DIFFERENCES IN BOTH INOSITOL 1,4,5-TRISPHOSPHATE MASS AND INOSITOL 1,4,5-TRISPHOSPHATE RECEPTORS BETWEEN NORMAL AND DYSTROPHIC SKELETAL-MUSCLE CELL-LINES

Human normal (RCMH) and Duchenne muscular dystrophy (RCDMD) 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-trisphosphat e (IP3) mass and IP3 binding to receptors. Basal levels of IP3 were in creased two- to threefold in dystrophic human and murine cell lines co mpared to normal cell lines. Potassium depolarization induced a time-d ependent IP3 rise in normal human cells and cells of the myogenic mous e cell line (129CB3), which returned to their basal levels alter 60 s. However, in the human dystrophic cell line (RCDMD), IP3 levels remain ed high up to 200 s after potassium depolarization. Expression of IP3 receptors was studied measuring specific binding of H-3-IP3 in the mur ine cell lines (normal 129CB3 and dystrophic mdx XLT 4-2), All the cel l 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 significantly higher in dystrophic cells compared to normal. These findings together with high basal levels of IP3 mass suggest a possible role for this system in the deficiency of intracel lular calcium regulation in Duchenne muscular dystrophy. (C) 1998 John Wiley & Sons, Inc.