Erythrocytes may contain a ouabain-insensitive K+-ATPase which plays a role in internal K+ balance.
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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Laboratório de Pesquisa Básica (LIM 12), Nefrologia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, SP, Brasil.
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D000818:Animals; D001692:Biological Transport / Q000502:physiology; D004910:Erythrocyte Membrane / Q000737:chemistry; D004912:Erythrocytes / Q000737:chemistry*; D017506:H(+)-K(+)-Exchanging ATPase / Q000032:analysis* / Q000502:physiology; D008297:Male; D010042:Ouabain / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D010042:Ouabain; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium