K-K+-ATPASE] AND IMPROVES EXTRARENAL K+ HOMEOSTASIS IN RATS( SUPPLEMENTATION INCREASES MUSCLE [NA+)

Effects of K+ supplementation (similar to 200 mmol KCl/100 g chow) on plasma K+, K+ content, and Na+-K+-adeonsinetriphosphatase (ATPase) con centration ([Na+-K+-ATPase]) in skeletal muscles as well as on extrare nal K+ clearance were evaluated in rats. After 2 days of K+ supplement ation, hyperkalemia prevailed (K+-supplemented vs. weight-matched cont rol 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 observe d in gastrocnemius muscle (104 +/- 2 vs. 97 +/- 1 mu mol/g wet wt, P < 0.05, n = 5-6). After 7 days of K+ supplementation, a significant inc rease in [H-3] ouabain binding site concentration (344 +/- 5 vs. 239 /- 8 pmol/g wet wt, P < 0.05, n = 4) was observed in gastrocnemius mus cle. After 2 wk, increases in plasma K+, K+ content, and [H-3] ouabain binding site concentration in gastrocnemius muscle amounted to 40, 8, and 68% (P < 0.05) above values observed in weight-matched control an imals, respectively. The latter change was confirmed by K+-dependent p -nitrophenyl phosphatase activity measurements. Fasting for 1 day redu ced 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 mu mol/g wet wt (P < 0.05, n = 5), respectively. After i nduction of anesthesia, arterial plasma K+ was measured during intrave nous KCl infusion (0.75 mmol KCl . 100 g body wt(-1). h(-1)). The K+ s upplemented fasted group demonstrated a 42% (P < 0.05) lower plasma K rise, associated with a significantly higher increase in K+ content i n gastrocnemius muscle of 7 mu mol/g wet wt (P < 0.05, n = 5) compared with their control animals. In conclusion, K+ supplementation increas es plasma K+, K+ content, and [Na+-K+-ATPase] in skeletal muscles and improves extrarenal K+ clearance capacity.