Antagonists-resistant calcium currents in rat embryo motoneurons

Area of Science:

• Neuroscience
• Molecular Biology
• Electrophysiology

Background:

• Calcium channels are crucial for neuronal function, including neurotransmitter release.
• Understanding the diversity of calcium channels in motoneurons is essential for elucidating synaptic transmission.
• Previous research has identified various calcium channel subtypes, but their specific roles and distribution in motoneurons require further investigation.

Purpose of the Study:

• To investigate the diversity of calcium (Ca2+) channels in cultured rat embryo motoneurons.
• To characterize the properties and distribution of different Ca2+ channel types, including L-, N-, P-, and R-type currents.
• To identify the contribution of specific Ca2+ channel subtypes to the overall calcium currents in motoneurons.

Main Methods:

• Whole-cell patch-clamp recordings were used to measure Ca2+ currents in cultured rat embryo motoneurons.
• Barium ions (Ba2+) were used as charge carriers to record both low-voltage-activated (LVA) and high-voltage-activated (HVA) currents.
• Specific calcium channel blockers, including omega-Aga-IVA and omega-CTx-MVIIC, were applied to pharmacologically isolate and identify different Ca2+ channel subtypes.

Main Results:

• Whole-cell currents were separated into LVA and HVA components, with HVA currents increasing over time in culture.
• After 4 days in culture, recordings showed approximately 20% L-type, 45% N-type, and 35% P/R-type currents.
• P-type currents were present in only 40% of motoneurons, suggesting heterogeneous distribution and compensation by resistant HVA channels, identified as R-type.
• A significant antagonists-resistant current with distinct biophysical characteristics, identified as R-type, was uncovered.
• This R-type current activates around -20 mV, inactivates slowly, and is larger with Ba2+ than Ca2+.

Conclusions:

• Cultured rat embryo motoneurons express a diverse array of Ca2+ channels, including significant contributions from N-type and R-type currents.
• The identified R-type calcium current exhibits unique properties and plays a role in presynaptic Ca2+ currents controlling neurotransmitter release at the mammalian neuromuscular junction.
• The R-type current's resistance to common antagonists highlights its importance in contexts where other channel types are blocked, such as at the mammalian neuromuscular junction.