THE EFFECTS OF VITAMIN-D DEFICIENCY ON RAT SKELETAL-MUSCLE ULTRASTRUCTURE AND CALBINDIN-D-9K AND CALBINDIN-D-28K

The aim of this study was to investigate the detailed changes in the u ltrastructure of skeletal muscle of vitamin D-deficient rats. An elect ron microscopic study of the skeletal muscle ultrastructure of vitamin D-deficient rats showed many abnormalities, including wavy, clear Z-d isks, myosin filaments juxtaposed to the Z-disks, loss of myofibrils a t the periphery of the bundles, reduced sarcoplasmic reticulum membran es, fewer and smaller mitochondria and fewer glycogen granules, and di storted T-tubules. Calbindins-D 9K and 28K, as revealed by specific an tibodies, were found only along mitochondrial membranes in vitamin D s upplemented muscles; their amount was decreased in vitamin D-deficient rats. Blood calcium was also low in vitamin D-deficient rats, but nor mal in vitamin D-deficient sorbitol-supplemented rats. Nevertheless, t he skeletal muscles of these rats showed most of the features of vitam in D-deficient muscles. Vitamin D and 1,25-dihydroxycholecalciferol, i ts active metabolite, restored normal muscle ultrastructure and normal plasma calcium to vitamin D-deficient rats. In conclusion, skeletal m uscle ultrastructure is profoundly altered in vitamin D-deficiency and the response of muscle to the hormone is specific.