An integrative, in situ approach to examining K+ flux in resting skeletal muscle.
The contributions of Na+/K+-ATPase, K+ channels, and the NaK2Cl cotransporter (NKCC) to total and unidirectional K+ flux were determined in mammalian skeletal muscle at rest. Rat hindlimbs were perfused in situ via the femoral artery with a bovine erythrocyte perfusion medium that contained either 86Rb or 42K, or both simultaneously, to determine differences in ability to trace unidirectional K+ flux in the absence and presence of K+-flux inhibitors. In most experiments, the unidirectional flux of K+ into skeletal muscle (J(in)K) measured using 86Rb was 8-10% lower than J(in)K measured using 42K. Ouabain (5 mM) was used to inhibit Na+/K+-ATPase activity, 0.06 mM bumetanide to inhibit NKCC activity, 1 mM tetracaine or 0.5 mM barium to block K+ channels, and 0.05 mM glybenclamide (GLY) to block ATP-sensitive K+ (K(ATP)) channels. In controls, J(in)K remained unchanged at 0.31 +/- 0.03 micromol x g(-1) x min(-1) during 55 min of perfusion. The ouabain-sensitive Na+/K+-ATPase contributed to 50 +/- 2% of basal J(in)K, K+ channels to 47 +/- 2%, and the NKCC to 12 +/- 1%. GLY had minimal effect on J(in)K, and both GLY and barium inhibited unidirectional efflux of K+ (J(out)K) from the cell through K+ channels. Combined ouabain and tetracaine reduced J(in)K by 55 +/- 2%, while the combination of ouabain, tetracaine, and bumetanide reduced J(in)K by 67 +/- 2%, suggesting that other K+-flux pathways may be recruited because the combined drug effects on inhibiting J(in)K were not additive. The main conclusions are that the NKCC accounted for about 12% of J(in)K, and that K(ATP) channels accounted for nearly all of the J(out)K, in resting skeletal muscle in situ.
Lindinger
M I
MI
Department of Human Biology and Nutritional Sciences, University of Guelph, ON, Canada. mlinding@uoguelph.ca
Hawke
T J
TJ
Vickery
L
L
Bradford
L
L
Lipskie
S L
SL
D000465:Algorithms; D000818:Animals; D001784:Blood Gas Analysis; D002417:Cattle; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000201:enzymology; D006614:Hindlimb / Q000502:physiology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000201:enzymology / Q000378:metabolism; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013449:Sulfonamides; D013779:Tetrodotoxin / Q000494:pharmacology
D004232:Diuretics; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D013449:Sulfonamides; D013779:Tetrodotoxin; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D004121:Dimethyl Sulfoxide