Many neurons of the central and peripheral nervous systems display multiple high voltage-activated (HVA) Ca2+ currents, often classified as L-, N-, P-, Q, and R-type. The heterogeneous properties of these channels have been attributed to diversity in their pore-forming α1, subunits, in association with various β subunits. However there are large gaps in understanding how individual subunits contribute to Ca2+ channel diversity. Here we describe experiments to investigate the roles of α(1E) and β3 subunits in mammalian neurons. The α(1E) subunit is the leading candidate to account for the R-type channel, the least understood of the various types of high voltage-activated Ca2+ channels. Incubation with α(1E) antisense oligonucleotide caused a 53% decrease in the peak R-type current density, while no significant changes in the current expression were seen in sense oligonucleotide treated cells. The specificity of the α(1E) antisense oligonucleotides was supported by the lack of change in the amplitude of P/Q current. These results upheld the hypothesis that members of the E class of α1 subunits support the high voltage-activated R-type current in cerebellar granule cells. We studied the role of the Ca2+ channel β3 subunit using a gene targeting strategy. In sympathetic β3-/- neurons, the L-type current was significantly reduced relative to wild type (wt). In addition, N-type Ca2+ channels made up a smaller proportion of the total Ca2+ current than in wt due to a lower N-type current density in a group of neurons with small total currents. Voltage-dependent activation of P/Q-type Ca2+ channels was described by two Boltzmann components with different voltage dependence. The absence of the β3 subunit was associated with a shift in the more depolarized component of the activation along the voltage axis toward more negative potentials. The overall conclusion is that deletion of the β3 subunit affects at least three distinct types of HVA Ca2+ channel, but no single type of channel is solely dependent on β3.
|Original language||English (US)|
|Number of pages||24|
|Journal||Annals of the New York Academy of Sciences|
|State||Published - Jan 1 1999|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- History and Philosophy of Science