Characterization of exchange-labeled saxitoxin and the origin of linear uptake by excitable tissue
Ritchie, J.M.; Rogart, R.B.
Molecular Pharmacology 13(6): 1136-1146
1977
ISSN/ISBN: 0026-895X PMID: 22807 Document Number: 111925
Tritium-labeled saxitoxin, which binds saturably to the Na+ channels of excitable tissue, also was taken up linearly [by lobster walking leg nerves, desheathed rabbit vagus nerves and homogenized rabbit brain]. Some of the linear uptake seemed to represent intracellular uptake of tritiated water. The main component of linear uptake was of true toxin and not of radioactive impurity. It resulted from an accumulation of the divalent toxin in the immediate vicinity of the axonal (and other cell) membranes because of the fixed negative charges on them. A new and general method for determining the radiochemical purity of the exchange-labeled tritiated saxitoxin was described. The temperature dependence of the kinetics of loss of the label from the methylene H of C 12 of labeled saxitoxin was also reported.