K+-selective microelectrode study of internally dialyzed squid giant axons

Area of Science:

• Neuroscience
• Cell Physiology
• Biochemistry

Background:

• Intracellular potassium activity ((aK)i) and concentration ([K+]i) are critical for neuronal function.
• Understanding potassium ion dynamics within the axoplasm is essential for comprehending nerve impulse propagation.

Purpose of the Study:

• To investigate the extent of intracellular potassium depletion in squid giant axons under specific experimental conditions.
• To determine if a fraction of axoplasmic potassium remains inaccessible to dialysis.

Main Methods:

• Measurement of intracellular potassium activity ((aK)i) using K+-selective microelectrodes.
• Quantification of axoplasmic potassium concentration ([K+]i) via atomic absorption spectroscopy.
• Experimental setup involved dialysis of squid giant axons with K+-free solutions and bathing in K+-free artificial seawater.

Main Results:

• (aK)i measurements confirmed that dialysis could deplete free axoplasmic K+.
• [K+]i measurements revealed substantial retention of K+ (15.5 +/- 1.7 mmol/kg axoplasm) in dialyzed axons.
• Compared to freshly dissected axons (330 +/- 16 mmol/kg axoplasm), dialyzed axons retained approximately 5% of their K+.

Conclusions:

• A small fraction of axoplasmic potassium is resistant to removal by dialysis.
• This retained potassium is likely bound to macromolecules or sequestered within organelles.
• These findings highlight the complex compartmentalization and binding of intracellular potassium in axons.