Series resistance compensation for whole-cell patch-clamp studies using a membrane state estimator

Whole-cell patch-clamp techniques are widely used to measure membrane currents from isolated cells. While suitable for a broad range of ionic currents, the series resistance (R(s)) of the recording pipette limits the bandwidth of the whole-cell configuration, making it difficult to measure rapid ionic currents. To increase bandwidth, it is necessary to compensate for R(s). Most methods of R(s) compensation become unstable at high bandwidth, making them hard to use. We describe a novel method of R(s) compensation that overcomes the stability limitations of standard designs. This method uses a state estimator, implemented with analog computation, to compute the membrane potential, V(m), which is then used in a feedback loop to implement a voltage clamp; we refer to this as state estimator R(s) compensation. To demonstrate the utility of this approach, we built an amplifier incorporating state estimator R(s) compensation. In benchtop tests, our amplifier showed significantly higher bandwidths and improved stability when compared with a commercially available amplifier. We demonstrated that state estimator R(s) compensation works well in practice by recording voltage-gated Na(+) currents under voltage-clamp conditions from dissociated neonatal rat sympathetic neurons. We conclude that state estimator R(s) compensation should make it easier to measure large rapid ionic currents with whole-cell patch-clamp techniques.

Pharmacokinetics of dapsone administered daily and weekly in human immunodeficiency virus-infected children

Although dapsone is a commonly used alternative agent for prophylaxis against Pneumocystis carinii pneumonia in children intolerant to trimethoprim-sulfamethoxazole, there are few data that describe dapsone pharmacokinetics in children. We studied dapsone pharmacokinetics in 30 children (median age, 2.8 years; age range, 0. 3 to 12 years) receiving a new proprietary liquid preparation by three dosing regimens (1 mg/kg of body weight daily, 2 mg/kg daily, or 4 mg/kg weekly). Dosing of children with 2 mg/kg daily or 4 mg/kg weekly resulted in peak concentrations equivalent to those reached in adults receiving 100-mg tablets daily. For the entire population, the median half-life was 22.2 h (range, 7.1 to 40.3 h), the median oral clearance was 0.0365 liter/kg/h (range, 0.0104 to 0.1021 liter/kg/h), and the median oral apparent volume of distribution was 1.13 liters/kg (range, 0.50 to 2.32 liters/kg). The median dapsone oral clearance was significantly increased in those infants less than 2 years of age compared to the oral clearance in those over 2 years of age (0.0484 versus 0.0278 liter/kg/h; P = 0.011). These data suggest that absorption of this liquid preparation is adequate and that the concentrations in the sera of children receiving 2 mg/kg daily or 4 mg/kg weekly are equivalent to those seen in adults receiving standard dapsone dosing. Dapsone oral clearance appears to be increased in children under 2 years of age.

Chimeric analysis of a neuronal nicotinic acetylcholine receptor reveals amino acids conferring sensitivity to alpha-bungarotoxin

We have investigated the molecular determinants responsible for alpha-bungarotoxin (alphaBgtx) binding to nicotinic acetylcholine receptors through chimeric analysis of two homologous alpha subunits, one highly sensitive to alphaBgtx block (alpha1) and the other, alphaBgtx-insensitive (alpha3). By replacing rat alpha3 residues 184-191 with the corresponding region from the Torpedo alpha1 subunit, we introduced a cluster of five alpha1 residues (Trp-184, Trp-187, Val-188, Tyr-189, and Thr-191) into the alpha3 subunit. Functional activity and alphaBgtx sensitivity were assessed following co-expression in Xenopus oocytes of the chimeric alpha3 subunit (alpha3/alpha1[5]) with either rat beta2 or beta4 subunits. Agonist-evoked responses of alpha3/alpha1[5]-containing receptors were blocked by alphaBgtx with nanomolar affinity (IC(50) values: 41 nM for alpha3/alpha1[5]beta2 and 19 nM for alpha3/alpha1[5]beta4). Furthermore, receptors containing the single point mutation alpha3K189Y acquire significant sensitivity to alphaBgtx block (IC(50) values: 186 nM for alpha3K189Ybeta2 and 179 nM for alpha3K189Ybeta4). Another alpha3 chimeric subunit, alpha3/alpha7[6], similar to alpha3/alpha1[5] but incorporating the corresponding residues from the alphaBgtx-sensitive alpha7 subunit, also conferred potent alphaBgtx sensitivity to chimeric receptors when co-expressed with the beta4 subunit (IC(50) value = 31 nM). Our findings demonstrate that the residues between positions 184 and 191 of the alphaBgtx-sensitive subunits alpha1 and alpha7 play a critical functional role in the interaction of alphaBgtx with nicotinic acetylcholine receptors sensitive to this toxin.

Cytomegalovirus infection and HIV-1 disease progression in infants born to HIV-1-infected women. Pediatric Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV Infection Study Group

BACKGROUND AND METHODS

Cytomegalovirus (CMV) has been implicated as a cofactor in the progression of human immunodeficiency virus type 1 (HIV-1) disease. We assessed 440 infants (75 of whom were HIV-1-infected and 365 of whom were not) who had known CMV status and were born to HIV-1-infected women and who were followed prospectively. HIV-1 disease progression was defined as the presence of class C symptoms (according to the criteria of the Centers for Disease Control and Prevention [CDC]) or CD4 counts of less than 750 cells per cubic millimeter by 1 year of age and less than 500 cells per cubic millimeter by 18 months of age.

RESULTS

At birth the frequency of CMV infection was similar in the HIV-1-infected and HIV-1-uninfected infants (4.3 percent and 4.5 percent, respectively), but the HIV-1-infected infants had a higher rate of CMV infection at six months of age (39.9 percent vs. 15.3 percent, P=0.001) and continued to have a higher rate of CMV infection through four years of age (P=0.04). By 18 months of age, the infants with both infections had higher rates of HIV-1 disease progression (70.0 percent vs. 30.4 percent, P=0.001), CDC class C symptoms or death (52.5 percent vs. 21.7 percent, P=0.008), and impaired brain growth or progressive motor deficits (35.6 percent vs. 8.7 percent, P=0.005) than infants infected only with HIV-1. In a Cox regression analysis, CMV infection was associated with an increased risk of HIV-1 disease progression (relative risk, 2.59; 95 percent confidence interval, 1.13 to 5.95). Among children infected with HIV-1 alone, but not among those infected with both viruses, children with rapid progression of HIV-1 disease had higher mean levels of HIV-1 RNA than those with slower or no progression of disease.

CONCLUSIONS

HIV-1-infected infants who acquire CMV infection in the first 18 months of life have a significantly higher rate of disease progression and central nervous system disease than those infected with HIV-1 alone.

Toxicity and efficacy of daily vs. weekly dapsone for prevention of Pneumocystis carinii pneumonia in children infected with human immunodeficiency virus. ACTG 179 Study Team. AIDS Clinical Trials Group

BACKGROUND

Dapsone is an alternative drug for Pneumocystis carinii pneumonia (PCP) prophylaxis in individuals intolerant to trimethoprim-sulfamethoxazole (T/S). There are, however, few data on the pharmacokinetics, toxicity or efficacy of dapsone in children. Design. Randomized, multicenter trial comparing daily (1 or 2 mg/kg) with weekly (4 mg/kg) dapsone regimens in 94 HIV-infected children intolerant to T/S.

METHODS

Hematologic and hepatic toxicity was monitored, as well as the occurrence of skin rash, PCP or death.

RESULTS

Initial pharmacokinetic data indicated that adequate serum dapsone concentrations were not achieved with the daily 1-mg/kg regimen; the daily dose was then increased to 2 mg/kg. Both short and long term hematologic toxicities were marginally greater in children receiving the daily 2 mg/kg compared with the weekly regimen. Allergic skin rashes were similar in children receiving the daily and weekly regimens (17% in both) and were not associated with prior history of rash with T/S. PCP occurred most frequently with the daily 1-mg/kg regimen (22.0 cases/100 patient years), least frequently with the daily 2-mg/kg regimen (0 case/100 patient years) and at intermediate frequency with the weekly regimen (9.5 cases/100 patient years). More deaths were observed in patients receiving the daily than the weekly regimen (8 vs. 2, respectively), although the deaths were not directly attributable to dapsone treatment.

CONCLUSION

Although a weekly dapsone regimen of 4 mg/kg produced less hematologic toxicity than a daily regimen of 2 mg/kg, this advantage was offset by a trend toward higher breakthrough rates of PCP.

Lack of tumors in infants with perinatal HIV-1 exposure and fetal/neonatal exposure to zidovudine

Zidovudine (ZDV) therapy during pregnancy and to the neonate reduced perinatal HIV transmission by nearly 70% in Pediatric AIDS Clinical Trials Group (PACTG) protocol 076. ZDV has been reported as positive in several in vitro carcinogenicity screening tests. We evaluated the short-term risk for tumors in 727 children with known ZDV exposure enrolled into the PACTG 076/219 and the Women and Infants Transmission Study (WITS). ZDV exposure in utero (antepartum) occurred in 97% and 99% of infants in PACTG 076/219 or WITS, respectively. Mean follow-up was 38.3 months with 366.9 person years follow-up for PACTG 076/219 and 14.5 months with 743.7 person years follow-up for WITS. No tumors of any nature were observed; relative risk was 0 (95% confidence interval [CI], 0-17.6). These data are reassuring regarding the short-term lack of tumors for ZDV-exposed infants observed to date. Longitudinal, standardized follow-up for infants with in utero antiretroviral exposure is necessary to assess long-term carcinogenicity.

Maternal and perinatal factors related to maternal-infant transmission of HIV-1 in the P2C2 HIV study: the role of EBV shedding. Pediatric Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV-1 Infection (P2C2 HIV) Study Group

The association of maternal and perinatal factors with mother-infant transmission of HIV-1 was examined in a prospective multicenter cohort of singleton live births to 508 HIV-1-infected women with children of known HIV-1 infection status (91 [18%] HIV-1-infected, 417 [82%] uninfected). From multivariate logistic regression, independent predictors of HIV-1 transmission included maternal CD4 percentage (CD4%) (odds ratio [OR] per 10% increase in CD4% = 0.70; p = .003), ruptured membranes <24 hours (OR = 3.15; p = .02), and maternal bleeding (OR = 2.90; p = .03), whereas maternal zidovudine (ZDV) use was marginally associated (OR = 0.60; p = .08). The associations of maternal urinary cytomegalovirus (CMV) shedding, oropharyngeal Epstein-Barr virus (EBV) shedding, and serology profiles during pregnancy with HIV-1 transmission were examined in the subset of mothers in whom the CMV and EBV measurements were available. Maternal EBV seropositivity, CMV shedding, and CMV seropositivity were 100% (279 of 279), 7% (16 of 229), and 92% (270 of 274), respectively. These rates did not differ between transmitting and nontransmitting mothers. In univariate analyses, maternal EBV shedding was higher among transmitting than nontransmitting mothers (40 of 49 [82%] compared with 154 of 226 [68%]; p = .06) and was independently associated with transmission in multivariate logistic analyses adjusting for CD4%, ruptured membranes, and ZDV use, with an OR of 2.45 (95% confidence interval (CI), 1.03-5.84; p = .04). This permits the conclusion that EBV shedding is associated with maternal-infant HIV-1 transmission, independent of CD4%.

Dumping syndrome in a young Jamaican child

The dumping syndrome in childhood is an uncommon complication of gastro-oesophageal surgery, principally Nissen fundoplication. A Jamaican child developed the syndrome after fundoplication and pyloroplasty to relieve gastro-oesophageal reflux complicating the repair of a congenital tracheo-oesophageal fistula. He developed marasmus and failed to gain weight on the standard remedial milk-based high-energy diet. An oral glucose tolerance test confirmed the diagnosis of dumping syndrome. A low sugar low milk diet based on adult type meals with continuous nibbling of fried dumplings relieved his diarrhoea and hypoglycaemia and he gained weight. This is a cheaper and more practical dietary therapy than the regimens described previously.

Growth of human osteoblast-like cells on alkanethiol on gold self-assembled monolayers: the effect of surface chemistry

Primary human osteoblasts were cultured on self-assembled monolayers (SAMs) of alkylthiols on gold with carboxylic acid and methyl termini, and the kinetics of cell attachment and proliferation were measured. Over 90 min approximately twice as many cells attached to carboxylic-acid-terminated monolayers as attached to methyl-terminated monolayers. After 24 h the number of cells attached to carboxylic-acid-terminated monolayers was ten times that attached to the methyl-terminated monolayers. Cell morphology and cytoskeletal actin organization also were found to be different. Osteoblasts were cultured on SAMs that were patterned by photolithographic techniques. Cells attached almost exclusively to carboxylic-acid-functionalized areas of the patterned surfaces, leaving methyl-functionalized regions bare. The patterns strongly influenced the morphology of the attached cells. After 24 h, cells were observed to bridge between carboxylic-acid-terminated regions separated by 75 microns, methyl-terminated regions but not those separated by 150 microns methyl-terminated regions. After 6 days in culture osteoblasts formed multilayers on the carboxylic-acid-terminated regions of the pattern.

Neuronal nicotinic acetylcholine receptors are blocked by intracellular spermine in a voltage-dependent manner

A common feature of neuronal nicotinic acetylcholine receptors (nAChRs) is that they conduct inward current at negative membrane potentials but little outward current at positive membrane potentials, a property referred to as inward rectification. Physiologically, inward rectification serves important functions, and the main goal of our study was to investigate the mechanisms underlying the rectification of these receptors. We examined recombinant alpha3beta4 and alpha4beta2 neuronal nAChR subtypes expressed in Xenopus oocytes and native nAChRs expressed on superior cervical ganglion (SCG) neurons. Whole-cell ACh-evoked currents recorded from these receptors exhibited strong inward rectification. In contrast, we showed that single-channel currents from these neuronal nAChRs measured in outside-out patches outwardly rectify. On the basis of recent findings that spermine, a ubiquitous intracellular polyamine, confers rectification to glutamate receptors and inwardly rectifying potassium channels, we investigated whether spermine causes neuronal nAChRs to inwardly rectify. When spermine was added to the patch electrode in outside-out recordings, it caused a concentration- and voltage-dependent block of ACh-evoked single-channel currents. Using these single-channel data and physiological concentrations of intracellular spermine, we could account for the inward rectification of macroscopic whole-cell ACh-evoked conductance-voltage relationships. Therefore, we conclude that the voltage-dependent block by intracellular spermine underlies inward rectification of neuronal nAChRs. We also found that extracellular spermine blocks both alpha3beta4 and alpha4beta2 receptors; this finding points to a mechanism whereby increases in extracellular spermine, perhaps during pathological conditions, could selectively block these receptors.

Credentialing and privileging nurse-midwives

Nurse-midwives are one category of advanced practice nurse increasingly seeking hospital privileges to admit patients on their own recognizance. This article provides a framework for those health care institutions and insurers who are credentialing nurse-midwives. Nurse-midwifery educational preparation, licensure, scope of practice, relationships with collaborative physicians, and professional liability are discussed. Standards of the Joint Commission on Accreditation of Healthcare Organizations that pertain to credentialing and privileging nonphysician providers are reviewed. Various privileging routes are explored and directions recommended.

Salmeterol inhibition of mediator release from human lung mast cells by beta-adrenoceptor-dependent and independent mechanisms

1. The long-acting beta2-adrenoceptor agonist, salmeterol (10(-9)-10(-5) M), inhibited the IgE-mediated release of histamine from human lung mast cells (HLMC) in a dose-dependent fashion. Additional beta-adrenoceptor agonists were studied and the rank order of potency for the inhibition of histamine release from HLMC was isoprenaline > salmeterol > salbutamol. Approximate EC50 values for the inhibition of histamine release were 10 nM for isoprenaline and 100 nM for salbutamol. An EC50 value for salmeterol could not be calculated because maximal responses to salmeterol were not observed over the concentration range employed. 2. Both salmeterol and isoprenaline inhibited the generation of sulphopeptidoleukotrienes (sLT) more potently and more efficaciously than the release of histamine from immunologically-activated HLMC. Salmeterol (EC50 < 0.1 nM) was more potent than isoprenaline (EC50 0.4 nM) at attenuating sLT generation. 3. The beta-adrenoceptor antagonist, propranolol (1 microM), and the selective beta2-adrenoceptor antagonist, ICI 118,551 (0.1 microM), both caused rightward shifts in the dose-response curve for the inhibition of histamine release by isoprenaline. The antagonism of salmeterol effects by propranolol and ICI 118,551 was more complex. At lower concentrations (< 1 microM) of salmeterol, both antagonists shifted the dose-reponse curve to salmeterol rightward. At a higher concentration (10 microM) of salmeterol, neither ICI 118,551 nor propranolol was an effective antagonist of the salmeterol-mediated inhibition of histamine release. 4. Prolonged exposure (4 h) of HLMC to isoprenaline (1 microM) caused an approximately 50% reduction in the effectiveness of a second exposure to isoprenaline (10 microM) at inhibiting the release of histamine. whereas this pretreatment did not affect the salmeterol (10 microM) inhibition of histamine release. 5. Isoprenaline (10(-9)-10(-5) M) caused a dose-dependent increase in total cell cyclicAMP levels in purified HLMC which paralleled the inhibition of histamine release. Salmeterol (10(-9)-10(-5) M) was considerably less potent than isoprenaline at increasing HLMC cyclicAMP levels. 6. In summary, these data indicate that salmeterol is an effective inhibitor of the stimulated release of mediators from HLMC. The present data also suggest that salmeterol may act to inhibit mediator release from HLMC by beta-adrenoceptor-dependent and independent mechanisms.

HIV vertical transmission rate determinations are subject to differing definitions and therefore different rates. The Pediatric Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV Infection Study Group

The HIV infection status of a cohort of 600 prospectively followed children born to HIV infected mothers was determined using HIV peripheral blood culture tests at 0, 3, and 6 months of age, HIV serology at > or = 15 months, and CDC AIDS criteria. We estimated transmission rates using five methods which differed in how HIV indeterminates are handled. These methods were applied at two points in time to illustrate effects of length of follow-up of the cohort on results. In January 1997, 30 months after the last birth, transmission rate estimates ranged from 15.5% (known positives/known positives x known negatives) to 18.1% (known positives x those with one positive culture x deaths/entire cohort minus those lacking negative cultures at age > or = 5 months). Estimates ranged from 14.8% to 20.7% using the subcohort of 284 children followed > or = 12 months as of May 1993. These results indicate that methods for assigning HIV infection status and for handling HIV indeterminates should be carefully defined when estimating transmission rates.

Lymphocyte phenotyping in infants: maturation of lymphocyte subpopulations and the effects of HIV infection

Changes in the distribution of lymphocyte subpopulations in infants with perinatally acquired HIV infection are confounded by the rapid changes that are the result of normal maturation of the immune system. We describe the changes in seven lymphocyte phenotypes (CD3+ CD4+, CD3+ CD8+, CD8+ HLA- DR+, CD8+ CD38+, CD8+ CD57+, CD3-/ CD16+ 56+, and CD19+) over the first 2 years of life in 390 HIV-1 exposed but uninfected and 98 HIV-1-infected infants enrolled in the Women and Infants Transmission Study. The greatest changes in uninfected infants were declines in the CD3+ CD4+ lymphocytes and increases in CD8+ HLA- DR+ and CD19+ lymphocytes. All phenotypes were affected by HIV infection but the greatest changes were declines in the CD3+ CD4+ subset and increases in the CD3+ CD8+ and CD8+ HLA- DR+ subsets. Thus, this study provides reference data for the maturational changes in lymphocyte phenotypes in HIV-exposed but uninfected infants and describes the overall changes that occur with perinatally acquired HIV infection.

Developing neonatal rat sympathetic and sensory neurons differ in their regulation of 5-HT3 receptor expression

Serotonin 5-HT3 receptors (5-HT3Rs) are ligand-gated ion channels expressed by many peripheral neurons and are involved in several physiological processes. To learn more about the developmental regulation of 5-HT3R expression, we investigated rat sympathetic and vagal sensory neurons. We found that sympathetic and sensory neurons differ in their regulation of 5-HT3R expression during early postnatal life and as these neurons develop in culture. In SCG neurons 5-HT3R transcript levels are low at postnatal day 1 (P1) and increase 7.5-fold by P21; this increase occurs even after elimination of preganglionic innervation. In comparison, 5-HT3R mRNA levels in P1 nodose neurons are over 14-fold greater than in P1 SCG and change little by P21. We show that 5-HT3R transcript levels in nodose neurons depend on intact target innervation and drop by 60% after axotomy. When P1 SCG neurons develop in culture, we observed a significant increase in 5-HT3R expression: after 7 d in culture, transcript levels increase ninefold versus a threefold increase for neurons developing for 7 d in vivo. In contrast, 5-HT3R mRNA levels in cultured nodose neurons drop by 70% within 24 hr; however, this drop is transient. After 2 d, transcript levels begin to increase, and after 7 d, they are above initial values. We show that this delayed increase in 5-HT3R expression depends on neurotrophins. In both nodose and sympathetic neurons we found that the changes in 5-HT3R gene expression correlate directly with the appearance of 5-HT-evoked current densities.

Elevated CD8+DR+ lymphocytes in HIV-exposed infants with early positive HIV cultures: a possible early marker of intrauterine transmission. Women and Infants Transmission Study Group

The associations among timing of maternal-fetal human immunodeficiency virus (HIV) transmission, infant age at first positive HIV culture, and CD8+ lymphocyte activation were examined for 74 perinatally infected infants. Nineteen of the infected infants had positive HIV cultures at < or =7 days of life, and 55 had negative HIV cultures at < or =7 days but were positive later. Of the infants with early positive HIV-1 cultures, 15 of the 17 tested with DNA polymerase chain reaction methods had concordant results. The percentage of CD8+ and HLA-DR+ lymphocytes (CD8+DR+%) during the first week of life was significantly higher in infants with early compared with late positive cultures (median CD8+DR+% of 5.0% versus 2.0%, p = 0.0006). The CD8+DR+% was similar between uninfected infants and infants with late positive cultures during the first week of life (median 2%) but increased in infants with late positive cultures to 6% by 1 month. The CD4+% during the first 6 months of life was not different between infants with early or with late positive cultures, but infants with the highest CD8+DR+% at < or =7 days of life had significantly lower CD4+% at < or =7 days and at 1, 2, and 4 months of age. These data show that early CD8+ lymphocyte activation is associated with early positive HIV cultures and lower CD4+ percentages during early infancy and are consistent with the hypothesis that early positive cultures positivity may indicate in utero HIV infection.

Adenovirus-mediated gene transfer of the tumor suppressor, p53, induces apoptosis in postmitotic neurons

Programmed cell death is an ongoing process in both the developing and the mature nervous system. The tumor suppressor gene, p53, can induce apoptosis in a number of different cell types. Recently, the enhanced expression of p53 has been observed during acute neurological disease. To determine whether p53 overexpression could influence neuronal survival, we used a recombinant adenovirus vector carrying wild type p53 to transduce postmitotic neurons. A control consisting of the same adenovirus vector background but carrying the lacZ reporter expression cassette was used to establish working parameters for the effective genetic manipulation of sympathetic neurons. We have found that recombinant adenovirus can be used at titers sufficiently high (10 to 50 multiplicity of infection) to transduce the majority of the neuronal population without perturbing survival, electrophysiological function, or cytoarchitecture. Moreover, we demonstrate that overexpression of wild type p53 is sufficient to induce programmed cell death in neurons. The observation that p53 is capable of inducing apoptosis in postmitotic neurons has major implications for the mechanisms of cell death in the traumatized mature nervous system.

Diagnosis of infection with human immunodeficiency virus type 1 by a DNA polymerase chain reaction assay among infants enrolled in the Women and Infants' Transmission Study

Early diagnosis of infection with human immunodeficiency virus type 1 (HIV- 1) in young infants is essential to decisions on their medical and social care. Whereas studies have suggested that polymerase chain reaction (PCR) is a sensitive and timely method of diagnosing HIV infection in children, these evaluations have been limited by the number of specimens studied. Recently, Roche Molecular Systems developed a complete HIV-1 DNA PCR testing kit (from specimen preparation to detection). In this study, use of this PCR test kit was evaluated for the detection of HIV infection in infants of seropositive mothers who were enrolled in the longitudinal, multicenter Women and Infants' Transmission Study. A total of 1209 blood specimens from 483 infants were tested and analyzed. The overall sensitivity and specificity of a single PCR test in determining HIV infection status in infants more than 1 but less than 36 months of age were 95% and 97%, respectively. For infected infants 1 to 6 months of age the sensitivity of the DNA-PCR test was 90% to 100%. In a direct comparison with coculture, the Roche DNA-PCR test was significantly more sensitive than coculture in the detection of HIV-1 in infected infants and was equivalent to coculture for the diagnosis of HIV in infants when a standardized algorithm was used to define infection status.

Formulation and antitumor activity evaluation of nanocrystalline suspensions of poorly soluble anticancer drugs

PURPOSE

Determine if wet milling technology could be used to formulate water insoluble antitumor agents as stabilized nanocrystalline drug suspensions that retain biological effectiveness following intravenous injection.

METHODS

The versatility of the approach is demonstrated by evaluation of four poorly water soluble chemotherapeutic agents that exhibit diverse chemistries and mechanisms of action. The compounds selected were: piposulfan (alkylating agent), etoposide (topoisomerase II inhibitor), camptothecin (topoisomerase I inhibitor) and paclitaxel (antimitotic agent). The agents were wet milled as a 2% w/v solids suspension containing 1% w/v surfactant stabilizer using a low energy ball mill. The size, physical stability and efficacy of the nanocrystalline suspensions were evaluated.

RESULTS

The data show the feasibility of formulating poorly water soluble anticancer agents as physically stable aqueous nanocrystalline suspensions. The suspensions are physically stable and efficacious following intravenous injection.

CONCLUSIONS

Wet milling technology is a feasible approach for formulating poorly water soluble chemotherapeutic agents that may offer a number of advantages over a more classical approach.

A novel neuronal P2x ATP receptor ion channel with widespread distribution in the brain

There is strong evidence that ATP acts as an excitatory neurotransmitter in the periphery, yet little is known about fast central ATP-mediated transmission. We report here the molecular cloning of a novel neuronal ionotropic ATP receptor of the P2x subtype (P2x3) isolated from rat brain. This central P2x channel subunit has significant amino acid homology with two recently cloned ATP-gated channels from rat smooth muscle (47%) and pheochromocytoma PC12 cells (37%). P2x3 receptor contains the characteristic 10 conserved cysteines of ATP-gated channels, a putative extracellular region homologous to the Walker type A motif found in various nucleotide-binding proteins, and two potential sites for phosphorylation by protein kinase C. Homomeric receptor P2x3 channels expressed in Xenopus oocytes produce rapid cation-selective purinergic currents that are potentiated by zinc ions and reversibly blocked by the P2x antagonists suramin, Reactive Blue 2, and pyridoxalphosphate-6-axophenyl-2U,4U-disulfonic acid. P2x3-receptor subunit mRNA is found in the Purkinje cells and the granule cells of the cerebellum as well as in CA3 pyramidal cells of the hippocampus that are innervated by zinc-rich axon terminals of mossy fibers. Our results suggest that fast excitatory synaptic transmission mediated by zinc-sensitive ATP-gated channels is widespread in mammalian brain.

Differential regulation of neuronal nicotinic ACh receptor subunit genes in cultured neonatal rat sympathetic neurons: specific induction of alpha 7 by membrane depolarization through a Ca2+/calmodulin-dependent kinase pathway

We have examined the regulation of neuronal nicotinic ACh receptor (nAChR) genes and ACh-evoked currents by neonatal rat sympathetic neurons developing in culture. These neurons contain 5 nAChR transcripts: alpha 3, alpha 5, alpha 7, beta 2, and beta 4. When developing in culture, the neurons express 4 of these transcripts, alpha 3, alpha 5, beta 2, and beta 4, at levels similar to those in neurons developing in vivo: alpha 3 mRNA levels increase two- to threefold over the first week, whereas the levels for alpha 5, beta 2, and beta 4 remain essentially constant. In contrast, alpha 7 mRNA levels drop by 60-75% within the first 48 hr and remain low. We show that during the first week, the ACh-evoked current densities on these cultured neurons increase twofold and correlate well with the increase in alpha 3 mRNA levels. Depolarizing the neurons with 40 mM KCl for 1-2 d upregulates the alpha 7 gene; this specific change in alpha 7 mRNA level correlates with an increase in alpha-bungarotoxin (alpha-BTX) binding on the surface of the neurons. Depolarization has little effect on the expression of the other four transcripts, or on the magnitude or kinetics of the ACh-evoked currents. Furthermore, activators or inhibitors of protein kinase A (PKA), protein kinase C (PKC), or tyrosine kinase do not affect nAChR transcript levels in these cultured neurons. The effect of membrane depolarization on alpha 7 expression is a result of Ca2+ influx through L-type Ca2+ channels, and we show that alpha 7 is upregulated through a Ca2+/calmodulin-dependent protein kinase (CaM kinase) pathway. The identification of CaM kinase as a link between activity and neurotransmitter receptor expression may indicate a novel mechanism that underlies some forms of synaptic plasticity.

Fifty years on: Colin Davis interviews Eric Cooper. Interview by Colin Davis

Just over 50 years ago, Eric Cooper was released from the gloomy fortress castle of Colditz after almost 4 years as a prisoner of war. He recently retired to a small village near Yarmouth on the Isle of Wight where his garden looks out over a great sweep of cornland with the long line of the chalk downs in the distance. It is impossible to imagine two more contrasted pictures and I was eager to find out about the old warrior's odyssey as we sat sipping sherry and looking out to that incomparable view.

Agonist and toxin sensitivities of ACh-evoked currents on neurons expressing multiple nicotinic ACh receptor subunits

1. We have investigated the pharmacological properties of functional nicotinic acetylcholine receptors (nAChRs) on neonatal rat sympathetic neurons from the superior cervical ganglion (SCG) to learn more about the subunit composition of these receptors. These neurons express five nAChR transcripts: alpha 3, alpha 5, alpha 7, beta 2, and beta 4; this finding suggests that SCG neurons may express several different, physiologically distinct, subtypes of nAChRs. 2. To identify potential subtypes, we have characterized currents evoked by different nicotinic agonists and determined their sensitivity to blockade by alpha-bungarotoxin (alpha-BTX) and by neuronal bungarotoxin (n-BTX). From dose-response curves, we find that the ED50 for both cytisine and dimethylphenylpiperazinium (DMPP) is 20 microM and for ACh is 52 microM. n-BTX blocks the ACh-gated currents rapidly, but the kinetics for n-BTX removal is dependent on the duration of the application: brief applications were quickly reversible, whereas prolonged applications took orders of magnitude longer to reverse. 3. Using fast (ms) agonist application, we observed no rapidly desensitizing currents despite the high levels of alpha 7 in these neurons, nor did we observe any currents that could be blocked by alpha-BTX. 4. Using Xenopus oocytes expressing alpha 7 receptors, we show that choline evokes a significant current that is blocked by alpha-BTX. In contrast, choline is much less potent on alpha 3 beta 4 receptors expressed in Xenopus oocytes. Choline can also act as a weak agonist for nAChRs on rat SCG neurons, but its evoked current is not blocked by alpha-BTX. 5. Our results indicate that, when measured at the macroscopic level, most functional nAChRs on SCG neurons behave as a uniform population of receptors, at least with respect to agonist activation and toxin blockade. In comparison with known receptors expressed in heterologous systems, the physiological properties of ACh-evoked currents on SCG neurons are most similar to receptors that have coassembled with both beta 2 and beta 4.