Sarco(Endo)Plasmic Reticulum Ca²⁺ Pump and Metabolic Enzyme Expression in Rabbit Fast‐type and Slow‐type Denervated Skeletal Muscles

Abstract

Recent reports by d'Albis et al. have shown that denervation of 8-day-old rabbit fast-twitch muscle (gastrocnemius) leads to the transformation of the muscle towards a slow phenotype but the changes towards slow-type myosin isoforms and contractile properties of the muscle were temporally uncoordinated. We analysed the time course of the effects of denervation of the gastrocnemius on the expression of the sarcoplasmic reticulum calcium pump isoforms (SERCA) and on the metabolic state of the muscle. Northern-blot analysis showed a rapid loss of the fast Ca2+ pump isoform (SERCA 1) mRNA from the denervated gastrocnemius which became of the oxidative type. The changes observed were complete as early as 35 days post-natal, i.e at the time when changes in contractile properties were previously observed. Denervation of the slow-twitch soleus led to a 50% decrease in the level of the slow Ca" pump isoform (SERCA 2 ) mRNA and was without effect on the metabolic state of the muscle.These findings extend previous results suggesting that in rabbit, continuous innervation is required for differentiation of fast-twitch muscles but is not an absolute requirement for differentiation of the slowtwitch muscle.Keywords: muscle denervation ; muscle metabolic state ; Ca2+-transporting ATPase ; glyceraldehyde-3-phosphate dehydrogenase.Innervation contributes to muscle specificity. In rat, mouse and cat, continuous innervation is believed to be required for differentiation of slow-twitch muscles but not of fast-twitch muscles (reviewed by Gunning and Hardeman, 1991). However, in rabbit, previous data indicate that denervation of fast and slow-twitch muscles at the age of 8 days leads to the transformation to the slow phenotype (d'Albis et al., 1994). Both denervated muscles contain slow-type myosin and have the properties of a slow-twitch muscle but there was an asynchrony between changes in muscle myosin isoform composition and contractile properties in the fast-twitch denervated muscle. Coinplete conversion to slow-type myosin occurred 52 days after denervation (60 days post-natal) whereas conversion to slow-twitch contractile features (muscle maximal shortening velocity V,,;,, and contraction time) occurred 27 days after denervation (35 days post-natal) (d'Albis et al., 1995b). These results suggest that modification of the phenotype of proteins other than myosin is involved in the alteration of the mechanical properties of the denervated gastrocnemius.We examined the expression of genes coding for proteins which contribute to the calcium regulatory mechanisms and toCorrespondence to M. Nozais, Gknes et protkines nzuscultr;re-es: ,stnrcture, ,foncrion et rigubtiorz, URA CNRS 11 31, Universite ParisSud,

Expression of Sarco(endo)Plasmic Reticulum Ca2+‐Atpase Slow (SERCA2) Isoform in Regenerating Rat Soleus Skeletal Muscle Depends on Nerve Impulses

“…The same result was obtained with the TTXparalysed muscles, providing a direct demonstration of nerve impulse dependence of SERCA2a isoform expression in the regenerating slow muscle. These results are consistent with data in the literature, such as denervation (Schulte et al 1994;Nozais et al 1996;Hamalainen & Pette, 2001) and electrical stimulation experiments (Leberer et al 1989;Briggs et al 1990;Hamalainen & Pette, 1997;Ohlendiek, 2000), showing that innervation influences the expression of proteins involved in the Ca 2+ sequestration mechanisms in adult mammalian muscles. In avian muscle, the role of innervation was also studied during regeneration of fast twitch and slow tonic muscles (Kaprielian et al 1991).…”

“…In avian muscle, the role of innervation was also studied during regeneration of fast twitch and slow tonic muscles (Kaprielian et al 1991). However, the effects of denervation on adult avian muscle during regeneration (Kaprielian et al 1991) diverge with data from mammals (Schulte et al 1994;Nozais et al 1996;Hamalainen & Pette, 2000), suggesting that the role played by innervation in avian muscles is different.…”

“…Expression of adult isoforms during regeneration appears in fact to be concomitant with the reestablishment of innervation (Zador et al 1996). In the rabbit, denervation has been reported to cause a rapid loss of SERCA1 mRNA in fast muscle, and a 50 % decrease in the level of SERCA2 mRNA in slow muscle (Nozais et al 1996). In the rat, long-term soleus muscle denervation led to pronounced slow-to-fast transition, with a significant reduction of SERCA2 isoform compensated by an increase of SERCA1 (Hamalainen & Pette, 2001).…”

SERCA pump isoforms: Their role in calcium transport and disease

“…By contrast, studies in rabbit showed that denervation of soleus muscle induced a slow‐to‐fast transition of the Ca 2+ ATPase isoform with a decrease in the expression of SERCA2a and an increase in SERCA1a protein levels 30. Studies carried out in 8‐day‐old rabbits showed that denervation of gastrocnemius caused a decrease in SERCA1a isoform without replacement by SERCA2a 72…”

Denervation of rabbit gastrocnemius and soleus muscles

“…In previous studies, we have shown the importance of innervation for the differentiation of the rabbit fast‐twitch gastrocnemius muscle as regards to myosin isoform pattern, contractile features, Ca 2+ transport and metabolic state [12,13]. Reductions in glycolytic enzyme activities have been observed in rabbit fast‐twitch muscle after chronic low frequency stimulation, known to induce a transition towards a slow‐twitch phenotype, and after denervation [13–15].…”