Pericardiocentesis over 3 years at a tertiary referral Australian hospital

Funding Acknowledgements

Type of funding sources: None.

Background

 Pericardiocentesis is a lifesaving intervention performed both percutaneously or surgically. We analysed 3 years of experience in a major tertiary hospital in Sydney Australia. 

Purpose

 To examine the indications, safety and delivery of a pericardiocentesis service at a major teaching hospital. 

Methods

 We retrospectively audited consecutive patients who underwent pericardiocentesis for  pericardial effusion[PE] at a major teaching hospital from February 2018 to December 2020. Eligible patients were identified from the electronic medical records with this coding diagnosis.

Results

89 patients identified with mean age 60.8 ± 18.9years and 58.4%(51/89) male. Follow-up to August 2021 showed 41.5% had died, with an index hospitalisation mortality of 19%(17/89). Malignancy was the most common aetiology 30.3%(27/89) and attributable cause of hospitalisation death in 29.4%. Alternate causes included pericarditis 14.6%, idiopathic 13.4%, percutaneous-coronary-intervention(PCI) 5.6%(6/89) and electrophysiology 4.5%(4/89) complications. Three patients had aortic dissection (3.3%) and two were fatal. Clinical tamponade was present in 66.2%(55/89), PE identification occurred via echocardiography(TTE) in 55% cases (49/89) and incidental CT-diagnosis in 20.2%. TTE findings: right atrial collapse 54%(47/87), right ventricular collapse 60.9%(53/87), fixed and dilated inferior vena cava 64.7%. Pericardiocentesis was performed by cardiology trainees in 90.5% cases, 64.5% with consultant supervision and during working hours in 57.3% of cases. Percutaneous drainage was successful in 96%(72/75) of cases and was performed in the coronary care unit (30.3%), catheterisation laboratory (23.5%), emergency department (19.1%) and ICU (11.2%). Subxiphoid approach in 70%(62/89) was the most common then trans-apical 15%(13/89), parasternal 3%(3/89) and surgical 16%(14/89). TTE confirmed drain position in 76%(54/71), fluoroscopy in 28.5%(6/21) and agitated saline in 38.9%(30/77). Haemo-serous fluid noted in 77%(67/87) with average initial fluid drainage 480 ± 326mls and mean drain removal time 54 ± 33hrs. 17%(15/89) required re-drainage with adenocarcinoma found in 33.3%(5/15). Background antiplatelet treatment in 30.6%(27/88) and of these 67%(18/27) were on dual antiplatelets. 33%(29/89) patients were anticoagulated and 31.3%(9/29) required reversal prior to drainage. Complications were rare, 4%(3/75) had right heart chamber perforation needing emergency surgery. Two were post complex PCI (one died during admission from multiorgan failure) and one with pericarditis . 

Conclusions

 Pericardiocentesis is a safe and effective procedure for tamponade treatment and largely guided by echocardiography in our experience. Complications are rare and prognosis depends on aetiology with malignancy the most common. Drainage is often successfully performed emergently where the patient is located. Tamponade resulting from procedural complications are rare in our cohort.

Shaping the Future: Strategy Making as Artificial Evolution

To investigate how firms engage in forward-looking action, we examined the processes by which a pioneering firm actively influenced the future of its industry over five decades. From our longitudinal field study, we generated a process model of strategy making that helps to explain how firms work to shape the future in some preferred fashion. Specifically, we describe our findings on shaping-oriented forward-looking strategy making in terms of “artificial evolution” processes—interventions by which a firm’s leaders challenge the status quo and leverage the internal ecology of the organization to nudge the evolution of the business landscape toward a preferred direction. This is distinct from the more conventional and commonly invoked natural selection processes that describe how firms adapt to markets or unintentionally shape them. These findings on strategy making as akin to artificial evolution complement and extend the traditional view of strategic management, which has historically focused on processes anchored in models of search and adaptation. Our findings also shed light on an exceptional mode of strategy making—one that goes beyond concerns of firm survival and competitive advantage, and tackles societal grand challenges. By accounting for constructivist, forward-looking dimensions of strategic agency, our findings also contribute to the microfoundations of strategic decision making and to organization theories, more generally.

IL-1 induces p62/SQSTM1 and autophagy in ERα+ /PR+ BCa cell lines concomitant with ERα and PR repression, conferring an ERα- /PR- BCa-like phenotype

Estrogen receptor α (ERα)^low/- tumors are associated with breast cancer (BCa) endocrine resistance, where ERα low tumors show a poor prognosis and a molecular profile similar to triple negative BCa tumors. Interleukin-1 (IL-1) downregulates ERα accumulation in BCa cell lines, yet the cells can remain viable. In kind, IL-1 and ERα show inverse accumulation in BCa patient tumors and IL-1 is implicated in BCa progression. IL-1 represses the androgen receptor hormone receptor in prostate cancer cells concomitant with the upregulation of the prosurvival, autophagy-related protein, Sequestome-1 (p62/SQSTM1; hereinafter, p62); and given their similar etiology, we hypothesized that IL-1 also upregulates p62 in BCa cells concomitant with hormone receptor repression. To test our hypothesis, BCa cell lines were exposed to conditioned medium from IL-1-secreting bone marrow stromal cells (BMSCs), IL-1, or IL-1 receptor antagonist. Cells were analyzed for the accumulation of ERα, progesterone receptor (PR), p62, or the autophagosome membrane protein, microtubule-associated protein 1 light chain 3 (LC3), and for p62-LC3 interaction. We found that IL-1 is sufficient to mediate BMSC-induced ERα and PR repression, p62 and autophagy upregulation, and p62-LC3 interaction in ERα⁺ /PR⁺ BCa cell lines. However, IL-1 does not significantly elevate the high basal p62 accumulation or high basal autophagy in the ERα^- /PR^- BCa cell lines. Thus, our observations imply that IL-1 confers a prosurvival ERα^- /PR^- molecular phenotype in ERα⁺ /PR⁺ BCa cells that may be dependent on p62 function and autophagy and may underlie endocrine resistance.

Real-world outcomes of unrestricted direct-acting antiviral treatment for hepatitis C in Australia: The South Australian statewide experience

In March 2016, the Australian government offered unrestricted access to direct-acting antiviral (DAA) therapy for chronic hepatitis C virus (HCV) to the entire population. This included prescription by any medical practitioner in consultation with specialists until sufficient experience was attained. We sought to determine the outcomes and experience over the first twelve months for the entire state of South Australia. We performed a prospective, observational study following outcomes of all treatments associated with the state's four main tertiary centres. A total of 1909 subjects initiating DAA therapy were included, representing an estimated 90% of all treatments in the state. Overall, SVR12 was 80.4% in all subjects intended for treatment and 95.7% in those completing treatment and follow-up. 14.2% were lost to follow-up (LTFU) and did not complete SVR12 testing. LTFU was independently associated with community treatment via remote consultation (OR 1.50, 95% CI 1.04-2.18, P = .03), prison-based treatment (OR 2.02, 95% CI 1.08-3.79, P = .03) and younger age (OR 0.98, 95% CI 0.97-0.99, P = .05). Of the 1534 subjects completing treatment and follow-up, decreased likelihood of SVR12 was associated with genotype 2 (OR 0.23, 95% CI 0.07-0.74, P = .01) and genotype 3 (OR 0.23, 95% CI 0.12-0.43, P ≤ .01). A significant decrease in treatment initiation was observed over the twelve-month period in conjunction with a shift from hospital to community-based treatment. Our findings support the high responses observed in clinical trials; however, a significant gap exists in SVR12 in our real-world cohort due to LTFU. A declining treatment initiation rate and shift to community-based treatment highlight the need to explore additional strategies to identify, treat and follow-up remaining patients in order to achieve elimination targets.

Pim2 is important for regulating DNA damage response in multiple myeloma cells

Pan proviral integrations of Moloney virus (PIM) inhibition in multiple myeloma (MM) results in reduced cell viability in tested human-derived MM cell lines and reduces tumor burden in xenograft mouse models, making PIMs important therapeutic targets for the disease. PIM kinase inhibitors are currently being tested clinically in MM. We sought to elucidate the role of the various PIMs in MM. Our data demonstrate that Pim2 has a significant role in MM cell cytotoxicity. Our data provide evidence for a novel role for Pim2 in the regulation of the DNA damage response (DDR). Knockdown of Pim2 upregulates several downstream DDR markers, mimicking the effects of doxorubicin (Dox) treatment of MM cells, and suggesting a role for the kinase as a negative regulator of this pathway. Dox-induced DNA damage results in a decrease in Pim2 levels, placing the kinase directly downstream of the site of Dox-DNA binding. Overexpression of Pim2 confers a slight survival advantage against Dox through antiapoptotic activity, further underscoring its relevance in the DDR pathway. These data provide insights into a novel mechanism of PIM kinase activity and provide the framework for designing therapeutic approaches in MM.

Antiviral efficacy of adefovir dipivoxil in the treatment of chronic hepatitis B subjects from Indian subcontinent

Adefovir is one of the therapeutic options for the treatment of chronic hepatitis B. A total of 30 adefovir-experienced subjects with the median treatment duration of 12 (interquartile range (IQR) 6-18) months were studied. Virological response was measured by hepatitis B virus deoxyribonucleic acid (HBV DNA) levels. HBV reverse transcriptase (rt) domains were sequenced for the identification of resistance mutations. Among the 30 subjects, two (7%) showed virological response and 19 (63%) were non-responders. The virological response for the remaining nine (30%) subjects was not determined. On sequence analysis, two subjects were identified with rtI169L and rtA181V mutation after 9 months and 18 months of adefovir treatment, respectively. Though the frequencies of adefovir resistance mutations are low, a large majority of subjects showed non-response. Therefore, adefovir in the management of HBV should be used judiciously.

Cases of human fascioliasis in India: tip of the iceberg

This report presents two cases of human fascioliasis from different states in India. Although only few cases of human fascioliasis have been reported from India previously, both these cases were encountered within a span of three months at this tertiary care centre. Case 1 had significant symptoms with episodes of fever, abdominal pain and eosiniphilia and underwent multiple diagnostic procedures before the correct diagnosis was reached. Case 2, who had few symptoms, had fascioliasis diagnosed with minimal evaluation. These different presentations seen at two ends of the clinical spectrum of disease along with findings of peripheral eosinophilia, and radiological findings led to a presumptive diagnosis that was then confirmed by microscopic examination of bile. Morphometric analysis of ova from these cases was suggestive of infestation with F. gigantica or a F. gigantica-like hybrid. Both patients were treated with triclabendazole which was imported from Geneva. The need to be aware of the possibility of occurrence of this disease and the inclusion of drugs used for treating the disease, in the Indian drug list, should be emphasized.

Role of Q-type Ca2+ channels in vasopressin secretion from neurohypophysial terminals of the rat

1. The nerve endings of rat neurohypophyses were acutely dissociated and a combination of pharmacological, biophysical and biochemical techniques was used to determine which classes of Ca2+ channels on these central nervous system (CNS) terminals contribute functionally to arginine vasopressin (AVP) and oxytocin (OT) secretion. 2. Purified neurohypophysial plasma membranes not only had a single high-affinity binding site for the N-channel-specific omega-conopeptide MVIIA, but also a distinct high-affinity site for another omega-conopeptide (MVIIC), which affects both N- and P/Q-channels. 3. Neurohypophysial terminals exhibited, besides L- and N-type currents, another component of the Ca2+ current that was only blocked by low concentrations of MVIIC or by high concentrations of omega-AgaIVA, a P/Q-channel-selective spider toxin. 4. This Ca2+ current component had pharmacological and biophysical properties similar to those described for the fast-inactivating form of the P/Q-channel class, suggesting that in the neurohypophysial terminals this current is mediated by a 'Q'-type channel. 5. Pharmacological additivity studies showed that this Q-component contributed to rises in intraterminal Ca2+ concentration ([Ca2+]i) in only half of the terminals tested. 6. Furthermore, the non-L- and non-N-component of Ca(2+)-dependent AVP release, but not OT release, was effectively abolished by the same blockers of Q-type current. 7. Thus Q-channels are present on a subset of the neurohypophysial terminals where, in combination with N- and L-channels, they control AVP but not OT peptide neurosecretion.

Determination of disulfide bridge pattern in omega-conopeptides

Synthetic versions of seven naturally occurring omega-conopeptides were subjected to structural analyses in order to determine their disulfide bridge pattern. The method applied in this study uses a combination of amino-acid composition and peptide sequence analysis of various peptide fragments generated by different enzymatic digestions. A temperature modification in the Edman degradation cycles of a protein sequencer allowed the unambiguous detection of the cleavage of cystine residues. The appearance of the cystine residues in particular cycles of the sequence analysis was characteristic of one or several of the theoretically possible 15 isomers. In the case of multiple choices, possible isomers were further eliminated by the amino-acid and sequence analysis of peptide fragments generated by the enzymatic digestion. All synthetic peptides, SNX-111, -157, -159, -183, -185, -230 and -231, were found to have the same disulfide bridge pattern as determined for the naturally occurring omega-conopeptide G-VI-A, i.e. disulfide bridges between the half-cystines 1-16, 8-20 and 15-25 (using the amino-acid numbering of SNX-111).

Solution structure of omega-conotoxin MVIIA using 2D NMR spectroscopy

The solution structure of omega-conotoxin MVIIA (SNX-111), a peptide toxin from the fish hunting cone snail Conus magus and a high-affinity blocker of N-type calcium channels, was determined by 2D NMR spectroscopy. The backbones of the best 44 structures match with an average pairwise RMSD of 0.59 angstroms. The structures contain a short segment of triple-stranded beta-sheet involving residues 6-8, 20-21, and 24-25. The structure of this toxin is very similar to that of omega-conotoxin GVIA with which is has only 40% sequence homology, but very similar calcium channel binding affinity and selectivity.

Structure-activity analysis of a Conus peptide blocker of N-type neuronal calcium channels

The synthetic peptide SNX-111 corresponding to the sequence of the omega-conopeptide MVIIA from the venom of the marine snail Conus magus is a highly potent and selective antagonist of N-type calcium channels. We have synthesized and characterized a large number of analogs of SNX-111 in order to elucidate the structural features of the peptide involved in blocking N-type calcium channels. Comparison of the binding of SNX-111 and its analogs to rat brain synaptosomal membranes rich in N-type channels revealed that, among the four lysines and two arginines in the molecule, lysine in position 2 and arginines at position 10 and 21 are important for the interaction of SNX-111 with N-type channels. The importance of the middle segment from residues 9 through 14 for this binding interaction was revealed by substitution of the individual residues as well as by the construction of hybrid peptides in which the residues 9-12 in SNX-111 and another conopeptide, SNX-183, corresponding to a peptide SVIB from Conus striatus, were interchanged. Introduction of the sequence SRLM from SNX-111 in place of RKTS in position 9-12 in SNX-183 resulted in a 38-fold increase in affinity.

Solution structure of omega-conotoxin MVIIC, a high affinity ligand of P-type calcium channels, using 1H NMR spectroscopy and complete relaxation matrix analysis

We have determined the solution structure of the omega-conotoxin MVIIC from Conus magus by 1H NMR. This conopeptide preferentially blocks P and Q type Ca2+ currents by binding with high affinity to voltage-sensitive Ca2+ channels in neurons. This 26 residue peptide with three disulfide bonds was chemically synthesized and refolded for NMR structural studies. The 1H NMR NOESY spectrum of this peptide was completely assigned, with stereospecific assignments made for 12 of the beta prochiral centers. Complete relaxation matrix analysis using MARDIGRAS was used to obtain initial interproton distances from peak intensities. The correlation time necessary for these calculations was determined by measuring 13C relaxation times using inversely detected natural abundance spectra. Distances were input to DG, which provided 15 starting structures which were then subjected to restrained molecular dynamics calculations using SANDER with the AMBER 91 force field in vacuo. 1H-1H vicinal coupling constants were obtained using a combination of line fitting of both E. COSY and NOESY spectra and used to generate angle restraints that were included explicitly in the restrained molecular dynamics calculations. The final set of the 15 best structures had a backbone rmsd of 0.84 A. The ensemble R1/6 factor calculated by CORMA for the final 15 structures was 11%. The final structure consists of an anti-parallel, triple-stranded beta-sheet, with four turns. In spite of significant differences in amino acid sequence and affinities for calcium channel subtypes, the backbone structure of omega-conotoxin MVIIC is very similar to the previously reported structure of omega-conotoxin GVIA.

Antagonists of neuronal calcium channels: structure, function, and therapeutic implications

This article reviews the structural and functional diversity of neuronal calcium channels and the therapeutic potential of antagonizing such channels. Through spatial and temporal control of intracellular calcium concentration, voltage-sensitive calcium channels regulate a host of neuronal processes, including neurotransmitter secretion, electrical activity, cytoskeletal function, cell metabolism and proliferation, and gene expression. Several genes elaborate a number of calcium channel isoforms or subtypes--each tailored to specific roles in neuronal function and possessing distinct biophysical properties, distribution, modulation, and pharmacological sensitivity. This diversity has raised the possibility that subtype-specific antagonists could provide novel treatments for some neuropathologies. In fact, neuroprotective and analgesic actions of N-type channel blockers in animals appear to confirm this supposition. These properties prompted human clinical studies evaluating these agents for prevention of neuronal degeneration following ischemic brain trauma and for relief of pain. Future medical applications for these blockers and antagonists of other channels subtypes are discussed.

Differential blockade of voltage-sensitive calcium channels at the mouse neuromuscular junction by novel omega-conopeptides and omega-agatoxin-IVA

This investigation assessed the ability of a variety of calcium channel blocking peptides to block synaptic transmission in the isolated mouse phrenic nerve-hemidiaphragm. The synthetic version of the naturally occurring N-type voltage-sensitive calcium channel (VSCC) blocker omega-conopeptide MVIIA (SNX-111) had no effect on nerve-evoked muscle contractions. The non-N-, non-L-type VSCC blocker, omega-conopeptide MVIIC (SNX-230), blocked neuromuscular transmission completely, as did the selective P-type VSCC blocker, omega-Aga-IVA. Subsequent evaluation of other synthetic omega-conopeptides and analogs disclosed a significant positive correlation between the test compounds' affinities for high-affinity SNX-230 brain binding sites and their neuromuscular blocking potencies. Quantal analysis of transmitter release showed that SNX-230 abolished evoked endplate potentials completely, but had little effect on the amplitude and frequency of spontaneous miniature endplate potentials. Perineural focal recordings of presynaptic currents showed that SNX-230 did not block the neuronal action potential. These and other findings indicated that SNX-230 prevents transmitter release at the mouse neuromuscular junction by blocking calcium channels at presynaptic nerve endings. These calcium channels correspond pharmacologically to VSCCs associated with high-affinity binding sites in rat brain and are most probably either of the P- or Q-type.

Calcium channel antagonist peptides define several components of transmitter release in the hippocampus

The use of subtype-selective voltage-sensitive calcium channel (VSCC) antagonists has established that neurotransmitter release in mammalian brain is mediated by N-like and P-like VSCCs, and that other subtypes also contribute significantly. To determine the roles presynaptic VSCCs play in nervous system function and to evaluate the therapeutic potential of their selective inhibition, it is necessary to define further the contributions of VSCC subtypes to neurotransmitter release. The novel conopeptide, SNX-230 (omega-conopeptide MVIIC), has revealed a new VSCC subtype, the Q-type, in cerebellar granule cells. We have compared the effects of SNX-230 on release of tritiated D-aspartate ([3H]D-Asp; a non-metabolizable analog of glutamate), gamma-aminobutyric acid ([3H]GABA), and norepinephrine ([3H]NE) from rat hippocampal slices to those of the N-type VSCC blocker, SNX-111 (omega-conopeptide MVIIA), and the P-type blocker, omega-agatoxin-IVA (AgaIVA). SNX-230 blocks both [3H]D-Asp and [3H]GABA release completely, whereas AgaIVA blocks them potently but partially and SNX-111 has no effect. These results suggest that glutamate and GABA release are mediated by two VSCC subtypes, a P-type and another, perhaps Q-like. SNX-111 blocks [3H]NE release potently but partially, while SNX-230 blockade is complete, consisting of one very potent phase and one less potent phase. AgaIVA also blocks [3H]NE release potently but partially. These results suggest that at least two VSCC subtypes, an N-type and a novel non-N-type, mediate NE release. Pair-wise combinations of the three ligands indicate that at least three pharmacologically distinct components comprise [3H]NE release in the hippocampus.

Neuroanatomical distribution of receptors for a novel voltage-sensitive calcium-channel antagonist, SNX-230 (omega-conopeptide MVIIC)

Neuronal voltage-sensitive calcium channels (VSCCs) are a diverse family of proteins that regulate entry of Ca2+ into neurons. Selective antagonists of VSCCs have proven to be powerful pharmacological tools for identifying and characterizing these channels. A new VSCC antagonist, SNX-230 (also known as omega-conopeptide MVIIC), binds with high affinity to receptors in rat brain and blocks one or more high-threshold VSCCs that are neither L- nor N-type. We have defined the neuroanatomical distribution of the high-affinity non-L, non-N VSCC receptors for SNX-230 using [125I]SNX-230 bound to rat brain sections and compared it with that of [125I]SNX-111, a reversible blocker of N-type VSCCs. Highest densities of binding for both ligands were seen in areas rich in synaptic connections, such as the oriens, radiatum and molecular layers of the hippocampus. In general, the density of [125I]SNX-230-binding was higher in cerebellum compared with that in forebrain. In contrast, this general distribution of density was reversed for [125I]SNX-111. In the glomeruli of the olfactory bulb, binding of [125I]SNX-230 was undetectable compared with the high density of [125I]SNX-111-binding. Differential localization of the two ligands was also seen in cervical spinal cord. The clearly different localization of [125I]SNX-230 compared with that of [125I]SNX-111 in the olfactory bulb and spinal cord suggested that the binding sites for [125I]SNX-230 in other brain regions, while co-localized macroscopically, are also distinct from those for [125I]SNX-111. This was confirmed when addition of saturating concentrations of SNX-111 did not affect the distribution pattern of [125I]SNX-230-binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium channel subtypes in rat brain: biochemical characterization of the high-affinity receptors for omega-conopeptides SNX-230 (synthetic MVIIC), SNX-183 (SVIB), and SNX-111 (MVIIA)

High-threshold voltage-sensitive calcium channels of the N-type, L-type, and P-type have been distinguished in the mammalian CNS predominantly on the basis of their sensitivity to selective antagonists. Matching them with genes identified by molecular cloning is an ongoing undertaking. Whereas L-type channels are characterized by their sensitivity to dihydropyridines and P-type channels by sensitivity to the funnel-web spider toxin AgaIVA, the N-type channel has been shown to be recognized by the omega-conopeptides GVIA and MVIIA. Recently, two new members of the family of omega-conopeptides--MVIIC from the marine snail Conus magus and SVIB from Conus striatus--have been described. Binding and electrophysiological data suggest that these two peptides, in addition to interacting with N-type calcium channels, interact with a widely distributed receptor in neuronal membranes that is distinct from N-type channels. In this report we demonstrate through biochemical and pharmacological differentiation at individual receptor polypeptide resolution, by affinity cross-linking, SDS-PAGE, and autoradiography, that SNX-230 (synthetic MVIIC) binds with high affinity to a calcium channel alpha 1 subunit distinct from the high-affinity alpha 1 target of SNX-111 (synthetic MVIIA). SNX-183 (synthetic SVIB) interacts with both alpha 1 subunits with lower affinity. Whereas the alpha 1 subunit recognized with high affinity by MVIIA corresponds to the N-type channel, the other represents a novel calcium channel distinct from N-, L-, and perhaps P-type channels.

Characterization of the binding of omega-conopeptides to different classes of non-L-type neuronal calcium channels

The interaction of two synthetic omega-conopeptides SNX-111 (MVIIA) and SNX-230 (MVIIC) both derived from the marine snail Conus magus, with non-L-type neuronal voltage-sensitive calcium channels (VSCC) in rat brain synaptosomal preparations has been investigated with the aid of well-characterized 125I derivatives of the two peptides. To assess the effects of iodination on the binding characteristics of SNX-111 and SNX-230, the corresponding peptides containing monoiodotyrosine in place of tyrosine, namely, SNX-259 ([127I]SNX-111) and SNX-260 ([127I]SNX-230), respectively, were prepared by solid-phase synthesis. Saturation analysis showed that [125I]SNX-111 and [125I]SNX-230 bound to two distinct classes of high-affinity sites with apparent Kd's of 9 and 11 pM and Bmax's of 0.54 and 2.2 pmol/mg protein, respectively. Kinetic analysis revealed that both peptides exhibited high association rates as well as rapid dissociation rates in contrast to the 125I derivative of the synthetic omega-conopeptide from Conus geographus, GVIA (SNX-124), which binds irreversibly to N-type channels in rat brain synaptosomes. Competition binding experiments with [125I]SNX-111 and [125I]SNX-124 established that both of them bind to the same site, namely, N-type VSCC. The site detected by the binding of [125I]SNX-230 is distinct from N-type VSCC since SNX-111 has very low affinity (K(i) = 135 nM) in competition studies. Recent findings that a novel high-voltage-activated calcium channel in rat cerebellar granule neurons is resistant to blockers of L-, N-, and P-type VSCC but is highly sensitive to SNX-230 suggest that the [125I]SNX-230 binding site may represent this novel type of calcium channel or another, as yet undescribed, VSCC.

Characterization and partial purification of the human receptor for the heat-stable enterotoxin

The receptor for the Escherichia coli heat-stable enterotoxin has been characterized and partially purified from the T84 human colonic cell line. Using a novel mutant heat-stable enterotoxin peptide as a radioligand (the C-terminal tyrosine residue is replaced by phenylalanine in the mutant), a single class of high-affinity receptor sites was detected in T84 cells, with a Kd of 0.1 nM, similar in affinity to the receptor described in human intestinal tissue. The receptor was solubilised from T84 cell membranes and affinity cross-linking of the solubilised preparation indicated that a single species of M(r) 160,000 served as the receptor. Freshly solubilised preparations of the receptor retained heat-stable enterotoxin-activable guanylyl cyclase activity. Purification of the receptor was achieved through sequential affinity chromatography on GTP--epoxy-Sepharose and wheat-germ-agglutinin columns resulting in purification of the receptor by 3000 fold. The heat-stable enterotoxin-binding characteristics of the receptor were unchanged during the purification and silver staining of the purified receptor preparation indicated a band of M(r) 160,000, which was specifically cross-linked to the 125I-labeled mutant peptide. The purified receptor retained guanylyl cyclase activity, but the activity was not stimulated on addition of human heat-stable enterotoxin, suggesting that accessory structural factors may be involved in the activation of the guanylyl cyclase/receptor.

A new Conus peptide ligand for Ca channel subtypes

A cDNA clone encoding a new omega-conotoxin was identified from Conus magus. The predicted peptide was chemically synthesized using a novel strategy that efficiently yielded the biologically active disulfide-bonded isomer. This peptide, omega-conotoxin MVIID, targets other voltage-gated calcium channels besides the N-subtype and exhibits greater discrimination against the N-channel subtype than any other omega-conotoxin variant to date. Consequently, omega-conotoxin MVIID may be a particularly useful ligand for calcium channel subtypes that are not of the L- or N-subclasses. Of the eight major sequence variants of omega-conotoxins that have been elucidated, four come from Conus magus venom. We suggest that sequence variants from the same venom may be designed to optimally interact with different molecular variants of calcium channels; such omega-conotoxin sets from a single venom may therefore be useful for helping to identify novel calcium channel subtypes.

Solution structure of omega-conotoxin GVIA using 2-D NMR spectroscopy and relaxation matrix analysis

We report here the solution structure of omega-conotoxin GVIA, a peptide antagonist of the N-type neuronal voltage-sensitive calcium channel. The structure was determined using two-dimensional NMR in combination with distance geometry and restrained molecular dynamics. The full relaxation matrix analysis program MARDIGRAS was used to generate maximum and minimum distance restraints from the crosspeak intensities in NOESY spectra. The 187 restraints obtained were used in conjunction with 23 angle restraints from vicinal coupling constants as input for the structure calculations. The backbones of the best 21 structures match with an average pairwise RMSD of 0.58 A. The structures contain a short segment of triple-stranded beta-sheet involving residues 6-8, 18-21, and 24-27, making this the smallest published peptide structure to contain a triple-stranded beta-sheet. Conotoxins have been shown to be effective neuroprotective agents in animal models of brain ischemia. Our results should aid in the design of novel nonpeptide compounds with potential therapeutic utility.

Novel alpha- and omega-conotoxins from Conus striatus venom

Three neurotoxic peptides from the venom of Conus striatus have been purified, biochemically characterized, and chemically synthesized. One of these, an acetylcholine receptor blocker designated alpha-conotoxin SII, has the sequence GCCCNPACGPNYGCGTSCS. In contrast to all other alpha-conotoxins, SII has three disulfide bonds (instead of two), has no net positive charge, and has a free C-terminus. The other two paralytic peptides are Ca channel-targeted omega-conotoxins, SVIA and SVIB. omega-SVIA is the smallest natural omega-conotoxin so far characterized and has the sequence CRSSGSPCGVTSICCGRCYRGKCT-NH2. Although omega-conotoxin SVIA is a potent paralytic toxic in lower vertebrate species, it was much less effective in mammals. The third toxin, omega-conotoxin SVIB, has the sequence CKLKGQSCRKTSYDCCSGSCGRSGKC-NH2. This peptide has a different pharmacological specificity from other omega-conotoxins previously purified from Conus venoms; only omega-conotoxin SVIB has proven to be lethal to mice upon ic injection. Binding competition experiments with rat brain synaptosomal membranes indicate that the high-affinity binding site for omega-conotoxin SVIB is distinct from the high-affinity omega-conotoxin GVIA or MVIIA site.

A new Conus peptide ligand for mammalian presynaptic Ca2+ channels

Voltage-sensitive Ca2+ channels that control neurotransmitter release are blocked by omega-conotoxin (omega-CgTx) GVIA from the marine snail Conus geographus, the most widely used inhibitor of neurotransmitter release. However, many mammalian synapses are omega-CgTx-GVIA insensitive. We describe a new Conus peptide, omega-CgTx-MVIIC, that is an effective inhibitor of omega-CgTx-GVIA-resistant synaptic transmission. Ca2+ channel targets that are inhibited by omega-CgTx-MVIIC but not by omega-CgTx-GVIA include those mediating depolarization-induced 45Ca2+ uptake in rat synaptosome preparations, "P" currents in cerebellar Purkinje cells, and a subset of omega-CgTx-GVIA-resistant currents in CA1 hippocampal pyramidal cells. The characterization of omega-CgTx-MVIIC by a combination of molecular genetics and chemical synthesis defines a general approach for obtaining ligands with novel receptor subtype specificity from Conus.

Hm1 muscarinic cholinergic receptor internalization requires a domain in the third cytoplasmic loop

Selected regions of the Hm1 muscarinic cholinergic receptor were mutated to analyze the molecular mechanisms of agonist-induced receptor internalization (or sequestration). The wild-type and mutant Hm1 genes were expressed, using pSG5, in U293 human kidney cells. Whereas surface receptor density measured with the polar tracer N-[3H]methylscopolamine was rapidly reduced by carbachol exposure, total receptor content measured with [3H]quinuclidinyl benzilate did not decline for at least 24 h, indicating the absence of extensive receptor down-regulation in U293 cells. Carbachol stimulation of phosphatidylinositol turnover paralleled receptor internalization, both with EC50 values of 10-20 microM. Furthermore, a D71N point mutation that prevented receptor activation also abolished carbachol-induced receptor internalization, indicating that receptor activation (but not necessarily second messenger stimulation) was required for internalization. Truncation of the COOH-terminal tail (K447 trunc) and point mutations of several potential Ser and Thr phosphorylation sites to Ala failed to affect receptor activation and internalization. In contrast, partial deletions of the third intracellular loop (i3) (Tyr208-Thr366) resulted in receptor mutants deficient in agonist-induced receptor internalization/sequestration. Various deletions caused either complete loss of internalization (d 232-358) or impaired internalization, ranging from 10 to 30% over 2 h, whereas wild-type Hm1 internalized to approximately 50%. Whereas the reason for the observed differences among the deficient deletion mutants remains unclear, the initial rate of N-[3H]methylscopolamine binding loss from the cell surface was much slower than that of wild-type Hm1 in each case. The deletion of only one single domain, 284-292 (SMESLTSSE), in the middle of i3 was consistently associated with impaired internalization. Domain 284-292 is partially conserved among closely related muscarinic receptors, whereas most of the remainder of i3 is not (except for the i3 membrane junctions), and similar Ser- and Thr-rich regions are present in many other G protein-coupled receptors. We propose that a small receptor domain in the middle of the i3 loop of Hm1 is involved in agonist-induced receptor internalization.

Structure and function of G protein coupled receptors

The G protein coupled receptors (GPC-Rs) comprise a large superfamily of genes encoding numerous receptors which all show common structural features, e.g., seven putative membrane spanning domains. Their biological functions are extremely diverse, ranging from vision and olfaction to neuronal and endocrine signaling. The GPC-Rs couple via multiple G proteins to a growing number of recognized second messenger pathway, e.g., cAMP and phosphatidyl inositol turnover. This review summarizes our current knowledge of the molecular mechanisms by which the GPC-Rs activate second messenger systems, and it addresses their regulation and structure.

Internalization of the Hm1 muscarinic cholinergic receptor involves the third cytoplasmic loop

The m1 muscarinic receptor was previously shown to stimulate phosphatidyl inositol (PI) turnover and to internalize rapidly upon agonist activation. Three receptor mutants with large deletions of the third cytoplasmic loop (i3) of human Hm1, leaving only 11 and 8 amino acids at the amino and carboxy terminal junctions of i3, respectively, retained full ability to stimulate PI turnover, when expressed in U293 cells, but receptor internalization was greatly reduced in two mutants with deletions reaching close to the NH2 terminal of i3. We propose that a receptor domain located toward the amino terminal junction of i3 plays a role in Hm1 internalization.

Functional diversity of muscarinic receptor subtypes in cellular signal transduction and growth

The regulation of cellular signal transduction and growth by four human muscarinic acetylcholine receptor (mAChR) subtypes has been studied comparatively. The four mAChRs fall into two functional sub-groups, based on their primary effects on second messenger formation; two of the receptors strongly inhibit adenylyl cyclase activity, whereas the other two strongly stimulate PI hydrolysis. Studies on mAChR regulation of two cellular events involved in cellular growth regulation, the transcription of proto-oncogene c-fos and DNA synthesis, indicate that these events are efficiently activated by those mAChRs which couple primarily to phospholipase C.

Peptide-based radioimmunoassay for insulin receptor. Detection of insulin-stimulated downregulation in IM-9 lymphocytes

To overcome the difficulties encountered in quantifying the insulin receptor number by Scatchard analysis, a radioimmunoassay (RIA) for the human insulin receptor (hIR) has been developed that uses an antibody raised against a synthetic peptide (Gly-Lys-Lys-Asn-Gly-Arg-Ile-Leu-Thr-Leu-Pro-Arg-Ser-Asn-Pro-Ser) corresponding to the carboxyl terminal of the hIR. A second peptide (Tyr-Gly-Arg-Ile-Leu-Thr-Leu-Pro-Arg-Ser-Asn-Pro-Ser) was used as a standard and allowed preparation of monoiodinated derivative of theoretical specific activity for use as the radioactive ligand. The assay is specific, highly reproducible, and sensitive, with a detection limit of 10 fmol of receptor. One mole of purified receptor, measured by Scatchard analysis or amino acid analysis, is read as one mole of receptor in the RIA with peptide being the standard. The assay is effective with receptor from multiple sources and could determine the decrease in number of insulin receptors seen in IM-9 lymphocytes after treatment with insulin (downregulation).

Acetylcholine analogue stimulates DNA synthesis in brain-derived cells via specific muscarinic receptor subtypes

Little is known about the factors which regulate the growth and development of the mammalian brain. Although proliferation of neuronal cells ceases relatively early in development, certain types of glial cells proliferate and differentiate mainly perinatally. In the perinatal period, the ability of acetylcholine to stimulate phosphoinositide (PI) hydrolysis in brain reaches peak levels, and indeed the stable acetylcholine analogue carbachol can stimulate PI hydrolysis of primary neonatal astroglial cells. As PI hydrolysis is thought to be important in the regulation of cell proliferation, we investigated whether cellular DNA synthesis can be induced by carbachol. Our results show that carbachol stimulates DNA synthesis via muscarinic acetylcholine receptors (mAChRs), in primary astrocytes derived from perinatal rat brain, in an age-dependent fashion. Carbachol is also mitogenic in certain brain-derived astrocytoma and neuroblastoma cell lines, as well as in chinese hamster ovary (CHO) cells expressing recombinant muscarinic receptors. DNA synthesis is strongly activated by carbachol in those brain-derived cell lines and transfected CHO cells that express mAChR subtypes which activate PI hydrolysis efficiently, and poorly activated in cells expressing mAChR subtypes which only weakly activate PI hydrolysis. These results strongly support a role for acetylcholine in regulating astroglial cell growth in the developing brain, and indicate that the specificity of acetylcholine-induced cell proliferation may be determined by the expression of those mAChR subtypes which activate PI hydrolysis.

Functionally distinct G proteins selectively couple different receptors to PI hydrolysis in the same cell

The number of G proteins identified by molecular cloning exceeds the number of known G protein functions. Here we show that a cell can possess multiple G proteins that carry out a similar function, the activation of phospholipase C, but couple selectively to different receptors, which are endogenous to the cell or introduced by DNA transfection. These G proteins (termed Gp) can be distinguished by their sensitivity to pertussis toxin. The assignment of a given Gp pathway to specific receptors is confirmed by the additivity relationships of the PI hydrolysis response mediated by the different receptors. Significantly different amounts of PI hydrolysis are activated through each Gp pathway, suggesting that Gp proteins also differ in their coupling to phospholipase C. These results indicate that distinct Gp pathways in a given cell exist to couple different receptors to PI hydrolysis selectively, and may specify the nature of the cellular response to different receptors by determining the magnitude of PI hydrolysis.

The structural and functional interrelationships of muscarinic acetylcholine receptor subtypes

Molecular cloning of the genes encoding the muscarinic acetylcholine receptors has shown that receptor subtypes classified on the basis of pharmacological properties are related polypeptides encoded by distinct genes. These studies have also revealed the existence of novel muscarinic receptor subtypes. Functional analysis of each of the subtypes expressed in mammalian cells indicates that the different subtypes activate distinct biochemical pathways, a finding that explains the tissue-specific physiological response elicited by the neurotransmitter, acetylcholine.

Structure and function changes in rat adrenal glands during aging

The current study examines corticosterone production in young and old rats with a view to understanding how hormone production is related to aging changes in the adrenal gland. For this purpose, we compared total (plasma volume-corrected) values for adrenocorticotropic hormone (ACTH)-induced maximal corticosterone production in young, mature (5-mo-old), and aging (18-mo-old) rats. These values were subsequently corrected for measured age-related differences in adrenal weight, adrenal cortex volume, specific adrenal zone volumes, and total number of corticosterone-producing cells in the adrenals of the differently aged rats. In addition, corticosterone disposal rates were measured in the two groups of rats, and adrenal cortical ACTH binding sites were identified by autoradiography after perfusion with 125I-labeled ACTH analogue. The results show that maximal serum ACTH-induced corticosterone concentrations (per ml serum) in the 18-mo-old rats are somewhat less than those seen in the younger animals. However, because the plasma volume is greater in the older animals (and corticosterone disposal rates do not vary), total circulating corticosterone production is, in fact, equivalent in the two groups of animals. When these total values for corticosterone are corrected for various structural changes in the adrenal gland with age, corticosterone production was found to be lower in the older group of rats: i.e., one sees an approximately 50% decline when corticosterone is expressed per adrenal weight or zonal volume and an approximately 20% decline when expressed per number of endocrine cells per adrenal.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of PI hydrolysis and adenylyl cyclase by muscarinic receptor subtypes

Muscarinic acetylcholine receptors (mAChRs), like many other neurotransmitter and hormone receptors, transduce agonist signals by activating G proteins to regulate ion channel activity and the generation of second messengers via the phosphoinositide (PI) and adenylyl cyclase systems. Human mAChRs are a family of at least four gene products which have distinct primary structures, ligand-binding properties and patterns of tissue-specific expression. To examine the question of whether functional differences exist between multiple receptor subtypes, we have investigated the ability of each subtype to regulate PI hydrolysis and adenylyl cyclase when expressed individually in a cell lacking endogenous mAChRs. We show that the HM2 and HM3 mAChRs efficiently inhibit adenylyl cyclase activity but poorly activate PI hydrolysis. In contrast, the HM1 and HM4 mAChRs strongly activate PI hydrolysis, but do not inhibit adenylyl cyclase, and in fact can substantially elevate cAMP levels. Interestingly, the subtypes that we find to be functionally similar are also more similar in sequence. Our results indicate that the different receptor subtypes are functionally specialized.

Carboxyl terminal domain of Gs alpha specifies coupling of receptors to stimulation of adenylyl cyclase

The alpha subunits of Gs and Gi link different sets of hormone receptors to stimulation and inhibition, respectively, of adenylyl cyclase. A chimeric alpha i/alpha s cDNA was constructed that encodes a polypeptide composed of the amino terminal 60% of an alpha i chain and the carboxyl terminal 40% of alpha s. The cDNA was introduced via a retroviral vector into S49 cyc- cells, which lack endogenous alpha s. Although less than half of the hybrid alpha chain is derived from alpha s, its ability to mediate beta-adrenoceptor stimulation of adenylyl cyclase matched that of the normal alpha s polypeptide expressed from the same retroviral vector in cyc- cells. This result indicates that carboxyl terminal amino acid sequences of alpha s contain the structural features that are required for specificity of interactions with the effector enzyme, adenylyl cyclase, as well as with the hormone receptor.