Microanalysis of calcium in nerve

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Intracellular free calcium (Ca2+) is a critical signaling molecule in neurons.
• Understanding calcium dynamics is essential for comprehending nerve function and dysfunction.
• Accurate measurement of low nanomolar calcium concentrations is technically challenging.

Purpose of the Study:

• To quantify free calcium concentrations in single squid nerve fibers.
• To identify the primary cellular calcium buffering mechanisms in axoplasm.
• To explore the role of organelles in maintaining resting calcium levels.

Main Methods:

• Utilized the photoprotein aequorin for calcium detection.
• Employed Arsenazo III, a spectral dye sensitive to calcium binding.
• Applied these analytical methods to single, isolated squid nerve fibers and axoplasm.

Main Results:

• Established that free calcium in squid nerve fibers can be accurately measured in the 20–60 nM range.
• Determined the resting free calcium concentration in fresh squid axoplasm to be 20–50 nM.
• Observed that approximately 0.1% of total cellular calcium is ionized, with the remainder buffered by organelles.

Conclusions:

• Smooth endoplasmic reticulum and mitochondria are significant calcium buffers in squid axoplasm.
• Organelles play a crucial role in maintaining low, physiologically relevant levels of ionized calcium.
• These findings provide insight into neuronal calcium homeostasis and signaling.