Role of the Na+-Ca2+ exchange in the calcium paradox in frog auricular trabeculae.
After a Ca2+-free ouabain perfusion of 8-10 min duration, reperfusion of isolated stimulated frog auricular trabeculae with Ca2+ ouabain containing medium resulted in a large and transient contracture. The contracture was weaker in a quiescent preparation or in the absence of ouabain. In sodium-free (Li+ substitute) ouabain containing medium, the amplitude of the contracture was largely decreased while it disappeared completely in Na+-free medium without ouabain. Moreover this contracture was suppressed by 15 mM Mn2+. Although the approach was only indirect, these results suggest that the contracture is due to an entry of Ca2+ ions through the Na+-Ca2+ exchange mechanism and that this could be the unique route of calcium entry during calcium repletion.
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations; D006321:Heart / Q000502:physiology; D006325:Heart Atria / Q000378:metabolism; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011893:Rana esculenta; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D002412:Cations; D008345:Manganese; D010042:Ouabain; D012964:Sodium; D002118:Calcium