Erythrocytes may contain a ouabain-insensitive K+-ATPase which plays a role in internal K+ balance

Brazilian Journal of Medical and Biological Research

L.f.b.c. Seguro¹  D.l.b.c. Seguro¹  C.m.b. Helou¹ 

[1] ,Universidade de São Paulo Faculdade de Medicina Hospital das ClínicasSão Paulo SP ,Brasil

关键词: Erythrocyte;    K+-ATPase;    Potassium;    Acid-base status;    H+;    K+-ATPase;    Ouabain;   

DOI  :  10.1590/S0100-879X2003001200020

来源: SciELO

【 摘 要 】

Erythrocytes are useful in evaluating K+ transport pathways involved in internal K+ balance. Several forms of H+,K+-ATPase have been described in nephron segments active in K+ transport. Furthermore, the activity of a ouabain-insensitive isoform of H+,K+-ATPase expressed in collecting duct cells may be modulated by acid-base status. Various assays were performed to determine if a ouabain-insensitive K+-ATPase is present in rat erythrocytes and, if so, whether it plays a role in internal K+ balance. Kinetic studies demonstrated that maximal stimulation of enzyme activity was achieved with 2.5 mM K+ at pH 7.4. Subsequent experiments were performed on erythrocyte membranes collected from animals submitted to varying degrees of K+ homeostasis: control rats, K+-depleted rats, K+-loaded rats, and rats rendered hyperkalemic due to acute renal failure. As observed in the collecting duct cell studies, there was a significant decrease in the activity of ouabain-insensitive K+-ATPase in the erythrocytes of both K+-loaded and metabolically alkalotic K+-depleted rats. However, this enzyme activity in erythrocyte membranes of rats with metabolic acidosis-related hyperkalemia was similar to that of control animals. This finding may be interpreted as resulting from two potentially modulating factors: the stimulating effect that metabolic acidosis has on K+-ATPase and the counteracting effect that hyperkalemia and uremia have on metabolic acidosis. In summary, we present evidence of a ouabain-insensitive K+-ATPase in erythrocytes, whose activity is modulated by acid-base status and K+ levels.

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