Increased phosphorylation of myosin light chain associated with slow-to-fast transition in rat soleus.
In striated muscles myosin light chain (MLC)2 phosphorylation regulates calcium sensitivity and mediates sarcomere organization. Little is known about the changes in MLC2 phosphorylation in relation to skeletal muscle plasticity. We studied changes in MLC2 phosphorylation in rats receiving three treatment conditions causing slow-to-fast transitions: 1) atrophy induced by 14 days of hindlimb suspension (HS), 2) hypertrophy induced by 14 days of clenbuterol administration (CB), and 3) 14 days of combined treatment (CB-HS). Three variants of the slow (MLC2s) and two variants of the fast MLC2 (MLC2f) isoform were separated with two-dimensional electrophoresis and identified with monoclonal and polyclonal antibodies specific for MLC2; their relative proportions were densitometrically quantified. In control soleus muscle MLC2s predominated over MLC2f (91.4 +/- 3.9% vs. 8.5 +/- 3.9%) and was separated into two spots, the less acidic spot being 73.5 +/- 4.3% of the total. All treatments caused a decrease of the less acidic unphosphorylated spot of MLC2s (CB: 64.1 +/- 5.6%, HS: 62.4 +/- 6.8%, CB-HS: 56.4 +/- 4.4%), the appearance of a third more acidic variant of MLC2s (representing 3.9-5.9% of total MLC2s), an increase of MLC2f (CB: 30.9 +/- 3.1%, HS: 23.9 +/- 3.3%, CB-HS: 25.3 +/- 3.9%), and the phosphorylation of a large fraction of MLC2f (CB: 30.4 +/- 6.7%, HS: 28.7 +/- 6.5%, CB-HS: 21.8 +/- 2.1%). Treatment with alkaline phosphatase or with protein phosphatase 1 (PP1) removed the most acidic spots of both MLC2f and MLC2s. We conclude that in rat skeletal muscles an increase of MLC2 phosphorylation is associated with the slow-to-fast transition regardless of whether hypertrophy or atrophy develops.
Department of Anatomy and Physiology, University of Padova, Via Marzolo 3, 35131 Padua, Italy.
Cyril
C
Bozzo
Laurence
L
Stevens
Luana
L
Toniolo
Yvonne
Y
Mounier
Carlo
C
Reggiani
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001284:Atrophy; D024722:Cardiac Myosins / Q000378:metabolism*; D002976:Clenbuterol / Q000494:pharmacology; D019417:Hindlimb Suspension; D006984:Hypertrophy; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D018994:Myosin Light Chains / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D051381:Rats; D017208:Rats, Wistar
D000318:Adrenergic beta-Agonists; D018994:Myosin Light Chains; C107184:myosin light chain 2; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D024722:Cardiac Myosins; D002976:Clenbuterol