Myotonic dystrophy: calcium-dependent phosphatidic acid synthesis in erythrocytes

Recently it was reported that calcium-dependent phosphatidic acid synthesis in erythrocyte of patients with myotonic muscular dystrophy (MyD) is markedly impaired when compared to that in control subjects. Using 32P-loaded erythrocytes, we found no significant difference in the levels of 32P-phosphatidic acid synthesized after exposure to calcium and its ionophore A23187 between patients with MyD and controls. In a batch experiment typical of the experiments with 32P, and a twofold increase of phosphatidic acid in both groups was determined by inorganic phosphate measurements. Thus, the specific activity of the 32P-phosphatidic acid increased four- to five-fold in response to calcium Analyses of 32P-polyphosphoinositide breakdown in ghosts and in adenosine triphosphate-depleted erythrocytes also appeared normal for patients with myotonic muscular dystrophy. Possible discrepancies between the results presented here and those reported previously are discussed.