The Journal of General Physiology
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The Journal of General Physiology, Vol 55, 665-687, Copyright © 1970 by The Rockefeller University Press

ARTICLE

Effects of Caffeine on Crayfish Muscle Fibers

II. Refractoriness and factors influencing recovery (repriming) of contractile responses



Dante J. Chiarandini 1, John P. Reuben 1, Lucien Girardier 1, George M. Katz 1, and Harry Grundfest 1

1 From the Laboratory of Neurophysiology, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York 10032.

Dr. Chiarandini's present address is Instituto de Anatomia General, Facultad de Medicina, Buenos Aires, Argentina. Dr. Girardier's present address is Institut de Physiologie, Ecole de Medecine, Geneva, Switzerland.

When caffeine evokes a contraction, and only then, crayfish muscle fibers become refractory to a second challenge with caffeine for up to 20 min in the standard saline (5 mM Ko). However, the fibers still respond with contraction to an increase in Ko, though with diminished tension. Addition of Mn slows recovery, but the latter is greatly accelerated during exposure of the fiber to high Ko, or after a brief challenge with high Ko. Neither the depolarization induced by the K, nor the repolarization after its removal accounts for the acceleration, which occurs only if the challenge with K had itself activated the contractile system; acceleration is blocked when contractile responses to K are blocked by reducing the Ca in the bath or by adding Mn. Recovery is accelerated by redistribution of intracellular Cl and by trains of intracellularly applied depolarizing pulses, but not by hyperpolarization. The findings indicate that two sources of Ca can be mobilized to activate the contractile system. Caffeine mobilizes principally the Ca store of the SR. Depolarizations that are induced by high Ko, by transient efflux of Cl, or by intracellularly applied currents mobilize another source of Ca which is strongly dependent upon the entry of Ca from the bathing medium. The sequestering mechanism of the SR apparently can utilize this second source of Ca to replenish its own store so as to accelerate recovery of responsiveness to a new challenge with caffeine.

Submitted on September 11, 1969


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[Abstract] [PDF]


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