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 alpha-subunit of rat skeletal muscle Na(+) channels (micro1) (micro1-I433K, micro1-N434K and micro1-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 alpha-subunit of rat heart Na(+) channels (RH1) (RH1-V406K and RH1-L410K) which match with micro1-I433 and micro1-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, micro1 and RH1.