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The inhibitory effects of omega-conotoxins on Ca channels and synapses
D Yoshikami1, Z Bagabaldo, B M Olivera
1Department of Biology, University of Utah, Salt Lake City 84112.
Abstract:
Omega conotoxins are peptides from snail venom. Two variants, omega CgTX and omega CmTX derived from two species of Conus, are the subjects of this report. Part I of this report reviews and discusses the ability of these toxins to inhibit Ca channels and synapses in different tissues from various species of animals. The potencies of these toxins vary depending on the target tissue, consonant with the notion that synaptic Ca channels have changed in the course of evolution. Part II introduces the notion that in contrast to inorganic Ca channel blockers, which act by reducing the amount of Ca2+ ions that can permeate an open channel, omega toxins act by reducing the availability of functional Ca channels. Thus, Ca channel-inhibition by omega toxins and that by inorganic blockers are expected to produce qualitatively different alterations in the distribution of intracellular Ca2+. Consistent with this expectation, the dose-response curves of inorganic blockers and omega CmTX differ. The dose-response curves of inorganic blockers are thought to reflect the cooperativity of Ca2+ ions in mediating transmitter release. In contrast, comparison of experimental and theoretical dose-response curves of omega CmTX leads us to propose the hypothesis that Ca channels normally do not act cooperatively to effect transmitter release.
Insights
Omega conotoxins from snail venom inhibit calcium channels differently than inorganic blockers. These omega toxins reduce functional channels, suggesting calcium channels may not act cooperatively in neurotransmitter release.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Omega conotoxins are peptides found in cone snail venom.
- Two variants, omega CgTX and omega CmTX, are studied.
- These toxins target calcium channels and synapses.
Purpose of the Study:
- To review and discuss the inhibitory effects of omega conotoxins on calcium channels and synapses.
- To explore the evolutionary divergence of synaptic calcium channels.
- To differentiate the mechanism of action of omega conotoxins from inorganic calcium channel blockers.
Main Methods:
- Review of existing literature on omega conotoxins and calcium channel inhibition.
- Comparative analysis of the dose-response curves of omega CmTX and inorganic blockers.
- Theoretical modeling of calcium channel function.
Main Results:
- The potency of omega conotoxins varies across different animal tissues and species.
- Omega conotoxins reduce the availability of functional calcium channels, unlike inorganic blockers that reduce ion permeation.
- Dose-response curves of omega CmTX differ from inorganic blockers, suggesting a distinct mechanism.
Conclusions:
- Calcium channel inhibition by omega toxins and inorganic blockers leads to different intracellular calcium distributions.
- The study proposes that calcium channels may not act cooperatively in neurotransmitter release, based on omega CmTX dose-response data.