The alpha 1 Na(+)-K+ pump of the Dahl salt-sensitive rat exhibits altered Na+ modulation of K+ transport in red blood cells.
The properties of the alpha 1 Na(+)-K+ pump were compared in Dahl salt-sensitive (DS) and salt-resistant (DR) strains by measuring ouabain-sensitive fluxes (mmol/liter cell x hr = FU, Mean +/- SE) in red blood cells (RBCs) and varying internal (i) and external (o) Na+ and K+ concentrations. Kinetic parameters of several modes of operation, i.e., Na+/K+, K+/K+, Na+/Na+ exchanges, were characterized and analyzed for curve-fitting using the Enzfitter computer program. In unidirectional flux studies (n = 12 rats of each strain) into fresh cells incubated in 140 mM Na(+) + 5 mM K+, ouabain-sensitive K+ influx was substantially lower in the DS than in DR RBCs, while ouabain-sensitive Na+ efflux and Nai were similar in both strains. Thus, the coupling ratio between unidirectional Na+:K+ fluxes was significantly higher in DS than in DR cells at similar RBC Na+ content. In the presence of 140 mM Nao, activation of ouabain-sensitive K+ influx by Ko had a lower Km and Vmax in DS as estimated by the Garay equation (N = 2.70 +/- 0.33, Km 0.74 +/- 0.09 mM; Vmax 2.87 +/- 0.09 FU) than in DR rats (N = 1.23 +/- 0.36, Km 2.31 +/- 0.16 mM; Vmax 5.70 +/- 0.52 FU). However, the two kinetic parameters were similar following Nao removal. The activation of ouabain-sensitive K+ influx by Nai had significantly lower Vmax in DS (9.3 +/- 0.4 FU) than in DR (14.5 +/- 0.6 FU) RBCs but similar Km. These data suggest that the low K+ influx in DS cells is caused by a defect in modulation by Nao and Nai. Na+ efflux showed no differences in Nai activation or trans effects by Nao and Ko, thus accounting for the different Na+:K+ coupling ratio in the Dahl strains. Further evidence for the differences in the coupling of ouabain-sensitive fluxes was found in studies of net Na+ and K+ fluxes, where the net ouabain-sensitive Na+ losses showed similar magnitudes in the two Dahl strains while the net ouabain-sensitive K+ gains were significantly greater in the DR than the DS RBCs. Ouabain-sensitive Na+ influx and K+ efflux were also measured in these rat RBCs. The inhibition of ouabain-sensitive Na+ influx by Ko was fully competitive for the DS but not for the DR pumps. Thus, for DR pumps, Ko could activate higher K+ influx in DR pumps without a complete inhibition of ouabain-sensitive Na+ influx.(ABSTRACT TRUNCATED AT 400 WORDS)
Canessa
M
M
Endocrine-Hypertension Division, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Romero
J R
JR
Ruiz-Opazo
N
N
Herrera
V L
VL
D000244:Adenosine Diphosphate / Q000032:analysis; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D015153:Blotting, Western; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D004910:Erythrocyte Membrane / Q000502:physiology; D004912:Erythrocytes / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D010758:Phosphorus / Q000032:analysis; D011188:Potassium / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000493:pharmacokinetics* / Q000494:pharmacology / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*
D010758:Phosphorus; D012965:Sodium Chloride; D010042:Ouabain; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium