Williams H M, Ianuzzo C D
Department of Biology, York University, Toronto, Ontario, Canada.
J Mol Cell Cardiol. 1988 Aug;20(8):689-99. doi: 10.1016/s0022-2828(88)80014-2.
The purpose of this study was to determine whether thyroid hormone could directly affect the phenotypic expression of two isozymic systems [lactate dehydrogenase (LDH) and myosin] and the energy transducing potential of cultured neonatal heart cells. In addition we determined if these biochemical systems developed in culture as they normally do during in vivo post-natal development. Cells were maintained for 14 days in culture medium containing 10% horse serum and Earle's salts. Experimental cultures were supplemented with 10 nmol/l 3,3',5-triiodo-L-thyronine (T3). Hearts used to study in vivo development were excised from rats at the ages of 2 and 14 days post-natal to correspond with the time of isolating and harvesting the cultured heart cells, respectively. Adult hearts were used to represent the final developmental stage. Cultured cardiomyocytes without T3 administered to the culture medium showed no change in the isozymic profiles (myosin and LDH) or in metabolic potential during the 2 week culture period. The T3 treated cultures showed a complete shift to the V1 myosin isozyme. The glycolytic and aerobic metabolic potential [i.e., phosphofructokinase (PFK) and citrate synthase (CS) activities] and the LDH isozyme distribution were unaltered by T3 treatment. During in vivo development a shift toward the V1 myosin and H-LDH isozymes along with an increase in aerobic metabolism occurred in the rat heart. These findings indicate that the development of these selected biochemical systems in cultured cardiac myocytes does not result from an intrinsic myogenetic program and thus must be regulated in vivo by epigenetic factor(s). These results show that T3 has the potential to be the prime determinant of the phenotypic expression of the myosin isoforms, but does not have the potential to be the sole determinant for the expression of the LDH isozymes or the glycolytic (PFK) and aerobic (CS) capacities of cardiac muscle cells.
本研究的目的是确定甲状腺激素是否能直接影响两种同工酶系统[乳酸脱氢酶（LDH）和肌球蛋白]的表型表达以及培养的新生心脏细胞的能量转换潜能。此外，我们还确定了这些生化系统在培养过程中是否如在体内出生后发育期间正常发育那样进行发育。细胞在含有10%马血清和Earle氏盐的培养基中培养14天。实验培养物补充有10 nmol/l 3,3',5-三碘-L-甲状腺原氨酸（T3）。用于研究体内发育的心脏分别从出生后2天和14天的大鼠身上切除，以对应分离和收获培养的心脏细胞的时间。成年心脏用于代表最终发育阶段。在培养基中未添加T3的培养心肌细胞在2周培养期内同工酶谱（肌球蛋白和LDH）或代谢潜能没有变化。经T3处理的培养物显示完全转变为V1肌球蛋白同工酶。糖酵解和有氧代谢潜能[即磷酸果糖激酶（PFK）和柠檬酸合酶（CS）活性]以及LDH同工酶分布不受T3处理的影响。在体内发育过程中，大鼠心脏向V1肌球蛋白和H-LDH同工酶转变，同时有氧代谢增加。这些发现表明，培养的心肌细胞中这些选定生化系统的发育并非源于内在的肌发生程序，因此必须在体内由表观遗传因素调节。这些结果表明，T3有可能成为肌球蛋白同工型表型表达的主要决定因素，但没有可能成为心肌细胞LDH同工酶表达或糖酵解（PFK）和有氧（CS）能力表达的唯一决定因素。
