

Time to relief of episodic symptoms of gastro-oesophageal reflux disease. A crossover comparison of single doses of the effervescent and standard formulations of ranitidine

BACKGROUND

The length of time until symptom relief and the consistency of response are important aspects of the management of episodes of gastro-oesophageal reflux disease (GORD).

METHODS

In an open, randomized, crossover study 98 patients treated 3 episodes of GORD with ranitidine effervescent formulation and 3 with ranitidine standard formulation. The patients filled in a diary card during the 1st h after each study medication. Satisfaction with the formulations and the formulation of choice were determined at the end of the study.

RESULTS

A higher percentage of episodes with acceptable symptom relief (82.4% versus 73.1% P=0.024) and a shorter time to acceptable symptom relief (27 min versus 36 min; P < 0.001) were achieved with the effervescent formulation. Sixty-five per cent preferred the effervescent formulation (P < 0.01).

CONCLUSIONS

An increased consistency of response and a more rapid symptom relief were achieved with treatment with the ranitidine effervescent formulation, indicating it may be more appropriate for on-demand treatment in patients with episodes of GORD.

BCL-2 expression does not not correlate with patient outcome in pediatric acute myelogenous leukemia

Although the Bcl-2 protein inhibits apoptosis (programmed cell death) of lymphoid cells induced by a variety of stimuli, its effects on myeloid cell short- and long-term survival after chemotherapy are less defined. We sought to elucidate the short- and long-term effect of Bcl-2 in a well-studied myeloid cell line (HL-60) treated with specific anti-AML chemotherapy. HL-60 cells overexpressing Bcl-2 (HL-60/BCL-2) were more resistant than parental HL-60 cells to multiple chemotherapeutic agents in short-term apoptosis and viability assays. Significantly, HL-60/BCL-2 cells retained greater long-term proliferative capacity than HL-60 cells when treated with low doses of doxorubicin. To assess the importance of Bcl-2 expression in pediatric AML we correlated clinical outcome and levels of Bcl-2 protein in 22 patient specimens. The correlation did not achieve statistical significance with patient response to chemotherapy or long-term outcome, suggesting that analysis of larger numbers of patient samples would not be useful. Our study suggests that although Bcl-2 clearly promotes short and long-term survival in a myeloid cell line, measurement of Bcl-2 levels alone are not sufficient to be of prognostic significance in pediatric AML.

Identification of a pore lining segment in gap junction hemichannels

The ability of certain connexins to form open hemichannels has been exploited to study the pore structure of gap junction (hemi)channels. Cysteine scanning mutagenesis was applied to cx46 and to a chimeric connexin, cx32E(1)43, which both form patent hemichannels when expressed in Xenopus oocytes. The thiol reagent maleimido-butyryl-biocytin was used to probe 12 cysteine replacement mutants in the first transmembrane segment and two in the amino-terminal segment. Maleimido-butyryl-biocytin was found to inhibit channel activity with cysteines in two equivalent positions in both connexins: I33C and M34C in cx32E(1)43 and I34C and L35C in cx46. These two positions in the first transmembrane segment are thus accessible from the extracellular space and consequently appear to contribute to the pore lining. The data also suggest that the pore structure is complex and may involve more than one transmembrane segment.

A chimeric connexin forming gap junction hemichannels

Connexins are the subunits of gap junction channels which connect neighboring cells. With the exception of lens connexins, they usually do not form open hemichannels in the cell membrane of single cells. Here we describe a chimeric connexin consisting of cx32 where the first extracellular loop sequence is replaced by the corresponding cx43 sequence. This chimera, cx32E143, forms conventional gap junction channels in the paired oocyte assay. In addition cx32E143 induces a membrane conductance in single oocytes. This membrane conductance is voltage dependent and is similarly sensitive to CO2 as are gap junction channels formed by the chimera or by wild-type cx32. These data suggest that cx32E143 forms patent hemichannels in the plasma membrane of single oocytes. This conclusion is further supported by the observation that oocytes expressing cx32E143 take up from the bath medium tracer molecules known to pass through gap junction channels.

Where are the gates in gap junction channels?

1. In the formation and function of gap junction channels two types of gates ought to be discriminated: the docking gate and the channel gates proper. The docking gate is involved in the transformation of a closed hemichannel to a patent gap junction channel. By definition the trigger mechanism for this gate and maybe even the gate itself is contained within the extracellular loops of the gap junction proteins, the connexins. The channel gates proper determine the open and closed states of the complete gap junction channels. 2. Probing the docking gate by mutagenesis of connexins and by synthetic peptides indicates that this gate is the consequence of complex interactions between a large fraction of the amino acids comprising the extracellular loops. Probably both inter- and intra-molecular interactions are involved, and disulfide exchange may be entailed in the stabilization of the open and closed states. 3. Of the various effectors on the channel gate(s) the voltage effects have obtained the most scrutiny to date. The response of gap junction channels and hemichannels is diverse, the various channels respond differently to transjunctional and membrane potential. No equivalent to the S4 segment representing the voltage sensor in other voltage dependent ion channels is present in the connexin sequences, instead mutations in various segments of connexins have been reported to affect the voltage dependence of gap junction channels. To understand the complexity of voltage effects on gap junction channels, non-connexin peptides may need to be considered as voltage sensors or as modifiers thereof.