The depolarizing afterpotential of crab muscle fibres. A sodium-dependent process mediated by intracellular calcium

The Journal of Physiology
G Suarez-Kurtz


1. A study was made of the depolarizing afterpotential (d.a.p.) which follows the initial graded electrogenesis of crab muscle fibres. 2. Increasing the strength, duration or amplitude of the stimulating current pulses enhanced both the d.a.p. and the local contractions. 3. Arsenazo III was injected intracellularly and changes in light absorbance by the dye were used to monitor the increase in free sarcoplasmic Ca concentration during excitation-contraction (E-C) coupling. The onset of the absorbance changes occurred during the depolarizing phase of the initial electrogenesis and the maximum value coincided with the peak of the d.a.p. An exponential decay of the absorbance signal occurred during the repolarizing phase of the d.a.p. 4. Ionophoretic injection of EGTA into the sarcoplasm did not affect the initial electrogenesis but did reduce changes in dye absorbance, blocked tension development and abolished the d.a.p. 5. Caffeine (0.1--0.4 mM) markedly enhanced both the d.a.p. and the local contractions, but had no effect on the initial electrogenesis. 6. Replacement of extracellular Na ions with Li, Tris or choline abolished the d.a.p. The initial electrogenesis was enhanced in the choline-containing medium, but was not affec...Continue Reading

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