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Protein kinase A-dependent modulation of Ca2+ sensitivity in cardiac and fast skeletal muscles after reconstitution with cardiac troponin.

Matsuba D, Terui T, O-Uchi J, Tanaka H, Ojima T, Ohtsuki I, Ishiwata S, Kurihara S, Fukuda N - J. Gen. Physiol. (2009)

Bottom Line: PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca2+ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC).The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF.It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca2+ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology, Jikei University School of Medicine, Tokyo 105-8461, Japan.

ABSTRACT
Protein kinase A (PKA)-dependent phosphorylation of troponin (Tn)I represents a major physiological mechanism during beta-adrenergic stimulation in myocardium for the reduction of myofibrillar Ca2+ sensitivity via weakening of the interaction with TnC. By taking advantage of thin filament reconstitution, we directly investigated whether or not PKA-dependent phosphorylation of cardiac TnI (cTnI) decreases Ca2+ sensitivity in different types of muscle: cardiac (porcine ventricular) and fast skeletal (rabbit psoas) muscles. PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca2+ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC). Reconstitution of cardiac muscle with the fast skeletal Tn complex (sTn) not only increased Ca2+ sensitivity, but also abolished the Ca2+-desensitizing effect of PKA, supporting the view that the phosphorylation of cTnI, but not that of other myofibrillar proteins, such as myosin-binding protein C, primarily underlies the PKA-induced Ca2+ desensitization in cardiac muscle. Reconstitution of fast skeletal muscle with cTn decreased Ca2+ sensitivity, and PKA further decreased Ca2+ sensitivity, which was almost completely restored to the original level upon subsequent reconstitution with sTn. The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF. It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca2+ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.

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Effect of PKA on Ca2+ sensitivity in PCRF-reconstituted RP. (A; Left) 15% gel showing reconstitution of RP with PCRF. Cont., control fibers; PCRF, PCRF-reconstituted fibers; PCRF-sTn, PCRF-reconstituted fibers treated with sTn; LC-3, myosin light chain 3. For other abbreviations, see legend to Fig. 2 A. (B) Typical chart recording showing force-pCa protocols. A fiber was treated with PCRF, PKA, and sTn, in this order. Green arrows (blue arrows) indicate percentage of force at pCa 6.0 (pCa 5.75) compared with the maximum obtained at the end of each force-pCa protocol. (C) Force-pCa curves showing the effects of PCRF reconstitution, PKA treatment, and sTn reconstitution in RP. Black solid line, control with no treatment; gray solid line, PCRF reconstitution; red solid line, PKA treatment; black dashed line, sTn reconstitution. (Inset) Summary of pCa50 values. *, P < 0.05 compared with control; #, P < 0.05 compared with PCRF; †, P < 0.05 compared with PKA. n = 10.
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fig5: Effect of PKA on Ca2+ sensitivity in PCRF-reconstituted RP. (A; Left) 15% gel showing reconstitution of RP with PCRF. Cont., control fibers; PCRF, PCRF-reconstituted fibers; PCRF-sTn, PCRF-reconstituted fibers treated with sTn; LC-3, myosin light chain 3. For other abbreviations, see legend to Fig. 2 A. (B) Typical chart recording showing force-pCa protocols. A fiber was treated with PCRF, PKA, and sTn, in this order. Green arrows (blue arrows) indicate percentage of force at pCa 6.0 (pCa 5.75) compared with the maximum obtained at the end of each force-pCa protocol. (C) Force-pCa curves showing the effects of PCRF reconstitution, PKA treatment, and sTn reconstitution in RP. Black solid line, control with no treatment; gray solid line, PCRF reconstitution; red solid line, PKA treatment; black dashed line, sTn reconstitution. (Inset) Summary of pCa50 values. *, P < 0.05 compared with control; #, P < 0.05 compared with PCRF; †, P < 0.05 compared with PKA. n = 10.

Mentions: Summary of the values of maximal active force and nH before and after PKA treatment in RP after reconstitution with cTn or PCRF


Protein kinase A-dependent modulation of Ca2+ sensitivity in cardiac and fast skeletal muscles after reconstitution with cardiac troponin.

Matsuba D, Terui T, O-Uchi J, Tanaka H, Ojima T, Ohtsuki I, Ishiwata S, Kurihara S, Fukuda N - J. Gen. Physiol. (2009)

Effect of PKA on Ca2+ sensitivity in PCRF-reconstituted RP. (A; Left) 15% gel showing reconstitution of RP with PCRF. Cont., control fibers; PCRF, PCRF-reconstituted fibers; PCRF-sTn, PCRF-reconstituted fibers treated with sTn; LC-3, myosin light chain 3. For other abbreviations, see legend to Fig. 2 A. (B) Typical chart recording showing force-pCa protocols. A fiber was treated with PCRF, PKA, and sTn, in this order. Green arrows (blue arrows) indicate percentage of force at pCa 6.0 (pCa 5.75) compared with the maximum obtained at the end of each force-pCa protocol. (C) Force-pCa curves showing the effects of PCRF reconstitution, PKA treatment, and sTn reconstitution in RP. Black solid line, control with no treatment; gray solid line, PCRF reconstitution; red solid line, PKA treatment; black dashed line, sTn reconstitution. (Inset) Summary of pCa50 values. *, P < 0.05 compared with control; #, P < 0.05 compared with PCRF; †, P < 0.05 compared with PKA. n = 10.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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Show All Figures
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fig5: Effect of PKA on Ca2+ sensitivity in PCRF-reconstituted RP. (A; Left) 15% gel showing reconstitution of RP with PCRF. Cont., control fibers; PCRF, PCRF-reconstituted fibers; PCRF-sTn, PCRF-reconstituted fibers treated with sTn; LC-3, myosin light chain 3. For other abbreviations, see legend to Fig. 2 A. (B) Typical chart recording showing force-pCa protocols. A fiber was treated with PCRF, PKA, and sTn, in this order. Green arrows (blue arrows) indicate percentage of force at pCa 6.0 (pCa 5.75) compared with the maximum obtained at the end of each force-pCa protocol. (C) Force-pCa curves showing the effects of PCRF reconstitution, PKA treatment, and sTn reconstitution in RP. Black solid line, control with no treatment; gray solid line, PCRF reconstitution; red solid line, PKA treatment; black dashed line, sTn reconstitution. (Inset) Summary of pCa50 values. *, P < 0.05 compared with control; #, P < 0.05 compared with PCRF; †, P < 0.05 compared with PKA. n = 10.
Mentions: Summary of the values of maximal active force and nH before and after PKA treatment in RP after reconstitution with cTn or PCRF

Bottom Line: PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca2+ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC).The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF.It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca2+ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology, Jikei University School of Medicine, Tokyo 105-8461, Japan.

ABSTRACT
Protein kinase A (PKA)-dependent phosphorylation of troponin (Tn)I represents a major physiological mechanism during beta-adrenergic stimulation in myocardium for the reduction of myofibrillar Ca2+ sensitivity via weakening of the interaction with TnC. By taking advantage of thin filament reconstitution, we directly investigated whether or not PKA-dependent phosphorylation of cardiac TnI (cTnI) decreases Ca2+ sensitivity in different types of muscle: cardiac (porcine ventricular) and fast skeletal (rabbit psoas) muscles. PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca2+ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC). Reconstitution of cardiac muscle with the fast skeletal Tn complex (sTn) not only increased Ca2+ sensitivity, but also abolished the Ca2+-desensitizing effect of PKA, supporting the view that the phosphorylation of cTnI, but not that of other myofibrillar proteins, such as myosin-binding protein C, primarily underlies the PKA-induced Ca2+ desensitization in cardiac muscle. Reconstitution of fast skeletal muscle with cTn decreased Ca2+ sensitivity, and PKA further decreased Ca2+ sensitivity, which was almost completely restored to the original level upon subsequent reconstitution with sTn. The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF. It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca2+ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.

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