Evolutionary loss of inflammasomes in the Carnivora and implications for the carriage of zoonotic infections

Zoonotic pathogens, such as COVID-19, reside in animal hosts before jumping species to infect humans. The Carnivora, like mink, carry many zoonoses, yet how diversity in host immune genes across species affect pathogen carriage is poorly understood. Here, we describe a progressive evolutionary downregulation of pathogen-sensing inflammasome pathways in Carnivora. This includes the loss of nucleotide-oligomerization domain leucine-rich repeat receptors (NLRs), acquisition of a unique caspase-1/-4 effector fusion protein that processes gasdermin D pore formation without inducing rapid lytic cell death, and the formation of a caspase-8 containing inflammasome that inefficiently processes interleukin-1β. Inflammasomes regulate gut immunity, but the carnivorous diet has antimicrobial properties that could compensate for the loss of these immune pathways. We speculate that the consequences of systemic inflammasome downregulation, however, can impair host sensing of specific pathogens such that they can reside undetected in the Carnivora.

International Union of Basic and Clinical Pharmacology. XCVI. Pattern recognition receptors in health and disease

Since the discovery of Toll, in the fruit fly Drosophila melanogaster, as the first described pattern recognition receptor (PRR) in 1996, many families of these receptors have been discovered and characterized. PRRs play critically important roles in pathogen recognition to initiate innate immune responses that ultimately link to the generation of adaptive immunity. Activation of PRRs leads to the induction of immune and inflammatory genes, including proinflammatory cytokines and chemokines. It is increasingly clear that many PRRs are linked to a range of inflammatory, infectious, immune, and chronic degenerative diseases. Several drugs to modulate PRR activity are already in clinical trials and many more are likely to appear in the near future. Here, we review the different families of mammalian PRRs, the ligands they recognize, the mechanisms of activation, their role in disease, and the potential of targeting these proteins to develop the anti-inflammatory therapeutics of the future.

Insights into the molecular basis of the NOD2 signalling pathway

The cytosolic pattern recognition receptor NOD2 is activated by the peptidoglycan fragment muramyl dipeptide to generate a proinflammatory immune response. Downstream effects include the secretion of cytokines such as interleukin 8, the upregulation of pro-interleukin 1β, the induction of autophagy, the production of antimicrobial peptides and defensins, and contributions to the maintenance of the composition of the intestinal microbiota. Polymorphisms in NOD2 are the cause of the inflammatory disorder Blau syndrome and act as susceptibility factors for the inflammatory bowel condition Crohn's disease. The complexity of NOD2 signalling is highlighted by the observation that over 30 cellular proteins interact with NOD2 directly and influence or regulate its functional activity. Previously, the majority of reviews on NOD2 function have focused upon the role of NOD2 in inflammatory disease or in its interaction with and response to microbes. However, the functionality of NOD2 is underpinned by its biochemical interactions. Consequently, in this review, we have taken the opportunity to address the more ‘basic’ elements of NOD2 signalling. In particular, we have focused upon the core interactions of NOD2 with protein factors that influence and modulate the signal transduction pathways involved in NOD2 signalling. Further, where information exists, such as in relation to the role of RIP2, we have drawn comparison with the closely related, but functionally discrete, pattern recognition receptor NOD1. Overall, we provide a comprehensive resource targeted at understanding the complexities of NOD2 signalling.

Secreted effectors in Toxoplasma gondii and related species: determinants of host range and pathogenesis?

Recent years have witnessed the discovery of a number of secreted proteins in Toxoplasma gondii that play important roles in host-pathogen interactions and parasite virulence, particularly in the mouse model. However, the role that these proteins play in driving the unique features of T. gondii compared to some of its nearest apicomplexan relatives (Hammondia hammondi and Neospora caninum) is unknown. These unique features include distinct dissemination characteristics in vivo and a vast host range. In this review we comprehensively survey what is known about disease outcome, the host response and host range for T. gondii, H. hammondi, and N. caninum. We then review what is presently known about recently identified secreted virulence effectors in these three genetically related, but phenotypically distinct, species. Finally we exploit the existence of genome sequences for these three organisms and discuss what is known about the presence, and functionality, of key T. gondii effectors in these three species.

Diverse mechanisms underlying the regulation of ion channels by carbon monoxide

Carbon monoxide (CO) is firmly established as an important, physiological signalling molecule as well as a potent toxin. Through its ability to bind metal-containing proteins, it is known to interfere with a number of intracellular signalling pathways, and such actions can account for its physiological and pathological effects. In particular, CO can modulate the intracellular production of reactive oxygen species, NO and cGMP levels, as well as regulate MAPK signalling. In this review, we consider ion channels as more recently discovered effectors of CO signalling. CO is now known to regulate a growing number of different ion channel types, and detailed studies of the underlying mechanisms of action are revealing unexpected findings. For example, there are clear areas of contention surrounding its ability to increase the activity of high conductance, Ca(2+) -sensitive K(+) channels. More recent studies have revealed the ability of CO to inhibit T-type Ca(2+) channels and have unveiled a novel signalling pathway underlying tonic regulation of this channel. It is clear that the investigation of ion channels as effectors of CO signalling is in its infancy, and much more work is required to fully understand both the physiological and the toxic actions of this gas. Only then can its emerging use as a therapeutic tool be fully and safely exploited.

Blau syndrome polymorphisms in NOD2 identify nucleotide hydrolysis and helical domain 1 as signalling regulators

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NOD2 SNPs that cause Blau syndrome cluster in two regions of the NACHT.

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The ATP/Mg2+ binding pocket cluster are likely to dysregulate ATP hydrolysis.

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SNPs in helical domain 1 are predicted to influence receptor autoinhibition.

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Complementary mutations in NOD1 do not all result in hyperactivation.

Understanding how single nucleotide polymorphisms (SNPs) lead to disease at a molecular level provides a starting point for improved therapeutic intervention. SNPs in the innate immune receptor nucleotide oligomerisation domain 2 (NOD2) can cause the inflammatory disorders Blau Syndrome (BS) and early onset sarcoidosis (EOS) through receptor hyperactivation. Here, we show that these polymorphisms cluster into two primary locations: the ATP/Mg²⁺-binding site and helical domain 1. Polymorphisms in these two locations may consequently dysregulate ATP hydrolysis and NOD2 autoinhibition, respectively. Complementary mutations in NOD1 did not mirror the NOD2 phenotype, which indicates that NOD1 and NOD2 are activated and regulated by distinct methods.

Engagement of nucleotide-binding oligomerization domain-containing protein 1 (NOD1) by receptor-interacting protein 2 (RIP2) is insufficient for signal transduction

Following activation, the cytoplasmic pattern recognition receptor nucleotide-binding oligomerization domain-containing protein 1 (NOD1) interacts with its adaptor protein receptor-interacting protein 2 (RIP2) to propagate immune signaling and initiate a proinflammatory immune response. This interaction is mediated by the caspase recruitment domain (CARD) of both proteins. Polymorphisms in immune proteins can affect receptor function and predispose individuals to specific autoinflammatory disorders. In this report, we show that mutations in helix 2 of the CARD of NOD1 disrupted receptor function but did not interfere with RIP2 interaction. In particular, N43S, a rare polymorphism, resulted in receptor dysfunction despite retaining normal cellular localization, protein folding, and an ability to interact with RIP2. Mutation of Asn-43 resulted in an increased tendency to form dimers, which we propose is the source of this dysfunction. We also demonstrate that mutation of Lys-443 and Tyr-474 in RIP2 disrupted the interaction with NOD1. Mapping the key residues involved in the interaction between NOD1 and RIP2 to the known structures of CARD complexes revealed the likely involvement of both type I and type III interfaces in the NOD1·RIP2 complex. Overall we demonstrate that the NOD1-RIP2 signaling axis is more complex than previously assumed, that simple engagement of RIP2 is insufficient to mediate signaling, and that the interaction between NOD1 and RIP2 constitutes multiple CARD-CARD interfaces.

Comparative Genomic and Sequence Analysis Provides Insight into the Molecular Functionality of NOD1 and NOD2

Amino acids with functional or key structural roles display higher degrees of conservation through evolution. The comparative analysis of protein sequences from multiple species and/or between homologous proteins can be highly informative in the identification of key structural and functional residues. Residues which in turn provide insight into the molecular mechanisms of protein function. We have explored the genomic and amino acid conservation of the prototypic innate immune genes NOD1 and NOD2. NOD1 orthologs were found in all vertebrate species analyzed, whilst NOD2 was absent from the genomes of avian, reptilian and amphibian species. Evolutionary trace analysis was used to identify highly conserved regions of NOD1 and NOD2 across multiple species. Consistent with the known functions of NOD1 and NOD2 highly conserved patches were identified that matched the Walker A and B motifs and provided interaction surfaces for the adaptor protein RIP2. Other patches of high conservation reflect key structural functions as predicted by homology models. In addition, the pattern of residue conservation within the leucine-rich repeat (LRR) region of NOD1 and NOD2 is indicative of a conserved mechanism of ligand recognition involving the concave surface of the LRRs.

Beyond the genome: recent advances in Toxoplasma gondii functional genomics

Recent years have witnessed an explosion in the amount of genomic information available for Toxoplasma gondii and other closely related pathogens. These data, many of which have been made publicly available prior to publication, have facilitated a wide variety of functional genomics studies. In this review, we provide a brief overview of existing database tools for querying the Toxoplasma genome and associated genome-wide data and review recent publications that have been facilitated by these data. Topics covered include strain comparisons and quantitative trait loci mapping, gene expression analyses during the cell cycle as well as during parasite differentiation, and proteomics.

Computational analysis predicts the Kaposi's sarcoma-associated herpesvirus tegument protein ORF63 to be alpha helical

The innate immune response provides our first line of defence against infection. Over the course of evolution, pathogens have evolved numerous strategies to either avoid activating or to limit the effectiveness of the innate immune system. The Kaposi's sarcoma-associated herpesvirus (KSHV) contains tegument proteins in the virion that contribute to immune evasion and aid the establishment of viral infection. For example, the KSHV tegument protein ORF63 modulates inflammasome activation to inhibit the innate immune response against the virus. Understanding the likely structure of proteins involved in immune evasion enables potential mechanisms of action to be proposed. To understand more fully how ORF63 modulates the innate immune system we have utilized widely available bioinformatics tools to analyze the primary protein sequence of ORF63 and to predict its secondary and tertiary structure. We found that ORF63 is predicted to be almost entirely alpha-helical and may possess similarity to HEAT repeat containing proteins. Consequently, ORF63 is unlikely to be a viral homolog of the NLR protein family. ORF63 may inhibit the innate immune response by flexibly interacting with its target protein and inhibiting the recruitment of protein co-factors and/or conformational changes required for immune signaling.

Pathogen sensing by nucleotide-binding oligomerization domain-containing protein 2 (NOD2) is mediated by direct binding to muramyl dipeptide and ATP

Nucleotide binding and oligomerization domain-containing protein 2 (NOD2/Card15) is an intracellular protein that is involved in the recognition of bacterial cell wall-derived muramyl dipeptide. Mutations in the gene encoding NOD2 are associated with inherited inflammatory disorders, including Crohn disease and Blau syndrome. NOD2 is a member of the nucleotide-binding domain and leucine-rich repeat-containing protein gene (NLR) family. Nucleotide binding is thought to play a critical role in signaling by NLR family members. However, the molecular mechanisms underlying signal transduction by these proteins remain largely unknown. Mutations in the nucleotide-binding domain of NOD2 have been shown to alter its signal transduction properties in response to muramyl dipeptide in cellular assays. Using purified recombinant protein, we now demonstrate that NOD2 binds and hydrolyzes ATP. Additionally, we have found that the purified recombinant protein is able to bind directly to muramyl dipeptide and can associate with known NOD2-interacting proteins in vitro. Binding of NOD2 to muramyl dipeptide and homo-oligomerization of NOD2 are enhanced by ATP binding, suggesting a model of the molecular mechanism for signal transduction that involves binding of nucleotide followed by binding of muramyl dipeptide and oligomerization of NOD2 into a signaling complex. These findings set the stage for further studies into the molecular mechanisms that underlie detection of muramyl dipeptide and assembly of NOD2-containing signaling complexes.

Toxoplasma co-opts host gene expression by injection of a polymorphic kinase homologue

Toxoplasma gondii, an obligate intracellular parasite of the phylum Apicomplexa, can cause severe disease in humans with an immature or suppressed immune system. The outcome of Toxoplasma infection is highly dependent on the strain type, as are many of its in vitro growth properties. Here we use genetic crosses between type II and III lines to show that strain-specific differences in the modulation of host cell transcription are mediated by a putative protein kinase, ROP16. Upon invasion by the parasite, this polymorphic protein is released from the apical organelles known as rhoptries and injected into the host cell, where it ultimately affects the activation of signal transducer and activator of transcription (STAT) signalling pathways and consequent downstream effects on a key host cytokine, interleukin (IL)-12. Our findings provide a new mechanism for how an intracellular eukaryotic pathogen can interact with its host and reveal important differences in how different Toxoplasma lineages have evolved to exploit this interaction.

Amyloid peptides mediate hypoxic increase of L-type Ca2+ channels in central neurones

Prolonged hypoxia, encountered in individuals suffering from various cardiorespiratory diseases, enhances the likelihood of subsequently developing Alzheimer's disease (AD). However, the underlying mechanisms are unknown, as are the mechanisms of neurodegeneration of amyloid beta peptides (AbetaPs), although the latter involves disruption of Ca2+ homeostasis. Here, immunohistochemistry demonstrated that hypoxia increased production of AbetaPs, an effect which was prevented by inhibition of either beta or gamma secretase, the enzymes required for liberation of AbetaP from its precursor protein. Whole-cell patch clamp recordings showed that hypoxia selectively increased functional expression of L-type Ca2+ channels. This was prevented by inhibition of either beta or gamma secretase, indicating that hypoxic channel up-regulation is dependent upon AbetaP formation. Our results indicate for the first time that hypoxia promotes AbetaP formation in central neurons, and show that this leads to abnormally high selective expression of L-type Ca2+ channels whose blockade has previously been shown to be neuroprotective in AD models. These findings provide a cellular basis for understanding the increased incidence of AD following prolonged hypoxia.

Hypoxic regulation of Ca2+ signalling in astrocytes and endothelial cells

Acute hypoxia is well known to modulate plasmalemmal ion channels in specific tissue types, thereby modulating [Ca2+]i. Alternative mechanisms by which acute hypoxia could modulate [Ca2+]i are less well explored, particularly in non-excitable cells. Here, we describe experiments employing microfluorimetric recordings from Fura-2-loaded rat cortical astrocytes and human saphenous vein endothelial cells designed to explore any effects of hypoxia (pO2 20-30 mmHg) on [Ca2+]i. In both cell types, hypoxia evoked small rises of [Ca2+]i in the majority of cells during perfusion with a Ca(2+)-free solution, indicating hypoxia can release Ca2+ from an intracellular pool. Capacitative Ca2+ entry was observed when Ca2+ was subsequently restored to the extracellular solution. These effects were abolished by pre-treatment of cells with thapsigargin or prior application of inositol 1,4,5-trisphosphate (IP3)-generating agonists. Antioxidants fully prevented this effect of hypoxia in both cell types. Mitochondrial uncoupling significantly enhanced the effects of hypoxia in astrocytes, yet markedly suppressed the effects of hypoxia in endothelial cells. Our findings indicate that hypoxia can modulate [Ca2+]i in non-excitable cells; most importantly, it can evoke Ca2+ release from intracellular stores via a mechanism which involves reactive oxygen species. The involvement of mitochondria in this effect appears to be tissue specific.

Hypoxic regulation of Ca2+ signaling in cultured rat astrocytes

Acute hypoxia modulates various cell processes, such as cell excitability, through the regulation of ion channel activity. Given the central role of Ca2+ signaling in the physiological functioning of astrocytes, we have investigated how acute hypoxia regulates such signaling, and compared results with those evoked by bradykinin (BK), an agonist whose ability to liberate Ca2+ from intracellular stores is well documented. In Ca2+-free perfusate, BK evoked rises of [Ca2+]i in all cells examined. Hypoxia produced smaller rises of [Ca2+]i in most cells, but always suppressed subsequent rises of [Ca2+]i induced by BK. Thapsigargin pre-treatment of cells prevented any rise of [Ca2+]i evoked by either BK or hypoxia. Restoration of Ca2+ to the perfusate following a period of acute hypoxia always evoked capacitative Ca2+ entry. During mitochondrial inhibition (due to exposure to carbonyl cyanide p-trifluromethoxyphenyl hydrazone (FCCP) and oligomycin), rises in [Ca2+]i (observed in Ca2+-free perfusate) evoked by hypoxia or by BK, were significantly enhanced, and hypoxia always evoked responses. Our data indicate that hypoxia triggers Ca2+ release from endoplasmic reticulum stores, efficiently buffered by mitochondria. Such liberation of Ca2+ is sufficient to trigger capacitative Ca2+ entry. These findings indicate that the local O2 level is a key determinant of astrocyte Ca2+ signaling, likely modulating Ca2+-dependent astrocyte functions in the central nervous system.

Pharmacological and autoradiographical characterization of serotonin transporter-like activity in sporocysts of the human blood fluke, Schistosoma mansoni

The present study focuses on the role of the biogenic monoamine serotonin (5-hydroxytryptamine) in the biology of sporocyst stages of the human blood fluke, Schistosoma mansoni, and its importance during obligate development within its snail host Biomphalaria glabrata. Based on previous work demonstrating that snails infected with S. mansoni have reduced levels of 5-hydroxytryptamine, we hypothesized that sporocysts actively transport this molecule from the host milieu. Intact sporocysts isolated in vitro take up exogenous 5-hydroxytryptamine via a high-affinity mechanism (K(m)=1.4 micromol l(-1)), and this serotonin transporter-like activity is dependent upon extracellular Na(+) and Cl(-) and is highly sensitive to previously characterized serotonin transporter inhibitors. Autoradiography suggests that transported [(3)H]5-hydroxytryptamine localizes within the body of the sporocyst, and in many cases is found in apical gland cells. Moreover, serotonin transporter-like activity is absent in free-swimming miracidia, the infective stage for the snail host, and the increase in larval serotonin transporter-like activity after miracidium-to-sporocyst transformation is accompanied by a corresponding decrease in steady-state levels of transcripts for tryptophan hydroxylase, the rate-limiting enzyme in serotonin biosynthesis. Overall our data suggest that S. mansoni larvae express surface-exposed serotonin transporter-like molecules, and that the transition from free-living miracidium to parasitic mother sporocyst is characterized by an increased dependence upon exogenous 5-hydroxytryptamine.

Chronic hypoxia potentiates capacitative Ca2+ entry in type-I cortical astrocytes

Prolonged hypoxia exerts profound effects on cell function, and has been associated with increased production of amyloid beta peptides (A beta Ps) of Alzheimer's disease. Here, we have investigated the effects of chronic hypoxia (2.5% O2, 24 h) on capacitative Ca2+ entry (CCE) in primary cultures of rat type-I cortical astrocytes, and compared results with those obtained in astrocytes exposed to A beta Ps. Chronic hypoxia caused a marked enhancement of CCE that was observed after intracellular Ca2+ stores were depleted by bradykinin application or by exposure to thapsigargin (1 microM). Exposure of cells for 24 h to 1 microM A beta P(1-40) did not alter CCE. Enhancement of CCE was not attributable to cell hyperpolarization, as chronically hypoxic cells were significantly depolarized as compared with controls. Mitochondrial inhibition [by FCCP (10 microM) and oligomycin (2.5 microg/mL)] suppressed CCE in all three cell groups, but more importantly there were no significant differences in the magnitude of CCE in the three astrocyte groups under these conditions. Similarly, the antioxidants melatonin and Trolox abolished the enhancement of CCE in hypoxic cells. Our results indicate that chronic hypoxia augments CCE in cortical type-I astrocytes, a finding which is not mimicked by A beta P(1-40) and appears to be dependent on altered mitochondrial function.

Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells expressing a familial Alzheimer's disease presenilin-1 mutation

Presenilins are involved in the proteolytic production of Alzheimer's amyloid peptides, but are also known to regulate Ca(2+) homeostasis in various cells types. In the present study, we examined intracellular Ca(2+) stores coupled to muscarinic receptors and capacitative Ca(2+) entry (CCE) in the human neuroblastoma SH-SY5Y cell line, and how these were modulated by over-expression of either wild-type presenilin 1 (PS1wt) or a mutant form of presenilin 1 (PS1 deltaE9) which predisposes to early-onset Alzheimer's disease. Ca(2+) stores discharged by application of 100 microM muscarine (in Ca(2+)-free perfusate) in PS1wt and PS1 DeltaE9 cells were significantly larger than those in control cells, as determined using Fura-2 microfluorimetry. Subsequent CCE, observed in the absence of muscarine when Ca(2+) was re-admitted to the perfusate, was unaffected in PS1wt cells, but significantly suppressed in PS1 deltaE9 cells. However, when Ca(2+) stores were fully depleted with thapsigargin, CCE was similar in all three cell groups. Western blots confirmed increased levels of PS1 in the transfected cells, but also demonstrated that the proportion of intact PS1 in the PS1 deltaE9 cells was far greater than in the other two cell groups. This study represents the first report of modulation of both Ca(2+) stores and CCE in a human, neurone-derived cell line, and indicates a distinct effect of the PS1 mutation deltaE9 over wild-type PS1.

Receptor-ligand interactions and cellular signalling at the host-parasite interface

Although the effects of trematode infection on snail host physiology or host responses on parasite development have been well described in the literature, very little is known regarding the underlying mechanisms and specific molecules responsible for mediating those effects. It is presumed that many host-parasite interactions are communicated through receptor-mediated events, in particular those involving haemocytic immune responses to invading parasites, larval motility and migration through host tissues, and larval acquisition of host molecules either as nutrients or critical developmental factors. The intent of this chapter is to review current knowledge of molecules (both receptors and their ligands or counter-receptors) involved in molecular communication at the interface between larval trematodes, especially the mother or primary sporocyst stage, and host cells/tissues in intimate proximity to developing larvae. Information to date suggests that the molecular exchange at this interface is a highly complex and dynamic process, and appears to be regulated in specific cases. Topics discussed will focus on snail cell receptor interactions with the sporocyst tegument and its secretions, host cell-cell and cell-substrate adhesion receptors and their related signal transduction pathways, and sporocyst tegumental surface receptors and ligands involved in the binding of soluble host molecules.

Effects of chronic hypoxia on Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells

Microfluorimetric measurements of intracellular calcium ion concentration [Ca(2+)](i) were employed to examine the effects of chronic hypoxia (2.5% O(2), 24 h) on Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells. Activation of muscarinic receptors evoked rises in [Ca(2+)](i) which were enhanced in chronically hypoxic cells. Transient rises of [Ca(2+)](i) evoked in Ca(2+)-free solutions were greater and decayed more slowly following exposure to chronic hypoxia. In control cells, these transient rises of [Ca(2+)](i) were also enhanced and slowed by removal of external Na(+), whereas the same manoeuvre did not affect responses in chronically hypoxic cells. Capacitative Ca(2+) entry, observed when re-applying Ca(2+) following depletion of intracellular stores, was suppressed in chronically hypoxic cells. Western blots revealed that presenilin-1 levels were unaffected by chronic hypoxia. Exposure of cells to amyloid beta peptide (1-40) also increased transient [Ca(2+)](i) rises, but did not mimic any other effects of chronic hypoxia. Our results indicate that chronic hypoxia causes increased filling of intracellular Ca(2+) stores, suppressed expression or activity of Na(+)/Ca(2+) exchange and reduced capacitative Ca(2+) entry. These effects are not attributable to increased amyloid beta peptide or presenilin-1 levels, but are likely to be important in adaptive cellular remodelling in response to prolonged hypoxic or ischemic episodes.

Projection of diabetes burden through 2050: impact of changing demography and disease prevalence in the U.S

OBJECTIVE

To project the number of people with diagnosed diabetes in the U.S. through 2050, accounting for changing demography and diabetes prevalence rates.

RESEARCH DESIGN AND METHODS

We combined age-, sex-, and race-specific diagnosed diabetes prevalence rates-predicted from 1980-1998 trends in prevalence data from the National Health Interview Survey-with Bureau of Census population demographic projections. Sensitivity analyses were performed by varying both prevalence rate and population projections.

RESULTS

The number of Americans with diagnosed diabetes is projected to increase 165%, from 11 million in 2000 (prevalence of 4.0%) to 29 million in 2050 (prevalence of 7.2%). The largest percent increase in diagnosed diabetes will be among those aged > or =75 years (+271% in women and +437% in men). The fastest growing ethnic group with diagnosed diabetes is expected to be black males (+363% from 2000-2050), with black females (+217%), white males (+148%), and white females (+107%) following. Of the projected 18 million increase in the number of cases of diabetes in 2050, 37% are due to changes in demographic composition, 27% are due to population growth, and 36% are due to increasing prevalence rates.

CONCLUSIONS

If recent trends in diabetes prevalence rates continue linearly over the next 50 years, future changes in the size and demographic characteristics of the U.S. population will lead to dramatic increases in the number of Americans with diagnosed diabetes.

Schistosoma mansoni: effects of serotonin and serotonin receptor antagonists on motility and length of primary sporocysts in vitro

The effects of serotonin (5-hydroxytryptamine; 5-HT) on in vitro transformed primary sporocysts of Schistosoma mansoni were investigated. Serotonin treatment significantly increased parasite motility (percentage of motile sporocysts) and length at concentrations as low as 1 microM. These effects were mimicked by the 5-HT agonist tryptamine, albeit with 10- to 100-fold less potency. The effects of 10 microM 5-HT on sporocyst motility were observed within 15 min posttreatment and on parasite length by 6 h posttreatment, and both effects were stable for up to 48 h. Receptor antagonists with varying affinities for defined vertebrate neurotransmitter receptor subtypes were examined for their effects on parasite behavior in the absence and presence of 10 microM 5-HT. In the absence of 5-HT, only methiothepin significantly inhibited normal parasite growth after 48 h of incubation. In the presence of 10 microM 5-HT, the serotonin receptor antagonists mianserin, ketanserin (both at 100 microM), and methiothepin (at 10 microM) significantly inhibited 5-HT-induced lengthening of primary sporocysts, while 3-tropanyl-indole-3-carboxylate and chlorpromazine had no significant effect. The effects of these same drugs on parasite motility were also examined. In the absence of 5-HT, 10 microM chlorpromazine increased parasite motility, while the other antagonists had no effect. When sporocysts were treated with 10 microM 5-HT for 2 h in the continued presence of antagonist, 100 microM mianserin, ketanserin, 3-tropanyl-indole-3-carboxylate, and 10 microM methiothepin inhibited 5-HT induced increases in parasite motility, while 10 microM chlorpromazine had no effect. These results show that primary sporocysts of S. mansoni exhibit behavioral responses to serotonin much like adult stages of this parasite. Furthermore, these responses appear to be mediated via receptors with pharmacological similarities to those previously described in adult worms.

Evidence against potassium as an endothelium-derived hyperpolarizing factor in rat mesenteric small arteries

1. Endothelium-derived hyperpolarizing factor (EDHF) has recently been identified as potassium released from endothelial cells into the myo-endothelial space. The present study was designed to test this hypothesis. 2. In rat small mesenteric arteries, mounted in a wire myograph, relaxation to acetylcholine or potassium was not significantly changed following incubation with oxadiazolo-quinoxalin-1-one (ODQ, 4 microM) and indomethacin (10 microM, n = 9). 3. Maximal relaxations to acetylcholine occurred in all arteries, were maintained and were significantly greater (P < 0.01, n = 9) than the transient relaxations to potassium, which only occurred in 30-40% of vessels. 4. Removal of the vascular endothelium abolished relaxant responses both to potassium and acetylcholine (P < 0.005, n = 9). 5. Compared with responses in 5.5 mM potassium PSS, relaxation responses to added potassium in arteries maintained in 1.5 mM potassium PSS were more marked and were not dependent on the presence of an intact endothelium (n = 8). 6. Incubation with BaCl2 (50 microM) significantly inhibited the maximal relaxant response to potassium in the presence of an intact endothelium in 5.5 mM potassium PSS (P < 0.05, n = 4), but had no effect on relaxation of de-endothelialized preparations in 1.5 mM potassium PSS (n = 5). 7. Treatment with ouabain (0.1 mM) abolished the relaxant response to potassium in 1.5 mM potassium PSS (P < 0.001, n = 9), but only partly inhibited the maximal relaxant response to acetylcholine in 5.5 mM potassium PSS (P < 0.01, n = 5). 8. These data show that at physiological concentrations of potassium an intact endothelium is necessary for potassium-induced relaxation in rat mesenteric arteries. Furthermore, the response to potassium is clearly different to that from acetylcholine, indicating that potassium does not mimic EDHF released by acetylcholine in these arteries.

The use of population attributable risk to estimate the impact of prevention and early detection of type 2 diabetes on population-wide mortality risk in US males

The Population Attributable Risk (PAR) represents the proportion of the deaths (in a specified time) in the whole population that may be preventable if a cause of mortality were totally eliminated. This population-based measure was used to assess the potential impact of three public health interventions for type 2 diabetes (early detection + standard therapy; early detection + intensive therapy; and primary prevention) on the mortality risk from all causes and from cardiovascular (CVD) diseases. Potential reduction in mortality risks for several levels of compliance or implementation (25%, 50%, 75%, 100%) for each intervention were also estimated. Results suggest that among males aged 45-74 years, the interventions may have greater population-wide impact on total deaths among black males, and greater impact on the CVD deaths among white males. Overall, primary prevention (reduction in all-cause mortality 6.2-10.0%, and CVD mortality 7.9-9.0%) may offer greater marginal benefit than screening and early treatment (reduction in all-cause mortality 3.5-8.3%, and CVD mortality 2.8-8.6%). Often the question facing policy makers is not simply whether to but how much of an intervention is worth implementing? Estimated benefits for various intensities of intervention (as provided) may be useful to assess the likely marginal benefits of each intervention, and can be especially useful if combined with estimated marginal costs.

Cannabinoid CB1 receptors fail to cause relaxation, but couple via Gi/Go to the inhibition of adenylyl cyclase in carotid artery smooth muscle

1. The aim of the current study was to characterize which cannabinoid receptors, if any, are present on rat carotid artery smooth muscle. Additionally, the effects of cannabinoids on carotid artery tone, on cyclic AMP accumulation and on forskolin-induced relaxation were examined in the same tissue. 2. Stimulation of carotid arteries with forskolin (10 microM) significantly increased cyclic AMP accumulation, an effect that was inhibited in a concentration-dependent manner by the cannabinoid receptor agonist, methanandamide. 3. Similar inhibition was seen with the CB1 agonist HU-210 but this inhibition was not mimicked by the CB2 agonist, WIN 55,2212-2. 4. The inhibitory effect of methanandamide on cyclic AMP accumulation was prevented by incubation of the arteries with pertussis toxin and was significantly reduced by LY320135, a selective CB1 antagonist, but not by SR 144528, a CB2-selective antagonist. 5. Methanandamide failed to relax carotid arteries pre-contracted with phenylephrine, but inhibited forskolin-induced relaxation of these arteries. This functional inhibition of relaxation by methanandamide was inhibited by CB1-selective (LY320135 and SR 141716A), but not a CB2-selective antagonist (SR 144528). 6. These data demonstrate the presence of functional G protein-linked cannabinoid receptors of the CB1 subtype in the rat carotid artery, but show that these receptors inhibit cyclic AMP accumulation rather than cause relaxation.

Estimating prevalence of type 1 and type 2 diabetes in a population of African Americans with diabetes mellitus

The pathogenesis, treatment, and outcomes of type 1 and type 2 diabetes differ. Current surveys derive population-based estimates of diabetes prevalence by type using limited clinical information and applying classification rules developed in white populations. How well these rules perform when deriving similar estimates in African American populations is unknown. For this study, data were collected on a group of African Americans with diabetes who enrolled at the Diabetes Unit of Grady Memorial Hospital in Atlanta, Georgia, from April 16, 1991, to November 1, 1996. The data were used to develop some simple classification rules for African Americans based on a classification tree and a logistic regression model. Sensitivities and specificities, in which fasting C-peptide was used as the gold standard, were determined for these rules and for two current rules developed in mostly white, non-Hispanic populations. Rules that yielded precise (minimum variance unbiased) estimates of the prevalence of type 1 diabetes were preferred. The authors found that a rule based on the logistic regression model was best for estimating type 1 prevalences ranging from 1% to 17%. They concluded that simple classification rules can be used to estimate prevalence of diabetes by type in African American populations and that the optimal rule differs somewhat from the current rules.

Regulation of brain capillary endothelial cells by P2Y receptors coupled to Ca2+, phospholipase C and mitogen-activated protein kinase

1. The blood-brain barrier is formed by capillary endothelial cells and is regulated by cell-surface receptors, such as the G protein-coupled P2Y receptors for nucleotides. Here we investigated some of the characteristics of control of brain endothelial cells by these receptors, characterizing the phospholipase C and Ca2+ response and investigating the possible involvement of mitogen-activated protein kinases (MAPK). 2. Using an unpassaged primary culture of rat brain capillary endothelial cells we showed that ATP, UTP and 2-methylthio ATP (2MeSATP) give similar and substantial increases in cytosolic Ca2+, with a rapid rise to peak followed by a slower decline towards basal or to a sustained plateau. Removal of extracellular Ca2+ had little effect on the peak Ca2+-response, but resulted in a more rapid decline to basal. There was no response to alpha,beta-MethylATP (alpha,beta MeATP) in these unpassaged cells, but a response to this P2X agonist was seen after a single passage. 3. ATP (log EC50 -5.1+/-0.2) also caused an increase in the total [3H]-inositol (poly)phosphates ([3H]-InsPx) in the presence of lithium with a rank order of agonist potency of ATP=UTP=UDP>ADP, with 2MeSATP and alpha,beta MeATP giving no detectable response. 4. Stimulating the cells with ATP or UTP gave a rapid rise in the level of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), with a peak at 10 s followed by a decline to a sustained plateau phase. 2MeSATP gave no detectable increase in the level of Ins(1,4,5)P3. 5. None of the nucleotides tested affected basal cyclic AMP, while ATP and ATPgammaS, but not 2MeSATP, stimulated cyclic AMP levels in the presence of 5 microM forskolin. 6. Both UTP and ATP stimulated tyrosine phosphorylation of p42 and p44 mitogen-activated protein kinase (MAPK), while 2MeSATP gave a smaller increase in this index of MAPK activation. By use of a peptide kinase assay, UTP gave a substantial increase in MAPK activity with a concentration-dependency consistent with activation at P2Y2 receptors. 2MeSATP gave a much smaller response with a lower potency than UTP. 7. These results are consistent with brain endothelial regulation by P2Y2 receptors coupled to phospholipase C, Ca2+ and MAPK; and by P2Y1-like (2MeSATP-sensitive) receptors which are linked to Ca2+ mobilization by a mechanism apparently independent of agonist stimulated Ins(1,4,5)P3 levels. A further response to ATP, acting at an undefined receptor, caused an increase in cyclic AMP levels in the presence of forskolin. The differential MAPK coupling of these receptors suggests that they exert fundamentally distinct influences over brain endothelial function.

Evidence that anandamide and EDHF act via different mechanisms in rat isolated mesenteric arteries

The endogenous cannabinoid, anandamide, has been suggested as an endothelium-derived hyperpolarizing factor (EDHF). We found that anandamide-evoked relaxation in isolated segments of rat mesenteric artery was associated with smooth muscle hyperpolarization. However, although anandamide-evoked relaxation was inhibited by either charybdotoxin (ChTX) or iberiotoxin, inhibition of the relaxation to EDHF required a combination of ChTX and apamin. The relaxations induced by either anandamide or EDHF were not inhibited by the cannabinoid receptor (CB1) antagonist SRI41716A, or mimicked by selective CB1 agonists. Thus, anandamide appears to cause smooth muscle relaxation via a CB1 receptor-independent mechanism and cannabinoid receptor activation apparently does not contribute to EDHF-mediated relaxation in this resistance artery.

Comparison of fasting and 2-hour glucose and HbA1c levels for diagnosing diabetes. Diagnostic criteria and performance revisited

OBJECTIVE

Nearly two decades ago, the National Diabetes Data Group (NDDG) and the World Health Organization (WHO) Expert Committee on Diabetes Mellitus published diagnostic criteria for diabetes. We undertook this study to compare the performance of three glycemic measures for diagnosing diabetes and to evaluate the performance of the WHO criteria.

RESEARCH DESIGN AND METHODS

In a cross-sectional population-based sample of 1,018 Egyptians > or = 20 years of age, fasting and 2-h glucose and HbA1c levels were measured, and diabetic retinopathy was assessed by retinal photograph. Evidence for bimodal distributions was examined for each glycemic measure by fitting models for the mixture of two distributions using maximum likelihood estimates. Sensitivity and specificity for cutpoints of each glycemic measure were calculated by defining the true diabetes state (gold standard) as 1) the upper (diabetic) component of the fitted bimodal distribution for each glycemic measure, and 2) the presence of diabetic retinopathy. Receiver operating characteristic (ROC) curves were constructed to determine the performance of the glycemic measures in detecting diabetes as defined by diabetic retinopathy.

RESULTS

In the total population, the point of intersection of the lower and upper components that minimized misclassification for the fasting and 2-h glucose and HbA1c were 7.2 mmol/l (129 mg/dl), 11.5 mmol/l (207 mg/dl), and 6.7%, respectively. When diabetic retinopathy was used to define diabetes, ROC curve analyses found that fasting and 2-h glucose values were superior to HbA1c (P < 0.01). The performance of a fasting glucose of 7.8 mmol/l (140 mg/dl) was similar to a 2-h glucose of 12.2-12.8 mmol/l (220-230 mg/dl), and the performance of a 11.1 mmol/l (200 mg/dl) 2-h glucose was similar to a fasting glucose of 6.9-7.2 mmol/l (125-130 mg/dl).

CONCLUSIONS

Optimal cutpoints for defining diabetes differ according to how diabetes itself is defined. When diabetes is defined as the upper component of the bimodal population distribution, a fasting glucose level somewhat lower than the current WHO cutpoint and a 2-h glucose level somewhat higher than the current WHO cutpoint minimized misclassification. When diabetic retinopathy defines diabetes, we found that the current fasting diagnostic criterion favors specificity and the current 2-h criterion favors sensitivity. These results should prove valuable for defining the optimal tests and cutpoint values for diagnosing diabetes.

Effects of the BKCa channel activator, NS1619, on rat cerebral artery smooth muscle

1. We have investigated the actions of NS1619, a putative activator of large conductance calcium-activated potassium channels (BKCa) by use of the patch-clamp technique on smooth muscle cells enzymatically isolated from the rat basilar artery. 2. Using whole cell current-clamp to measure membrane potential, addition of 30 microM NS1619 produced cellular hyperpolarization, moving the membrane potential towards the calculated equilibrium potential for potassium. This hyperpolarization was rapidly reversed by IbTX (100 nM), a selective inhibitor of BKCa. 3. In whole cell recordings made from cells voltage-clamped at 0 mV using the perforated-patch technique, addition of NS1619 (10-30 microM) activated an outward current, which reversed following washout of NS1619. 4. This outward current was unaffected by application of either glibenclamide (5 microM), an inhibitor of ATP-sensitive potassium channels, or apamin (100 nM), an inhibitor of small-conductance calcium-activated potassium channels. However, this current was almost completely abolished by iberiotoxin (IbTX; 50-100nM). 5. Depolarizing voltage steps activated small outward currents from cells held at -15 mV. Application of NS1619 (10-30 microM) increased the size of these currents, producing a shift to the left of the current-voltage (I-V) relationship. These currents were largely inhibited by IbTX (100 nM). 6. Measurements of the unitary amplitude of the single channels activated by NS1619 which could be resolved in whole cell recordings yielded a value of 5.6 +/- 0.14 pA at 0 mV. 7. NS1619 (10-30 microM) directly activated single channels contained in excised inside-out and outside-out membrane patches. In both configurations NS1619 (10-30 microM) rapidly increased the open probability of a large conductance calcium-dependent channel. The activation produced by NS1619 was calcium-dependent and inhibited by external IbTX (100 nM). The unitary current amplitude was unaffected by NS1619. 8. By use of conventional whole cell recording methods and conditions that suppressed BKCa openings, outward potassium currents were activated by depolarizing potentials positive to -35 mV from a holding potential of -65 mV. NS1619 (10-30 microM) inhibited this current in a concentration-dependent manner. This inhibition was reversed following washout of NS1619, recovering to 60-90% of control values within 2 min. 9. Ba2+ currents, measured by conventional whole cell recording, were activated by depolarizing voltage steps from negative holding potentials. NS1619 (1-30 microM) inhibited the evoked current in a concentration-dependent manner, yielding an IC50 value of 7 microM with a Hill coefficient approaching unity. This inhibition was reversible, with the currents recovering to 65-100% of control values after washout of NS1619 for 2 min. 10. NS1619 (0.3-100 microM) induced concentration-dependent relaxation of basilar artery segments contracted with histamine/5-HT (IC50 = 12.5 +/- 2.0 microM; n = 4). This relaxation curve was shifted to the right, but not abolished, when the tissue was treated with a blocker of BKCa channels (IbTX; 100nM). Additionally, NS1619 produced concentration-dependent relaxation of basilar artery contracted with a depolarizing, isotonic salt solution containing 80 mM K+. 11. Thus NS1619 produces hyperpolarization of basilar artery myocytes through direct activation of BKCa and also directly inhibits Ca2+ currents and voltage-activated K+ channels. We discuss the implications of these results for its vasorelaxant actions.

Correlation of cyclic AMP accumulation and relaxant actions of salmeterol and salbutamol in bovine tracheal smooth muscle

1. The ability of salmeterol to stimulate cyclic AMP accumulation and relaxation has been compared with that of salbutamol in bovine tracheal smooth muscle. In addition, the anti-spasmogenic effects of these agents and their abilities to modulate histamine-stimulated [3H]-inositol phosphate accumulation have also been investigated. 2. In tissue strips, a close temporal correlation was found to exist between salmeterol (0.1 microM)-induced relaxation of methacholine (500 nM)-induced tone and cyclic AMP accumulation, both maximal reversal of induced tone (26.2 +/- 6.0%) and maximal levels of cyclic AMP accumulation being achieved after 30-40 min. In contrast to salmeterol, salbutamol exerted greater and more rapid effects on both parameters. Maximal reversal of methacholine-induced tone (79.3 +/- 14.0%) and maximal levels of cyclic AMP accumulation were produced within 5 min. 3. Salmeterol-induced cyclic AMP accumulation (EC50 = 5.3 [1.8 - 15.2] nM) and inhibition of histamine (0.1 mM)-stimulated [3H]-inositol phosphate accumulation (IC50 = 1.4 [0.3-6.3] nM) were both more potent than those induced by salbutamol (EC50 = 169 [99 - 290] nM; IC50 = 13.8 [7.0 - 27.4] nM). However, maximal effects exerted by each of these agents were similar in magnitude. 4. Anti-spasmogenic effects were examined by beta-adrenoceptor agonist application to tissue strips prior to construction of spasmogen concentration-effect curves. Both salmeterol and salbutamol exerted more marked inhibition of the contractile response induced by histamine than that induced by methacholine, salmeterol being the more potent agent, while salbutamol produced a greater maximal inhibitory effect. 5. The results demonstrate that salmeterol is a more potent agent than salbutamol and have highlighted a close temporal correlation between promotion of cyclic AMP accumulation and tissue relaxation stimulated by each agent when both parameters are measured under identical conditions.

Comparative effects of activation of soluble and particulate guanylyl cyclase on cyclic GMP elevation and relaxation of bovine tracheal smooth muscle

1. The effects of nitric oxide-donating compounds and atrial natriuretic peptide on cyclic GMP accumulation and mechanical tone were compared with the effects of isoprenaline in bovine tracheal smooth muscle. 2. Sodium nitroprusside, glyceryl trinitrate, S-nitroso-N-acetylpenicillamine (SNAP), atrial natriuretic peptide and isoprenaline each caused concentration-dependent inhibitions of histamine-maintained tone (EC50 values 320 +/- 80, 150 +/- 45, 14,000 +/- 4,000, 2.8 +/- 0.8 and 6.6 +/- 4.3 nM respectively). 3. When compared with their effects on histamine-induced tone, sodium nitroprusside was equally potent and effective in causing relaxation of methacholine-supported tone (EC50 290 +/- 90 nM) while isoprenaline was as effective, but less potent (EC50 30 +/- 7 nM). SNAP was more potent and equi-effective as a relaxant of methacholine-supported tone (EC50 340 +/- 140 nM). At the maximum concentrations of glyceryl trinitrate and atrial natriuretic peptide tested against methacholine-supported tone, relaxations of 52% and 14% of the isoprenaline maximum were seen. 4. Sodium nitroprusside, glyceryl trinitrate and atrial natriuretic peptide each induced concentration-dependent increases in cyclic GMP accumulation. The time-courses of accumulation correlated closely with the relaxant actions of these compounds. 5. Pretreatment of tracheal smooth muscle with sodium nitroprusside or SNAP caused a rightward shift of the concentration-effect curve for histamine while reducing the maximum response. 6. LY 83583, a putative guanylyl cyclase inhibitor, caused a concentration-dependent reduction in basal cyclic GMP accumulation in tracheal smooth muscle and inhibited the effects of sodium nitroprusside on cyclic GMP accumulation. 7. LY 83583 also inhibited the relaxation of histamine-supported tone by glyceryl trinitrate, sodium nitroprusside, SNAP and atrial natriuretic peptide, and also sodium nitroprusside- and SNAP-induced relaxation of methacholine-supported tone. However, it had no significant effect on glyceryl trinitrate-induced relaxation of methacholine-supported tone. 8. It is concluded that the relaxant actions of sodium nitroprusside, glyceryl trinitrate, SNAP and atrial natriuretic peptide follow as a result of their ability to activate either soluble or particulate guanylyl cyclase leading to cyclic GMP accumulation. Although there does not seem to be any functional difference in the relaxant response to cyclic GMP generated by the particulate as opposed to soluble form(s) of guanylyl cyclase, atrial natriuretic peptide receptor/guanylyl cyclase activation was much less effective in causing relaxation of methacholine-supported tone when compared to activators of soluble guanylyl cyclase.

The folding of the bifunctional TRP3 protein in yeast is influenced by a translational pause which lies in a region of structural divergence with Escherichia coli indoleglycerol-phosphate synthase

The yeast TRP3 gene encodes a bifunctional protein with anthranilate synthase II and indoleglycerol-phosphate synthase activities. Replacing ten consecutive non-preferred codons in the indoleglycerol-phosphate synthase region of the TRP3 gene with synonymous preferred codons (to create the TRP3pr gene; translational pause replaced) causes a 1.5-fold reduction in relative indoleglycerol-phosphate synthase activity [Crombie, T., Swaffield, J.C. & Brown, A.J.P. (1992) J. Mol. Biol. 228, 7-12]. Here, we report that both the anthranilate synthase II and indoleglycerol-phosphate synthase domains are affected to similar extents when the translational pause is removed. Also, structural modelling of the yeast indoleglycerol-phosphate synthase domain against the X-ray crystal structure of indoleglycerol-phosphate synthase from Escherichia coli indicates that the translational pause lies in a region of structural divergence between similar structures. To probe the role of cytoplasmic heat-shock protein 70 (Hsp 70) chaperones in Trp3 protein folding, anthranilate synthase and indoleglycerol-phosphate synthase activities were measured in ssa and ssb mutants. Neither indoleglycerol-phosphate synthase nor anthranilate synthase were affected significantly in the ssb mutant. However, depletion of Hsp70 proteins encoded by the SSA genes led to decreased anthranilate synthase and indoleglycerol-phosphate synthase activities from the TRP3 gene, suggesting that both domains depend to some extent upon the SSA chaperone family. The data are consistent with roles for both the translational pause and Ssa chaperones in Trp3 protein folding in vivo.

Contractile agonists activate voltage-dependent calcium channels in airway smooth muscle cells

To determine whether agents that cause contraction of airway smooth muscle affect sarcolemmal calcium channel activity, unitary calcium channel currents (using Ba2+ as the charge carrier) were recorded in on-cell configuration from acutely dissociated (dog, pig, and ferret) and cultured (human) airway smooth muscle cells. Addition of the contractile agonists methacholine or bradykinin increased the open-state probability of the large-conductance calcium channel 37.2- and 45-fold, respectively. The increase in open-state probability was not due to cellular depolarization because increases occurred in the absence of depolarization. Channel activation by the agonist was determined to result in the favoring of a long (16.5 +/- 5.0 ms) open lifetime for the channel, which was not observed under control conditions, in the absence of BAY K 8644. We also report the unitary calcium channel currents from a second, smaller conductance calcium channel. This channel was present in all cell types and had a mean conductance of 9.5 +/- 0.8 pS (80 mM Ba2+). Exposure of cells to agonist also resulted in an increase in the open-channel probability of the small-conductance calcium channel (10.4-fold), which did not result from cellular depolarization. These experiments demonstrate that the molecular pathways exist between contractile agonist receptors and sarcolemmal calcium channels in airway smooth muscle cells. Because membrane patches were not directly exposed to agonist, receptor-channel linkage probably occurs via a second messenger-coupling pathway.

Delayed rectifier potassium channels in canine and porcine airway smooth muscle cells

1. In order to define the ion channels underlying the inactivating, calcium-insensitive current in airway smooth muscle cells, unitary potassium currents were recorded from canine and porcine trachealis cells, and compared with macroscopic currents. On-cell and inside-out single-channel currents were compared with whole-cell recordings made in dialysed cells. 2. Depolarizing voltage steps evoked outward unitary currents. In addition to a large conductance, calcium-activated potassium channel (KCa), a lower conductance potassium channel was identified. This channel has a conductance of 12.7 pS (on-cell; 1 mM-K+ in the pipette). 3. The lower conductance channel (Kdr) was not sensitive to cytosolic Ca2+ concentration and unitary current openings occurred following a delay after the voltage step. The time course of activation of the current composed of averaged single-channel events was very similar to that of the whole-cell, delayed rectifier potassium current (IdK), recorded under conditions of low intracellular calcium (Kotlikoff, 1990). 4. Kdr channels also inactivated with kinetics similar to those of the macroscopic current. Averaged single-channel records revealed a current that inactivated with kinetics that could be described by two exponentials (tau 1 = 0.14 s, tau 2 = 1.1 s; at 5 mV). These values corresponded well with previously determined values for time-dependent inactivation of IdK. Inactivation of Kdr channels was markedly voltage dependent, and was well fitted by a Boltzmann equation with V50 = -53 mV; this was similar to measurements of the macroscopic current, although the V50 value was shifted to more positive potentials in whole-cell measurements. When only the inactivating component of the macroscopic current was considered, the voltage dependence of inactivation of the single-channel current and macroscopic current were quite similar. 5. Single-channel kinetics indicated that Kdr channels occupy one open and two closed states. The mean open time was 1.7 ms. Inactivation results in a prominent increase in the long closed time, with little effect on the mean open time or short closed time. 6. The Kdr channel was not blocked by tetraethylammonium (TEA; 1 mM), charybdotoxin (ChTX; 100 nM) or glibenclamide (20 microM), but was blocked by 4-aminopyridine (4-AP; 1 mM). Similarly, 4-AP blocked the inactivating component of the macroscopic current, but a non-inactivating current remained. KCa currents were blocked by TEA (0.5-1 mM) and charybdotoxin (40 nM), but were insensitive to to 4-AP (1 mM) and glibenclamide (20 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical and electrical aspects of the tracheal relaxant action of AH 21-132

In Triton X-100-skinned trachealis muscle, neither papaverine nor AH 21-132 modified responses to Ca2+. The (-)-enantiomer of AH 21-132 was more potent than the (+)-enantiomer both in relaxing intact trachealis muscle and in inhibiting tracheal cAMP phosphodiesterase (PDE). AH 21-132 (0.6 microM) potentiated forskolin in causing tracheal relaxation but did not potentiate isoprenaline, cromakalim or sodium nitrate. AH 21-132 (2 microM) potentiated all four agents in relaxing the trachea. AH 21-132 (1 microM) potentiated forskolin in increasing tissue cAMP content and, in higher concentration, itself increased tissue cAMP. Electrical effects of AH 21-132 included suppression of spontaneous slow waves and cellular hyperpolarisation. It is concluded that AH 21-132 lacks a direct depressant effect on the intracellular contractile machinery. The weight of evidence suggests that AH 21-132-induced relaxation results from inhibition of cAMP-PDE. However, in common with other PDE inhibitors. AH 21-132 increases tissue cAMP content only at concentration greater than that required to cause full relaxation.

Cromakalim-induced relaxation of guinea-pig isolated trachealis: antagonism by glibenclamide and by phentolamine

1. Tested against the spontaneous tone of guinea-pig isolated trachealis, cromakalim (0.1-100 microM), isoprenaline (1 nM-1 microM) and theophylline (1 microM-1 mM) each produced concentration-dependent relaxation. 2. Glibenclamide (0.1-10 microM) did not itself alter the spontaneous tone of the trachea nor did it modify the relaxant actions of isoprenaline or theophylline. In contrast, glibenclamide (0.1 and 1 microM) caused a concentration-dependent rightward shift of the log concentration-effect curve of cromakalim. Glibenclamide (10 microM) reduced the slope of the log concentration-effect curve of cromakalim and moved the foot of the curve back towards the control position. 3. Phentolamine (1, 10 and 100 microm) did not itself alter the spontaneous tone of the trachea nor did it modify the relaxant actions of isoprenaline or theophylline. In contrast phentolamine caused concentration-dependent depression of the log concentration-effect curve of cromakalim. 4. Neither prazosin (1 microM) nor yohimbine (10 microM) modified the spontaneous tone of the trachea. Prazosin and yohimbine each failed to antagonise the effects of cromakalim, isoprenaline and theophylline. 5. Intracellular electrophysiological recording showed that glibenclamide (1 microM) and phentolamine (100 microM) caused minor change in the resting membrane potential of trachealis cells. Slow wave activity was slightly depressed by these agents. In contrast tetraethylammonium (TEA; 8 mM) caused marked depolarisation, and promoted the conversion of slow waves into regenerative action potentials. These electrical changes were accompanied by tonic tension development. 6. Phentolamine (100 microM) and glibenclamide (1 microM) reduced and reversed both the relaxation and the hyperpolarisation induced by cromakalim (10 microM). 7. It is concluded that glibenclamide and phentolamine each provide selective antagonism of the relaxant action of cromakalim in guinea-pig trachealis. These agents also inhibit the plasmalemmal hyperpolarisation induced by cromakalim. The effect of phentolamine is unrelated to the blockade of alpha 1- or alpha 2-adrenoceptors. If either glibenclamide or phentolamine act to block the K+ channels opened by cromakalim, then such channels are not identical to those which endow the trachealis plasmalemma with its powerful rectifying behaviour.

Inhibitory effects of AH 21-132 in guinea-pig isolated ileum and taenia caeci

1. AH 21-132 is being investigated as a potential chemotherapeutic agent for bronchial asthma. The present experiments were designed to determine whether AH 21-132 shares the activity of theophylline as an antagonist at adenosine A1 receptors and to assess its potency as a relaxant in intestinal smooth muscle. 2. In the transmurally-stimulated guinea-pig ileum, theophylline (1 mM), but not AH 21-132 (1 and 10 microM), antagonized twitch depression induced by adenosine. Higher concentrations (100 microM and 1 mM) of AH 21-132 themselves had a depressant effect. Neither theophylline (1 mM) nor AH 21-132 (1 and 10 microM) antagonized twitch depression induced by noradrenaline. 3. AH 21-132 (100 microM and 1 mM) depressed maximum contractions of ileum induced by both acetylcholine (ACh) and histamine. 4. In ileum treated with hyoscine (1 microM), AH 21-132 (greater than 10 microM) caused a concentration-dependent depression of the log concentration-effect curve for potassium chloride. 5. Simultaneous extracellular electrophysiological and mechanical recording from taenia caeci showed that AH 21-132 (100 microM-1 mM) inhibited spontaneous tension waves and their associated bursts of electrical spike activity. 6. Intracellular electrophysiological recording from taenia caeci showed that the mechano-inhibitory effect of 1 mM AH 21-132 was accompanied by abolition of spontaneous spike activity. Following spike abolition, the membrane potential assumed a value very close to that observed during periods of electrical quiescence prior to drug exposure. 7. AH 21-132 inhibited the activity of cyclic AMP-dependent and cyclic GMP-dependent phosphodiesterases derived from homogenates of ileal smooth muscle. The effective concentration ranges were 0.1-1OOO microM and 1-1000 microM, respectively. Theophylline, too, inhibited these enzymes but in each case was less potent than AH 21-132. 8. It is concluded that AH 21-132 is devoid of antagonist activity at adenosine Al receptors which modulate ACh release from intramural cholinergic nerves in the ileum. At concentrations greater than IO microM, AH 21-132 has a relaxant effect on intestinal smooth muscle characterized by suppression of spontaneous action potentials but by minor change in resting membrane potential. AH 21-132 previously has been reported to depress the spontaneous tone of trachealis muscle with an EC50 value of less than lO microM and the present experiments therefore show that this agent is much less potent in inhibiting intestinal muscle. This potency difference cannot be attributed to a tissuerelated difference in the potency of AH 21-132 as an inhibitor of cyclic AMP- or cyclic GMPdependent phosphodiesterases.

Analysis of the relaxant effects of AH 21-132 in guinea-pig isolated trachealis

1. Experiments have been performed with the dual intent of analysing the mechanism by which AH 21-132 relaxes airways smooth muscle and determining whether the effects of this compound can be distinguished from those of theophylline. 2. AH 21-132 (0.25-8 microM) and theophylline (1-1000 microM) each caused concentration-dependent suppression of the spontaneous tone of guinea-pig isolated trachealis. The maximal effect of AH 21-132 was equivalent to that of theophylline. No evidence was obtained that the tissue became sensitized or desensitized to the action of AH 21-132. 3. Propranolol (1 microM) profoundly antagonized the tracheal relaxant action of isoprenaline but not that of AH 21-132. 4. In indomethacin (2.8 microM)-treated tissues, tone was induced by K+-rich (120 mM) Krebs solution, acetylcholine (ACh, 1 mM) or histamine (200 microM). Log concentration-relaxation curves for AH 21-132, isoprenaline and theophylline were all moved to the right in the presence of the spasmogens, the smallest rightward shift being induced by histamine and the greatest by ACh. While maximal effects of AH 21-132 and theophylline were unaffected by the spasmogens, that of isoprenaline was reduced by KCl and ACh. 5. In tissues treated with indomethacin (2.8 microM), AH 21-132 (0.1-100 microM) inhibited the spasmogenic effects of potassium chloride (KCl), ACh and histamine in a concentration-dependent manner. The inhibition was characterized by rightward shifts in the spasmogen concentration-effect curves with depression of their maxima. 6. In tissues treated with both indomethacin (2.8 microM) and ACh (1 mM), the removal of tracheal epithelium caused a small but significant leftward shift in the log concentration-relaxation curve for AH 21-132 but did not alter that for theophylline. 7. In tissues treated with indomethacin (2.8 microM) and maintained at 12 degrees C, theophylline (0.1-3.2 mM) caused concentration-dependent spasm. This effect was not shared by AH 21-132. 8. AH 21-132 (0.1-1000 microM) more potently inhibited the activity of cyclic AMP-dependent than of cyclic GMP-dependent phosphodiesterase derived from homogenates of guinea-pig trachealis. Theophylline, too, inhibited these enzymes but was less potent in each case than AH 21-132 and did not exhibit selectivity for the cyclic AMP-dependent enzyme. 9. It is concluded that AH 21-132 exerts a non-specific (i.e. effective no matter what agent is used to support tone) relaxant effect on the trachealis muscle which does not involve the activation of beta l-adrenoceptors. The profile of the relaxant action of AH 21-132 more closely resembles that of theophylline than that of isoprenaline. However, AH 21-132 can be differentiated from theophylline in that: (a) its relaxant potency is increased by epithelial removal; (b) it does not cause tracheal spasm; (c) it exhibits selectivity as an inhibitor of cyclic AMP-dependent as opposed to cyclic GMP-dependent phosphodiesterase. It is possible that the relaxant effects of AH 21-132 are related to its ability to inhibit cyclic nucleotide phosphodiesterases.

The relaxant and spasmogenic effects of some xanthine derivatives acting on guinea-pig isolated trachealis muscle

1. Caffeine (10 mM)-induced relaxation of guinea-pig isolated trachealis was attenuated and converted to a small spasmogenic response on cooling to 22 degrees C. The relaxant response was restored on rewarming to 37 degrees C and was abolished by indomethacin (2.8 microM). Cooling to 22 degrees C in the presence of indomethacin revealed spasmogenic responses to caffeine which were abolished on rewarming to 37 degrees C. 2. Trachealis treated with indomethacin (2.8 microM) was repeatedly dosed with acetylcholine (ACh, 10 microM). Caffeine (1 or 10 mM), added as each ACh-induced spasm reached equilibrium, transiently augmented but then suppressed the spasm. On cooling from 37 degrees C to 12 degrees C, the increment in spasm evoked by caffeine increased relative to the spasm evoked by ACh. 3. Trachealis treated with indomethacin (2.8 microM) was repeatedly dosed with caffeine (10 mM). At 37 degrees C caffeine had little effect but it caused spasm when the tissue was cooled to 32 degrees C. Spasm amplitude increased as cooling progressed to 12 degrees C. Similar results were obtained with caffeine (1 mM). 4. At 37 degrees C, caffeine, enprofylline, 1,3,7,9-tetramethylxanthinium (TMX), theobromine, theophylline, xanthine and forskolin each caused concentration-dependent suppression of tracheal tone. Among the xanthine derivatives the rank order of potency was enprofylline greater than theophylline greater than caffeine greater than theobromine greater than xanthine greater than TMX. 5. In trachealis treated with indomethacin (2.8 microM) and maintained at 12 degrees C, the xanthines each caused concentration-dependent spasm. The rank order of potency was theobromine greater than or equal to theophylline greater than or equal to caffeine greater than or equal to enprofylline greater than xanthine greater than TMX. Forskolin was devoid of spasmogenic activity. 6. Trachealis treated with indomethacin (2.8 microM) and maintained at 12 degrees C, was repeatedly dosed with either caffeine (10 mM) or potassium chloride (KCl, 40 mM). Caffeine-induced spasm was attenuated in a Ca2+-free medium containing EGTA (2 mM), modestly at first but subsequently more profoundly. KCl did not evoke spasm at 12 degrees C but at 37 degrees C the KCl-induced spasm was virtually abolished at its first trail in the Ca2+-free, EGTA-containing medium. 7. It is concluded that caffeine, other alkylated xanthines and xanthine itself share a spasmogenic action in guinea-pig isolated trachealis which is best observed when the tissue is treated with indomethacin (2.8 microM) and maintained at 12 degrees C. The spasmogenic action represents the release of Ca2+ from intracellular sites of sequestration and may not depend on the intracellular accumulation of cyclic AMP. The rank order of spasmogenic potency of the xanthine derivatives differs markedly from their rank order of potency in suppressing the spontaneous tone of the trachealis observed at 370C. Since, at 12 degrees C, TMX is spasmogenic at concentrations identical to those causing relaxation at 37 degrees C, it is likely that TMX penetrates the cell. The relaxant effects of TMX do not, therefore, indicate that methylxanthine-induced relaxation is mediated by a receptor located on the external surface of the cell.

Spasmogen action in guinea-pig isolated trachealis: involvement of membrane K+-channels and the consequences of K+-channel blockade

1. Acetylcholine (ACh), histamine, prostaglandin E2 and potassium chloride (KCl) each evoked concentration-dependent spasm of guinea-pig isolated trachealis treated with indomethacin (2.8 microM). 2. Neither tetraethylammonium (TEA; 0.1-10 mM) nor procaine (0.1-10 mM) potentiated these spasmogens. Indeed, procaine (10 mM) depressed the log concentration-effect curves of all the spasmogens while TEA (1-10 mM) caused some depression of the log concentration-effect curve of prostaglandin E2. 3. Intracellular electrophysiological recording was performed in trachealis bathed by normal Krebs solution or by Krebs solution containing 2.8 microM indomethacin. In either medium the majority of trachealis cells exhibited spontaneous electrical slow waves while some cells were electrically quiescent. In either medium the spasmogenic effects of ACh (1 mM) and histamine (0.2 mM) were accompanied by depolarization and abolition of slow wave discharge. In many cases the record of membrane potential subsequently exhibited noise which incorporated fast, hyperpolarizing transients. 4. In the absence and presence of indomethacin, TEA (10 mM) and procaine (5 mM) markedly reduced the membrane noise and hyperpolarizing transients evoked by ACh or histamine without augmenting the evoked tension. 5. It is concluded that slow wave discharge does not depend on prostaglandin synthesis. The membrane noise and hyperpolarizing transients evoked by ACh and histamine represent the opening of membrane K+-channels. While such K+-channel opening may offset spasmogen-induced depolarization it does not moderate the evoked tension.

Inhibitory responses to nicotine and transmural stimulation in hyoscine-treated guinea-pig isolated trachealis: an electrical and mechanical study

Guinea-pig isolated trachealis muscle treated with hyoscine (1 microM) exhibited mechanical tone which could be suppressed by transmural stimulation and, in a concentration-dependent manner, by nicotine (10-1000 microM). Hexamethonium (500 microM) did not itself cause tone changes, antagonized effects of nicotine but did not antagonize those of isoprenaline. Tetrodotoxin (0.3 microM) did not itself cause tone changes, did not modify the action of isoprenaline but antagonized the effects of nicotine and very markedly reduced responses to transmural electrical stimulation. Guanethidine (50 microM) did not itself cause tone changes, potentiated the action of isoprenaline, antagonized effects of nicotine and reduced responses to transmural electrical stimulation. Propranolol (1 microM) did not itself cause tone changes, antagonized effects of both isoprenaline and nicotine and reduced responses to transmural electrical stimulation. Propranolol (10 microM) caused greater antagonism of isoprenaline but did not further antagonize nicotine or further reduce responses to electrical stimulation. Intracellular electrophysiological recording from hyoscine-treated trachealis showed that 10 microM nicotine caused little or no mechanical or electrical change. Higher concentrations (100 microM and 1 mM) evoked relaxation which was often though not invariably accompanied by transient hyperpolarization and transient inhibition of electrical slow waves in the impaled cell. Hexamethonium (500 microM), tetrodotoxin (0.3 microM), guanethidine (50 microM) and propranolol (1 microM) each suppressed the electrical or mechanical changes evoked by nicotine (100 microM). However, nicotine (1 mM) tested in the presence of propranolol (1 microM), caused relaxation which could be accompanied by slow wave suppression but not by change in resting membrane potential. Transmural stimulation of hyoscine-treated trachea with single pulses of supramaximal voltage and 0.5 ms duration evoked neither relaxation nor membrane potential changes. Stimulation with similar pulses in trains of 5 s duration evoked relaxation which was dependent on pulse frequency. In many cells this relaxation was not accompanied by membrane potential change. In other cells suppression of slow waves occurred. At high pulse frequencies (greater than 16 Hz) this was generally accompanied by membrane hyperpolarization. In tissue treated with hyoscine and propranolol (both 1 microM), transmural stimulation with pulse trains as described above always evoked relaxation but no membrane potential changes were observed. 10 It is concluded that nicotine and transmural stimulation can excite intramural noradrenergic nerves in guinea-pig trachea and thereby evoke relaxation. The membrane potential changes (slow wave suppression and hyperpolarization) are similar to those evoked by the administration of agonists at beta-adrenoceptors. Nicotine and transmural stimulation also excite non-adrenergic non-cholinergic inhibitory (NANCI) nerves. The relaxation evoked by the NANCI neurotransmitter is accompanied by little, if any, membrane potential change.

Electrical and mechanical effects of BRL34915 in guinea-pig isolated trachealis

BRL34915 (0.1-10 microM) suppressed the spontaneous tone of guinea-pig isolated trachealis in a concentration-dependent manner. BRL34915 was not antagonized by propranolol (1 microM). In trachea where spontaneous tone was suppressed by indomethacin (2.8 microM) but subsequently restored to the same level with acetylcholine or histamine, the relaxant potency of BRL34915 was reduced. In Krebs solution containing K+ (120 mM), isolated trachealis muscle developed near-maximal tension. The relaxant effects of BRL34915 were virtually abolished in this medium. Concentration-effect curves for KCl, acetylcholine and histamine were constructed in tissues treated with indomethacin (2.8 microM). BRL34915 (10 microM) depressed the foot of the concentration-effect curve for KCl and caused minor rightward shifts in the concentration-effect curves of acetylcholine and histamine. Four K+-channel inhibitors were tested. Apamin (0.1 microM) did not modify the action of BRL34915. Tetraethylammonium (8 mM) had little effect but procaine (5 mM) and 4-aminopyridine (5 mM) each significantly inhibited the relaxant action of BRL34915. Intracellular electrophysiological recording showed that BRL34915 (0.1 microM) caused very minor relaxation and little, if any, electrical change. Higher concentrations (1-10 microM) evoked relaxation, suppression of spontaneous electrical slow waves and marked hyperpolarization of the trachealis cells. In the presence of TEA (8 mM) or procaine (5 mM) the hyperpolarization induced by BRL34915 was significantly reduced. In trachealis skinned of its plasma membranes, tension development induced by Ca2+ (20 microM) was unaffected either by BRL34915 (10 microM) or by nicorandil (1 mM). In studies of the efflux of 86Rb+ from muscle-rich strips of trachea, BRL34915 (1 and 10 microM) increased the efflux rate constant. It is concluded that BRL34915 evokes relaxation of the trachealis by a mechanism that involves neither beta-adrenoceptor activation nor direct reduction of the sensitivity of the intracellular contractile machinery to cytosolic free Ca2+. The action of BRL34915 may depend on the opening of K+ channels in the plasma membrane which are permeable to 86Rb+. The opening of these channels, or the effects of their opening, may be reduced by K+-channel inhibitors such as 4-aminopyridine, procaine and TEA but not by apamin.

Electromyographic responses in infants after auditory stimulation

49 of 50 newborn infants, when presented with a strong auditory stimulus, showed significant increases in EMG potential. The infant who failed initially responded when rechecked in 1 mo. The results suggest it may be possible to develop an EMG-Audiometric process which could be employed in screening hearing of newborn infants.