Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Nai/Cao exchange in squid axon


Until recently, intracellular free calcium has been amenable to measurement and investigation only in cells large enough to permit either microinjection of a suitable Ca sensor such as aequorin or arsenazo III or insertion of a Ca-sensitive microelectrode1,2. This constraint on cell size was removed by the development of the fluorescent Ca2+-sensitive dye Quin-2 and its acetoxymethyl ester, which can be introduced into a wide range of cell types3,4. A major requirement of any intracellular Ca2+ indicator is that it should not disturb intracellular Ca2+ homeostasis and Quin-2 is generally considered to be satisfactory in this respect5. We now report that injection of Quin-2 into squid (Loligo forbesi) axons can almost completely abolish one component of Ca2+ entry—intracellular Na+ (Nai)-dependent Ca2+ inflow, which occurs via Na/Ca exchange6. Mixtures of Ca and Quin-2 that buffer an ionized Ca2+ at close to physiological concentrations also block Nai-dependent Ca2+ influx but these same mixtures fail to block the extracellular Na+ (NaO)-dependent extrusion of Ca2+, showing that Quin-2 acts specifically on Ca2+ inflow.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Baker, P. F. Prog. Biophys. molec. Biol. 24, 177–223 (1972).

    CAS  Article  Google Scholar 

  2. 2

    Baker, P. F. & Dipolo, R. Curr. Topics Membranes Transp. 22, 195–247 (1984).

    CAS  Article  Google Scholar 

  3. 3

    Tsien, R. Y. Biochemistry 19, 2396–2404 (1980).

    CAS  Article  Google Scholar 

  4. 4

    Tsien, R. Y. Nature 290, 527–528 (1981).

    ADS  CAS  Article  Google Scholar 

  5. 5

    Tsien, R. Y., Pozzan, T. & Rink, T. J. J. Cell Biol. 94, 325–334 (1982).

    CAS  Article  Google Scholar 

  6. 6

    Baker, P. F., Blaustein, M. P., Hodgkin, A. L. & Steinhardt, R. A. J. Physiol., Lond. 200, 431–458 (1969).

    CAS  Article  Google Scholar 

  7. 7

    Baker, P. F. in Calcium and Cell Function (ed. Cuthbert, A. W.) (Macmillan, London, 1970).

    Google Scholar 

  8. 8

    Baker, P. F. & McNaughton, P. A. J. Physiol., Lond. 259, 103–144 (1976).

    CAS  Article  Google Scholar 

  9. 9

    Simons, T. J. B. J. Membrane Biol. 84, 61–77 (1985).

    CAS  Article  Google Scholar 

  10. 10

    Arslan, P., Di Virgilio, F., Beltrame, M., Tsien, R. Y. & Pozzan, T. J. biol. Chem. (in the press).

  11. 11

    Dipolo, R. J. gen. Physiol. 73, 91–113 (1979).

    CAS  Article  Google Scholar 

  12. 12

    Alien, T. J. A. & Baker, P. F. J. Physiol., Lond. 345, 80p (1983).

Download references

Author information



Rights and permissions

Reprints and Permissions

About this article

Cite this article

Allen, T., Baker, P. Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Nai/Cao exchange in squid axon. Nature 315, 755–756 (1985).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.