Aclu Physiol Scund 1991, 143, 131-132

ADONIS

000167729100l7 15

Expressions of myosin heavy chain Ild isoform in rat soleus muscle during hindlimb suspension H. TAKAHASHI, M. WADA" and S. KATSUTA-1. Department of Radiology, Institute of Clinical Medicine, University of Tsukuba, Tsukuba 305, * Faculty of Integrated Arts and Sciences, Hiroshima University, Hiroshima 730, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba 305, Japan

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The transition of slow-twitch to fast-twitch muscle resulting from hindlimb suspension has been documented in rat soleus muscle. As the speed of muscle shortening is correlated with the distribution ofmyosin heavy chain (HC) isoforms (Reiser et ul. 1985), suspended soleus could express more fast HC isoforms than normal ones. Although three fast HC isoforms have been found in adult rat skeletal muscle (Bar & Pette 1988), it remained unclear which fast isoforms are expressed in suspended soleus. In the present study we have addressed this question with the use of an improved electrophoretic method (Sugiura & Murakami 1990). Both normal and suspended soleus displayed HCI as the most prominent isoform together with low amounts of fast H C (Fig. 1). In normal soleus fast H C isoform expressed was only HCIIa ; its distribution exhibited almost equal amounts over experimental periods (Fig. 1). As compared to normal soleus, 21and 28- day suspended muscles were characterized by the increase in fast H C isoforms and by the expression of HCIId in addition to HCIIa (Figs 1 & 2 ) . The increase in fast HC isoforms presented here is consistent with the observations that disuse, as obtained by denervation (L0mo 1986) or immobilization (Booth & Kelso 1973), speeds up the soleus. The amount of activity seems chiefly to affect the contractile property in skeletal muscle. Therefore, reduced activity in relation to suspension may be responsible for the increase in fast HC isoforms. Literature concerning the distribution of H C isoforms has demonstrated that HCIId is not expressed in normal soleus (Bar & Pette 1988, Sugiura & Murakami 1990). We show here for the first time that suspension causes not only the increase in HCIIa but also the expression of HCIId. Schiaffino et al. (1988) have reported that the soleus, which is denervated and Received 15 May 1991, accepted 13 June 1991. Key words : hindlimb suspension, soleus muscle, myosin heavy chain IId. Correspondence : S. Katsuta, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba 305, Japan.

electrically stimulated with high-frequency impulse pattern, contains HCIIX, most likely corresponding to HCIId (Bar & Pette 1988). It remains unclear whether or not reduction in the amount of activity and high-frequency activity are regarded as essential factors to evoke the expression of HCIId.

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HClla\

/HClla HClld L H C l l b I H C I

HClldHCllbHCI

Fig. 1. Separation of myosin heavy chain (HC) isoforms of rat skeletal muscles by SDS-PAGE. Lane 1, mixture of soleus, plantaris and diaphragm ; lane 2 , control soleus; lanes 3 and 4,14- and 28-day suspended soleus, respectively.

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Suspension period (days)

Fig. 2. Changes in the percentage of fast myosin heavy chain (HC) isoforms of suspended soleus. Silver-stained electrophoreses were densitometrically evaluated. Animal numbers: 1, 3 and 7 d, n = 2 ; 14, 21 and 28 d, n = 3 .

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ff. Takahashi, M .Wuda and S . Kutsuta

R E F E R I

Expressions of myosin heavy chain IId isoform in rat soleus muscle during hindlimb suspension.

Aclu Physiol Scund 1991, 143, 131-132 ADONIS 000167729100l7 15 Expressions of myosin heavy chain Ild isoform in rat soleus muscle during hindlimb s...
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