Title: Specific inhibition of [3H] saxitoxin binding to skeletal muscle sodium channels by geographutoxin II, a polypeptide channel blocker.
Abstract: Geographutoxin I1 (GTX 11), a peptide toxin isolated from Conus geographus, inhibited [3H]saxitoxin binding to receptor sites associated with voltage-sensitive Na channels in rat skeletal muscle homogenates and rabbit T-tubular membranes with K o .~ values of 6 0 .n ~ for homogenates and 35 n M for T-tubular membranes in close agreement with concentrations that block muscle contraction.Scatchard analysis of [3H]saxitoxin binding to T-tubular membranes gave values of KD = 9.3 n M and B,,, = 300 fmol/mg of protein and revealed