EFFECT OF CYANIDE ON EFFLUX OF CALCIUM FROM SQUID AXONS

1. The average rate constant for loss of 45Ca from an unpoisoned squid axon was 1·8 × 10−3 min−1, corresponding to an efflux of 0·2 p‐mole/cm2 sec. 2. The Ca efflux from unpoisoned axons was reduced if external calcium was replaced with magnesium, or external sodium with lithium, choline or dextrose. Replacing both sodium and calcium reduced the efflux to about 40%. 3. Cyanide caused little immediate change in Ca efflux but after 1½‐2½ hr the efflux increased to 5‐15 times its normal value. The effect was rapidly reversed when cyanide was removed. 4. The large Ca efflux into cyanide was reduced by a factor of three when external calcium was replaced with magnesium and by a further factor of about six when external sodium was replaced with lithium. 5. The Ca efflux from both poisoned and unpoisoned axons had a Q10 of 2‐3, was not affected by ouabain and was greatly reduced by injecting ethyleneglycol bis (aminoethylether)‐N,N′‐tetra‐acetic acid (EGTA). 6. After injecting 45Ca along the axis, the efflux of calcium reached its maximum much more rapidly in a cyanide‐treated axon than in an unpoisoned axon. 7. Pre‐treatment with cyanide greatly increased the rate at which calcium was lost from axoplasm extruded into flattened dialysis bags. A similar effect was observed when cyanide was applied after extrusion. 8. Replacing external sodium glutamate with potassium glutamate greatly reduced the loss of 45Ca from intact axons poisoned with cyanide but had little effect on the loss from extruded axoplasm. 9. The rate constant for loss of the Ca EGTA complex was about 3 × 10−5 min−1 for intact axons and 2 × 10−2 min−1 for extruded axoplasm. 10. A possible explanation of the cyanide effect is that, after poisoning, calcium ions are released from a store and can then exchange at a higher rate with external sodium or calcium. 11. The experiments suggest that part of the calcium efflux may be coupled to sodium entry. 12. Theoretical equations for ‘diffusion and chemical reaction in a cylinder’ are described in the Appendix. © 1969 The Physiological Society