Length dependence of Ca(2+)-tension relationship in aequorin-injected ferret papillary muscles.
The possible contractile proteins, which are related to the length-dependent change in the relationship between intracellular Ca2+ concentration ([Ca2+]i) and tension, were investigated using aequorin-injected ferret papillary muscles. Tetanic contraction was produced by applying repetitive stimulation to the ryanodine-treated preparations, and the relationships between [Ca2+]i and tension were measured. When the muscle length was decreased from maximal length (Lmax), at which maximal tension is produced, to 95 and 90% Lmax, the maximal tension was significantly decreased. [Ca2+]i required for producing 50% of the maximal tension was significantly increased from 1.05 +/- 0.04 microM (Lmax) to 1.17 +/- 0.04 microM (95% Lmax) and to 1.22 +/- 0.04 microM (90% Lmax). Isoproterenol (Iso) accentuated the length-dependent change in the [Ca2+]i-tension relationship. The decrease in the Ca2+ sensitivity induced by Iso was larger at shorter muscle lengths compared with that at Lmax. It is, therefore, suggested that adenosine 3',5'-cyclic monophosphate-dependent phosphorylation of troponin I and/or C protein alters the length dependence of the [Ca2+]i-tension relationship and that troponin I and/or C protein might be involved in the length-tension-dependent change in the affinity of the contractile elements for Ca2+.
Komukai
K
K
Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
Kurihara
S
S
D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D005289:Ferrets; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D012433:Ryanodine / Q000494:pharmacology; D019209:Troponin C / Q000378:metabolism; D019210:Troponin I / Q000378:metabolism
D019209:Troponin C; D019210:Troponin I; D012433:Ryanodine; D000331:Aequorin; D007545:Isoproterenol; D002118:Calcium