pumiliotoxin-b and Neuroblastoma

Pumiliotoxin B (PTX-B) and a variety of congeneric alkaloids and synthetic analogs stimulated sodium flux and phosphoinositide breakdown in guinea pig cerebral cortical synaptoneurosomes. The effects of PTX-B and active congeners and analogs on sodium flux in synaptoneurosomes were potentiated markedly by scorpion venom (Leiurus quinquestriatus). In neuroblastoma cells, PTX-B and active congeners had no effect on sodium flux unless synergized by alpha-scorpion toxin or scorpion venom. Certain inactive congeners, lacking hydroxyl groups in the 6-alkylidene side chain, inhibited sodium flux elicited by PTX-B, scorpion venom, or the sodium channel activator batrachotoxin. Such inhibition appeared different from inhibition by local anesthetics, since pumiliotoxins, unlike local anesthetics, had little or no effect on binding of [3H]batrachotoxinin A benzoate to sodium channels. Thus, it appears likely that some "inactive" congeners bind to the PTX-B binding site, but do not activate sodium channels. In the absence of scorpion venom the stimulation of phosphoinositide breakdown in synaptoneurosomes was consonant with the stimulatory effects of these compounds on sodium flux through voltage-dependent sodium channels.

Topics: Alkaloids; Amphibian Venoms; Animals; Guinea Pigs; In Vitro Techniques; Indolizines; Neuroblastoma; Phosphatidylinositols; Piperidines; Scorpion Venoms; Sodium; Sodium Channels; Structure-Activity Relationship

Pumiliotoxin B (PTX-B), an alkaloid that has cardiotonic and myotonic activity, increases sodium influx in guinea pig cerebral cortical synaptoneurosomes. In the presence of scorpion venom (Leiurus) or purified alpha-scorpion toxin, the PTX-B-induced sodium influx is enhanced severalfold. PTX-B alone has no effect on sodium flux in N18 neuroblastoma cells but, in the presence of alpha-scorpion toxin, stimulation of sodium influx by PTX-B reaches levels comparable to that attained with the sodium channel activator veratridine. In neuroblastoma LV9 cells, a variant mutant that lacks sodium channels, neither veratridine nor PTX-B induces sodium fluxes in either the presence or absence of alpha-scorpion toxin. In synaptoneurosomes and in N18 cells, the sodium influx induced by the combination of PTX-B and alpha-scorpion toxin is inhibited by tetrodotoxin and local anesthetics. PTX-B does not interact with two of the known toxin sites on the sodium channel, as evidenced by a lack of effect on binding of [3H]saxitoxin or [3H]batrachotoxinin A benzoate to brain synaptoneurosomes. Synergistic effects on sodium influx with alpha-scorpion toxin, beta-scorpion toxin, and brevetoxin indicate that PTX-B does not interact directly with three other toxin sites on the sodium channel. Thus, PTX-B appears to activate sodium influx by interacting with yet another site on the voltage-dependent sodium channel, a site that is coupled allosterically to sites for alpha-scorpion toxin, beta-scorpion toxin, and brevetoxin.

Topics: Alkaloids; Allosteric Site; Anesthetics, Local; Animals; Binding Sites; Biological Transport; Cells, Cultured; Cerebral Cortex; Drug Interactions; Guinea Pigs; Indolizines; Ion Channels; Neuroblastoma; Piperidines; Sodium; Stimulation, Chemical; Synaptosomes; Toxins, Biological