Abstract
The magnitude of the activating effect of ATP on the Ca efflux was explored at different [Ca++]i in squid axons previously exposed to cyanide seawater and internally dialyzed with a medium free of ATP and containing p-trifluoro methoxy carbonyl cyanide phenyl hydrazine. At the lowest [Ca++]i used (0.06 micron more than 95% of the Ca efflux depends on ATP. At high [Ca++]i (100 micron), 50-60% of the Ca efflux still depends on ATP. The apparant affinity constant for ATP was not significantly affected in the range of [Ca++]i from 0.06 to 1 micron. Axons dialyzed to reduce their internal magnesium failed to show the usual activation of the Ca efflux when the Tris or the sodium salt of ATP was used. Only in the presence of internal magnesium is ATP able to stimulate the Ca efflux. Nine naturally occurring high-energy phosphate compounds were ineffective in supporting calcium efflux. These compounds were: UTP, GTP, CTP, UDP, CDP, ADP, AMP, CAMP, and acetyl phosphate. The compounds 2' deoxy-ATP and the hydrolyzable analog alpha,beta-methylene ATP were able to activate the Ca efflux. The nonhydrolyzable analog beta,gamma-methylene ATP competes with ATP for the activating site, but is unable to activate the Ca efflux. The results are discussed in terms of the specificity of the nucleotide site responsible for the ATP-dependent Ca efflux.
Full Text
The Full Text of this article is available as a PDF (1.1 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- 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]
- 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]
- Blaustein M. P., Russell J. M., Weer P. Calcium efflux from internally dialyzed squid axons: the influence of external and internal cations. J Supramol Struct. 1974;2(5-6):558–581. doi: 10.1002/jss.400020505. [DOI] [PubMed] [Google Scholar]
- 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]
- 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]
- 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]
- 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]
- EGGLESTON L. V., HEMS R. Separation of adenosine phosphates by paper chromotography and the equilibrium constant of the myokinase system. Biochem J. 1952 Sep;52(1):156–160. doi: 10.1042/bj0520156. [DOI] [PMC free article] [PubMed] [Google Scholar]
- KAPELLER-ADLER R., IGGO B. Histamine and its derivatives in human urine. Biochim Biophys Acta. 1957 Aug;25(2):394–402. doi: 10.1016/0006-3002(57)90484-5. [DOI] [PubMed] [Google Scholar]
- 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]
- Schatzmann H. J., Vincenzi F. F. Calcium movements across the membrane of human red cells. J Physiol. 1969 Apr;201(2):369–395. doi: 10.1113/jphysiol.1969.sp008761. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Simons T. J. The interaction of ATP-analogues possessing a blocked gamma-phosphate group with the sodium pump in human red cells. J Physiol. 1975 Jan;244(3):731–739. doi: 10.1113/jphysiol.1975.sp010822. [DOI] [PMC free article] [PubMed] [Google Scholar]