Ca²⁺-associated triphasic pH changes in mitochondria during brown adipocyte activation.

Area of Science:

• Cell Biology
• Mitochondrial Biology
• Metabolism

Background:

• Brown adipocytes (BAs) possess high metabolic capacity due to abundant mitochondria.
• Mitochondrial pH regulation is crucial for metabolic processes, but its role in adrenergic stimulation-induced thermogenesis is unclear.

Purpose of the Study:

• To investigate the spatial and temporal dynamics of mitochondrial pH in stimulated BAs.
• To elucidate the mechanisms underlying mitochondrial pH changes during adrenergic stimulation.

Main Methods:

• Constructed and utilized a mito-pHluorin probe in BAs for real-time pH monitoring.
• Stimulated BAs with isoproterenol and employed dual-color imaging for mitochondrial membrane potential and heat production.
• Assessed the roles of electron transport chain (ETC) activity, mitochondrial Ca2+, and endoplasmic reticulum (ER) Ca2+ release.

Main Results:

• Observed a triphasic mitochondrial pH change upon adrenergic stimulation.
• Mitochondrial pH increase (phases 1 and 2) preceded thermogenesis, while a pH decrease (phase 3) occurred during thermogenesis.
• pH increase is partly mediated by ETC activity and coincides with increased mitochondrial Ca2+, originating from ER calcium release.

Conclusions:

• Mitochondrial pH increase is an early event in adrenergically stimulated BAs.
• This early mitochondrial alkalinization may potentiate thermogenesis in brown adipocytes.