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J Physiol Vol 476, Issue 2 pp 315-322
Copyright © 1994 by The Physiological Society
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Ca(2+)-dependent negative control mechanism for Ca(2+)-induced Ca2+ release in crayfish muscle.

 S Györke and P Palade

Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.

The mechanism of termination of Ca(2+)-induced Ca2+ release (CICR) from the sarcoplasmic reticulum has been investigated in voltage clamped cut crayfish muscle fibres loaded with rhod-2. During depolarizing steps evoking calcium current (ICa), Ca2+ release was first activated. Then the release rapidly (tau approximately 6 ms) declined, as evidenced by the rate of change of the intracellular fluorescence signal representing a Ca2+ transient. The rapid termination of release was not accounted for by inactivation of the trigger ICa or depletion of Ca2+ from the SR, since the rate at which release declined was constant under conditions where the rate of ICa inactivation and the amount of Ca2+ released varied widely. Pre-elevations of [Ca2+]i with prepulses or photolysis of caged Ca2+ caused depression of Ca2+ release during a subsequent test pulse. When the rate of ICa onset was varied by applying voltage ramps with different slopes, currents with fast onset elicited larger Ca2+ release than calcium currents with slower onset, even though the amplitude of the currents was the same. These results suggest that a Ca(2+)-dependent negative control mechanism exists which mediates the termination of CICR independently of the duration of the trigger ICa and before significant depletion of Ca2+ in the SR occurs.




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