K+supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+homeostasis in rats

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Abstract
Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, and Keld Kjeldsen. K+supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+homeostasis in rats. J. Appl. Physiol.82(4): 1136–1144, 1997.—Effects of K+supplementation (∼200 mmol KCl/100 g chow) on plasma K+, K+content, and Na+-K+-adeonsinetriphosphatase (ATPase) concentration ([Na+-K+-ATPase]) in skeletal muscles as well as on extrarenal K+clearance were evaluated in rats. After 2 days of K+supplementation, hyperkalemia prevailed (K+-supplemented vs. weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5–6], and after 4 days a significant increase in K+content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 μmol/g wet wt, P < 0.05, n = 5–6). After 7 days of K+supplementation, a significant increase in [3H]ouabain binding site concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt, P < 0.05, n = 4) was observed in gastrocnemius muscle. After 2 wk, increases in plasma K+, K+content, and [3H]ouabain binding site concentration in gastrocnemius muscle amounted to 40, 8, and 68% ( P < 0.05) above values observed in weight-matched control animals, respectively. The latter change was confirmed by K+-dependent p-nitrophenyl phosphatase activity measurements. Fasting for 1 day reduced plasma K+and K+content in gastrocnemius muscle in rats that had been K+supplemented for 2 wk by 3.1 ± 0.3 mmol/l ( P < 0.05, n = 5) and 15 ± 2 μmol/g wet wt ( P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K+was measured during intravenous KCl infusion (0.75 mmol KCl ⋅ 100 g body wt−1⋅ h−1). The K+-supplemented fasted group demonstrated a 42% ( P < 0.05) lower plasma K+rise, associated with a significantly higher increase in K+content in gastrocnemius muscle of 7 μmol/g wet wt ( P < 0.05, n = 5) compared with their control animals. In conclusion, K+supplementation increases plasma K+, K+content, and [Na+-K+-ATPase] in skeletal muscles and improves extrarenal K+clearance capacity.