Cation Transport in Intact Erythrocytes of Hyperthyroid Patients: Role of the NaK-ATPase Pump

Summary

Studies of erythrocyte (RBC) cation fluxes and concentrations in hyperthyroid subjects have recently been reported with the suggestion that Na-K ATPase activity was decreased. We have studied the kinetics of total and ouabain-sensitive K⁺ uptake utilizing ⁸⁶Rb as a tracer in the intact erythrocytes of 7 hyperthyroid subjects and compared the results to those of a healthy control population. We find total K⁺ transport is depressed in the RBC of hyperthyroid subjects. The V_max for K⁺ transport for hyperthyroid subjects is 1.8 ± 0.17 × 10^-4 mM K⁺/10⁹ RBC/hour versus a control of 2.3±0.14 × 10^-4 mM K⁺/10⁹ RBC/hour. This depression in V_max is evident in spite of no significant differences in the Km for the system when hyperthyroid subjects (2.7 ± 0.19 mM) are compared to controls (2.38 ± 0.21 mM). Further, the depressed K⁺ transport appears to be the result of depressed ouabain-insensitive K⁺ transport. Although the percent of the ouabain-sensitive K⁺ transport is greater in the hyperthyroid subject (82.5 %) versus controls (72.5 %), this simply reflects a relative change in a system where total transport is dropping but the ouabain-sensitive component is remaining unchanged. None of these findings can be directly or indirectly Related to thyroid hormone and it is suggested that the ion transport changes reflect factors independent of thyroid hormone.

Key-Words:

Ion Transport - Hyperthyroidism - (NA, K) ATPase - Potassium Transport