Estimating intracellular calcium concentrations and buffering without wavelength ratioing

Area of Science:

• Neuroscience
• Biophysics
• Cell Biology

Background:

• Intracellular free calcium concentration ([Ca(2+)]) is critical for neuronal function.
• Accurate measurement of [Ca(2+)] is essential for understanding cellular processes.
• Existing single-wavelength calibration methods have limitations, often requiring independent estimates of resting [Ca(2+)].

Purpose of the Study:

• To present a novel method for determining intracellular [Ca(2+)] from single-wavelength fluorescence signals.
• To overcome limitations of previous methods by not requiring independent estimates of resting [Ca(2+)].
• To provide a technique suitable for indicators achieving saturation under physiological conditions and possessing large dynamic ranges.

Main Methods:

• Utilized single-wavelength fluorescence measurements near indicator saturation.
• Employed Oregon Green BAPTA-1 and 2-photon laser scanning microscopy.
• Applied the method to CA1 pyramidal neurons in rat hippocampal slices.

Main Results:

• Successfully measured resting [Ca(2+)] in proximal apical dendrites (32-59 nM).
• Estimated endogenous buffering capacity (44-80) and peak [Ca(2+)] changes (178-312 nM).
• Results were comparable to previous ratiometric methods in both young and older animals.

Conclusions:

• The developed method provides a robust way to measure intracellular [Ca(2+)] using single-wavelength fluorescence.
• It is particularly advantageous for indicators that saturate easily and for experiments where ratio imaging is not feasible.
• The technique is broadly applicable to studying [Ca(2+)] dynamics in small neuronal compartments.