scholarly journals Studies on the phosphorylation of the inhibitory subunit of troponin during modification of contraction in perfused rat heart

1976 ◽  
Vol 160 (2) ◽  
pp. 295-304 ◽  
Author(s):  
P J England
Keyword(s):  
Cyclic Amp ◽  
Cyclic Gmp ◽  
Rat Heart ◽  
Troponin I ◽  
Cardiac Contractility ◽  
Specific Radioactivity ◽  
Contractile Force ◽  
Adrenergic Stimulation ◽  
Control Value ◽  
Inhibitory Subunit Of Troponin

1. Rat hearts were perfused with 32Pi, and contractile force was increased by positive inotropic agents (agents that increase contractility). The inhibitory subunit of troponin (troponin I) was then isolated by affinity chromatography in 8M-urea, and its 32P content measured. Incorporation of phosphate into the subunit was calculated on the basis of the [gamma-32P]ATP specific radioactivity in the hearts. 2. When hearts were perfused with 30 nM-DL-isoprenaline (N-isopropylnoradrenaline), there was an increase in contractile force over 30s which was paralleled by an increase in troponin I phosphorylation. When hearts were perfused for 25s with increasing concentrations of isoprenaline from 1 NM to 0.6 muM, there was again a parallel increase in contractile force and troponin I phosphorylation. The maximum phosphorylation observed was 1.5 mol of phosphate/mol of troponin I, which was reached after 25s with 0.1 muM-isoprenaline. 3. Hearts were stimulated with a 15s pulse perfusion of 30nM-DL-isoprenaline. There was an increase in contractile force which was followed by a return to the control value within 50s. Troponin I phosphorylation increased to a plateau value which was reached within 30s, and remained constant for 60s after the isoprenaline pulse. Phosphorylase a and 3′:5′-cyclic AMP concentration showed changes similar to that of the contractile force. There was no change in 3′:5′-cyclic GMP concentration. 4. When hearts stimulated with a 15S pulse of isoprenaline were subsequently perfused with 0.6 muM-acetylcholine, the changes in contractile force, phosphorylase a and 3′:5′-cyclic AMP were very similar to those seen with the 15s pulse of isoprenaline alone. Troponin I phosphorylation increased to a maximum 30s after the end of the isoprenaline pulse, but then rapidly decreased during the subsequent 30s. This decrease was preceded by a 60% increase in the concentration of 3′:5′-cyclic GMP. 5. Hearts were perfused with 0.2 muM-glucagon for periods up to 60s. Contractile force showed little change for the first 30s, but then increased rapidly. This was paralleled by changes in 3′:5′-cyclic AMP concentration. Troponin I phosphorylation increased slowly, but the increase in contractile force had reached a maximum before significant phosphorylation had occurred. 6. It is concluded that under certain conditions, e.g. immediately after β-adrenergic stimulation, there is a good correlation between contractile force and troponin I phosphorylation. However, under other conditions, e.g. when contractile force is decreasing after removal of β-adrenergic stimulation or in the presence of glucagon, contractile force and troponin I phosphorylation are not well correlated. These results suggest that mechanisms for modifying cardiac contractility, other than troponin I phosphorylation, must be present in rat heart.

scholarly journals Ruthenium Red inhibits the activation of pyruvate dehydrogenase caused by positive inotropic agents in the perfused rat heart

1983 ◽  
Vol 214 (2) ◽  
pp. 581-585 ◽  
Author(s):  
J G McCormack ◽  
P J England
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Rat Heart ◽  
Contractile Force ◽  
Ruthenium Red ◽  
Inotropic Agents ◽  
Similar Increase ◽  
Perfused Rat Heart ◽  
Control Value ◽  
Positive Inotropic Agents ◽  
Total Enzyme

The increases in the amount of active, non-phosphorylated, pyruvate dehydrogenase caused by positive inotropic agents (from a control value of about 10%, to 40% of total enzyme) in the perfused rat heart could be completely blocked by prior perfusion with 2.5 micrograms of Ruthenium Red/ml. A similar increase caused by 5 mM-pyruvate was not blocked. This concentration of Ruthenium Red caused a 25% decrease in contractile force of hearts perfused in the absence of positive inotropic agents; however, in their presence the contractile force reached the same value in the absence or presence of Ruthenium Red. Neither control nor stimulated phosphorylase a content was affected by Ruthenium Red. Verapamil (0.1 microM) also decreased control contraction (by 40%), but did not block the activation of pyruvate dehydrogenase caused by a rise in extracellular [Ca2+]. The results support the hypothesis that positive inotropic agents activate pyruvate dehydrogenase in rat heart by increasing intramitochondrial [Ca2+].

Tl+-Ions: Influence on Cardiac Contractility

1982 ◽  
Vol 37 (10) ◽  
pp. 995-1005 ◽  
Author(s):  
R. Ziskoven ◽  
C. Achenbach ◽  
J. Wiemer ◽  
U. Winter
Keyword(s):  
Cardiac Contractility ◽  
Contractile Force ◽  
Slow Inward Current ◽  
Cellular Energy ◽  
Control Value ◽  
Intentional Ingestion ◽  
Beating Rate ◽  
Series Of Experiments ◽  
Thallium Exposure ◽  
Control Behaviour

Abstract Attention has recently focussed on the heavy metal thallium as an environmental contaminant of increasing importance. From accidental or suicidal ingestions of thallium it has been known for many years that cardiovascular disorders regularly emerge, and for this reason, a variety of investigations of cardiological interest have been conducted. Amongst these, the effects of thallium on the contractile force o f isolated myocardial tissues have been studied. Previous experiments were all carried out at concentrations far beyond those encountered during intoxication and yielded controversal data. We therefore reinvestigated the effects of thallium on myocardial tissue at levels between 10-8 and 10-3 ᴍ, thus covering the range o f thallium concentrations encountered after uptake from a polluted environm ent through those seen after unintentional or intentional ingestion to levels at which previous studies were performed.Sheep interventricular cordis muscles were used at a stimulation frequency of 0.4 Hz showing three types of responses to thallium exposure. From a total of 32 experim ents in 15% of all cases thallium caused a persistant increase in contractility which tended to decrease with time and thallium concentration but always remained greater than the control value.50% of the experiments showed a progressive loss of contractile force with time and thallium concentration, despite transient increases in contractility which lasted for only 2-5 m in after the application of each new thallium concentration. A combination o f these types of reaction was observed in the remaining experiments in that at low thallium concentrations myocardial contractility increased considerably but then decreased progressively with time and thallium concentration. Guinea pig papillary muscles were used to test one thallium concentration only for up to 75 min. At 10-8 ᴍ there was no effect, at 10-7 , 10-6 , 10-5 ᴍ Tl+ there were positive inotropic transients follow ed by an inotropic decay; at 10- 4 M Tl+ only a progressive decrease of contractility was observed.The relationships between time and thallium concentration at different rates of stimulation were examined in two series of experiments at 0.1, 0.2, 0.4, 1.0, and 2.0 Hz. The effects of thallium were accelerated with increased beating rate and the decay o f contraction also proceeded to markedly lower levels. In the rested state, thallium was also very effectual; this was illustrated in two series o f experiments in which after 10 min intervals of quiescency 15 or more test stimuli were applied at different beating rates (0.1 to 2.0 Hz).The configurations of the resulting staircase phenomena were analyzed with respect to control behaviour for each frequency of the test stimuli and for each thallium concentration. These results suggested an involvement of the slow inward current. The steady state values after quiescency showed a pronounced thallium-induced decay similar to that obtained at high constant stimulation rates. The effects are discussed in terms of distortion of cellular energy production by thallium.

The Effect of Noradrenaline and Tyramine on Cardiac Contractility, Cyclic AMP, and Phosphorylase a in Normal and Hyperthyroid Rats

1974 ◽  
Vol 52 (3) ◽  
pp. 375-383 ◽  
Author(s):  
Beverley A. Young ◽  
John H. McNeill
Keyword(s):  
Cyclic Amp ◽  
Rat Heart ◽  
Cardiac Contractility ◽  
Time Response ◽  
Dependent Manner ◽  
Perfused Rat Heart ◽  
Isolated Perfused Rat Heart ◽  
Hyperthyroid State ◽  
Dose Dependent ◽  
Higher Doses

Noradrenaline and tyramine increased contractility, phosphorylase a, and cyclic AMP in a dose-dependent manner in the isolated perfused rat heart. Time–response studies revealed that cyclic AMP was increased by both amines before the increase in contractility. Hearts from hyperthyroid rats responded to noradrenaline in a manner similar to control hearts when contractility or cyclic AMP was measured. The phosphorylase activating effect of noradrenaline was enhanced in the hyperthyroid hearts. It was concluded that a non-cyclic AMP mechanism was involved in the enhancement. The effects of tyramine on contractility and cyclic AMP were decreased in the hearts from hyperthyroid animals when compared with control hearts. Phosphorylase activation by tyramine was not enhanced by the hyperthyroid state and was in fact reduced at higher doses of tyramine.

scholarly journals PDE1 inhibition modulates Cav1.2 channel to stimulate cardiomyocyte contraction

2020 ◽  
Author(s):  
Grace K Muller ◽  
Joy Song ◽  
Vivek Jani ◽  
Yuejin Wu ◽  
Mark E Anderson ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Troponin I ◽  
Cardiac Contractility ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Dependent Manner ◽  
Adrenergic Stimulation ◽  
Inotropic Effects ◽  
Intracellular Ca ◽  
Adenylate Cyclase Stimulation

ABSTRACTRationaleCyclic adenosine monophosphate (cAMP) activation of protein kinase A (PKA) stimulates excitation-contraction coupling, increasing cardiac contractility. This is clinically leveraged by beta-adrenergic stimulation (β-ARs) or phosphodiesterase-3 inhibition (PDE3i), though both approaches are limited by arrhythmia and chronic myocardial toxicity. Phosphodiesterase-1 inhibition (PDE1i) also augments cAMP and was recently shown in rabbit cardiomyocytes to augment contraction independent of β-AR stimulation or blockade, and with less intracellular calcium rise than β-ARs or PDE3i. Early testing of PDE1 inhibition in humans with neuro-degenerative disease and dilated heart failure has commenced. Yet, the molecular mechanisms for PDE1i inotropic effects remain largely unknown.ObjectiveDefine the mechanism(s) whereby PDE1i increases contractility.Methods and ResultsPrimary guinea pig myocytes which express the cAMP-hydrolyzing PDE1C isoform found in larger mammals and humans were studied. The potent, selective PDE1i (ITI-214) did not alter cell shortening or Ca2+ transients under resting conditions whereas both increased with β-ARs or PDE3i. However, PDE1i enhanced shortening with less Ca2+ rise in a PKA-dependent manner when combined with low-dose adenylate cyclase stimulation (Forskolin). Unlike PDE3i, PDE1i did not augment β-AR responses. Whereas β-ARs reduced myofilament Ca2+ sensitivity and increased sarcoplasmic reticular Ca2+ content in conjunction with greater phosphorylation of troponin I, myosin binding protein C, and phospholamban, PDE1i did none of this. However, PDE1i increased Cav1.2 channel conductance similar to PDE3i in a PKA-dependent manner. Myocyte shortening and peak Ca2+ transients were more sensitive to Cav1.2 blockade with nitrendipine combined with PDE1i versus PDE3i. Lastly, PDE1i was found to be far less arrythmogenic than PDE3i.ConclusionsPDE1i enhances contractility by a PKA-dependent increase in Cav1.2 conductance without concomitant myofilament desensitization. The result is less rise in intracellular Ca2+ and arrhythmia compared to β-ARs and/or PDE3i. PDE1i could be a novel positive inotrope for failing hearts without the toxicities of β-ARs and PDE3i.

scholarly journals Effects of forskolin on contractile responses and protein phosphorylation in the isolated perfused rat heart

1987 ◽  
Vol 246 (3) ◽  
pp. 687-695 ◽  
Author(s):  
P J England ◽  
M Shahid
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Rat Heart ◽  
Kinase Activity ◽  
Troponin I ◽  
Contractile Proteins ◽  
Protein Kinase Activity ◽  
Dependent Protein Kinase ◽  
Perfused Rat Heart ◽  
Dependent Protein

Continuous perfusion of rat hearts with concentrations of forskolin between 0.1 and 12 microM resulted in transient increases in tension after 45 s, followed by a return to the control value after 5 min. In contrast, the content of cyclic AMP increased linearly with time over this period, reaching values up to 35 times control after 5 min. Increases in contractile force, intracellular cyclic AMP concentration and the proportion of phosphorylase in the a form were dependent on the concentration of forskolin when measured 45 s and 120 s after initiation of perfusion. In hearts perfused for 45 s with various concentrations of forskolin, the measured cyclic AMP-dependent protein kinase activity ratio and phosphorylase a content for a given measured intracellular cyclic AMP concentration were both much less than the corresponding values in hearts perfused for 30 s with various concentrations of isoprenaline. The phosphorylation of the contractile proteins troponin-I and C-protein also showed a concentration-dependent increase in hearts perfused with forskolin. There was a strong correlation between the cyclic AMP-dependent protein kinase activity ratios and the phosphorylation of the contractile proteins under all perfusion conditions. These results suggest that cyclic AMP is compartmented in perfused rat heart, and that much of the cyclic AMP produced in response to forskolin is unavailable to activate cyclic AMP-dependent protein kinase.

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