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. 1976 Apr 1;67(4):433–467. doi: 10.1085/jgp.67.4.433

Ionized calcium concentrations in squid axons

PMCID: PMC2214921  PMID: 818340

Abstract

Values for ionized [Ca] in squid axons were obtained by measuring the light emission from a 0.1-mul drop of aequorin confined to a plastic dialysis tube of 140-mum diameter located axially. Ionized Ca had a mean value of 20 x 10(-9) M as judged by the subsequent introduction of CaEGTA/EGTA buffer (ratio ca. 0.1) into the axoplasm, and light measurement on a second aequorin drop. Ionized Ca in axoplasma was also measured by introducing arsenazo dye into an axon by injection and measuring the Ca complex of such a dye by multichannel spectrophotometry. Values so obtained were ca. 50 x 10(-9) M as calibrated against CaEGTA/EGTA buffer mixtures. Wth a freshly isolated axon in 10 mM Ca seawater, the aequorin glow invariably increased with time; a seawater [Ca] of 2-3 mM allowed a steady state with respect to [Ca]. Replacement of Na+ in seawater with choline led to a large increase in light emission from aequorin. Li seawater partially reversed this change and the reintroduction of Na+ brought light levels back to their initial value. Stimulation at 60/s for 2-5 min produced an increase in aequorin glow about 0.1% of that represented by the known Ca influx, suggesting operationally the presence of substantial Ca buffering. Treatment of an axon with CN produced a very large increase in aequorin glow and in Ca arsenazo formation only if the external seawater contained Ca.

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Selected References

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  1. Ashley C. C. An estimate of calcium concentration changes during the contraction of single muscle fibres. J Physiol. 1970 Sep;210(2):133P–134P. [PubMed] [Google Scholar]
  2. Azzi A., Chance B. The "energized state" of mitochondria: lifetime and ATP equivalence. Biochim Biophys Acta. 1969 Oct 21;189(2):141–151. doi: 10.1016/0005-2728(69)90042-5. [DOI] [PubMed] [Google Scholar]
  3. Baker P. F., Blaustein M. P., Hodgkin A. L., Steinhardt R. A. The influence of calcium on sodium efflux in squid axons. J Physiol. 1969 Feb;200(2):431–458. doi: 10.1113/jphysiol.1969.sp008702. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Baker P. F., Crawford A. C. Mobility and transport of magnesium in squid giant axons. J Physiol. 1972 Dec;227(3):855–874. doi: 10.1113/jphysiol.1972.sp010062. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Baker P. F., Hodgkin A. L., Ridgway E. B. Depolarization and calcium entry in squid giant axons. J Physiol. 1971 Nov;218(3):709–755. doi: 10.1113/jphysiol.1971.sp009641. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Blaustein M. P., Hodgkin A. L. The effect of cyanide on the efflux of calcium from squid axons. J Physiol. 1969 Feb;200(2):497–527. doi: 10.1113/jphysiol.1969.sp008704. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Blaustein M. P. The interrelationship between sodium and calcium fluxes across cell membranes. Rev Physiol Biochem Pharmacol. 1974;70:33–82. doi: 10.1007/BFb0034293. [DOI] [PubMed] [Google Scholar]
  8. Boron W. F., De Weer P. Intracellular pH transients in squid giant axons caused by CO2, NH3, and metabolic inhibitors. J Gen Physiol. 1976 Jan;67(1):91–112. doi: 10.1085/jgp.67.1.91. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Brinley F. J., Jr, Mullins L. J. Sodium extrusion by internally dialyzed squid axons. J Gen Physiol. 1967 Nov;50(10):2303–2331. doi: 10.1085/jgp.50.10.2303. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Brinley F. J., Jr, Scarpa A. Ionized magnesium concentration in axoplasm of dialyzed squid axons. FEBS Lett. 1975 Jan 15;50(1):82–85. doi: 10.1016/0014-5793(75)81046-5. [DOI] [PubMed] [Google Scholar]
  11. Brinley F. J., Jr, Spangler S. G., Mullins L. J. Calcium and EDTA fluxes in dialyzed squid axons. J Gen Physiol. 1975 Aug;66(2):223–250. doi: 10.1085/jgp.66.2.223. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. CALDWELL P. C. The phosphorus metabolism of squid axons and its relationship to the active transport of sodium. J Physiol. 1960 Jul;152:545–560. doi: 10.1113/jphysiol.1960.sp006508. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Doane M. G. Fluorometric measurement of pyridine nucleotide reduction in the giant axon of the squid. J Gen Physiol. 1967 Dec;50(11):2603–2632. doi: 10.1085/jgp.50.11.2603. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. HODGKIN A. L., KEYNES R. D. Experiments on the injection of substances into squid giant axons by means of a microsyringe. J Physiol. 1956 Mar 28;131(3):592–616. doi: 10.1113/jphysiol.1956.sp005485. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. HODGKIN A. L., KEYNES R. D. Movements of labelled calcium in squid giant axons. J Physiol. 1957 Sep 30;138(2):253–281. doi: 10.1113/jphysiol.1957.sp005850. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Meech R. W., Standen N. B. Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx. J Physiol. 1975 Jul;249(2):211–239. doi: 10.1113/jphysiol.1975.sp011012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Moisescu D. G., Ashley C. C., Campbell A. K. Comparative aspects of the calcium-sensitive photoproteins aequorin and obelin. Biochim Biophys Acta. 1975 Jul 8;396(1):133–140. doi: 10.1016/0005-2728(75)90196-6. [DOI] [PubMed] [Google Scholar]
  18. Mullins L. J., Brinley F. J., Jr Sensitivity of calcium efflux from squid axons to changes in membrane potential. J Gen Physiol. 1975 Feb;65(2):135–152. doi: 10.1085/jgp.65.2.135. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Mullins L. J., Brinley F. J., Jr Some factors influencing sodium extrusion by internally dialyzed squid axons. J Gen Physiol. 1967 Nov;50(10):2333–2355. doi: 10.1085/jgp.50.10.2333. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Rottenberg H., Scarpa A. Calcium uptake and membrane potential in mitochondria. Biochemistry. 1974 Nov 5;13(23):4811–4817. doi: 10.1021/bi00720a020. [DOI] [PubMed] [Google Scholar]
  22. SHIMOMURA O., JOHNSON F. H., SAIGA Y. Extraction, purification and properties of aequorin, a bioluminescent protein from the luminous hydromedusan, Aequorea. J Cell Comp Physiol. 1962 Jun;59:223–239. doi: 10.1002/jcp.1030590302. [DOI] [PubMed] [Google Scholar]
  23. Scarpa A. Indicators of free magnesium in biological systems. Biochemistry. 1974 Jul 2;13(14):2789–2794. doi: 10.1021/bi00711a001. [DOI] [PubMed] [Google Scholar]
  24. Scarpa A. Spectrophotometric measurement of calcium by murexide. Methods Enzymol. 1972;24:343–351. doi: 10.1016/0076-6879(72)24082-4. [DOI] [PubMed] [Google Scholar]
  25. Shimomura O., Johnson F. H. Properties of the bioluminescent protein aequorin. Biochemistry. 1969 Oct;8(10):3991–3997. doi: 10.1021/bi00838a015. [DOI] [PubMed] [Google Scholar]

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