Stoichiometry of sodium and potassium transport in erythrocytes from patients with myotonic muscular dystrophy.

1. 22Na and 42K radioisotopes were used to measure Na efflux and K influx in identical suspensions of fresh erythrocytes from myotonic dystrophy patients and matched controls under the same conditions and in the same time interval. K was present in concentration 10 mM in the suspending medium to prevent Na-for-Na exchange. Each flux was measured in the presence and absence of ouabain. The mean ouabain-sensitive Na efflux rate in controls (2-33+/-0-13, S.E. of mean, m-equiv/1. cells.hr) was significantly greater (P less than 0-001) than the corresponding rate in myotonic dystrophy (1-64+/-0-09). 2. No significant differences between myotonic dystrophy and controls in mean ouabain-insensitive Na efflux, mean ouabain-sensitive K influx, or mean ouabain-insensitive K influx were found. 3. The stoichiometric ratio (ouabain-sensitive Na efflux)/(ouabain-sensitive K influx) was determined for each flux experiment. The mean stoichiometric ratio determined in controls (1-46+/-0-08) reconfirms extensive previous evidence favouring a 3Na-for-2K active exchange in controls. 4. The mean stoichiometric ratio determined in myotonic dystrophy (1-01+/-0-06) is statistically significantly different (P less than 0-001) from that in controls. These findings are interpreted as indication of 2Na-for-2K exchange in erythrocytes from patients with myotonic dystrophy.