Increasing muscle length in rat and cat ventricular muscles caused an immediate tension increase followed by a slow increase in peak intracellular calcium over minutes.
The study demonstrates that muscle length affects intracellular calcium transients in cardiac muscle, suggesting that the binding constant of troponin for calcium is tension-dependent.
The calcium-sensitive photoprotein aequorin was micro-injected into cells of rat and cat ventricular muscles. The resulting light emission is a function of intracellular free calcium concentration (Ca2+i). The transient increases in Ca2+i that accompany contraction were monitored. 2. After an increase in muscle length, the developed tension increased immediately and then showed a slow increase over a period of minutes. The peak Ca2+i in each contraction was initially unchanged after an increase in muscle length but then showed a slow increase with a time course similar to that of the slow tension change. 3. As a consequence of these slow changes, the shape of the tension-length relation depends on the procedure used to determine it and this change in shape can be attributed to changes in activation. 4. Immediately after an increase in muscle length the calcium transient was abbreviated. 5. When a quick release was performed during a contraction, a short-lived increase in the Ca2+i was observed following the release. 6. The two previous observations can both be explained if the binding constant of troponin for calcium is a function of developed tension.
Allen et al. (Tue,) conducted a other in mammalian cardiac muscle. Increase in muscle length was evaluated on Intracellular free calcium concentration ([Ca2+]i) transients and developed tension. Increasing muscle length in rat and cat ventricular muscles caused an immediate tension increase followed by a slow increase in peak intracellular calcium over minutes.
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