Concentration of adenosine 3':5'-cyclic monophosphate in mouse pancreatic islets measured by a protein-binding radioassay

A protein-binding radioassay for cyclic AMP was modified to detect less than 0.025pmol of the nucleotide. The method was applied to the measurement of cyclic AMP in small numbers of mouse pancreatic islets (as little as 25mug of tissue) by use of barium acetate-H(2)SO(4) for deproteinization. The concentration of cyclic AMP in mouse islets incubated in media containing 3.3 or 20mm-glucose was 0.016pmol/10 islets (approx. 1mum in intracellular water). Glucose concentration (3.3 or 20mm) had no detectable effect on islet concentrations of cyclic AMP with periods of incubation or perifusion ranging from 0.5 to 60min, although insulin release rate was rapidly increased by 20mm-glucose. Caffeine (5mm) or 3-isobutyl-1-methylxanthine (1mm), which are known inhibitors of islet cyclic AMP phosphodiesterase, produced marked and rapid increases in islet cyclic AMP concentration at 3.3 or 20mm-glucose, but only enhanced the insulin release rate at the higher glucose concentration. The role of cyclic AMP in insulin release induced by glucose is discussed.

Testing of Materials at Medium rates of Strain

The problems involved in the measurement of the mechanical properties of rate-dependent materials are discussed, with special reference to the role of the elastic stiffness of the testing machine and specimen.

A description is given of a newly developed universal testing machine, operated by hydraulic pressure and capable of testing at crosshead velocities up to about 40 in/s. The machine has been used in two ways: for tensile tests at approximately constant strain rates in the range 10-1 to 10-2 s-1; and for compression tests in which a load is applied in a few milliseconds and maintained at a nearly constant value while the specimen is plastically deformed.

The machine is instrumented so that the applied load and cross-head velocity are recorded throughout the test. The testing technique and the accuracy of measurement are discussed with reference to experimental results obtained in tests on annealed copper, mild steel, silicon-iron, and a high-strength aluminium alloy.

Fatal duodenocaval fistula caused by peptic ulcer

Gastrointestinal bleeding caused by a duodenocaval fistula is rare, diagnostically challenging, and associated with a high mortality rate. We describe the case of a patient with polymicrobial fungemia and fatal gastrointestinal bleeding related to a duodenocaval fistula caused by peptic ulcer. Polymicrobial fungemia, which has not previously been associated with this condition, raises the possibility of candidal endocarditis.

Azithromycin for empirical treatment of the nongonococcal urethritis syndrome in men. A randomized double-blind study

OBJECTIVE

To evaluate the use of single-dose azithromycin for empirical treatment of nongonococcal urethritis.

DESIGN

Randomized, double-blind, multicenter trial comparing azithromycin vs doxycycline therapy, with a 2:1 randomization ratio. Patients were evaluated clinically and microbiologically for Chlamydia trachomatis and Ureaplasma urealyticum infection before therapy and at 2 and 5 weeks after study entry.

SETTING

Eleven sexually transmitted disease clinics throughout the United States.

PATIENTS

A total of 452 men aged 18 years or older with symptomatic nongonococcal urethritis of less than 14 days' duration.

INTERVENTION

Patients were treated with either 1.0 g of azithromycin as a single oral dose or 100 mg of doxycycline taken orally twice daily for 7 days.

MAIN OUTCOME MEASURES

Clinical resolution of symptoms and signs of nongonococcal urethritis, microbiological cure of C trachomatis and U urealyticum, and occurrence of adverse experiences.

RESULTS

Of the 452 patients enrolled, 248 in the azithromycin-treated group and 123 in the doxycycline-treated group were evaluable for clinical response. The two treatment groups were comparable in terms of age, weight, ethnic distribution, sexual preference, sexual activity, and history of prior nongonococcal urethritis or gonorrhea. Sixteen percent of the azithromycin group and 24% of the doxycycline group were culture positive for C trachomatis before therapy, while 38% and 28%, respectively, were culture positive for U urealyticum. The cumulative clinical cure rate was 81% (95% confidence interval [CI], 75% to 85%) in the azithromycin-treated group and 77% (95% CI, 69% to 84%) in the doxycycline-treated group. Clinical cure rates in the two groups were also comparable when patients were stratified by presence or absence of infection with C trachomatis or U urealyticum prior to therapy. Among those infected with C trachomatis, overall microbiological cure rates were 83% (95% CI, 65% to 94%) for azithromycin-treated patients (n = 30) and 90% (95% CI, 68% to 98%) for doxycycline-treated patients (n = 21). Among those infected with U urealyticum, overall microbiological cure rates were 45% (95% CI, 34% to 57%) for azithromycin-treated patients (n = 75) and 47% (95% CI, 30% to 65%) for doxycycline-treated patients (n = 32). Adverse reactions were generally mild to moderate and occurred in 23% of the azithromycin-treated group and 29% of the doxycycline-treated group.

CONCLUSIONS

For empirical treatment of the acute nongonococcal urethritis syndrome in men, a single oral dose of azithromycin was as effective as a standard 7-day course of doxycycline in achieving clinical cure. Further, clinical cure rates were comparable with either regimen, regardless of the presence or absence of Chlamydia or Ureaplasma infection.

Regulation of hepatocyte plasma membrane alpha 1-adrenergic receptors by 4 beta-phorbol 12-myristate 13-acetate

The effect of phorbol 12-myristate 13-acetate (PMA) on hepatocyte alpha 1-adrenergic receptors was determined by [3H]prazosin binding to plasma membranes from control and PMA-treated hepatocytes. Membranes from hepatocytes incubated with PMA (1 microgram/ml) for 1 h exhibited a 40% decrease in alpha 1-adrenergic receptors (481 +/- 10 fmol/mg of protein; mean +/- S.E.M. for three separate experiments) relative to vehicle-treated (dimethylformamide) hepatocytes (802 +/- 91 fmol/mg of protein; n = 3), with no significant effect on the KD. The PMA-induced decrease in alpha 1-adrenergic receptors was maximal by 30 min and half-maximal inhibition of [3H]prazosin binding occurred with a PMA concentration of approx. 15 ng/ml. Pretreatment of hepatocytes with staurosporine (5 microM) blocked the effect of PMA, and 4 beta-phorbol 13-monoacetate was ineffective, suggesting the involvement of protein kinase C (PKC). Treatment of hepatocytes with primaquine (300 microM) for 15 min decreased hepatocyte plasma membrane alpha 1-adrenergic receptors by 34.0 +/- 2.4% (mean +/- S.E.M. of three experiments). Removal of primaquine allowed essentially complete recovery (98 +/- 4%; mean +/- S.E.M. for five separate experiments) of plasma membrane [3H]prazosin binding within 20 min, suggesting that the alpha 1-adrenergic receptor undergoes endocytotic recycling. Addition of PMA (1 microgram/ml) to hepatocytes immediately after removal of primaquine, completely inhibited the increase in plasma membrane alpha 1-adrenergic receptors relative to control cells, but had no effect on hepatocytes whose cell surface alpha 1-receptors remaining after primaquine treatment had been inactivated by alkylation. These observations suggested that activation of PKC may facilitate the internalization of the alpha 1-adrenergic receptor in hepatocytes.

Intravenous streptomycin: a useful route of administration

Streptomycin is an aminoglycoside antibiotic that is indicated for the treatment of tuberculous and nontuberculous infections. Intramuscular injection is the recommended route of administration. There are few reports on intravenous administration of streptomycin. We describe the use of intravenous streptomycin to treat endocarditis due to a strain of Enterococcus faecalis with high-level resistance to gentamicin. Physicians should consider the intravenous route as an alternate method of administering streptomycin.

Use of fluorescent latex microspheres to measure coronary blood flow distribution

Radioactive microspheres have long been in use to measure blood flow distribution to various vascular beds. Their drawbacks are the short half-lives of the radioactive material, the need for appropriate care in handling and disposing of such material, and their relative expensiveness. We investigated the use of fluorescent microspheres as indicators of coronary blood flow distribution in a canine model. Radioactive (125I) microspheres were used as a comparison standard. Four colors of fluorescent microspheres were used: blue, yellow-green, orange, and red, having emission frequencies ranging from 385 to 605 nM. The experiments were carried out in dogs under pentobarbital anesthesia, in which the microspheres were given during pump perfusion of the left circumflex artery with the animal's own blood. The hearts were removed, fixed for 3 days in 10% formalin, and sectioned. Samples from the endocardial, myocardial, and epicardial layers were read on a gamma counter. The fluorescent microspheres were extracted from the same tissues into ethyl acetate, and read in a fluorescence spectrophotometer at the appropriate excitation/emission frequencies. Comparable results were obtained from the two methods, with good sensitivity and resolution of dye colors, using the fluorescent microspheres.

Rapid and reversible uncoupling of the hepatic alpha 1-adrenergic receptor and guanine-nucleotide-binding protein by phorbol 12,13-dibutyrate

Phorbol 12,13-dibutyrate (PDBU), 1 microgram/ml for 2 min, abolished alpha 1-adrenergic receptor (AR)-mediated signal transduction in rat hepatocytes and converted 100% of alpha 1-ARs to a low-affinity state, similar to effects of a non-hydrolyzable GTP analog. Reversal of PDBU inhibition restored high-affinity alpha 1-ARs towards control values. The rapid uncoupling of the alpha 1-AR and guanine-nucleotide-binding protein by PDBU, and reversibility associated with reactivation of alpha 1-adrenergic signaling, identify this as an important inhibitory locus for PDBU.

Transforming growth factor-beta 1 rapidly activates phosphorylase in a calcium-dependent manner in rat hepatocytes

Transforming growth factor-beta 1 (TGF-beta 1) rapidly activated phosphorylase in isolated rat hepatocytes (half-maximal rate of activation with approximately 0.1 ng/ml). Removal of Ca2+ from the external medium just before TGF-beta 1 addition markedly attenuated phosphorylase activation. TGF-beta 1 (1 ng/ml) produced a small increase in [Ca2+]i (approximately 10% increase after 30 s), which appears sufficient to account for phosphorylase activation. These observations indicate that activation of the TGF-beta 1 signal transduction system in hepatocytes is linked with a small increase in [Ca2+]i, and external Ca2+ may contribute in part to this increase.

Membrane-specific association of annexin I and annexin II in anterior pituitary cells

Calpactins are members of the annexin family of structurally related Ca2(+)-dependent membrane binding proteins. Recent studies suggest a role for calpactins in the membrane fusion event of exocytosis. We show in this work that two members of the annexin family which are immunologically related to calpactin I (p36, annexin II) and calpactin II (p35, annexin I) are present in anterior pituitary cells. When sheep adenohypophyseal cells are disrupted in the absence of a Ca2+ chelator, immunoreactive calpactins associate with the crude vesicle fraction. Further purification of this subcellular fraction by sucrose density gradient centrifugation revealed a differential distribution: calpactin I was associated with secretory granule membranes and with plasma membranes, whereas calpactin II was found primarily with the plasma membrane fraction. Consistent with the Ca2+ and phospholipid binding properties of the calpactins, extraction of these proteins from the pituitary membranous fractions required sequential treatment with a detergent, octylglucoside, in the presence of 1 mM Ca2+ followed by solubilization with EGTA. Calpactins contain sites for phosphorylation by protein kinase C, and in this study we found phosphoprotein substrates for protein kinase C associated with secretory granule and plasma membranes which could be immunoprecipitated with calpactin antisera. In summary, the characteristics in anterior pituitary secretory cells of these two members of the annexin family lend support to the hypothesis that calpactins, potentially regulated by Ca2+ and by phosphorylation, may have a role in exocytosis.

Insulin stimulates the activity of a protamine kinase in isolated rat hepatocytes

Treatment of isolated rat hepatocytes with 10-100 nM insulin for 5-10 min increased by about 2-fold the activity of a protamine kinase which exhibited properties similar to those of a protamine kinase from bovine kidney (Damuni, Z., Amick, G. D., and Sneed, T. R. (1989) J. Biol. Chem. 264, 6412-6416). Half-maximal increase in protamine kinase activity occurred at about 1 nM insulin. This effect of insulin was detected only when 25 mM NaF or 50 mM KPO4 were included in the homogenization buffers and was not prevented by preincubation of the hepatocytes with 10 microM cycloheximide. Insulin stimulation of protamine kinase was maintained following chromatography of extracts on protamine-agarose, DEAE-cellulose, and Sephacryl S-200 gel filtration. The apparent Mr of the protamine kinase from control and insulin-treated hepatocytes was 45,000 as estimated by gel permeation chromatography. Experiments utilizing partially purified protamine kinase from control and insulin-treated hepatocytes indicated that insulin did not affect the apparent Km for protamine, Mg2+, or ATP, but increased the Vmax for the protamine kinase reaction by 1.6-2-fold. Incubation with the catalytic subunit of protein phosphatase 2A completely inactivated the protamine kinase from control and insulin-treated cells. The results indicate that the insulin-stimulated increase in protamine kinase activity may be due to a covalent modification, possibly phosphorylation, of the protamine kinase.

Protein kinase C phosphorylates leukemia RNA polymerase II

Purified RNA polymerase II from chicken leukemia cells was found to be an effective substrate for protein kinase C but not cAMP-dependent protein kinase. Protein kinase C catalyzed the incorporation of 1-2 mol of phosphate per mol of polymerase II and the reaction was totally calcium and lipid dependent. Electrophoresis studies revealed a time-dependent increase of phosphate incorporation into RNA polymerase II subunits of 220 KDa, 180 KDa and 150 KDa, with a preferential phosphorylation of the 180 KDa polypeptide. The phosphorylated enzyme has a preference for using single-stranded DNA as the template for transcription, including transcription of the single-stranded myb oncogene sequence. Phosphoamino acid analysis indicated that both serine and threonine residues were phosphorylated at equal amounts. Phosphorylation by protein kinase C increased the affinity of substrate-polymerase binding and the initial rate of RNA synthesis, suggesting a mechanism by which gene expression can be activated by protein kinase C.

Protein kinase C and an endogenous substrate associated with adenohypophyseal secretory granules

Secretory granules isolated from anterior pituitary glands were examined for Ca2+/phospholipid-dependent protein kinase (protein kinase C) activity as well as the occurrence of granule-associated substrate proteins. Sheep adenohypophyses were fractionated by differential and sucrose-density-gradient centrifugation to yield a granule fraction enriched for luteinizing-hormone (lutropin)-containing secretory granules. Marker-enzyme analysis showed no detectable cytosolic contamination, although there were small amounts of plasma membranes (2-4%) and lysosomes (4-6%) associated with the preparation. As determined by histone-H1 phosphorylation after DEAE-cellulose DE-52 chromatography, protein kinase C activity with a marked dependence on Ca2+ and lipid (4-fold increase in their presence) was evident in the secretory-granule fraction. Phosphorylation in vitro of the secretory-granule fraction by endogenous and exogenous protein kinase C revealed a protein of Mr 36,000, which by two-dimensional SDS/polyacrylamide-gel electrophoresis showed multiple sites of phosphorylation. The Mr-36,000 protein was not found in cytosolic or plasma-membrane fractions and was not phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase. Several secretory-granule proteins served as substrates for the catalytic subunit, the most prominent of which were of Mr 63,000, 23,000 and 21,000. From these data, we suggest that phosphorylation of secretory-granule-associated proteins by protein kinase C and by cyclic AMP-dependent protein kinase may be important in secretion regulation in the anterior pituitary gland.

Differential effects of phorbol ester on phenylephrine and vasopressin-induced Ca2+ mobilization in isolated hepatocytes

Receptor-mediated breakdown of PtdIns(4,5)P2 produces two cellular signals, Ins(1,4,5)P3, which can release intracellular Ca2+, and diacylglycerol, which activates a Ca2+- and phospholipid-dependent protein kinase (protein kinase C). This study assesses the significance of protein kinase C in relation to phenylephrine- and vasopressin-induced Ca2+ mobilization in hepatocytes. Phorbol ester (4 beta-phorbol-12-myristate-13-acetate), which can directly activate protein kinase C, had no effect either on Ca2+ efflux from the cell (measured with arsenazo III) or on Ca2+ influx (measured with Quin-2), processes which are inhibited and stimulated, respectively, by both phenylephrine and vasopressin. No evidence of synergism between phorbol ester pretreatment of hepatocytes and the Ca2+ ionophore (ionomycin)-mediated effects on the increase of cytosolic free Ca2+ and phosphorylase activation could be obtained. These findings suggest that protein kinase C is not obligatorily involved in the regulation of hepatocyte Ca2+ fluxes. Pretreatment of hepatocytes with phorbol ester (PMA) or 1-oleoyl-2-acetylglycerol totally inhibited the effects of phenylephrine in elevating the cytosolic free Ca2+; half-maximal inhibitory effects occurred at PMA and 1-oleoyl-2-acetylglycerol concentrations of 1 ng/ml and 12 micrograms/ml, respectively. In contrast, pretreatment with PMA had a much smaller effect on Ca2+ mobilization induced by vasopressin. These observations suggest that protein kinase C may be involved in "down-regulation" of the alpha 1-receptor in hepatocytes and may thus exert a negative influence on the Ca2+-signalling pathway.

Inositol trisphosphate and diacylglycerol as intracellular second messengers in liver

Receptor occupation by a variety of Ca2+-mobilizing hormones, such as alpha 1-adrenergic agents, vasopressin and angiotensin II, causes a rapid phosphodiesterase-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate in the plasma membrane with the production of the water soluble compound myo-inositol-1,4,5-trisphosphate (IP3) and the lipophilic molecule 1,2-diacylglycerol (DG). This review summarizes the recent evidence obtained in the liver that defines the roles of these products as intracellular messengers of hormone action. Intracellular Ca2+ mobilization is mediated by IP3, which releases Ca2+ from a subpopulation of the endoplasmic reticulum, resulting in a rapid increase of the cytosolic free Ca2+ concentration ( [Ca2+]i). Further effects of receptor occupancy are inhibition of the plasma membrane Ca2+-ATPase, despite net Ca2+ efflux, and an increased permeability of the plasma membrane to extracellular Ca2+. The activation of the phospholipid-dependent protein kinase C by DG does not alter Ca2+ fluxes across the plasma membrane. In contrast to some secretory cells, a synergism between protein kinase C activation and increased [Ca2+]i is not observed in liver. Activation of protein kinase C profoundly inhibits the response to alpha 1-adrenergic agonists, with only minimal effects on the vasopressin response. It is concluded that in liver the two inositol-lipid messenger systems, IP3 and DG, exert their effects by essentially separate pathways.

Risk of infection after penetrating abdominal trauma

To identify the risk factors for the development of postoperative septic complications in patients with intestinal perforation after abdominal trauma, and to compare the efficacies of single-drug and dual-drug prophylactic antibiotic therapy, we studied 145 patients who presented with abdominal trauma and intestinal perforation at two hospitals between July 1979 and June 1982. Logistic-regression analysis showed that a higher risk of infection (P less than 0.05) was associated with increased age, injury to the left colon necessitating colostomy, a larger number of units of blood or blood products administered at surgery, and a larger number of injured organs. The presence of shock on arrival, which was found to increase the risk of infection when this factor was analyzed individually, did not add predictive power. Patients with postoperative sepsis were hospitalized significantly longer than were patients without infection (13.8 vs. 7.7 days, P less than 0.0001). Both treatment regimens--cefoxitin given alone and clindamycin and gentamicin given together--resulted in similar infection rates, drug toxicity, duration of hospitalization, and costs.

Phosphorylation of a 16-kDa protein by diacylglycerol-activated protein kinase C in vitro and by vasopressin in intact hepatocytes

A 16-kDa protein present in a purified rat liver plasma membrane fraction and also in cytosol can be phosphorylated by endogenous diacylglycerol-activated protein kinase C. In intact hepatocytes prelabeled with 32P, vasopressin causes a rapid increase in the phosphorylation of a 16-kDa protein having a similar pI value to that observed in in vitro studies. These findings suggest that vasopressin-induced phosphorylation of the 16-kDa in the intact hepatocyte may reflect increased activity of protein kinase C, secondary to membrane polyphosphoinositide breakdown. Phosphorylation of the 16-kDa protein may thus be part of the coordinated mechanism associated with hormonal regulation of cellular Ca2+ fluxes.

Mechanisms underlying calcium homeostasis in isolated hepatocytes

The steady state relationship between intra- and extramitochondrial free Ca2+ across the inner mitochondrial membrane has been investigated in isolated liver mitochondria. The extramitochondrial free Ca2+ concentration was essentially independent of the mitochondrial calcium content above 4 nmol/mg of protein. Below this value, a decrease in the mitochondrial calcium content was accompanied by a decrease in the extramitochondrial free Ca2+ concentration. The experimental data are compatible with a model in which the steady state distribution of calcium is described in terms of the kinetic parameters of the separate carriers catalyzing Ca2+ influx and efflux across the mitochondrial inner membrane. The corresponding relationship between cytosolic free Ca2+ concentration and the amounts of calcium in the mitochondria and endoplasmic reticulum was investigated in isolated river cells over a range of cellular Ca2+ contents by using a nondisruptive technique based on the selective release of calcium from mitochondrial and total cellular pools by addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone and A23187, respectively. A net increase in cell calcium from 1 to 5 nmol/mg dry weight, increased the cytosolic free Ca2+ concentration from 0.1 to about 0.3 microM and increased the calcium contents of both mitochondria and endoplasmic reticulum. Above 5 nmol of calcium/mg cell dry weight, the endoplasmic reticulum calcium pool became filled, and further increases in calcium content were accounted for by increases of the mitochondrial pool but no further increase of the cytosolic free Ca2+ concentration. These studies and experiments with mixtures of isolated microsomes and mitochondria suggest that, in cells as normally isolated (containing 5 to 6 nmol of calcium/mg dry weight), the endoplasmic reticulum is saturated with calcium and is unlikely to play a major role as an intracellular calcium buffer. The in situ mitochondrial calcium content is sufficiently high (approximately 16 nmol/mg of protein) for these organelles to buffer effectively the cytosolic free Ca2+ concentration at a value of about 0.3 microM. In addition, it may be concluded that intramitochondrial Ca2+-dependent enzymes will be exposed to saturating concentrations of free Ca2+.

Phosphorylation and activation of the cardiac isoenzyme of phosphorylase kinase by the cAMP-dependent protein kinase

The cAMP-dependent protein kinase catalyzes the phosphorylation of the alpha- and beta-subunits of the cardiac isozyme of phosphorylase kinase. beta-Subunit phosphorylation achieves a maximum level of between 1 to 2 mol of phosphate/mol of phosphorylase kinase, a value less than the stoichiometric content of beta-subunits in the enzyme. This, less than stoichiometric incorporation, is not a result of the presence of endogenous phosphate in equivalent sites in the remaining beta-subunit moieties. Pretreatment of phosphorylase kinase with phosphoprotein phosphatase, under conditions proven to dephosphorylate such sites, does not modify the observed extent of beta-subunit phosphorylation. alpha'-Subunit phosphorylation is initiated at a slower rate than beta but achieves a higher maximum level of incorporation. alpha'-Subunit phosphorylation, but not the extent of beta-subunit phosphorylation, is stimulated by MnCl2 and partially inhibited by NaF; neither is effected by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The activation of cardiac phosphorylase kinase that occurs concomitantly with phosphorylation appears to be dependent upon phosphate incorporation into both the alpha- and beta-subunits. At low levels of activation a close correlation is observed between activation and either alpha-subunit phosphorylation, beta-subunit phosphorylation, or total phosphorylation. However, the cAMP-dependent catalyzed phosphorylation of alpha, at a time after which beta-subunit phosphorylation is already maximal, also results in activation of cardiac phosphorylase kinase.

Evaluation of ceforanide as treatment for staphylococcal and streptococcal endocarditis

Ceforanide administered parenterally twice daily was used as the sole agent to treat 17 patients with right-sided endocarditis due to Staphylococcus aureus or nonenterococcal streptococci. Fifteen patients were cured of their original infection. Two patients were withdrawn from the study. One patient was transferred to another hospital 4 days after ceforanide therapy was initiated, and the other was changed to a different antibiotic regimen when his viridans streptococcus proved tolerant to ceforanide. The intramuscular form of ceforanide was well tolerated. It was stopped in two patients after week 3 of therapy because of adverse effects, possibly related to the study drug. These findings resolved with discontinuation of the ceforanide, and no additional antimicrobial therapy was necessary. Two patients who continued to abuse drugs intravenously during the study developed bacteremia with new organisms and required additional antimicrobial therapy. Ceforanide proved to be a useful agent in the treatment of right-sided endocarditis due to susceptible S. aureus and nonenterococcal streptococci.

Purification and properties of the cardiac isoenzyme of phosphorylase kinase

This study reports the purification of bovine cardiac phosphorylase kinase to near homogeneity (approximately 1240-fold), as based upon SDS gel electrophoresis and sucrose density gradient ultracentrifugation (co-migration of enzyme activity and protein with constant specific activity throughout the peak). The molecular weight of the enzyme following purification is identical with that in the soluble extract from beef hearts, and similar to that of the rabbit skeletal muscle isoenzyme (i.e. approximately 1.3 X 10(6)) based on co-migration in sucrose density gradient ultracentrifugation. The molecular weights of the subunits determined by SDS gel electrophoresis are: alpha', 134,000; beta, 125,000; gamma, 48,000. The subunit stoichiometry is determined to be alpha 1 beta 1.01 gamma 1.35 with a faint band co-migrating with purified bovine brain calmodulin. The enzyme displays little, if any, activity below pH 6.0, but activity increases markedly in the pH range of 6.8 to 8.2. After phosphorylation with pure cAMP-dependent protein kinase catalytic subunit and [gamma-32P]ATP (0.14 mM ATP, 4 mM magnesium acetate) in which the beta subunit was maximally phosphorylated (stoichiometry, 0.25 mol/mol; ratio of 32P in the alpha' and beta subunits, 1.90:1), enzyme activity was increased approximately 2-fold at pH 6.8, while at higher pH values, the effect of phosphorylation was less marked (20 to 50% increase at pH 8.2). Ca2+ is required for enzyme activity; ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (0.5 mM) completely inhibited the activity of th nonphosphorylated and phosphorylated enzyme, and activity was restored by the addition of Ca2+ (Ka for Ca2+, 1.94 and 1.35 microM for the nonphosphorylated and phosphorylated enzyme, respectively.

The elementary reactions of the pig heart pyruvate dehydrogenase complex. A study of the inhibition by phosphorylation

1. A method was devised for preparing pig heart pyruvate dehydrogenase free of thiamin pyrophosphate (TPP), permitting studies of the binding of [35S]TPP to pyruvate dehydrogenase and pyruvate dehydrogenase phosphate. The Kd of TPP for pyruvate dehydrogenase was in the range 6.2-8.2 muM, whereas that for pyruvate dehydrogenase phosphate was approximately 15 muM; both forms of the complex contained about the same total number of binding sites (500 pmol/unit of enzyme). EDTA completely inhibited binding of TPP; sodium pyrophosphate, adenylyl imidodiphosphate and GTP, which are inhibitors (competitive with TPP) of the overall pyruvate dehydrogenase reaction, did not appreciably affect TPP binding. 2. Initial-velocity patterns of the overall pyruvate dehydrogenase reaction obtained with varying TPP, CoA and NAD+ concentrations at a fixed pyruvate concentration were consistent with a sequential three-site Ping Pong mechanism; in the presence of oxaloacetate and citrate synthase to remove acetyl-CoA (an inhibitor of the overall reaction) the values of Km for NAD+ and CoA were 53+/- 5 muM and 1.9+/-0.2 muM respectively. Initial-velocity patterns observed with varying TPP concentrations at various fixed concentrations of pyruvate were indicative of either a compulsory order of addition of substrates to form a ternary complex (pyruvate-Enz-TPP) or a random-sequence mechanism in which interconversion of ternary intermediates is rate-limiting; values of Km for pyruvate and TPP were 25+/-4 muM and 50+/-10 nM respectively. The Kia-TPP (the dissociation constant for Enz-TPP complex calculated from kinetic plots) was close to the value of Kd-TPP (determined by direct binding studies). 3. Inhibition of the overall pyruvate dehydrogenase reaction by pyrophosphate was mixed non-competitive versus pyruvate and competitive versus TPP; however, pyrophosphate did not alter the calculated value for Kia-TPP, consistent with the lack of effect of pyrophosphate on the Kd for TPP. 4. Pyruvate dehydrogenase catalysed a TPP-dependent production of 14CO2 from [1-14C]pyruvate in the absence of NAD+ and CoA at approximately 0.35% of the overall reaction rate; this was substantially inhibited by phosphorylation of the enzyme both in the presence and absence of acetaldehyde (which stimulates the rate of 14CO2 production two- or three-fold). 5. Pyruvate dehydrogenase catalysed a partial back-reaction in the presence of TPP, acetyl-CoA and NADH. The Km for TPP was 4.1+/-0.5 muM. The partial back-reaction was stimulated by acetaldehyde, inhibited by pyrophosphate and abolished by phosphorylation. 6. Formation of enzyme-bound [14C]acetylhydrolipoate from [3-14C]pyruvate but not from [1-14C]acetyl-CoA was inhibited by phosphorylation. Phosphorylation also substantially inhibited the transfer of [14C]acetyl groups from enzyme-bound [14C]acetylhydrolipoate to TPP in the presence of NADH. 7...

Regulation of pyruvate dehydrogenase in rat heart. Mechanism of regulation of proportions of dephosphorylated and phosphorylated enzyme by oxidation of fatty acids and ketone bodies and of effects of diabetes: role of coenzyme A, acetyl-coenzyme A and reduced and oxidized nicotinamide-adenine dinucleotide

The proportion of active (dephosphorylated) pyruvate dehydrogenase in perfused rat heart was decreased by alloxan-diabetes or by perfusion with media containing acetate, n-octanoate or palmitate. The total activity of the dehydrogenase was unchanged. 2. Pyruvate (5 or 25mM) or dichloroacetate (1mM) increased the proportion of active (dephosphorylated) pyruvate dehydrogenase in perfused rat heart, presumably by inhibiting the pyruvate dehydrogenase kinase reaction. Alloxan-diabetes markedly decreased the proportion of active dehydrogenase in hearts perfused with pyruvate or dichloroacetate. 3. The total activity of pyruvate dehydrogenase in mitochondria prepared from rat heart was unchanged by diabetes. Incubation of mitochondria with 2-oxo-glutarate plus malate increased ATP and NADH concentrations and decreased the proportion of active pyruvate dehydrogenase. The decrease in active dehydrogenase was somewhat greater in mitochondria prepared from hearts of diabetic rats than in those from hearts of non-diabetic rats. Pyruvate (0.1-10 mM) or dichloroacetate (4-50 muM) increased the proportion of active dehydrogenase in isolated mitochondria presumably by inhibition of the pyruvate dehydrogenase kinase reaction. They were much less effective in mitochondria from the hearts of diabetic rats than in those of non-diabetic rats. 4. The matrix water space was increased in preparations of mitochondria from hearts of diabetic rats. Dichloroacetate was concentrated in the matrix water of mitochondria of non-diabetic rats (approx. 16-fold at 10 muM); mitochondria from hearts of diabetic rats concentrated dichloroacetate less effectively. 5. The pyruvate dehydrogenase phosphate phosphatase activity of rat hearts and of rat heart mitochondria (approx. 1-2 munit/unit of pyruvate dehydrogenase) was not affected by diabetes. 6. The rate of oxidation of [1-14C]pyruvate by rat heart mitochondria (6.85 nmol/min per mg of protein with 50 muM-pyruvate) was approx. 46% of the Vmax. value of extracted pyruvate dehydrogenase (active form). Palmitoyl-L-carnitine, which increased the ratio of [acetyl-CoA]/[CoA] 16-fold, inhibited oxidation of pyruvate by about 90% without changing the proportion of active pyruvate dehydrogenase.

Regulation of mammalian pyruvate dehydrogenase

In mammalian tissues, two types of regulation of the pyruvate dehydrogenase complex have been described: end product inhibition by acetyl CoA and NADH: and the interconversion of an inactive phosphorylated form and an active nonphosphorylated form by an ATP requiring kinase and a specific phosphatase. This article is largely concerned with the latter type of regulation of the complex in adipose tissue by insulin (and other hormones) and in heart muscle by lipid fuels. Effectors of the two interconverting enzymes include pyruvate and ADP which inhibit the kinase, acetoin which activates the kinase and Ca2+ and Mg2+ which both activate the phosphatase and inhibit the kinase. Evidence is presented that all components of the pyruvate dehydrogenase complex including the phosphatase and kinase are located within the inner mitochondrial membrane. Direct measurements of the matrix concentration of substrates and effectors is not possible by techniques presently available. This is the key problem in the identification of the mechansims involved in the alterations in pyruvate dehydrogenase activity observed in adipose tissue and muscle. A number of indirect approaches have been used and these are reviewed. Most hopeful is the recent finding in this laboratory that in both adipose tissue and heart muscle, differences in activity of pyruvate dehydrogenase in the intact tissue persist during preparation and subsequent incubation of mitochondria.

Regulation of heart muscle pyruvate dehydrogenase kinase

1. The activity of pig heart pyruvate dehydrogenase kinase was assayed by the incorporation of [(32)P]phosphate from [gamma-(32)P]ATP into the dehydrogenase complex. There was a very close correlation between this incorporation and the loss of pyruvate dehydrogenase activity with all preparations studied. 2. Nucleoside triphosphates other than ATP (at 100mum) and cyclic 3':5'-nucleotides (at 10mum) had no significant effect on kinase activity. 3. The K(m) for thiamin pyrophosphate in the pyruvate dehydrogenase reaction was 0.76mum. Sodium pyrophosphate, adenylyl imidodiphosphate, ADP and GTP were competitive inhibitors against thiamin pyrophosphate in the dehydrogenase reaction. 4. The K(m) for ATP of the intrinsic kinase assayed in three preparations of pig heart pyruvate dehydrogenase was in the range 13.9-25.4mum. Inhibition by ADP and adenylyl imidodiphosphate was predominantly competitive, but there was nevertheless a definite non-competitive element. Thiamin pyrophosphate and sodium pyrophosphate were uncompetitive inhibitors against ATP. It is suggested that ADP and adenylyl imidodiphosphate inhibit the kinase mainly by binding to the ATP site and that the adenosine moiety may be involved in this binding. It is suggested that thiamin pyrophosphate, sodium pyrophosphate, adenylyl imidodiphosphate and ADP may inhibit the kinase by binding through pyrophosphate or imidodiphosphate moieties at some site other than the ATP site. It is not known whether this is the coenzyme-binding site in the pyruvate dehydrogenase reaction. 5. The K(m) for pyruvate in the pyruvate dehydrogenase reaction was 35.5mum. 2-Oxobutyrate and 3-hydroxypyruvate but not glyoxylate were also substrates; all three compounds inhibited pyruvate oxidation. 6. In preparations of pig heart pyruvate dehydrogenase free of thiamin pyrophosphate, pyruvate inhibited the kinase reaction at all concentrations in the range 25-500mum. The inhibition was uncompetitive. In the presence of thiamin pyrophosphate (endogenous or added at 2 or 10mum) the kinase activity was enhanced by low concentrations of pyruvate (25-100mum) and inhibited by a high concentration (500mum). Activation of the kinase reaction was not seen when sodium pyrophosphate was substituted for thiamin pyrophosphate. 7. Under the conditions of the kinase assay, pig heart pyruvate dehydrogenase forms (14)CO(2) from [1-(14)C]pyruvate in the presence of thiamin pyrophosphate. Previous work suggests that the products may include acetoin. Acetoin activated the kinase reaction in the presence of thiamin pyrophosphate but not with sodium pyrophosphate. It is suggested that acetoin formation may contribute to activation of the kinase reaction by low pyruvate concentrations in the presence of thiamin pyrophosphate. 8. Pyruvate effected the conversion of pyruvate dehydrogenase phosphate into pyruvate dehydrogenase in rat heart mitochondria incubated with 5mm-2-oxoglutarate and 0.5mm-l-malate as respiratory substrates. It is suggested that this effect of pyruvate is due to inhibition of the pyruvate dehydrogenase kinase reaction in the mitochondrion. 9. Pyruvate dehydrogenase kinase activity was inhibited by high concentrations of Mg(2+) (15mm) and by Ca(2+) (10nm-10mum) at low Mg(2+) (0.15mm) but not at high Mg(2+) (15mm).

Mechanism of activation of pyruvate dehydrogenase by dichloroacetate and other halogenated carboxylic acids

1. Monochloroacetate, dichloroacetate, trichloroacetate, difluoroacetate, 2-chloropropionate, 2,2'-dichloropropionate and 3-chloropropionate were inhibitors of pig heart pyruvate dehydrogenase kinase. Dichloroacetate was also shown to inhibit rat heart pyruvate dehydrogenase kinase. The inhibition was mainly non-competitive with respect to ATP. The concentration required for 50% inhibition was approx. 100mum for the three chloroacetates, difluoroacetate and 2-chloropropionate and 2,2'-dichloropropionate. Dichloroacetamide was not inhibitory. 2. Dichloroacetate had no significant effect on the activity of pyruvate dehydrogenase phosphate phosphatase when this was maximally activated by Ca(2+) and Mg(2+). 3. Dichloroacetate did not increase the catalytic activity of purified pig heart pyruvate dehydrogenase. 4. Dichloroacetate, difluoroacetate, 2-chloropropionate and 2,2'-dichloropropionate increased the proportion of the active (dephosphorylated) form of pyruvate dehydrogenase in rat heart mitochondria with 2-oxoglutarate and malate as respiratory substrates. Similar effects of dichloroacetate were shown with kidney and fat-cell mitochondria. Glyoxylate, monochloroacetate and dichloroacetamide were inactive. 5. Dichloroacetate increased the proportion of active pyruvate dehydrogenase in the perfused rat heart, isolated rat diaphragm and rat epididymal fat-pads. Difluoroacetate and dichloroacetamide were also active in the perfused heart, but glyoxylate, monochloroacetate and trichloroacetate were inactive. 6. Injection of dichloroacetate into rats starved overnight led within 60 min to activation of pyruvate dehydrogenase in extracts from heart, psoas muscle, adipose tissue, kidney and liver. The blood concentration of lactate fell within 15 min to reach a minimum after 60 min. The blood concentration of glucose fell after 90 min and reached a minimum after 120 min. There was no significant change in plasma glycerol concentration. 7. In epididymal fatpads dichloroacetate inhibited incorporation of (14)C from [U-(14)C]glucose, [U-(14)C]fructose and from [U-(14)C]lactate into CO(2) and glyceride fatty acid. 8. It is concluded that the inhibition of pyruvate dehydrogenase kinase by dichloroacetate may account for the activation of pyruvate dehydrogenase and pyruvate oxidation which it induces in isolated rat heart and diaphragm muscles, subject to certain assumptions as to the distribution of dichloroacetate across the plasma membrane and the mitochondrial membrane. 9. It is suggested that activation of pyruvate dehydrogenase by dichloroacetate could contribute to its hypoglycaemic effect by interruption of the Cori and alanine cycles. 10. It is suggested that the inhibitory effect of dichloroacetate on fatty acid synthesis in adipose tissue may involve an additional effect or effects of the compound.

Comparison of ultrasound and cineangiographic measurements of the mean rate of circumferential fiber shortening in man

It has been shown that cineangiographic measurement of the mean rate of circumferential fiber shortening (mean V CF ) at the minor left ventricular equator is a reliable method for evaluating the mechanics of cardiac performance. Since fiber shortening can be derived from the echocardiogram, we sought to validate the measurement of mean V CF by this noninvasive technic in patients studied by both methods. In 15 patients considered to have normal left ventricular function, the average mean V CF determined by ultrasound was 1.29 ± 0.23 circumferences/sec, while in the 13 patients with reduced left ventricular performance this value was 0.75 ± 0.16 circumferences/sec ( P < 0.001). Values of mean V CF by the two technics were similar and separated normal from abnormal ventricular function in 27 of 28 patients. The average mean velocity of posterior wall motion was 4.7 ± 1.1 cm/sec in normal patients and 3.9 ± 1.3 cm/sec in abnormals, but posterior wall velocities did not correlate well with either ultrasound or cineangiographic determinations of mean V CF . Ejection fraction calculated from ultrasound measurements correlated significantly with the ejection fraction calculated by cineangiography (r = 0.83, P < 0.0001). The ejection fraction and mean V CF , as determined by ultrasound in the 28 patients, correlated well (r = 0.92, P < 0.0001), but there were six discordant points.

From these studies we conclude that the ultrasound determination of mean V CF is a valid method for distinguishing normal from abnormal myocardial performance of the left ventricle. These data also support the use of ultrasound in determining ejection fraction. Estimation of posterior wall velocity, although perhaps useful in the serial study of the same patient, seems limited in its ability to assess cardiac performance accurately.

The effect of prostaglandins on ox pituitary content of adenosine 3':5'-cyclic monophosphate and the release of growth hormone

1. An assay, based on competition between adenosine 3':5'-cyclic monophosphate (cyclic AMP) and cyclic [(3)H]AMP for binding to a rabbit skeletal muscle protein, has been used to measure tissue contents of cyclic AMP. The assay has a sensitivity of 0.05pmol of cyclic AMP. Cyclic GMP and cyclic CMP have 0.5%, and cyclic IMP 6.5%, of the ability of cyclic AMP to displace cyclic [(3)H]AMP from binding protein; AMP, ADP and ATP have no effect. 2. By using this method, the cyclic AMP content of ox pituitary slices exposed to prostaglandin was determined; release of growth hormone was measured by radioimmunoassay. 3. Release of growth hormone was increased by 45min incubation in 1mum-prostaglandin E(2) in the absence of theophylline, or in 10nm-prostaglandin E(2), 0.1mum-prostaglandin A(1) or 1mum-prostaglandin B(1) in the presence of 0.5mm-theophylline. 4. Pituitary cyclic AMP content was increased by 10min incubation in 1mum-prostaglandin E(2) in the absence of theophylline, or in 0.1mum-prostaglandin E(2) in the presence of 0.5mm-theophylline. 5. The maximum increase in cyclic AMP content was observed 10min, and significant changes in growth hormone release 30min, after introduction of prostaglandin E(2). 6. The increase in pituitary cyclic AMP content, but not in the rate of release of growth hormone, was observed in the absence of external Ca(2+). 7. The stimulation of release of growth hormone by prostaglandin was decreased by preincubation of tissue for 2h in colchicine (100mum) or cytochalasin B (10mug/ml). 8. These results support the suggestion that increased release of growth hormone after treatment with prostaglandin is the result of increased tissue cyclic AMP content, and possibly involves a microfilamentous or microtubular protein.

On a Change occurring in the Pelvis in a Case of Prepuberal Atrophy of the Testicles

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