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Expression and modulation of voltage-gated calcium channels after RNA injection in Xenopus oocytes
Abstract:
Calcium ions flow into cells through several distinct classes of voltage-dependent calcium-selective channels. Such fluxes play important roles in electrical signaling at the cell membrane and in chemical signaling within cells. Further information about calcium channels was obtained by injecting RNA isolated from rat brain, heart and skeletal muscle into Xenopus oocytes. Macroscopic currents through voltage-operated calcium channels were resolved when the endogenous calcium-dependent chloride current was blocked by replacing external calcium with barium and chloride with methanesulfonate. The resulting barium current was insensitive to tetrodotoxin but was completely blocked by cadmium or cobalt. With both heart and brain RNA at least two distinct types of calcium ion conductance were found, distinguishable by their time course and inactivation properties. In oocytes injected with heart RNA, the slowly inactivating component was selectively blocked by the calcium-channel antagonist nifedipine. Barium ion currents induced by heart RNA were modulated by isoproterenol, cyclic adenosine monophosphate, and acetylcholine.
Insights
Researchers identified distinct types of calcium channels in rat heart and brain cells using Xenopus oocytes. These channels, crucial for cell signaling, showed varied properties and sensitivities to blockers and modulators.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Physiology
Background:
- Calcium ions are essential for cellular electrical and chemical signaling.
- Voltage-dependent calcium channels mediate these crucial ion fluxes.
- Understanding different calcium channel types is key to cellular function.
Purpose of the Study:
- To characterize distinct classes of voltage-dependent calcium channels.
- To investigate calcium channel properties using heterologous expression in Xenopus oocytes.
- To identify differences in calcium channel subtypes from rat brain and heart.
Main Methods:
- RNA isolated from rat brain, heart, and skeletal muscle was injected into Xenopus oocytes.
- Macroscopic currents were measured by voltage-clamping oocytes.
- Endogenous chloride currents were blocked by replacing external calcium with barium and chloride with methanesulfonate.
Main Results:
- Two distinct calcium ion conductance types were identified from both heart and brain RNA, differing in time course and inactivation.
- Heart RNA-expressed channels showed a slowly inactivating component sensitive to nifedipine.
- Barium currents from heart RNA were modulated by isoproterenol, cyclic adenosine monophosphate, and acetylcholine.
Conclusions:
- Xenopus oocytes are a viable system for studying functional voltage-dependent calcium channels.
- Distinct calcium channel subtypes with unique properties exist in rat brain and heart.
- These findings contribute to understanding the diversity and regulation of calcium channels.