Temperature-dependent differences between readily releasable and reserve pool vesicles in chromaffin cells

Area of Science:

• Cell biology
• Neuroscience
• Biophysics

Background:

• Chromaffin cells release hormones via vesicle exocytosis.
• Distinct vesicle pools, readily releasable pool (RRP) and reserve pool (RP), are proposed but their specific properties remain debated.
• Understanding these pools is crucial for regulating cellular secretion.

Purpose of the Study:

• To differentiate the functional characteristics of RRP and RP vesicles in chromaffin cells.
• To investigate pool-specific secretagogue actions.
• To analyze temperature-dependent release kinetics and membrane properties of RRP and RP vesicles.

Main Methods:

• Amperometry was used to record vesicle exocytosis from chromaffin cells.
• Potassium ions (K+) and Barium ions (Ba2+) were employed as pool-specific secretagogues.
• Exocytosis was analyzed across a range of temperatures to assess release dynamics.

Main Results:

• K+ selectively evoked release from the RRP, while Ba2+ evoked release from the RP.
• Both pools showed similar temperature-dependent changes in spike area and half-width, suggesting comparable vesicle content.
• RP spike frequency exhibited a significantly higher temperature dependence (12% per degree C) than RRP (2.8% per degree C), indicating temperature-dependent RP mobilization.
• RP vesicles showed more "foot events" at room temperature, suggesting altered membrane tension compared to RRP vesicles.

Conclusions:

• The study successfully differentiates RRP and RP vesicles using pool-specific secretagogues and temperature-dependent analysis.
• Distinct mobilization and membrane properties distinguish the RRP and RP.
• These findings provide critical insights into the regulation of vesicle pools and exocytosis in neuroendocrine cells.