Measures of skeletal muscle calcium channels and acetylcholine receptors in thyroidectomized rats

Hypothyroidism frequently presents with muscle complaints. No consistent histopathology nor electrophysiology explains these symptoms and signs. As well, no previous study shows specific changes in components of the nerve-muscle synapse nor excitation-contraction coupling in adult muscles, but changes are seen in hormone-treated embryonic myoblasts. In this study, adult male Holtzman rats underwent thyroidectomy and their age-matched euthyroid controls were simultaneously subjected to sham operation. Thirty days post-operative, animals were sacrificed for anterior tibialis muscles harvest. Muscle dihydropyridine type calcium channel (isradipine) and acetylcholine receptor (alpha-bungarotoxin) binding were measured and compared between experimental treatment groups. There were no significant differences in either the affinity or density of isradipine binding. However, hypothyroid muscles showed a nearly 50% reduction in acetylcholine receptor density when compared to control muscles. Thyroidectomy is associated with specific effects on components of neuromuscular transmission in adult fast twitch muscle.