Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Single ventricular myocytes were enzymatically isolated, incubated with the A1-purinergic and beta-adrenergic receptor-specific agonists N6-cyclopentyladenosine (CPA) and isoprenaline (Iso), and then rapidly skinned. Ca2+ sensitivity of isometric tension and unloaded shortening velocity (Vo) were measured, and protein kinase A (PKA)-specific phosphorylations of troponin I (TnI) and C-protein were assessed by back-phosphorylation of cell suspensions with [gamma-32P]-ATP. 2. Isoprenaline treatment decreased the Ca2+ sensitivity of isometric tension relative to propranolol-treated controls, as did simultaneous stimulation with Iso and CPA (Iso + CPA). CPA alone had no effect on Ca2+ sensitivity. Vo was greater in Iso-treated cells than in paired controls, while Vo was significantly less than control in both Iso + CPA-treated and CPA-treated cells. 3. Phosphorylation of TnI and C-protein was increased by Iso treatment and also when Iso and CPA were simultaneously applied. CPA alone caused a significant decrease in the phosphorylation state of these two proteins. 4. From these results we conclude that A1-purinergic receptor stimulation does not inhibit beta-adrenergic receptor-mediated phosphorylation of myofilament proteins, nor does it alter the Ca2+ sensitivity of isometric tension at the level of the myofilaments. However, A1-receptor stimulation does decrease Vo at the level of the myofilaments by a mechanism that is independent of beta-adrenergically mediated phosphorylation of TnI and C-protein.
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PMID:Slowing of shortening velocity of rat cardiac myocytes by adenosine receptor stimulation regardless of beta-adrenergic stimulation. 747 28

We studied the Ca2+ responsiveness of skinned muscle fibre preparations from the right and left ventricles of normal (FIB) and genetically cardiomyopathic (Bio-To-2) Syrian hamsters. Thus, we compared the Ca2+/force relationships of preparations from myopathic hamsters to those of age-matched (11-16 months old) normal animals. The pCa (i.e. -log10 [Ca2+]) required for 50% force activation (Ca2+ sensitivity) was higher in the myopathic hamsters than in controls (pCa50 values of 5.3 +/- 0.03 and 5.17 +/- 0.04, respectively); this difference might be due to an alteration in regulatory proteins. Indeed, after extraction (with vanadate) and replacement of troponin I with bovine cardiac troponin the pCa50 values were similar (pCa 5.35) to those of bovine ventricular fibres. The Ca2+ sensitizer EMD 53998 (10 microM) increased Ca2+ sensitivity in preparations from normal and cardiomyopathic hamsters equally, by 0.4 pCa units. Incubation of fibre bundles with the catalytic subunit of cyclic-adenosine-monophosphate-dependent protein kinase decreased Ca2+ sensitivity, thereby "normalizing" the enhanced Ca2+ responsiveness of fibres from cardiomyopathic hamsters. It is not clear, however, whether the pathologically increased Ca2+ sensitivity of the hearts of aged myopathic hamsters reflects a maladaptation, or a compensatory mechanism of the failing heart.
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PMID:Myofibrillar Ca2+ sensitivity of cardiomyopathic hamster hearts. 761 44

Two serine residues located adjacently in the heart-specific N-terminus of cardiac troponin I can be phosphorylated in vivo. Both residues are sequentially phosphorylated and dephosphorylated by cAMP-dependent protein kinase (PKA) and protein phosphatase 2A (PP2A). The concentration changes of the different troponin I species have been determined separately for the phosphorylation and dephosphorylation reaction and approximated by time courses predicted by a reaction model. Dependent on the concentration ratio of active protein kinase/protein phosphatase, four different troponin I species can be generated; one nonphosphorylated, two monophosphorylated and one bisphosphorylated. This pattern generation will be observed in proteins phosphorylated and dephosphorylated by a single protein kinase and phosphatase on more than one site and is a new principle inherent in signal cascades.
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PMID:Pattern formation on cardiac troponin I by consecutive phosphorylation and dephosphorylation. 763 59

To characterize the effect of an altered substrate utilization for cardiac sarcoplasmic reticulum (SR) Ca2+ transport, normotensive rats were treated for 5 wk with 15 mg.kg-1.day-1 enantiomeric etomoxir, which inhibits mitochondrial carnitine palmitoyltransferase-1 (CPT-1) and fatty acid synthesis. Ca2+ uptake rates of left and right ventricular homogenates were differentially (P < 0.05, two-way analysis of variance) increased by 38 and 13%, respectively. Increased (P < 0.05) transport rates were also observed in the presence of ryanodine. The differences were considerably reduced in the protein kinase A-stimulated state. The levels of phosphorylated phospholamban (PLB) and troponin I as well as immunoreactive PLB were not affected. By contrast, phosphoenzyme levels (E-P) of the SR Ca2+ pump were increased in left ventricular (LV) homogenates. Values of LV E-P and Ca2+ uptake were linearly correlated (P < 0.05) with the myosin V1 proportions in control (31.7 +/- 1.8% V1) and treated (58.3 +/- 2.5% V1) rats. Thus in the left ventricle the metabolic influences have a coordinated action on two distinct proteins involved in relaxation or contraction. The chamber-specific differences in SR function suggest a more pronounced effect of etomoxir in functional states characterized by a reduced Ca2+ transport rate and myosin V1 proportion.
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PMID:CPT-1 inhibition by etomoxir has a chamber-related action on cardiac sarcoplasmic reticulum and isomyosins. 781 Jul 10

During development of the myocardium the troponin I (TNI) isoform expression is switched from a cAMP-insensitive, slow skeletal muscle TNI to a cAMP-sensitive, cardiac TNI isoform (cTNI). To study the functional consequence of alterations in cTNI expression in the rat heart we investigated the cAMP-controlled cTNI phosphorylation in comparison with alterations of functional properties of isolated cardiac myofibrils during the first postnatal month. cTNI was identified by Western blot analysis followed by a semiquantitative assessment. From the third to the 28th postnatal day the relative concentrations of the cardiac isoform of TNI increased 2.9 +/- 0.3-fold. In the same period the amount of phosphate incorporated into cTNI in the presence of exogenous cAMP-dependent protein kinase (PKA) and 32P[gamma]-ATP was increased 5.8 +/- 0.2-fold (24.2 +/- 3.5 v 140.2 +/- 7.6 pmolP/mg protein loaded onto the gel) whereas the phosphorylation of C-protein was only increased 1.6 +/- 0.2-fold. Ca(2+)-activated isometric tension generation of skinned heart fibres measured in the range of pCa from 6 to 4.5 was not affected by PKA at day 3. However, isometric tension generation of fibres prepared from 28-day-old rats was suppressed by incubation with PKA which was accompanied by a rightward shift in the force/pCa relation. Under these conditions half-maximal tension development was found at pCa 5.38 v 5.52 (p < 0.05) in the absence of PKA. The Ca2+ sensitivity of the contractile apparatus was not affected by PKA-induced phosphorylation of C-protein. These data give direct evidence for the physiological relevance of the onset of cAMP-induced phosphorylation of cTNI for the Ca(2+)-activated tension generation in cardiac myofibrils during postnatal development.
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PMID:Cardiac troponin I and tension generation of skinned fibres in the developing rat heart. 781 56

Two patients were investigated for unexplained increases in troponin T. In the first patient, who had rhabdomyolysis and acute renal failure, troponin T reached a peak value of 13.50 micrograms/L (67.5-fold the upper reference limit). The second patient had chronic renal failure and the troponin T peak value was 2.85 micrograms/L (14.3-fold the upper reference limit). Clinical investigations indicated no evidence of myocardial damage. Serum or plasma specimens were analyzed for total creatine kinase (CK), CK-2 mass, CK-2 isoform ratio, myoglobin, troponin T, troponin I, and myosin light chains; all except troponin I were at above-normal concentrations. We also investigated six additional renal patients with above-normal troponin T; troponin I was slightly increased in only one of these six patients. Our findings demonstrate discordance between results for troponin T and troponin I in renal patients.
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PMID:Discordance between results for serum troponin T and troponin I in renal disease. 758 66

The interaction of troponin I (CTnI) with troponin C (CTnC) from bovine cardiac muscle was studied using CTnC modified at Cys35 and Cys84 with the fluorescent probe 2-[(4'-iodoacetamido)-anilino]naphthalene-6-sulfonic acid (CTnCIAANS). The association constant for complex formation between the two proteins was determined at 20 degrees C in 0.4 M KCl, 1 mM DTT, 1 mM EGTA, and 25 mM MOPS, pH 7.2. In the presence of EGTA, Mg2+, and Ca2+ these constants were 1.46 x 10(7), 4.1 x 10(7), and 12.7 x 10(7) M-1, respectively, with corresponding free energy values of -9.62, -10.23, and -10.88 kcal mol-1. The CTnI-CTnCIAANS complex was stabilized by -0.61 kcal when the two Ca/Mg sites of CTnCIAANS were saturated with Mg2+ and by -1.26 kcal when all three Ca2+ sites were occupied by Ca2+. These results suggest that calcium activation in cardiac muscle may be accompanied by a coupling free energy of -0.65 kcal. This value is a factor of 4 smaller than the value previously determined, using a similar method, for the (troponin I).(troponin C) complex from skeletal muscle [Wang, C.-K., & Cheung, H.C. (1985) Biophys. J.48, 727-739]. Since CTnC has only one Ca(2+)-specific site and troponin C from skeletal muscle has two such sites, the present result is a factor of 2 smaller than that for the skeletal complex on the basis of a single specific site. Phosphorylation of CTnI by 3',5'-cyclic AMP-dependent protein kinase resulted in a decrease of the association constants by a factor of 2.5-3.5.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Coupling of calcium to the interaction of troponin I with troponin C from cardiac muscle. 791 99

Phosphorylation of phospholamban and troponin I of dog hearts was measured depending on the cardiac cycle. Myocardium biopsies were obtained with the help of an ECG-triggered cryobiopsy device. A standardized back phosphorylation technique was performed with (32P)ATP and an excess of exogenically applied c-AMP dependent protein kinase, which was followed by electrophoretic fractionation. This standardized method enables quantitative measuring especially of the c-AMP-stimulated protein phosphorylation. A dichotomous behaviour in the phosphorylation of troponin I and phospholamban was detected in the cardiac cycle. Like c-AMP and the c-AMP depended protein kinase troponin I reach a maximum phosphorylation in the systole. In contrast to this, phospholamban in vivo shows the highest degree of phosphorylation in the diastole and drops to a significant lower value (by approximately 25%) in the systole. The surprising dichotomy support the assumption that the Ca-detensivation of the contractile proteins by phosphorylation of troponin I was a dynamic counterregulation in the presence of a high Ca-level takes effect before the Ca-accumulation which can be stimulated by phospholamban. The results show that covalent modifications of regulatory proteins come to pass in the ms-range and have to be considered in distinctive conditions of myocardial function.
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PMID:[Basic research in cardiology]. 794 Dec 18

The plant phenol tannin stimulated severalfold the Ca(2+)-dependent ATPase and Ca(2+)-uptake activities of dog cardiac sarcoplasmic reticulum (SR) with an EC50 value of 0.6 microM. The stimulation was due to a marked increase in the apparent affinity of the cardiac SR ATPase for Ca2+ ions while the Vmax was not affected. No stimulation of skeletal muscle SR preparations could be observed. The characteristics of stimulation were similar to those observed after phosphorylation of the regulatory protein phospholamban (PLN) by protein kinase A. The ability of protein kinase A to phosphorylate PLN was prevented by tannin with an IC50 of 3 microM. Phosphorylation of troponin I, another physiological substrate of protein kinase A, was resistant to tannin inhibition. The data show that submicromolar concentrations of tannin prevent PLN phosphorylation by interacting with the cytosolic portion of PLN. The specific binding of tannin reverses the inhibition that PLN exerts on cardiac SR ATPase.
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PMID:Reversal of phospholamban-induced inhibition of cardiac sarcoplasmic reticulum Ca(2+)-ATPase by tannin. 806 Mar 55

In vitro biochemical experiments have suggested that stimulation of beta-adrenergic receptor may increase the rate of crossbridge cycling in mammalian myocardium, but recent attempts to demonstrate a mechanical correlate have yielded conflicting results. To investigate this issue, we measured the effect of isoproterenol (ISO) and cAMP-dependent protein kinase (PKA) on unloaded shortening velocity (Vo). Vo is thought to be determined by the rate-limiting step of the crossbridge cycle, ie, the rate of crossbridge detachment from actin, and is therefore an index of the cycling rate. Single rat ventricular myocytes were enzymatically isolated, incubated in Ringer's solution without (control) or with 0.1 mumol/L ISO, and then rapidly skinned. Some control cells were subsequently treated with 3 micrograms/mL PKA for 40 minutes. Vo was then measured during maximal activation (pCa 4.5) in control, ISO-treated, and PKA-treated cells using the slack-test method. To test the efficacy of the agonist treatments, Ca2+ sensitivity of isometric tension was also assessed for each treatment by determining the [Ca2+] required for half-maximal tension (ie, pCa50). Both ISO and PKA treatment reduced the Ca2+ sensitivity of isometric tension compared with same-day control cells, in agreement with previous studies in intact and in skinned preparations. Vo was increased 38% by ISO treatment and 41% by PKA treatment compared with same-day control cells. 32P autoradiography showed that troponin I and C protein were the principal proteins phosphorylated by PKA treatment. We conclude that beta-adrenergic stimulation increases the rate of crossbridge release from actin, by a mechanism that most likely involves the phosphorylation of troponin I and/or C protein by PKA.
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PMID:Beta-adrenergic receptor stimulation increases unloaded shortening velocity of skinned single ventricular myocytes from rats. 811 62


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