Intrinsic oscillatory activity arising within the electrically coupled AII amacrine-ON cone bipolar cell network is driven by voltage-gated Na+ channels

In the rd1 mouse model for retinal degeneration, the loss of photoreceptors results in oscillatory activity (∼10–20 Hz) within the remnant electrically coupled network of retinal ON cone bipolar and AII amacrine cells. We tested the role of hyperpolarization-activated currents (I(h)), voltage-gated Na(+) channels and gap junctions in mediating such oscillatory activity. Blocking I(h) (1 mm Cs(+)) hyperpolarized the network and augmented activity, while antagonizing voltage-dependent Na(+) channels (1 μm TTX) abolished oscillatory activity in the AII amacrine-ON cone bipolar cell network. Voltage-gated Na(+) channels were only observed in AII amacrine cells, implicating these cells as major drivers of activity. Pharmacologically uncoupling the network (200 μm meclofenamic acid (MFA)) blocked oscillations in all cells indicating that Na(+) channels exert their influence over multiple cell types within the network. In wt retina, occluding photoreceptor inputs to bipolar cells (10 μm NBQX and 50 μm l-AP4) resulted in a mild (∼10 mV) hyperpolarization and the induction of oscillatory activity within the AII amacrine-ON cone bipolar cell network. These oscillations had similar properties to those observed in rd1 retina, suggesting that no major degeneration-induced network rewiring is required to trigger spontaneous oscillations. Finally, we constructed a simplified computational model that exhibited Na(+) channel-dependent network oscillations. In this model, mild heterogeneities in channel densities between individual neurons reproduced our experimental findings. These results indicate that TTX-sensitive Na(+) channels in AII amacrine cells trigger degeneration-induced network oscillations, which provide a persistent synaptic drive to downstream remnant neurons, thus appearing to replace photoreceptors as the principal drivers of retinal activity.

Actinomyces turicensis infection mimicking ovarian tumour

This case report explores an unusual presentation of a commensal organism, Actinomyces, which mimicked a presentation of ovarian cancer. A 73-year-old woman presented to a tertiary level hospital with persistent left iliac fossa abdominal pain, anorexia and fever lasting over one week, with a three-month history of bright rectal bleeding. Imaging was suggestive of malignancy. Fine needle aspiration of an enlarged lymph node was non-diagnostic. Blood cultures taken at presentation became positive after two days for Gram-positive rods, which were most likely Actinomyces. The patient was treated with penicillin 1.8 g four hourly with rapid improvement. Actinomycosis is frequently misdiagnosed as malignancy initially due to its relatively indolent course. Lesions often resolve with antibiotics, without the need for surgical intervention.

Modulation of voltage-gated ion channels in rat retinal ganglion cells mediated by somatostatin receptor subtype 4

Somatostatin (somatotropin release-inhibiting factor [SRIF]) is known to modulate the excitability of retinal ganglion cells, but the membrane mechanisms responsible and the extent to which intracellular calcium signaling is affected have not been determined. We show that somatostatin receptor subtype 4 (sst(4)) is expressed specifically in rat ganglion cells and that the generation of repetitive action potentials by isolated ganglion cells is reduced in the presence of L-803,087, a selective sst(4) agonist (10 nM). Under voltage clamp, L-803,087 increased outward K(+) currents by 51.1 ± 13.1% at 0 mV and suppressed Ca(2+) channel currents by 32.5 ± 9.4% at -10 mV in whole cell patch-clamped ganglion cells. The N-type Ca(2+) channel blocker ω-conotoxin GVIA (CTX, 1 μM) reduced L-type Ca(2+) current (I(Ca)) in ganglion cells by 43.5 ± 7.2% at -10 mV, after which addition of L-803,087 further reduced I(Ca) by 28.0 ± 16.0% . In contrast, ganglion cells treated first with nifedipine (NIF, 10 μM), which blocked 46.1 ± 3.5% of the control current at -10 mV, did not undergo any further reduction in I(Ca) in the presence of L-803,087 (-3.5 ± 3.8% vs. NIF), showing that stimulation of sst(4) reduces Ca(2+) influx through L-type Ca(2+) channels. To assess the effects of sst(4) stimulation on intracellular Ca(2+) levels ([Ca(2+)](i)) in ganglion cells, fura-2 was used to measure changes in [Ca(2+)](i) in response to depolarization induced by elevated [K(+)](o). [Ca(2+)](i) was increased to a lesser extent (86%) in the presence of L-803,087 compared with recordings made in the absence of the sst(4) agonist and this effect was blocked by NIF (10 μM). Suppression of spiking and Ca(2+) signaling via sst(4) may contribute to the reported neuroprotective actions of somatostatin and promote ganglion cell survival following ischemia and axonal trauma.

Antiresorptive effects of phytoestrogen supplements compared with estradiol or risedronate in postmenopausal women using (41)Ca methodology

INTRODUCTION

Reduction of ovarian estrogen secretion at menopause increases net bone resorption and leads to bone loss. Isoflavones have been reported to protect bone from estrogen deficiency, but their modest effects on bone resorption have been difficult to measure with traditional analytical methods.

METHODS

In this randomized-order, crossover, blinded trial in 11 healthy postmenopausal women, we compared four commercial sources of isoflavones from soy cotyledon, soy germ, kudzu, and red clover and a positive control of oral 1 mg estradiol combined with 2.5 mg medroxyprogesterone or 5 mg/d oral risedronate (Actonel) for their antiresorptive effects on bone using novel (41)Ca methodology.

RESULTS

Risedronate and estrogen plus progesterone decreased net bone resorption measured by urinary (41)Ca by 22 and 24%, respectively (P < 0.0001). Despite serum isoflavone profiles indicating bioavailability of the phytoestrogens, only soy isoflavones from the cotyledon and germ significantly decreased net bone resorption by 9% (P = 0.0002) and 5% (P = 0.03), respectively. Calcium absorption and biochemical markers of bone turnover were not influenced by interventions.

CONCLUSIONS

Dietary supplements containing genistein-like isoflavones demonstrated a significant but modest ability to suppress net bone resorption in postmenopausal women at the doses supplied in this study over a 50-d intervention period.

Barriers to advance care planning in chronic obstructive pulmonary disease

The English End of Life Care Strategy promises that all patients with advanced, life limiting illness will have the opportunity to participate in Advance Care Planning (ACP). For patients with Chronic Obstructive Pulmonary Disease (COPD), the barriers to this being achieved in practice are under-explored. Five focus groups were held with a total of 39 health care professionals involved in the care of patients with COPD. Participants reported that discussions relating to ACP are very rarely initiated with patients with COPD and identified the following barriers: inadequate information provision about the likely course of COPD at diagnosis; lack of consensus regarding who should initiate ACP and in which setting; connotations of comparing COPD with cancer; ACP discussions conflicting with goals of chronic disease management; and a lack of understanding of the meaning of 'end of life' within the context of COPD. The findings from this study indicate that, for patients with COPD, significant service improvement is needed before the objective of the End of Life Care Strategy regarding patient participation in end of life decision-making is to be achieved. Whilst the findings support the Strategy's recommendations regarding an urgent for both professional education and increased public education about end of life issues, they also indicate that these alone will not be enough to effect the level of change required. Consideration also needs to be given to the integration of chronic disease management and end of life care and to developing definitions of end of life care that fit with concepts of 'continuous palliation'.

How should accredited specialists be trained to do new procedures?

When and how specialists should receive training to perform newly introduced procedures is a topic which has received relatively scant attention. The demands of clinical governance and the prospect of revalidation make this an issue which clinicians and their specialist organisations cannot ignore. NICE has been advised by specialist clinical advisers to make recommendations about training in its guidance, but wanted both to review the literature and to consider the views of specialists on how this might best be done. All this is about accredited specialists who have completed their specialist training: it is not about 'training for trainees'.

Topical interferon alpha 2b eye-drops for treatment of ocular surface squamous neoplasia: a dose comparison study

BACKGROUND/AIMS To compare the effectiveness and side-effect profile of two doses of interferon alpha2b (IFNalpha2b) eye-drops (1 million international units (IU)/ml versus 3 million IU/ml) in the treatment of ocular surface squamous neoplasia (OSSN). METHODS Retrospective case series. RESULTS Thirty-five eyes were identified over an 11-year period (1996-2007). Twenty-one eyes (19 patients) with conjunctival intraepithelial neoplasia (CIN) were treated with 1 million IU/ml of topical IFN-alpha2b; 12 eyes (nine patients) with CIN were treated with 3 million IU/ml. Two patients with squamous cell carcinoma (SCC) were treated with topical interferon, one with 1 million IU/ml and one with 3 million IU/ml. Baseline demographic information was not statistically different between the two groups. In patients with CIN, topical therapy eliminated disease in 81% of eyes in the 1 million IU/ml group versus 92%, in the 3 million IU/ml group, p=0.41. The median time to OSSN resolution was 2.8 months in the 1 million IU/ml group and 1.9 months in the 3 million IU/ml group, p=0.55. Neither eye with SCC responded to interferon therapy. Topical therapy was well tolerated. After a median follow-up of 24 months, three recurrences were seen in eyes successfully treated with topical therapy. CONCLUSION In our study, there were no significant differences between the 1 million IU/ml group and the 3 million IU/ml group for the treatment of CIN.

Comparison of three plating media for the isolation of Salmonella from poultry environmental samples in Great Britain using ISO 6579:2002 (Annex D)

AIMS

To evaluate the performance of three Salmonella plating media (Rambach, Xylose Lysine Deoxycholate agar and modified Brilliant Green Agar plus Novobiocin) as part of the ISO 6579: 2002 (Annex D) on poultry environmental samples.

METHODS AND RESULTS

The samples analysed were those for the European Union Salmonella baseline surveys of laying (N = 3087), broiler (N = 1550), turkey fattening (N = 1540) and turkey breeding (N = 580) flocks for Great Britain. Results were considered separately for Rambach (including and excluding pale orange colonies) and for growth on selective media [Modified semi-solid Rappaport Vassiliadis (MSRV)] after 24 and 48 h of incubation. Overall, Rambach was the most sensitive medium, provided that pale orange colonies were checked. In all cases, an increase in the sensitivity of detection was obtained by plating growth on MSRV after 48 h of incubation. In broilers and laying flocks, the specificity significantly improved when Rambach only was used.

CONCLUSION

The use of Rambach results in considerable savings compared with the two-plate method prescribed by ISO 6579:2002 (Annex D) without compromising sensitivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Salmonella isolation protocols should be reviewed in terms of their efficiency and cost.

Calcium-activated chloride channels in the retina

This review examines the function of calcium-activated chloride currents (I(Cl(Ca))) in the retina with an emphasis on their physiological role in photoreceptors. Although found in a variety of neurons and glial cells of the retina, I(Cl(Ca)) has been most prominently studied in cones, where it activates in response to depolarization-evoked Ca(2+) influx. The slow and complex gating kinetics of the chloride current have been considered to reflect the changing submembrane concentration of intracellular calcium. It is likely that the role of I(Cl(Ca)) is to stabilize the membrane potential of cones during synaptic activity and presynaptic Ca channel modulation. Several candidates in the molecular identification of the channel have been put forward but the issue remains unresolved.

Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer

Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated attenuation of 0.6 dB cm(-1) MHz(-1), scatterer size estimates for an in vivo breast tumor also demonstrate improvements using elevational compounding with data from the 2D CMUT transducer.

Metabotropic receptor-activated calcium increases and store-operated calcium influx in mouse Müller cells

PURPOSE

Metabotropic receptor agonists that signal through G(q)-coupled pathways increase Ca(2+) in mammalian Müller cells by release from intracellular stores and Ca(2+) influx pathways that have not been well described. The authors examined the involvement of voltage-dependent and non-voltage-dependent Ca(2+) channels in metabotropic muscarinic receptor-activated Ca(2+) increases and store-operated Ca(2+) influx in cultured mouse Müller cells.

METHODS

Intracellular Ca(2+) was measured using fluorescence imaging with the ratiometric dye fura-2. Currents were recorded using the whole-cell patch-clamp recording method: mRNA and protein were identified using reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemical approaches.

RESULTS

The muscarinic receptor agonist carbachol (3-20 microM) produced increases in Ca(2+) that were blocked by the muscarinic receptor antagonists atropine and pirenzepine. RT-PCR confirmed mRNA for metabotropic M1 muscarinic receptors. Depletion of Ca(2+) stores by the sarcoplasmic/endoplasmic Ca(2+) ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid or the inhibition of phospholipase C occluded the carbachol-activated increase in Ca(2+). Carbachol-activated Ca(2+) increases in Müller cells were enhanced by the diacylglycerol derivative 1-oleyl-2-acetyl-sn-glycerol and were blocked by transient receptor potential (TRP) channel blockers Gd(3+), La(3+), 2-APB, and flufenamic acid. Both muscarinic receptor activation and thapsigargin treatment depleted Ca(2+) stores and produced Ca(2+) entry that was attenuated by La(3+), 2-APB, Gd(3+), and flufenamic acid. mRNA and protein for TRPC1 and TRPC6 were present in mouse Müller cells, and carbachol activated a Gd(3+)-sensitive, TRP-like cation channel.

CONCLUSIONS

Metabotropic muscarinic receptor-activated Ca(2+) increases in mouse Müller cells require the release of Ca(2+) from intracellular stores and the activation of Ca(2+) entry that involves TRP-like cation channels but is independent of voltage-dependent Ca(2+) channels.

Proton modulation of ion channels in isolated horizontal cells of the goldfish retina

Transient changes in extracellular pH (pH(o)) occur in the retina and may have profound effects on neurotransmission and visual processing due to the pH sensitivity of ion channels. The present study characterized the effects of acidification on the activity of membrane ion channels in isolated horizontal cells (HCs) of the goldfish retina using whole-cell patch-clamp recording. Currents recorded from HCs were characterized by prominent inward rectification at potentials negative to -80 mV, a negative slope conductance between -70 and -40 mV, a sustained inward current, and outward rectification positive to 40 mV. Inward currents were identified as those of inward rectifier K(+) (Kir) channels and Ca(2+) channels by their sensitivity to 10 mM Cs(+) or 20 microm Cd(2+), respectively. Both of these currents were reduced when pH(o) decreased from 7.8 to 6.8. Glutamate (1 mM)-activated currents were also identified, as were hemichannel currents that were enhanced by removal of extracellular Ca(2+) and application of 1 mM quinidine. Both glutamate-activated and hemichannel currents were suppressed by a similar reduction of pH(o). When all of these H(+)-inhibited currents were blocked, a small, sustained inward current at -60 mV increased following a decrease in pH(o) from 7.8 to 6.8. In addition, slope conductance between -70 and -20 mV increased during this acidification. Suppression of this H(+)-activated current by removal of extracellular Na(+), and an extrapolated E(rev) near E(Na), indicated that this current was carried predominantly by Na(+) ions.

Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca

INTRODUCTION

The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments.

METHODS

Thirteen postmenopausal women (>or=6 yr since menopause) were predosed with 41Ca iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for 41Ca/Ca analysis by accelerator mass spectrometry.

RESULTS

Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary 41Ca/Ca ratios.

CONCLUSIONS

Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary 41Ca excretion from prelabeled bone.

A comparative linkage map of oilseed rape and its use for QTL analysis of seed oil and erucic acid content

We have developed a new DH mapping population for oilseed rape, named TNDH, using genetically and phenotypically diverse parental lines. We used the population in the construction of a high stringency genetic linkage map, consisting of 277 loci, for use in quantitative genetic analysis. A proportion of the markers had been used previously in the construction of linkage maps for Brassica species, thus permitting the alignment of maps. The map includes 68 newly developed Sequence Tagged Site (STS) markers targeted to the homologues of defined genes of A. thaliana. The use of these markers permits the alignment of our linkage map with the A. thaliana genome sequence. An additional 74 loci (31 newly developed STS markers and 43 loci defined by SSR and RFLP markers that had previously been used in published linkage maps) were added to the map. These markers increased the resolution of alignment of the newly constructed linkage map with existing Brassica linkage maps and the A. thaliana genome sequence. We conducted field trials with the TNDH population at two sites, and over 2 years, and identified reproducible QTL for seed oil content and erucic acid content. The results provide new insights into the genetic control of seed oil and erucic acid content in oilseed rape, and demonstrate the utility of the linkage map and population.

Diagnostic adequacy and accuracy of fine needle aspiration cytology in neck lump assessment: results from a regional cancer network over a one year period

Aim: To establish the diagnostic accuracy and adequacy of fine needle aspiration cytology (FNAC) within a regional cancer network, and to determine what service improvements may be required to allow successful implementation of an FNAC-based, ‘one-stop’ head and neck clinic, as proposed by the current National Institute for Clinical Excellence guidelines.

Materials and methods: The Sussex cancer network serves a population of 1 200 000 and contains five hospitals within three acute trusts. In 2004, an audit was undertaken retrospectively to examine the diagnostic adequacy and accuracy of head and neck FNAC across the network. Comparisons were then made with the results of subsequent relevant surgery. For the purposes of the audit, FNAC was subdivided into three main groups: salivary gland, thyroid gland and neck node. As part of the data analysis, we also noted the clinical source of the FNAC and whether it was performed blind or under image guidance.

Results: In 2004, 712 FNAC procedures were undertaken in 647 patients, 276 of whom underwent subsequent surgery. Fine needle aspiration cytology was non-diagnostic in 52 per cent of patients in the neck node group, in 50 per cent in the salivary gland group and in 30 per cent in the thyroid group. With these non-diagnostic results removed, statistical analysis was performed on data from those patients who had undergone both FNAC and subsequent surgery. This gave a sensitivity of 89 per cent and a specificity of 57 per cent in the neck node group, a sensitivity of 64 per cent and specificity of 100 per cent in the salivary gland group, and a sensitivity of 62 per cent and specificity of 86 per cent in the thyroid group. Diagnostic problems with FNAC were noted, particularly in the differentiation of reactive nodal hyperplasia from lymphoma and in diagnosing follicular thyroid lesions. Ultrasound guidance was used in 50 per cent of the thyroid FNAC procedures but in only a minority of patients in the neck node and salivary gland groups.

Conclusion: This audit demonstrated widespread diagnostic difficulties associated with head and neck FNAC in a large patient sample. It is likely that these problems will be mirrored in other cancer networks. In order for one-stop head and neck clinics to succeed, the non-diagnostic rate of FNAC in particular must be minimised. There are strategies to enable this, depending on local resources, including increased access to cytologists or cytology technicians, diagnostic ultrasound, image guidance for FNAC and the use of ultrasound-guided core biopsy.

Cannabinoid receptor-mediated inhibition of calcium signaling in rat retinal ganglion cells

PURPOSE

The physiological actions of CB(1) cannabinoid receptors (CB(1)Rs) in mammalian retina have yet to be fully described in all cell types. Here we investigate the actions of CB(1)R activation on high-voltage-activated (HVA) Ca(2+) channel currents in purified cultures of rat retinal ganglion cells (RGCs).

METHODS

Reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry were used to determine the presence of CB(1)R mRNA and protein in a purified RGC culture generated from neonatal rats using a two-step panning procedure. Ruptured-patch whole-cell voltage clamp was used to test the effect of CB(1)R agonists (WIN 55,212-2) and antagonists (SR141716A, AM281) on HVA Ca(2+) channel currents.

RESULTS

RT-PCR analysis confirmed CB(1)R mRNA in cultured RGCs and immunocytochemistry for CB(1)R protein revealed labeling in both the cell body and neurites of isolated RGCs. Patch-clamp recording from cultured rat RGCs showed that the CB(1)R agonist WIN 55,212-2 inhibited HVA Ca(2+) channel currents up to 50% in a concentration-dependent manner (0.5, 1, and 5 muM). The Ca(2+) channel current inhibition by WIN 55,212-2 was blocked by CB(1)R antagonists AM281 and SR141716.

CONCLUSIONS

Activation of CB(1)Rs in cultured RGCs inhibits HVA Ca(2+) channel currents. These data show that cannabinoids can modify the excitability of RGCs and could affect retinal output. This finding has implications for retinal signal processing as it suggests that endogenous cannabinoids have inhibitory effects on RGCs and that exogenous cannabinoids could modulate retinal function by this pathway as well.

Calcium-activated chloride channels in müller cells acutely isolated from tiger salamander retina

Ca(2+)-activated chloride channels were identified with whole-cell patch-clamp recording techniques in salamander retinal Müller cells. Cl(Ca) channels were activated by membrane depolarizations that elicited Ca2+ influx or the application of the Ca2+ ionophore, ionomycin. The Ca channel blocker, Cd2+, abolished the Cl(Ca) channel tail currents. Increasing the duration of the depolarizing pulse resulted in enhancement of the Cl(Ca) channel tail current. Repetitive depolarizations with rapid pulses to +20 mV produced a buildup of I(Cl(Ca)), which reversed at 0 mV in symmetrical [Cl-] and at -40 mV when intracellular [Cl-] was reduced to 10% of the external concentration. I(Cl(Ca)) was blocked by the Cl channel blocker niflumic acid, while niflumic acid had no effect on voltage-gated Ca channels. These results offer the first demonstration of Cl(Ca) channels in a nonastrocytic glial cell and expand our understanding of the functional capacities of retinal glial cells.

Proton-mediated feedback inhibition of presynaptic calcium channels at the cone photoreceptor synapse

Generation of center-surround antagonistic receptive fields in the outer retina occurs via inhibitory feedback modulation of presynaptic voltage-gated calcium channels in cone photoreceptor synaptic terminals. Both conventional and unconventional neurotransmitters, as well as an ephaptic effect, have been proposed, but the intercellular messaging that mediates the inhibitory feedback signal from postsynaptic horizontal cells (HCs) to cones remains unknown. We examined the possibility that proton concentration in the synaptic cleft is regulated by HCs and that it carries the feedback signal to cones. In isolated, dark-adapted goldfish retina, we assessed feedback in the responses of HCs to light and found that strengthened pH buffering reduced both rollback and the depolarization to red light. In zebrafish retinal slices loaded with Fluo-4, depolarization with elevated K(+) increased Ca signals in the synaptic terminals of cone photoreceptors. Kainic acid, which depolarizes HCs but has no direct effect on cones, depressed the K(+)-induced Ca signal, whereas CNQX, which hyperpolarizes HCs, increased the Ca signals, suggesting that polarization of HCs alters inhibitory feedback to cones. We found that these feedback signals were blocked by elevated extracellular pH buffering, as well as amiloride and divalent cations. Voltage clamp of isolated HCs revealed an amiloride-sensitive conductance that could mediate modulation of cleft pH dependent on the membrane potential of these postsynaptic cells.

Cav3.1 splice variant expression during neuronal differentiation of Y-79 retinoblastoma cells

A decrease in transient-type calcium channel current, Ca(v)3.1 protein and the mRNA encoding these channels has been reported during differentiation of human retinoblastoma cells. In this study, we examined splice variants of Ca(v)3.1 before and after neuronal differentiation of the Y-79 retinoblastoma cell line to investigate the potential contribution of Ca(v)3.1 to Y-79 differentiation. In Ca(v)3.1, alternative splicing induces variations in three cytoplasmic regions, e.g. the link between domains II and III (producing isoforms e+ and e-), the link between domains III and IV (producing isoforms a, b, ac and bc) and the carboxy terminal region (producing isoforms f and d). Our results demonstrate that Ca(v)3.1e was not expressed in either undifferentiated or differentiated retinoblastoma cells. Splice variants Ca(v)3.1ac; Ca(v)3.1bc and Ca(v)3.1b were all identified in undifferentiated retinoblastoma cells, while expression of these variants in differentiated cells was restricted to the Ca(v)3.1bc isoform. The carboxy terminal variant Ca(v)3.1f is expressed independently of the differentiation status of retinoblastoma cells with or without Ca(v)3.1d. Examination of the functional contribution of Ca(v)3.1 protein to Y-79 cell differentiation revealed that in Y-79 cells transfected with Ca(v)3.1 antisense oligodeoxynucleotides, knockdown of Ca(v)3.1 did not alter the time-course of differentiation or neuritogenesis. The changes in Ca(v)3.1 splice variants were not required for the initiation of differentiation but may be associated with tissue-specific expression or localized alterations in Ca(2+) signaling that are essential for establishment of the mature differentiated phenotype.

Mutation of the calcium channel gene Cacna1f disrupts calcium signaling, synaptic transmission and cellular organization in mouse retina

Retinal neural transmission represents a key function of the eye. Identifying the molecular components of this vital process is helped by studies of selected human genetic eye disorders. For example, mutations in the calcium channel subunit gene CACNA1F cause incomplete X-linked congenital stationary night blindness (CSNB2 or iCSNB), a human retinal disorder with abnormal electrophysiological response and visual impairments consistent with a retinal neurotransmission defect. To understand the subcellular basis of this retinal disorder, we generated a mouse with a loss-of-function mutation by inserting a self-excising Cre-lox-neo cassette into exon 7 of the murine orthologue, Cacna1f. Electroretinography of the mutant mouse revealed a scotopic a-wave of marginally reduced amplitude compared with the wild-type mouse and absence of the post-receptoral b-wave and oscillatory potentials. Cone ERG responses together with visual evoked potentials and multi-unit activity in the superior colliculus were also absent. Calcium imaging in Fluo-4 loaded retinal slices depolarized with KCl showed 90% less peak signal in the photoreceptor synapses of the Cacna1f mutant than in wild-type mice. The absence of post-receptoral ERG responses and the diminished photoreceptor calcium signals are consistent with a loss of Ca((2+)) channel function in photoreceptors. Immunocytochemistry showed no detectable Ca(v)1.4 protein in the outer plexiform layer of Cacna1f-mutant mice, profound loss of photoreceptor synapses, and abnormal dendritic sprouting of second-order neurons in the photoreceptor layer. Together, these findings in the Cacna1f-mutant mouse reveal that the Ca(v)1.4 calcium channel is vital for the functional assembly and/or maintenance and synaptic functions of photoreceptor ribbon synapses. Moreover, the outcome of this study provides critical clues to the pathophysiology of the human retinal channelopathy of X-linked incomplete CSNB.

Characterization of vancomycin-resistant Enterococcus faecium isolates from broiler poultry and pig farms in England and Wales

This study aimed to investigate the occurrence and molecular epidemiology of vancomycin-resistant Enterococcus faecium (VREF) isolates on poultry and pig farms in England and Wales. A total of 217 VREF isolates were obtained from fresh feces and environmental swabs collected from conventional and organic farms. A predominant pulsed-field gel electrophoresis (PFGE) profile was found for each VREF-positive farm, together with less frequent types. All isolates presented the vanA genotype and were esp negative. Seventy-six percent of the VREF isolates were additionally resistant to nine or more antimicrobials, presenting a diverse range of resistance phenotypes. The multiresistance traits did not appear to be specific to individual farms or sample types (i.e., environmental or fecal), nor did they correlate with any specific PFGE type. Ninety-three percent of the isolates were resistant to penicillin, 89% were resistant to tetracycline, 87.5% were resistant to erythromycin, and 50% were resistant to quinupristin-dalfospristin (Synercid). The lack of clonality among these populations may suggest the horizontal transfer of resistance genes and/or a dynamic replacement of clonal lines rather than persistence.