Crotoxin, the major toxin from the rattlesnake Crotalus durissus terrificus, inhibits H-3-choline uptake in guinea pig ileum

We examined the effect of crotoxin, the neurotoxic complex from the venom o f the South American rattlesnake Crotalus durissus terrificus, on the uptak e of H-3-choline in minces of smooth muscle myenteric plexus from guinea pi g ileum. In the concentration range used (0.03- 1 mu M) and up to 10 min of treatment, crotoxin decreased H-3-choline uptake by 50-75% compared to con trol. This inhibition was time dependent and did not seem to be associated with the disruption of the neuronal membrane, because at least for the firs t 20 min of tissue exposure to the toxin (up to 1 mu M) the levels of lacta te dehydrogenase (LDH) released into the supernatant were similar to those of controls. Higher concentrations of crotoxin or more extensive incubation times with this toxin resulted in elevation of LDH activity detected in th e assay supernatant. The inhibitory effect of crotoxin on H-3-choline uptak e seems to be associated with its phospholipase activity since the equimola r substitution of Sr2+ for Ca2+ in the incubation medium or the modificatio n of the toxin with p-bromophenacyl bromide substantially decreased this ef fect. Our results show that crotoxin inhibits H-3-choline uptake with high affinity (EC25 = 10 +/- 5 nM). We suggest that this inhibition could explai n, at least in part, the blocking effect of crotoxin on neurotransmission.