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

• Main Authors: Seguro L.F.B.C., Seguro D.L.B.C., Helou C.M.B.
• Format: Article
• Language: English
• Published: Associação Brasileira de Divulgação Científica 2003-01-01
• Series: Brazilian Journal of Medical and Biological Research
• Subjects: Erythrocyte; K+-ATPase; Potassium; Acid-base status; H+,K+-ATPase; Ouabain
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2003001200020
• ISSN: 0100-879X; 0034-7310

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.