APStracts 3:0558A, 1996.

(na,k-atpase) concentration and improves extrarenal k homeostasis in rats. Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, and Keld Kjeldsen. Department of Medicine B, The Heart Centre, Rigshospitalet, National University Hospital, Copenhagen, Denmark

APStracts 3:0558A, 1996.

The effects of K supplementation (200 mmol KCl x 100 g-1 chow) on plasma K, K content and Na,K-ATPase concentration in skeletal muscles as well as on extrarenal K clearance were evaluated in rats. Skeletal muscle Na,K-ATPase was quantified by vanadate facilitated 3H-ouabain binding to intact samples and by K-dependent pNPPase activity measurements in crude homogenates. After 2 days of K supplementation hyperkalemia prevailed (mean +/- SEM, K supplemented vs weight matched controls) (5.1 +/- 0.2 vs 3.2 +/- 0.1 mmol x l-1, p&LT;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 _mol x g wet wt.-1, p&LT;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 x g wet wt.-1, p&LT;0.05, n=4) was observed in gastrocnemius muscle. After 2 weeks, increases in plasma K, K content and Na,K-ATPase concentration in gastrocnemius muscle amounted to 40, 8 and 68% (p&LT;0.05) above values observed in weight matched controls, respectively. Changes observed in 3H-ouabain binding site concentration were confirmed by K-dependent pNPPase activity measurements. After induction of anesthesia arterial plasma K was measured during intravenous KCl infusion (0.75 mmol KCl x 100 g body wt.-1 x h-1). After KCl infusion for 15 min a less pronounced plasma K increase was seen in rats K supplemented for 2 weeks as compared to weight matched controls (3.4 +/- 0.4 vs 4.7 +/- 0.3 mmol x l-1, p&LT;0.05, n=4 -5). Fasting for one day reduced plasma K and K content in gastrocnemius muscle in rats that had been K supplemented for 2 weeks by 3.1 +/- 0.3 mmol x l-1 (p&LT;0.05, n=5) and 15 +/- 2 _mol x g wet wt.-1 (p&LT;0.05, n=5), respectively. The K supplemented group demonstrated an improved ability to tolerate a K load. In specific, when challenged with KCl infusion, the K supplemented group demonstrated a 42% (p&LT;0.05) lower plasma K rise, associated with a significantly higher increase in K content in gastrocnemius muscle of 7 _mol x g wet wt.-1 (p&LT;0.05, n=5). In conclusion, K supplementation increases plasma K, K content and Na,K-ATPase concentration in skeletal muscles and improves extrarenal K clearance capacity.

Received 12 March 1996; accepted in final form 25 November 1996.
APS Manuscript Number A244-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996