A generalised method to estimate the kinetics of fast Ca(2+) currents from Ca(2+) imaging experiments

Area of Science:

• Neuroscience
• Biophysics
• Cellular Physiology

Background:

• Fast calcium (Ca2+) imaging using low-affinity fluorescent indicators enables high temporal resolution tracking of neuronal influx.
• The standard time derivative method for Ca2+ current kinetics fails in systems with Ca2+ binding proteins, such as Purkinje neuron dendrites, due to non-linear fluorescence changes.

Purpose of the Study:

• To develop and validate a novel method for estimating Ca2+ current kinetics in complex cellular environments where the time derivative approach is unreliable.
• To enable accurate quantification of Ca2+ influx in systems previously limited by indicator buffering and sequestration.

Main Methods:

• A two-buffer and two-indicator model was employed to simulate Ca2+ dynamics, mimicking sequestration via Ca2+ binding to a slow buffer.
• A semi-automatic protocol was developed to optimize model parameters and estimate input current kinetics by matching simulated and experimental fluorescence data.

Main Results:

• The novel method accurately estimates Ca2+ current kinetics, validated through computer simulations and experiments on real neurons.
• The study provides the first quantitative estimates of Ca2+ currents linked to climbing fiber excitatory postsynaptic potentials in Purkinje neurons.

Conclusions:

• This method overcomes limitations of the time derivative approach, expanding the study of Ca2+ currents in diverse neuronal systems.
• The technique offers a powerful tool for investigating the physiological behavior of Ca2+ channels under a wide range of conditions.