Stochastic events underlie Ca2+ signalling in neutrophils

Area of Science:

• Cellular Biology
• Biophysics
• Signaling Pathways

Background:

• Receptor occupancy triggers an increase in cytosolic free calcium (Ca2+).
• The precise timing and mechanisms coupling receptor activation to Ca2+ elevation remain incompletely understood.
• Neutrophils are key immune cells where Ca2+ signaling plays a critical role.

Purpose of the Study:

• To investigate the temporal dynamics of the initial phase of the Ca2+ response in neutrophils.
• To elucidate the molecular events linking receptor stimulation to cytosolic Ca2+ increase.
• To determine the number and nature of stochastic processes involved in initiating the Ca2+ signal.

Main Methods:

• Utilized fast laser scanning of fluo3-loaded neutrophils to monitor real-time Ca2+ changes.
• Measured the delay between stimulus addition and the onset of the Ca2+ signal.
• Applied stochastic process modeling, including the Poisson equation, to analyze lag time distributions.

Main Results:

• A variable delay (75 ms to >1.5 s) was observed between stimulus and Ca2+ signal onset.
• The distribution of these delays closely matched a model with six obligatory stochastic steps.
• The inferred stochastic rate was consistent with the diffusion of small intracellular signaling molecules.

Conclusions:

• The observed delays in neutrophil Ca2+ response are likely caused by a series of diffusion-limited stochastic steps.
• Each step involves a small number of intracellular messenger molecules, leading to stochastic behavior.
• This provides a quantitative model for the initial phase of receptor-mediated calcium signaling.