Tension-dependent changes of the intracellular Ca2+ transients in ferret ventricular muscles.
1. We measured the change in intracellular Ca2+ transients, using aequorin, in response to muscle length change during twitch contraction in ferret ventricular muscles. 2. Intracellular Ca2+ concentration ([Ca2+]i) was transiently increased when the muscle length was quickly shortened to 92% of maximum length (Lmax) at various times after stimulation (this increase in [Ca2+] is termed extra-Ca2+). The magnitude of extra-Ca2+, measured at different extracellular Ca2+ concentrations ([Ca2+]o), showed a dependence upon the magnitude of tension reduction and upon [Ca2+]i immediately before the length change. 3. In the presence of caffeine (5 mM), the difference between the Ca2+ transient at Lmax and at shorter lengths showed a time course similar to the difference between the developed tension at both lengths. A quick release in the caffeine-treated preparation produced the extra-Ca2+ with a slower time course compared with that observed in the absence of caffeine. Stretching the muscle from 96% Lmax to Lmax produced more active tension and decreased [Ca2+]i. 4. These results indicate that the affinity of troponin-C, a major Ca2+ binding protein, which controls contraction, is influenced by developed tension i.e. cross-bridge attachment and detachment.
Kurihara
S
S
Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
Komukai
K
K
D000331:Aequorin; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004558:Electric Stimulation; D005289:Ferrets; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*
D015220:Calcium Channels; D000697:Central Nervous System Stimulants; D002110:Caffeine; D000331:Aequorin; D002118:Calcium