Membrane-coated glass electrodes for stable, low-noise electrophysiology recordings in Drosophila central neurons

BACKGROUND

Electrophysiological recording with glass electrodes is one of the best techniques to measure membrane potential dynamics and ionic currents of voltage-gated channels in neurons. However, artifactual variability of the biophysical state variables that determine recording quality can be caused by insufficient affinity between the electrode and cell membrane during the recording.

NEW METHOD

We introduce a phospholipid membrane coating on glass electrodes to improve intracellular electrophysiology recording quality. Membrane-coated electrodes were prepared with a tip-dip protocol for perforated-patch, sharp-electrode current-clamp, and cell-attached patch-clamp recordings from specific circadian clock neurons in Drosophila. We perform quantitative comparisons based on the variability of functional biophysical parameters used in various electrophysiological methods, and advanced statistical comparisons based on the degree of stationariness and signal-to-noise ratio.

RESULTS

Results indicate a dramatic reduction in artifactual variabilities of functional parameters from enhanced stability. We also identify significant exclusions of a statistically estimated noise component in a time series of membrane voltage signals, improving signal-to-noise ratio.

COMPARISON WITH EXISTING METHODS

Compared to standard glass electrodes, using membrane-coated glass electrodes achieves improved recording quality in intracellular electrophysiology.

CONCLUSIONS

Electrophysiological recordings from Drosophila central neurons can be technically challenging, however, membrane-coated electrodes will possibly be beneficial for reliable data acquisition and improving the technical feasibility of axonal intracellular activities measurements and single-channel recordings. The improved electrical stability of the recordings should also contribute to increased mechanical stability, thus facilitating long-term stable measurements of neural activity. Therefore, it is possible that membrane-coated electrodes will be useful for any model system.

A phase I and pharmacologic study of the MDR converter GF120918 in combination with doxorubicin in patients with advanced solid tumors

BACKGROUND

Resistance to chemotherapy can partly be explained by the activity of membrane bound P-glycoprotein. Competitive inhibition of P-glycoprotein, by multidrug resistance (MDR) converters, may overcome this MDR. Previously studied MDR converters either have serious intrinsic side effects or considerably influence the pharmacokinetics of cytotoxic agents at concentrations theoretically required to convert MDR. GF120918 is a third-generation MDR converter with high affinity for P-glycoprotein and can be given orally. We performed a phase 1 study with escalating doses of GF120918 in combination with doxorubicin.

PATIENTS AND METHODS

The study group comprised 46 patients with advanced solid tumors. Doxorubicin was administered on day 1 (cycle 1), GF120918 on days 22-24 (cycle 2), and on days 29-33 with doxorubicin administered on day 31 (cycle 3). Pharmacokinetics of both GF120918 and doxorubicin were studied. The starting daily dose of GF120918 was 50 mg and was to be increased in subsequent cohorts until a steady state plasma level of 100 ng/ml was reached. The starting dose of doxorubicin was 50 mg/m2 and was to be increased after reaching the target dose level of GF120918.

RESULTS

In 37 of the 46 patients, full pharmacokinetic data from the three scheduled cycles were obtained. Pharmacokinetics of GF120918 showed a less than linear increase in Cmax with increasing doses, with considerable interpatient variation. The target steady-state plasma level for GF120918 was exceeded in 12 out of 19 patients who received 400 mg GF120918 alone twice daily and in 12 of 17 patients who received 400 mg GF120918 twice daily in combination with doxorubicin. GF120918 pharmacokinetics were not influenced by coadministration of doxorubicin. The doxorubicin AUC was only marginally influenced by GF120918 and only at the highest dose levels. In these patients there was a significant increase in the AUC of doxorubicinol in cycle 3 as compared to cycle 1. Hematologic toxicity mainly consisted of neutropenia and was more severe in cycle 3 than in cycle 1 (13 vs 5 patients with grade 4 neutropenia, P=0.003). Neutropenic fever was the dose-limiting toxicity at a doxorubicin dose of 75 mg/m2 with 400 mg GF120918 twice daily. The toxicity of GF120918 was limited to somnolence in eight patients and occasional gastrointestinal complaints.

CONCLUSION

GF120918 is an MDR converter with only minimal side effects at a dose level yielding concentrations able to convert the action of P-glycoprotein in vitro. A doxorubicin dose of 60 mg/m2 on day 3 in combination with 400 mg GF120918 twice daily on days 1-5 is an acceptable regimen for further clinical trials.

Increased oral bioavailability of topotecan in combination with the breast cancer resistance protein and P-glycoprotein inhibitor GF120918

PURPOSE

We discovered that breast cancer resistance protein (BCRP), a recently identified adenosine triphosphate-binding cassette drug transporter, substantially limits the oral bioavailability of topotecan in mdr1a/1b(-/-) P-glycoprotein (P-gp) knockout and wild-type mice. GF120918 is a potent inhibitor of BCRP and P-gp. The aim was to increase the bioavailability of topotecan by GF120918.

PATIENTS AND METHODS

In cohort A, eight patients received 1.0 mg/m(2) oral topotecan with or without coadministration of one single oral dose of 1,000 mg GF120918 (day 1 or day 8). In cohort B, eight other patients received 1.0 mg/m(2) intravenous topotecan with or without 1,000 mg oral GF120918 to study the effect of GF120918 on the systemic clearance of topotecan.

RESULTS

After oral topotecan, the mean area under the plasma concentration-time curve (AUC) of total topotecan increased significantly from 32.4 +/- 9.6 microg.h/L without GF120918 to 78.7 +/- 20.6 microg.h/L when GF120918 was coadministered (P =.008). The mean maximum plasma concentration of total topotecan increased from 4.1 +/- 1.5 microg/L without GF120918 to 11.5 +/- 2.4 microg/L with GF120918 (P =.008). The apparent bioavailability in this cohort increased significantly from 40.0% (range, 32% to 47%) to 97.1% (range, 91% to 120%) (P =.008). Interpatient variability of the apparent bioavailability was 17% without and 11% with GF120918. After intravenous administration of topotecan, coadministration of oral GF120918 had a small but statistically significant effect on the AUC and systemic clearance of total topotecan but no statistically significant effect on maximum plasma concentration and terminal half-life of total topotecan.

CONCLUSION

Coadministration of the BCRP and P-gp inhibitor GF120918 resulted in a significant increase of the systemic exposure of oral topotecan. The apparent oral bioavailability increased from 40.0% without to 97.1% with GF120918.

Co-administration of GF120918 significantly increases the systemic exposure to oral paclitaxel in cancer patients

Oral bioavailability of paclitaxel is very low, which is due to efficient transport of the drug by the intestinal drug efflux pump P-glycoprotein (P-gp). We have recently demonstrated that the oral bioavailability of paclitaxel can be increased at least 7-fold by co-administration of the P-gp blocker cyclosporin A (CsA). Now we tested the potent alternative orally applicable non-immunosuppressive P-gp blocker GF120918. Six patients received one course of oral paclitaxel of 120 mg/m(2)in combination with 1000 mg oral GF120918 (GG918, GW0918). Patients received intravenous (i.v.) paclitaxel 175 mg/m(2)as a 3-hour infusion during subsequent courses. The mean area under the plasma concentration-time curve (AUC) of paclitaxel after oral drug administration in combination with GF120918 was 3.27 +/- 1.67 microM x h. In our previously performed study of 120 mg/m(2)oral paclitaxel in combination with CsA the mean AUC of paclitaxel was 2.55 +/- 2.29 microM x h. After i.v. administration of paclitaxel the mean AUC was 15.92( )+/- 2.46 microM x h. The oral combination of paclitaxel with GF120918 was well tolerated. The increase in systemic exposure to paclitaxel in combination with GF120918 is of the same magnitude as in combination with CsA. GF120918 is a good and safe alternative for CsA and may enable chronic oral therapy with paclitaxel.

Clinical pharmacokinetics of doxorubicin in combination with GF120918, a potent inhibitor of MDR1 P-glycoprotein

Previous clinical investigations with doxorubicin indicated that modulators of P-glycoprotein dramatically decrease the systemic clearance of the drug, which complicates the interpretation of toxicity and response data. In the present study, we examined the pharmacokinetics of doxorubicin and GF120918, a novel potent P-glycoprotein inhibitor, in cancer patients in a search for more selective modulation of multidrug resistance (MDR). Seven cohorts (46 patients) received sequential treatments with doxorubicin alone by a 5 min i.v. bolus (50-75 mg/m2), oral GF120918 alone (50 mg q.d.-400 mg b.i.d.), and the combination of doxorubicin and GF120918. Serial blood and urine samples were taken during both treatment courses and analyzed for doxorubicin and its metabolite doxorubicinol by a liquid chromatographic assay. The pharmacokinetic characteristics of doxorubicin in the presence or absence of GF120918 indicate a very minor overall effect of the modulator, except at the highest combined dose level (i.e. 75 mg/m2 plus 400 mg b.i.d.). A limited number of patients experienced significantly increased exposure to doxorubicinol upon combined treatment, which was associated with concomitantly higher plasma levels of GF120918. Sigmoidal maximum-effect models revealed significant correlations (p<0.02) between the area under the curve of doxorubicinol and the percent decrease in neutrophils and platelets. Sigmoidicity factors in the fitted Hill equation were similar between both treatment courses, suggesting no pharmacodynamic potentiation of doxorubicinol myelotoxicity by GF120918. Our data indicate that GF120918 at the tested doses of combination treatment achieves plasma concentrations that reverse MDR in experimental models and it lacks the significant kinetic interaction with doxorubicin observed previously with other modulators. Hence, it may be possible in future trials to assess the contribution of a potent inhibitor of P-glycoprotein activity to the toxicity and activity of doxorubicin with the knowledge that profound plasma pharmacokinetic interactions are unlikely.

Comparison of fixation methods for preventing pelvic ring expansion

Several methods of external and internal fixation are used in urgent situations to lessen intrapelvic bleeding associated with unstable pelvic fractures. Pelvic stabilization limits pelvic expansion and thereby restricts the space for potential blood loss. This study compared several fixation methods using cadaveric pelves to determine which method best prevents pelvic expansion. Three methods of internal fixation and three methods of external fixation were compared. Anteroposterior fixation provided the greatest control against pelvic expansion; however, it is clinically impractical for emergency use. Therefore, external fixation provided the most reliable control of pelvic expansion in the emergency setting.

Characterization of the thyroid Na+/I- symporter with an anti-COOH terminus antibody

The Na+/I- symporter (NIS) is the plasma membrane protein that catalyzes active I- transport in the thyroid, the first step in thyroid hormone biogenesis. The cDNA encoding NIS was recently cloned in our laboratory and a secondary structure model proposed, suggesting that NIS is an intrinsic membrane protein (618 amino acids; approximately 65.2 kDa predicted molecular mass) with 12 putative transmembrane domains. Here we report the generation of a site-directed polyclonal anti-COOH terminus NIS antibody (Ab) that immunoreacts with a approximately 87 kDa-polypeptide present in membrane fractions from a rat thyroid cell line (FRTL-5). The model-predicted cytosolic-side location of the COOH terminus was confirmed by indirect immunofluorescence experiments using anti-COOH terminus NIS Ab in permeabilized FRTL-5 cells. Immunoreactivity was competitively blocked by the presence of excess synthetic peptide. Treatment of membrane fractions from FRTL-5 cells, Xenopus laevis oocytes, and COS cells expressing NIS with peptidyl N-glycanase F converted the approximately 87 kDa-polypeptide into a approximately 50 kDa-species, the same relative molecular weight exhibited by NIS expressed in E. coli. Anti-NIS Ab immunoprecipitated both the NIS precursor molecule (approximately 56 kDa) and the mature approximately 87 kDa form. Furthermore, a direct correlation between circulating levels of thyroid-stimulating hormone and NIS expression in vivo was demonstrated.

A simple method to measure compartment pressures using an intravenous catheter

A simple method was investigated to measure compartment pressures using 16-ga intravenous catheters with or without side ports attached by arterial line tubing to a pressure transducer. Pressure measurements from the experimental catheters were within 4 mm Hg of the slit catheter for 99% of all readings, and pressure measurements from the Stryker device were within 5 mm Hg of the slit catheter for 95% of all readings. The addition of one or two side ports to the experimental catheters did not alter the pressure readings. This method is comparable in accuracy to the slit catheter and in simplicity to the Stryker device.

The effectiveness of the cervical halo: open versus closed ring. A preliminary report

The halo cervical orthosis has proven extremely effective in stabilizing the spine, both non-operatively and as a supplement to operative procedures. Current designs of the available halo utilize either a closed or an open stabilizing ring. Twenty-four patients with various indications for halo application are reviewed. Eleven were treated with a closed ring apparatus (Ace Medical, Los Angeles, California), and thirteen with an open ring device (Bremer, Inc, Jacksonville, Florida). X-rays of the treated patients were compared by group, and patients were interviewed regarding their complaints while wearing the halo. Rates of complication were compared. Results showed no significant differences between radiographs (kyphosis or translation) throughout the follow-up period. Patients experienced a significantly higher incidence of halo-associated pain in the open group. Otherwise, there were no statistical differences in the complication rates of either device. Whether or not the higher incidence of pain in the open group is related to decreased device rigidity is unknown. The open design may theoretically permit bending and opening of the ring to occur, the so-called 'wishbone' effect. Based on these data, it cannot be determined whether the advantages of the open ring--ease of application--are offset by this potential disadvantage. Clearly, a larger, randomized prospective study is required to investigate this.

Comparison of primate and canine models for bone ingrowth experimentation, with reference to the effect of ovarian function on bone ingrowth potential

Bone growth into porous composite (mesh-bead) titanium plugs was compared in elderly (postmenopausal) female monkeys and female dogs as a means of validating the cross-species interpretations so often made between data from research on dogs and human applications. The effect of oophorectomy on bone ingrowth in the canine model was defined by the comparison of data on fractional ingrowth in animals that had had oophorectomy and in control animals that had had a sham operation. No significant difference in bone growth into the experimental plugs was identified between the two animal models, which lends credence to cross-species interpretation of existing data from dogs. The presence or absence of active ovaries did not affect the ingrowth fraction in the canine model; this suggests that existing data are not confounded by the lack of control of ovarian function. Estrogen depletion does not appear to influence bone ingrowth adversely.

Field performance of derived generations of transgenic tobacco

Two inbred cultivars of Nicotiana tabacum (tobacco), 'Samsun' and 'Xanthi', were transformed with the plasmid pBI 121 using Bin 19 in Agrobacterium tumefaciens. The plasmid carries the nptII gene conferring kanamycin resistance and the uidA gene encoding β-glucuronidase (GUS). Progeny carrying the genes in the homozygous condition were identified and selfed over several generations. One line homozygous for the introduced genes and one untransformed control from each cultivar were then selected and crossed reciprocally to give four families per cultivar. Seeds from each family were grown in a replicated field trial and all plants scored for a range of morphological and agronomic characters. In addition, leaf samples were taken and GUS activity measured. In the 'Samsun' material, which contained one copy of the introduced gene at a single locus and showed high levels of GUS expression, the transformed homozygote showed twice the level of GUS activity as the hemizygotes, wheareas in the 'Xanthi' line, which had a lower level of GUS, the hemizygotes showed the same level of GUS activity as the transformed homozygote. The agronomic data showed differences between the families, but the source of such differences could not be ascribed unambiguously. The results are discussed in the light of related information on gene expression and field performance from other transgenic material.

The influence of age, sex, and initial fit on bony ingrowth stabilization with the AML femoral component in primary THA

A radiographic review of 178 consecutive primary total hip arthroplasties using the AML femoral component with a mean follow up of 40.1 months identified 92.3% to be stabilized by bony ingrowth and 7.7% by fibrous tissue. None were classified as loose. The quality of fit in the isthmus and calcar regions was identified as an important factor in achieving bony ingrowth stabilization. Bony ingrowth was achieved in all age groups with equal frequency. No relationship between sex and the type of stabilization was identified. A clinical correlation utilizing a subset of patients with identical prosthetic components identified equivalent clinical results across all age groups. Thirty-four percent of patients experienced some residual thigh pain. No statistically significant relationship between the presence of thigh pain and the type of femoral component stabilization (bony vs fibrous) could be identified. Ninety-eight percent of patients expressed unconditional satisfaction with their hip replacements.

[Avoidable deaths in the evaluation of the performance of health services. II. European Atlas of avoidable deaths: initial data and several reflections]

The second European Atlas of Avoidable deaths, which will be shortly issued, concerns the period 1979-83 for Italy. The causes of deaths included were: tuberculosis, neoplasms of the cervix uteri and those of the uterus with no specified site, Hodgkin's disease, chronic rheumatic heart disease, hypertensive and cerebrovascular disease, childhood respiratory infections, asthma, appendicitis, abdominal hernia, cholecystitis and cholelithiasis, maternal and perinatal deaths. In Italy marked excesses for cholecystitis-cholelithiasis, Hodgkin's disease, hypertensive and cerebrovascular disease and perinatal mortality were observed. A remarkable decrease was observed in comparison with the first Atlas (1974-78); but the European countries generally maintained the differences amongst them and their rank. Proposals to assess the causes of the observed differences are suggested (death certificate quality evaluation studies, case-reference studies, cohort studies) and the role of confidential enquiries is discussed.

Ulnar styloid fixation in the treatment of posttraumatic instability of the radioulnar joint: a biomechanical study with clinical correlation

Biomechanical displacement testing was done on nine fresh human upper extremities to define the stabilizing influence of the triangular fibrocartilage on the radioulnar joint and the efficacy of triangular fibrocartilage-ulnar styloid avulsion fracture repair in restoring lost stability. Test data confirmed that the triangular fibrocartilage is a major stabilizer of the radioulnar joint and internal fixation of triangular fibrocartilage-ulnar styloid avulsion fractures can restore preavulsion stability in all positions of forearm rotation. On the basis of this data and a successful clinical experience, primary repair of displaced ulnar styloid avulsion fractures is advised as a means of stabilizing the radioulnar joint and preventing the disability associated with chronic radioulnar joint instability.

Purification and properties of Acid phosphatase-1 from a nematode resistant tomato cultivar

In tomato the acid phosphatase-1 isozyme (Apase-1) is inherited as a single locus linked to the nematode resistance gene (Mi). The Apase-1(1) electrophoretic variant has been purified from a tomato cell suspension culture using ion exchange and concanavalin A sepharose affinity chromatography. A cellulose acetate electrophoresis method was used to distinguish Apase-1(1) rapidly from other Apase isozymes in tomato. The subunit molecular weight of the purified enzyme was estimated to be 31,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native size of the enzyme, which is reported to be a dimer, was determined to be approximately 51,000 by high performance liquid chromatography gel filtration. Apase-1(1) has a lower pH optimum and a distinct substrate specificity as compared to Apases extracted from tomato fruit or from other plant species. The amino acid composition of Apase-1(1) is similar to that of a potato Apase.

Amniotic fluid alpha-fetoprotein measurements by laser immunonephelometry

A method is described for measuring human alpha-fetoprotein concentration (AFP) in amniotic fluid by laser immunonephelometry showing results comparable with those obtained by radioimmunoassay. Advantages gained with the laser technique lie in its simplicity as a method which avoids use of radioactive materials, a more rapid 2 h turnaround time and a relatively small capital equipment outlay with minimal operating costs. Laser immunonephelometry appears to be an excellent alternative to radioimmunoassay for measuring AFP in amniotic fluid.