Divalent cations differentially support transmitter release at the squid giant synapse.

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Divalent cations are crucial for neurotransmitter release.
• The specific roles of calcium (Ca), strontium (Sr), and barium (Ba) ions in synaptic function are not fully elucidated.

Purpose of the Study:

• To investigate and compare the abilities of Ca, Sr, and Ba ions to support neurotransmitter release at the squid giant synapse.
• To determine how these ions affect presynaptic current and post-synaptic responses.

Main Methods:

• Examined presynaptic current and post-synaptic responses in squid giant synapse using Ca, Sr, and Ba containing solutions.
• Utilized voltage-clamped presynaptic terminals to analyze inward currents.
• Assessed spontaneous miniature post-synaptic potentials and resting potential.

Main Results:

• Transmitter release was highest with Ca, lower with Sr, and lowest with Ba.
• Inward currents carried by Ca, Sr, or Ba through presynaptic channels were similar, though slightly larger in Ba.
• Action potential duration was unaffected by Sr but slightly prolonged by Ba.

Conclusions:

• Divalent cations differentially support neurotransmitter release at the squid giant synapse in the order Ca > Sr >> Ba.
• This differential efficacy is not due to post-synaptic changes, presynaptic potential shifts, or variations in presynaptic divalent cation conductance.
• The findings suggest the exocytotic process itself exhibits cation selectivity, influencing neurotransmitter release efficiency.