Caffeine alters cardiac myofilament activity and regulation independently of Ca2+ binding to troponin C

1995 ◽  
Vol 268 (6) ◽  
pp. C1348-C1353 ◽  
Author(s):  
F. M. Powers ◽  
R. J. Solaro
Keyword(s):  
Atpase Activity ◽  
Isometric Force ◽  
Troponin C ◽  
Fiber Bundles ◽  
Direct Effects ◽  
Skinned Fiber ◽  
Myofilament Function ◽  
Cardiac Myofilament ◽  
Myosin Interaction ◽  
Skinned Fiber Bundles

We investigated the mechanism by which caffeine influences myofilament responsiveness to Ca2+ by measuring isometric force, Ca2+ binding, and ATPase activity of dog cardiac myofilament proteins. Caffeine (20 mM) increased submaximal and depressed maximal force in skinned fiber bundles. Although the Ca2+ sensitivity of myofilament activity was increased by caffeine, there was no effect on Ca2+ binding to troponin C (TnC) in skinned fiber bundles. To determine if caffeine altered actin-myosin interaction or affected myosin directly, myofibrillar, actomyosin, and myosin ATPase activities were measured. Maximal Ca(2+)-activated myofibrillar Mg(2+)-ATPase activity was depressed by 20 mM caffeine, whereas submaximal Mg(2+)-ATPase activities were not changed. Actomyosin Mg(2+)-ATPase activity was significantly depressed by caffeine concentrations > or = 15 mM. Myosin Ca(2+)-ATPase activity was depressed by caffeine, whereas Mg(2+)-ATPase and K(EDTA)-ATPase activities were not affected. These data suggest that caffeine affects myofilament function via a mechanism that is independent of TnC-Ca2+ binding but that may involve direct effects on actin-cross-bridge interaction.

CGP-48506 increases contractility of ventricular myocytes and myofilaments by effects on actin-myosin reaction

1996 ◽  
Vol 270 (1) ◽  
pp. H24-H32 ◽  
Author(s):  
B. M. Wolska ◽  
Y. Kitada ◽  
K. A. Palmiter ◽  
M. V. Westfall ◽  
M. D. Johnson ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Late Phase ◽  
Troponin C ◽  
Fiber Bundles ◽  
Intact Cells ◽  
Fura 2 ◽  
Skinned Fiber ◽  
Force Relation ◽  
Skinned Fiber Bundles ◽  
Cgp 48506

We measured the effects of the benzodiazocine derivative, CGP-48506 (5-methyl-6-phenyl-1,3,5,6-tetrahydro-3,6-methano-1, 5-benzodiazocine-2,4-dione), on contraction of intact myocytes and permeabilized fibers of rat ventricular muscle. CGP-48506 is unique in that it is able to sensitize cardiac myofilaments to Ca2+, but unlike all other agents in this class, it is not an inhibitor of type III phosphodiesterase. When added to isolated intact myocytes, CGP-48506 significantly increased the amplitude of cell shortening with little or no change in the Ca2+ transient, as determined by the fluorescence ratio of fura 2. The late phase of the relation between fura 2 ratio and cell length was shifted to the left in the presence of CGP-48506. CGP-48506 also induced a relatively small decrease in diastolic length. However, compared with the thiadiazinone EMD-57033, CGP-48506 had a much smaller effect on diastolic length at concentrations in which there was a bigger inotropic effect. When added to solutions bathing detergent-extracted (skinned) fiber bundles, CGP-48506 increased maximum force. CGP-48506 also increased submaximal force and shifted the pGa-force relation to the left. However, compared with EMD-57033, there was less of an effect of CGP-48506 on force at relatively high pCa values. CGP-48506 did not alter Ca2+ binding to myofilament troponin C. CGP-48506 was able to reverse inhibition of contraction induced by butanedione monoxime both in intact cells and in skinned fiber bundles. Our results indicate that CGP-48506, like EMD-57033, is a positive inotropic agent working through a direct effect downstream from troponin C. CGP-48506, however, appears to have a unique mechanism resulting in less effect on diastolic function.

scholarly journals Biphasic Ca2+ dependence of inositol 1,4,5-trisphosphate-induced Ca release in smooth muscle cells of the guinea pig taenia caeci.

1990 ◽  
Vol 95 (6) ◽  
pp. 1103-1122 ◽  
Author(s):  
M Iino
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Smooth Muscle Cells ◽  
Feedback Loop ◽  
Muscle Cells ◽  
Fiber Bundles ◽  
Release Mechanism ◽  
Skinned Fiber ◽  
Inositol 1,4,5 Trisphosphate ◽  
Skinned Fiber Bundles

Ca2+ dependence of the inositol 1,4,5-trisphosphate (IP3)-induced Ca release was studied in saponin-skinned smooth muscle fiber bundles of the guinea pig taenia caeci at 20-22 degrees C. Ca release from the skinned fiber bundles was monitored by microfluorometry of fura-2. Fiber bundles were first treated with 30 microM ryanodine for 120 s in the presence of 45 mM caffeine to lock open the Ca-induced Ca release channels which are present in approximately 40% of the Ca store of the smooth muscle cells of the taenia. The Ca store with the Ca-induced Ca release mechanism was functionally removed by this treatment, but the rest of the store, which was devoid of the ryanodine-sensitive Ca release mechanism, remained intact. The Ca2+ dependence of the IP3-induced Ca release mechanism was, therefore, studied independently of the Ca-induced Ca release. The rate of IP3-induced Ca release was enhanced by Ca2+ between 0 and 300 nM, but further increase in the Ca2+ concentration also exerted an inhibitory effect. Thus, the rate of IP3-induced Ca release was about the same in the absence of Ca2+ and at 3 microM Ca2+, and was about six times faster at 300 nM Ca2+. Hydrolysis of IP3 within the skinned fiber bundles was not responsible for these effects, because essentially the same effects were observed with or without Mg2+, an absolute requirement of the IP3 phosphatase activity. Ca2+, therefore, is likely to affect the gating mechanism and/or affinity for the ligand of the IP3-induced Ca release mechanism. The biphasic effect of Ca2+ on the IP3-induced Ca release is expected to form a positive feedback loop in the IP3-induced Ca mobilization below 300 nM Ca2+, and a negative feedback loop above 300 nM Ca2+.

scholarly journals The effect of calcium activation of skinned fiber bundles on the structure of Limulus thick filaments.

1991 ◽  
Vol 113 (3) ◽  
pp. 573-583 ◽  
Author(s):  
R J Levine ◽  
J L Woodhead ◽  
H A King
Keyword(s):  
Thick Filament ◽  
Distal Region ◽  
Fiber Bundles ◽  
Direct Result ◽  
Elastic Recoil ◽  
Calcium Activation ◽  
Skinned Fiber ◽  
Molecular Weights ◽  
Thick Filaments ◽  
Skinned Fiber Bundles

Here we present evidence that strongly suggests that the well-documented phenomenon of A-band shortening in Limulus telson muscle is activation dependent and reflects fragmentation of thick filaments at their ends. Calcium activation of detergent-skinned fiber bundles of Limulus telson muscle results in large decreases in A-band (from 5.1 to 3.3 microns) and thick filament (from 4.1 to 3.3 microns) lengths and the release of filament end fragments. In activated fibers, maintained stretched beyond overlap of thick and thin filaments, these end fragments are translocated to varying depths within the I-bands. Here they are closely associated with fine filamentous structures that also span the gap between A- and I-bands and attach to the distal one-third of the thick filaments. End-fragments are rarely, if ever, present in similarly stretched and skinned, but unstimulated fibers, although fine "gap filaments" persist. Negatively stained thick filaments, separated from skinned, calcium-activated, fiber bundles, allowed to shorten freely, are significantly shorter than those obtained from unstimulated fibers, but are identical to the latter with respect to both the surface helical array of myosin heads and diameters. Many end-fragments are present on grids containing thick filaments from activated fibers; few, if any, on those from unstimulated fibers. SDS-PAGE shows no evidence of proteolysis due to activation and demonstrates the presence of polypeptides with very high molecular weights in the preparations. We suggest that thick filament shortening is a direct result of activation in Limulus telson muscle and that it occurs largely by breakage within a defined distal region of each polar half of the filament. It is possible that at least some of the fine "gap filaments" are composed of a titin-like protein. They may move the activation-produced, fragmented ends of thick filaments to which they attach, into the I-bands by elastic recoil, in highly stretched fibers.

Troponin I serines 43/45 and regulation of cardiac myofilament function

2002 ◽  
Vol 283 (3) ◽  
pp. H1215-H1224 ◽  
Author(s):  
W. Glen Pyle ◽  
Marius P. Sumandea ◽  
R. John Solaro ◽  
Pieter P. De Tombe
Keyword(s):  
Cardiac Troponin ◽  
Troponin I ◽  
Troponin T ◽  
Fiber Bundles ◽  
Maximum Tension ◽  
Myofilament Function ◽  
Cardiac Myofilament ◽  
Myofilament Activation ◽  
Tension Cost ◽  
Mgatpase Activity

We studied Ca2+ dependence of tension and actomyosin ATPase rate in detergent extracted fiber bundles isolated from transgenic mice (TG), in which cardiac troponin I (cTnI) serines 43 and 45 were mutated to alanines (cTnI S43A/S45A). Basal phosphorylation levels of cTnI were lower in TG than in wild-type (WT) mice, but phosphorylation of cardiac troponin T was increased. Compared with WT, TG fiber bundles showed a 13% decrease in maximum tension and a 20% increase in maximum MgATPase activity, yielding an increase in tension cost. Protein kinase C (PKC) activation with endothelin (ET) or phenylephrine plus propranolol (PP) before detergent extraction induced a decrease in maximum tension and MgATPase activity in WT fibers, whereas ET or PP increased maximum tension and stiffness in TG fibers. TG MgATPase activity was unchanged by ET but increased by PP. Measurement of protein phosphorylation revealed differential effects of agonists between WT and TG myofilaments and within the TG myofilaments. Our results demonstrate the importance of PKC-mediated phosphorylation of cTnI S43/S45 in the control of myofilament activation and cross-bridge cycling rate.

scholarly journals Peroxisome proliferator-activated receptor-α expression induces alterations in cardiac myofilaments in a pressure-overload model of hypertrophy

2017 ◽  
Vol 312 (4) ◽  
pp. H681-H690 ◽  
Author(s):  
Chehade N. Karam ◽  
Chad M. Warren ◽  
Marcus Henze ◽  
Natasha H. Banke ◽  
E. Douglas Lewandowski ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Negative Impact ◽  
Pressure Overload ◽  
Fiber Bundles ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Skinned Fiber ◽  
Skinned Fiber Bundles

Although alterations in fatty acid (FA) metabolism have been shown to have a negative impact on contractility of the hypertrophied heart, the targets of action remain elusive. In this study we compared the function of skinned fiber bundles from transgenic (Tg) mice that overexpress a relatively low level of the peroxisome proliferator-activated receptor α (PPARα), and nontransgenic (NTg) littermates. The mice (NTg-T and Tg-T) were stressed by transverse aortic constriction (TAC) and compared with shams (NTg-S and Tg-S). There was an approximate 4-fold increase in PPARα expression in Tg-S compared with NTg-S, but Tg-T hearts showed the same PPARα expression as NTg-T. Expression of PPARα did not alter the hypertrophic response to TAC but did reduce ejection fraction (EF) in Tg-T hearts compared with other groups. The rate of actomyosin ATP hydrolysis was significantly higher in Tg-S skinned fiber bundles compared with all other groups. Tg-T hearts showed an increase in phosphorylation of specific sites on cardiac myosin binding protein-C (cMyBP-C) and β-myosin heavy chain isoform. These results advance our understanding of potential signaling to the myofilaments induced by altered FA metabolism under normal and pathological states. We demonstrate that chronic and transient PPARα activation during pathological stress alters myofilament response to Ca2+ through a mechanism that is possibly mediated by MyBP-C phosphorylation and myosin heavy chain isoforms. NEW & NOTEWORTHY Data presented here demonstrate novel signaling to sarcomeric proteins by chronic alterations in fatty acid metabolism induced by PPARα. The mechanism involves modifications of key myofilament regulatory proteins modifying cross-bridge dynamics with differential effects in controls and hearts stressed by pressure overload.

Ca2+, pH and the regulation of cardiac myofilament force and ATPase activity

1989 ◽  
Vol 89 (2) ◽  
Author(s):  
R.John Solaro ◽  
SalehC. El-Salehl ◽  
JonC. Kentish
Keyword(s):  
Atpase Activity ◽  
Cardiac Myofilament

Skeletal muscle force and actomyosin ATPase activity reduced by nitric oxide donor

1997 ◽  
Vol 83 (4) ◽  
pp. 1326-1332 ◽  
Author(s):  
William J. Perkins ◽  
Young-Soo Han ◽  
Gary C. Sieck
Keyword(s):  
Nitric Oxide ◽  
Mechanical Properties ◽  
Atpase Activity ◽  
Muscle Force ◽  
Isometric Force ◽  
Nitric Oxide Donor ◽  
No Donor ◽  
Single Fibers ◽  
Actomyosin Atpase ◽  
Cross Bridge

Perkins, William J., Young-Soo Han, and Gary C. Sieck.Skeletal muscle force and actomyosin ATPase activity reduced by nitric oxide donor. J. Appl. Physiol.83(4): 1326–1332, 1997.—Nitric oxide (NO) may exert direct effects on actin-myosin cross-bridge cycling by modulating critical thiols on the myosin head. In the present study, the effects of the NO donor sodium nitroprusside (SNP; 100 μM to 10 mM) on mechanical properties and actomyosin adenosinetriphosphatase (ATPase) activity of single permeabilized muscle fibers from the rabbit psoas muscle were determined. The effects of N-ethylmaleimide (NEM; 5–250 μM), a thiol-specific alkylating reagent, on mechanical properties of single fibers were also evaluated. Both NEM (≥25 μM) and SNP (≥1 mM) significantly inhibited isometric force and actomyosin ATPase activity. The unloaded shortening velocity of SNP-treated single fibers was decreased, but to a lesser extent, suggesting that SNP effects on isometric force and actomyosin ATPase were largely due to decreased cross-bridge recruitment. The calcium sensitivity of SNP-treated single fibers was also decreased. The effects of SNP, but not NEM, on force and actomyosin ATPase activity were reversed by treatment with 10 mMdl-dithiothreitol, a thiol-reducing agent. We conclude that the NO donor SNP inhibits contractile function caused by reversible oxidation of contractile protein thiols.

Altered hemodynamics in transgenic mice harboring mutant tropomyosin linked to hypertrophic cardiomyopathy

2000 ◽  
Vol 279 (5) ◽  
pp. H2414-H2423 ◽  
Author(s):  
Christian C. Evans ◽  
James R. Pena ◽  
Ronald M. Phillips ◽  
Mariappan Muthuchamy ◽  
David F. Wieczorek ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Protein Kinase ◽  
Left Ventricular ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Fiber Bundles ◽  
Papillary Muscles ◽  
Adrenergic Stimulation ◽  
Skinned Fiber Bundles ◽  
Force Relationship ◽  
Kinase A

We used transgenic (TG) mice overexpressing mutant α-tropomyosin [α-Tm(Asp175Asn)], linked to familial hypertrophic cardiomyopathy (FHC), to test the hypothesis that this mutation impairs cardiac function by altering the sensitivity of myofilaments to Ca2+. Left ventricular (LV) pressure was measured in anesthetized nontransgenic (NTG) and TG mice. In control conditions, LV relaxation was 6,970 ± 297 mmHg/s in NTG and 5,624 ± 392 mmHg/s in TG mice ( P < 0.05). During β-adrenergic stimulation, the rate of relaxation increased to 8,411 ± 323 mmHg/s in NTG and to 6,080 ± 413 mmHg/s in TG mice ( P < 0.05). We measured the pCa-force relationship (pCa = −log [Ca2+]) in skinned fiber bundles from LV papillary muscles of NTG and TG hearts. In control conditions, the Ca2+ concentration producing 50% maximal force (pCa50) was 5.77 ± 0.02 in NTG and 5.84 ± 0.01 in TG myofilament bundles ( P < 0.05). After protein kinase A-dependent phosphorylation, the pCa50 was 5.71 ± 0.01 in NTG and 5.77 ± 0.02 in TG myofilament bundles ( P < 0.05). Our results indicate that mutant α-Tm(Asp175Asn) increases myofilament Ca2+-sensitivity, which results in decreased relaxation rate and blunted response to β-adrenergic stimulation.

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