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Preferential interaction of omega-conotoxins with inactivated N-type Ca2+ channels
J W Stocker1, L Nadasdi, R W Aldrich
1Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, USA.
Abstract:
The selective block of N-type Ca2+ channels by omega-conotoxins has been a hallmark of these channels, critical in delineating their biological roles and molecular characteristics. Here we report that the omega-conotoxin-channel interaction depends strongly on channel gating. N-type channels (alpha1B, alpha2, and beta1) expressed in Xenopus oocytes were blocked with a variety of omega-conotoxins, including omega-CTx-GVIA, omega-CTx-MVIIA, and SNX-331, a derivative of omega-CTx-MVIIC. Changes in holding potential (HP) markedly altered the severity of toxin block and the kinetics of its onset and removal. Notably, strong hyperpolarization renders omega-conotoxin block completely reversible. These effects could be accounted for by a modulated receptor model, in which toxin dissociation from the inactivated state is approximately 60-fold slower than from the resting state. Because omega-conotoxins act exclusively outside cells, our results suggest that voltage-dependent inactivation of Ca2+ channels must be associated with an externally detectable conformational change.
Insights
Omega-conotoxins selectively block N-type calcium channels, but this interaction is highly dependent on channel gating. The toxin block is reversible with hyperpolarization, suggesting external conformational changes during channel inactivation.
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Omega-conotoxins are known for their selective blockade of N-type calcium (Ca2+) channels.
- Understanding the molecular basis of this interaction is crucial for delineating channel function.
Purpose of the Study:
- To investigate the influence of channel gating on the interaction between omega-conotoxins and N-type Ca2+ channels.
- To elucidate the mechanism underlying the voltage-dependent block of these channels.
Main Methods:
- Expression of N-type Ca2+ channels (alpha1B, alpha2, beta1) in Xenopus oocytes.
- Application of various omega-conotoxins (e.g., omega-CTx-GVIA, omega-CTx-MVIIA, SNX-331).
- Assessment of toxin block severity and kinetics under different holding potentials (HP).
Main Results:
- The severity and kinetics of omega-conotoxin block were significantly altered by changes in holding potential.
- Strong hyperpolarization resulted in a completely reversible toxin block.
- Toxin dissociation from the inactivated state was approximately 60-fold slower than from the resting state.
Conclusions:
- The interaction between omega-conotoxins and N-type Ca2+ channels is strongly modulated by channel gating.
- These findings support a modulated receptor model for toxin interaction.
- The voltage-dependent inactivation of Ca2+ channels involves an externally detectable conformational change.