Thyrotoxic periodic paralysis and the sodium/potassium pump

The hypothesis of altered Na+/K+ transport in thyrotoxic periodic paralysis (TPP) was tested in an investigation of the K+ influx into erythrocytes from two patients with episodes of thyrotoxic muscle weakness. A patient with primary hypokalemic periodic paralysis (HPP) and three healthy volunteers served as controls. The TPP patients were of Oriental and Caucasian origin and differed in their clinical symptoms. For the Caucasian patient, the Na+ content of the erythrocytes was twice the control, for the Oriental patient it was normal. The K+ dependence of the ouabain-inhibitable K+ influx (the pump action) was also abnormal in the Caucasian patient, the flux being 70% of control at 2 mM [K+]e and normal at 4 mM [K+]e. The K+ influx was normal in the Oriental patient. By contrast, the K+ leak of the cells was normal in the Caucasian and was increased in the Oriental patient. The pump/leak ratio was thus reduced in both TPP patients. All parameters investigated were normal in the patient with primary HPP. It is concluded that the ion transport systems of muscle may be altered in TPP, but that the patho-mechanism might be different in the rare Caucasian cases and the rather more common Oriental cases.