Potassium depletion improves myocardial potassium uptake in vivo.
Potassium depletion (KD) is a very common clinical entity often associated with adverse cardiac effects. KD is generally considered to reduce muscular Na-K-ATPase density and secondarily reduce K uptake capacity. In KD rats we evaluated myocardial Na-K-ATPase density, ion content, and myocardial K reuptake. KD for 2 wk reduced plasma K to 1.8 +/- 0.1 vs. 3.5 +/- 0.2 mM in controls (P < 0.01, n = 7), myocardial K to 80 +/- 1 vs. 86 +/- 1 micromol/g wet wt (P < 0.05, n = 7), increased Mg, and induced a tendency to increased Na. Myocardial Na-K-ATPase alpha(2)-subunit abundance was reduced by approximately 30%, whereas increases in alpha(1)- and K-dependent pNPPase activity of 24% (n = 6) and 13% (n = 6), respectively, were seen. This indicates an overall upregulation of the myocardial Na-K pump pool. KD rats tolerated a higher intravenous KCl dose. KCl infusion until animals died increased myocardial K by 34% in KD rats and 18% in controls (P < 0.05, n = 6 for both) but did not induce different net K uptake rates between groups. However, clamping plasma K at approximately 5.5 mM by KCl infusion caused a higher net K uptake rate in KD rats (0.22 +/- 0.04 vs. 0.10 +/- 0.03 micromol x g wet wt(-1) x min(-1); P < 0.05, n = 8). In conclusion, a minor KD-induced decrease in myocardial K increased Na-K pump density and in vivo increased K tolerance and net myocardial K uptake rate during K repletion. Thus the heart is protected from major K losses and accumulates considerable amounts of K during exposure to high plasma K. This is of clinical interest, because a therapeutically induced rise in myocardial K may affect contractility and impulse generation-propagation and may attenuate increased myocardial Na, the hallmark of heart failure.
Medical Department B 2142, Heart Centre, Rigshospitalet, National University Hospital, University of Copenhagen, 2100 Copenhagen, Denmark. henningbundgaard@dadlnet.dk
Henning
H
Bundgaard
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008274:Magnesium / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000037:antagonists & inhibitors* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D004791:Enzyme Inhibitors; D010042:Ouabain; D011189:Potassium Chloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium