ryanodine and Muscular-Atrophy

Calsequestrin (CS), the major Ca(2+)-binding protein in the sarcoplasmic reticulum (SR), is thought to play a dual role in excitation-contraction coupling: buffering free Ca(2+) increasing SR capacity, and modulating the activity of the Ca(2+) release channels (RyRs). In this study, we generated and characterized the first murine model lacking the skeletal CS isoform (CS1). CS1-null mice are viable and fertile, even though skeletal muscles appear slightly atrophic compared to the control mice. No compensatory increase of the cardiac isoform CS2 is detectable in any type of skeletal muscle. CS1-null muscle fibres are characterized by structural and functional changes, which are much more evident in fast-twitch muscles (EDL) in which most fibres express only CS1, than in slow-twitch muscles (soleus), where CS2 is expressed in about 50% of the fibres. In isolated EDL muscle, force development is preserved, but characterized by prolonged time-to-peak and half-relaxation time, probably related to impaired calcium release from and re-uptake by the SR. Ca(2+)-imaging studies show that the amount of Ca(2+) released from the SR and the amplitude of the Ca(2+) transient are significantly reduced. The lack of CS1 also causes significant ultrastructural changes, which include: (i) striking proliferation of SR junctional domains; (ii) increased density of Ca(2+)-release channels (confirmed also by (3)H-ryanodine binding); (iii) decreased SR terminal cisternae volume; (iv) higher density of mitochondria. Taken together these results demonstrate that CS1 is essential for the normal development of the SR and its calcium release units and for the storage and release of appropriate amounts of SR Ca(2+).

Topics: Animals; Blotting, Western; Calcium; Calcium-Binding Proteins; Calsequestrin; Carrier Proteins; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Kinetics; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Contraction; Muscle Fibers, Skeletal; Muscle Proteins; Muscle, Skeletal; Muscular Atrophy; Ryanodine; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Sarcoplasmic Reticulum Calcium-Transporting ATPases

Unloading of skeletal muscles by hindlimb unweighting is known to induce muscle atrophy and a shift toward faster contractile properties associated with an increase in the expression of fast contractile proteins, particularly in slow soleus muscles. Contractile properties suggest that slow soleus muscles acquire SR properties close to those of a faster one. We studied the expression and properties of the sarcoplasmic reticulum calcium release (RyR) channels in soleus and gastrocnemius muscles of rats submitted to hindlimb unloading (HU). An increase in RyR1 and a slight decrease in RyR3 expression was detected in atrophied soleus muscles only after 4 weeks of HU. No variation appeared in fast muscles. [(3)H]Ryanodine binding experiments showed that HU neither increased the affinity of the receptors for [(3)H]ryanodine nor changed the caffeine sensitivity of [(3)H]ryanodine binding. Our results suggested that not only RyR1 but also RyR3 expression can be regulated by muscle activity and innervation in soleus muscle. The changes in the RyR expression in slow fibers suggested a transformation of the SR from a slow to a fast phenotype.

Topics: Animals; Caffeine; Hindlimb Suspension; Major Histocompatibility Complex; Male; Muscle, Skeletal; Muscular Atrophy; Protein Isoforms; Radioligand Assay; Rats; Rats, Wistar; Ryanodine; Ryanodine Receptor Calcium Release Channel; Tritium

Topics: Calcium Channels; Calcium Metabolism Disorders; Child, Preschool; Chromosome Aberrations; Chromosome Disorders; Chromosomes, Human, Pair 19; Ear Diseases; Humans; Male; Malignant Hyperthermia; Muscular Atrophy; Postoperative Complications; Protein Binding; Ryanodine