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.

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