Intracellular sodium-activity at rest and after tetanic stimulation in muscles of normal and dystrophic (dy2J/dy2J) C57BL/6J mice.
Intrafiber Na+-activity, (aNa)i, was measured in vivo in single muscle fibers in the gastrocnemius and soleus muscles of normal and dystrophic (dy2J/dy2J) C57BL/6J mice by means of double-barrel Na+-selective microelectrodes. Values of (aNa)i in normal gastrocnemius and soleus muscles were 9.8 +/- 1.0 mM (means +/- SE; N = 15) and 13.7 +/- 1 mM (N = 19), respectively. Values of (aNa)i in dystrophic gastrocnemius and soleus muscles were 18.7 +/- 1.3 mM (N = 10) and 26.2 +/- 3.3 mM (N = 15), respectively. The soleus muscle of both normal and dystrophic mice was "Na+ loaded" by an intermittent tetanus delivered via the sciatic nerve. Muscles from both normal and dystrophic mice could extrude the Na+ load at similar rates. The results suggest that in the dystrophic mice the elevated (aNa)i is not due to inability of the Na+ pump to respond to a Na+ load; rather, it may be due to an alteration in the affinity of the pump for Na+, resulting in a different "set point" for (aNa)i.
D000818:Animals; D004558:Electric Stimulation; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008839:Microelectrodes; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D009137:Muscular Dystrophy, Animal / Q000378:metabolism* / Q000503:physiopathology; D012016:Reference Values; D012146:Rest; D012964:Sodium / Q000378:metabolism*
D012964:Sodium