Myotonic dystrophy: Calcium‐dependent phosphatidic acid synthesis in erythrocytes

Recently it was reported that calcium-dependent phosphatidic acid synthesis in erythrocytes 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, a 2-fold increase of phosphatidic acid in both groups was determined by inorganic phosphate measurements. Thus, the specific activity of the ³²P-phospatidic acid increased 4- to 5-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.