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Biomedical subjects

W Schmitz

Publications and source records attributed to W Schmitz.

At least 109 records · Page 6Linked to original sources
PubMed1995

Isoproterenol infusion induces alterations in expression of hypertrophy-associated genes in rat heart.

Chronic infusion of isoproterenol (Iso) in rats results in cardiac hypertrophy via incompletely understood mechanisms. Our purpose was to determine whether Iso infusion would alter the expression of genes associated with hypertrophy. Male Wistar rats received either 2.4 mg Iso.kg-1.day-1, 9.9 mg propranolol (Prop).kg-1.day-1, both Iso and Prop, or vehicle (NaCl) via subcutaneously implanted osmotic pumps. In Iso-treated rats, the ventricular weight-to-body weight ratio was increased by 27% after 1 day and peaked on day 3 (+ 40%). Levels of atrial natriuretic factor (ANF) and fibronectin (FN) mRNA in the left ventricles were elevated 20-fold and 13-fold in Iso-treated rats, respectively, peaking at 3 days of infusion. The increase in FN mRNA accumulation was at least partially accounted for by elevated expression of extra type IIIA and IIIB (EIIIA and EIIIB) splicing variants. Levels of transforming growth factor (TGF)-beta 1 mRNA were elevated twofold after 3 days of Iso infusion. The abundance of skeletal alpha-actin (SK) mRNA increased fourfold after 1 day of Iso and declined thereafter. Iso infusion decreased sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and preproenkephalin (PNK) gene expression by approximately 50% and induced a myosin heavy chain (MHC) isogene switch favoring beta-MHC. Prop partially inhibited the Iso-evoked increases in ANF and FN mRNA, completely prevented the Iso-induced changes in TGF-beta 1 and SERCA mRNA, but had no effect on the Iso-stimulated changes in SK and PNK gene expression. These results demonstrate that chronic Iso infusion elicits alterations in cardiac gene expression that are consistent with the development of myocyte hypertrophy and interstitial fibrosis and are directionally identical to those previously reported for pressure overload hypertrophy.

Animals↗
PubMed1995

On the cardiac contractile, biochemical and electrophysiological effects of cantharidin, a phosphatase inhibitor.

Cantharidin concentration dependently increased the force of contraction in isolated guinea pig papillary muscles (1-100 microM). The positive inotropic effect is accompanied by a reduction in time to peak tension and relaxation time. Cantharidin did not exert a positive chronotropic effect in spontaneously beating right atria. L-type calcium channel currents of guinea pig cardiomyocytes were moderately increased by cantharidin (by about 20%), both at the whole-cell level (2 mM Ca2+) and at the single channel level (70 mM Ba2+). There was a correspondingly small increment of single channel availability. Additionally, a larger proportion of single-channel sweeps displayed high open probability-gating (so-called mode 2-gating). Cantharidin inhibited both type 1 and type 2A phosphatase activity in phosphatases purified from guinea pig ventricles [IC50 2.70 (2.06-3.53) and 0.13 (0.05-0.34) microM, n = 5-6, with 95% confidence intervals, respectively]. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, cantharidin (10 microM) increased the phosphorylation state of phospholamban (to 210% of control), the inhibitory subunit of troponin (to 155% of control), C-protein (to 156% control) and various additional proteins. It is concluded that the effects of cantharidin are likely mediated by increasing the phosphorylation state of several regulatory proteins. Furthermore, cantharidin might be an economical tool to investigate the function of phosphatases in model organ systems.

Animals↗
PubMed1995

Characterization of the phosphodiesterase inhibition by 2-(3-methoxy-5-methylsulfinyl-2-thienyl)-1H-imidazo-(4,5-c)-pyridine HCl and its sulfide- and sulfone derivatives in myocardial preparations from failing human hearts.

The effects of HN-10200 (2-(3-methoxy-5-methylsulfinyl-2-thienyl)-1H-imidazo(4,5-c)-pyridine HCl) and its derivatives HN-10201-sulfide and HN-10202-sulfone on the activities of the phosphodiesterase (PDE) isoenzyme activities isolated from ventricular myocardium of failing human hearts (end-stage myocardial failure, NYHA IV) were investigated. Four PDE isoenzymes (PDE I-IV) were separated by DEAE-sepharose chromatography. Milrinone, 3-isobutyl-1-methylxanthine (IBMX), and a derivative of pimobendan (2-(4-hydroxyphenyl)-5-(5-methyl-3-oxo-4,5-dihydro-2H-6-pyridazinyl)- benzimidazole HCl, PiD) were studied for comparison. Furthermore, the influence of HN-10200 on force of contraction and cAMP content of ventricular trabeculae of these hearts were determined. HN-10200 inhibited the activities of PDE I-IV concentration-dependently. The IC50 values were (mumol/l): 218.7, 283.1, 119.6, and 85.8 for PDE I-IV, respectively. The IC50 values of its derivatives were in the same range, i.e. the parent compound or its derivatives inhibited the PDE isoenzymes nonselectively. IBMX also inhibited PDE I-IV nonselectively, but was about ten times more potent based on IC50 values. In contrast, PiD was the most selective and potent PDE III inhibitor tested. Milrinone inhibited both, PDE III and IV, up to two orders of magnitude more potently than PDE I and II, HN-10200 (30 mumol/l) only marginally and insignificantly increased force of contraction and cAMP content of the ventricular trabeculae. Thus, HN-10200 and it's derivatives HN-10201-sulfide and HN-10202-sulfone are nonselective inhibitors of myocardial PDE I-IV. HN-10200 revealed only neglectable positive inotropic effects in preparations from failing human heart.

1-Methyl-3-isobutylxanthine↗
PubMed1994

Purification and properties of an alpha-methylacyl-CoA racemase from rat liver.

The (R)- and (S)-isomers of alpha-methyl-branched fatty acids were shown to be rapidly interconverted as coenzyme A thioesters, by an alpha-methylacyl-CoA racemase. The enzyme was purified some 5600-fold from rat liver, to apparent homogeneity. It is a monomer of 45 kDa with an isolectric point of pH 6.1 and is optimally active between pH 6 and pH 7. It acts only on coenzyme A thioesters, not on free fatty acids, and accepts as substrates a wide range of alpha-methylacyl-CoAs, including pristanoyl-CoA and trihydroxycoprostanoyl-CoA (an intermediate in bile acid synthesis), but neither 3-methyl-branched nor linear-chain acyl-CoAs. The racemase catalyzes a rapid exchange of the H atom in the alpha-position of the fatty acid against a proton from water, indicating that the mechanism involves abstraction of a proton. Based on this observation, a very sensitive and convenient radiometric assay, with 2-methyl[2-(3)H]acyl-CoAs as substrates, was developed. The enzyme was inactivated by micromolar concentrations of Hg2+ and to a lesser extent by Cu2+ but not by iodoacetamide and only slightly by N-ethylmaleimide and thimerosal.

Acyl Coenzyme A↗
PubMed1994

Radioimmunochemical quantification of Gi alpha in right and left ventricles from patients with ischaemic and dilated cardiomyopathy and predominant left ventricular failure.

An increase of Gi alpha-related pertussis toxin substrates has been observed in the failing myocardium. In order to quantify the protein expression of Gi alpha directly, we developed a fast radioimmunoassay using the iodinated synthetic peptide 125I-KENLKDCGLF. beta-adrenoceptors were studied with 125I-cyanopindolol binding for comparison. Immunoblot experiments using recombinant G-protein alpha-subunits showed that DS4 immunostained the G-protein alpha-subunits with a rank order of potency rGi alpha 1 = rGi alpha 2 > rGo alpha >> rGi alpha 3. The G-protein alpha-subunits recognized by DS4 in human ventricular membranes comigrated with rGi alpha 1 and rGi alpha 2. The radioimmunoassay had a sensitivity of 2.5 micrograms/ml transducin alpha with an interassay variation of less than 10%. The non-labelled peptide selectively competed with the myocardial 40 kDa membrane protein for binding to the antiserum DS4. Radioimmunochemical quantification of Gi alpha from cardiac membranes showed that in left ventricular membranes (LV) from dilated cardiomyopathy (DCM), there was an increase of Gi alpha by 138.5% when related to mg protein and 135% when related to 3H-ouabain binding sites as membrane marker. In LV from ischaemic cardiomyopathy (ICM), the increase was smaller (58.4%) when related to mg protein compared to the increase of Gi alpha when related to 3H-ouabain binding sites as membrane marker (155% v NF). In contrast, in the right ventricles (RV) there was no increase of Gi alpha in ICM or DCM. The numbers of beta-adrenoceptors were reduced in RV and LV of both, ICM and DCM. It is concluded that the radioimmunoassay may become an important tool for studying the expression of Gi alpha-protein levels and changes thereof in pathological conditions. The amount of immunodetectable Gi alpha-proteins is increased in failing LV due to DCM and ICM but not in RV, while beta-adrenoceptor down-regulation occurred in RV and LV in both conditions. These findings might indicate that the liability of the LV but not of RV to express Gi alpha-proteins may be increased in predominant LV heart failure. Alternatively, the underlying mechanism, e.g. sympathetic activation, may be regulated locally in the failing heart producing different changes in adjacent chambers.

Adolescent↗
PubMed1994

Pharmacological characterization of A2-adenosine receptors in guinea-pig ventricular cardiomyocytes.

The aim of the present study was to elucidate the question of whether cardiomyocytes possess stimulatory adenylyl cyclase-coupled A2-adenosine receptors and whether these receptors modify contractility. In isolated electrically driven ventricular cardiomyocytes from guinea-pig hearts the effects of the A2-adenosine receptor agonist 2-[(p-2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamide-adenos ine (CGS 21680C) alone and in the presence of isoprenaline on cAMP content and contractile response were investigated. In addition, we characterized these effects with selective A1- and A2-adenosine receptor antagonists [1,3-dipropyl-8-cyclopentylxanthine, DPCPX and 9-chloro-2-(2-furanyl)-5,6-dihydro-1,2,4-triazolo-(1,5-c)quinazolin++ +-5-imine, CGS 15943A, respectively]. To investigate the signal transduction pathway, the influence of pertussis toxin, known to inhibit signal transducing GTP-binding proteins (Gi/o-proteins), on these effects was studied. CGS 21680C alone and in the presence of isoprenaline increased cAMP content concentration-dependently (0.1 nmol/l-10 mumol/l) to maximally 154% of control and 137% of isoprenaline value, respectively. In the presence of the A1-adenosine receptor antagonist DPCPX (0.3 mumol/l) or after pertussis toxin-pretreatment (18 micrograms/kg i.v. 24-26 h) the cAMP increase was further elevated. The A2-adenosine receptor antagonist CGS 15943A (0.01 mumol/l) abolished these effects, indicating that these effects are mediated by A2-adenosine receptors. The elevation in cAMP content was not accompanied by an increase in contractile response. However, in the presence of isoprenaline CGS 21680C reduced contractile response to 62% of the isoprenaline value. The A1-adenosine receptor antagonist DPCPX abolished the decrease in contractility, whereas the A2-adenosine receptor antagonist CGS 15943A did not effect contractility. Thus the reduction in contractility is mediated via cAMP-decreasing A1-adenosine receptors. The results provide evidence for the coexistence of cAMP-reducing A1- and cAMP-elevating A2-adenosine receptors on ventricular cardiomyocytes. Only stimulation of A1-adenosine receptors leads to a subsequent reduction in contractile response, whereas A2-adenosine receptors do not affect contractility.

Adenosine↗
PubMed1994

In vivo beta-adrenergic stimulation leads to biphasic regulation of Gi alpha-2 gene transcriptional activity in rat heart.

The G1 alpha-2 gene transcriptional activity is increased by 40% in ventricular nuclei of rats stimulated in vivo with the beta-adrenoceptor agonist isoprenaline for 96 h. In the present study the time course of this regulation was investigated using in vitro transcription assays with ventricular nuclei of rats treated for 12, 48 and 96 h, respectively with isoprenaline (2.4 mg/kg per day) or with 0.9% NaCl as control. Whereas the G1 alpha-2 gene specific hybridization was unchanged in ventricular nuclei after isoprenaline stimulation for 12 h the same treatment led to a 37% decrease of G1 alpha-2 gene transcriptional activity 48 h and to a 45% increase after 96 h. The beta-adrenoceptor antagonist propranolol antagonized both the isoprenaline induced reduction and induction of G1 alpha-2 gene transcriptional activity. There was no change in Gs alpha gene transcriptional activity in the respective groups. In conclusion, these results show that in rat heart in vivo beta-adrenergic stimulation regulates G1 alpha-2 gene transcription in a biphasic manner, i.e. a transient decrease is followed by an increase in transcriptional activity. This biphasic regulation by a single stimulus might be due to complex modulations of gene expression by transcription factors.

Animals↗
PubMed1994

Signal transduction pathway of the muscarinic receptors mediating gallbladder contraction.

In gallbladder smooth muscle, carbachol interacts with M3 receptors to mediate contraction. To examine components of the intracellular second messenger system that is coupled to these receptors we have tested whether carbachol stimulates the formation of inositol phosphates (IP) to cause contraction. Guinea pig gallbladder muscle strips were prelabeled with [3H]inositol and were incubated with 0.1 mmol/l carbachol, a concentration causing maximal contraction. [3H]inositol monophosphates, [3H]inositol bisphosphates and [3H]inositol trisphosphates and contraction were measured at various times (0-90 s). To examine whether a pertussis toxin-sensitive guanine nucleotide binding protein is coupled to the muscarinic receptors, guinea pigs were pretreated with pertussis toxin (180 micrograms/kg i.v./24 h). The effectiveness of pertussis toxin treatment was determined by measuring [32P]ADP-ribosylation of a approximately 40/41 kDa protein from gallbladder homogenates. Carbachol caused a significant time-dependent increase in the formation of [3H]inositol monophosphates, [3H]inositol bisphosphates and [3H]inositol trisphosphates. The time course of [3H]inositol trisphosphate turnover caused by carbachol was biphasic, and was detectable at 15 s and maximal at 60 s; at 75 s and 90 s formation of [3H]inositol trisphosphates decreased, whereas the time course of carbachol-induced contraction of the gallbladder smooth muscle strips reached a plateau after 90 s. The effects of carbachol on [3H]inositol trisphosphates and on contraction were abolished by atropine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗
PubMed1994

Impaired degradation of phytanic acid in cells from patients with mitochondriopathies: evidence for the involvement of ETF and the respiratory chain in phytanic acid alpha-oxidation.

Phytanic acid alpha-oxidation was studied in cultures of skin fibroblasts and myoblasts from patients with various defects of the respiratory chain in order to obtain information on the subcellular site and the mechanism of this pathway. In fibroblasts from patients with complex IV (cytochrome c oxidase) deficiency or glutaricaciduria type II, phytanic acid alpha-oxidation was reduced to 14% of normal, whereas in myoblasts from patients with complex I (NADH-Q reductase) deficiency, it was normal. Apparently, at least one step of phytanic acid alpha-oxidation occurs in mitochondria and in this process electrons are transferred to the respiratory chain via the electron-transfer flavoprotein (ETF).

Cells, Cultured↗
PubMed1994

Biochemical and electrophysiological mechanisms of the positive inotropic effect of calyculin A, a protein phosphatase inhibitor.

Calyculin A (CyA; 1 microM) increased the force of contraction in isolated guinea pig papillary muscles to 144% of control without affecting contraction parameters. The effect of CyA on L-type calcium channels was assessed in cell-attached patches of guinea pig ventricular cardiomyocytes. Unitary Ba++ current recordings revealed that CyA at micromolar concentrations enhanced channel availability almost 2-fold, whereas the duration of individual openings and closures remained unchanged. In whole-cell recordings with Ca++ as the charge carrier, intracellular dialysis of 1 microM CyA enhanced peak current to a similar extent. In homogenates from guinea pig ventricles, 1 microM CyA completely inhibited phosphorylase phosphatase activity. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, 1 microM CyA increased the phosphorylation state of phospholamban (to 267% of control), that of the inhibitory subunit of troponin (to 182% of control) and those of various additional proteins. We conclude that the effects of CyA are likely to be mediated by increasing the phosphorylation state of several regulatory proteins.

Animals↗
PubMed1994

Effects of adenosine receptor and muscarinic cholinergic receptor agonists on cardiac protein phosphorylation. Influence of pertussis toxin.

In isolated 32P-labeled guinea pig ventricular cardiomyocytes phospholamban (PLB), myosin light chain 2 and the inhibitory subunit of troponin (Tnl) were identified by antibodies. In isolated 32P-labeled guinea pig ventricular cardiomyocytes isoproterenol (0.1 mumol/l) increased phosphorylation of PLB and of the inhibitory subunit of Tnl to 159 and 119% of control, respectively, without effect on the phosphorylation state of myosin light chain 2. Additionally applied carbachol or (-)-N6-phenylisopropyladenosine reduced phosphorylation of PLB and Tnl without reducing cyclic AMP content. After pretreatment of guinea pigs with pertussis toxin (18 micrograms/100 g b.wt.), carbachol or (-)-N6-phenylisopropyladenosine failed to reduce isoproterenol-stimulated phosphorylation of both PLB and Tnl. It is concluded that the reductions by carbachol and (-)-N6-phenylisopropyladenosine of isoproterenol-stimulated PLB phosphorylation and Tnl phosphorylation are pertussis toxin-sensitive.

Animals↗
PubMed1993

Pertussis toxin unmasks stimulatory myocardial A2-adenosine receptors on ventricular cardiomyocytes.

Pertussis toxin-pretreatment abolished the contractility- and cAMP-decreasing effects of the A1-adenosine receptor agonist (-)-N6-phenylisopropyladenosine (R-PIA) in the presence of isoprenaline in isolated ventricular cardiomyocytes from guinea-pigs, indicating that these stimulatory effects of A1-adenosine receptors are mediated via pertussis toxin-sensitive G-proteins. Furthermore, the decrease in contractile response by the A1/A2-adenosine receptor agonist 5'-N-ethylcarboxamidadenosine (NECA) was abolished. Moreover, NECA increased cAMP content in pertussis toxin-pretreated cells. Thus, pertussis toxin unmasked cAMP-augmenting effects of NECA, indicating that NECA can stimulate A2-adenosine receptors on cardiomyocytes. Thereby, the present study provides evidence that besides cAMP- and contractility-decreasing A1-adenosine receptors, cAMP-increasing A2-adenosine receptors coexist on ventricular cardiomyocytes, which do not influence contractile response.

Adenosine↗
PubMed1993

Changes in cardiac beta-adrenoceptors in human heart diseases: relationship to the degree of heart failure and further evidence for etiology-related regulation of beta 1 and beta 2 subtypes.

Radioligand binding studies were performed to investigate total beta-adrenoceptor density (Bmax) and beta 1 and beta 2 subtype distribution in left ventricular biopsies obtained from 8 prospective transplant donors serving as controls and from 143 patients with different degrees of heart failure (NYHA class II to IV) undergoing aortic or mitral valve surgery due to aortic or mitral stenosis, aortic or mitral regurgitation, as well as combined aortic or mitral valve lesions (stenosis and regurgitation). In 13 other patients, heart failure was due to hypertrophic obstructive cardiomyopathy (N = 6, NYHA III), tetralogy of Fallot (N = 4, NYHA III), or Becker's muscular dystrophy (N = 3, NYHA IV). Bmax was assessed by (-)-(125I)-iodocyanopindolol used as radioligand. Competition experiments with the highly selective beta 1-adrenoceptor antagonist CGP 20712A were performed for determination of beta 1- and beta 2-adrenoceptor subtypes. In biopsies taken from transplant donors, the Bmax was found to be 70.1 +/- 5.8 fmol/mg protein. In all groups investigated the extent of total beta-adrenoceptor downregulation was related to the degree of heart failure. The decrease in Bmax was found to be about 20% (NYHA II), 45% (NYHA III), and 60% (NYHA IV) when compared with controls. There was no significant difference in the reduction of total beta-adrenoceptor density between isolated aortic or mitral valve diseases and combined valve lesions. Independent of the degree of heart failure, selective downregulation of the beta 1 subtype was found in patients with isolated or combined aortic valve diseases, hypertrophic obstructive cardiomyopathy, and Becker's muscular dystrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

High selectivity for inhibition of phosphodiesterase III and positive inotropic effects of MCI-154 in guinea pig myocardium.

MCI-154 (0.3-100 microM) exerted a concentration-dependent positive inotropic effect in isolated guinea pig papillary muscles (EC50 0.8 microM). The efficacy of MCI-154 (253% of predrug value) was 1.7-fold higher than that of saterinone but comparable to that of milrinone. Carbachol markedly reduced the increase in force of contraction (FOC) of MCI-154. In intact contracting papillary muscles, the positive inotropic effect was accompanied by an increase in cyclic AMP content to 0.78 +/- 0.09 pmol/mg wet weight (n = 10), corresponding to 150% of the basal value (0.51 +/- 0.05 pmol/mg wet weight, n = 21) in the presence of submaximal cyclic AMP phosphodiesterase (PDE) isoenzyme III inhibiting concentrations of MCI-154 (30 microM). MCI-154 (1-1,000 microM) concentration-dependently inhibited the activity of PDE III from homogenates of guinea pig myocardium. The IC50 was 3.8 microM. PDE I, II, and IV were not significantly affected up to 100 microM (PDE I and IV) and up to 1,000 microM (PDE II). In comparison, milrinone and saterinone were PDE III/IV-selective PDE inhibitors. Rolipram inhibited PDE IV only. IBMX and theophylline were nonselective PDE inhibitors. MCI-154 had only a marginal positive chronotropic effect. The frequency of spontaneously beating right auricles from guinea pig heart was increased by 8.7% at most (n = 5). MCI-154 increased Ca2+ sensitivity in chemically skinned porcine ventricular muscle fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Biochemical changes in malignant hyperthermia susceptible swine: cyclic AMP, inositol phosphates, alpha 1, beta 1- and beta 2-adrenoceptors in skeletal and cardiac muscle.

It has been presumed that alteration in the concentrations of second messengers leads to alterations in the function of the ryanodine receptor. Consequently, we have determined the basal content of cyclic AMP and inositol phosphates in skeletal and cardiac muscle of malignant hyperthermia (MH) susceptible (MHS) and healthy normal control (MHN) swine. Since alpha 1- and beta-adrenoceptors are linked to these second messenger systems, the densities of alpha 1- and beta-adrenoceptors were also determined. In skeletal as well as cardiac muscle, a higher basal concentration of almost all of the inositol phosphates was found. Of all inositol phosphates measured, the presumed second messenger inositol 1,4,5-trisphosphate (1,4,5-IP3) was mostly concentrated in both tissues. Each MHS sample contained more 1,4,5-IP3 than the highest value observed in MHN muscle, indicating that a threshold of 1,4,5-IP3 concentration for determination of MHS or MHN status can be defined. In addition, MHS skeletal muscle contained more cAMP than MHN, whereas there was no difference between MHS and MHN in cardiac muscle. The changes observed in the different inositol phosphate and cAMP contents were not accompanied by an altered alpha 1- or beta-adrenoceptor density in skeletal or cardiac muscle between MHS and MHN. However, the total number of beta-adrenoceptors of MHN and MHS was significantly higher in cardiac (about 80 fmol/mg protein) than skeletal muscles (about 30 fmol/mg protein). The cardiac muscles revealed about 80% beta 1- and beta 2- and 20% beta 2-adrenoceptors, whereas skeletal muscles were characterized by over 95% beta 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Evidence for physiological functions of protein phosphatases in the heart: evaluation with okadaic acid.

Okadaic acid exerts a positive inotropic effect in cardiac preparations. We studied whether the positive inotropic effect of okadaic acid in cardiac preparations could be due to phosphatase inhibition and whether this inhibition affects the phosphorylation of cardiac proteins. In papillary muscles from guinea pigs, 30 microM okadaic acid increased force of contraction to 175% of predrug value. In isolated guinea pig ventricular cardiomyocytes, okadaic acid augmented single Ca(2+)-channel currents by enhancing channel availability. In homogenates from ventricles, 1 microM okadaic acid completely inhibited phosphorylase a phosphatase activity. In isolated 32P-labeled ventricular cardiomyocytes, 30 microM okadaic acid increased phosphorylation of phospholamban (PLB) and troponin inhibitor (TnI) to 325 and 284% of control, respectively. Furthermore, 30 microM okadaic acid increased phosphorylation of a hitherto unknown 23-kDa protein to 352% of control. It is concluded that the effects of okadaic acid could be mediated by increasing the phosphorylation state of several proteins including PLB, a 23-kDa protein, and TnI.

Animals↗
PubMed1993

Isoprenaline stimulates gene transcription of the inhibitory G protein alpha-subunit Gi alpha-2 in rat heart.

In vitro transcription reactions were performed with isolated ventricular nuclei of adult rats to investigate whether increased mRNA levels of the inhibitory G protein alpha-subunit Gi alpha-2 after prolonged in vivo stimulation with the beta-adrenoceptor agonist isoprenaline are caused by increased transcription. Rats were treated by a 4-day subcutaneous infusion of isoprenaline (2.4 mg/kg per day) or 0.9% NaCl as control. To avoid the influence of developmental expression patterns, adult rats were chosen for all experiments. Signals for Gi alpha-2 and the stimulatory G protein alpha-subunit Gs alpha were specific and due to hybridization of nascent mRNA transcripts. In the isoprenaline group the transcriptional activity of Gi alpha-2 gene increased to 140% of the control value, whereas gene specific hybridization for Gs alpha remained unchanged. These results show that increased Gi alpha-2 mRNA levels after stimulation with isoprenaline are at least partially caused by enhanced transcription of Gi alpha-2 mRNA.

Animals↗