Single channel Ca2+ currents in Helix pomatia neurons

Area of Science:

• Neuroscience
• Ion Channel Physiology

Background:

• Helix neurons are a model system for studying neuronal excitability.
• Calcium (Ca2+) channels play crucial roles in neuronal function, including neurotransmitter release and gene expression.

Purpose of the Study:

• To characterize the unitary calcium currents in Helix neurons.
• To determine the permeability and conductance of calcium channels.
• To investigate the gating properties and kinetics of calcium channels.

Main Methods:

• Unitary Ca2+ currents were recorded from microscopic membrane patches of TEA-injected Helix neurons using the "Giga seal" technique.
• Experiments were conducted under specific ionic conditions: 50 mM [Ca2+]o, 0 [Na+]o, 20 mM [TEA+]o, and 2.5 microM [TTX]o.
• Constant field assumptions were applied to analyze channel properties.

Main Results:

• Calcium channel permeability was calculated as 2.9 +/- 1.0 x 10(-14) cm3s-1.
• Slope conductances ranged from 5 to 15 pS between 0 and -30 mV.
• The frequency of channel openings increased with depolarization.
• The mean open time of Ca2+ channels was approximately 3 ms, independent of voltage.
• Barium ions ([Ba2+]o) produced similar open times but approximately doubled the current strength compared to calcium ions ([Ca2+]o).

Conclusions:

• Helix neuron calcium channels exhibit voltage-dependent gating kinetics.
• The channel's permeability and conductance were quantified under specific experimental conditions.
• Barium ions serve as a useful tool for enhancing Ca2+ current measurements in these neurons.