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T-type and N-type calcium channels of Xenopus oocytes: evidence for specific interactions with beta subunits
A E Lacerda1, E Perez-Reyes, X Wei
1Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030.
Abstract:
We used amplifying effects of calcium channel beta subunits to identify endogenous calcium channels in Xenopus oocytes. Expression of rat brain beta 4 increased macroscopic endogenous current magnitude with a small effect on kinetics. In contrast, expression of rat brain/cardiac beta 2 produced a much larger increase in current magnitude and dramatically slowed current decay. Low concentrations of omega-conotoxin GVIA irreversibly blocked currents in both uninjected and beta 2-injected oocytes. Single channel recordings revealed both T- and N-type calcium channels with conductances of 9 and 18 pS, respectively, in uninjected oocytes and in oocytes expressing either beta subunit. Expression of either beta subunit slowed average current decay of T-type single channels. Slowing of T-type current decay by expression of beta 2 was due to reopening of the channels. N-type single channel average current decay showed little change with expression of beta 4, whereas expression of beta 2 slowed average current decay.
Insights
Calcium channel beta subunits modulate endogenous Xenopus oocyte currents. Beta subunits influence calcium channel kinetics and current decay, revealing distinct T- and N-type channel properties.
Area of Science:
- Neuroscience
- Molecular Biology
- Biophysics
Background:
- Calcium channels are crucial for cellular functions.
- Beta subunits are known to modulate calcium channel activity.
- Endogenous calcium channels in Xenopus oocytes are not fully characterized.
Purpose of the Study:
- To identify and characterize endogenous calcium channels in Xenopus oocytes.
- To investigate the role of calcium channel beta subunits (beta 2 and beta 4) in modulating channel activity.
- To determine the types and properties of calcium channels present in Xenopus oocytes.
Main Methods:
- Xenopus oocytes were injected with rat brain beta 4 or rat brain/cardiac beta 2 subunits.
- Macroscopic currents were measured using electrophysiology.
- Omega-conotoxin GVIA was used to block specific channel types.
- Single channel recordings were performed to analyze channel kinetics and conductances.
Main Results:
- Beta 4 and beta 2 subunits increased macroscopic current magnitude.
- Beta 2 significantly slowed current decay, attributed to channel reopening.
- Both T-type (9 pS) and N-type (18 pS) calcium channels were identified.
- Beta subunits affected T-type channel decay, with beta 2 causing significant slowing.
Conclusions:
- Calcium channel beta subunits amplify endogenous currents in Xenopus oocytes.
- Beta 2 and beta 4 subunits differentially modulate calcium channel kinetics and current decay.
- Xenopus oocytes express functional T- and N-type calcium channels, influenced by beta subunits.