Impaired muscle Ca2+ and K+ regulation contribute to poor exercise performance post-lung transplantation.
Lung transplant recipients (LTx) exhibit marked peripheral limitations to exercise. We investigated whether skeletal muscle Ca2+ and K+ regulation might be abnormal in eight LTx and eight healthy controls. Peak oxygen consumption and arterialized venous plasma [K+] (where brackets denote concentration) were measured during incremental exercise. Vastus lateralis muscle was biopsied at rest and analyzed for sarcoplasmic reticulum Ca2+ release, Ca2+ uptake, and Ca2+-ATPase activity rates; fiber composition; Na+-K+-ATPase (K+-stimulated 3-O-methylfluorescein phosphatase) activity and content ([3H]ouabain binding sites); as well as for [H+] and H+-buffering capacity. Peak oxygen consumption was 47% less in LTx (P < 0.05). LTx had lower Ca2+ release (34%), Ca2+ uptake (31%), and Ca2+-ATPase activity (25%) than controls (P < 0.05), despite their higher type II fiber proportion (LTx, 75.0 +/- 5.8%; controls, 43.5 +/- 2.1%). Muscle [H+] was elevated in LTx (P < 0.01), but buffering capacity was similar to controls. Muscle 3-O-methylfluorescein phosphatase activity was 31% higher in LTx (P < 0.05), but [3H]ouabain binding content did not differ significantly. However, during exercise, the rise in plasma [K+]-to-work ratio was 2.6-fold greater in LTx (P < 0.05), indicating impaired K+ regulation. Thus grossly subnormal muscle calcium regulation, with impaired potassium regulation, may contribute to poor muscular performance in LTx.
McKenna
Michael J
MJ
School of Human Movement, Recreation and Performance (FO22 Victoria Univ. of Technology, P.O. Box 14428, MCMC, Melbourne, Melbourne, Victoria 8001, Australia. michael.mckenna@vu.edu.au
Fraser
Steve F
SF
Li
Jia L
JL
Wang
Xiao N
XN
Carey
Michael F
MF
Side
Eleonora A
EA
Morton
Judith
J
Snell
Gregory I
GI
Kjeldsen
Keld
K
Williams
Trevor J
TJ
D000328:Adult; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016040:Lung Transplantation; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000378:metabolism; D010101:Oxygen Consumption; D010809:Physical Fitness; D011184:Postoperative Period; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D010042:Ouabain; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium