Evaluation of the cross-bridge-dependent change in the Ca2+ affinity of troponin C in aequorin-injected ferret ventricular muscles.
Ca2+ affinity of cardiac troponin C (TnC) is regulated by the active cross-bridges (downstream-dependent mechanism). In the present study, we showed one of the methods to evaluate the downstream-dependent change in the Ca2+ affinity of TnC during contraction using the aequorin-injected ferret papillary muscle. For this purpose, the tension-dependent change in the extra-Ca2+ (a transient increase in the intracellular Ca2+ concentration ([Ca2+]i) in response to a quick length reduction) was measured under various conditions. We examined whether the regression line between the magnitude of tension reduction and the magnitude of the normalized extra-Ca2+ (the extra-Ca2+ was divided by [Ca2+]i immediately before length change) (the normalized extra-Ca2+-tension relation) in twitch contraction can be used for the estimation of the downstream-dependent change in the Ca2+ affinity of TnC. The normalized extra-Ca2+-tension relation became shallow by EMD 57033 (EMD) (one of the Ca2+ sensitizers) and by an increase in Ca2+ concentration in the solution ([Ca2+]o) in a concentration-dependent manner. However, 2,3-butanedione monoxime (BDM) (one of the desensitizers) antagonized the effects of EMD and higher [Ca2+]o in a concentration-dependent manner. These effects of EMD and BDM were also observed in the normalized extra-Ca2+-tension relation in tetanic contraction. The normalized extra-Ca2+-tension relation became steep by shortening the initial muscle length before contraction in tetanic contraction. Length-tension relation in twitch contraction was significantly shifted upward by higher [Ca2+]o and EMD, but BDM showed the opposite effects on them in a concentration-dependent manner. Thus, the downstream-dependent change in the Ca2+ affinity of TnC which physiologically functions in intact cardiac muscle can be evaluated using the normalized extra-Ca2+-tension relation.
Ishikawa
Tetsuya
T
Department of Internal Medicine, The Jikei University School of Medicine, 3-25-8 Nishi-Shimbashi, Minato-ku, Tokyo 105-8461, Japan. ishikawa@jikei.ac.jp
O-Uchi
Jin
J
Mochizuki
Seibu
S
Kurihara
Satoshi
S
D000331:Aequorin / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D005289:Ferrets / Q000378:metabolism; D006352:Heart Ventricles / Q000187:drug effects; D049408:Luminescent Agents / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D019209:Troponin C / Q000187:drug effects / Q000378:metabolism*
D049408:Luminescent Agents; D019209:Troponin C; C004717:diacetylmonoxime; D000331:Aequorin; D003931:Diacetyl; D002118:Calcium