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Block of Sodium Channels in Planar Lipid Bilayers by Guanidinium Toxins and Calcium
Author(s) -
KRUEGER BRUCE K.,
WORLEY JENNINGS F.,
FRENCH ROBERT J.
Publication year - 1986
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1986.tb15574.x
Subject(s) - medical school , annals , library science , medicine , gerontology , history , medical education , classics , computer science
The block of single, batrachotoxin-activated sodium channels by saxitoxin (STX), tetrodotoxin (TTX), and Ca2+ has been investigated in planar bilayers. All three substances block in a voltage-dependent manner with hyperpolarizing potentials favoring block. Extracellular Ca2+ competitively inhibits binding of STX and relieves STX block. Trimethyloxonium, a carboxyl-methylating agent, eliminates block by STX and TTX and dramatically reduces block by Ca2+. These results suggest that STX, TTX, and Ca2+ compete for a negative site on the outside of the channel. The voltage dependence of block by STX (divalent cation) and TTX (monovalent) was similar (40 mV/e-fold), suggesting that voltage dependence is due to a conformational change in the channel rather than to the toxins entering the membrane electric field to block. A physical model, with an external binding site for toxins and Ca2+ and another site deeper within the electric field (associated with the "selectivity filter") that is accessible to Ca2+ but not toxins, predicts voltage-dependence Ca2+ block without invoking the conformational change needed to explain the voltage dependence of block by TTX and STX.