McCall Shannon J, Nassar Rashid, Malouf Nadia N, Saunders Aleister J, Oakeley Annette E, Henderson Paul M, Solaro R John, Pielak Gary J, Alexander Kenneth A, Anderson Page A W
Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA.
Pediatr Res. 2006 Sep;60(3):276-81. doi: 10.1203/01.pdr.0000233004.95404.1f. Epub 2006 Jul 20.
Cardiac contractility depends on calcium sensitivity of the myofilaments and cytosolic free calcium concentration (Ca(2+)) during activation. During development, the cardiac troponin T isoform cTnT(1) is replaced by shorter cTnT isoforms, including cTnT(4), and changes occur in other myofibrillar proteins and in calcium regulation. We expressed rabbit recombinant (r)cTnT(1) and rcTnT(4) in Spodoptera frugiperda cells and determined their effect on calcium binding to TnC in solution and on the calcium sensitivity of myofilaments in skinned rabbit ventricular fibers in vitro. We measured Ca(2+) and L-type calcium current (I(Ca)) in ventricular myocytes from 3-wk-old and adult rabbits. The dissociation constant (K(d)) of Ca-Tn(cTnT1) in solution was smaller than that of Ca-Tn(cTnT4) (mean +/- SE: 0.52 +/- 0.08 mumol/L versus 0.83 +/- 0.09 mumol/L). The Ca(2+) sensitivity of force development was greater in fibers reconstituted with rcTnT(1) (pCa(50) 6.07 +/- 0.04) than those reconstituted with rcTnT(4) (pCa(50) 5.75 +/- 0.07). Systolic Ca was lower in 3-wk-old than adult cells (443 +/- 35 nmol/L versus 882 +/- 88 nmol/L) as was I(Ca) (5.8 +/- 0.9 pA/pF versus 14.2 +/- 1.6 pA/pF). The higher calcium sensitivity of Tn-Ca binding and of force development conferred by rcTnT(1) suggest that higher neonatal cTnT(1) expression may partially compensate for the lower systolic Ca(2+).
心脏收缩力取决于激活过程中肌丝的钙敏感性和胞质游离钙浓度（Ca(2+)）。在发育过程中，心脏肌钙蛋白T同工型cTnT(1)被包括cTnT(4)在内的较短cTnT同工型所取代，并且其他肌原纤维蛋白和钙调节也发生了变化。我们在草地贪夜蛾细胞中表达了兔重组（r）cTnT(1)和rcTnT(4)，并确定了它们对溶液中钙与TnC结合以及对体外去表皮兔心室纤维中肌丝钙敏感性的影响。我们测量了3周龄和成年兔心室肌细胞中的Ca(2+)和L型钙电流（I(Ca)）。溶液中Ca-Tn（cTnT1）的解离常数（K(d)）小于Ca-Tn（cTnT4）的解离常数（平均值±标准误：0.52±0.08 μmol/L对0.83±0.09 μmol/L）。用rcTnT(1)重构的纤维中力产生的Ca(2+)敏感性高于用rcTnT(4)重构的纤维（pCa(50) 6.07±0.04）（pCa(50) 5.75±0.07）。3周龄细胞的收缩期Ca低于成年细胞（443±35 nmol/L对882±88 nmol/L），I(Ca)也是如此（5.8±0.9 pA/pF对14.2±1.6 pA/pF）。rcTnT(1)赋予的Tn-Ca结合和力产生更高的钙敏感性表明，新生儿较高的cTnT(1)表达可能部分补偿了较低的收缩期Ca(2+)。
