Skip to main content
PMC home page
The Journal of General Physiology logoLink to The Journal of General Physiology
. 1991 Mar 1;97(3):561–578. doi: 10.1085/jgp.97.3.561

Interactions of neosaxitoxin with the sodium channel of the frog skeletal muscle fiber

PMCID: PMC2216488  PMID: 1645395

Abstract

Neosaxitoxin (neoSTX) differs structurally from saxitoxin (STX) in that the hydrogen on N-1 is replaced by a hydroxyl group. On single frog skeletal muscle fibers in the vaseline-gap voltage clamp, the concentrations for reducing the maximum sodium current by 50% (ED50) at pH's 6.50, 7.25, and 8.25 are, respectively, 4.9, 5.1, and 8.9 nM for STX and 1.6, 2.7, and 17.2 nM for neoSTX. The relative potencies of STX at the different pH's closely parallel the relative abundance of the protonated form of the 7,8,9 guanidinium function, but the relative potencies of neoSTX at the same pH's vary with the relative abundance of the deprotonated N-1 group. In constant-ratio mixtures of the two toxins, the observed ED50's are consistent with the notion that the two toxins compete for the same site. At pH's 6.50 and 7.25, the best agreement between observed and computed values is obtained when the efficacy term (epsilon) for either toxin is 1. At pH 8.25 the best agreement is obtained if the efficacy is 1 for STX but 0.75 for neo- STX. The marked pH dependence of the actions of neoSTX probably reflects the presence of a site in the receptor that interacts with the N-1 -OH, in addition to those interacting with the 7,8,9 guanidinium and the C-12 hydroxyl groups. Considering the three-dimensional structure of the STX and neoSTX molecules, the various site points are probably located in a fold or a crevice of the channel protein, where the extracellular orifice of the sodium channel is located.

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. ARIENS E. J. Affinity and intrinsic activity in the theory of competitive inhibition. I. Problems and theory. Arch Int Pharmacodyn Ther. 1954 Sep 1;99(1):32–49. [PubMed] [Google Scholar]
  2. Barchi R. L. Biochemistry of sodium channels from mammalian muscle. Ann N Y Acad Sci. 1986;479:179–185. doi: 10.1111/j.1749-6632.1986.tb15569.x. [DOI] [PubMed] [Google Scholar]
  3. Barchi R. L., Weigele J. B. Characteristics of saxitoxin binding to the sodium channel of sarcolemma isolated from rat skeletal muscle. J Physiol. 1979 Oct;295:383–396. doi: 10.1113/jphysiol.1979.sp012975. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Genenah A. A., Shimizu Y. Specific toxicity of paralytic shellfish poisons. J Agric Food Chem. 1981 Nov-Dec;29(6):1289–1291. doi: 10.1021/jf00108a047. [DOI] [PubMed] [Google Scholar]
  5. Green W. N., Weiss L. B., Andersen O. S. Batrachotoxin-modified sodium channels in planar lipid bilayers. Characterization of saxitoxin- and tetrodotoxin-induced channel closures. J Gen Physiol. 1987 Jun;89(6):873–903. doi: 10.1085/jgp.89.6.873. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Guo X. T., Uehara A., Ravindran A., Bryant S. H., Hall S., Moczydlowski E. Kinetic basis for insensitivity to tetrodotoxin and saxitoxin in sodium channels of canine heart and denervated rat skeletal muscle. Biochemistry. 1987 Dec 1;26(24):7546–7556. doi: 10.1021/bi00398a003. [DOI] [PubMed] [Google Scholar]
  7. Hille B., Campbell D. T. An improved vaseline gap voltage clamp for skeletal muscle fibers. J Gen Physiol. 1976 Mar;67(3):265–293. doi: 10.1085/jgp.67.3.265. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Hille B. The receptor for tetrodotoxin and saxitoxin. A structural hypothesis. Biophys J. 1975 Jun;15(6):615–619. doi: 10.1016/S0006-3495(75)85842-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Hu S. L., Kao C. Y. Evaluation of a new tetrodotoxin preparation. Toxicon. 1985;23(5):723–724. doi: 10.1016/0041-0101(85)90001-7. [DOI] [PubMed] [Google Scholar]
  10. Kao C. Y., Kao P. N., James-Kracke M. R., Koehn F. E., Wichmann C. F., Schnoes H. K. Actions of epimers of 12-(OH)-reduced saxitoxin and of 11-(OSO3)-saxitoxin on squid axon. Toxicon. 1985;23(4):647–655. doi: 10.1016/0041-0101(85)90369-1. [DOI] [PubMed] [Google Scholar]
  11. Kao C. Y. Structure-activity relations of tetrodotoxin, saxitoxin, and analogues. Ann N Y Acad Sci. 1986;479:52–67. doi: 10.1111/j.1749-6632.1986.tb15561.x. [DOI] [PubMed] [Google Scholar]
  12. Kao C. Y., Walker S. E. Active groups of saxitoxin and tetrodotoxin as deduced from actions of saxitoxin analogues on frog muscle and squid axon. J Physiol. 1982 Feb;323:619–637. doi: 10.1113/jphysiol.1982.sp014095. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Kao P. N., James-Kracke M. R., Kao C. Y. The active guanidinium group of saxitoxin and neosaxitoxin identified by the effects of pH on their activities on squid axon. Pflugers Arch. 1983 Aug;398(3):199–203. doi: 10.1007/BF00657151. [DOI] [PubMed] [Google Scholar]
  14. Moczydlowski E., Garber S. S., Miller C. Batrachotoxin-activated Na+ channels in planar lipid bilayers. Competition of tetrodotoxin block by Na+. J Gen Physiol. 1984 Nov;84(5):665–686. doi: 10.1085/jgp.84.5.665. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Moczydlowski E., Hall S., Garber S. S., Strichartz G. S., Miller C. Voltage-dependent blockade of muscle Na+ channels by guanidinium toxins. J Gen Physiol. 1984 Nov;84(5):687–704. doi: 10.1085/jgp.84.5.687. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Noda M., Shimizu S., Tanabe T., Takai T., Kayano T., Ikeda T., Takahashi H., Nakayama H., Kanaoka Y., Minamino N. Primary structure of Electrophorus electricus sodium channel deduced from cDNA sequence. Nature. 1984 Nov 8;312(5990):121–127. doi: 10.1038/312121a0. [DOI] [PubMed] [Google Scholar]
  17. Numa S., Noda M. Molecular structure of sodium channels. Ann N Y Acad Sci. 1986;479:338–355. doi: 10.1111/j.1749-6632.1986.tb15580.x. [DOI] [PubMed] [Google Scholar]
  18. STEPHENSON R. P. A modification of receptor theory. Br J Pharmacol Chemother. 1956 Dec;11(4):379–393. doi: 10.1111/j.1476-5381.1956.tb00006.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Schantz E. J., Ghazarossian V. E., Schnoes H. K., Strong F. M., Springer J. P., Pezzanite J. O., Clardy J. Letter: The structure of saxitoxin. J Am Chem Soc. 1975 Mar 5;97(5):1238–1238. doi: 10.1021/ja00838a045. [DOI] [PubMed] [Google Scholar]
  20. Shimizu Y., Yoshioka M. Transformation of paralytic shellfish toxins as demonstrated in scallop homogenates. Science. 1981 May 1;212(4494):547–549. doi: 10.1126/science.7209548. [DOI] [PubMed] [Google Scholar]
  21. Strichartz G. Structural determinants of the affinity of saxitoxin for neuronal sodium channels. Electrophysiological studies on frog peripheral nerve. J Gen Physiol. 1984 Aug;84(2):281–305. doi: 10.1085/jgp.84.2.281. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Wagner H. H., Ulbricht W. The rates of saxitoxin action and of saxitoxin-tetrodotoxin interaction at the node of Ranvier. Pflugers Arch. 1975 Sep 29;359(4):297–315. doi: 10.1007/BF00581441. [DOI] [PubMed] [Google Scholar]

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

RESOURCES