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Biomedical subjects

M E Adams

Publications and source records attributed to M E Adams.

At least 19 recordsLinked to original sources
PubMed1992

Autoradiographic localization of the binding of calcium channel antagonist, [125I]omega-agatoxin IIIA, in rat brain.

The calcium channel antagonists omega-agatoxin IIIA (omega-Aga-IIIA) and omega-conotoxin GVIA (omega-CgTx) were radioiodinated and used to locate binding sites in the rat brain by receptor autoradiography. While patterns of regional binding to sagittal sections of rat brain were generally similar for the 2 toxins, notable differences in the cerebellum and hippocampus were observed. Specific [125I]omega-Aga-IIIA binding was greatest in the granule cell layers of the cerebellum and of the dentate gyrus. In contrast, binding of [125I]omega-CgTx was most intense in the molecular layers of these structures. Less than one-third of [125I]omega-Aga-IIIA binding in rat brain slices was inhibited by pre-exposure to 250 nM omega-CgTx, while 40 nM omega-Aga-IIIA virtually eliminated the binding of [125I]omega-CgTx under the same conditions. The P-type calcium channel antagonist omega-Aga-IVA blocked only a small fraction of [125I]omega-Aga-IIIA and [125I]omega-CgTx binding. These autoradiographic data are consistent with membrane binding experiments and indicate that the combined use of agatoxins and conotoxins may be useful in the characterization of separate types of neuronal calcium channels.

Agatoxins↗
PubMed1992

Heterodimeric structure of the spider toxin omega-agatoxin IA revealed by precursor analysis and mass spectrometry.

We report the first molecular characterization of a precursor sequence for a small, Ca2+ channel blocking, peptide spider toxin, omega-agatoxin IA. By integrating information generated from a molecular genetic approach using agatoxin cDNAs with data provided from mass spectrometry of the mature toxin, we were able to deduce the likely mechanisms by which the toxin precursor peptide is processed to its mature heterodimeric form. A particularly interesting feature of the prepropeptide is the occurrence of two glutamate-rich sequences interposed between the signal sequences, the major peptide toxin, and the minor toxin peptide. Excision of the more distal glutamate-rich region appears to be signaled by flanking arginine residues but likely occurs only after a disulfide linkage has formed between the major and minor chains of the mature toxin. Our molecular genetic approach toward characterizing this toxin will allow us to quickly generate a series of spider sequences from which mature toxin structures can be deduced and eventually expressed. Additionally, this approach will provide insights into the evolutionary divergence observed among spider peptide toxins.

Agatoxins↗
PubMed1992

Calcium channels coupled to glutamate release identified by omega-Aga-IVA.

Presynaptic calcium channels are crucial elements of neuronal excitation-secretion coupling. In mammalian brain, they have been difficult to characterize because most presynaptic terminals are too small to probe with electrodes, and available pharmacological tools such as dihydropyridines and omega-conotoxin are largely ineffective. Subsecond measurements of synaptosomal glutamate release have now been used to assess presynaptic calcium channel activity in order to study the action of peptide toxins from the venom of the funnel web spider Agelenopsis aperta, which is known to inhibit dihydropyridine and omega-conotoxin-resistant neuronal calcium currents. A presynaptic calcium channel important in glutamate release is shown to be omega-Aga-IVA sensitive and omega-conotoxin resistant.

Agatoxins↗
PubMed1992

P-type calcium channels blocked by the spider toxin omega-Aga-IVA.

Voltage-dependent calcium channels mediate calcium entry into neurons, which is crucial for many processes in the brain including synaptic transmission, dendritic spiking, gene expression and cell death. Many types of calcium channels exist in mammalian brains, but high-affinity blockers are available for only two types, L-type channels (targeted by nimodipine and other dihydropyridine channel blockers) and N-type channels (targeted by omega-conotoxin). In a search for new channel blockers, we have identified a peptide toxin from funnel web spider venom, omega-Aga-IVA, which is a potent inhibitor of both calcium entry into rat brain synaptosomes and of 'P-type' calcium channels in rat Purkinje neurons. omega-Aga-IVA will facilitate characterization of brain calcium channels resistant to existing channel blockers and may assist in the design of neuroprotective drugs.

Amino Acid Sequence↗
PubMed1992

Antagonism of synaptosomal calcium channels by subtypes of omega-agatoxins.

Venom of the funnel web spider Agelenopsis aperta inhibits the binding of 125I-omega-conotoxin GVIA (omega-CgTx) to calcium channels in chick brain synaptosomal membranes. Fractionation of the venom by liquid chromatography shows that this inhibitory activity is associated primarily with a diverse class of peptide toxins called omega-agatoxins (omega-Aga). Using binding inhibition as an assay, we purified and identified the novel, 76-amino acid toxin, omega-Aga-IIIA. Inhibition of 125I-omega-CgTx binding to chick synaptosomal membranes by omega-Aga-IIIA and omega-Aga-IIA is correlated with block of potassium-stimulated 45Ca entry into synaptosomes; omega-Aga-IA neither inhibits 125I-omega-CgTx binding nor 45Ca entry under identical conditions. omega-Aga-IIA and omega-Aga-IIIA are 20-30-fold more potent than omega-CgTx as antagonists of synaptosomal calcium channels. However, whereas omega-CgTx completely blocks 45Ca entry into synaptosomes at saturating concentrations, the omega-agatoxins maximally block only 60-70% of 45Ca entry. Pretreatment of synaptosomes with omega-Aga-IIIA occludes block of 45Ca entry by omega-CgTx. The results indicate that, while the omega-agatoxins bind to the entire population of omega-CgTx-sensitive calcium channels in chick synaptosomal membranes, they exert only a partial block of 45Ca flux. Such block could occur via two distinct mechanisms. Toxin binding may alter the kinetics of a homogeneous population of channels, resulting in lower overall conductance upon depolarization. Alternatively, the omega-agatoxins may bind to two distinct channel subtypes, only one of which is blocked as a result of toxin occupation.

Agatoxins↗
PubMed1992

Extraction and isolation of mRNA from adult articular cartilage.

We have developed a method to isolate RNA in high yield from adult articular cartilage. Homogenization of the articular cartilage with a freezer mill, extraction with 4 M guanidinium isothiocyanate/acid-phenol, and ultracentrifugation in cesium trifluoroacetate was found to be an effective and practical method for isolating a high yield of intact RNA from adult canine articular cartilage. The total RNA was suitable for Northern blot analysis. The mRNA that could then be isolated by oligo-dT affinity chromatography was found to be a suitable substrate for in vitro translation, for making a cDNA library, and for PCR amplification.

Aggrecans↗
PubMed1992

Omega-agatoxins differentially block calcium channels in locust, chick and rat synaptosomes.

Three toxins (omega-Agatoxins IA, IIA and IIIA) isolated from the venom of the funnel web spider, Agelenopsis aperta, differentially block depolarization-induced calcium influx in chick, rat and locust synaptosomes. In chick, this block of calcium influx is observed with omega-Agatoxins IIA and IIIA but not with omega-Agatoxin IA. Block by omega-Agatoxin IIA and IIIA is maximal at 70 and 82% respectively of the total depolarization-induced calcium influx; maximal suppression of calcium influx by omega-Conotoxin GVIA (omega-CgTx) is 100%. The IC50 for block with omega-Agatoxin IIA is ca 3 nM as compared with an IC50 of 38 nM for omega-CgTx. Incomplete block of calcium influx at saturating concentrations of omega-Agatoxins IIA and IIIA (above 100 nM) suggests that both omega-Agatoxin-sensitive and -insensitive calcium channels occur in chick brain synaptosomes. In rat cerebrocortical synaptosomes, omega-Agatoxins IA and IIA are only partially effective at blocking depolarization-induced calcium influx, as is omega-CgTx, whilst IIIA blocks 47% of this effective at blocking depolarization-induced calcium influx, as is omega-CgTx, whilst IIIA blocks 47% of this influx. In synaptosomes prepared from the CNS of adult locusts, omega-Agatoxins IA and IIA are most effective at blocking depolarization-induced calcium influx; omega-CgTx and omega-Agatoxin IIIA are ineffective. Block of depolarization-induced calcium influx in chick brain synaptosomes by omega-Agatoxins IIA, IIIA and omega-CgTx suggests that the spider toxin interacts directly with the voltage-dependent calcium channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Agatoxins↗
PubMed1992

P-type calcium channels in rat central and peripheral neurons.

The peptide toxin omega-Aga-IVA blocked P-type Ca2+ channel current in rat Purkinje neurons (KD approximately 2 nM) but had no effect on identified T-type, L-type, or N-type currents in a variety of central and peripheral neurons. omega-Aga-IVA blocked a substantial fraction of high threshold Ca2+ channel current in neurons from the hippocampal CA1 region (mean 26%), visual cortex (32%), spinal cord (45%), and dorsal root ganglia (23%), but less in hippocampal CA3 neurons (14%) and none in sympathetic neurons. In all cases, omega-Aga-IVA block could be reversed by a brief train of strong depolarizations. There was no overlap between current blocked by omega-Aga-IVA and the fractions blocked by dihydropyridines and omega-conotoxin GVIA, but not all current resistant to dihydropyridines and omega-conotoxin was blocked by omega-Aga-IVA. The results suggest that omega-Aga-IVA is highly selective for P-type channels and that many central neurons and some peripheral neurons possess substantial P-type current.

Animals↗
PubMed1992

Use of platelets and other transfusion products in patients with malignancy.

The need for blood components for oncology patients is small compared with the need for patients with hematologic malignancies. Appropriate use of blood components is necessary, not only medically, but also because of limited supply and availability. Agreement on when to use components is extremely important. In fact, at the time of this writing, the Transfusion Practices Committee of the AABB is conducting an extensive survey on the use of platelets in the oncology and hematology cancer patients (Questionnaire on Institutional Policy on Platelet Transfusion Practice for Hematology/Oncology Patients). The results will, it is hoped, provide a consensus on the proper times and counts that require prophylactic use of components for these patients. Since these patients use the vast majority of components (see Table 15), their proper use is imperative to maintaining an adequate platelet and frozen plasma supply. Transfusion support in cancer patients is vital for their survival. Platelets, in particular, are necessary to prevent serious bleeding. However, refractoriness to platelet transfusions can develop. It must be appreciated that refractoriness is not a general problem and need not require the expensiveness of a universal decision for handling all platelet transfusions in the same manner. Total refractoriness probably occurs in 15 to 20% of patients frequently transfused. In patients in whom frequent platelet transfusion is anticipated, that is, bone marrow transplantation, the development of platelet refractoriness may be reduced by using SDPC and administering them through leukocyte filters. Patients who become refractory to either random or SDPC can either be cross-matched for single-donor platelets that are compatible or can be given HLA-A,B matched platelets. Certainly, the success of platelet transfusion in leukemic patients cannot be denied, since only a small number of these patients now die because of bleeding due to platelet refractoriness. Most of the serious bleeding still seen is associated with sepsis. The risks from transfusion must always be considered. Fortunately, with increased monitoring of the blood supply, they have been reduced. As with any therapeutic regimen, these risks must be weighed against the benefit the patient may gain. Transfusion should always be used prudently.

Blood Component Transfusion↗
PubMed1992

Economic analysis in randomized control trials.

In medical technology assessment, randomized control trials (RCTs) play an important role in determining the relative efficacy of compared treatments. As scarce resources necessitate choosing among options for care, comparing costs of alternative tests, treatments, or programs also becomes important. This study assessed the prevalence and completeness of economic analyses in RCTs published from January 1966 through June 1988. It was found that only 121 of over 50,000 published randomized trials (0.2%) included economic analyses. For a random sample of 51 of these 121 studies, results revealed a mean quality of research score of 0.32 (SD of measurement = 0.14) and a mean economic analysis completeness score of 0.52 (SD = 0.13) on scales of 0 to 1. It was also found that higher economic completeness scores were positively correlated with later dates of publication (r = 0.28, P = 0.046) and with the presence of a statement of study perspective (r = 0.38, P = 0.006). A near-zero correlation between the economic completeness and the quality of research scores was revealed. Also noted were several deficiencies among the economic analyses, including improper allocation of overhead costs, absence of sensitivity analyses, and the fact that only 28% of the 51 studies included some form of aggregation of treatment costs and consequences. Progress in health care depends on accurate assessments of both relative efficacy and costs. The quality of both needs improvement.

Cost-Benefit Analysis↗
PubMed1992

Patients as reliable reporters of medical care process. Recall of ambulatory encounter events.

This study explores the reliability of a data source on the quality and content of care rarely used in studies comparing the performance of health care organizations, that is, patient reports obtained from surveys. Evidence of patient survey reliability and validity and report data on patient reporting accuracy were reviewed for ten events that may have occurred during an initial health assessment for new adult enrollees of a health maintenance organization (HMO). Reports of 380 patients obtained through telephone survey were compared with medical records. For chest radiograph, mammogram, and electrocardiogram (EKG), patient reports exhibited both sensitivity and specificity. For serum cholesterol test, patients proved to be sensitive but not specific reporters. For blood pressure measurement, stool kit, and rectal examination, false negative rates were low (less than or equal to 0.10); they were somewhat higher for breast self-examination instruction and pelvic examination (0.21 and 0.22, respectively). Only for testicular self-examination instruction did patient reports fail to confirm medical record documentation (false negative rate = 0.53). Multivariate analysis showed a small association between increasing patient age and decreasing confirmation. Gender did not affect reporting ability, and agreement did not deteriorate over a 2- to 3-month postencounter interval. Patient reports appear to merit greater use in comparative studies of technical quality of care. Key words: quality of health care; quality assurance; health care; ambulatory care; patient recall; patient reports.

Ambulatory Care↗
PubMed1992

Use of blood components in cancer patients with bleeding.

The need for blood components for oncology patients is small compared with the need for patients with hematologic malignancies. The subject is important because use of these valuable components is dependent on a limited supply and availability. Agreement on when to use components is extremely important. In fact, at the time of this writing, the Transfusion Practices Committee of the American Association of Blood Banks is conducting an extensive survey on the use of platelets in oncology and hematology cancer patients (Questionnaire on Institutional Policy on Platelet Transfusion Practice for Hematology/Oncology Patients). The results will, we hope, provide a consensus on the proper times and counts that require prophylactic use of components for these patients. Because these patients use the vast majority of components (see Table 15), their proper use is imperative to maintaining an adequate platelet and frozen plasma supply. Transfusion support in cancer patients is vital for their survival. Platelets, in particular, are necessary to prevent serious bleeding. The risks from transfusion must always be considered. Fortunately, with increased monitoring of the blood supply, they have been reduced. As with any therapeutic regimen, these risks must be weighed against the benefit the patient may gain. Transfusion should always be used prudently.

Blood Coagulation Disorders↗
PubMed1992

High affinity block of myocardial L-type calcium channels by the spider toxin omega-Aga-toxin IIIA: advantages over 1,4-dihydropyridines.

The peptide omega-agatoxin IIIA (omega-Aga-IIIA) from venom of the funnel web spider Agelenopsis aperta blocks L-type Ca2+ channels in neurons and myocardial cells with high affinity. We report that omega-Aga-IIIA also blocks whole-cell Ca2+ channel currents in guinea pig atrial myocytes. Although other high affinity blockers of L-type Ca2+ channels are available (such as the 1,4-dihydropyridines), omega-Aga-IIIA is a valuable pharmacological tool; omega-Aga-IIIA is the only known ligand that blocks L-type Ca2+ channels with high affinity at all voltages (IC50 approximately 1 nM) and it causes little or no block of T-type Ca2+ channels, unlike the 1,4-dihydropyridines. We use omega-Aga-IIIA to selectively eliminate L-type Ca2+ currents and we show that felodipine blocks T-type Ca2+ currents. Consequently, the toxin is better than dihydropyridines for separating ionic currents through voltage-dependent Ca2+ channels and defining their physiological function.

Agatoxins↗
PubMed1992

Cartilage research and treatment of osteoarthritis.

Research in the past year involving the cartilage structural components, especially the collagens and proteoglycans, has helped to increase our understanding of their complex macromolecular interactions in both normal and osteoarthritic cartilage. The number of factors that regulate the synthesis, deposition in tissue, and catabolism of cartilage, and the complexity of their interactions, continually grows. One of the most significant advances is that the powerful techniques of molecular biology are beginning to be applied to the study of articular cartilage, improving our understanding of chondrogenesis, gene expression in both normal and diseased cartilage, and genetic disorders affecting cartilage. Studies of cartilage in culture suggest the possibility of therapeutic intervention that would have a meaningful impact on disease outcome, the so-called chondroprotective therapy, but none has been demonstrated conclusively. Nonsteroidal anti-inflammatory drugs continue to be the most common mode of therapy for osteoarthritis, but recent studies have called this form of treatment into question, suggesting that analgesic therapy may produce equivalent results.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1991

Purified omega-conotoxin GVIA receptor of rat brain resembles a dihydropyridine-sensitive L-type calcium channel.

The omega-conotoxin GVIA (CTX) receptor has been purified 1900-fold to apparent homogeneity by monitoring both reversible binding of 125I-labeled CTX (125I-CTX) and photoincorporation of N-hydroxysuccinimidyl-4-azidobenzoate-125I-CTX (HSA-125I-CTX). Photoincorporation of HSA-125I-CTX into a 230-kDa protein exhibits a pharmacologic and chromatographic profile indicating that the 230-kDa protein is the CTX-binding subunit of the receptor. The pharmacologic specificity of 125I-CTX binding to the purified CTX receptor closely resembles that of the native membrane-bound form with respect to sensitivity towards CTX (Kd = 32 pM) and other peptide toxin antagonists. The purified CTX receptor comprises the 230-kDa protein (alpha 1) and four additional proteins with apparent molecular masses of 140 (alpha 2), 110, 70 (beta 2), and 60 (beta 1) kDa. This subunit structure closely resembles that of the 1,4-dihydropyridine-sensitive L-type calcium channel.

Affinity Labels↗
PubMed1991

Inhibition of N- and L-type Ca2+ channels by the spider venom toxin omega-Aga-IIIA.

omega-Aga-IIIA, an 8.5-kDa peptide toxin isolated from the venom of Agelenopsis aperta, was found to be a highly potent inhibitor of Ca channels in cardiac muscle and in peripheral and central neurons of rats and frogs. Cardiac L-type Ca channels were completely (Kd approximately 0.6 nM) blocked by omega-Aga-IIIA. In sensory neurons, the toxin inhibited most high-threshold Ca current but not T-type Ca current. omega-Aga-IIIA blocked with similar potency (Kd approximately 1.5 nM) both omega-conotoxin GVIA-sensitive and dihydropyridine-sensitive current components but left a fraction (approximately 35%) of high-threshold current that was also resistant to omega-conotoxin and dihydropyridines. The toxin blocks N- and L-type channels with equal potency and therefore may identify a high-affinity binding site common to these two Ca channel types.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Functional duality and structural uniqueness of depressant insect-selective neurotoxins.

Depressant insect-selective neurotoxins derived from scorpion venoms (a) induce in blowfly larvae a short, transient phase of contraction similar to that induced by excitatory neurotoxins followed by a prolonged flaccid paralysis and (b) displace excitatory toxins from their binding sites on insect neuronal membranes. The present study was undertaken in order to examine the basis of these similarities by comparing the primary structures and neuromuscular effects of depressant and excitatory toxins. A new depressant toxin (LqhIT2) was purified from the venom of the Israeli yellow scorpion. The effects of this toxin on a prepupal housefly neuromuscular preparation mimic the effects on the intact animal; i.e., a brief period of repetitive bursts of junction potentials is followed by suppression of their amplitude and finally by a block of neuromuscular transmission. Loose patch clamp recordings indicate that the repetitive activity has a presynaptic origin in the motor nerve and closely resembles the effect of the excitatory toxin AaIT. The final synaptic block is attributed to neuronal membrane depolarization, which results in an increase in spontaneous transmitter release; this effect is not induced by excitatory toxin. The amino acid sequences of three depressant toxins were determined by automatic Edman degradation. The depressant toxins comprise a well-defined family of polypeptides with a high degree of sequence conservation. This group differs considerably in primary structure from the excitatory toxin, with which it shares identical or related binding sites, and from the two groups of scorpion toxins that affect sodium conductance in mammals. The two opposing pharmacological effects of depressant toxins are discussed in light of the above data.

Amino Acid Sequence↗