Comparative actions of synthetic omega-grammotoxin SIA and synthetic omega-Aga-IVA on neuronal calcium entry and evoked release of neurotransmitters in vitro and in vivo.
The effects of synthetic omega-grammotoxin SIA (omega-GsTxSIA) and synthetic omega-Aga-IVA were tested in in vitro and in vivo neurochemical assays that are reflective of voltage-sensitive calcium channel function. Synthetic omega-GsTx SIA inhibited K(+)-evoked rat and chick synaptosomal 45Ca2+ flux, K(+)-evoked release of [3H]D-aspartate and [3H]norepinephrine from rat hippocampal brain slices and K(+)-evoked release of [3H]norepinephrine from chick cortical brain slices with potency values that were comparable to those found previously with omega-GsTx SIA purified from the venom of the tarantula spider Grammostola spatulata. These results indicate that trace contaminants do not account for the pharmacology of purified omega-GsTx SIA. omega-GsTx SIA caused a complete inhibition of rat synaptosomal 45Ca2+ flux and hippocampal slice [3H]D-aspartate release, whereas omega-Aga-IVA caused a maximal inhibition of approx 75%. omega-GsTx SIA and omega-Aga-IVA caused an identical partial inhibition of K(+)-evoked increases of intracellular calcium in cortical neurons in primary culture. The addition of nitrendipine to either omega-GsTx SIA or omega-Aga-IVA resulted in an additive and virtually complete inhibition of the cortical neuron intracellular calcium response. In in vivo microdialysis studies, the K(+)-evoked release of glutamate from hippocampus of awake freely moving rats was inhibited with the following rank order of potency: omega-conotoxin GVIA > omega-GsTx SIA > omega-Aga-IVA. Complete inhibition of K(+)-evoked hippocampal glutamate release was observed with 300 nM omega-conotoxin GVIA and 3 microM omega-GsTx SIA. In urethane anesthetized rats, omega-CgTx GVIA caused a partial inhibition, whereas omega-GsTx SIA caused a concentration-dependent and complete inhibition, of basal serotonin release in the hippocampus. Therefore, omega-GsTx SIA was shown to inhibit responses that are sensitive to omega-conotoxin GVIA, omega-Aga-IVA and omega-conotoxin MVIIC, consistent with the notion that omega-GsTx SIA inhibits N-, P- and Q-type high threshold voltage-sensitive calcium channels.
Keith
R A
RA
Department of Pharmacology, Zeneca Pharmaceuticals, Wilmington, DE 19850-5437, USA.
Mangano
T J
TJ
Lampe
R A
RA
DeFeo
P A
PA
Hyde
M J
MJ
Donzanti
B A
BA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D006624:Hippocampus / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008978:Mollusk Venoms / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010455:Peptides / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013111:Spider Venoms / Q000008:administration & dosage / Q000494:pharmacology*; D013112:Spiders; D009435:Synaptic Transmission / Q000187:drug effects*; D013574:Synaptosomes / Q000187:drug effects; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D008978:Mollusk Venoms; D018377:Neurotransmitter Agents; D010455:Peptides; D013111:Spider Venoms; D020866:omega-Conotoxin GVIA; D002118:Calcium