Ouabain stimulates unidirectional and net potassium efflux in resting mammalian skeletal muscle.
The present study compared ouabain-sensitive unidirectional K+ flux into (JinK) and out of (JoutK) perfused rat hindlimb skeletal muscle in situ and mouse flexor digitorum brevis (FDB) in vitro. In situ, 5 mM ouabain inhibited 54 +/- 4% of the total JinK in 28 +/- 1 min, and increased the net and unidirectional efflux of K+ within 4 min. In contrast, 1.8 mM ouabain inhibited 40 +/- 8% of the total JinK in 38 +/- 2 min, but did not significantly affect JoutK. In vitro, 1.8 and 0.2 mM ouabain decreased JinK to a greater extent (83 +/- 5%) than in situ, but did not significantly affect 42K loss rate compared with controls. The increase in unidirectional K+ efflux (JoutK) with 5 mM ouabain in situ was attributed to increased K+ efflux through cation channels, since addition of barium (1 mM) to ouabain-perfused muscles returned JoutK to baseline values within 12 min. Perfusion with 5 mM ouabain plus 2 mM tetracaine for 30 min decreased JinK 46 +/- 9% (0.30 +/- 0.03 to 0.16 +/- 0.02 micromol x min(-1) x g(-1)), however tetracaine was unable to abolish the ouabain-induced increase in unidirectional K+ efflux. In both rat hindlimb and mouse FDB, tetracaine had no effect on JoutK. Perfusion of hindlimb muscle with 0.1 mM tetrodotoxin (TTX, a Na+ channel blocker) decreased JinK by 15 +/- 1%, but had no effect on JoutK; subsequent addition of ouabain (5 mM) decreased JinK a further 32 +/- 2%. The ouabain-induced increase in unidirectional K+ efflux did not occur when TTX was perfused prior to and during perfusion with 5 mM ouabain. We conclude that 5 mM ouabain increases the unidirectional efflux of K+ from skeletal muscle through a barium and TTX-sensitive pathway, suggestive of voltage sensitive Na+ channels, in addition to inhibiting Na+/K+-ATPase activity.
Hawke
T J
TJ
Department of Human Biology and Nutritional Sciences, University of Guelph, ON, Canada. thomas.hawke@utsouthwestern.edu
Lessard
S
S
Vickery
L
L
Lipskie
S L
SL
Lindinger
M I
MI
D000818:Animals; D001464:Barium / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006614:Hindlimb; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D051379:Mice; D018482:Muscle, Skeletal / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013748:Tetracaine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D026941:Sodium Channel Blockers; D013748:Tetracaine; D001464:Barium; D013779:Tetrodotoxin; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium