Immunochemical quantification of sarcoplasmic reticulum Ca2+-ATPase and calsequestrin in muscle biopsies from patients with myotonia congenita and paramyotonia congenita Eulenburg

Summary A sensitive enzyme-linked immunoadsorbant assay was developed to quantify Ca²⁺ -ATPase and calsequestrin from sarcoplasmic reticulum in human muscle biopsies. Tissue levels of Ca²⁺ -ATPase and calsequestrin averaged 51.5 ± 28.1 and 6.4 ± 1.8mg/g muscle protein, respectively, in control muscles (means ± SD, n=12). The high sensitivity and specificity of the antibodies make the assay a useful tool in the diagnosis of human neuromuscular disorders where defects in sarcoplasmic reticulum function may be expected. The assay was applied to muscle biopsies from patients with myotonia congenita and paramyotonia congenita Eulenburg. The calsequestrin concentration was normal in all patient muscles. The Ca²⁺ -ATPase content was also within the normal range but varied considerably with the percentage distribution of slowtwitch fibres. This indicates that the prolonged relaxation observed in the muscles of patients with these disorders is not caused by faulty expression of Ca²⁺-ATPase and calsequestrin.