A fluorometric method for estimating the calcium content of internal stores

Area of Science:

• Cellular Biology
• Biochemistry
• Physiology

Background:

• Intracellular calcium (Ca2+) concentration is crucial for cellular signaling, influencing processes like Ca2+ spikes, oscillations, mitochondrial respiration, and store-operated Ca2+ channel activation.
• Accurate estimation of Ca2+ content in intracellular stores is vital for understanding these diverse cellular functions.

Purpose of the Study:

• To establish a consistent and quantitative method for estimating the content of intracellular Ca2+ stores.
• To validate this method in human T cells and explore its utility in characterizing Ca2+ dynamics.

Main Methods:

• Utilized thapsigargin (TG) or ionomycin (IO) to induce the release of stored Ca2+.
• Monitored the transient increase in intracellular Ca2+ concentration ([Ca2+]i) following release.
• Applied a quantitative approach that relates the kinetics and amplitude of the Ca2+ transient to the total releasable Ca2+, assuming a known Ca2+ pump rate.

Main Results:

• Validated the quantitative method in human T cells, demonstrating an approximately linear Ca2+ clearance rate.
• Supported the assumption of unregulated endoplasmic reticulum (ER) Ca2+ leak in resting T cells, proportional to luminal Ca2+.
• Determined a characteristic time constant for basal Ca2+ release (110-140 s), consistent with CRAC channel activation and store depletion.

Conclusions:

• The developed method provides a reliable way to estimate the total amount of releasable Ca2+ from intracellular stores.
• This approach can be valuable for quantifying the overlap between different functionally distinct Ca2+ stores.
• It enables a better definition of the relationship between intracellular Ca2+ store content and specific cellular responses.