Abstract
Ca efflux in dialyzed squid axons was measured with 45Ca as a function of internal ionized Ca in the range 0.005-10 muM. Internal Ca stores were depleted by treatment with CN and dialysis with media free of high energy compounds. The [Ca]iota was stabilized with millimolar concentrations of EDTA, EGTA, or DTPA. Nonspecific leak of chelated Ca was measured with [14C]-EDTA and found to be 0.02 pmol/cm2s/mM EDTA. Correction of the measured Ca efflux for this leak of chelated calcium was made when appropriate. Ca efflux was roughly linear with internal free Ca in the range 0.005-0.1 muM. Above 0.1 muM, efflux was less than proportional to concentration but did not saturate at the highest concentration studied. Ca efflux was reduced about 50% by replacement of external Na with Li at Caiota approximately 1 muM, but was insensitive to such replacement for Ca less than 0.1 muM. Ca efflux was insensitive to internal Mg in the range 0-4 mM, indicating that the Ca pump favors Ca over Mg by a factor of about 10(6). Ca efflux was reduced about 60% by increasing internal Na from 1 to 80 mM. This effect could represent weak interference of a Ca carrier by Na or a loss of driving force because of a reduction in ENa - Em occasioned by an increase in Naiota. A few measurements were made of Ca influx in intact and in dialyzed fibers. In both cases, Ca influx increased when external Na was replaced by Li.
Full Text
The Full Text of this article is available as a PDF (1.8 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- 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]
- Ashley C. C., Ellory J. C., Hainaut K. Calcium movements in single crustacean muscle fibres. J Physiol. 1974 Oct;242(1):255–272. doi: 10.1113/jphysiol.1974.sp010705. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ashley C. C., Ellory J. C. The efflux of magnesium from single crustacean muscle fibres. J Physiol. 1972 Nov;226(3):653–674. doi: 10.1113/jphysiol.1972.sp010002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 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]
- Baker P. F., Glitsch H. G. Does metabolic energy participate directly in the Na+-dependent extrusion of Ca2+ -Ca2+ ions from squid giant axons? J Physiol. 1973 Aug;233(1):44P–46P. [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, Mullins L. J. Effects of membrane potential on sodium and potassium fluxes in squid axons. Ann N Y Acad Sci. 1974;242(0):406–433. doi: 10.1111/j.1749-6632.1974.tb19106.x. [DOI] [PubMed] [Google Scholar]
- 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]
- Brinley F. J., Jr, Mullins L. J. Sodium fluxes in internally dialyzed squid axons. J Gen Physiol. 1968 Aug;52(2):181–211. doi: 10.1085/jgp.52.2.181. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 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]
- 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]
- 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]
- Mullins L. J. Ion and molecule fluxes in squid axons. Ann N Y Acad Sci. 1966 Jul 14;137(2):830–836. doi: 10.1111/j.1749-6632.1966.tb50203.x. [DOI] [PubMed] [Google Scholar]
- Russell J. M., Blaustein M. P. Calcium efflux from barnacle muscle fibers. Dependence on external cations. J Gen Physiol. 1974 Feb;63(2):144–167. doi: 10.1085/jgp.63.2.144. [DOI] [PMC free article] [PubMed] [Google Scholar]
- van Breemen C., De Weer P. Lanthanum inhibition of 45Ca efflux from the squid giant axon. Nature. 1970 May 23;226(5247):760–761. doi: 10.1038/226760a0. [DOI] [PubMed] [Google Scholar]