Modification of wild-type and batrachotoxin-resistant muscle mu1 Na+ channels by veratridine.
Biochemical evidence indicates that veratridine (VTD) and batrachotoxin (BTX) share a common binding site in Na+ channels. Under whole-cell voltage-clamp conditions, we examined this single receptor hypothesis by studying the VTD phenotype in BTX-resistant muscle Na+ channels, microl-I433K, N434K, L437K, F1579K, and N1584K. Derived from point mutations at segments D1-S6 and D4-S6, these mutant Na+ channels are resistant to 5 microM BTX when expressed in human embryonic kidney cells. In contrast to the wild-type phenotype, VTD at 200 microM elicits little or no maintained current during a test pulse at +50 mV, and little or no "tail" current after the test pulse in all BTX-resistant mutant channels. Paradoxically, VTD retains its ability to inhibit the peak Na+ current in BTX-resistant mutant Na+ channels. To explain these mutant phenotypes, we propose a two-step binding reaction scheme. An initial VTD-binding interaction with the Na+ channel results in the inhibition of peak current amplitude, and a second binding reaction results in the trapping of VTD within the D1-S6 and D4-S6 domain interface. The failure of BTX-resistant mutant Na+ channels to trap VTD suggests that segments of D1-S6 and D4-S6 form a common receptor for VTD and BTX.
Wang
G K
GK
Department of Anesthesia, Harvard Medical School and Brigham and Women's Hospital, Boston, MA 02115, USA. wang@zeus.bwh.harvard.edu.
Quan
C
C
Seaver
M
M
Wang
S Y
SY
D001496:Batrachotoxins / Q000494:pharmacology*; D002460:Cell Line; D003064:Cnidarian Venoms / Q000494:pharmacology; D004338:Drug Combinations; D004351:Drug Resistance; D004594:Electrophysiology; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000235:genetics; D009132:Muscles / Q000378:metabolism*; D010641:Phenotype; D017354:Point Mutation; D012016:Reference Values; D015222:Sodium Channels / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D014701:Veratridine / Q000494:pharmacology*
D001496:Batrachotoxins; D003064:Cnidarian Venoms; D004338:Drug Combinations; D007473:Ion Channels; D015222:Sodium Channels; C028800:toxin II (Anemonia sulcata); D014701:Veratridine