Properties of different Ca2+ pools in permeabilized rat thymocytes

Area of Science:

• Cellular Biology
• Biochemistry
• Physiology

Background:

• Cytosolic free Ca2+ concentration ([Ca2+]i) regulation is crucial for cellular signaling.
• Intracellular Ca2+ pools play a significant role in modulating [Ca2+]i.
• Mitogen-induced cellular responses often involve alterations in [Ca2+]i.

Purpose of the Study:

• To investigate the regulation of free Ca2+ concentration by intracellular pools in rat thymocytes.
• To determine the role of these pools in mitogen-induced changes of cytosolic free Ca2+ concentration.
• To elucidate the mechanism of Ca2+ release by inositol 1,4,5-triphosphate (IP3).

Main Methods:

• Digitonin-permeabilized and intact rat thymocytes were used.
• Measurements of Ca2+ concentration were performed using a Ca2+-selective electrode.
• Chlortetracycline fluorescence and the Ca2+ indicator quin-2 were employed.

Main Results:

• Rat thymocytes possess two intracellular Ca2+ compartments: mitochondrial and non-mitochondrial.
• The non-mitochondrial compartment, likely the endoplasmic reticulum, sequesters Ca2+ at low concentrations (<1 microM) and releases it upon IP3 stimulation.
• Mitochondria accumulate Ca2+ only at higher concentrations (>1 microM).
• Mitogen concanavalin A induces an increase in [Ca2+]i by mobilizing intracellular Ca2+ pools, likely through the IP3 pathway.

Conclusions:

• The non-mitochondrial Ca2+ pool is the primary intracellular reservoir at physiological Ca2+ concentrations.
• IP3 mobilizes intracellular Ca2+ by activating a specific efflux pathway from the non-mitochondrial pool.
• Mitogen-induced Ca2+ signaling in thymocytes involves the release of Ca2+ from intracellular stores via the IP3 pathway.