Effect of external sodium substitution on potassium contractures of mammalian muscles: possible involvement of sarcolemma-bound calcium and Na+-Ca2+ exchange.
Isometric tension of K+ contractures, membrane potential, internal Na+ activity (alpha iNa) and intracellular pH (pHi) have been measured in vitro under conditions which modify sarcolemma-bound calcium and the activity of the Na+-Ca2+ exchange of normal mammalian soleus muscle. In the absence of external Na+ and for a given high external K+, the maximum amplitude of the contracture was increased (Na+ replaced by TEA+) or decreased (Na+ replaced by Li+ or Cs+) compared with that obtained in the presence of Na+. Replacement of external Na+ by another monovalent cation (TEA+) did not induce any change of pHi. However the concomitant decrease of alpha iNa was related to a Na+-Ca2+ exchange across the sarcolemmal membrane. The data suggest that in soleus muscle, a sarcolemmal calcium pool is involved during the development of K+ contractures.
Noireaud
J
J
Laboratory of General Physiology, National Veterinary School, University of Nantes, France.
Leoty
C
C
D000818:Animals; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D007474:Ion Exchange; D007537:Isometric Contraction / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*
D012964:Sodium; D011188:Potassium; D002118:Calcium