Mitochondrial Ca2+ activates a cation current in Aplysia bag cell neurons

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Calcium ions (Ca2+) are critical regulators of neuronal function, typically sourced from extracellular space or endoplasmic reticulum.
• Bag cell neurons in Aplysia californica initiate ovulation via an afterdischarge, a process involving Ca2+ influx and release.

Purpose of the Study:

• To investigate the impact of Ca2+ on ion channels in Aplysia bag cell neurons.
• To determine the specific role of mitochondrial Ca2+ in neuronal excitability and afterdischarge.

Main Methods:

• Utilized carbonyl cyanide-4-trifluoromethoxyphenyl-hydrazone (FCCP) to release mitochondrial Ca2+ and cyclopiazonic acid to deplete endoplasmic reticulum Ca2+.
• Measured ion currents and voltage changes using electrophysiology.
• Employed fura imaging to monitor intracellular Ca2+ levels.
• Investigated the role of the mitochondrial permeability transition pore using N-ethylmaleimide.

Main Results:

• FCCP depolarized bag cell neurons and elicited a voltage-independent, nonselective cation current, unlike endoplasmic reticulum Ca2+ depletion.
• The FCCP-induced current reversed near -40 mV and was dependent on intracellular Ca2+ and mitochondrial function.
• Inhibition of the mitochondrial permeability transition pore reduced both the FCCP-induced current and Ca2+ elevation.

Conclusions:

• Mitochondrial Ca2+ directly gates a nonselective cation current in Aplysia bag cell neurons.
• This mitochondrial Ca2+-gated current contributes to neuronal afterdischarge and reproductive processes.
• This study reveals a novel mechanism of Ca2+ signaling in neurons, highlighting mitochondria as a direct source for gating ion channels.