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The Journal of General Physiology, Vol 55, 640-664, Copyright © 1970 by The Rockefeller University Press

ARTICLE

Effects of Caffeine on Crayfish Muscle Fibers

I. Activation of contraction and induction of Ca spike electrogenesis



Dante J. Chiarandini 1, John P. Reuben 1, Philip W. Brandt 1, and Harry Grundfest 1

1 From the Laboratory of Neurophysiology, Department of Neurology, and the Department of Anatomy, 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.

Contractions are evoked in single muscle fibers of crayfish by intracellular as well as extracellular applications of caffeine. Responses to external applications in concentrations above 2 mM could be induced indefinitely. With concentrations above 5 mM the caffeine-induced responses were highly repeatable. Tensions were transient even when the caffeine remained in the bath. There was no change in resting potential, but during the contraction the effective resistance decreased about 10%. A number of factors (change in pH, Ca, K, and Cl) modified the responses. The time course of the tension was greatly prolonged when the transverse tubular system (TTS) was s swollen and was again shortened when the TTS was caused to shrink. An increased permeability to Ca induced by caffeine was evidenced by the transformation of the normally graded electrical responses to Ca spikes, which are insensitive to tetrodotoxin. The overshoot is a function of both external Ca and caffeine. A 10-fold change in Ca changed the overshoot by 19 mv in the presence of 10 mM caffeine and by 29 mv in 80 mM caffeine. The role of the increased permeability to Ca for caffeine-induced contractions will be analyzed in the accompanying paper.

Submitted on September 11, 1969


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