The interrelationship of alpha4 integrin and matrix metalloproteinase-2 in the pathogenesis of experimental autoimmune encephalomyelitis

Previous studies have suggested that surface expression of alpha4 integrin by autoreactive T-cell clones is necessary for the clones to induce experimental autoimmune encephalomyelitis (EAE), a mouse model for human multiple sclerosis. To provide direct evidence for this phenomenon, we have transfected alpha4 integrin into C19alpha4-LO, a myelin basic protein-reactive T-cell clone that does not express alpha4 integrin and does not induce EAE when adoptively transferred into a susceptible mouse strain. Transfection of alpha4 integrin converted this clone to an alpha4 integrin-expressing clone that induced EAE. We then examined potential mechanisms by which alpha4 integrin may facilitate the disease process. C19 T-cell clones adhered equally to a monolayer of microvascular endothelial cells, regardless of level of alpha4 integrin expression. However, in contrast to T-cell clones that do not express alpha4 integrin, T-cell clones that express alpha4 integrin (endogenously or by transfection) transmigrated through an endothelial cell layer and subendothelial matrix at an enhanced rate and adhered to recombinant vascular cell adhesion molecule-1 (rVCAM-1) and the CS1 fragment of fibronectin, and after adhesion to these ligands, a matrix-degrading metalloproteinase (MMP-2) was induced and activated. The clones were also shown to constitutively express the membrane-type matrix metalloproteinase (MT1-MMP), an enzyme that activates MMP-2. GM6001 and UK-221,316, inhibitors of metalloproteinases, reduced alpha4 integrin-mediated transmigration and EAE induction by C19 T-cell clones. In addition, we studied a second EAE-inducing T-cell clone, MM4, which constitutively expresses alpha4 integrin and MMP-2. Engagement of alpha4 integrin on the MM4 clone up-regulated the expression and activation of MMP-2, without changing the expression of MT1-MMP. MMP inhibitors also reduced transmigration of and EAE induction by the MM4 T-cell clone. These studies demonstrate directly that expression of alpha4 integrin by autoreactive T-cell clones is required for adoptive transfer of EAE in this model. We also define a role for alpha4 integrin in the disease process in mediating the induction and coordinate activation of a matrix metalloproteinase (MMP-2), which facilitates T-cell transmigration.

Desensitization of beta2-adrenergic receptors with mutations of the proposed G protein-coupled receptor kinase phosphorylation sites

Tentative identification of the G protein-coupled receptor kinase 2 and 5 (GRK2 and GRK5) sites of phosphorylation of the beta2-adrenergic receptor (betaAR) was recently reported based on in vitro phosphorylation of recombinant receptor (Fredericks, Z. L., Pitcher, J. A., and Lefkowitz, R. J. (1996) J. Biol. Chem. 271, 13796-13803). Phosphorylated residues identified for GRK2 were threonine 384 and serines 396, 401, and 407. GRK5 phosphorylated these four residues as well as threonine 393 and serine 411. To determine if mutation of these sites altered desensitization, we have constructed betaARs in which the threonines and serines of the putative GRK2 and GRK5 sites were substituted with alanines. These constructs were further modified to eliminate the cAMP-dependent protein kinase (PKA) consensus sites. Mutants betaARs were transfected into HEK 293 cells, and standard kinetic parameters were measured following 10 microM epinephrine treatment of cells. The mutant and wild type (WT) receptors were all desensitized 89-94% after 5 min of 10 microM epinephrine stimulation and 96-98% after a 30-min pretreatment. There were no significant changes observed for any of the mutant betaARs relative to the WT in the extent of 10 microM epinephrine-induced internalization (77-82% after 30 min). Epinephrine treatment for 1 min induced a rapid increase in the phosphorylation of the GRK5 and PKA- mutant betaARs as well as the WT. We conclude that sites other than the GRK2 and GRK5 sites identified by in vitro phosphorylation are involved in mediating the major effects of the in vivo GRK-dependent desensitization of the betaAR.

A method for visualization of ventricular fibrillation: Design of a cooled fiberoptically coupled image intensified CCD data acquisition system incorporating wavelet shrinkage based adaptive filtering

The measurement of cardiac transmembrane potential changes with voltage sensitive dyes is in increasing use. Detection of these very small fluorescent alterations using large multiplexed arrays, such as charge coupled device (CCD) cameras at high sampling rates, has proven challenging and usually requires significant averaging to improve the signal-to-noise ratio. To minimize the damage of living tissue stained with voltage sensitive dyes, excitation photon exposure must be limited, with the inevitable consequence of diminishing the fluorescence that is generated. State-of-the-art high frame rate CCD cameras have read noise levels in the 5-10 e(-) rms range, which is at least two orders of magnitude above that required to detect voltage sensitive dye alterations at individual pixels corresponding to 1 mm(2) heart regions illuminated with levels of 100 mW/cm(2) at frame rates approaching 1000 frames/sec. Image intensification is thus required prior to photon quantification. We report here the development of such a data acquisition system using commercially available hardware. Additionally, in the past ten years, a mathematical theory of multiresolution has been developed, and new building blocks called wavelets, allow a signal to be observed at different resolutions. Wavelet analysis also makes possible a new method of extricating signals from noise. We have incorporated spatially adaptive filters based on wavelet denoising of individual pixels to significantly reduce the multiple noise sources present in the acquired data. (c) 1998 American Institute of Physics.

Salmeterol-induced desensitization, internalization and phosphorylation of the human beta2-adrenoceptor

1. Partial agonists of the beta2-adrenoceptor which activate adenylyl cyclase are widely used as bronchodilators for the relief of bronchoconstriction accompanying many disease conditions, including bronchial asthma. The bronchodilator salmeterol has both a prolonged duration of action in bronchial tissue and the ability to reassert this activity following the temporary blockade of human beta2-adrenoceptors with antagonist. 2. We have compared the activation and desensitization of human beta2-adrenoceptor stimulation of adenylyl cyclase induced by salmeterol, adrenaline and salbutamol in a human lung epithelial line, BEAS-2B, expressing beta2-adrenoceptor levels of 40-70 fmol mg(-1), and in human embryonic kidney (HEK) 293 cell lines expressing 2-10 pmol mg(-1). The efficacy observed for the stimulation of adenylyl cyclase by salmeterol was only approximately 10% of that observed for adrenaline in BEAS-2B cells expressing low levels of beta2-adrenoceptor, but similar to adrenaline in HEK 293 cells expressing very high levels of receptors. Salmeterol pretreatment of these cells induced a rapid and stable activation of adenylyl cyclase activity which resisted extensive washing and beta2-adrenoceptor antagonist blockade, consistent with binding to a receptor exosite and/or to partitioning into membrane lipid. 3. The desensitization and internalization of beta2-adrenoceptors induced by the partial agonists salmeterol and salbutamol were considerably reduced relative to the action of adrenaline. Consistent with these observations, the initial rate of phosphorylation of the receptor induced by salmeterol and salbutamol was much reduced in comparison to adrenaline. 4. Our data suggest that the reduction in the rapid phase of desensitization of beta2-adrenoceptors after treatment with salmeterol or salbutamol is caused by a decrease in the rate of beta2-adrenoceptor kinase (betaARK) phosphorylation and internalization. In contrast, the rate of cyclic AMP-dependent protein kinase (PKA)-mediated phosphorylation by these partial agonists appears to be similar to adrenaline.

Adoptively transferred EAE in gamma delta T cell-knockout mice

Recently there has been evidence suggesting that gamma delta receptor-bearing T cells may play a role in both multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). We have recently described approaches for the generation of encephalitogenic T-cell populations from EAE-resistant strains of mice. Using encephalitogenic T-cell lines and clones generated from wild-type C57BL/6 mice we have studied adoptively transferred EAE in C57BL/6-TCR delta-knockout mice. We now report that the adoptive transfer of encephalitogenic T cells into TCR delta T-knockout mice leads to clinical EAE that is not significantly different in severity or time course than that seen after transfer into wild-type C57BL/6 mice. We conclude that gamma delta T cells do not play an integral role in the mediation or regulation of the effector-phase mechanisms in EAE.

Mathematical model of an adult human atrial cell: the role of K+ currents in repolarization

We have developed a mathematical model of the human atria myocyte based on averaged voltage-clamp data recorded from isolated single myocytes. Our model consists of a Hodgkin-Huxley-type equivalent circuit for the sarcolemma, coupled with a fluid compartment model, which accounts for changes in ionic concentrations in the cytoplasm as well as in the sarcoplasmic reticulum. This formulation can reconstruct action potential data that are representative of recordings from a majority of human atrial cells in our laboratory and therefore provides a biophysically based account of the underlying ionic currents. This work is based in part on a previous model of the rabbit atrial myocyte published by our group and was motivated by differences in some of the repolarizing currents between human and rabbit atrium. We have therefore given particular attention to the sustained outward K+ current (I[sus]), which putatively has a prominent role in determining the duration of the human atrial action potential. Our results demonstrate that the action potential shape during the peak and plateau phases is determined primarily by transient outward K+ current, I(sus) and L-type Ca2+ current (I[Ca,L]) and that the role of I(sus) in the human atrial action potential can be modulated by the baseline sizes of I(Ca,L), I(sus) and the rapid delayed rectifier K+ current. As a result, our simulations suggest that the functional role of I(sus) can depend on the physiological/disease state of the cell.

Adoptively transferred EAE in mice bearing the lpr mutation

We have recently developed approaches for the generation of encephalitogenic T cell clones from mouse strains considered resistant to experimental allergic encephalomyelitis (EAE). By allowing for the direct use of knockout and mutant strains of mice, such clones allow for the efficient characterization of the relevance of specific gene products in the effector phase of EAE. Recent studies have suggested that Fas/FasL-mediated cell death may play a role in the pathogenesis of MS. To assess the role of Fas/FasL in EAE, we have tested the ability of wild-type C57BL/6-derived, encephalitogenic T cell clones to mediate adoptively transferred EAE in Fas-deficient C57BL/6-lpr mice. We now report that mice with the lpr mutation are fully susceptible to the adoptive transfer of EAE. Our results suggest that Fas/FasL-mediated cell death in the central nervous system does not play an integral role in the effector phase of acute EAE.

Voltage-sensitive dye recordings of electrophysiological activation in a Langendorff-perfused mouse heart

The pattern of electrophysiological activation of adult mouse ventricles was measured with the use of voltage-sensitive dye methods. Di-4-ANEPPS was used to monitor membrane potential as small changes in fluorescence, which were detected by a state of the art, cooled, charged coupled device camera/image intensifier system. The extremely rapid conduction velocity, coupled with the small size of this preparation, necessitated taking these measurements at room temperature (22 to 23 degrees C). Initial experiments demonstrate that ventricular activation can be identified and its conduction pattern can be monitored reproducibly and with high resolution for extended time periods (10 to 20 mins) during spontaneous activity.

A rapidly activating sustained K+ current modulates repolarization and excitation-contraction coupling in adult mouse ventricle

1. The K+ currents which control repolarization in adult mouse ventricle, and the effects of changes in action potential duration on excitation-contraction coupling in this tissue, have been studied with electrophysiological methods using single cell preparations and by recording mechanical parameters from an in vitro working heart preparation. 2. Under conditions where Ca(2+)-dependent currents were eliminated by buffering intracellular Ca2+ with EGTA, depolarizing voltage steps elicited two rapidly activating outward K+ currents: (i) a transient outward current, and (ii) a slowly inactivating or 'sustained' delayed rectifier. 3. These two currents were separated pharmacologically by the K+ channel blocker 4-amino-pyridine (4-AP). 4-AP at concentrations between 3 and 200 microM resulted in (i) a marked increase in action potential duration and a large decrease in the sustained K+ current at plateau potentials, as well as (ii) a significant increase in left ventricular systolic pressure in the working heart preparation. 4. The current-voltage (I-V) relation, kinetics, and block by low concentrations of 4-AP strongly suggest that the rapid delayed rectifier in adult mouse ventricles is the same K+ current (Kv1.5) that has been characterized in detail in human and canine atria. 5. These results show that the 4-AP-sensitive rapid delayed rectifier is a very important repolarizing current in mouse ventricle. The enhanced contractility produced by 4-AP (50 microM) in the working heart preparation demonstrates that modulation of the action potential duration, by blocking a K+ current, is a very significant inotropic variable.

The generation of encephalitogenic T cell lines from experimental allergic encephalomyelitis-resistant strains of mice

While only a few strains of mice are susceptible to the primary induction or passive transfer of experimental allergic encephalomyelitis (EAE), the basis of EAE resistance remains unclear. In the present studies, we have defined two approaches that allow for the generation of encephalitogenic, myelin basic protein-reactive, T cell lines from EAE-resistant strains of mice. The first approach, based on the putative relevance of apoptosis to autoimmune disease, involves repeat antigenic stimulation of recently initiated T cell lines. The second approach involves the initiation of lymph node cultures in the absence of exogenous splenocytes as antigenic-presenting cells and the use of a higher antigen concentration. Both approaches lead to the generation of encephalitogenic T cell lines from EAE-resistant mouse strains and will be useful for identifying factors relevant to the pathogenesis of EAE.

beta2-adrenergic receptor desensitization, internalization, and phosphorylation in response to full and partial agonists

Previous studies indicated that partial agonists cause less desensitization of the beta2-adrenergic receptor (betaAR) than full agonists; however, the molecular basis for this in intact cells has not been investigated. In the present work, we have determined the rates of desensitization, internalization, and phosphorylation caused by a series of betaAR agonists displaying a 95-fold range of coupling efficiencies. These studies were performed with HEK-293 cells overexpressing the betaAR with hemagglutinin and 6-histidine epitopes introduced into the N and C termini, respectively. This modified betaAR behaved identically to the wild type receptor with regard to agonist Kd, coupling efficiency, and desensitization. The coupling efficiencies for betaAR agonist activation of adenylyl cyclase relative to epinephrine (100%) were 42% for fenoterol, 4.9% for albuterol, 2.5% for dobutamine, and 1.1% for ephedrine. At concentrations of these agonists yielding >90% receptor occupancy, the rate and extent (0-30 min) of agonist-induced desensitization of betaAR activation of adenylyl cyclase followed the same order as coupling efficiency, i.e. epinephrine >/= fenoterol > albuterol > dobutamine > ephedrine. The rate of internalization of the betaAR with respect to these agonists also followed the same order as the desensitization and exhibited a slight lag. Like internalization and desensitization, betaAR phosphorylation exhibited a dependence on agonist strength. The two strongest agonists, epinephrine and fenoterol, provoked 11-13-fold increases in the level of betaAR phosphorylation after just 1 min, whereas the weak agonists dobutamine and ephedrine caused only 3-4-fold increases, similar to levels induced by cAMP-dependent protein kinase activation with forskolin. With longer treatment times, the level of betaAR phosphorylation declined with strong agonists, but it progressively increased with the weaker partial agonists, such that after 30 min the -fold elevation with epinephrine (6.2 +/- 0.82) was not appreciably different from ephedrine (5.0 +/- 0.96) and significantly less than that caused by albuterol (10.4 +/- 1.7). In summary, our results demonstrate an excellent proportionality between the agonist strength and agonist-induced desensitization, internalization, and the rapid initial phase of phosphorylation. The data support the hypothesis that increasing agonist-coupling efficiency primarily affects desensitization by increasing the rate of betaARK phosphorylation of the betaAR.

Evidence for the shuttle model for Gs alpha activation of adenylyl cyclase

Knowledge of the nature of the interaction between the stimulatory G protein (Gs) and the adenylyl cyclase catalytic unit (C) is essential for interpreting the effects of Gs mutations and expression levels on cellular response to a wide variety of hormones, drugs, and neurotransmitters. It has been proposed that beta-adrenergic receptor activation of adenylyl cyclase occurs either by a two-step "shuttle" mechanism where the receptor activates Gs independently of cyclase followed by Gs alpha activation of cyclase independent of the receptor; or the receptor activates a "precoupled" Gs-C complex in a single step. Simulations of the two models revealed that the two forms of activation are distinguishable by the effect of Gs levels on epinephrine-stimulated EC50 values for cyclase activation; specifically, the shuttle model predicts an increased potency of epinephrine stimulation as levels of Gs alpha increase. To address this problem, S49 cyc- cells were stably transfected with the gene for Gs alpha(long) regulated by the MMTV LTR promoter, which allowed for an induction of Gs alpha(long) expression levels over a 40-fold range by incubation of the cells for various times with 5 microM dexamethasone. Expression of Gs alpha was strongly correlated to the appearance of GTP shifts in the competitive binding of epinephrine with [125I]iodocyanopindolol to the beta-adrenergic receptors and epinephrine-stimulated adenylyl cyclase activity. Most importantly, high expression of Gs alpha resulted in lower EC50 values for epinephrine and prostaglandin E1 stimulation of adenylyl cyclase activity. The decrease in EC50 did not occur as a result of a change in beta2-adrenergic receptor, Gi alpha, G betagamma, or adenylyl cyclase levels. These novel findings demonstrate that a change in the level of a protein downstream of a plasma membrane receptor can influence hormone potency. We explain these results by using kinetic arguments to suggest that some fraction of hormone-activated adenylyl cyclase occurs via a shuttle mechanism, and not a purely precoupled mechanism.

Agonist-induced desensitization, internalization, and phosphorylation of the sst2A somatostatin receptor

Cellular responsiveness to the inhibitory peptide somatostatin (SRIF) or its clinically used analogs can desensitize with agonist exposure. While desensitization of other seven-transmembrane domain receptors is mediated by receptor phosphorylation and/or internalization, the mechanisms mediating SRIF receptor (sst) desensitization are unknown. Therefore, we investigated the susceptibility of the sst2A receptor isotype to ligand-induced desensitization, internalization, and phosphorylation in GH-R2 cells, a clone of pituitary tumor cells overexpressing this receptor. A 30-min exposure of cells to either SRIF or the analog SMS 201-995 (SMS) reduced both the potency and efficacy of agonist inhibition of adenylyl cyclase. Internalization of receptor-bound ligand was rapid (t1/2 = 4 min) and temperature-dependent. SRIF and SMS increased the phosphorylation of the 71-kDa sst2A protein 25-fold within 15 min. Receptor phosphorylation was dependent on both the concentration and time of agonist exposure and was not affected by pertussis toxin pretreatment, indicating that receptor occupancy rather than second messenger formation was required. Receptor phosphorylation was also stimulated by phorbol 12-myristate 13-acetate activation of protein kinase C. Both ligand-stimulated and phorbol 12-myristate 13-acetate-stimulated receptor phosphorylation occurred primarily on serine. These studies are the first demonstration of agonist-dependent desensitization, internalization, and phosphorylation of the sst2A receptor and suggest that phosphorylation may mediate the homologous and heterologous regulation of this receptor.

Thyroid hormone regulates postnatal expression of transient K+ channel isoforms in rat ventricle

1. The ability of thyroid hormone to regulate the postnatal changes of the Ca2+-independent transient outward K+ current (It) was studied in rat ventricular myocytes. 2. In rat ventricle, It is very small at birth and then increases markedly between postnatal days 8 and 20. The time course of this increase in current density is similar to that of a significant rise in plasma thyroid hormone (T3) levels. 3. During early development, the density of expression of It can be altered by changes in thyroid hormone levels. Eight days after birth the density of It measured at +50 mV in control animals is 2.2 +/- 0.4 pA pF(-1). This value is about 3-fold larger (6.5 +/- 0.8 pA pF(-1)) in myocytes from age-matched hyperthyroid animals. When the plasma T3 level in newborn rats is not allowed to increase, or is decreased by making animals hypothyroid, this age-dependent increase in It fails to occur. 4. Using RNase protection assays, Kv4.2 and Kv4.3 mRNA levels were measured in ventricular tissues obtained from age-matched 8-day-old control and hyperthyroid rats. In hyperthyroid animals, where an approximately 3-fold increase in It was identified, increases in the mRNA levels for Kv4.2 and Kv4.3 were 1.6-fold and 2.6-fold, respectively. 5. These results show that thyroid hormone can regulate the development of It in rat ventricle. Direct measurements of It density and mRNA levels as a function of development and thyroid hormone levels also strongly suggest that the Kv4.2 and Kv4.3 channels are essential components of It in rat ventricular cells.

Shal-type channels contribute to the Ca2+-independent transient outward K+ current in rat ventricle

1. The hypothesis that Kv4.2 and Kv4.3 are two of the essential K+ channel isoforms underlying the Ca2+-independent transient outward K+ current (It) in rat ventricle has been tested using a combination of electrophysiological measurements and antisense technology in both native myocytes and a stably transfected mammalian cell line, mouse Ltk- cells (L-cells). 2. The transient outward currents generated by Kv4.2 channels in L-cells exhibit rapid activation and inactivation properties similar to those produced by It in rat ventricular cells. The current-voltage relationships and the voltage dependence of steady-state inactivation are also very similar in these two preparations. However, the recovery from inactivation of Kv4.2 is much slower (time constant, 378 ms) than that of It in rat ventricular cells (58 ms). 3. The K+ current due to Kv4.2 can be blocked by millimolar concentrations of 4-aminopyridine in L-cells; a similar pharmacological response has been observed in rat ventricular myocytes. 4. Quinidine inhibits Kv4.2 in L-cells and It in rat ventricular cells in a similar fashion. In L-cells quinidine reduced the amplitude of Kv4.2 and accelerated its time course of inactivation, suggesting that quinidine may act as an open channel blocker of Kv4.2, as has been described for It in rat ventricle. 5. To provide further independent evidence that Kv4.2 and Kv4.3 channel isoforms contribute to It in rat ventricular cells, the effects of 20-mer antisense phosphorothioate oligodeoxynucleotides directed against Kv4.2 and Kv4.3 mRNAs were examined in ventricular myocytes isolated from 14- and 20-day-old rats, and in L-cells. In both preparations, Kv4.2 antisense pretreatment significantly reduced the transient outward K+ current (by approximately 55-60%). Similar reduction of It was produced by the Kv4.3 antisense oligonucleotide on the 14-day-old rat myocytes. 6. In 14-day rat ventricular cells, combination of Kv4.2 and Kv4.3 antisense oligonucleotides did not produce a significantly larger reduction of It than that observed after pretreatment with either antisense oligonucleotide alone. 7. L-cells stably transfected with Kv4.2 were treated with Kv4.3 antisense oligonucleotide to evaluate the possibility of cross-reactivity between Kv4.3 antisense and Kv4.2 mRNA. This antisense treatment produced no change in It, verifying the lack of cross-reactivity. 8. These biophysical and pharmacological results together with the antisense data show that Kv4.2 and Kv4.3 are essential components of the Ca2+-independent transient outward K+ current, It, in rat ventricular myocytes.

Elevation of intracellular cyclic AMP induces an anergic-like state in Th1 clones

Because elevated intracellular cAMP suppresses T cell receptor (TCR)-mediated effector activity and/or proliferation in response to antigen but does not always affect IL-2-stimulated proliferation, the effects of cAMP on a T lymphocyte response to antigen resemble antigen-induced anergy. To test the hypothesis that elevated cAMP induces anergy in T lymphocytes, we have precultured murine Th1 clones responsive to porcine myelin basic protein (PMBP) with dibutyryl cyclic AMP (dbcAMP) or forskolin and subsequently removed the dbcAMP or forskolin and measured the proliferative response of the clones to antigen and antigen-presenting cells (APC) in the presence or absence of exogenously added interleukin-2 (IL-2). Cells precultured with dbcAMP or forskolin for 3 days did not proliferate or produce IL-2 in response to antigen and APC, but did proliferate to antigen and APC in the presence of IL-2. Cells that had not been stimulated recently with antigen/APC or IL-2 were not affected by dbcAMP, while cells stimulated recently with antigen/APC and IL-2 were susceptible to the anergizing effect of dbcAMP. These observations support the hypothesis that elevation in intracellular cAMP in antigen-activated Th1 clones, prior to subsequent culture with antigen, induces a state of anergy.

Comparative epitope mapping of sera from United States (US) and Japanese patients with bullous pemphigoid (BP) to fusion proteins encoded by BPAG1

Sera from patients with bullous pemphigoid (BP) from the United States (US), Japan, and Britain demonstrate similar reactivity to the major target antigens BPAG1 and BPAG2. The purpose of the present study was to determine if the epitope specificity of circulating autoantibodies in patients with BP from the US and Japan is similar as mapped by binding to fusion proteins encoded by BPAG1. Sera from patients and controls with BP from the US and Japan were assayed for reactivity to intact BPAG1 and BPAG2 by immunoblot, and to fusion proteins encoded by BPAG1 by immunoblot and enzyme-linked immunosorbant assay (ELISA). Significant reactivity to fusion proteins encoded by the carboxyl region (FP 16-8) and coiled-coil region (FP3) was seen in sera from the US and Japanese patients, but not from normal controls from the US or Japan. Sera from US and Japanese patients differed in their response to FP7; namely, the reactivity of sera from US patients but not from Japanese patients to FP7 was significantly different from the reactivity of their respective control sera. The reasons for this difference in reactivity are unknown but may reflect genetic or environmental factors relevant in the generation of an autoantibody response to these target antigens.

Repetitive endocytosis and recycling of the beta 2-adrenergic receptor during agonist-induced steady state redistribution

The human beta 2-adrenergic receptor (beta 2AR) rapidly internalizes after binding agonist, resulting in a dramatic redistribution of receptors from the plasma membrane and into endocytic vesicles. We sought to determine whether intracellular receptors constitute a static pool or represent a fraction of dynamically internalizing and recycling receptors. Using cells expressing a beta 2AR with an epitope tag at its amino-terminal ectodomain, changes in surface receptor levels were measured by flow cytometry and radioligand binding assays. The addition of a saturating level of a strong agonist (isoproterenol) caused the endocytosis of receptors with first-order kinetics (ke for naive cells, 0.222 min-1). After 10 min, the level of surface receptors remained stable at approximately 20% that of untreated cells, even though endocytosis continued with similar kinetics (ke for pretreated cells, 0.258 min-1), suggesting that internalized receptors were cycling in steady state with surface receptors. This prediction was confirmed directly by showing that internalized beta 2ARs recycled to the cell surface in the continued presence of agonist. The calculated transit times (1/k) in the presence of isoproterenol were 3.9 min for endocytosis and 11.2 min for recycling. The endocytic rate constant and the steady state redistribution to the internal pool were much lower after treatment with the partial agonist albuterol, suggesting a correlation between the efficiency of endocytosis and that of receptor coupling to the downstream signal transduction pathway. These findings indicate that in the presence of agonist, beta 2ARs are in a dynamic steady state between the plasma membrane and endosomes that is regulated principally by agonist efficacy.

Imipenem resistance among Acinetobacter baumannii: association with reduced expression of a 33-36 kDa outer membrane protein

The mechanism of imipenem resistance of two Acinetobacter baumannii isolates (A-1 and A-24) was characterized in this study. A spontaneous revertant (A-1 (rev)) derived from isolate A-1 showed susceptibility to imipenem. beta-Lactamase hydrolysis studies showed no evidence of an imipenem hydrolyzing enzyme among A-1, A-24, A-1 (rev), or two other imipenem susceptible A. baumannii isolates. Outer membrane protein (OMP) analysis indicated decreased expression of a 33-36 kDa protein by isolates A-1 and A-24 when compared with A-1 (rev) and the other A. baumannii isolates. In conclusion, decreased expression of a 33-36 kDa OMP is associated with imipenem resistance among A. baumannii.

Action potential duration modulates calcium influx, Na(+)-Ca2+ exchange, and intracellular calcium release in rat ventricular myocytes

The experimental work summarized in this paper and described in more detail in our previous publication demonstrates a very important functional role for Na(+)-Ca2+ exchange in intracellular Ca2+ homeostasis in ventricular myocytes from rat hearts. Ca2+ homeostasis in mammalian cardiac myocytes can be considered to be the result of four interactive processes: (i) Ca2+ influx through L-type Ca2+ channels, (ii) Ca2+ release from the SR and its subsequent re-uptake, (iii) intracellular Ca/+ buffering, and (iv) Ca2+ extrusion across the sarcolemma. Our results demonstrate a number of interesting features of these processes. (1) When the action potential voltage-clamp technique is used to identify the size and time-course of Ca2+ fluxes during the action potential, both the peak current and the associated influx of Ca2+ are relatively large as was previously demonstrated by Isenberg and his colleagues. (2) Nevertheless, this source of Ca2+ is unable, by itself, to produce a significant twitch, which is consistent with previous data from rat ventricle. (3) This Ca2+ influx, however, does represent the trigger for SR Ca2+ release. (4) The Na(+)-Ca2+ exchanger on the SR is able, on average, to extrude all the Ca2+ which enters through L-type Ca2+ channels, although it provides relatively little Ca2+, i.e., during the course of the normal action potential there is no significant reverse Na(+)-Ca2+ exchange activity, at least under our experimental conditions. Our results also suggest that although the L-type Ca2+ current cannot by itself trigger and control contraction its amplitude, frequency, and time-course can alter the rate and the extent of Ca2+ release from the SR. Recently, detailed mathematical formulations and a direct demonstration of some of these phenomena have been published. Stern and Stern and Lakatta predicted more than three years ago that the concentration and the time-course of change in concentration of Ca2+ very near the release sites of the SR may be critical determinants of the overall release process. Within the past year Wier and his colleagues and also Lederer et al. have combined electrophysiological measurements with recordings of localized intracellular Ca2+ (made using a confocal microscope) and have shown that rapid, and relatively large, but very localized changes in intracellular Ca2+ due to Ca2+ influx through L-type Ca2+ channels are responsible for triggering, and to some extent, controlling the release of Ca2+ from the SR. However, it has also been shown that this release depends importantly on the loading or priming state of the SR. Perhaps not surprisingly, the massive release of Ca2+ from the SR can, itself, alter the pattern of subsequent SR release events (cf. Ref. 46) and the time-course of Ca2+ influx through the L-type Ca2+ channels. Thus, although our relatively crude measurements have clearly demonstrated the relationship between L-type Ca2+ channel activity and Na+-Ca2+ exchanger function during a normal cardiac action potential in rat ventricle, they fall far short of any delineation of the functional roles of either of these processes in overall Ca2+ homeostasis. This additional information can, in principle, be obtained from studies in which cellular microanatomy can be visualized dynamically in conjunction with localized changes in intracellular Ca2+ as well as Ca2+ of L-type Ca2+ channels, SR release, and cell shortening.

Positive chronotropic responses of rabbit sino-atrial node cells to flash photolysis of caged isoproterenol and cyclic AMP

The kinetics of onset and the intracellular biochemical signalling mechanisms which are responsible for the positive chronotropic effect of sympathetic stimulation in rabbit cardiac pacemaker cells were examined by using flash photolysis of caged isoproterenol (ISO) and cyclic AMP (cAMP). When caged ISO (10 microM) was present in the superfusate, a single ultraviolet flash caused gradual increases in the spontaneous beating frequency and action potential height of S-A node cells. Both these effects developed after an initial latency of approximately 5 s. Photorelease of ISO also increased the L-type Ca2+ current (ICa-L) with a time-course similar to that of the changes in action potential waveform and heart rate. All of these ISO-induced effects were blocked completely by 1 microM propranolol, demonstrating that they were beta-adrenergic responses. Flash photolysis of caged cAMP (50 microM) also resulted in increased firing frequency and ICa-L. However, these responses to cAMP developed with little or no latency. Intracellular dialysis with a selective inhibitor of the cAMP-dependent protein kinase, Rp-cAMPS, completely abolished the increase in ICa-L demonstrating that it is mediated exclusively via cAMP-dependent activation of protein kinase A, as opposed to a direct G-protein mediated mechanism.

Comparison of five different susceptibility test methods for detecting antimicrobial agent resistance among Haemophilus influenzae isolates

The detection of antimicrobial agent resistance among ninety-eight Haemophilus influenzae isolates was assessed by six different antibiotic test methods: agar dilution on Mueller-Hinton agar supplemented with 5% lysed horse blood (MH-LHB), E-test using both Haemophilus test medium (HTM) agar and chocolate Mueller-Hinton (CMH) agar plates, Vitek Haemophilus susceptibility cards, and three overnight microdilution systems that included two commercial systems, Micro-Media and MicroScan, and the reference broth microdilution method using HTM broth. Agents tested in the study included ampicillin, amoxicillin/clavulanic acid (A/C), cefaclor, cefuroxime, cefotaxime, ceftriaxone, chloramphenicol, and trimethoprim/sulfamethoxazole. Both the reference HTM microbroth dilution method and agar dilution correctly classified all nine of the beta-lactamase negative ampicillin resistant (BLNAR) isolates. Each of the other test methods failed to detect one of the BLNAR strains, either because of growth failure (Micro-Media and MicroScan) or miscategorization of an isolate as susceptible (E-Test HTM, E-Test CMH, and Vitek). None of the test methods detected all six isolates identified as A/C resistant by HTM microbroth dilution. Of the remaining antimicrobials tested, ampicillin and cefuroxime yielded data that could be compared by all test methods. The very major, major, and minor errors for these two antimicrobials in comparison to the reference HTM microdilution method were as follows: Micro-Media (1.7%, 0%, and 4.8%); MicroScan (11.9%, 0%, and 8.1%); E-Test HTM (1.6%, 0%, and 2.0%); E-Test CMH (1.6%, 1.6%, and 4.6%); Vitek (8.1%, 0%, and 3.1%); and agar dilution on MH-LHB (0%, 0%, and 4.6%). Micro-Media and MicroScan panels failed to support the growth of 4.1% and 5.1% of the isolates, respectively.

Stable activation and desensitization of beta 2-adrenergic receptor stimulation of adenylyl cyclase by salmeterol: evidence for quasi-irreversible binding to an exosite

The relaxation of tracheal smooth muscle by the beta 2-adrenergic receptor (beta AR) agonist salmeterol displays several unusual properties: (i) slow onset of action (t1/2 = 5-15 min), (ii) prolonged activation (t1/2 = 8-14 hr), and (iii) the ability to recover from beta AR blockade. These properties led to the hypothesis that salmeterol binds with very high affinity to an exosite in addition to the beta AR activating site. Despite extensive characterization of salmeterol-induced bronchodilation, little is known about the molecular actions of salmeterol. We report the unique properties of salmeterol binding to the beta AR, activation of adenylyl cyclase, and desensitization of the hamster beta AR expressed in L cells. First, we found that salmeterol activation of adenylyl cyclase, although rapid and potent (low EC50 relative to epinephrine), was nevertheless remarkably inefficient relative to the full agonist epinephrine. Reduced coupling efficiency of salmeterol was demonstrated using formulations recently introduced by our group. Second, we found that pretreatment of L cells with salmeterol led to a stable activation of adenylyl cyclase that survives extensive wash procedures and sucrose step gradient purification of plasma membrane fractions. This activation of basal adenylyl cyclase did not require salmeterol binding to the classic active site during pretreatment, as it occurred in the presence of an excess of a beta AR antagonist. Third, we found that the rapid phase of salmeterol-induced desensitization was much reduced relative to epinephrine, consistent with its poor coupling efficiency and with its prolonged activation of adenylyl cyclase. These unique properties of salmeterol support the proposal that it binds reversibly to the activating or active site and as well to an extremely high affinity exosite from which it has access to the active site.

Presence of T cells with activated and memory phenotypes in inflammatory spinal cord lesions

The phenotypic and functional characteristics of activated T cells and recruited unactivated T cells at an inflammatory site were examined using a V beta 4+ myelin basic protein-specific T cell clone in a passively transferred model of experimental allergic encephalomyelitis. A high percentage of the T cells isolated from the central nervous system (CNS) were V beta 4+. This population exhibited the characteristics of activated T cells based on the proportion of cells in the blast state, their ability to proliferate in response to IL-2 or CNS Ag, and their expression of activation/memory cell markers. Activated V beta 4+ T cells were also observed in the periphery. Large numbers of V beta 4- T cells, which are entirely host-recruited, were also found in the CNS, where they demonstrated the properties of memory cells. There were differences in adhesion molecule expression between CNS V beta 4+ T cells and peripheral V beta 4+ T cells, although both populations were in activated state. V beta 4+ T cells at the site of Ag expression (the spinal cord) demonstrated higher levels of LFA-1 and CD44, but lower levels of VLA-4 and intercellular adhesion molecule-1, than did V beta 4+ T cells in the spleen. In contrast, the levels of all of these adhesion molecules on recruited V beta 4- T cells were higher in the CNS than in the periphery. This experimental model allows the detailed characterization of different T cell populations isolated from the same inflammatory site.

Presence of T cells with activated and memory phenotypes in inflammatory spinal cord lesions

The phenotypic and functional characteristics of activated T cells and recruited unactivated T cells at an inflammatory site were examined using a V beta 4+ myelin basic protein-specific T cell clone in a passively transferred model of experimental allergic encephalomyelitis. A high percentage of the T cells isolated from the central nervous system (CNS) were V beta 4+. This population exhibited the characteristics of activated T cells based on the proportion of cells in the blast state, their ability to proliferate in response to IL-2 or CNS Ag, and their expression of activation/memory cell markers. Activated V beta 4+ T cells were also observed in the periphery. Large numbers of V beta 4- T cells, which are entirely host-recruited, were also found in the CNS, where they demonstrated the properties of memory cells. There were differences in adhesion molecule expression between CNS V beta 4+ T cells and peripheral V beta 4+ T cells, although both populations were in activated state. V beta 4+ T cells at the site of Ag expression (the spinal cord) demonstrated higher levels of LFA-1 and CD44, but lower levels of VLA-4 and intercellular adhesion molecule-1, than did V beta 4+ T cells in the spleen. In contrast, the levels of all of these adhesion molecules on recruited V beta 4- T cells were higher in the CNS than in the periphery. This experimental model allows the detailed characterization of different T cell populations isolated from the same inflammatory site.

Effects of action potential duration on excitation-contraction coupling in rat ventricular myocytes. Action potential voltage-clamp measurements

Although each of the fundamental processes involved in excitation-contraction coupling in mammalian heart has been identified, many quantitative details remain unclear. The initial goal of our experiments was to measure both the transmembrane Ca2+ current, which triggers contraction, and the Ca2+ extrusion due to Na(+)-Ca2+ exchange in a single ventricular myocyte. An action potential waveform was used as the command for the voltage-clamp circuit, and the membrane potential, membrane current, [Ca2+]i, and contraction (unloaded cell shortening) were monitored simultaneously. Ca(2+)-dependent membrane current during an action potential consists of two components: (1) Ca2+ influx through L-type Ca2+ channels (ICa-L) during the plateau of the action potential and (2) a slow inward tail current that develops during repolarization negative to approximately -25 mV and continues during diastole. This slow inward tail current can be abolished completely by replacement of extracellular Na+ with Li+, suggesting that it is due to electrogenic Na(+)-Ca2+ exchange. In agreement with this, the net charge movement corresponding to the inward component of the Ca(2+)-dependent current (ICa-L) was approximately twice that during the slow inward tail current, a finding that is predicted by a scheme in which the Ca2+ that enters during ICa is extruded during diastole by a 3 Na(+)-1 Ca2+ electrogenic exchanger. Action potential duration is known to be a significant inotropic variable, but the quantitative relation between changes in Ca2+ current, action potential duration, and developed tension has not been described in a single myocyte. We used the action potential voltage-clamp technique on ventricular myocytes loaded with indo 1 or rhod 2, both Ca2+ indicators, to study the relation between action potential duration, ICa-L, and cell shortening (inotropic effect). A rapid change from a "short" to a "long" action potential command waveform resulted in an immediate decrease in peak ICa-L and a marked slowing of its decline (inactivation). Prolongation of the action potential also resulted in slowly developing increases in the magnitude of Ca2+ transients (145 +/- 2%) and unloaded cell shortening (4.0 +/- 0.4 to 7.6 +/- 0.4 microns). The time-dependent nature of these effects suggests that a change in Ca2+ content (loading) of the sarcoplasmic reticulum is responsible. Measurement of [Ca2+]i by use of rhod 2 showed that changes in the rate of rise of the [Ca2+]i transient (which in rat ventricle is due to the rate of Ca2+ release from the sarcoplasmic reticulum) were closely correlated with changes in the magnitude and the time course of ICa-L.(ABSTRACT TRUNCATED AT 400 WORDS)

Quinidine-induced open channel block of K+ current in rat ventricle

1. The effects of quinidine on calcium-independent outward K+ currents in rat ventricular myocytes were studied using whole-cell patch clamp techniques. 2. Quinidine sulphate (6 microM) significantly prolonged repolarization of the ventricular action potential. This effect was larger during early repolarization (25% level) than at later times (90% level). 3. Quinidine reduced the amplitude of a transient outward current, and accelerated its rate of decay by approximately 4 fold at membrane potentials between 0 to +50 mV. Quinidine also reduced the amplitude of a slowly inactivating, tetraethylammonium-sensitive 'pedestal' component of the outward current. 4. The quinidine-induced block of the transient outward current was dependent on time and membrane potential. Maximal block occurred with depolarizations of about 100 ms duration, and longer depolarizations (up to 1.5 s) produced little additional block. The membrane potential dependence of quinidine-induced block was very similar to the membrane potential dependence of activation of the transient outward current. The membrane potential dependence of steady-state inactivation of the transient outward current was not significantly affected by quinidine. 5. These results show that quinidine blocks outward K+ currents in rat ventricular cells. The time and potential dependence of this block suggests that quinidine blocks the transient outward K+ current by acting primarily on the open state of these channels.

Effects of intracellular calcium on sodium current density in cultured neonatal rat cardiac myocytes

1. Na+ channel mRNA levels in the heart can be modulated by changes in intracellular Ca2+ ([Ca2+]i). We have investigated whether this regulation of Na+ channel biosynthesis by cytosolic Ca2+ translates into functional Na+ channels that can be detected electrophysiologically. 2. Whole-cell Na+ currents (INa) were recorded using patch-clamp techniques from single ventricular myocytes isolated from neonatal rats and maintained in tissue culture for 24 h. Na+ current density, measured at a membrane potential of -10 mV, was significantly decreased in the cells which were exposed for 24 h to culture medium containing 10 mM of both external Ca2+ and K+ in order to raise [Ca2+]i compared with control cells which were maintained in culture medium containing 2 and 5 mM of Ca2+ and K+, respectively. In contrast, Na+ current density (at -10 mV) was significantly increased in cells exposed for 24 h to 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetraacetoxymethyl ester (BAPTA AM; a cell membrane-permeable Ca2+ chelator) which lowered the average [Ca2+]i compared with control. 3. Changes in current density were not associated with changes in the voltage dependence of activation and inactivation of INa. There were no changes in single-channel conductances. 4. It is concluded that Na+ current density in neonatal rat cardiac myocytes is modulated by [Ca2+]i. The findings suggest that the differences in current density are attributable to a change in Na+ channel numbers rather than to changes in single-channel conductance or gating. These changes are consistent with the previously documented modulation of Na+ channel biosynthesis by cytosolic Ca2+.

SCIENTIFIC CRITERIA TO OPTIMIZE OIL SPILL CLEANUP

Aberdeen University Research and Industrial Services (AURIS) undertook a joint industry pilot investigation on “Scientific Criteria for Optimizing Oil Spill Cleanup Operations and Effort” from October 1993 to March 1994. This project examined the worldwide scientific literature on the effects of oil spills, and experimental and natural clearances, on both rocky shores and salt marshes, to ascertain whether defensible scientific criteria could be used to establish the appropriate end point for oil spill cleanup operations. After exhaustive screening of the literature, the investigation found that ecological recovery of shore biota usually follows natural time scales of up to three years for rocky shores and five years for salt marshes, regardless of cleanup. Cleanup has a negative or marginal influence on these time scales, so there is little scientific justification for shore treatment. It may be justified, however, by socioeconomic factors relating to recreation, tourism, fisheries, aquaculture, visual amenity, or birds and mammals. In exceptional cases, where oil has formed heavy smothering deposits or toxic subsurface deposits, there are grounds for treatment to promote ecological recovery of the shore biota within the expected time scales.

Histochemical localization of nitric oxide synthase in the bullfrog intracardiac ganglion

Histochemical and immunohistological methods have been used to demonstrate the presence of nitric oxide synthase (NOS) in the intracardiac parasympathetic ganglion of bullfrog heart. Both NADPH-diaphorase staining and indirect immunofluorescence with polyclonal antibodies raised against the C-terminal regions of a cloned NOS from rat cerebellum show that the postganglionic, parasympathetic neurons in the intracardiac ganglion contain NOS. This suggests that nitric oxide may have a role in neuronal activity in frog heart.

cAMP-dependent protein kinase and protein kinase C consensus site mutations of the beta-adrenergic receptor. Effect on desensitization and stimulation of adenylylcyclase

Activation of cAMP-dependent protein kinase (cAPK) or protein kinase C (PKC) causes a rapid desensitization of beta 2-adrenergic receptor (beta AR) stimulation of adenylylcyclase in L cells, which previous studies suggest involves the cAPK/PKC consensus phosphorylation site in the third intracellular loop of the beta AR, RRSSK263. To determine the role of the individual serines in the cAPK- and PKC-mediated desensitizations, wild type (WT) and mutant beta ARs containing the substitutions, Ser261-->Ala, Ser262-->Ala, Ser262-->Asp, and Ser261/262-->Ala, were constructed and stably transfected into L cells. Results showed that serine 262 was the primary site of the cAPK-induced desensitization, whereas either serine 261 or serine 262 was sufficient to confer the 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA)/PKC-mediated desensitization. Coincident stimulation of cAPK and PKC caused an additive desensitization (6-8-fold increase in the EC50) which was significantly reduced (80%) only by the double substitution mutation. Quantitative evaluation of the coupling efficiencies and the GTP-shift of the WT and mutant receptors demonstrated that only one of the mutants, Ser262-->Ala, was partially uncoupled. The Ser262-->Asp mutation did not significantly uncouple, demonstrating that introducing a negative charge did not appear to mimic the desensitized state of the receptor. The beta AR expression level played a critical role in determining the pattern of beta AR desensitization; i.e. while the overall desensitization was unaltered within a large range of beta AR expression level (10-300 fmol/mg), the increase in EC50 and decrease in Vmax were differentially affected by the change in the receptor level.

Effects of different test conditions on the susceptibility of Mycobacterium fortuitum and Mycobacterium chelonae to amikacin

Eighteen rapidly growing mycobacteria were tested for susceptibility to amikacin by six different antibiotic susceptibility procedures to assess method variability and factor variation within a single method. Using amikacin MICs determined by the microdilution method as the reference standard, results for Mycobacterium chelonae were on average eight-fold higher by the macrodilution method and two-fold higher by the BACTEC, 1% standard proportion, and agar dilution methods. For Mycobacterium fortuitum, macrodilution MICs were on average four-fold higher than microdilution results; however, for this species, agar dilution, the 1% standard proportion method, and the BACTEC method showed good correlation with microdilution testing. The use of different test media and incubation in increased CO2 tension increased amikacin MICs for Mycobacterium chelonae. An inoculum effect was observed with both species, especially when the organism concentration increased from 10(5) cfu/mL to 10(6) cfu/mL for broth testing and 10(5) to 10(6) cfu per spot for agar dilution. These results indicate that different antibiotic susceptibility methods and test conditions markedly influence MICs of amikacin for these rapidly growing mycobacteria.

Differential expression of the beta-adrenergic receptor modifies agonist stimulation of adenylyl cyclase: a quantitative evaluation

The effect of varying levels of beta 2-adrenergic receptor (beta AR) expression on the capacity of the receptor to activate adenylyl cyclase through regulatory G proteins has been systematically explored in this paper, using differential expression of hamster and human beta AR in L cells. Equations have been developed based on the cycle of G protein activation first proposed by Cassel and Selinger and the mobile receptor model, which assumes that hormone-bound beta AR can stimulate a number of different adenylyl cyclase moieties through the G protein during a single cycle of activation. These equations predict the relationship of receptor number to the EC50 (potency) and Vmax (efficacy) for adenylyl cyclase activation. L cell clones were selected with stable expression of the beta AR over a 2000-fold range of levels (from 5 to 10,000 fmol/mg of membrane protein). Experimentally determined values for the EC50 and the Vmax for epinephrine stimulation of adenylyl cyclase over the entire range of receptor levels were found to be in excellent agreement with predictions of the traditionally accepted models. A method is introduced that allows calculation of beta AR coupling efficiency while taking into account the effect of variable receptor levels. The approach provides a quantitative means for the determination of coupling efficiency of the receptor/G protein/adenylyl cyclase system over wide variations in receptor levels and allows for a rational comparison of coupling efficiencies of wild-type and mutant receptors when receptor levels differ.

Role of sodium-calcium exchange in activation of contraction in rat ventricle

1. The functional role of reverse Na(+)-Ca2+ exchange in the activation of contraction of rat ventricular myocytes has been studied. Mechanical activity of single cells, measured as unloaded cell shortening, was recorded simultaneously with membrane current and voltage using a single microelectrode voltage clamp and a video edge detection device. 2. The voltage dependence of contraction was studied by applying trains of depolarizations. At test potentials between +20 and +80 mV (under conditions where large outward currents were activated) a plateau on the shortening vs. voltage (S-V) relationship was observed. Significant cell shortening also occurred at test potentials between -70 and -40 mV; and these contractions were accompanied by large inward Na+ currents. We have investigated the ionic mechanisms for three components of the S-V relation in rat ventricle: (i) shortening which occurs between -70 and -40 mV and is thought to be dependent on the sodium current; (ii) phasic contractions in the voltage range -40 to +40 mV where the L-type Ca2+ current is present; (iii) the plateau of the S-V relation at strongly depolarized voltages where reverse Na(+)-Ca2+ exchange may occur. 3. Experiments in which two independent microelectrode impalements were made in a single myocyte showed that during activation of contraction at test potentials between -70 and -40 mV, and during very large depolarizations (+20 to +80 mV), there were significant deviations of the measured membrane potential from the applied voltages. Activation of cell shortening in these voltage ranges could be eliminated by electronic series resistance compensation, which significantly reduced these voltage errors. Consistent with these findings, when tetrodotoxin (TTX) and 4-aminopyridine (4-AP) were used to block inward Na+ and transient outward K+ currents, respectively, no significant voltage errors were present and a bell-shaped shortening-voltage (S-V) relationship was obtained. 4. When Na+ and K+ currents were blocked, depolarizations from holding potentials of either -80 or -50 mV demonstrated that the threshold for activation of contraction was about -30 mV, and that the voltage dependence of peak shortening was very similar to that of the L-type Ca2+ current (ICa,L). These contractions were suppressed completely by either Cd2+ or ryanodine, showing that activation of cell shortening was due to Ca2+ influx through L-type channels which induced release of Ca2+ from the sarcoplasmic reticulum (SR). No T-type calcium currents were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Heterogeneity of action potential waveforms and potassium currents in rat ventricle

OBJECTIVE

The ionic mechanisms for differences in action potential waveforms in rat left ventricle were studied by recording L-type Ca2+ current, transient outward K+ current, and inwardly rectifying background K+ current in single myocytes.

METHODS

Single cells were obtained from adult rat hearts by enzymatic dispersion of tissue segments from the epicardium at the apex and the endocardium at the base of the left ventricle. Whole cell voltage clamp methods together with cell shortening measurements were used to identify the K+ currents involved in early and late repolarisation and to correlate changes in action potential shape with inotropic responses. 4-Aminopyridine was used to block the transient outward K+ current, I(t), to evaluate the contribution of this current to repolarisation.

RESULTS

Action potential recordings demonstrated that cells from endocardial tissue at the base of the left ventricle have a considerably longer action potential than those from epicardial tissue at the apex. 4-Aminopyridine had a much more pronounced action potential lengthening and inotropic effects on cells from epicardium than on myocytes from endocardium suggesting that I(t) is larger in the epicardium. Voltage clamp measurements confirmed this. In contrast, the L-type Ca2+ current, the resting membrane potential, and the inwardly rectifying background K+ current were very similar in these two regions of left ventricle.

CONCLUSIONS

One significant factor contributing to the heterogeneity of action potential waveforms in rat left ventricle is a differential distribution of a Ca+ independent transient outward K+ current, I(t). Regional differences in action potential duration have important implications for the gradient of repolarisation in rat left ventricle, for the genesis of the T wave of the electrocardiogram, and for both electrical and mechanical restitution (refractoriness).

Comparison of susceptibility test methods to detect penicillin-resistant Streptococcus pneumoniae

The detection of penicillin-resistant Streptococcus pneumoniae was assessed by six different methods: agar dilution, oxacillin screen by disk diffusion, E-test, and three overnight microdilution test methods that included commercial panels from MicroScan and Micro Media and in-house-made conventional panels using a commercial Haemophilus test medium (HTM) broth. Of the 52 pneumococcal isolates tested, 12 were resistant, 16 were relatively resistant, and 24 were susceptible to penicillin as defined by the reference agar dilution method. The oxacillin screen detected as resistant all 28 resistant and relatively resistant strains. The percentage of penicillin-resistant isolates detected by each minimum inhibitory concentration (MIC) test method was as follows: E-test (100%), Micro Media (75%), MicroScan (0%), and HTM (0%). With the relatively resistant isolates, the detection percentage was as follows: E-test (88%), Micro Media (94%), MicroScan (69%), and HTM (69%). In conclusion, the E-test and Micro Media MIC tests are acceptable confirmatory tests for detecting penicillin resistance among S. pneumoniae isolates.

Beta 2-adrenergic receptor mutants reveal structural requirements for the desensitization observed with long-term epinephrine treatment

In the present study wild-type and various mutant hamster beta 2-adrenergic receptors (beta ARs) expressed in L cells were used to examine potential molecular mechanisms involved in the desensitization of hormonal stimulation of adenylyl cyclase observed after long term exposure to low concentrations of epinephrine. The mutant beta ARs included deletion mutants, D(259-262)beta AR and D(343-348)beta AR, that lack the consensus sites for cAMP-dependent protein kinase (cAPK) and protein kinase C (PKC) and a truncation mutant, T(354)beta AR, that lacks the putative consensus sites for beta AR kinase. Epinephrine stimulation of adenylyl cyclase was desensitized in all four cell lines after growth for 24 hr in the presence of 3 nM epinephrine, and this desensitization was characterized by a 3-4-fold increase in the EC50 for epinephrine stimulation of adenylyl cyclase. In addition, the Vmax was significantly decreased in the cells with the wild-type beta AR and the D(343-348)beta AR. The desensitization was not masked by high concentrations of magnesium and was accompanied by a 40-70% down-regulation of beta ARs. In the cells treated with 3 nM epinephrine, prostaglandin E1 stimulation of adenylyl cyclase was decreased 11% in cells with the wild-type beta AR and forskolin stimulation was decreased 25-36% with all but the D(259-262)beta AR mutant. These results demonstrated that phosphorylations of the cAPK/PKC consensus sites and the serine- and threonine-rich segment of the carboxyl-terminal tail of the beta AR were not required for the desensitization caused by 3 nM epinephrine, thus further differentiating it from cAPK- or PKC-mediated desensitization and the desensitization attributed to beta AR kinase.

Identification of nonselective cation channels in cultured adult rat alveolar type II cells

There is evidence supporting the role of active transport of Na+ in the resolution of pulmonary edema, but the exact cellular mechanism(s) underlying this process remain unknown. This study demonstrated the presence of ion channels on adult rat alveolar type II cells that might be associated with this active transport of Na+. Patch-clamp techniques were used to characterize a nonselective cation channel in adult rat alveolar type II epithelial cells held in culture for 24 to 72 h. Single-channel currents were recorded from inside-out, cell-free membrane patches. The most common type of single channel had a linear slope conductance of 20.4 +/- 0.6 pS (n = 22) in symmetrical NaCl (150 mM) solutions. The channel was approximately equally permeable to Na+ and K+ ions (PK/PNa = 1.15) and was highly selective for cations (PCl/PNa < 0.05). Channel activity was Ca(2+)-dependent, and it required at least 10 microM Ca2+ on the cytosolic side of an inside-out patch to activate the channel. Amiloride (1 to 10 microM), a Na+ channel blocker in epithelial tissue, reduced the steady-state open probability of the channel 10-fold but had no significant effect on the magnitude of the single-channel conductance. Single channels with similar properties were not found in cultured rat alveolar macrophages. The possible role of this amiloride-sensitive, nonselective cation channel in Na+ transport and lung liquid clearance is discussed.

Regulation of unloaded cell shortening by sarcolemmal sodium-calcium exchange in isolated rat ventricular myocytes

1. Regulation of unloaded cell shortening and relaxation by sarcolemmal Na(+)-Ca2+ exchange was investigated in rat ventricular myocytes. Contraction of single cells at 22 +/- 1 degrees C was measured simultaneously with membrane current and voltage using the whole-cell voltage clamp technique in combination with a video edge-detection device. 2. The extent of mechanical activation (cell shortening amplitude) was strongly dependent on diastolic membrane potential over the voltage range -140 to -50 mV. This voltage sensitivity of contraction was abolished completely when a recently described inhibitory peptide of the cardiac Na(+)-Ca2+ exchanger (XIP, 2 x 10(-5) M) was present in the recording pipette, demonstrating that in rat ventricular cells Na(+)-Ca2+ exchange is modulated by diastolic membrane potential. 3. Possible influences of Na(+)-Ca2+ exchange on contraction were studied from a holding potential of -80 mV. Depolarizations (-50 to +60 mV) resulted in a bell-shaped shortening-voltage (S-V) relationship. These contractions were suppressed completely by either Cd2+ (10(-4) M) or verapamil (10(-5) M), but remained unchanged during superfusion with tetrodotoxin (TTX, 1.5 x 10(-5) M), when [NA+]o was reduced from 140 to 10 mM by substitution with either Li+ or Cs+ ions or when pipette Na+ was varied between 8 and 13 mM. XIP (2 x 10(-5) M) increased the magnitude and duration of twitch contractions, but had no effect on the shape of the S-V relationship. Thus, the Ca2+ current but not the Na+ current or Ca2+ influx due to reversed Na(+)-Ca2+ exchange can release Ca2+ from the sarcoplasmic reticulum (SR) under these experimental conditions. 4. The effect of the rate of repolarization on cell shortening was studied under voltage clamp by applying ramp waveforms immediately following the depolarizations which activated contraction. Although slowing of the rate of repolarization had no effect on the first contraction following a train of conditioning depolarizations, a positive inotropic effect developed thereafter. 5. Caffeine (10 mM) was applied to determine whether Na(+)-Ca2+ exchange and/or Ca2+ sequestration/buffering by the sarcoplasmic reticulum were primarily responsible for these inotropic effects. In the presence of caffeine the positive inotropic effect developed fully during the first test depolarization. Changes in the rate of repolarization had much less effect on shortening in cells dialysed intracellularly with XIP (2 x 10(-5) M). In combination, these results suggest that the changes in the inotropic effects resulting from changes in rate of repolarization may be due to altered loading and release of Ca2+ from the SR.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity of meropenem and other antimicrobial agents against uncommon gram-negative organisms

The in-vitro activity of meropenem and other antimicrobial agents was tested by agar dilution against 113 uncommon Gram-negative pathogens. Both meropenem and ceftriaxone showed the most activity against the test isolates. The potency of meropenem was greater than imipenem against Pasteurella multocida, Eikenella corrodens, Haemophilus parainfluenzae, Moraxella spp., Kingella spp., and Actinobacillus actinomycetemcomitans. Further work is necessary to assess the in-vivo activity of meropenem against these Gram-negative isolates.

Aortic stenosis, cesarean delivery, and epidural anesthesia

A 23-year-old female was referred to the University of Arkansas for Medical Sciences at 32 weeks' gestation with a history of aortic stenosis following aortic valve replacement. Evaluation by echocardiography showed an approximately 90 mmHg transvalvular pressure gradient. Pregnancy progressed to 36 weeks' gestation without problem, at which time the patient underwent cesarean section with lumbar epidural anesthesia. Invasive hemodynamic monitors were used to assess cardiac performance and as a guide for anesthetic management. The impact of aortic stenosis on pregnancy is discussed, as are management aspects of lumbar epidural anesthesia in such patients.

Okadaic acid induces both augmentation and inhibition of beta 2-adrenergic stimulation of cAMP accumulation in S49 lymphoma cells

To address the role of protein phosphatases in regulating hormonal responses in mammalian cells, we investigated the effects of okadaic acid, a potent inhibitor of protein phosphatases 1 and 2A, on epinephrine and prostaglandin E1 stimulation of cAMP accumulation and adenylyl cyclase in S49 WT and kin- lymphoma cells. Depending on the dose and time of okadaic acid pretreatment of both cell lines, there were two distinguishable effects on cAMP accumulation, an augmentation and an inhibition. The augmentation occurred rapidly (t1/2 < 1 min), was maximal with 3 microM okadaic acid, and was observed with concentrations of okadaic acid as low as 0.3 microM. Prolonged (t1/2 of 5-15 min) pretreatment of cells with okadaic acid caused an inhibition of epinephrine-stimulated cAMP accumulation, which was characterized by a 2-3-fold increase in the EC50 for the response to epinephrine. The EC50 for the okadaic acid-mediated inhibition was similar to that for the augmentation. In assays of adenylyl cyclase in membrane fractions prepared from okadaic acid-pretreated cells the inhibitory, but not the stimulatory, effects of okadaic acid pretreatment were observed. The data demonstrate that protein phosphatases play an important role in regulating adenylyl cyclase and suggest that cAMP-dependent protein kinase is not involved in either of its actions.

Hyperthyroidism selectively modified a transient potassium current in rabbit ventricular and atrial myocytes

1. Transient outward potassium currents (I(t)) were compared in single cardiac myocytes obtained from normal and hyperthyroid rabbits. Currents were recorded using the suction electrode whole-cell voltage clamp technique. 2. In ventricular myocytes from hyperthyroid animals (at 22 degrees C and a stimulation rate of 0.2 Hz), I(t) was 4- to 5-fold larger than in normal myocytes, in a potential range of -20 to +60 mV. As in normal myocytes, I(t) in hyperthyroid myocytes was calcium insensitive, and was more than 90% suppressed by 2 mM 4-aminopyridine. 3. The increase in I(t) was observed over a wide range of stimulation rates, even at rates sufficiently slow to enable complete reactivation of the I(t) channels. However, there was a major change in the rate dependence of I(t) in hyperthyroid myocytes, with significant I(t) current still present at rates (e.g. 1-2 Hz) at which it is normally completely suppressed. 4. The augmentation of I(t) in the hyperthyroid myocytes could not be accounted for by changes in the voltage dependence or the kinetics of channel activation or inactivation. There was no change in the reversal potential of I(t), implying no change in the selectivity of the channel. 5. Single-channel activity was recorded using the cell-attached mode of recording. In myocytes from hyperthyroid rabbit we observed the following: (a) active patches (often containing two channels) were obtained more frequently in comparison to control; (b) the unitary conductance of the channel was the same; (c) single-channel openings persisted at high stimulation rates. 6. In contrast to hyperthyroid ventricular cells, I(t) in atrial cells from the same hearts was not substantially changed. 7. The rate dependence of I(t) in atrial cells was also unaffected by hyperthyroidism, in contrast to the large changes observed in ventricular cells. Thus, in atrial cells from hyperthyroid hearts the current was totally suppressed at rates of 1-2 Hz, as in euthyroid conditions. 8. Single-channel recordings in the cell-attached mode showed a unitary conductance similar to that found in normal atrial cells. Channel activity was suppressed at 2 Hz, in contrast to hyperthyroid ventricular cells. 9. In conclusion, I(t) is drastically changed in hyperthyroid rabbit ventricle cells. The changes are in the magnitude of the macroscopic current and its rate dependence. Since the unitary conductance is unchanged (and the peak open probabilities are normally high at positive membrane potential(s) the number of active channels in the membrane must be increased. In atrial cells from the same hyperthyroid hearts no changes are apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

From Fanny to Fernand: the development of consumerism in pain control during the birth process

Obstetric anesthesia has been the object of public interest and patient advocacy from its introduction in the 1840s to the present. Early arguments concerned the significance of pain in childbearing and became a popular issue involving physicians, clergymen, and journalists. The first obstetric anesthesia, either, given in the United States was administered in Cambridge, Massachusetts, in 1847. For the next several decades general anesthesia was the only feasible means of relieving labor pain. At the turn of the century a combination of scopolamine and morphine was introduced in the United States by a popular women's magazine; the National Twilight Sleep Association was launched. After the decline of this movement, the "natural" childbirth method came into national prominence. In spite of their differing pharmacologic characteristics, there are sociologic parallels between the patient advocacy of Twilight Sleep and that of psychoprophylaxis. This study focuses on the public perception of these movements, which were begun by physicians and subsequently endorsed by militant lay groups.

Comparison of CNS homing pattern among murine TH cell lines responsive to myelin basic protein

A myelin basic protein (MBP)-reactive TH cell line capable of inducing experimental allergic encephalomyelitis (EAE), and a MBP-reactive TH cell clone that does not cause EAE were labeled with a fluorescent vital dye, and transferred into naive syngeneic SJL/J mice. Animals were killed before the appearance of symptoms (3 and 4 days post-injection). Sections obtained from the spleen, spinal cord and brain of both groups of animals were examined by fluorescence microscopy to localize labeled TH cells. At all time points examined, the spleens of both groups contained innumerable labeled cells. The spinal cords and brains of animals that had received EAE-causing cells had a basal level of 20 labeled cells/cm2 at 3 days; this number increased rapidly to 150 cells/cm2 in the spinal cord at 4 days. Perivascular infiltrates and small foci of astrogliosis were already apparent in this group 3 days after injection. The spinal cords and brains of animals that had received the non-EAE-causing TH cells contained 50 labeled cells/cm2 at 3 days. The density of these transferred cells, as compared to that of the EAE-causing cells, suggested that they have an unaltered CNS-homing capability. However, by 4 days, the number of non-EAE-causing labeled cells had returned to near basal level. Our findings suggest that discrimination between disease and non-disease causing MBP-responsive TH cells occurs within the first 3 days following transfer, requires the presence in the CNS of a limited number of TH cells, and depends on yet unidentified TH cell factor(s).

Antibiotic susceptibilities of the Vibrionaceae to meropenem and other antimicrobial agents

The in vitro activity of meropenem was compared with imipenem and other selected antimicrobial agents against 115 isolates from the family Vibrionaceae. No resistance was observed with meropenem or imipenem against these isolates. However, meropenem was generally four- to 16-fold more active than imipenem against the aeromonads and Vibrio cholerae. Meropenem showed excellent in vitro activity against the Vibrionaceae and may be useful for eradicating infections produced by these organisms.

Beta-adrenergic receptor levels and function after growth of S49 lymphoma cells in low concentrations of epinephrine

Growth of S49 wild-type (WT) lymphoma cells for 24 hr with 3 nM epinephrine produces a very pronounced attenuation of cAMP accumulation in response to subsequent challenges with much higher concentrations of the catecholamine [Mol. Pharmacol. 36:459-464 (1989)]. We report here the effects of this treatment, in S49 WT, cyc-, and kin- cells, on the responsiveness of adenylate cyclase in partially purified membranes. The desensitization of adenylate cyclase in the S49 WT cells after 24-hr treatment was homologous, in that only responses to epinephrine were attenuated. The EC50 for epinephrine stimulation of adenylate cyclase was 54 +/- 8% (mean +/- standard error) higher in treated cells than in controls, and there was a 32 +/- 3% reduction in Vmax at supramaximal epinephrine concentrations. The treatment also caused a 34 +/- 9% reduction in the levels of the beta-adrenergic receptor (beta AR), which was of a sufficient magnitude to account for the homologous desensitization seen. The 24-hr treatment had similar effects in S49 kin- cells, where we observed a 28 +/- 4% decrease in Vmax, a 35 +/- 6% increase in EC50 for epinephrine stimulation of adenylate cyclase, and a 25 +/- 3% decrease in beta AR. In contrast, the 24-hr treatment had no measurable effect on adenylate cyclase activity in S49 cyc- cells. That is, the responsivity of adenylate cyclase reconstituted with Gs from S49 WT cells was not attenuated, although beta AR levels were significantly decreased. The desensitization of S49 cells with the 24-hr treatment was additive with that mediated by the cAMP-dependent protein kinase (cAPK). Further, unlike the cAPK-mediated attenuation, it was relatively insensitive to the levels of free Mg2+ in the adenylate cyclase reaction mixture. The characteristics of the desensitization produced by 24-hr treatment with 3 nM epinephrine, together with the observation that it is similar in S49 WT and kin- cells, demonstrates that the process in WT cells is, at least in part, independent of the rapid cAPK-mediated desensitization. It is also most likely that it is unrelated to the rapid cAMP-independent processes involving sequestration/internalization or the beta AR kinase, because those mechanisms require much higher receptor occupancies than the 0.2% occurring with 3 nM epinephrine. Thus, 24-hr treatment appears to produce attenuation of adenylate cyclase by causing down-regulation of beta AR, without involving any other known form of desensitization.