Voltage-dependent Ca2+ influx into identified leech neurones

Area of Science:

• Neuroscience
• Cellular Electrophysiology
• Calcium Signaling

Background:

• Understanding neuronal excitability and calcium dynamics is crucial in neuroscience.
• Leech neurons provide a model system for studying fundamental electrophysiological properties.

Purpose of the Study:

• To investigate the relationship between intracellular free Ca2+ concentration ([Ca2+]i) and membrane potential (Em) in six distinct leech neuron types.
• To characterize the properties of voltage-dependent calcium channels in these neurons.

Main Methods:

• Utilized iontophoretically injected fura-2 to monitor [Ca2+]i in leech neurons.
• Manipulated extracellular K+ concentration ([K+]o) to induce membrane depolarization and observed changes in [Ca2+]i.
• Tested the effects of Na+-free solutions, polyvalent cations (Co2+, Ni2+, Mn2+, Cd2+, La3+), and menthol on [Ca2+]i and Em.

Main Results:

• Depolarization with high [K+]o caused a Ca2+ influx-dependent increase in [Ca2+]i, abolished in Ca2+-free solution.
• Threshold potentials for [Ca2+]i increase varied from -40 to -25 mV across neuron types, influenced by action potential generation.
• Polyvalent cations and menthol inhibited K+-induced [Ca2+]i increase without significantly affecting membrane depolarization.

Conclusions:

• Leech neurons exhibit voltage-dependent calcium channels with largely similar properties, despite variations in threshold potentials.
• Action potential generation contributes to cell-specific differences in [Ca2+]i/Em relationships.
• The findings provide insights into calcium influx mechanisms underlying neuronal excitability in the leech nervous system.