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The status of voltage-dependent calcium channels in alpha 1E knock-out mice
1Mouse Cancer Genetics Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
Abstract:
It has been hypothesized that R-type Ca currents result from the expression of the alpha(1E) gene. To test this hypothesis we examined the properties of voltage-dependent Ca channels in mice in which the alpha(1E) Ca channel subunit had been deleted. Application of omega-conotoxin GVIA, omega-agatoxin IVA, and nimodipine to cultured cerebellar granule neurons from wild-type mice inhibited components of the whole-cell Ba current, leaving a "residual" R current with an amplitude of approximately 30% of the total Ba current. A minor portion of this R current was inhibited by the alpha(1E)-selective toxin SNX-482, indicating that it resulted from the expression of alpha(1E). However, the majority of the R current was not inhibited by SNX-482. The SNX-482-sensitive portion of the granule cell R current was absent from alpha(1E) knock-out mice. We also identified a subpopulation of dorsal root ganglion (DRG) neurons from wild-type mice that expressed an SNX-482-sensitive component of the R current. However as with granule cells, most of the DRG R current was not blocked by SNX-482. We conclude that there exists a component of the R current that results from the expression of the alpha(1E) Ca channel subunit but that the majority of R currents must result from the expression of other Ca channel alpha subunits.
Insights
The alpha(1E) gene contributes to R-type calcium (Ca) currents, but this study shows other Ca channel alpha subunits are primarily responsible for the majority of these currents.
Area of Science:
- Neuroscience
- Molecular Biology
- Ion Channel Physiology
Background:
- R-type calcium (Ca) currents are crucial for neuronal function.
- The alpha(1E) gene was hypothesized to be the primary source of R-type Ca currents.
Purpose of the Study:
- To investigate the role of the alpha(1E) gene in generating R-type Ca currents.
- To determine the contribution of alpha(1E) to R-type currents in cerebellar granule neurons and dorsal root ganglion (DRG) neurons.
Main Methods:
- Utilized alpha(1E) knock-out mice to study Ca channel properties.
- Applied specific toxins (omega-conotoxin GVIA, omega-agatoxin IVA, nimodipine, SNX-482) to analyze whole-cell Ba currents.
- Examined voltage-dependent Ca channels in cultured neurons.
Main Results:
- A minor, SNX-482-sensitive component of R-type current was identified and linked to alpha(1E).
- This alpha(1E)-dependent R current was absent in alpha(1E) knock-out mice.
- The majority of R-type currents in both granule and DRG neurons were insensitive to SNX-482, indicating other alpha subunits are involved.
Conclusions:
- The alpha(1E) Ca channel subunit contributes to a small fraction of R-type currents.
- Most R-type currents are generated by other, yet unidentified, Ca channel alpha subunits.
- This challenges the hypothesis that alpha(1E) is the sole or primary determinant of R-type currents.