RT Journal Article
SR Electronic
T1 Structure-activity relationships for the irreversible blockade of nicotinic receptor agonist sites by lophotoxin and congeneric diterpene lactones.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 436
OP 444
VO 28
IS 5
A1 P Culver
A1 M Burch
A1 C Potenza
A1 L Wasserman
A1 W Fenical
A1 P Taylor
YR 1985
UL http://molpharm.aspetjournals.org/content/28/5/436.abstract
AB Lophotoxin, a diterpene lactone paralytic toxin from gorgonian corals of the genus Lophogorgia, inhibits [125I]-alpha-toxin binding to surface nicotinic receptors of BC3H-1 cells by irreversible occupation of the primary agonist sites. In contrast, receptor-bearing membrane fragments or detergent-solubilized receptors prepared from BC3H-1 cells are not susceptible to lophotoxin block. Thus, lophotoxin inhibition requires intact cells. However, when intact cells were incubated with lophotoxin, subsequent membrane-fragment preparation or detergent solubilization of the receptors did not diminish lophotoxin occupation of [125I]-alpha-toxin-binding sites, indicating that lophotoxin binds very tightly to nicotinic receptors. These studies further demonstrate that both surface and nonsurface nicotinic receptors of BC3H-1 cells are susceptible to irreversible occupation by lophotoxin, indicating that the lipophilic toxin freely permeates intact cells. We also examined several structural analogs of lophotoxin, one of which was equipotent with lophotoxin for inhibition of [125I]-alpha-toxin binding to intact cells and, notably, also blocked alpha-toxin binding to detergent-extracted receptor. Furthermore, this active analog inhibited [125I]-alpha-toxin binding to receptor-rich membrane fragments prepared from Torpedo electric organ, a preparation in which lophotoxin was inactive. Structure-activity relationships exhibited by the lophotoxin congeners suggest mechanisms for covalent bonding to the receptor by way of a Michael addition or by Schiff base formation.