Myotonic dystrophy: Calcium‐dependent phosphatidic acid synthesis in erythrocytes

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Abstract
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 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.