Potassium channel block by internal calcium and strontium

Area of Science:

• Neuroscience
• Biophysics
• Ion Channel Physiology

Background:

• Potassium (K) channels are crucial for neuronal electrical activity.
• Intracellular ions can modulate ion channel function.
• Previous studies indicated internal strontium (Sr) blocks K channels in squid axons.

Purpose of the Study:

• To investigate the blocking mechanism of intracellular calcium (Ca) on K channels in squid giant fiber lobe neurons.
• To compare the Ca block with the previously observed Sr block.
• To elucidate the voltage and concentration dependence of ion channel block.

Main Methods:

• Voltage-clamp electrophysiology on squid giant fiber lobe neurons and axons.
• Reexamination of internal Sr block in squid axons.
• Electrical distance measurements to probe ion binding sites.
• Varying intracellular and extracellular ion concentrations and membrane potentials.

Main Results:

• Intracellular Ca blocks open K channels in a time-dependent manner at strong depolarizations (above +90 mV).
• The Ca block shares similarities with Sr block, requiring millimolar concentrations and high energy barriers for ion entry.
• Block is voltage-dependent and can be prevented by external rubidium (Rb).
• Recovery from block is rapid and parallels normal K channel activation kinetics.

Conclusions:

• Intracellular Ca acts as a voltage-dependent blocker of K channels in squid neurons.
• The blocking site is likely deep within the channel pore.
• The findings suggest a potential link between ion channel block and normal channel gating mechanisms.