Skip to main content
PMC home page
The Journal of General Physiology logoLink to The Journal of General Physiology
. 1979 Jan 1;73(1):91–113. doi: 10.1085/jgp.73.1.91

Calcium influx in internally dialyzed squid giant axons

PMCID: PMC2215233  PMID: 438767

Abstract

A method has been developed to measure Ca influx in internally dialyzed squid axons. This was achieved by controlling the dialyzed segment of the axon exposed to the external radioactive medium. The capacity of EGTA to buffer all the Ca entering the fiber was explored by changing the free EGTA at constant [Ca++]i. At a free [EGTA]i greater than 200 microM, the measured resting Ca influx and the expected increment in Ca entry during electrical stimulation were independent of the axoplasmic free [EGTA]. To avoid Ca uptake by the mitochondrial system, cyanide, oligomycin, and FCCP were included in the perfusate. Axons dialyzed with a standard medium containing: [ATP] = 2 mM, [Ca++]i = 0.06 microM, [Ca++]o = 10 mM, [Na+]i = 70 mM, and [Na+]o = 465 mM, gave a mean Ca influx of 0.14 +/- 0.012 pmol.cm-2.s-1 (n = 12. Removal of ATP drops the Ca influx to 0.085 +/- 0.007 pmol.cm-2.s-1 (n = 12). Ca influx increased to 0.35 pmol.cm-2,s-1 when Nao was removed. The increment was completely abolished by removing Nai+ and (or) ATP from the dialysis medium. At nominal zero [Ca++]i, no Nai-dependent Ca influx was observed. In the presence of ATP and Nai [Ca++]i activates the Ca influx along a sigmoid curve without saturation up to 1 microM [Ca++]i. Removal of Nai+ always reduced the Ca influx to a value similar to that observed in the absence of [Ca++]i (0.087 +/- 0.008 pmol.cm-2.s-1; n = 11). Under the above standard conditions, 50-60% of the total Ca influx was found to be insensitive to Nai+, Cai++, and ATP, sensitive to membrane potential, and partially inhibited by external Co++.

Full Text

The Full Text of this article is available as a PDF (1.2 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. 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]
  2. 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]
  3. Baker P. F., McNaughton P. A. Kinetics and energetics of calcium efflux from intact squid giant axons. J Physiol. 1976 Jul;259(1):103–144. doi: 10.1113/jphysiol.1976.sp011457. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Baker P. F. Transport and metabolism of calcium ions in nerve. Prog Biophys Mol Biol. 1972;24:177–223. doi: 10.1016/0079-6107(72)90007-7. [DOI] [PubMed] [Google Scholar]
  5. 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]
  6. Blaustein M. P., Russell J. M. Sodium-calcium exchange and calcium-calcium exchange in internally dialyzed squid giant axons. J Membr Biol. 1975 Jul 24;22(3-4):285–312. doi: 10.1007/BF01868176. [DOI] [PubMed] [Google Scholar]
  7. Blaustein M. P., Santiago E. M. Effects of internal and external cations and of ATP on sodium-calcium and calcium-calcium exchange in squid axons. Biophys J. 1977 Oct;20(1):79–111. doi: 10.1016/S0006-3495(77)85538-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. 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]
  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, 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]
  11. Brinley F. J., Jr, Tiffert T., Scarpa A., Mullins L. J. Intracellular calcium buffering capacity in isolated squid axons. J Gen Physiol. 1977 Sep;70(3):355–384. doi: 10.1085/jgp.70.3.355. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. DiPolo R. Characterization of the ATP-dependent calcium efflux in dialyzed squid giant axons. J Gen Physiol. 1977 Jun;69(6):795–813. doi: 10.1085/jgp.69.6.795. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Dipolo R. Calcium efflux from internally dialyzed squid giant axons. J Gen Physiol. 1973 Nov;62(5):575–589. doi: 10.1085/jgp.62.5.575. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Dipolo R. Effect of ATP on the calcium efflux in dialyzed squid giant axons. J Gen Physiol. 1974 Oct;64(4):503–517. doi: 10.1085/jgp.64.4.503. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Dipolo R., Requena J., Brinley F. J., Jr, Mullins L. J., Scarpa A., Tiffert T. Ionized calcium concentrations in squid axons. J Gen Physiol. 1976 Apr;67(4):433–467. doi: 10.1085/jgp.67.4.433. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. 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]
  17. Hoffman P. G., Tosteson D. C. Active sodium and potassium transport in high potassium and low potassium sheep red cells. J Gen Physiol. 1971 Oct;58(4):438–466. doi: 10.1085/jgp.58.4.438. [DOI] [PMC free article] [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. Requena J. Calcium efflux from squid axons under constant sodium electrochemical gradient. J Gen Physiol. 1978 Oct;72(4):443–470. doi: 10.1085/jgp.72.4.443. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Requena J., DiPolo R., Brinley F. J., Jr, Mullins L. J. The control of ionized calcium in squid axons. J Gen Physiol. 1977 Sep;70(3):329–353. doi: 10.1085/jgp.70.3.329. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from The Journal of General Physiology are provided here courtesy of The Rockefeller University Press

RESOURCES