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J Macri

Publications and source records attributed to J Macri.

At least 19 recordsLinked to original sources
PubMed2003

Frequency and clinical consequences of extremely high maternal serum PAPP-A levels.

A multicentre study was carried out to determine the frequency and clinical consequences of extremely high maternal serum pregnancy-associated plasma protein (PAPP)-A. There was a total of 79 pregnancies with PAPP-A exceeding 5.0 multiples of the gestation-specific median in a series of 46 776 pregnancies tested (0.2%) at the 7 collaborating centres. Five pregnancies were lost to follow-up, one miscarried and one with Noonan's syndrome was terminated. Of the remaining 72 that ended in a live birth, one infant had gastroschisis and five pregnancies had obstetric complications: pre-eclampsia, pregnancy-induced hypertension, gestational diabetes and two with growth retardation. Among women with high PAPP-A and no complications or adverse outcomes, there was no evidence of a substantial change in the levels of other Down syndrome markers or the extent of nuchal translucency. Three analytical methods were used to assay PAPP-A and yielded different frequencies of extremely high levels (0.05%, 0.4% and 0.6%) possibly owing to cross-reaction with another substance. We conclude that women with high PAPP-A can be reassured that there is no reason to suppose that the outcome of pregnancy will differ from those with normal levels, provided other markers are normal. If, as more centres move their Down syndrome screening practice to the first trimester, additional cases emerge with Noonan's syndrome or gastroschisis and raised PAPP-A, this advice will need to be modified.

Adult↗
PubMed2001

Application of proteomics to the study of cardiovascular biology.

Proteomics involves the integration of a number of technologies with the aim of analyzing the complete complement of proteins expressed by a biological system in response to various stimuli and/or under different physiological or pathophysiological conditions. Recent technical improvements to the methods employed for protein separation and protein identification have resulted in a dramatic increase in the number of proteomics-based research projects. More importantly, it has become readily apparent that examining changes in the proteome offers insight into understanding cellular and molecular mechanisms that cannot be obtained through genomic analysis. There are numerous examples of cardiovascular functions whose molecular pathways are mediated through post-translational processes such as phosphorylation. The use of proteomics offers the ability to simultaneously monitor the changes in protein expression and/or cell signaling pathways in response to such conditions as cardiac hypertrophy and heart failure. Together with complementary genomic data, proteomics-based research can greatly increase our understanding of cardiovascular biology.

Cardiovascular Diseases↗
PubMed2000

Translocational status of ApoB in the presence of an inhibitor of microsomal triglyceride transfer protein.

Despite numerous studies demonstrating that microsomal triglyceride transfer protein (MTP) activity is critical to apoB secretion, there is still controversy as to whether MTP directly facilitates the translocation of apoB across the membrane of the endoplasmic reticulum (ER) through either the recruitment of lipids and/or chaperone activity. In the present study, a specific inhibitor of MTP (BMS 197636) was utilized in HepG2 cells to investigate whether a direct relationship exists between the translocation of apoB across the ER membrane and the lipid-transferring activity of MTP. Inhibition of MTP (with 10 and 50 nmol/L of the inhibitor) did not significantly affect the translocation of newly synthesized apoB (P = 0.77) or the translocational efficiency of the steady-state apoB mass (P = 0.45), despite a 49% decrease in apoB secretion and increased proteosomal degradation. These results compared well with subcellular fractionation experiments which showed no significant change in the fraction of apoB accumulated in the lumen of isolated microsomes in MTP-treated cells (P = 0.35). In summary, MTP lipid transfer activity does not appear to influence translocational status of apoB, but its inhibition is associated with an increased susceptibility to proteasome-mediated degradation and reduced assembly and secretion of apoB lipoprotein particles.

Apolipoproteins B↗
PubMed2000

Cardiac sarcoplasmic reticulum and sarcolemmal proteins separated by two-dimensional electrophoresis: surfactant effects on membrane solubilization.

We evaluated the use of the alkyaryl amidosulfobetaine zwitterionic detergent, designated as C8psi, to facilitate the solubilization of cardiac subcellular, membrane-associated proteins. Hearts from 7-week-old male Sprague-Dawley rats were isolated, and the left ventricles dissected and subsequently homogenized. The sarcolemma (SL) and the sarcoplasmic reticulum (SR) were isolated from different homogenate preparations originating from rat hearts by ultracentrifugation methods. The isolated membrane preparations were solubilized and the proteins precipitated. After resuspension, protein separation was achieved in first-dimensional IEF using an immobilized (pH 4-7) gradient and in the second dimension using 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Gels were then stained, images analyzed, and protein spots excised for subsequent identification. Protein identification from both SR and SL samples did not identify any of the known major membrane-associated proteins. Solubilization of whole tissue lysates with C8psi resulted in no increase in the total number of proteins detected relative to samples solubilized in the presence of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulforate (CHAPS). The data suggest the utility of newer surfactants such as C8psi to improve both the resolution of (2-D) protein profiles and increase the number of proteins extracted from subcellular organelle fractions.

Animals↗
PubMed2000

First trimester biochemical screening for Down syndrome: free beta hCG versus intact hCG.

To compare free beta hCG versus intact hCG in first trimester Down syndrome screening we analysed 63 cases of Down syndrome and 400 unaffected control pregnancies between 10 and 13 weeks' gestation. The Down syndrome median multiple of the median (MoM) was significantly higher (p=0.001) for free beta hCG (1.89 MoM) than for intact hCG (1.37 MoM). Although distributions for free beta hCG (unaffected, 0.2157; DS, 0.2322) are wider than for intact hCG (unaffected, 0.1697; DS, 0.2158), overall 27% of Down syndrome cases were above the 95th percentile for free beta hCG compared to 19% for intact hCG. Combined with maternal age, free beta hCG detected 45% of Down syndrome pregnancies at a 5% false positive rate. Intact hCG combined with maternal age demonstrated a detection efficiency comparable to maternal age alone (35% versus 32%). In contrast, a recent study (Haddow et al., 1998-NEJM 338: 955-961) indicated that intact hCG yielded a higher first trimester Down syndrome detection efficiency than free beta hCG (29% versus 25% respectively). Re-analysis of distribution parameters in the Haddow et al. study, however, show that free beta hCG was actually the better marker (23% detection for intact hCG versus 29% for free beta hCG).

Adult↗
PubMed1999

Studies on degradative mechanisms mediating post-translational fragmentation of apolipoprotein B and the generation of the 70-kDa fragment.

It has been well established that the biogenesis of apoB is mediated co-translationally by the cytosolic proteasome. Here, however, we investigated the role of both the cytosolic proteasome as well as non-proteasome-mediated degradation systems in the post-translational degradation of apoB. In pulse-chase labeling experiments, co-translational (0-h chase) apoB degradation in both intact and permeabilized cells was sensitive to proteasome inhibitors. Interestingly, turnover of apoB in intact cells over a 2-h chase was partially inhibitable by lactacystin, thus suggesting a role for the cytosolic proteasome in the post-translational degradation of apoB. In permeabilized cells, however, there was no post-translational protection of apoB by lactacystin. Further investigations of proteasomal activity in HepG2 cells revealed that, following permeabilization, there was a dramatic loss of the 20 S proteasomal subunits, and consequently the cells exhibited no detectable lactacystin-inhibitable activity. Thus, apoB fragmentation and the generation of the 70-kDa apoB degradation fragment, characteristic of permeabilized cells, continued to occur in these cells despite the absence of functional cytosolic proteasome. Similar results were observed when we used a derivative of lactacystin, clastolactacystin beta-lactone, which represents the active species of the inhibitor. Interestingly, however, the abundance of the 70-kDa fragment could be modulated by the microsomal triglyceride transfer protein inhibitor, BMS-197636, as well as by pretreatment of the permeabilized cells with dithiothreitol. These data thus suggest that although the cytosolic proteasome appears to be involved in the post-translational turnover of apoB in intact cells, the specific post-translational fragmentation of apoB generating the 70-kDa fragment observed in permeabilized cells occurs independent of the cytosolic proteasome.

Acetylcysteine↗
PubMed1998

Functional analysis of disulfide linkages clustered within the amino terminus of human apolipoprotein B.

We tested the involvement of N-terminal six disulfide bonds (Cys-1 through Cys-12) of human apolipoprotein (apo) B in the assembly and secretion of lipoproteins using two C-terminal-truncated apoB variants, namely B50 and B18. In transfected rat hepatoma McA-RH7777 cells, B50 could assemble very low density lipoproteins (VLDL), and B18 was secreted as high density lipoproteins. When all 12 cysteine residues were substituted with alanines in B50, the mutant protein (B50C1-12) lost its ability to assemble lipid and was degraded intracellularly. However, mutation had no effect on B50C1-12 translation or translocation across the microsomal membrane. Post-translational degradation of B50C1-12 was partially inhibited by the proteasome inhibitor MG132. To determine which cysteines were critical in VLDL assembly and secretion, we prepared three additional mutant B50s, each containing four selected Cys-to-Ala substitutions in tandem (i.e. Cys-1 to Cys-4, Cys-5 to Cys-8, and Cys-9 to Cys-12). Expression of these mutants showed that disruption of disulfide bond formation within Cys-5 to Cys-8 diminished apoB secretion, whereas within Cys-1 to Cys-4 or Cys-9 to Cys-12 had lesser or no effect. In another two mutants in which only one disulfide bond (i.e. between Cys-5 and Cys-6 or between Cys-7 and Cys-8) was eliminated, only secretion of B50 with mutations at Cys-7 and Cys-8 was decreased. Thus, the disulfide bond involving Cys-7 and Cys-8 is most important for VLDL assembly and secretion. In addition, assembly and secretion of VLDL containing endogenous B100 or B48 were impaired in cells transfected with B50s containing Cys-7 and Cys-8 mutation. The Cys-to-Ala substitution abolished recognition of B50 by MB19, a conformational antibody with an epitope at the N terminus of human apoB. The Cys-to-Ala substitution also attenuated secretion of B18, but the effect of the mutation on B18 secretion was less evident than on B50.

Amino Acid Substitution↗
PubMed1998

Effects of atorvastatin on the intracellular stability and secretion of apolipoprotein B in HepG2 cells.

We investigated the effects of atorvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on the biogenesis of apolipoprotein B (apoB) in intact and permeabilized HepG2 cells. Intact cells were pretreated either with single or multiple doses of atorvastatin (0.1 to 20 micromol/L) for periods of 6 to 20 hours and pulsed with [35S]methionine. In some cases the cells were permeabilized with digitonin. Experiments were performed to investigate the effects of atorvastatin on (1) the rates of lipid synthesis and secretion, (2) the synthesis and accumulation of apoB, (3) the intracellular stability of apoB, (4) the amount of apoB-containing lipoprotein particles assembled in HepG2 microsomes, and (5) the secretion and accumulation of apoB into the culture medium. ApoB synthesis, degradation, and secretion were measured by pulse-chase experiments with [35S]methionine in both intact and permeabilized HepG2 cells. Lipid synthesis was assessed by pulse-labeling experiments with [3H]acetate or [3H]oleate bound to bovine serum albumin. Comparisons were made under basal conditions and in the presence of oleate (0.36 micromol/L). Atorvastatin acutely inhibited the synthesis of cholesterol and cholesterol ester but did not have a significant effect on triglyceride or phospholipid synthesis. Atorvastatin did not affect the uptake of [35S]methionine by the cells nor did it influence the synthesis of apoB or a control protein, albumin. However, atorvastatin reduced the secretion of apoB into the culture medium, apparently by enhancing the degradation of apoB in the cell under basal and induced conditions with oleate. The stability of apoB associated with the lipoprotein particles was also significantly lowered by atorvastatin. The stimulated degradation of apoB in atorvastatin-treated cells was sensitive to MG132, a proteasome inhibitor. The net effect of atorvastatin was a reduction in the number of apoB-containing lipoprotein particles of different sizes isolated from microsomes and a reduction in apoB secretion into the culture medium. The data suggest that atorvastatin may impair the translocation of apoB into the lumen of the endoplasmic reticulum, thus increasing the amount of apoB degraded intracellularly. It is hypothesized that atorvastatin alters these parameters primarily as a result of inhibiting cholesterol synthesis and limiting the availability of cholesterol and/or cholesterol ester for the normal assembly of apoB-containing lipoprotein particles.

Albumins↗
PubMed1997

Apolipoprotein B is intracellularly associated with an ER-60 protease homologue in HepG2 cells.

Two ALLN (N-acetyl-leucyl-leucyl-norleucinal)-sensitive endoplasmic reticulum (ER)-localized proteases (ER-60 and ER-72) were recently purified from rat liver. We used an antibody to rat ER-60 to investigate the possible role of this protease in apolipoprotein B (apoB) degradation. First, immunoprecipitation and immunoblotting experiments with the anti-rat ER-60 antibody suggested that HepG2 cells contain a homologue of ER-60 with an approximate molecular mass of 58-60 kDa. The ER-60 homologue was mostly associated with the luminal contents of HepG2 microsomes. Evidence from co-immunoprecipitation and cross-linking experiments appear to suggest that the ER-60 homologue in HepG2 cells is associated with apoB intracellularly. A small pool of apoB was recovered when HepG2 lysates were subjected to immunoprecipitation with anti-rat ER-60 antibody followed by a second immunoprecipitation with anti-apoB antibody. Furthermore, cross-linking of permeabilized cells with dithiobis(succinimidylpropionate) further demonstrated association of apoB with the ER-60 homologue in HepG2 cells. Three polypeptides with molecular masses of 78, 66, and 50 kDa were consistently found to be associated with apoB as well as the 58-kDa ER-60 homologue. The 78-kDa protein associated with both apoB and ER-60 appeared to represent immunoglobulin heavy chain-binding protein (BiP) based on immunoprecipitation with a monoclonal antibody. Cross-linking and immunoblotting experiments suggested the association of the 78-kDa BiP with both the 58-kDa ER-60 homologue as well as the 550-kDa apoB. In summary, the data suggests that HepG2 cells contain a 58-kDa protein which is homologous to the rat liver ER-60 in size, antigenecity, and intracellular localization. The ER-60 homologue in HepG2 cells appears to be closely associated with apoB, as well as other proteins possibly representing ER chaperones such as BiP. We hypothesize that the ER-60 homologue may be involved in the degradation of apoB in the ER lumen of HepG2 cells.

Animals↗
PubMed1997

Studies on intracellular translocation of apolipoprotein B in a permeabilized HepG2 system.

Recent evidence suggests that the rate of apolipoprotein B-100 (apoB) translocation may be a key regulatory point in the production of apoB-containing lipoproteins. We have developed an in vitro system to measure the translocation rate of apoB in HepG2 cells. Intact cells were initially pretreated with oleate and N-acetyl-Leu-Leu-norleucinal to maximize the translocation rate while minimizing degradation. Cells were pulsed with [35S]methionine, chased (5-30 min), and then permeabilized with digitonin (75 microg/ml). Permeabilized cells were incubated with or without trypsin (200 microg/ml) for 10 min, and digestion was halted with soybean trypsin inhibitor (2 mg/ml). The rate of translocation was determined by comparing the amount of immunoprecipitable intact apoB in trypsin-treated cells with that in control cells at each time point. Under these conditions, two control proteins, alpha1-antitrypsin and transferrin, were fully protected from trypsin digestion, confirming the integrity of the secretory pathway in permeabilized cells. The percentage of apoB translocated steadily increased from 36% after 5 min to 71% after a 30-min chase (mean percentage, n = 3). A characteristic apoB fragmentation pattern resulted from trypsin digestion, and protected fragments of various size including N-terminal 60-70-kDa fragments were identified. Subcellular fractionation of the cells confirmed that the apoB pool protected from trypsin digestion was luminal in nature, confirming its translocation. ApoB translocation was significantly increased in oleate-treated cells compared with untreated cells. Inhibition of peptidylprolyl isomerase through the use of cyclosporin A and disruption of disulfide bond formation using dithiothreitol reduced the percentage of translocated apoB by 37 and 63%, respectively. Dithiothreitol induced specific changes in the pattern of protected apoB fragments, suggesting a conformational change in apoB that may hinder its translocation. Inhibition of N-linked glycosylation with tunicamycin did not significantly alter the rate of apoB translocation but appeared to stimulate its degradation. Together, the data suggest that the rate of apoB translocation across the membrane of the ER is determined by both lipid availability as well as the correct conformation of nascent apoB molecules.

Apolipoproteins B↗
PubMed1997

Intracellular assembly and degradation of apolipoprotein B-100-containing lipoproteins in digitonin-permeabilized HEP G2 cells.

Permeabilized Hep G2 cells have been used to investigate the turnover of apolipoprotein B-100 (apoB-100). When such cells were chased in the presence of buffer, there was no biosynthesis of apoB-100, nor was the protein secreted from the cells. Thus the turnover of apoB-100 in these cells reflected the posttranslational degradation of the protein. Pulse-chase studies indicated that apoB-100 was degraded both when associated with the membrane and when present as lipoproteins in the secretory pathway. Neither albumin nor alpha1-antitrypsin showed any significant posttranslational intracellular degradation under the same condition. The kinetics for the turnover of apoB-100 in the luminal content differed from that of apoB-100 that was associated with the microsomal membrane. Moreover, while the degradation of the luminal apoB-100 was inhibited by N-acetyl-leucyl-leucyl-norleucinal (ALLN), this was not the case for the membrane-associated protein. Together these results suggest the existence of different pathways for the degradation of luminal apoB-100 and membrane-associated apoB-100. This was further supported by results from pulse-chase studies in intact cells, showing that ALLN increased the amount of radioactive apoB-100 that associated with the microsomal membrane during the pulse-labeling of the cells. However, ALLN did not influence the rate of turnover of the membrane-associated apoB-100. The presence of an ATP-generating system during the chase of the permeabilized cells prevented the disappearance of pulse-labeled apoB-100 from the luminal lipoprotein-associated pool. The ATP-generating system combined with cytosol protected the total apoB-100 in the system from being degraded. The cells cultured in the presence of oleic acid and chased after permeabilization in the presence of cytosol and the ATP-generating system showed an increase in the amount of apoB-100 present on dense ("high density lipoprotein-like") particles. This increase was linear during the time investigated (i. e. from 0 to 2 h chase) and independent of protein biosynthesis. Our results indicate that the dense particle was generated by a redistribution of apoB-100 within the secretory pathway and that it most likely was assembled from the membrane- associated form of apoB-100. These results indicate that the release of apoB-100 from this membrane-associated form to the microsomal lumen is dependent on cytosolic factors and a source of metabolic energy.

Apolipoproteins B↗
PubMed1997

Conformational changes in apolipoprotein B modulate intracellular assembly and degradation of ApoB-containing lipoprotein particles in HepG2 cells.

The linkage between the conformation of apolipoprotein B100 (apoB) and the intracellular assembly and degradation of apoB-containing lipoproteins was investigated in the present study. Disruption of disulfide bond formation in newly synthesized apoB molecules through the use of the reducing agent DTT resulted in a decrease in the secretion of apoB-containing lipoproteins from HepG2 cells compared with control cells. The synthesis of total apoB (apoB100 plus nascent chains), as well as a number of control proteins, such as albumin and alpha 1-antitrypsin, was decreased significantly in DTT-treated cells. However, the intracellular accumulation of full-length apoB100 molecules was not inhibited in the presence of DTT. Subcellular fractionation indicated that apoB molecules isolated from the microsomes of DTT-treated cells had an increased association with the microsomal membrane compared with apoB isolated from untreated cells. Analysis of the distribution of apoB-containing lipoproteins from the lumen of isolated microsomes demonstrated that in the presence of DTT, there was a shift in the distribution, such that there was a decrease in the formation of HDL-sized (lipid-poor) apoB-containing lipoproteins and a decrease in the formation of LDL/VLDL apoB particles. Alterations in apoB conformation and their impact on degradation were also investigated by using DTT and by inhibiting N-linked glycosylation with tunicamycin. DTT appeared to change the rate and pattern of apoB degradation. Degradation was accelerated in both intact and permeabilized HepG2 cells. ApoB degradation occurred in DTT-treated permeabilized cells without the usual generation of the 70-kD and 335-kD fragments and was largely N-acetyl-leucyl-leucyl-norleucinal (ALLN) insensitive. In tunicamycin-treated cells, DTT further accelerated the degradation of unglycosylated apoB. Overall, the data suggest that the misfolding of apoB may prevent the proper association of apoB with lipids, resulting in impairment of the assembly of mature apoB-containing lipoproteins. Alteration in the conformation of apoB also appears to alter the degradation pathway of apoB, such that the protein is degraded through a pathway that is at least in part ALLN insensitive.

Animals↗
PubMed1995

Regulation of apolipoprotein B biogenesis in human hepatocytes: posttranscriptional control mechanisms that determine the hepatic production of apolipoprotein B-containing lipoproteins.

OBJECTIVES: Hepatic overproduction of apolipoprotein B (apoB)-containing lipoproteins appears to be a common cause of hyperlipoproteinemia in humans. Patients with overproduction states secrete denser cholesterol ester-rich lipoprotein particles which are highly atherogenic. The formation of apoB particles involves a very complex process that requires the coordinated synthesis and assembly of apoB, triglycerides, cholesterol esters, phospholipids, and other components. ApoB expression is an important prerequisite for the assembly and secretion of apoB particles. Evidence to date appears to suggest that apoB expression is regulated posttranscriptionally. ApoB secretion rate is determined at the levels of apoB translocation into the endoplasmic reticulum (ER) as well as degradation within the ER. RESULTS AND HYPOTHESIS: Based on available data, we postulate that the rate of apoB particle secretion is determined at the critical point where newly-synthesized apoB interacts with core lipids, particularly triglycerides. The supply of these lipids determines the rate of translocation of the apoB molecule across the ER membrane and into the ER lumen. Lipidation of apoB facilitates its proper folding, its assembly into a lipoprotein particle, and its extracellular secretion. In the absence of lipids, apoB is misfolded resulting in the abortion of ER translocation and subsequent degradation by an apoB specific protease. CONCLUSIONS: The balance between intracellular degradation and extracellular secretion determines the rate at which the human liver secretes apoB particles.

Animals↗
PubMed1993

Development of an amplified enzyme-linked immunosorbent assay for sensitive measurement of apolipoprotein B in plasma and tissue culture media.

We have developed a non-competitive sandwich enzyme-linked immunosorbent assay for the quantitation of apolipoprotein B, which utilizes the biotin-avidin amplification system. All components were optimized with respect to either concentration or incubation time. The assay uses microtitre wells as a solid phase and polyclonal, affinity-purified capture antibody. The amplification system was composed of hydroxy-succinimide biotin conjugated to an affinity-purified anti-apolipoprotein B IgG and either ExtrAvidin-alkaline phosphatase or streptavidin-alkaline phosphatase. The within-run precision (n = 10) of the apolipoprotein B control (1.39 g/l) was 3%, while the between-run precision of the assay (n = 6) for 9 consecutive assays was determined to be 8%. A sensitivity of 3 ng was attained, with a mean analytical recovery of 110%. Comparison of the assay with an established immunoturbidometric method resulted in a correlation of 0.92 using patient plasma samples (n = 19). The use of the biotin-avidin amplification system provides the sensitivity required for measuring apolipoprotein B in tissue culture media samples and circumvents the many problems associated with the direct conjugation of enzymes to antibodies. Minimal amounts of reagents are required and the assay can be performed in 5 h, making it both economical and practical for clinical laboratories.

Apolipoproteins B↗
PubMed1983

Prenatal diagnosis of conjoined twins.

A case of conjoined twins with open spina bifida prenatally diagnosed at the twenty-third week of gestation is presented. The early detection of this rare and unusual malformation was initiated by the observation of markedly elevated maternal serum alphafetoprotein values. Ultrasound evidence of a misshaped cephalic pole and the appearance of one fetal body on real-time ultrasound was strongly suggestive. Elective midtrimester termination confirmed the prenatal diagnosis and was followed by a benign postpartum course.

Female↗
PubMed1980

Modification of ryanodine toxicity by dantrolene and halothane in a model of malignant hyperthermia.

Ryanodine toxicity in animals has been suggested to constitute a model of malignant hyperthermia. Dantrolene is known to block the development of malignant hyperthermia triggered by halothane in susceptible swine. The authors studied the influences of dantrolene and halothane on the effects of ryanodine in vitro in isolated rat diaphragm muscle segments, and in vivo in mice, to explore the validity of this model. In the diaphragm experiments, dantrolene was found to block or delay the development of contractures produced by ryanodine and to delay the potentiation of ryanodine-induced contractures caused by halothane. In mice, ryanodine at various dosages was injected and animals surviving after one hour were examined. Such survivors appeared grossly to be normal, and may constitute a model for the malignant hyperthermia patient. They were found to be susceptible to halothane and to succinylcholine, being killed by treatment with these two agents at dosages that were not lethal to control mice. Pretreatment of mice for 48 hours with orally administered dantrolene, followed by injection of ryanodine and then halothane anesthesia, decreased the lethality of ryanodine but did not reduce the number of deaths caused by the subsequent exposure to halothane. That the effects of ryanodine in vitro and in vivo are diminished and potentiated by dantrolene and halothane, respectively, would suggest that the ryanodine toxicity model of malignant hyperthermia may have validity and is worthy of further study. A prediction from this model is that the terminal cisternae of skeletal muscle sarcoplasmic reticulum may be altered in MH.

Alkaloids↗