Differences in both inositol 1,4,5-triphosphate mass and inositol 1,4,5- triphosphate receptors between normal and dystrophic between normal and dystrophic skeletal muscle cell lines

Human normal (RCMH) and Duchenne muscular dystrophy (RCD) cell lines, as well as newly developed normal and dystrophic murine cell lines, were used for the study of both changes in inositol 1,4,5-trisphosphate (IP3) mass and IP3 binding to receptors. Basal levels of IP3 were increased two- to threefold in dystrophic human and murine cell lines compared to normal cell lines. Potassium depolarization induced a time-dependent IP3 rise in normal human cells and cells of the myogenic mouse cell line (129CB3), which returned to their basal levels after 60 s. However, in the human dystrophic cell line (RCDMD), IP3 levels remained high up to 200 s after potassium depolarization. Expression of IP3 receptors was studied measuring specific binding of 3H-IP3 in the murine cell lines (normal 129CB3 and dystrophic mdx XLT 4-2). All the cell lines bind 3H-IP3 with relatively high affinity (K(d): between 40 and 100 nmol/L). IP3 receptors are concentrated in the nuclear fraction, and their density is