Interspecies Comparison of Platelet Aggregation, LIBS Expression and Clot Retraction: Observed Differences in GPIIb-IIIa Functional Activity

We examined interspecies differences in the function of the platelet fibrinogen receptor, GPIIb-IIIa, by comparing platelet aggregation responses to adenosine diphosphate (ADP) added alone or in combination with a GPIIIa specific monoclonal antibody (mAb), D3. D3 can activate the GPIIb-IIIa receptor in the absence of platelet activation, and it preferentially binds to a region on the GPIIIa subunit after the GPIIb-IIIa complex is occupied by ligand. Using human, monkey, dog, rabbit and pig platelets, we examined whether all species’ platelets bound the D3 mAb similarly, and if the binding of Arg-Gly-Asp-Ser (RGDS) peptides induced the exposure of the anti-LIBS (D3) epitope as previously described for human platelets. We also evaluated how blocking of this neoantigenic region by the D3 mAb affected clot retraction, a process that requires linkage of GPIIb-IIIa with fibrin(ogen) and the platelet cytoskeleton. We found that all species tested bound the D3 mAb. Only in human and monkey platelets did D3 cause aggregation as well as inhibit clot retraction. However, in all species tested, except for pig, D3 prevented disaggregation of platelets typically observed when platelets are treated with low dose ADP. With the exception of pig platelets, there was increased D3 binding to platelets in the presence of RGDS peptides. We propose that this region of GPIIIa is important in the conformational changes that GPIIb-IIIa undergoes during the binding of ligand in most species tested. Our studies suggest 1) there are measurable inter-species differences in GPIIb-IIIa mediated platelet aggregation and clot retraction, 2) LIBS expression due to receptor occupancy is a common but not all-inclusive response and 3) interspecies comparisons may be useful in understanding structural and functional aspects of platelet GPIIb-IIIa.

Platelet function recovery following exposure to triple anti-platelet inhibitors using an in vitro transfusion model

INTRODUCTION

Dual anti-platelet therapy (DAPT) with aspirin and a P2Y12 antagonist is standard of care to reduce risk of thrombosis, but does not directly target thrombin-dependent platelet activation. Therefore, PAR-1 antagonist addition to DAPT (i.e., triple anti-platelet therapy; TAPT) may improve the efficacy of treatment, though at the expense of an increase in bleeding risk. Using an in vitro transfusion model, we evaluated if platelet function loss associated with TAPT can be remedied by the addition of drug-naïve platelets.

METHODS

To mimic TAPT, platelet-rich plasma (PRP) prepared from consented DAPT patients (DPRP) was incubated with a vorapaxar at therapeutic plasma levels (TPRP). To simulate platelet transfusions, TPRP was mixed with increasing proportions of drug-naïve PRP (NPRP). Platelet function recovery was assessed by light transmission aggregometry (LTA), aggregate morphology, and P-selectin expression.

RESULTS

LTA results demonstrated that 20% NPRP was required to restore the ADP aggregation response in TPRP to the response observed in DPRP and 40% NPRP recovered aggregation to >65%. Higher NPRP fractions (60%) were required to restore the platelet reactivity using TRAP-6 (SFLLRN) or arachidonic acid (AA). PAR-4 aggregation was unaffected by platelet antagonists. A decrease in single, free platelets and incorporation of mepacrine-labeled naïve platelets into aggregates occurred with increasing NPRP portions. Upon agonist activation, the surface density and percent of P-selectin positive platelets increased linearly upon addition of NPRP.

CONCLUSION

This in vitro model demonstrated that administration of drug-naïve platelets can be a useful strategy for reversing overall platelet inhibition observed with TAPT.

Variations in the presence of chloride cells in the gills of lampreys (Petromyzontiformes) and their evolutionary implications

Although confined to fresh water, non-parasitic species of lampreys and the landlocked parasitic sea lamprey, all of which were derived relatively recently from an adromous ancestors, still develop chloride cells, whose function in their ancestors was for osmoregulation in marine waters during the adult parasitic phase. In contrast, such cells are not developed by the non-parasitic least brook lamprey Lampetra aepyptera, which has been separated from its ancestor for >2 million years, nor by the freshwater parasitic species of the genus Ichthyomyzon. The length of time that a non-parasitic species or landlocked parasitic form or species has spent in fresh water is thus considered the overriding factor determining whether chloride cells are developed by those lampreys.

Unusually high numbers of ribosomal RNA genes in copepods (Arthropoda: Crustacea) and their relationship to genome size

We report on copy numbers of 18S ribosomal RNA genes in three species of copepods (Crustacea: Copepoda), two of which possess an unusual arrangement in which 5S genes are included within the 18S-5.8S-28S repeat unit. Slot blots of genomic and standard DNA were hybridized with an 18S rRNA gene probe constructed from one of the marine species and hybridization was quantified using chemiluminescence. Diploid 18S rRNA gene copy numbers are estimated as ca. 15 300 and 33 500 in the marine species Calanus finmarchicus (13.0 pg DNA in 2C adult nuclei) and C. glacialis (24.2 pg DNA), respectively, and ca. 840 and 730 in two freshwater populations of Mesocyclops edax (both ca. 3 pg DNA) from Virginia and Nova Scotia, respectively. The roughly proportional relationship between 2C somatic nuclear DNA contents and rRNA gene copy number in the sibling species C. finmarchicus and C. glacialis may reflect polytenic replication of entire genomes during abrupt speciation events. Copy numbers may also reflect differential losses during embryonic chromatin diminution.

Orexin receptor subtype activation and locomotor behaviour in the rat

AIM

Orexin-producing neurones, located primarily in the perifornical region of the lateral hypothalamus, project to a wide spectrum of brain sites where they influence numerous behaviours as well as modulating the neuroendocrine and autonomic responses to stress. While some of the actions of orexin appear to be mediated via the type 1 receptor, some are not, including its action on the release of one stress hormone, prolactin. We describe here the ability of orexin to increase locomotor behaviours and identify the importance of both receptor subtypes in these actions.

METHODS

Rats were tested for their behavioural responses to the central activation of both the type 1 (OX(1)R) and type 2 (OX(2)R) receptor (ICV orexin A), compared to OX(2)R activation using a relatively selective OX(2)R agonist in the absence or presence of an orexin receptor antagonist that possesses highest affinity for OX(1)R.

RESULTS

Increases in locomotor activity were observed, effects which were expressed by not only orexin A, which binds to both the OX(1)R and the OX(2)R receptors, but also by the relatively selective OX(2)R agonist [(Ala(11), Leu(15))-orexin B]. Furthermore, the OX(1)R selective antagonist only partially blocked the action of orexin A on most locomotor behaviours and did not block the actions of [(Ala(11), Leu(15))-orexin B].

CONCLUSION

We conclude that orexin A exerts its effects on locomotor behaviour via both the OX(1)R and OX(2)R and that agonism or antagonism of only one of these receptors for therapeutic purposes (i.e. sleep disorders) would not provide selectivity in terms of associated behavioural side effects.

Cholesterol depletion activates rapid internalization of submicron-sized acetylcholine receptor domains at the cell membrane

Novel effects of cholesterol (Chol) on nicotinic acetylcholine receptor (AChR) cell-surface stability, internalization and function are reported. AChRs are shown to occur in the form of submicron-sized (240-280 nm) domains that remain stable at the cell-surface membrane of CHO-K1/A5 cells over a period of hours. Acute (30 min, 37 degrees C) exposure to methyl-beta-cyclodextrin (CDx), commonly used as a diagnostic tool of endocytic mechanisms, is shown here to enhance AChR internalization kinetics in the receptor-expressing clonal cell line. This treatment drastically reduced ( approximately 50%) the number of receptor domains by accelerating the rate of endocytosis (t(1/2) decreased from 1.5-0.5 h). In addition, Chol depletion produced ion channel gain-of-function of the remaining cell-surface AChR, whereas Chol enrichment had the opposite effect. Fluorescence measurements under conditions of direct excitation of the probe Laurdan and of Förster-type resonance energy transfer (FRET) using the intrinsic protein fluorescence as donor both indicated an increase in membrane fluidity in the bulk membrane and in the immediate environment of the AChR protein upon Chol depletion. Homeostatic control of Chol content at the plasmalemma may thus modulate cell-surface organization and stability of receptor domains, and fine tune receptor channel function to temporarily compensate for acute AChR loss from the cell surface.

Variability of platelet aggregate dispersal with glycoprotein IIb-IIIa antagonists eptifibatide and abciximab

BACKGROUND

Utilization of glycoprotein IIb-IIIa (GPIIb-IIIa) inhibitors improves outcomes of patients with acute coronary syndromes (ACS), including those undergoing percutaneous coronary intervention (PCI). These results may be related to the ability of the inhibitors to destabilize coronary thrombi, reduce microembolization, and restore vessel patency.

OBJECTIVE

To evaluate in vitro the ability of GPIIb-IIIa antagonists, abciximab and eptifibatide, to promote the disaggregation of platelet-rich thrombus.

METHODS

Antagonist-induced disaggregation was assayed in plasma by aggregometry, as well as in whole blood by point of care and capillary perfusion systems. Fibrinogen dissociation from the platelet surface was quantified by flow cytometry.

RESULTS

Significant disaggregation of 5 microm ADP-induced aggregates was observed after addition of either agent. The maximum extent and rate of disaggregation were significantly higher with eptifibatide than with abciximab. Both antagonists also dispersed 2 microg mL(-1) collagen-induced aggregates, again with eptifibatide having a greater effect. Eptifibatide, but not abciximab (up to 10 microg mL(-1)), was efficient at dissociating aggregates to single platelets in whole blood and dispersing aggregates that had been aged for 30 min before treatment. Eptifibatide also reduced existing thrombus burden in the perfusion model under arterial flow conditions. A key mechanism of aggregate dispersal was antagonist-induced displacement of platelet-bound fibrinogen, which was greater with eptifibatide, a competitive inhibitor of fibrinogen binding, than with the noncompetitive inhibitor, abciximab.

CONCLUSIONS

These results suggest that drug concentration and residence time, along with thrombus extent and age, may be critical determinants in promoting timely recanalization.

Regulation of CD40L (CD154) and CD62P (p-selectin) surface expression upon GPIIb-IIIa blockade of platelets from stable coronary artery disease patients

INTRODUCTION

The aim of this study was to further characterize the effect of the antiplatelet agents, aspirin and eptifibatide, on the surface expression of CD40L and CD62P on platelets from patients with stable coronary artery disease.

MATERIALS AND METHODS

Platelet function was evaluated using standard light transmission aggregometry. Measurements of CD62P and CD40L were carried out by flow cytometry and ELISA assays.

RESULTS

All patients had the expected level of platelet aggregation inhibition in response to 20 muM ADP in the presence of increasing eptifibatide concentrations. Platelet activation by adenosine diphosphate (ADP) or thrombin agonist peptide (TRAP) increased CD62P and CD40L surface density in the presence of aspirin by 1.9 - 2.8 -fold. Aspirin treatment did not prevent either CD62P or CD40L expression. Eptifibatide pretreatment at pharmacologically relevant concentrations blocked agonist-induced increases in CD62P platelet surface density. A marked percentage of platelets still expressed low levels of surface CD62P suggesting slight platelet activation even with potent platelet inhibition. Eptifibatide also blocked agonist-induced increases in CD40L surface expression and decreased the percent of platelets positive for surface CD40L. Decreased expression of CD40L was due to an inhibition of CD40L translocation and not caused by enhanced shedding from the surface, as soluble CD40L (sCD40L). Eptifibatide concentrations that effectively blocked platelet aggregation correlated with total inhibition of increased CD62P and CD40L surface density.

CONCLUSION

Blockade of the GPIIb-IIIa receptor on platelets from coronary artery disease patients may have significant bearing on reducing proinflammatory and procoagulant events mediated by CD62P and sCD40L.

Adolescent smoking decline during California's tobacco control programme

OBJECTIVE

California's comprehensive tobacco control programme was 13 years old in 2002; by then, children entering adolescence at the start of the programme were young adults. This study examines whether adolescent smoking declined over this period, whether any decline carried through to young adulthood, and whether it was specific to California.

SETTING AND PARTICIPANTS

Most data were from the 1990-2002 California Tobacco Surveys (CTS) (adolescents 12-17 years, > 5000/survey, young adults 18-24 years, > 1000/survey). Additional data were from the national 1992/93-2001/02 Current Population Survey (CPS) (young adults 18-24 years, > 15,000/survey).

RESULTS

Over the 13 year period in California, ever puffing declined by 70% in 12-13 year olds, by 53% in 14-15 year olds from 1992-2002, and by 34% in 16-17 year olds from 1996-2002 (CTS). As noted, the decline commenced progressively later in each older group. Smoking experimentation (1+ cigarettes) and established smoking (> 100 cigarettes in lifetime) showed similar patterns. Compared to 1990, the percentage of California young adults (CTS data) who ever experimented declined by 14%, with half of the decline from 1999-2002. CPS young adult smoking prevalence (established and now smoke everyday or some days) was constant in the rest of the USA over the entire period, but California showed a recent 18% decline from 1998/99 to 2001/02.

CONCLUSIONS

California's comprehensive programme may have kept new adolescent cohorts from experimenting with cigarettes. Low young adolescent experimentation rates at programme start appeared to carry through to young adulthood, resulting in a recent drop in young adult smoking prevalence in California not observed in the rest of the USA.

The use of the point of care Helena ICHOR/Plateletworks and the Accumetrics Ultegra RPFA for assessment of platelet function with GPIIB-IIIa antagonists

OBJECTIVE

To evaluate a newly modified rapid platelet function analysis system (ICHOR/ Plateletworks) and to compare the results obtained with those of traditional light transmission aggregometry (LTA), and the Ultegra/RPFA system.

BACKGROUND

Anti-platelet therapy is standard of care for patients as an adjunct to percutaneous coronary intervention (PCI) or for medical management of non-ST elevation acute coronary syndromes (NSTE ACS). Recent clinical trial results suggest that the three currently approved platelet GPIIb-IIIa receptor antagonists, eptifibatide, tirofiban and abciximab, may vary in extent of inhibition of platelet aggregation (IPA) at the approved doses. Thus, pharmacodynamic evaluations of these agents to determine the extent of platelet function inhibition, especially during the periprocedural time of a cardiac intervention, are necessary. A rapid measurement method as a surrogate for LTA, the current gold standard, would be ideal in order to have the option for dose monitoring or adjustment prior to or during an intervention. The Helena ICHOR/ Plateletworks may be useful for point of care testing.

METHODS

Blood samples collected in D-Phe-Pro-Arg-chloromethyl ketone dihydrochloride (PPACK) anticoagulant were treated with increasing concentrations of eptifibatide, tirofiban or abciximab. LTA was carried out in conjunction with the ICHOR/Plateletworks, using a modified method, and Accumetrics Ultegra with RPFA cartridges.

RESULTS

This study demonstrated that platelet inhibition measured by the ICHOR/Plateletworks mirrored the level of IPA obtained with LTA. In contrast, the Ultegra system had less correlation when compared to LTA at inhibition levels < 90%.

CONCLUSIONS

Based on these data, the ICHOR/ Plateletworks utilized under modified guidelines may serve as a surrogate for LTA when rapid measurements are necessary.A rapid platelet function measurement method as a surrogate for light transmission aggregometry (LTA), the current gold standard, is ideal in order to have the option for GPIIb-IIIa antagonist dose monitoring or adjustment prior to or during a coronary intervention. A newly modified rapid platelet function analysis system (ICHOR/Plateletworks was evaluated and compared to the results obtained with traditional light transmission aggregometry (LTA), and the Ultegra/RPFA system. Blood samples collected in D-Phe-Pro-Arg-chloromethyl ketone dihydrochloride (PPACK) anticoagulant were treated with increasing concentrations of eptifibatide, tirofiban or abciximab. LTA was carried out in conjunction with the ICHOR/Plateletworks, using a modified method, and Accumetrics Ultegra with RPFA cartridges. Based on these data, the ICHOR/Plateletworks utilized under modified guidelines may serve as a surrogate for LTA when rapid measurements are necessary.

Radioactive waste disposal implications of extending Part IIA of the Environmental Protection Act to cover radioactively contaminated land

A short study has been carried out of the potential radioactive waste disposal issues associated with the proposed extension of Part IIA of the Environmental Protection Act 1990 to include radioactively contaminated land, where there is no other suitable existing legislation. It was found that there is likely to be an availability problem with respect to disposal at landfills of the radioactive wastes arising from remediation. This is expected to be principally wastes of high volume and low activity (categorised as low level waste (LLW) and very low level waste (VLLW)). The availability problem results from a lack of applications by landfill operators for authorisation to accept LLW wastes for disposal. This is apparently due to perceived adverse publicity associated with the consultation process for authorisation coupled with uncertainty over future liabilities. Disposal of waste as VLLW is limited both by questions over volumes that may be acceptable and, more fundamentally, by the likely alpha activity of wastes (originating from radium and thorium operations). Authorised on-site disposal has had little attention in policy and guidance in recent years, but may have a part to play, especially if considered commercially attractive. Disposal at BNFL's near surface disposal facility for LLW at Drigg is limited to wastes for which there are no practical alternative disposal options (and preference has been given to operational type wastes). Therefore, wastes from the radioactively contaminated land (RCL) regime are not obviously attractive for disposal to Drigg. Illustrative calculations have been performed based on possible volumes and activities of RCL arisings (and assuming Drigg's future volumetric disposal capacity is 950,000 m3). These suggest that wastes arising from implementing the RCL regime, if all disposed to Drigg, would not represent a significant fraction of the volumetric capacity of Drigg, but could have a significant impact on the radiological capacity with respect to 226Ra plus 232Th. The government's decision-making programme for managing solid radioactive wastes in the UK may possibly achieve a general consensus that the use of landfill for LLW from the RCL regime has a fundamental role to play. However, this is unlikely to change the situation within the next few years. No new national facility arising from this programme is likely to be available during the first decade of the operation of a new RCL regime. Hence it appears that Drigg will need to play an important role for some years to come.

Role of in vitro cholesterol depletion in mediating human platelet aggregation

We investigated the direct role of cholesterol lowering on human platelet aggregation by in vitro cholesterol depletion using methyl-beta-cyclodextrin. Collagen and thrombin receptor agonist peptide induced maximal aggregation was significantly decreased in cholesterol depleted platelets. In contrast, anti-CD9 antibody, mAb7, or anti-beta(3) antibody, D3, induced percent maximal aggregation was unaffected by cholesterol depletion. Surface and total alpha(IIb)beta(3) levels were equivalent in both groups. Morphological and ultrastructural analysis of collagen induced aggregates revealed that normal and cholesterol depleted platelets changed shape and aggregated; however, cholesterol depletion impaired microtubule ring formation and aggregate size. Cholesterol depletion also diminished the extent of the open canalicular system and collagen induced platelet ATP release. These data suggest cholesterol depletion impairs platelet aggregation by altering platelet ultrastructure critical in mediating secretion. Temporal differences and differences in tyrosine phosphoprotein levels following collagen stimulation were observed, thereby indicating that platelet signaling was concurrently affected by cholesterol depletion.

Chinese hamster ovary cell motility to fibronectin is modulated by the second extracellular loop of CD9. Identification of a putative fibronectin binding site

CD9, a member of the tetraspanin family of proteins, is characterized by four transmembrane domains and two extracellular loops. Surface expression of CD9 on Chinese hamster ovary (CHO) cells dramatically enhances spreading and motility on fibronectin. To elucidate the mechanistic basis of CD9-fibronectin interaction, binding to fibronectin was investigated using purified and recombinant forms of CD9. The affinity of fibronectin for CD9 in enzyme-linked immunosorbent assay was 81 +/- 25 nm. The binding of fibronectin to immobilized CD9 was enhanced by Ca(2+) ions. Protein binding and peptide competition studies demonstrated that peptide 6 derived from CD9 extracellular loop 2 (amino acids 168-192) contained part of the fibronectin-binding domain. Additionally, enhanced adhesion of CD9-CHO-B2 cells to fibronectin was significantly reduced by peptide 6. CD9-CHO cells had a 5-fold increase in motility to fibronectin as compared with mock-transfected controls, an effect that correlated with CD9 cell surface density. Truncation of CD9 extracellular loop 2 and peptide 6 caused inhibition of CD9-CHO cell motility to fibronectin. Deletion of CD9 extracellular loop 1 had no significant effect on CHO cell motility. These findings demonstrate a critical role for CD9 extracellular loop 2 in cell motility to fibronectin and clarify the mechanism by which CD9-fibronectin interaction modulates cell adhesion and motility.

Was there significant tax evasion after the 1999 50 cent per pack cigarette tax increase in California?

OBJECTIVES

Several states, including California, have implemented large cigarette excise tax increases, which may encourage smokers to purchase their cigarettes in other lower taxed states, or from other lower or non-taxed sources. Such tax evasion thwarts tobacco control objectives and may cost the state substantial tax revenues. Thus, this study investigates the extent of tax evasion in the 6-12 months after the implementation of California's 0.50 dollars/pack excise tax increase.

DESIGN AND SETTING

Retrospective data analysis from the 1999 California Tobacco Surveys (CTS), a random digit dialled telephone survey of California households.

MAIN OUTCOME MEASURES

Sources of cigarettes, average daily cigarette consumption, and reported price paid.

RESULTS

Very few (5.1 (0.7)% (+/-95% confidence limits)) of California smokers avoided the excise tax by usually purchasing cigarettes from non- or lower taxed sources, such as out-of-state outlets, military commissaries, or the internet. The vast majority of smokers purchased their cigarettes from the most convenient and expensive sources: convenience stores/gas (petrol) stations (45.0 (1.9)%), liquor/drug stores (16.4 (1.6)%), and supermarkets (8.8 (1.2)%).

CONCLUSIONS

Despite the potential savings, tax evasion by individual smokers does not appear to pose a serious threat to California's excise tax revenues or its tobacco control objectives.

Does cigarette price influence adolescent experimentation?

The economics literature generally agrees that state and federal excise taxes can play an important role in deterring adolescent smoking. Teens' apparent responsiveness to cigarette prices is puzzling, since the majority of adolescent smokers do not buy their cigarettes. Teens typically do not begin to purchase cigarettes until they have developed an established pattern of smoking. Previous studies have not had adequate measures of smoking experience to explore whether adolescents' price responsiveness may vary by smoking experience. This paper uses data from a 1993 national survey of youth smoking to explore this hypothesis.

Copepod development rates in relation to genome size and 18S rDNA copy number

It is known that body sizes and temperature-independent developmental durations within two genera of calanoid Copepoda (Crustacea) are positively related to nuclear DNA contents of their somatic nuclei. Evidently because of the constraint of similar cell numbers among the species, (nucleotypic) effects of nucleus size on cell size and on cell-level processes are expressed at the whole-organism level. Here, we show that developmental durations of eight species of five genera are also negatively related to their greatly differing numbers of 18S rRNA genes per unit DNA. We propose that levels of rDNA iteration among copepods have been controlled by natural selection to regulate ribosome concentrations, therefore protein production and development rates, independently of the large variations in genome sizes, which are in turn adapted to regulating cell and therefore body sizes.

Active GPIIb-IIIa conformations that link ligand interaction with cytoskeletal reorganization

Glycoprotein (GP) IIb-IIIa plays a critical role in platelet aggregation and platelet-mediated clot retraction. This study examined the intramolecular relationship between GPIIb-IIIa activation and fibrinogen binding, platelet aggregation, and platelet-mediated clot retraction. To distinguish between different high-affinity activation states of GPIIb-IIIa, the properties of an antibody (D3) specific for GPIIIa that induces GPIIb-IIIa binding to adhesive protein molecules and yet completely inhibits clot retraction were used. Clot retraction inhibition by D3 was not due to altered platelet-fibrin interaction; however, combination treatments of D3 and adenosine diphosphate (ADP) inhibited full-scale aggregation and decreased the amounts of GPIIb-IIIa and talin incorporated into the core cytoskeletons. Morphologic evaluation of the D3/ADP aggregates showed platelets that were activated but to a lesser extent when compared to ADP only. ADP addition to platelets caused an increase in the number of D3 binding sites indicating that ligand had bound to the GPIIb-IIIa receptor. These data suggest that high-affinity GPIIb-IIIa- mediated ligand binding can be separated mechanistically from GPIIb-IIIa-mediated clot retraction and that clot retraction requires additional signaling through GPIIb-IIIa after ligand binding. The conformation recognized by D3 represents the expression of a GPIIb-IIIa activation state that participates in full-scale platelet aggregation, cytoskeletal reorganization, and clot retraction.

Forskolin modulates acetylcholine receptor gating by interacting with the small extracellular loop between the M2 and M3 transmembrane domains

1. Forskolin acts as an allosteric modulator of muscle-type nicotinic acetylcholine receptors. Receptors from mouse muscle and Torpedo electroplax demonstrate differential sensitivity to inhibition by forskolin. Previous work from this laboratory suggested that the gamma subunit is responsible for this differential sensitivity. 2. We have used a series of mouse/Torpedo species-chimeric gamma subunits to further define the site of forskolin interaction with the gamma subunit. Analysis of the patterns of forskolin inhibition of receptors containing mouse/Torpedo chimeric gamma subunits along with the mouse alpha, beta, and delta subunits suggests that forskolin interacts with the small extracellular domain that links the M2 and M3 transmembrane domains (the M2-M3 linker). 3. We suggest that the M2-M3 linker domain plays an important role in the transduction of ligand binding to the conformational changes that result in channel opening.

Association between household and workplace smoking restrictions and adolescent smoking

CONTEXT

Recent marked increases in adolescent smoking indicate a need for new prevention approaches. Whether workplace and home smoking restrictions play a role in such prevention is unknown.

OBJECTIVE

To assess the association between workplace and home smoking restrictions and adolescent smoking.

DESIGN, SETTING, AND SUBJECTS

Data were analyzed from 2 large national population-based surveys, the Current Population Surveys of 1992-1993 and 1995-1996, which included 17,185 adolescents aged 15 to 17 years.

MAIN OUTCOME MEASURES

Smoking status of the adolescents surveyed, compared by presence of home and workplace smoking restrictions.

RESULTS

After adjusting for demographics and other smokers in the household, adolescents who lived in smoke-free households were 74% (95% confidence interval [CI], 62%-88%) as likely to be smokers as adolescents who lived in households with no smoking restrictions. Similarly, adolescents who worked in smoke-free workplaces were 68% (95% CI, 51%-90%) as likely to be smokers as adolescents who worked in a workplace with no smoking restrictions. Adolescent smokers were 1.80 (95% CI, 1.23-2.65) times more likely to be former smokers if they lived in smoke-free homes. The most marked relationship of home smoking restrictions to current adolescent smoking occurred in households where all other members were never-smokers. Current smoking prevalence among adolescents in homes without smoking restrictions approached that among adolescents in homes with a current smoker but with smoking restrictions.

CONCLUSIONS

Parents with minor children should be encouraged to adopt smoke-free homes. Smoke-free workplaces can also augment smoking prevention. These findings emphasize the importance of tobacco control strategies aimed at the entire population rather than at youth alone. JAMA. 2000;284:717-722

Chronic hypoxia, pregnancy, and endothelium-mediated relaxation in guinea pig uterine and thoracic arteries

Vasodilation that occurs during normal pregnancy is associated with enhanced relaxation and decreased contractile response to agonists, which are in part due to increased stimulated and basal nitric oxide (NO). In preeclampsia and/or pregnancies carried at high altitude (HA), this normal vascular adjustment is reversed or diminished. We previously reported that HA exposure did not inhibit the pregnancy-associated decrease in contractile response to agonist or basal NO in guinea pig uterine arteries (UA). We therefore sought to determine whether altitude interfered with effects of pregnancy on endothelium-dependent relaxation through a reduction in stimulated NO. We examined the relaxation response to ACh in UA and bradykinin in thoracic arteries (TA) and effects of NO inhibition with 200 microM N(G)-nitro-L-arginine (L-NNA) in arterial rings isolated from nonpregnant and pregnant guinea pigs exposed throughout gestation to low altitude (LA, 1,600 m, n = 26) or HA (3,962 m, n = 22). In pregnant UA, relaxation to ACh was enhanced (P < 0.05) at both altitudes and NO inhibition diminished, but did not reverse, ACh relaxation. The effect of L-NNA on the relaxation response to ACh was less in HA than in LA animals (P = 0.0021). In nonpregnant UA, relaxation to ACh was similar in LA and HA animals. L-NNA reversed the relaxation response to ACh at HA but not at LA. In TA, relaxation to bradykinin was unaltered by pregnancy or altitude and was completely reversed by NO inhibition. These data suggest that effects of NO inhibition are diminished in UA during pregnancy at HA. Additional studies are needed to confirm whether these effects are mediated through inhibition of stimulated NO. HA exposure did not inhibit relaxation to ACh, perhaps because of stimulation of other vasodilators.

Acetylcholine receptor gating is influenced by the polarity of amino acids at position 9' in the M2 domain

Ligand-gated ion channels contain a conserved leucine at position 9' (L9') in the M2 transmembrane domain. We used multiple substitutions at this position in the gamma subunit of the mouse acetylcholine receptor (AChR) (gammaL9') to examine the role of residue polarity at this position in the gating process at both the macroscopic and single-channel levels. The midpoint of the macroscopic dose-response relationship (EC(50)) and the channel closing rate constant, alpha, decreased as the polarity of the residue at that position increased, suggesting a stabilization of the open state of the channel. Both parameters showed similar dependencies on the polarity of the substituted residue. These data support the notion that during AChR gating, the amino acid at the 9' position moves into a polar environment, and that interactions between this residue and the polar environment determine the stability of the open state. Since this residue is conserved in all other members of the ligand-gated ion channel family, we suggest that a similar mechanism applies to the other members of the family.

Effects of clomipramine hydrochloride on dominance-related aggression in dogs

OBJECTIVE

To compare effects of the serotonergic drug clomipramine hydrochloride with those of placebo for treatment of dominance-related aggression in dogs.

DESIGN

Randomized, placebo-controlled, double-blind clinical trial.

ANIMALS

28 neutered dogs > 1 year old with dominance-related aggression.

PROCEDURE

Dogs displaying > or = 3 aggressive episodes/wk toward > or = 1 human family member in response to identifiable behavioral triggers were included in the study. Owners were instructed not to change patterns of interaction with their dogs during the study. After 2 weeks of baseline observations, dogs were treated for 6 weeks with clomipramine (1.5 mg/kg [0.7 mg/lb] of body weight, q 12 h; n = 15) or placebo (13). Responses to triggers were assigned the following aggression scores: no response, 0; growl or lip curl, 1; snap or bite, 2. Mean scores for responses to triggers were obtained during the 2-week pretreatment period (baseline) and during the first and second weeks, third and fourth weeks, and fifth and sixth weeks of treatment. At the end of the study, owners assigned a score designed to evaluate their overall perceived change in aggressiveness; this was referred to as the global score.

RESULTS

Mean aggression scores decreased at the fifth and sixth week of treatment in both groups, compared with baseline scores. However, mean scores between groups were not different. Global scores, assigned by the owner, generally reflected changes in mean aggression scores.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with placebo, clomipramine administered to dogs at the dosage recommended for treatment of separation anxiety did not reduce aggressiveness toward human family members.

A CD9, alphaIIbbeta3, integrin-associated protein, and GPIb/V/IX complex on the surface of human platelets is influenced by alphaIIbbeta3 conformational states

A noncovalently associated complex comprising of CD9, the fibrinogen (Fg) receptor alphaIIbbeta3, integrin-associated protein (IAP), and glycoprotein (GP) Ib/V/IX complex was isolated from Chaps-solubilized human platelets. The CD9 complex was immunoprecipitated by mAbs specific for CD9 (mAb7), IAP (BRIC126), GPIb (SZ1), GPIX (GR-P), beta3 (AP3) and alphaIIb (C3). Additionally, the association between CD9 and alphaIIbbeta3 was demonstrated by ELISA. In this system, CD9 did not bind to vitronectin receptor (alphavbeta3) suggesting that CD9/alphaIIbbeta3 association was alphaIIb-subunit or alphaIIbbeta3-complex dependent. D3, an alphaIIbbeta3-activating mAb that is also an anti-LIBS (ligand-induced binding site), immunoprecipitated primarily alphaIIbbeta3 with GPIb and IAP. CD9 was not detected in D3 immunoprecipitates. D3 binding induced platelet aggregation via direct alphaIIbbeta3 activation and was upregulated by the alphaIIbbeta3 antagonist eptifibatide. In contrast, AP3 and C3 exhibited neither effect. In addition, D3 also inhibited whole blood clot retraction, in contrast to AP3 and C3, suggesting that conformational constraints on alphaIIbbeta3 by D3 binding not only influenced the CD9 complex but also affected alphaIIbbeta3 post receptor occupancy events. The CD9 complex was immunoprecipitated in the presence of eptifibatide, demonstrating that alphaIIbbeta3 receptor occupancy was not sufficient to cause complex dissociation. CD9 complex isolation was also independent of platelet activation, although a twofold increase in the quantity of CD9 complex was seen after platelet activation by alpha-thrombin in the presence of CaCl2 compared with that present in EDTA. Stirred platelets showed fibrinogen-mediated aggregation by alpha-thrombin in the presence of CaCl2 but not with EDTA, suggesting that fibrinogen crosslinking of CD9 complexes via alphaIIbbeta3 could be partially responsible for this increase. These findings imply that the platelet CD9 complex is independent of platelet activation although it is dependent upon the conformation state of alphaIIbbeta3.

Home smoking restrictions: which smokers have them and how they are associated with smoking behavior

Home smoking restrictions have primarily been promoted as a means of protecting non-smokers from secondhand tobacco smoke. However, research suggests that smokers who live in smoke-free homes may modify their smoking behavior. Population-based survey data from California (n = 8904) were used to confirm this association and to examine demographic and social characteristics of smokers who reported home smoking restrictions. Report of a recent quit attempt and intention to quit were associated with family preference that the smoker not smoke, with home smoking restrictions appearing to be a concrete expression of this social pressure. In contrast, light smoking (< 15 cigarettes/day) was negatively related to family preference (light smokers may not offend non-smokers) but very positively related to the level of home smoking restrictions. Additionally, smoke-free homes appear to prolong time to relapse following cessation. Male smokers were more likely than females to report smoke-free homes, and such reports decreased with age. While Hispanics and Asians were more likely to report smoke-free homes than Non-Hispanic whites, African Americans were less likely to report them. After adjusting for demographics, smokers were nearly 6 times more likely to report smoke-free homes if they lived with a non-smoking adult and child compared to when there was no child or adult non-smoker in the household, and over 5 times more likely to report a smoke-free home if they believed in the harmfulness of secondhand smoke. Tobacco Control efforts to promote smoke-free homes may give family members leverage to encourage smokers to quit, and to modify smokers' behavior in ways that would help them quit and stay quit.

Structural features of the ligand-binding domain of the serotonin 5HT3 receptor

The nicotinic acetylcholine receptor (AChR) and the serotonin type 3 receptor (5HT3R) are members of the ligand-gated ion channel gene family. Both receptors are inhibited by nanomolar concentrations of d-tubocurarine (curare) in a competitive fashion. Chemical labeling studies on the AChR have identified tryptophan residues on the gamma (gammaTrp-55) and delta (deltaTrp-57) subunits that interact with curare. Comparison of the sequences of these two subunits with the 5HT3R shows that a tryptophan residue is found in the homologous position in the 5HT3R (Trp-89), suggesting that this residue may be involved in curare-5HT3R interactions. Site-directed mutagenesis at position Trp-89 markedly reduces the affinity of the 5HT3R for the antagonists curare and granisetron but has little effect on the affinity for the agonist serotonin. To further examine the role of this region of the receptor in ligand-receptor interactions, alanine-scanning mutagenesis analysis of the region centered on Trp-89 (Thr-85 to Trp-94) was carried out, and the ligand binding properties of the mutant receptors were determined. Within this region of the receptor, curare affinity is reduced by substitution only at Trp-89, whereas serotonin affinity is reduced only by substitution at Arg-91. On the other hand, granisetron affinity is reduced by substitutions at Trp-89, Arg-91, and Tyr-93. This differential effect of substitutions on ligand affinity suggests that different ligands may have different points of interaction within the ligand-binding pocket. In addition, the every-other-residue periodicity of the effects on granisetron affinity strongly suggests that this region of the ligand-binding site of the 5HT3R (and by inference, other members of the ligand-gated ion channel family) is in a beta-strand conformation.

Effects of pregnancy and chronic hypoxia on contractile responsiveness to alpha1-adrenergic stimulation

Decreased contractile response to vasoconstrictors in uterine and nonuterine vessels contributes to increased blood flow to the uterine circulation during normal pregnancy. Pregnancies complicated by preeclampsia and/or chronic hypoxia show a reversal or diminution of these pregnancy-associated changes. We sought to determine whether chronic hypoxia opposes the reduction in contractile response in uterine and nonuterine vessels during normal pregnancy and, if so, whether decreased basal nitric oxide (NO) activity was involved. We examined the contractile response to phenylephrine (PE) in guinea pig uterine artery (UA), mesenteric artery (MA), and thoracic aorta (TA) rings isolated from nonpregnant or pregnant guinea pigs that had been exposed throughout gestation to either low (1,600 m, n = 47) or high (3,962 m, n = 43) altitude. In the UA, pregnancy reduced contractile sensitivity to PE and did so similarly at low and high altitude (EC50: 4.0 x 10(-8) nonpregnant, 9.3 x 10(-8) pregnant at low altitude; 4.8 x 10(-8) nonpregnant, 1.0 x10(-8) pregnant at high altitude; both P < 0.05). Addition of the NO synthase inhibitor nitro-L-arginine (NLA; 200 mM) to the vessel bath increased contractile sensitivity in the pregnant UA (P < 0.05) and eliminated the effect of pregnancy at both altitutes. NLA also raised contractile sensitivity in the nonpregnant high-altitude UA, but contractile response without NLA did not differ in the high- and low-altitude animals. In the MA, pregnancy decreased contractile sensitivity to PE at high altitude only, and this shift was reversed by NO inhibition. In the TA, neither pregnancy nor altitude affected contractile response, but NO inhibition raised contractile response in nonpregnant and pregnant TA at both altitudes. We concluded that pregnancy diminished contractile response to PE in the UA, likely as a result of increased NO activity, and that these changes were similar at low and high altitude. Counter to our hypothesis, chronic hypoxia did not diminish the pregnancy-associated reduction in contractile sensitivity to PE or inhibit basal NO activity in the UA; rather it enhanced, not diminished, basal NO activity in the nonpregnant UA and the pregnant MA.

Has the California tobacco control program reduced smoking?

CONTEXT

Comprehensive community-wide tobacco control programs are considered appropriate public health approaches to reduce population smoking prevalence.

OBJECTIVE

To examine trends in smoking behavior before, during, and after the California Tobacco Control Program.

DESIGN

Per capita cigarette consumption data (1983-1997) were derived from tobacco industry sales figures. Adult (> or =18 years) smoking prevalence data were obtained from the National Health Interview Surveys (1978-1994), the California Tobacco Surveys (1990-1996), the Current Population Surveys (1992-1996), and the California Behavioral Risk Factor Survey and its supplement (1991-1997). Trends were compared before and after introduction of the program, with the period after the program being divided into 2 parts (early, 1989-1993; late, 1994-1996).

MAIN OUTCOME MEASURES

Change in cigarette consumption and smoking prevalence in California compared with the rest of the United States.

RESULTS

Per capita cigarette consumption declined 52% faster in California in the early period than previously (from 9.7 packs per person per month at the beginning of the program to 6.5 packs per person per month in 1993), and the decline was significantly greater in California than in the rest of the United States (P<.001). In the late period, the decline in California slowed to 28% of the early program so that in 1996 an average of 6.0 packs per person per month were consumed. No decline occurred in the rest of the United States, and in 1996, 10.5 packs per person per month were consumed. Smoking prevalence showed a similar pattern, but in the late period, there was no significant decline in prevalence in either California or the rest of the United States. In 1996, smoking prevalence was 18.0% in California and 22.4% in the rest of the United States.

CONCLUSIONS

The initial effect of the program to reduce smoking in California did not persist. Possible reasons include reduced program funding, increased tobacco industry expenditures for advertising and promotion, and industry pricing and political activities. The question remains how the public health community can modify the program to regain its original momentum.

Interaction of D-tubocurarine analogs with the 5HT3 receptor

D-Tubocurarine is a potent competitive antagonist of two members of the ligand-gated ion channel family, the muscle-type nicotinic acetylcholine receptor (AChR) and serotonin type-3 receptor (5HT3R). We have used a series of analogs of D-tubocurarine to determine the effects of methylation, stereoisomerization and halogenation on the interaction of D-tubocurarine with the 5HT3R. The affinities of the analogs for the 5HT3R span a 200-fold concentration range and fall into three broad groups. The first group, with affinity constants (Ki) < 150 nM, consists of D-tubocurarine and analogs modified at the nitrogens or 7' hydroxyl. The fact that these compounds all have high affinity for the 5HT3R suggests that these portions of the ligand do not make interactions with the receptor that are critical for high-affinity binding. The second group, with Ki's in the 1-5 microM range, consists of analogs modified at the 12'-hydroxyl or the adjacent 13'-carbon, which suggests that this portion of the ligand makes interactions that are important for high-affinity binding. The third, very low affinity, group is a compound with altered stereoconfiguration at the 1 carbon, demonstrating the importance of proper configuration of the antagonist in ligand-receptor interactions. For the most part, this pattern of selectivity is similar to that for the AChR, suggesting that the structures of the ligand-binding sites of these two receptors share common structural features.

A Ser162-->Leu mutation within glycoprotein (GP) IIIa (integrin beta3) results in an unstable alphaIIbbeta3 complex that retains partial function in a novel form of type II Glanzmann thrombasthenia

Platelets from Glanzmann thrombasthenia patient BL express approximately 30% of the normal alphaIIbbeta3 content and support fibrin-mediated clot retraction, but fail to bind fibrinogen or aggregate following cellular activation. BL platelets bind neither activation-dependent nor activation-independent ligands. DNA sequence analysis of BL platelet mRNA revealed a homozygous C583-->T point mutation in a conserved region of beta3, resulting in a Ser162Leu amino acid substitution. This mutation appears to produce destabilizing effects on the alphaIIbbeta3 complex, as evidenced by the fact that (1) the BL alphaIIbbeta3 complex exhibited altered sedimentation velocity through sucrose gradients, (2) alphaIIb and beta3 was not recognized by complex-dependent monoclonal antibodies or co-precipitated by integrin subunit-specific antibodies, and (3) biosynthesis and trafficking of the alphaIIbbeta3Leu162 complex was delayed relative to that of the wild-type control. Taken together, these data implicate the region encompassing Ser162 in the stabilization and ligand binding properties of the alphaIIbbeta3 complex.

Expression of ligand-induced binding sites on glycoprotein IIb/IIIa complexes and the effect of various inhibitors

Glycoprotein (GP) IIb/IIIa is a therapeutic target for the blockade of platelet aggregation during acute coronary syndromes. Peptides, peptidomimetics, and antibodies are generated that competitively block the binding of fibrinogen or von Willebrand factor to the activated GPIIb/IIIa complex. Binding of these receptor blockades to GPIIb/IIIa effectively inhibits the formation of the platelet aggregate because ligand binding to the activated GPIIb/IIIa is the final common pathway to thrombus formation. In addition, bound antagonists induce a conformational change in the receptor. This conformational change, also called a ligand-induced binding site, can be used as a marker for receptor occupancy by GPIIb/IIIa receptor blockades. Using the binding properties of the D3 monoclonal antibody that binds with high affinity to the antagonist bound GPIIb/IIIa, we have developed a new method for monitoring the extent of receptor blockade by GPIIb/IIIa antagonists. This method has specific advantages over the interpatient variability of the aggregation assay and provides a method for the evaluation of appropriate target levels of GPIIb/IIIa blockade.

A single intravenous dose of murine megakaryocyte growth and development factor potently stimulates platelet production, challenging the necessity for daily administration

The thrombopoietic efficacy of recombinant forms of c-mpl ligand is being actively investigated in preclinical studies using daily dosing schedules. However, a comprehensive kinetic study of the thrombopoietic response to a single injection of recombinant c-mpl ligand has not been performed. Here, we present the results of a detailed kinetic analysis of the platelet response to a single intravenous administration of pegylated recombinant murine megakaryocyte growth and development factor (PEG-rmMGDF) in mice. In addition, we compare the efficacy of single versus daily dosing in stimulating platelet production. A single intravenous injection of PEG-rmMGDF produced a marked and dose-dependent elevation in platelet number and a moderate increase in mean platelet volume (MPV). After administration of 25 or 250 micrograms/kg of PEG-rmMGDF, platelet number was first increased on day 3 and peaked at 2.7-fold (25 micrograms/kg) and 5.7-fold of normal (250 micrograms/kg) on day 5. Thereafter, platelet number declined and returned to baseline by days 9 and 14, with the 25 and 250 micrograms/kg doses, respectively. MPV began to increase on day 2 after PEG-rmMGDF, reaching maximum values of 1.2-fold (25 micrograms/kg) and 1.5-fold of normal (250 micrograms/kg) on day 4. Subsequently, MPV declined and was downregulated on days 6 to 7 (25 micrograms/kg) and day 8 (250 micrograms/kg). Based on these results, we evaluated the platelet response to PEG-rmMGDF administered intravenously as a single dose versus daily for 5 days. A single administration of 100 micrograms/kg produced a higher platelet number on day 5 than daily administration of 100 or 20 micrograms/kg for 5 days. However, the thrombocytosis was less sustained after single versus daily dosing. The smaller platelet number increase on day 5 after daily dosing reflected the production of larger platelets, rather than suppression of thrombopoiesis. Our results indicate that PEG-rmMGDF administered as a single intravenous dose potently stimulates platelet production in mice, challenging the need for its daily administration. Adoption of an intermittent administration schedule of this cytokine could be more efficacious and is merited in future clinical trials.

Effect of Ca2+ on GP IIb-IIIa interactions with integrilin: enhanced GP IIb-IIIa binding and inhibition of platelet aggregation by reductions in the concentration of ionized calcium in plasma anticoagulated with citrate

BACKGROUND

Integrilin (eptifibatide), a potent inhibitor of the fibrinogen binding function of GP IIb-llla, has been shown to reduce the thrombotic complications of angioplasty and of acute coronary syndromes. The present study was designed to determine whether the reduced Ca2+ concentrations in plasma anticoagulated with citrate affect Integrilin binding to GP IIb-IIIa and the ex vivo pharmacodynamic measurements for this drug.

METHODS AND RESULTS

Lower concentrations of Integrilin were found to inhibit platelet aggregation in plasma anticoagulated with citrate (for ADP, mean+/-SD IC(50)=140+/-40 nmol/L, n=6; Ca2+ =40 to 50 micromol/L) than with PPACK (IC(50)=570+/-70 nmol/L, P<.0001, n=6; Ca2+ approximately 1 mmol/L). Chelation of Ca2+ with EDTA or citrate caused a similar degree of enhancement in the inhibitory activity of Integrilin. Measurements of D3 LIBS epitope expression showed that the enhanced inhibitory activity was caused by enhanced GP IIb-IIIa occupancy by Integrilin. Citrate anticoagulation decreased the amounts of Integrilin required to inhibit the binding of PAC1, a monoclonal antibody that mimics the GP IIb-IIIa binding activity of fibrinogen. Reduced Ca2+ also increased Integrilin inhibition of the binding of biotinylated fibrinogen to purified, immobilized GP IIb-IIIa.

CONCLUSIONS

These data suggest that citrate anticoagulation removes Ca2+ from GP IIb-IIIa and enhances the apparent inhibitory activity of Integrilin. This finding indicates that the inhibitory activity of Integrilin is overestimated in blood samples collected with citrate, suggesting that it may be possible to achieve greater antithrombotic efficacy beyond that observed in clinical trials to date with Integrilin.

Selective induction of a glycoprotein IIIa ligand-induced binding site by fibrinogen and von Willebrand factor

Ligand-induced binding sites (LIBS) are neoantigenic regions of glycoprotein (GP)IIb-IIIa that are exposed upon interaction of the receptor with the ligand fibrinogen or the ligand recognition sequence (RGDS). LIBS have been suggested to contribute to postreceptor occupancy events such as full-scale platelet aggregation, adhesion to collagen, and clot retraction. This study examined the induction requirements of a GPIIIa LIBS with regard to ligand specificity. Through the use of the anti-LIBS D3, we report that this complex-activating antibody induces fibrinogen- and von Willebrand factor-binding to GPIIb-IIIa on intact platelets. Bound ligand was detected by flow cytometric analysis and platelet aggregation assays. These bound ligands increased the number of D3-binding sites and altered the affinity of D3 for GPIIb-IIIa on platelets. In contrast, activation of platelet GPIIb-IIIa by D3 did not increase the binding of another RGD-containing ligand, vitronectin. Furthermore, bound vitronectin on thrombin-stimulated platelets did not cause the expression of the D3 LIBS epitope. We conclude direct activation of GPIIb-IIIa in the absence of platelet activation results in selective ligand interaction and that D3 LIBS induction requires the binding of the multivalent ligands, fibrinogen or von Willebrand factor. Thus, the region of GPIIIa recognized by D3 may be an important regulatory domain in ligand-receptor interactions that directly mediate platelet aggregation.

cAMP promotes gap junctional coupling in T84 cells

The effect of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) on dye and electrical coupling was studied in T84 cells, a cell line often used as a model for epithelial cell fluid secretion. Injections of lucifer yellow (LY) into single cells within a cluster of control cells resulted in LY localization to 1.3 +/- 0.2 (mean +/- SE) cells within a cluster. Twenty-six percent of control T84 cell pairs were electrically coupled as assayed by the dual patch-clamp technique. Treatment of cells with agents that either increase intracellular cAMP and/or activate protein kinase A (PKA) increased dye localization to 3.8 +/- 0.6 cells and the proportion of electrically coupled cell pairs to 65%. No electrical coupling was observed in the presence of the Rp diastereomer of adenosine-3',5'-cyclic monophosphothioate (Rp-cAMPS), a PKA antagonist. Excess of Rp-cAMPS prevented cell coupling elicited by 20 microM of the Sp diastereomer of adenosine-3',5'-cyclic monophosphothioate. Expression of connexin 32 mRNA, but not of connexins 26, 43, or 45, was detected by reverse transcription-polymerase chain reaction. These results suggest that communication between T84 cells is modulated by PKA, providing a mechanism for regulating multicellular activity, such as fluid secretion.

Interspecies comparison of platelet aggregation, LIBS expression and clot retraction: observed differences in GPIIb-IIIa functional activity

We examined interspecies differences in the function of the platelet fibrinogen receptor, GPIIb-IIIa, by comparing platelet aggregation responses to adenosine diphosphate (ADP) added alone or in combination with a GPIIIa specific monoclonal antibody (mAb), D3. D3 can activate the GPIIb-IIIa receptor in the absence of platelet activation, and it preferentially binds to a region on the GPIIIa subunit after the GPIIb-IIIa complex is occupied by ligand. Using human, monkey, dog, rabbit and pig platelets, we examined whether all species' platelets bound the D3 mAb similarly, and if the binding of Arg-Gly-Asp-Ser (RGDS) peptides induced the exposure of the anti-LIBS (D3) epitope as previously described for human platelets. We also evaluated how blocking of this neoantigenic region by the D3 mAb affected clot retraction, a process that requires linkage of GPIIb-IIIa with fibrin(ogen) and the platelet cytoskeleton. We found that all species tested bound the D3 mAb. Only in human and monkey platelets did D3 cause aggregation as well as inhibit clot retraction. However, in all species tested, except for pig, D3 prevented disaggregation of platelets typically observed when platelets are treated with low dose ADP. With the exception of pig platelets, there was increased D3 binding to platelets in the presence of RGDS peptides. We propose that this region of GPIIIa is important in the conformational changes that GPIIb-IIIa undergoes during the binding of ligand in most species tested. Our studies suggest 1) there are measurable inter-species differences in GPIIb-IIIa mediated platelet aggregation and clot retraction, 2) LIBS expression due to receptor occupancy is a common but not all-inclusive response and 3) interspecies comparisons may be useful in understanding structural and functional aspects of platelet GPIIb-IIIa.

The role of conserved leucines in the M2 domain of the acetylcholine receptor in channel gating

A highly conserved leucine is found in the middle of the porelining (M2) domain of the members of the ligand-gated ion channel family. Two very different roles have been proposed for this leucine. In one model, this residue swings into the lumen of the channel during desensitization to form the nonconducting desensitized state, whereas in the other model, the leucines from each subunit interact with each other to form a constriction in the channel that constitutes the actual gate of the channel. We examined the role of this leucine in the muscle-type acetylcholine receptor by replacing it with the polar amino acid threonine. Replacement of the leucine in any one subunit slows desensitization and shifts the dose-response relationship toward lower concentrations. Replacement of leucines in additional subunits leads to progressively larger shifts in the dose-response curves. The shift depends only on the number of leucines replaced, not on which particular subunits contain the mutation; in other words, the mutations act independently. At the single-channel level, the mutation greatly increases the channel mean open time. We conclude that the role of the conserved leucine is to set the mean open time of the channel through interactions with other regions of the receptor rather than to serve as the gate per se of the ion channel.

A flow cytometric assay using mepacrine for study of uptake and release of platelet dense granule contents

Diagnosis of platelet dense granule storage pool disease and release defects at present requires a combination of studies including lumiaggregometry, conventional platelet aggregation, radioactive serotonin uptake and release, and electron microscopy. Flow cytometric methods have been developed to study platelet activation, aggregation, and alpha-granule protein release. Here, we have investigated the use of flow cytometry for analysis of platelet dense granule content uptake and release using mepacrine as a fluorescent marker. Mepacrine (quinacrine) is rapidly taken up and localized in dense granules of platelets. For the assay, as little as 20 microliters of blood from a fingerstick collected without anticoagulant or venous blood collected in 3.8% sodium citrate were diluted 1:40 with 2 ml Hanks balanced salt solution (BSS). 300 microliters of this cell suspension were incubated with mepacrine alone, or simultaneously with a mouse monoclonal antibody to human platelet glycoprotein IIb (Tab), used as a platelet-specific marker. The bound monoclonal antibody was then indirectly labelled with the fluorochrome, RED670. 100 microliters of the sample were further diluted with Hanks BSS for one- or two-colour flow cytometric analysis. To verify that mepacrine uptake was related to platelet dense granule content, platelets of beige mice, a strain with dense granule deficiency, were examined. Their mepacrine uptake was substantially decreased compared to that of normal mice. Decreased mepacrine uptake also was demonstrated in platelets of a patient with Hermansky-Pudlak syndrome in which a deficiency of platelet dense granules is characteristic. In both human and mouse platelets, mepacrine uptake was proportional to platelet size. Thrombin induced mepacrine release in a dose-dependent manner from 0.003 to 0.4 U/ml. Therefore both platelet uptake and release of mepacrine can be readily detected by flow cytometry. Flow cytometry provides an attractive alternative to aggregation and radioactive serotonin as methods to study defects in platelet dense granule function.

Gating properties of mutant acetylcholine receptors

A number of affinity labeling studies have identified several tyrosine residues in the alpha subunit of the nicotinic acetylcholine receptor as being in or near the ligand binding site. Studies employing site-directed mutagenesis of these residues (alpha Y93, alpha Y190, and alpha Y198; the notation used is subunit/amino acid/position in the Torpedo receptor/substitution) in mouse muscle, Torpedo electroplax, and alpha 7 neuronal acetylcholine receptors have demonstrated that substitution of phenylalanine for tyrosine results in a shift towards higher concentrations in the macroscopic dose-response curves for acetylcholine-elicited currents from voltage-clamped Xenopus oocytes that express the receptors. This decrease in apparent affinity has been ascribed to either a reduction in binding affinity or a reduction in the coupling of agonist binding to ion channel opening; both mechanisms would give rise to shifts in the dose-response curves. We have used kinetic analysis of ion channel gating at the single-channel level to obtain estimates for the rate constants associated with the ligand binding and channel opening steps for wild-type, alpha Y93F, and alpha Y198F receptors. The results suggest that the underlying cause of the shifts in the macroscopic dose-response curves is a reduction in acetylcholine affinity for the resting activatable state of the receptor. Furthermore, it is the association rate for agonist binding, rather than the dissociation rate, that is most affected by the mutations.

Ligand-receptor interactions in the nicotinic acetylcholine receptor probed using multiple substitutions at conserved tyrosines on the alpha subunit

Affinity labeling studies have identified several conserved tyrosine residues in the alpha subunit of the nicotinic acetylcholine receptor (alpha Y93, alpha Y190, and alpha Y198) as being in or near the ligand binding site. Mutagenesis studies from several laboratories have shown that substitution of phenylalanine for tyrosine at these positions reduces the apparent affinity for ACh. We have examined this apparent reduction in affinity further through the use of multiple substitutions at each position. Substitution of either phenylalanine, tryptophan, or serine resulted in an apparent decrease in agonist affinity, but the degree of reduction depended on both the position and the nature of the substitution. Analysis of the effects of each substitution suggests that each residue interacts with the quaternary N of ACh, and that each residue may make a different type of interaction with the agonist.

Characterization of d-tubocurarine binding site of Torpedo acetylcholine receptor

d-Tubocurarine (curare) is a well-characterized competitive antagonist of nicotinic acetylcholine receptors (AChRs), and it is usually assumed that curare and agonists share a common binding site. We have examined the role of several highly conserved residues of the alpha-, gamma-, and delta-subunits in the interaction of curare with the Torpedo acetylcholine receptor (AChR). Curare inhibition of wild-type receptors is consistent with curare binding to a single high-affinity binding site [inhibitor constant (Ki) = 20 nM]. Phenylalanine substitutions for two tyrosine residues implicated as being in the ligand binding site (alpha Y93F, alpha Y190F) reduce curare affinity, indicating that these residues are also important for high-affinity curare binding. Phenylalanine substitution for alpha Y198 [alpha Y198F (notation used here: subunit/amino acid in wild-type/residue number/substitution)] causes a 10-fold increase in curare affinity (Ki = 3.1 nM), and measurement of the recovery from curare inhibition indicates that this increase in affinity is due to a reduction in the rate of curare dissociation from the receptor. In addition to the alpha-subunits, portions of the ligand binding sites also reside on the gamma- and delta-subunits, and photoaffinity studies have implicated two residues (gamma W55 and delta W57) as forming part of the curare sites. The gamma W55L mutation results in an eightfold decrease in curare affinity (Ki = 170 nM), whereas the delta W57L mutation has no effect. These data support the notion that the high-affinity curare binding site is formed by segments of the alpha- and gamma-subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine-induced platelet defects

BACKGROUND AND PURPOSE

Numerous studies have demonstrated an association between acute cardiac events, cerebrovascular accidents, and cocaine use. The underlying mechanisms leading to these complications have not been well defined. Using various in vitro model systems, it has been reported that cocaine, up to or greater than an order of magnitude of the lethal dose, causes either inhibitory or proaggregatory effects on platelet function.

METHODS

To address these reported discrepancies, we examined the effect of cocaine and its carrier on the activation and aggregation of human platelets in vitro.

RESULTS

We found that cocaine inhibited platelet aggregation when platelets were challenged with ADP, collagen, or arachidonic acid. This inhibition was due to a direct effect on fibrinogen binding to the activated platelet. Cocaine also caused the dissociation of preformed platelet aggregates. At these same concentrations, cocaine did not inhibit agonist-mediated increases in cytosolic calcium or inhibit platelet shape change, suggesting that its effect on platelet aggregation was a selective process and not due to a total destruction of platelet function. Interestingly, the organization of the cytoskeleton of activated platelets, a secondary event critical to cell receptor clustering and clot retraction, was disrupted by cocaine treatment. In addition, alterations in platelet protein electrophoretic patterns were observed on preincubation of platelets with cocaine.

CONCLUSIONS

We conclude that cocaine may have a direct inhibitory effect on the ability of platelets to participate in thrombus formation. The contribution of this effect as an underlying mechanism of sudden death in cocaine abusers is unknown.

Selective enhancement of the interaction of curare with the nicotinic acetylcholine receptor

Alteration of the ligand-binding domain of the nicotinic acetylcholine receptor through site-directed mutagenesis offers a powerful approach to the elucidation of structure-function relations in the receptor. Several conserved tyrosine residues in the large extracellular amino terminus of the alpha subunit of the receptor have been implicated by both chemical labeling and mutagenesis studies as playing an important role in the interaction of acetylcholine with the receptor. We and others have previously shown that substitution of phenylalanine for tyrosine at position 198 of the alpha subunit (alpha Y198F) leads to a rightward shift in the dose-response curve for acetylcholine-elicited currents. We have further investigated this particular mutation by examining the interaction of the competitive antagonist d-tubocurarine (curare) with the receptor. In contrast to the effect on the interaction of agonists with the receptor, this mutation leads to a marked increase in the affinity of the receptor for curare. Furthermore, this enhancement in affinity is selective for curare and is not seen with other competitive antagonists (pancuronium, beta-erythroidine, and gallamine). Examination of the structures of these competitive antagonists leads to the proposal that this enhancement is due to the formation of an aromatic-aromatic interaction between the phenylalanine ring at position alpha 198 in the mutant and one of the aromatic rings of curare and that this can provide information about the spatial arrangement of this residue in the binding site.