Point-mutations related to the loss of batrachotoxin binding abolish the grayanotoxin effect in Na+ channel isoforms

Abstract

The effect of grayanotoxin (GTX) on site-specific mutants of the α- subunit of rat skeletal muscle Na+ channels (μ1) (μ1-1433K, μ1-N434K and μ1-L437K), which are resistant to batrachotoxin (BTX) (Wang and Wang (1998) Proc Natl Acad Sci USA, 95, 2653-2658) was studied using a whole-cell patch- clamp method. The GTX modification of the Na+ channels was detected as a characteristic-sustained Na+ current flow with repetitive pulses. We also studied the GTX action on mutants of the α-subunit of rat heart Na+ channels (RH1) (RH1-V406K and RH1-L410K) which match with μ1-1433 and μ1- L437. All the mutants lost their sensitivity to GTX. This finding indicates that GTX may share a binding site with BTX in transmembrane segment I-S6 of two different Na+ channel isoforms, μ1 and RH1.