Bulteau L, Cogné M, Cognard C, Raymond G
Laboratoire de Physiologie Générale, URA CNRS 1869, 40 Avenue du Recteur Pineau, F-86022 Poitiers Cedex, France.
Pflugers Arch. 1997 Jan;433(3):376-8. doi: 10.1007/s004240050291.
Cardiac and skeletal type of excitation-contraction coupling (ECC) are quite different. Those differences could be explained by structural ones in the molecular entities involved in ECC, ie dihydropyridines (DHP) receptors (alpha1 subunit of L-type calcium channels) of the sarcolemma or ryanodine receptors of the sarcoplasmic reticulum membrane. As previously demonstrated by means of electrophysiology, the two types of ECC coexist during the first stages of in vitro development of skeletal muscle, whereas the skeletal type predominates at the later ones. In order to see whether evolution of ECC could be correlated with the one of alpha1 subunit expression, we determined by Northern Blotting which isoforms of alpha1 subunit are expressed during the in vitro myogenesis. mRNA corresponding to the cardiac isoform are present in myoblasts (before fusion), but patch-clamp experiments showed that they are not functional. After fusion, skeletal and cardiac mRNA are coexpressed in myotubes, with different intensities: whereas expression of skeletal mRNA (which are the more intensive) stabilized at the later stages tested, cardiac mRNA decreased. We conclude that evolution in mRNA alpha1 subunit isoforms expression could partly explained evolution of ECC features during in vitro myogenesis.
心脏型和骨骼肌型兴奋-收缩偶联（ECC）有很大不同。这些差异可以用参与ECC的分子实体的结构差异来解释，即肌膜上的二氢吡啶（DHP）受体（L型钙通道的α1亚基）或肌浆网膜上的兰尼碱受体。如先前通过电生理学所证明的，在骨骼肌体外发育的最初阶段，两种类型的ECC共存，而在后期阶段骨骼肌型占主导。为了探究ECC的演变是否与α1亚基表达的演变相关，我们通过Northern印迹法确定了在体外肌生成过程中表达的α1亚基的哪些同工型。对应心脏同工型的mRNA存在于成肌细胞中（融合前），但膜片钳实验表明它们没有功能。融合后，骨骼肌和心脏mRNA在肌管中共表达，强度不同：骨骼肌mRNA（强度更高）的表达在测试的后期阶段稳定下来，而心脏mRNA则减少。我们得出结论，mRNAα1亚基同工型表达的演变可以部分解释体外肌生成过程中ECC特征的演变。
