Is the A-ring lactone of brevetoxin PbTx-3 required for sodium channel orphan receptor binding and activity?
Brevetoxin PbTx-3 and non-toxic derivative 4 were investigated for their abilities to bind to the specific brevetoxin receptor site on rat brain synaptosomes and to modulate the normal function of voltage-gated sodium channels as determined by patch clamping of cultured neurons. Compounds 4 and 5 are produced from PbTx-3 by opening of the A-ring lactone to the saturated and unsaturated diols using sodium borohydride in ethanol. Natural PbTx-3 exhibited tighter binding to rat brain synaptosomes by at least 3 orders of magnitude as determined by competitive radioligand binding experiments, and was also more effective at activating voltage-gated channels. Patch clamping revealed the 3 orders of magnitude greater potency of PbTx-3 toxin over 5, although each produced delayed sodium channel opening and a pronounced delay in inactivation. Conformational modeling of the Brevetoxin B backbone indicates that the two molecules are identical except for the region of the A-Ring lactone. Thus, we conclude that the brevetoxin PbTx-3 backbone requires electrophilic functionality in the region of the lactone in PbTx-3, and that opening of the ring in 5 is sufficient to substantially reduce both binding and activity.
Marine and Freshwater Biomedical Sciences Center, RSMAS University of Miami, Florida.
D G
DG
Baden
K S
KS
Rein
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RE
Gawley
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G
Jeglitsch
D J
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Adams
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D003532:Cyprinodontiformes; D007783:Lactones / Q000494:pharmacology; D007928:Lethal Dose 50; D008387:Marine Toxins / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D008564:Membrane Potentials / Q000187:drug effects; D008958:Models, Molecular; D009466:Neuromuscular Blocking Agents / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D035964:Oxocins; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013574:Synaptosomes / Q000378:metabolism*; D000095702:Polyether Toxins
D007783:Lactones; D008387:Marine Toxins; D009466:Neuromuscular Blocking Agents; D035964:Oxocins; D015222:Sodium Channels; C072089:brevetoxin receptor; C041017:brevetoxin T17; D000095702:Polyether Toxins