Bortolotto S K, Stephenson D G, Stephenson G M
School of Life Sciences and Technology, Victoria University of Technology, Melbourne, Victoria 8001, Australia.
Am J Physiol. 1999 Mar;276(3):C628-37. doi: 10.1152/ajpcell.1999.276.3.C628.
Electrophoretic analyses of muscle proteins in whole muscle homogenates and single muscle fiber segments were used to examine myosin heavy chain (MHC) and myosin light chain 2 (MLC2) isoform composition and fiber type populations in soleus muscles from spontaneously hypertensive rats (SHRs) and their age-matched normotensive controls [Wistar-Kyoto (WKY) rats], at three stages in the development of high blood pressure (4 wk, 16 wk, and 24 wk of age). Demembranated (chemically skinned with 2% Triton X-100), single fiber preparations were used to determine the maximum Ca2+-activated force per cross-sectional area, calcium sensitivity, and degree of cooperativity of the contractile apparatus and Ca2+-regulatory system with respect to Ca2+. The results show that, at all ages examined, 1) SHR soleus contained a lower proportion of MHCI and MLC2 slow (MLC2s) and a higher proportion of MHCIIa, MHCIId/x, and MLC2 fast (MLC2f ) isoforms than the age-matched controls; 2) random dissection of single fibers from SHR and WKY soleus produced four populations of fibers: type I (expressing MHCI), type IIA (expressing MHCIIa), hybrid type I+IIA (coexpressing MHCI and MHCIIa), and hybrid type IIA+IID (coexpressing MHCIIa and MHCIId/x); and 3) single fiber dissection from SHR soleus yielded a lower proportion of type I fibers, a higher proportion of fast-twitch fibers (types IIA and IIA+IID), and a higher proportion of hybrid fibers (types I+IIA and IIA+IID) than the homologous muscles from the age-matched WKY rats. Because the presence of hybrid fibers is viewed as a marker of muscle transformation, these data suggest that SHR soleus undergoes transformation well into adulthood. Our data show also that, for a given fiber type, there are no significant differences between SHR and WKY soleus muscles with respect to any of the Ca2+-activation properties examined. This finding indicates that the lower specific tensions reported in the literature for SHR soleus muscles are not due to strain- or hypertension-related differences in the function of the contractile apparatus or regulatory system.
通过对全肌肉匀浆和单根肌纤维片段中的肌肉蛋白进行电泳分析，来检测自发性高血压大鼠（SHR）及其年龄匹配的正常血压对照大鼠[Wistar-Kyoto（WKY）大鼠]比目鱼肌中肌球蛋白重链（MHC）和肌球蛋白轻链2（MLC2）同工型组成以及纤维类型群体，检测时间为高血压发展的三个阶段（4周、16周和24周龄）。使用脱膜的（用2% Triton X-100化学去皮）单纤维制剂来确定每横截面积的最大Ca2+激活力、钙敏感性以及收缩装置和Ca2+调节系统相对于Ca2+的协同程度。结果表明，在所有检测年龄中，1）与年龄匹配的对照相比，SHR比目鱼肌中MHCI和MLC2慢型（MLC2s）的比例较低，而MHCIIa、MHCIId/x和MLC2快型（MLC2f）同工型的比例较高；2）从SHR和WKY比目鱼肌中随机分离单纤维产生了四种纤维群体：I型（表达MHCI）、IIA型（表达MHCIIa）、I+IIA型混合纤维（共表达MHCI和MHCIIa）以及IIA+IID型混合纤维（共表达MHCIIa和MHCIId/x）；3）与年龄匹配的WKY大鼠的同源肌肉相比，从SHR比目鱼肌中分离单纤维得到的I型纤维比例较低，快肌纤维（IIA型和IIA+IID型）比例较高，混合纤维（I+IIA型和IIA+IID型）比例也较高。由于混合纤维的存在被视为肌肉转变的标志，这些数据表明SHR比目鱼肌在成年期仍会发生转变。我们的数据还表明，对于给定的纤维类型，SHR和WKY比目鱼肌在所检测的任何Ca2+激活特性方面均无显著差异。这一发现表明，文献中报道的SHR比目鱼肌较低的比张力并非由于收缩装置或调节系统功能上与应变或高血压相关的差异所致。
